experimental design of a pen-like plasma torch with a ...... · 1 experimental design of a pen-like...

EXPERIMENTAL DESIGN OF A PEN-LIKE PLASMA TORCH WITH

A PARAMETRIC FEA TO IMPROVE EFFECTIVE TREATING AREA

A Synopsis

Submitted to Gujarat Technological University

For the Award of

Doctor of Philosophy

In

Mechanical Engineering

By

Patel Amitkumar Ramanlal

Enrollment No. 139997119009

Under Supervision of

Dr. Ajitkumar N. Shukla

Dean, R K University

GUJARAT TECHNOLOGICAL UNIVERSITY

AHMEDABAD

March - 2018

Contents Page No.

1. Title of the thesis and abstract 1 - 1

2. Brief description on the state of the art of the research topic 2 - 3

3. Definition of the problem 4 - 4

4. Objective and scope of work 4 - 4

5. Original contribution by the thesis 5 - 5

6. Methodology of research, Results / Comparisons 6 - 21

7. Achievements with respect to objectives 21 - 21

8. Conclusion 22 - 22

9. List of research papers publications 22 - 22

10. References

Annexure – I

Annexure – II

Annexure – III

Annexure – IV

1

EXPERIMENTAL DESIGN OF A PEN-LIKE PLASMA TORCH WITH

A PARAMETRIC FEA TO IMPROVE EFFECTIVE TREATING AREA

Abstract

This research describes a new concept of the non-thermal pen-shaped plasma torch. Plasma is

used for a variety of industrial applications like surface modifications, surface activation, and

surface treatment for coating technology and many more. The plasma device designed here is

simple and effective. This research and development was required because available device is

not useful for practical applications due to limited effective surface treating area. In this

context, this research investigates surface modification property of newly designed pen-shaped

plasma torch. In contrast to such status, the design of the novel device i.e. pen-shaped plasma

torch, reporting efficient performs in terms of surface modification of area is experimented

with change in the parameters. To achieve this, design parameters like anode-cathode material,

gas flow pattern, and supply power is changed. The new design of pen-shaped plasma torch

has DC power as novelty to generate non-thermal plasma. Most of non-thermal plasma torch

uses high-frequency AC power or radio frequency power. To validate the design, experiments

are carried out with designed pen-shaped plasma torch for investigating the behaviour of the

generated plasma for the surface modification on copper material. After plasma treatment,

lubrication fluid retaining ability of the copper material is improved significantly. The hardness

of the copper material is also increased from 49 Vickers to 75 Vickers due to hardening surface

reaction by plasma treatment. This research work documents the surface modification

characteristics of plasma generation by pen-shaped plasma torch for copper material with

improved effective surface treated area from 10 mm to 25 mm in terms of diameter. The results

successfully reflected important features of the studied pen-shaped plasma torch, which

provides preliminary knowledge in developing the new design of pen-like plasma torches for

practical applications.

Keywords: Plasma; Pen-Like; Non-thermal; Surface Treatment; Surface Characterization

2

2. Brief description on the state of the art of the research topic

Plasma is a fourth state of matter [1], i.e. solid, liquid, gas and then plasma, which is a high

temperature ionized gas.

Natural Plasma (Lightning) Manmade Plasma (Plasma torch)

Fig. 1 Fundamental of plasma

Plasma torch is a device used to control and stabilize an arc to efficiently convert the electrical

energy into thermal energy of the plasma [2].

Fig. 2 Generic plasma torch

Plasma processing at atmospheric pressure is suitable for wide industrial application due to the

simplicity and viability. Takayama et al. [3] proposed the first pen-like atmospheric plasma

torch device in the year 2002. It is obvious from the literature and mentioned by Wertheimer

et al. [4] that plasma technology with lower temperature has made many developments in past.

Stolarik et al. [5] experimentally investigated the effect of low-temperature plasma for surface

modification of pea seeds, germination, water uptake and content change. The author reported

the faster germination of the seeds due to plasma treatment. Ta-Lun Sung et al. [6] has reported

energy consumption of atmospheric pen-like plasma for discoloration for the textile industry.

Many authors have utilized plasma treatment for surface modification like, Kumar V. et al. [7]

has improved wettability of dielectric material, Srikanth S. et al. [8] has enhanced hardness and

corrosion resistance of low carbon steel, Luo X. et al. [9] has enriched tribological properties

of alloy steel and Rusu et al. [10] has improved dyeability of fabrics. However, it has been

3

noted that there is no significant development in pen-like plasma torch as there are few

researchers around the world aiming to investigate pen-like plasma torch for surface treatment

of the plastic material. Ko et al. [11] did a preliminary study and investigated the thermo-fluid

fields generated by the pen-like plasma torch. It is mentioned that the present status of the

device is still not feasible for practical applications because of its limited effective surface

treating area and thus is not in favour of industrialization.

Research Gap: The literature shows the following research issues are there in the existing

design of the pen-shaped atmospheric plasma torch. A). Literature review discussed only about

argon gas as a driving gas in pen-shaped plasma torch. It doesn’t mention anything about how

the driving gas affects the plasma temperature and thus effective treating area, which is very

important factor as well. B) Research papers demonstrate the use of stainless steel as a cathode

material for plasma generation. But, the cathode material which provides more free electrons

for better ionization process is the best material for plasma generation. Therefore it is to be

expected to use cathode material with higher electron emission capacity, to get a perfect

ionization of the driving gas and thus to get proper surface treatment of the component. C) The

literature review confirms the use of stainless steel as an anode material for plasma generation.

But, the anode material has to withstand maximum heat flux during the operation. Hence the

material with the higher thermal conductivity is the best option for anode material that carries

away the heat from anode surface. D) The researcher used ceramic tube as an insulating outer

body of the plasma torch but it is not lend itself for quick machining for various design

iterations like geometrical changes. Thus it is to be expected to use material with better

insulating properties and easy to machining to perform design iterations in case of requirement.

E) The existing pen-shaped plasma torch has not any plasma arc stabilization method to get

higher plasma temperature and to lower anode erosion. There are various arc stabilization

methods to get prolonged torch operation for better surface treatment.

In contrast to such status, the design of the novel device i.e. pen-shaped plasma torch, reporting

efficient performs in terms of surface modification of area is presented. To achieve this, design

parameters like anode-cathode material, flow pattern, and supply power is changed. The new

design of pen-shaped plasma torch has DC power as novelty to generate non-thermal plasma.

Most of non-thermal plasma torch uses high-frequency AC power or radio frequency power.

This work documents the surface modification characteristics of plasma generation for copper

material. The hardness of copper material is measured by sophisticated micro Vickers hardness

testing machine. Scanning Electron Microscopy (SEM) analysis is used to investigate surface

characterization changes on the copper material.

4

3. Definition of the problem

Based on extensive literature review, the need of research and development on novel device of

pen-shaped plasma torch is identified that the device is not useful for practical applications due

to limited effective surface treating area. This needs to be addressed as the research gap can be

closed by using better electrode material, better heat transfer and by introducing swirling gas

flow pattern to achieve better plasma stabilization. In this context, it is required to investigate

the surface modification ability of newly designed pen-shaped plasma torch to increase

effective treating area.

4. Objective and scope of work

The primary research objective is to improve effective surface treating area through:

O1: Design and develop a novel device of plasma torch.

O2: Study the effect of introduction of swirling effect into feed stoke gas.

O3: Improve the performance and prolonged life cycle by selecting different material for

anode, cathode and plasma body for better design.

O4: Conduct experiment on the designed plasma torch to make surface modification and

characterize.

Fig. 3 Objective and scope of research (Graphical)

The scope of work include design conducting parametric study through Finite Element

Analysis (FEA) and experiment on manufactured pen-like plasma torch for enhanced effective

treating area using combination of better heat transfer dynamics, combination of material and

gas dynamics. Finally, the characterization of treated material is conducted for hardness and

surface morphology.

5

5. Original contribution by the thesis

The original contribution made by the thesis is manifested by various improvements done

against the available plasma torch system and the creation of new one with swirl flow. The

novel design and contribution of this thesis is described as under:

As the improvement is first concern, the nitrogen gas which is a diatomic gas is used as a

driving gas for plasma generation by non-thermal pen-like plasma torch. The specific heats

of diatomic and monatomic gases vary widely and behave differently over temperature

ranges. Diatomic gases have higher specific heats than monoatomic gases. The specific

heat of diatomic nitrogen gas is 1.04 kJ/kg K and the specific heat of monatomic argon gas

is 0.52 kJ/kg K. The thermal conductivity of a gas is directly proportional to its specific

heat. So, a diatomic gas is more efficient in extracting thermal energy from an electric arc

[12] for which optimized parameters are found for stabilized plasma.

As the efficiency is another concern, the 2% thoriated tungsten is used as a cathode material

to obtain higher life, with maximize effective treating area. 2% thoriated tungsten is chosen

for the cathode because of its low thermionic work function and higher free electron

emission capacity which leads to perfect ionization process as the core of any plasma

generation method [13].

The third improvement is that the ETP copper as used as an anode material to obtain higher

life. ETP copper is recommended because of its higher thermal conductivity. The anode

has to withstand maximum heat flux. Hence copper is the best option for anode that carries

away the heat from anode surface for continuous torch operation. The thermal conductivity

for copper is 401 W/m-K and for stainless steel is 16 W/m-K which is very low

comparatively.

The next improvement claimed is use of Perspex as an insulating outer body of the plasma

torch. Perspex has better insulating properties and it is easy to machine for many design

iterations like geometrical changes.

Final improvement is the use of swirling effect of flow pattern of the feed gas introduced

for stabilization of the plasma arc. The gas is introduced in the torch tangentially leading

to the stabilization of the arc. The swirling motion of the flow causes the arc column to

remain in the center of the nozzle and rotates the anode arc attachment point and thus

greatly decreases erosion of the anode [14].

6

6. Methodology of research, Results / Comparisons

The methodology of research adopted for the novel design and development of the pen-shaped

plasma torch is described as under.

Table 1. New research methodology as design thinking

Fig. 4 Existing design vs new design of plasma torch (Graphical)

Actual manufacturing of the plasma torch.

Fig. 5 Bought out cathode Fig. 6 Machining anode

7

Fig. 7 Machining hollow body Fig. 8 Machining cathode holder

Fig. 9 Assembly of plasma torch

Thoriated tungsten cathode: Ø 3.2 mm

Thoriated tungsten cathode is selected to obtain greater life because of its low thermionic work

function and higher free electron emission capacity which leads to perfect ionization process

the goal of any plasma generation method [13]. S. Tashiro has used the tungsten cathode for

numerical analysis of keyhole welding of mild steel plate with the plasma arc [15]. The

experiments has been carried out on thermal plasma torch with Ø 3.2 mm cathode at Institute

of Plasma Research, Bhatt, Gandhinagar during master’s project.

Fig. 10 Experimental set-up @ IPR, Gandhinagar during master’s project

8

Copper anode : Nozzle Angle 60°

ETP copper is recommended for the anode because of its higher thermal conductivity. The

anode material has to withstand maximum heat flux during the operation of the plasma torch.

Hence copper is the best option for anode material that carries away the heat from anode surface

for continuous torch operation. M. Rashid recommendation on effect of inlet slot number on

the spray cone angle and discharge coefficient of swirl atomizer is selected [16].

Fig. 11 Nozzle cone angle from literature review

El. Fawzy recommendation of mixing and nozzle geometry effect on flame structure and

stability and shown that half cone of 30° gives better jet length and hence more effective area

is selected for experimentation [17].

Fig. 12 Nozzle geometry effect from literature review

Nitrogen gas : Mass flow rate 20 LPM, 4 Bar

S. Choi work on comparative study of air and nitrogen plasmas for PFCs decomposition for

the higher temperature and longer residence time in nitrogen plasma than air plasma because

of relatively low flow rate of nitrogen plasma gas is taken to fix input power compared with

air plasma gas [18].

Calculation of Swirl Number

The axial velocity component can be calculated from below relation:

𝑉𝑎𝑥𝑖𝑎𝑙 = √(1 − 𝑆𝑁2)

SN = Swirl Number

Intensity of swirl in a confined space is characterized by swirl number [19]. It is defined as a

ratio of axial flux of tangential momentum to the axial flux of axial momentum.

9

𝑆𝑁 = 𝐹𝑙𝑢𝑥 𝑜𝑓 𝑡𝑎𝑛𝑔𝑒𝑛𝑡𝑖𝑎𝑙 𝑚𝑜𝑚𝑒𝑛𝑡𝑢𝑚

𝐹𝑙𝑢𝑥 𝑜𝑓 𝑎𝑥𝑖𝑎𝑙 𝑚𝑜𝑚𝑒𝑛𝑡𝑢𝑚

The above nondimensional criterion, called the swirl number, is used to characterize the

amount of rotation imparted to the flow in a annular duct. For an annular swirler with constant

vane angle θ, the expression [20] recommended is:

𝑆𝑁 = 2

3 [

1 − (𝐷ℎ𝑢𝑏 𝐷𝑠𝑤⁄ )3

1 − (𝐷ℎ𝑢𝑏 𝐷𝑠𝑤⁄ )2] tan 𝜃

Dhub = Diameter of annular hub = 26 mm

Dsw = Diameter of swirl inlet = 6 mm

θ = Inlet angle = 25°, 30° and 35°

𝑆𝑁 = 2

3 [

1−(26 6⁄ )3

1−(26 6⁄ )2] tan 25 𝑆𝑁 = 1.40

Table 2. Swirl number at different inlet angle

Summary Swirl Angle, θ°

25 30 35

Swirl Number, SN 1.40 1.73 2.10

Finite Element Analysis – ANSYS Fluent

As per literature review, most of the simulations have been conducted in a 2D computational

domain [21]. Two dimensional models suppose an axial symmetry. 2D modelling can

significantly simplify the numerical efforts. But, modelling of plasma systems is still a

challenging problem [21, 22], as demonstrated by some recent publications.

Fig. 13 Computational domain, boundary conditions and meshing

10

The mathematical model of the present plasma system applies the following assumptions [23]:

The flow, temperature and electromagnetic fields are two-dimensional;

The flow is steady and isotropic turbulent;

All fluids are Newtonian;

The local thermodynamic equilibrium (LTE) is assumed. The plasma is treated as a single

continuous fluid with only one representative temperature for the flow.

The boundary conditions [24] are taken as follows:

A = Velocity inlet; B = Heat flux; C = Thermal wall copper; D = Free slip wall; E = Pressure

outlet; F = Symmetry

Results: Plasma velocity profile and temperature profile

Fig. 14 Plasma velocity profile

Fig. 15 Plasma temperature profile

11

Experimental Section

Schematic Diagram of Experimental Set-up

Fig. 16 Schematic diagram of experimental set-up of pen-shaped plasma torch

Actual Experimental Set-up

Fig. 17 Actual experimental set-up of pen-shaped plasm

Experiment on Copper Flat:

To increase lubrication retaining ability of copper material.

To reduce cost by replacing type of copper flat used.

Present solution used in industrial machinery moving mechanism:

Fig. 18 Use of copper flat as moving mechanism

12

Present Issues:

Higher cost: Imported Graphite Impregnated: 42 USD ~ (2750 INR) for size 300 x 75 x 10

Scratches on copper flat due to foreign particles.

Fig. 19 Present copper flat with scratches Fig. 20 Proposed copper flat

Achievement:

Cost reduction: Made In India Plain Copper Flat; Cost: 900 INR for size 300 x 75 x 10

Surface hardness can be improved by surface modification.

Plasma treatment can increase lubrication retaining ability of copper. Hence, to compensate

needs of graphite plugs.

A series of experiments were conducted to generate plasma and study the behavior of the pen-

shaped plasma torch. Initially, the nitrogen gas at a 25 L min-1 mass flow rate from the cylinder

at constant pressure was made to flow into the plasma torch body tangentially. The swirling

effect was examined visually, as the plasma torch body is transparent. The initial pressure was

set to the atmospheric pressure. The initial gap between two electrodes was set 5 mm and then

the power supply was switched on. Gradually, the various combination of gas flow rate and

electrode gap were set-up and experiments were conducted for each combination. The surface

of the copper flat was treated by generated plasma. The behavior of the surface before and after

plasma treatment was examined.

Fig. 21 Plasma treatment of copper flat

13

Experimental Results, Comparison and Discussion

The images shows effective treating area achieved by existing and new design respectively.

Fig. 22 Experimental results of existing design of plasma torch

Fig. 23 Experimental results of new design of plasma torch

Table 3. Results of existing design Table 4. Results of new design

14

Comparision of experimental results of effective treating area:

The effective treating area is increased by 2.5 times than existing design of the plasma torch

Table 5. Effective treating area achieved existing design vs new design

Experiment for lubrication retaining ability test on copper flat:

The lubrication fluid retaining area improved by plasma treatment

Fig. 24 Increased lubrication retaining ability after plasma treatment

Plasma activation [25, 26] is a process of surface modification using plasma, which improves

surface energy [27] of many materials. It is widely used in industrial processes to prepare

surfaces for bonding, gluing, coating and painting. Surface energy [28] quantifies the disruption

of intermolecular bonds that occur when a surface is created. Quality of adhesive coating and

bonding depends intensely on the capability of the adhesive to cover the substrate area. Good

quality coating and bonding can be achieved if surface energy of the adhesive is lower than the

surface energy of substrate. To improve surface energy of the substrate, surface treatment is

used as a ground work stage formerly adhesive bonding. Water Contact Angle measurements

can be used to determine the surface energy of a material [29, 30].

Fig. 25 Surface energy measurement by water contact angle

15

Water contact angle measuring instruments are very expensive. Hence, indirect method of

water contact angle measurement is used to examine surface energy improvement after plasma

treatment. Master angle measuring gauge is made by AutoCAD as shown. Master angle gauge

is focused with the help of the projector and laptop on a white board. A surface treated work

piece is placed in front of the projector. Then, a water drop is placed on both the treated area

as well as non-treated area of the work piece.

Fig. 26 Master angle measuring gauge Fig. 27 Treated work piece in front of projector

Projection of non-treated area Projection of treated area

Fig. 28 Projection of treated and non-treated work piece

Projection of non-treated area Projection of treated area

Fig. 29 Water contact angle measurement on projection by master angle gauge

Water contact angle is reduced from 45° to 30° thus surface energy is improved by 1.5 times.

16

Hardness Measurement:

Surface hardness is measured on Micro Vickers Hardness Testing Machine [31-34].

Fig. 30 Hardness measurement of copper flat on MITUTOYO HM - 112

Fig. 31 Coordinate (X,Y) along the length

Table 6. Hardness Measurement in Coordinate (X,Y) along length & Results

17

The Fig. 32 shows hardness achieved before and after plasma treatment on copper flat.

Fig. 32 Hardness (HV) result of plasma un-treated and plasma treated surface

SEM Analysis:

SEM analysis on copper flat with plasma un-treated & treated surface is done at IITGN.

Fig. 33 Scanning Electron Microscope machine, JEOL JSM – 7600F

SEM Analysis Results:

The following image shows results of SEM analysis [35-37] done on plasma un-treated and

plasma treated copper sample.

Fig. 34 SEM analysis results of plasma un-treated and plasma treated copper (Cu) surface

18

Fig. 35 SEM analysis results of plasma un-treated and plasma treated copper (Cu) surface

Due to plasma treatment surface hardness is greatly increased. The density of soft and saturated

pure copper is reduced due to plasma treatment and saturated pure copper with an alloying

element dissolved in the alpha phase, has undergone an ordering surface reaction [38].

Strengthening [39] is attributed to short-range ordering [40] of the solute atoms within the

copper matrix, which greatly slow down the motion of dislocations through the crystals. The

low-temperature treatment also acts as a stress-relieving treatment, which raises yield strength

by reducing stress concentrations in the lattice at the focuses of dislocation collisions [38]. As

a result, it exhibit improved stress-relaxation characteristics and improved hardness. Order

annealing is done for relatively short times i.e. ~ 5 minutes at relatively low temperatures i.e.

150 to 400 °C [38, 41], hence no special protective atmosphere is required.

Calibration & Uncertainty Analysis

Uncertainty analysis is often known as “propagation of error”. In any experiment, a number of

different measurements of different quantities may be carried out to determine a certain

parameter. To compute the overall uncertainty due to the combined effect of the uncertainties

of different variables, we consider the following equation in most general form [42]:

𝑦 = 𝑓 (𝑥1, 𝑥2,…𝑥𝑛 )

Overall Uncertainty,

Measuring Instruments:

Temperature Measurement: K – Type Temperature Sensor

Surface Area Measurement: Digital Vernier Caliper

Hardness Measurement: Hardness Testing Machine

19

Temperature Measurement:

Calibration and uncertainty analysis of K-type sensor is done by external.

Table 7. Temperature sensor calibration result

Area Measurement:

Surface area is measured by Digital Vernier Caliper, Uv = ± 0.01

𝑎 = 𝑓(𝑑)

𝑎 =𝜋

4𝑑2

𝜕𝑎

𝜕𝑑=

𝜋

4 2 𝑑

𝑈𝑎 = ± [(𝜕𝑎

𝜕𝑑)

2

(𝑈𝑣)2]

12⁄

𝑈𝑎 = ± [(

𝜋

4 x 2 x 25)

2 (0.01)2]

12⁄

x 100

25

𝑈𝑎 = ± 1.5 % Fig. 36 Area measured by Vernier

Calibration by standard hardness test block is done by Mitutoyo.

Fig. 37 Calibration by standard hardness test block

20

Repeatability of Experimental Results

Repeatability of experimental results is conditions where independent test results are obtained

with the same method on identical test piece in the same laboratory by the same operator using

the same equipment and instruments. Following the above conditions many experimental runs

are performed and results are obtained.

Fixed input parameters: Output parameters:

Power = 3800 to 4000 kV Surface area in terms of diameter, mm

Gas flow rate = 17 L min-1 Temperature at exit, K

Electrode Gap = 1 to 1.5 mm Surface hardness, HV

Table 8. Matrix of experimental runs and experimental results inside treated area

Fig. 38 Repeatability & probability plot of surface treated diameter

21

Fig. 39 Repeatability & probability plot of exit plasma temperature

Fig. 40 Repeatability & probability plot of surface hardness of copper

7. Achievements with respect to objectives

The research had primary objective to improve effective surface treating area and secondary

objective to explore modifications in surface characterization by plasma treatment of copper.

All objectives of the research have been achieved successively through experimental novel

design of pen-shaped plasma torch holding swirling gas flow and better electrode materials.

The effective surface treating area is increased by 150 % against the existing design of the

plasma torch in terms of surface diameter.

The lubrication fluid retaining ability of the copper is improved by plasma treatment due

to increase of surface energy that is measured by reducing water contact angle by 33%.

The surface hardness of the copper is increased by 53% by plasma treatment due to order

annealing surface reaction that acts as a stress-relieving action, which raises yield strength

by reducing stress concentrations in the lattice at the focuses of dislocation collisions.

22

8. Conclusions

The performance of the pen-like plasma torch for application of surface modification is one

of the pioneer work. The principal conclusions depicted during whole tenure of the research

can be summarized as below:

Comparison of existing design and novel design of pen-like plasma torch results shows

that, vortex stabilization play an important role in performance of the plasma torch. The

unique feature added as swirl flow pattern in feedstock gas helped to stabilized plasma arc.

The cathode and anode material changes facilitated plasma generation by perfect ionization

and prolonged torch operation by rapidly carrying away heats from anode surface.

It is also concluded that the glow of the plasma increases with reduction in the gas flow

rate and thus the stable plasma is achieved.

The design parameters considered in new design of pen-shaped plasma torch improving the

effective treating area. The result shows an increase in effective treating area from 10 mm

to 25 mm in terms of diameter.

After plasma treatment the lubrication retaining ability of the Copper (Cu) surface get

significantly improved. It shows an increase in surface hardness by around 57% with

surface modification at Nano level reducing working stress.

Thus, atmospheric pressure pen-shaped plasma torch made is a more effective tool for

industrial application leading to surface modification.

9. List of research papers publications

1. Title: Pen-Shaped Plasma Torch Design & Experiment for Surface Modification

Journal: Alexandria Engineering Journal – Elsevier, ISSN: 1110-0168, Status: Accepted,

November 2017

2. Title: Experimental Investigation of Surface Modification on Copper (Cu) with Pen-Shaped

Plasma Torch, Journal: Journal of Experimental & Applied Mechanics – STM, ISSN: 2321-

516X, Status: Accepted, Volume 9, Issue 1, April 2018

3. Title: Entrepreneurial Potential of Pen-Shaped Plasma Torch, International Conference:

International Conference on Research & Entrepreneurship. ISBN: 978-93-5254-061-7, R

K University, Rajkot, Jan. 5 – 6, 2016, Paper Code: ME – 104, Status: Published

4. Title: Pen-Like Plasma Torch: State-of-the-Art, International Conference: International

Conference on Industrial, Mechanical and Production Engineering: Advancements and

Current Trends. MANIT, Bhopal, Nov. 27 – 29 , 2014, Paper Code: IE – 1029, Status:

Published

23

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24

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Annexure – I

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Design & Experiments on Pen-Shaped Plasma Torch for Surface Modification

Amitkumar R. Patel1*, Ajitkumar N. Shukla2

1Rsearch Scholar, Gujarat Technological University, Chandkheda, Ahmedabad 382424, Gujarat, India

Email: [email protected]

2School of Engineering, R K University, Bhavnagar Highway, Rajkot 360020, Gujarat, India

Email: [email protected]

Abstract— The paper presents design and experiments on pen-shaped plasma torch that generates non-

thermal plasma for various surface modification applications. Plasma is used for a variety of industrial

applications like surface modifications, surface activation, and surface treatment for coating technology.

The hydrophilic property of plastic strip and polyethylene is enhanced by surface treatment done by the

plasma torch. The device construction is simple and effective. The present available device is still not

feasible for practical applications for its limited effective surface treating area. In this context, the new

design of the “pen-shaped plasma torch” performs efficiently in treating area due to swirl motion. To

validate this experiments are carried out with designed pen-shaped plasma torch at constant pressure

investigating the behavior of the generated plasma for various application of surface modification. The

result shows that the stable plasma is achieved at a gas flow rate in the range of 16-18 L min-1 along with

the electrode gap in the range of 1.0-1.2 mm. After plasma treatment, the writing ability on plastic film,

cleaning on steel plunger and etching ability on the copper strip was improved. The setup established

provides fundamental information on plasma generation and practical aspect of surface modification

characterization.

Keywords: Plasma torch, Non thermal plasma, Pen-shaped, Surface modification.

1 INTRODUCTION

Plasma processing at atmospheric pressure is suitable for industrial application due to the simplicity and viability.

Takayama et al. [1] have proposed the first pen-like atmospheric plasma torch device in the year 2002. It is obvious

from the literature and also mentioned by Wertheimer et al. [2] that low-temperature plasma technology and science

has made enormous strides during the past few years. Stolarik et al. [3] experimentally investigated the effect of

low-temperature plasma on pea seeds surface modification, germination, water uptake and content change. The au-

thor has stated the faster germination of the seeds due to plasma treatment. Ta-Lun Sung et al. [4] has reported ener-

gy consumption of atmospheric pen-like plasma for discoloration for the textile industry. Many authors has utilized

plasma treatment for surface modification like, Kumar V. et al. [5] has improved wettability of dielectric material,

Srikanth S. et al. [6] has enhanced hardness and corrosion resistance of low carbon steel, Luo X. et al. [7] has en-

riched tribological properties of alloy steel and Rusu et al. [8] has improved dyeability of fabrics. However, it has

been noted from literature survey that there is no significant development in pen-like plasma torch as there are few

researchers around the world aim to investigate on pen-like plasma torch for surface treatment of the plastic materi-

al. Ko et al. [9] did a preliminary study and investigated the thermo-fluid fields generated by the pen-like plasma

torch. The author has also mentioned in the paper that the present status of the device is still not feasible for practical

applications because of its limited effective surface treating area and thus is not in favor of industrialization.

In contrast to such status, the development of the new design of the “pen-shaped atmospheric plasma torch”,

which performs efficiently in terms of surface modification area, is essential. To achieve this, design parameters like

anode-cathode material, flow pattern, and supply power have been selected differently than pen-like plasma torch

reported in the literature. The present new design of pen-shaped plasma torch has novelty, as DC power is used to

generate non-thermal plasma. Most non-thermal plasma torch uses high-frequency AC power or radio frequency

power. The work presents the design and preliminary experimental investigation on plasma generation for surface

modification by novel design of pen-shaped plasma torch.

2 DESIGN AND EXPERIMENTAL SECTION

2.1 Material

The following materials were employed to design the pen-shaped plasma torch system: The thoriated tungsten rod

was chosen for the cathode, as supplied by Adinath Equipment Pvt. Ltd., Vatva, Ahmedabad, Gujarat, India. The

electrolytic tough pitch (ETP) copper was selected for a node, as supplied by Uma Control, Vatva, Ahmedabad, Gu-

jarat, India. The casted acrylic bar was chosen for plasma torch body and cathode holder, as supplied by Hiral Enter-

prise, Isanpur, Ahmedabad, Gujarat, India. The power source was fabricated by the assembly of the locally available

transformer, rectifier, capacitors and necessary electronics and electrical parts. The commercially available nitrogen

cylinder was employed as a feed stock gas for the plasma torch system.

2.2 Method of Experimental Set-Up

A schematic diagram of the experimental setup is shown in Fig. 1. The present new design of plasma device as de-

veloped using above material is quite different from as described by Ko et al. [9]. In the existing design proposed by

the author, the stainless steel electrodes are used with straight flow pattern of argon gas to generate plasma. Where-

as, in present design the 2% thoriated tungsten and the electrolytic tough pitch (ETP) copper were introduced to the

plasma torch served as an electrical connection between plasma and consequently forms the electrodes for the plas-

ma device. Gallimore et al. [10] mentioned that the tungsten has a low thermionic work function that means it has

very low rates of electrode erosion and higher free electron emission ability which leads to perfect ionization [11]

process the goal of any plasma generation method. Electrolytic-Tough-Pitch (ETP) is the most common copper uni-

versally used for electrical applications. It has a higher thermal conductivity which carries away heat flux faster dur-

ing plasma generation and keeps the anode cool relatively.

Fig. 1 Schematic diagram of the experimental set-up

The cathode holder and plasma torch outer body was manufactured by machining from a casted acrylic bar (Per-

spex). This material has good machinability which allowed required design iteration during the development of the

plasma torch. This material also behaves as an insulator between cathode and cathode holder. The manufacturing

tolerances between cathode holder and the cathode is kept as sliding fit, henceforth the gap between both the elec-

trodes is adjusted by moving cathode in the vertical direction as and when required as shown in Fig. 2.

Fig. 2 Plasma torch design

A nitrogen gas introduced tangentially into the plasma torch body through commercially available nitrogen gas

cylinder, which limits the diameter of the plasma jet due to swirling effect of the gas. The swirling effect of the gas

flow causes the arc column to remain in the center of the nozzle and rotates the anode arc attachment point and thus

greatly decreases erosion of the anode. The pressure regulator provided on the nitrogen gas cylinder was used to

control the gas flow pressure. The flow pressure was adjusted between 0 to 25 bar. The rotameter used to control the

mass flow rate to the plasma torch. All the tubing in the flow system was made from 6.0 mm nylon tubing connected

by fittings. The geometrical details of the plasma torch design are mentioned in Table 1.

Table 1 Geometrical details of plasma torch design

Parameters Dimension (mm)

Tungsten cathode 3

Copper anode

inner diameter 3.2

outer diameter 50

Nozzle cone angle 60

height 25

Torch body

inner diameter 30

outer diameter 50

gas inlet diameter 6

height 80

Perspex cathode holder

rod diameter 22

cap diameter 50

height 80

Helical annular space

groove depth

2

groove width 4

groove pitch 8

The plasma torch system powered by a high voltage DC power supply. The required DC breakdown voltage was

obtained using the transformer-rectifier circuit as shown in Fig. 3. A step-up transformer was used to step-up line

voltage followed by full bridge uncontrolled to rectify the AC voltage. With this arrangement 4 kV DC voltage was

obtained. As plasma arc resistance is very small, 1 kΩ resistance is used in primary side to limit the VA to a safe

value by limiting the primary current. The high voltage capacitor bank was used to make the smooth operation of the

plasma torch which provides the constant DC power to the plasma torch load. The specifications of the electrical and

electronics components are listed in Table 2.

Fig. 3 Electrical circuit for 4 kV DC power supply

Table 2 Specifications of electrical components

Components Specification

Step-up transformer

power 250 VA

input voltage 230 V @ 50 Hz

output voltage 4000 V

Diode

model HVM12

peak reverse voltage 12000 V

RMS voltage 8400 V

DC blocking voltage 12000 V

rectified current holder 350 mA

Capacitors

model H1423M

rated voltage 450 V

capacitance 470 µF

Resistor

resistance 1 kΩ

2.3 Experimental Run

A series of experiments were conducted to generate plasma and study the behavior of the pen-shaped plasma torch.

Initially, the nitrogen gas at a 25 L min-1 mass flow rate from the cylinder at constant pressure was made to flow into

the plasma torch body tangentially. The swirling effect was examined visually, as the plasma torch body is transpar-

ent. The initial pressure was set to the atmospheric pressure. The initial gap between two electrodes was set 5 mm

and then the power supply was switched on. The nature of plasma generated was observed. Gradually, the various

combination of gas flow rate and electrode gap were set-up and experiments were conducted for each combination.

The surface of the plastic film, steel plunger, and copper strip were treated by generated plasma. The behavior of the

surface before and after plasma treatment was examined. The initial experimental conditions are shown in Table 3.

Table 3 Initial experimental conditions

Parameters Specification

Type of plasma DC - APP

Power 0.25 kW

Current 62 mA

Voltage 4 kV

Atmosphere / Pressure Atmospheric

Gap between electrodes 5 mm

Gas flow rate 25 L min-1

3 RESULTS AND DISCUSSION

The plasma torch was operated initially with a nitrogen gas flow rate of 25 L min-1 along with the 5 mm electrode

gap, which resulted in no plasma generation. Then, the electrode gap was reduced from 5 to 2 mm with an increment

of 1 mm and keeping constant nitrogen gas flow rate of 20 L min-1. At this experimental stage, the voltage fluctua-

tion was observed and the plasma torch was found to be in loading condition at the electrode gap of 2 mm. The

cathode was found with black spot and carbon deposited at the tip of the cathode. Consequently, it was noted that the

reduction in electrode gap and the reduced nitrogen gas flow rate was favorable configurations to generate plasma.

In view of this, the further reduction in nitrogen gas flow rate and the electrode gap was attempted resulting consid-

erable improvement in plasma generation. It was observed that at the gas flow rate of 18 L min-1 and an electrode

gap of 1.5 mm the plasma was generated. However, the plasma was not sustained. The latter experiment was done at

the nitrogen gas flow rate of 20 to 16 L min-1 with the increment of 1 L min-1 and electrode gap of 1.2 to 1 mm

which resulted in the stable plasma generation. Thus, results of various configurations of gas flow rate and electrode

gap shown in Fig. 4 elucidate the significant influence of both the parameters on plasma generation.

Region A - No plasma generation zone, Region B – Unstable plasma generation zone, Region C – Stable plasma

generation zone

Fig. 4 Effect of gas flow rate & electrode gap on plasma generation

After getting stable plasma, the various surface modification tests were conducted as below.

3.1 Writing ability test on plastic film

The surface of the plastic film was treated by generated plasma. This is called the activation of plastic surfaces for

writing with different ink. The result was exciting, which showed the surface of the plastic film was activated and it

became easy writable. Initially, we were not able to write on plastic film with ball pen but after plasma treatment

[12], we can able to write easily. This process is used to increase printing ability on PVC pipes in industry. The writ-

ing ability before and after plasma treatment on plastic film is shown in Fig. 5.

Fig. 5 Writing ability before & after plasma treatment

3.2 Cleaning test on steel plunger

The surface of the steel plunger was treated by generated plasma. Plasma cleaning has a strong effect on the various

surfaces. The metal surfaces need to be degreased before coating applications in industry. The shining of the steel

plunger was improved after plasma treatment as shown in Fig. 6.

Fig. 6 Cleaning before & after plasma treatment

3.3 Etching ability test on copper strip

The surface of the copper strip was treated by generated plasma. Etching is the process of using strong acid to cut

into the unprotected parts of a metal surface to create a design in incised in the metal. This process is used to en-

grave part numbers on the surface of copper parts in the industry. Also, the lubrication fluid retaining area improved

by plasma etching as shown in Fig. 7.

Fig. 7 Etching ability before & after plasma treatment

4 CONCLUSION

The optimum conditions for plasma generation by pen-shaped plasma torch were deduced experimentally as 16-18 L

min-1 along with the electrode gap in the range of 1.0-1.2 mm. It is also concluded that the glow of the plasma in-

creases with reduction in the gas flow rate and thus the stable plasma is achieved. After plasma treatment, the writ-

ing ability, cleaning, and etching ability of the surface significantly improved. Especially, the atmospheric pressure

pen-shaped plasma torch is a more effective tool for industrial application of surface modification.

ACKNOWLEDGMENT

The authors gratefully acknowledge the support and contribution to the development of plasma torch and installation

of experimental set-up to Windsor Machines Limited, Chhatral, Gandhinagar, Gujarat, India.

CONTACT DETAILS

Postal address : B29, Akshardeep Tenaments, Opp. Manmohan Park, Viratnagar Road, Nikol, Odhav,

Ahmedabad, Pin Code Number 382 415, Gujarat, India.

E-mail address : [email protected]

Mobile number : +91 9925028781

REFERENCES

1. S. Takayama, S. Teii, S. Ono, “Surface Treatment of Plastics by an Atmospheric Pressure Corona Torch”

Transactions of IEE of Japan, 2002, vol. 122-A (8), p 722-728

http://www.ut.ee/hakone8/papers/T7/Ono(TP).pdf

2. M.R. Wertheimer, “Plasma Processing and Polymers: A Personal Perspective” Plasma Chem Plasma Process,

2014, vol. 34, Issue 3, p 363-376

http://link.springer.com/article/10.1007/s11090-013-9491-3

3. T. Stolarik, M. Henselova, “Effect of Low-Temperature Plasma on the Structure of Seeds, Growth and Metabo-

lism of Endogenous Phytohormones in Pea” Plasma Chem Plasma Process, 2015, vol. 35, Issue 4, p 659-676


4. T. Sung, W. Weng, A. Gu, X. Jhan, “Energy Consumption of Atmospheric Pen-like Plasma for Decoloration”

Surface & Coating Technology, 2010, vol. 205, p 459-461

http://www.sciencedirect.com/science/article/pii/S025789721000784X

5. V. Kumar, A. Dhillon, N. N. Sharma, “Surface Modification of Textured Dielectrics and Their Wetting Behav-

ior”, J. of Materi Eng and Perform, 2017, vol. 26, p 1-6,

https://link.springer.com/article/10.1007/s11665-017-2505-1

6. S. Srikanth, P. Saravanan, “Surface Modification of Commercial Low-Carbon Steel using Glow Discharge Ni-

trogen Plasma and its Characterization” J. of Materi Eng and Perform, 2013,vol. 22, Issue 9, p 2610-2622,

http://link.springer.com/article/10.1007/s11665-013-0533-z

7. X. Luo, Z. Yao, P. Zhang, Z. Wang, “Tribological Properties of the Fe-Al-Cr Alloyed Layer by Double Glow

Plasma Surface Metallurgy” J. of Materi Eng and Perform, 2016, vol. 25, Issue 9, p 3938-3947


8. G. B. Rusu, I. Topala, C. Borcia, N. Dumitrascu, G. Borcia, “Effects of Atmospheric Pressure Plasma Treatment

on the Processes Involved in Fabrics Dyeing” Plasma Chem Plasma Process, 2016, vol. 36, Issue 1, p 341-354,


9. T.H. Ko, J.C. Syu, “Numerical Investigation on Thermo-fluid Fields Induced by Pen-like Atmospheric Non-

thermal Plasma Torch with Array Type: A Preliminary Study” International Communications in Heat and Mass

Transfer, 2009, vol. 36, Issue 2, p 148-154,

http://www.sciencedirect.com/science/article/pii/S0735193308002200?np=y

10. S.D. Gallimore, “Operation of a High-Pressure Uncooled Plasma Torch with Hydrocarbon Feedstocks” Virginia

University, 1998, Sec. 4, p 41,

https://theses.lib.vt.edu/theses/available/etd-71998-13553/unrestricted/Sec4.pdf

11. V. Nagarajan, “Investigation on the structural stability and electronic properties of InSb nanostructures – A

DFT approach” Alexandria Engineering Journal, 2014, vol. 53, 437-444,

http://ac.els-cdn.com/S1110016814000295/1-s2.0-S1110016814000295-main.pdf?_tid=afbeaebc-02fe-11e7-

8209-00000aab0f26&acdnat=1488868035_6cd5716c0428e9ff2602d2783c82c889

12. E. Messiry, “Microcellulose particles for surface modification to enhance moisture management properties of

polyester, and polyester/cotton blend fabrics” Alexandria Engineering Journal, 2015, vol. 54, 127-140 http://ac.els-cdn.com/S1110016815000150/1-s2.0-S1110016815000150-main.pdf?_tid=8a8fc53e-0300-11e7-aea4-

00000aab0f26&acdnat=1488868831_3c3a99aa537272e9f2b5e61c879dd18a

mailto:[email protected]











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Annexure – II

ACCEPTANCE LETTER

Dear Amit Kumar Patel,

Greetings from STM Journals!!!

We feel glad to inform you that your manuscript entitled, “Experimental Investigation

of Surface Modification on Copper (Cu) with Pen-Shaped Plasma Torch” has been

accepted for publication in the Journal of Experimental & Applied Mechanics, ISSN:

2321–516X. Your paper will be published online in the month of February in Volume

9 Issue 1, 2018.

Have A Great Future Ahead.

Thanking you with best regards

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Director

Publication Management Team –

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Journal of Experimental & Applied Mechanics ISSN: 2230-9845 (Online), ISSN: 2321-516X (Print)

Volume 9, Issue 1

www.stmjournals.com

Experimental Investigation of Surface Modification on

Copper (Cu) with Pen-Shaped Plasma Torch

Amitkumar R. Patel1,*, Ajitkumar N. Shukla2

1Gujarat Technological University, Chandkheda, Ahmedabad, Gujarat, India 2School of Engineering, R.K. University, Bhavnagar Highway, Rajkot, Gujarat, India

Abstract The paper presents an experimental investigation on surface modification of copper (Cu)

material by plasma treatment using pen-shaped plasma torch. Plasma is used for a variety of

industrial applications like surface modifications, surface activation, and surface treatment

for coating technology. The plasma device construction here is simple and effective. This

development was required because available device is not useful for practical applications

due to limited effective surface treating area. In this context, the paper investigates surface

modification property of newly designed pen-shaped plasma torch. To validate this,

experiment is carried out with designed pen-shaped plasma torch for investigating the

behaviour of the generated plasma for the surface modification on copper material. After

plasma treatment, lubrication fluid retaining ability of the copper material is improved

significantly. The hardness of the copper material is also increased from 49 to 75 Vickers due

to hardening surface reaction by plasma treatment.

Keywords: Plasma torch, non-thermal plasma, pen-shaped, surface modification

*Author for Correspondence E-mail: [email protected], [email protected]

INTRODUCTION

Plasma processing at atmospheric pressure is

suitable for wide industrial applications due to

the simplicity and viability. Takayama et al.

proposed the first pen-like atmospheric plasma

torch device in the year 2002 [1]. It is obvious

from the literature and mentioned by

Wertheimer et al. that plasma technology with

lower temperature has made many

developments in the past [2]. Stolarik et al.

experimentally investigated the effect of low-

temperature plasma for surface modification of

pea seeds, germination, water uptake and

content change [3]. The author reported the

faster germination of the seeds due to plasma

treatment. Sung et al. has reported energy

consumption of atmospheric pen-like plasma

for discoloration in the textile industry [4].

Many authors have utilized plasma treatment

for surface modification like, Kumar et al.

have improved wettability of dielectric

material [5], Srikanth et al. have enhanced

hardness and corrosion resistance of low

carbon steel [6], Luo et al. have enriched

tribological properties of alloy steel [7], and

Rusu et al. have improved dyeability of

fabrics [8]. However, it has been noted that

there is no significant development in pen-like

plasma torch as there are few researchers

around the world aiming to investigate pen-

like plasma torch for surface treatment of the

plastic material. Ko et al. did a preliminary

study and investigated the thermo-fluid fields

generated by the pen-like plasma torch [9]. It

is mentioned that the present status of the

device is still not feasible for practical

applications because of its limited effective

surface treating area and thus is not in favour

of industrialization.

In contrast to such status, the design of the

novel device i.e. pen-shaped plasma torch,

reporting efficient performs in terms of surface

modification of area is presented. To achieve

this, design parameters like anode-cathode

material, flow pattern, and supply power is

changed. The new design of pen-shaped

plasma torch has DC power as novelty to

generate non-thermal plasma. Most of non-

thermal plasma torch uses high-frequency AC

power or radio frequency power. This work

documents the surface modification

characteristics of plasma generation for copper

material. The hardness of copper material is



Surface Modification on Copper by Pen-Shaped Plasma Torch Patel and Shukla


measured by sophisticated micro Vickers

hardness testing machine. Scanning Electron

Microscopy (SEM) analysis is used to

investigate surface characterization changes on

the copper material.

DESIGN AND EXPERIMENTAL

SECTION

Material

The materials employed to design the pen-

shaped plasma torch system are: The thoriated

tungsten rod was chosen for the cathode,

supplied by Adinath Equipment Pvt. Ltd.,

Vatva, Ahmedabad, Gujarat, India. The

electrolytic tough pitch (ETP) copper was

selected for anode, supplied by Uma Control,

Vatva, Ahmedabad, Gujarat, India. The casted

acrylic bar was chosen for plasma torch body

and cathode holder, supplied by Hiral

Enterprise, Isanpur, Ahmedabad, Gujarat,

India. The power source was fabricated locally

using available transformer, rectifier,

capacitors and necessary electronics and

electrical parts. The commercially available

nitrogen cylinder was employed as a feedstock

gas for the plasma torch system.

Method of Experimental Set-Up

A schematic diagram of the experimental

setup is shown in Figure 1. The new design of

plasma device developed using above material

is quite different from as described by Ko et

al., as they used the stainless-steel electrodes

with straight flow pattern of argon gas to

generate plasma [9]. Whereas, this design uses

2% thoriated tungsten and the electrolytic

tough pitch (ETP) copper as an electrical

connection between plasma and consequently

forms the electrodes for the plasma device.

Gallimore et al. mentioned that the tungsten

has a low thermionic work function; that

means it has very low rates of electrode

erosion and higher free electron emission

ability which leads to perfect ionization

process leading to the main goal of any plasma

discharge generation method [10–12].

Electrolytic-Tough-Pitch (ETP) is the most

common copper universally used for electrical

applications. It has a higher thermal

conductivity which carries away heat flux

faster during plasma generation and keeps the

anode cool relatively.

The cathode holder and plasma torch outer

bodies were machined using a casted acrylic

bar (Perspex) [13]. This material has good

machinability which allowed required design

iteration during the development of the plasma

torch. This material also behaves as an

insulator between cathode and cathode holder.

The nitrogen gas is introduced tangentially

into the plasma torch body through

commercially available nitrogen gas cylinder,

which limits the diameter of the plasma jet due

to swirling effect of the gas. The swirling

effect of the gas flow causes the arc column to

remain in the center of the nozzle and rotates

the anode arc attachment point and thus

greatly decreases erosion of the anode.

Fig. 1: Schematic Diagram of the Experimental Set-Up.


Journal of Experimental & Applied Mechanics

Volume 9, Issue 1

ISSN: 2230-9845 (Online), ISSN: 2321-516X (Print)


Fig. 2: Electrical Circuit for 4 kV DC Power Supply.

The pressure regulator on the nitrogen gas

cylinder was used to control the gas flow

pressure. The flow pressure was adjusted

between 0 and 25 bar. Rotameter was used to

control the mass flow rate to the plasma torch.

All the tubing in the flow system was made

from 6.0 mm nylon tubing, connected by

fittings. The plasma torch system was powered

by a high voltage DC power supply. The

required DC breakdown voltage was obtained

using the transformer-rectifier circuit as shown

in Figure 2. A step-up transformer was used to

step-up the line voltage using a full bridge

uncontrolled rectifier. This arrangement

resulted 4 kV DC voltage. As plasma arc

resistance is very small, 1 kΩ resistance was

used in primary side to limit the VA to a safe

value by limiting the primary current. The

high voltage capacitor bank was used to make

the operation smooth providing the constant

DC power to the plasma torch load.

Experimental Run

A series of experiments were conducted to

generate plasma and study the behaviour of the

pen-shaped plasma torch. Initially, the

nitrogen gas at a 25 l.min-1 mass flow rate

from the cylinder at constant pressure was

made to flow into the plasma torch body

tangentially. The swirling effect was examined

visually, as the plasma torch body is

transparent. The initial pressure was set to the

atmospheric pressure. The initial gap between

two electrodes was set 5 mm and then the

power supply was switched on. The nature of

plasma generated was noticed. Gradually, the

various combinations of gas flow rate and

electrode gap were used, and experiments

were conducted for each combination. The

surface of copper flat was treated with this

generated plasma. The surface hardness was

examined by micro Vickers hardness testing

machine as shown in Figure 3. The surface

characterization was also investigated using

SEM analysis machine as shown in Figure 4.

Fig. 3: Micro Vickers Hardness Testing

Machine.




Fig. 4: Scanning Electron Microscope

Machine.

RESULTS AND DISCUSSION

The plasma torch was operated initially with a

nitrogen gas flow rate of 25 l.min-1 along with

the 5 mm electrode gap, which resulted in no

plasma generation. Then, the electrode gap

was reduced from 5 to 2 mm with an

increment of 1 mm and keeping constant

nitrogen gas flow rate of 20 l.min-1. At this

stage, the voltage fluctuation was noticed, and

the plasma torch was found to get loaded at the

electrode gap of 2 mm. During loading, the

cathode was found with black spot and carbon

got deposited at the tip of the cathode.

Consequently, it was noted that the reduction

in electrode gap and the reduced nitrogen gas

flow rate were favorable configurations to

generate plasma. In view of this, the further

reduction in nitrogen gas flow rate and the

electrode gap were attempted resulting in

considerable improvement in plasma

generation. It was observed that at the gas flow

rate of 18 l.min-1 and an electrode gap of

1.5 mm the plasma was generated. However,

the plasma did not sustain long enough. The

latter experiment was done at the nitrogen gas

flow rate of 20 to 16 l.min-1 with the increment

of 1 l.min-1 and electrode gap of 1.2 to 1 mm

which resulted in the stable plasma generation.

The results of various configurations of gas

flow rate and electrode gap are shown in

Figure 5 elucidating the significant influence

of both the parameters on plasma generation.

After getting the stable plasma, the surface of

the copper (Cu) material was treated by

generated plasma for a total time of 120 min

with intermittent cooling of 10 min to avoid

burnout of circuitry. It is found that the

lubrication fluid retaining area got improved

by plasma treatment as shown in Figure 6.

Region A: No Plasma Generation Zone, Region B: Unstable Plasma Generation Zone, Region C:

Stable Plasma Generation Zone

Fig. 5: Effect of Gas Flow Rate and Electrode Gap on Plasma Generation.



Volume 9, Issue 1



Fig. 6: Surface Properties before and after Plasma Treatment.

The lubrication retaining area before plasma

treatment was ~10 mm and after plasma

treatment, the lubricating retaining area is

increased to ~25 mm.

Uncertainty Analysis of Area Measurement

Uncertainty analysis is often known as

“propagation of error”. In any experiment, a

number of different measurements of different

quantities may be carried out to determine a

certain parameter. To compute the overall

uncertainty due to the combined effect of the

uncertainties of different variables, we

consider the following equation in most

general form:

𝑦 = 𝑓(𝑥1, 𝑥2, … 𝑥𝑛)

Overall Uncertainty:

𝑈𝑦 = ± [(𝜕𝑦

𝜕𝑥1)2

(𝑈𝑥1)2+ (

𝜕𝑦

𝜕𝑥2)2

(𝑈𝑥2)2

+⋯+ (𝜕𝑦

𝜕𝑥𝑛)2

(𝑈𝑥𝑛)2]

12⁄

The lubrication retaining area is measured by

digital Vernier caliper with least count value

of, Uv =±0.01 mm.

a= Surface area, mm2; d= Diameter treated,

mm; Ua= Uncertainty in area measurement, %.

𝑎 = 𝑓(𝑑)

𝑎 =𝜋

4𝑑2

𝜕𝑎𝜕𝑑

=𝜋

4 2 𝑑

𝑈𝑎 = ± [(𝜕𝑎

𝜕𝑑)2

(𝑈𝑣)2]

12⁄

𝑈𝑎 = ± [(

𝜋

4 x 2 x 25)

2 (0.01)2]

12⁄

x 100

25

𝑈𝑎 = ± 1.5 %

The overall uncertainty in area measurement is

within ±1.5%.

The surface hardness of the copper material is

increased from ~49 to ~75 HV due to plasma

treatment as measured using micro Vickers

hardness testing machine. The Figure 7 shows

surface hardness measurement value for

copper increased by 57%.

Further, surface characterization was explored

using Scanning Electron Microscopy at 15 kV

with magnification X2000 and X3000

respectively. Figure 8 shows SEM picture of

surface modification of copper (Cu) material

with plasma treatment. It is observed that

surface gets cleaned of burr and surface line

gets smoothened.




Fig. 7: Surface Hardness before and after Plasma Treatment of Copper Flat.

Fig. 8: SEM Pictures of Plasma Treated and Un-Treated Copper (Cu) Surface.

The SEM results shows that surface hardness

of copper (Cu) material is greatly increased

using plasma. Plasma treatment reduces the

density of soft, saturated pure copper, and

saturated pure copper as an alloying element

gets dissolved in the alpha phase of copper at

surface level as found in SEM picture.

Strengthening of surface serration is attributed

to the short-range ordering of the solute atoms

within the copper matrix which greatly slow



Volume 9, Issue 1



down the motion of dislocations through the

crystals. It is a well-known fact that the low-

temperature treatment acts as a stress-relieving

treatment, which raises yield strength by

reducing stress concentrations at the lattice

axis of dislocation and collisions. As a result,

it is expected that copper flat will exhibit

improved stress-relaxation characteristics and

improved surface hardness. As order annealing

is done for relatively short times of 10 min

intervals at relatively low temperatures, no

special protective atmosphere is required for

this operation.

CONCLUSIONS

The optimum condition for plasma generation

of pen-shaped plasma torch is deduced

experimentally between 16 and 18 l.min-1

along with the electrode gap in the range of

1.0–1.2 mm. It is concluded that the glow of

the plasma increases with reduction in the gas

flow rate resulting in stable plasma. After

plasma treatment of around 120 min, the

lubrication retaining ability of the copper (Cu)

surface gets significantly improved. It shows

an increase in surface hardness by around 57%

with surface modification at nano level,

reducing working stress. Thus, atmospheric

pressure pen-shaped plasma torch made is a

more effective tool for industrial applications

leading to surface modification.

ACKNOWLEDGEMENT

The authors gratefully acknowledge the

support and contribution to the development of

plasma torch and installation of experimental

set-up to Windsor Machines Limited,

Chhatral, Gandhinagar, Gujarat, India.

REFERENCES

1. Takayama S, Teii S, Ono S. Surface

Treatment of Plastics by an Atmospheric

Pressure Corona Torch. Transactions of

IEE of Japan. 2002; 122-A(8): 722–728p.

http://www.ut.ee/hakone8/papers/T7/Ono(

TP).pdf

2. Wertheimer MR. Plasma Processing and

Polymers: A Personal Perspective. Plasma

Chem Plasma Process. 2014; 34(3): 363–

376p.

http://link.springer.com/article/10.1007/s1

1090-013-9491-3

3. Stolarik T, Henselova M. Effect of Low-

Temperature Plasma on the Structure of

Seeds, Growth and Metabolism of

Endogenous Phytohormones in Pea.

Plasma Chem Plasma Process. 2015;

35(4): 659–676p.


1090-015-9627-8

4. Sung T, Weng W, Gu A, et al. Energy

Consumption of Atmospheric Pen-like

Plasma for Decoloration. Surf Coat

Technol. 2010; 205: 459–461p.

http://www.sciencedirect.com/science/arti

cle/pii/S025789721000784X

5. Kumar V, Dhillon A, Sharma NN. Surface

Modification of Textured Dielectrics and

Their Wetting Behavior. J Mater Eng

Perform. 2017; 26: 1–6p.

https://link.springer.com/article/10.1007/s

11665-017-2505-1

6. Srikanth S, Saravanan P. Surface

Modification of Commercial Low-Carbon

Steel using Glow Discharge Nitrogen

Plasma and its Characterization. J Mater

Eng Perform. 2013; 22(9): 2610–2622p.


1665-013-0533-z

7. Luo X, Yao Z, Zhang P, et al. Tribological

Properties of the Fe-Al-Cr Alloyed Layer

by Double Glow Plasma Surface

Metallurgy. J Mater Eng Perform. 2016;

25(9): 3938–3947p.


1665-016-2235-9

8. Rusu GB, Topala I, Borcia C, et al. Effects

of Atmospheric Pressure Plasma

Treatment on the Processes Involved in

Fabrics Dyeing. Plasma Chem Plasma

Process. 2016; 36(1): 341–354p.


1090-015-9655-4

9. Ko TH, Syu JC. Numerical Investigation

on Thermo-fluid Fields Induced by Pen-

like Atmospheric Non-thermal Plasma

Torch with Array Type: A Preliminary

Study. Int Commun Heat Mass Transfer.

2009; 36(2): 148–154p.

http://www.sciencedirect.com/science/arti

cle/pii/S0735193308002200?np=y

10. Gallimore SD. Operation of a High-

Pressure Uncooled Plasma Torch with

Hydrocarbon Feedstocks. Virginia

University. 1998; Sec. 4: 41p.






















https://theses.lib.vt.edu/theses/available/et

d-71998-13553/unrestricted/Sec4.pdf

11. Nagarajan V. Investigation on the

Structural Stability and Electronic

Properties of InSb Nanostructures: A DFT

Approach. Alexandria Eng J. 2014; 53:

437–444p. http://ac.els-

cdn.com/S1110016814000295/1-s2.0-

S1110016814000295-

main.pdf?_tid=afbeaebc-02fe-11e7-8209-

00000aab0f26&acdnat=1488868035_6cd5

716c0428e9ff2602d2783c82c889

12. Ramakrishnan B. Numerical Simulation of

Non-Equilibrium Plasma Discharge for

High-Speed Flow Control. Journal of The

Institution of Engineers (India): Series C.

2017; 98(3): 285–293p.

https://link.springer.com/article/10.1007/s

40032-016-0314-1#citeas

13. Amitkumar Patel, Ajitkumar Shukla.

Entrepreneurial Potential of Pen-shaped

Plasma Torch. Int Conf on Research &

Entrepreneurship, R K University. 2016;

5p.

Cite this Article Patel Amitkumar R, Shukla Ajitkumar N.

Experimental Investigation of Surface

Modification on Copper (Cu) with Pen-

Shaped Plasma Torch. Journal of

Experimental & Applied Mechanics. 2018;

9(1):









https://link.springer.com/article/10.1007/s40032-016-0314-1#citeas

https://link.springer.com/article/10.1007/s40032-016-0314-1#citeas

Annexure – III

Proceedings of RK University’s First International Conference on Research & Entrepreneurship (Jan. 5th & Jan. 6th, 2016)

ISBN: 978-93-5254-061-7 (Proceedings available for download at rku.ac.in/icre)

RK University’s First International Conference on Research & Entrepreneurship (ICRE 2016)

Entrepreneurial Potential of Pen-shaped Plasma Torch

Amitkumar R. Patel1,*, Ajitkumar N. Shukla2

1Research Scholar, Mechanical, Gujarat Technological University, Ahmedabad-382424, Gujarat, India.

2Director, RK University, Rajkot-Bhavnagar Highway, Rajkot-360020, Gujarat, India.

*Corresponding author: Amitkumar R. Patel ([email protected])

ABSTRACT

The paper describes a new concept of the non-thermal pen-shaped plasma torch. Plasmas have found

applications in a variety of areas like plasma welding, melting, cutting, nitriding and treatment of

polymers and textiles. It is being used extensively nowadays for a variety of industrial applications. The

hydrophilic properties of plastic strip and polyethylene can be enhanced by surface treatment done by

plasma torch. This device has simple construction and has been efficaciously used for the same in past.

Conversely, the present status of the device is still not feasible for practical applications because of its

limited effective surface treating area. In this vision, the paper present a case of development of the new

design of the “pen-shaped atmospheric plasma torch”, which is efficient and necessary. It is anticipated

that entrepreneurial potential is huge in terms of enhancing the existing potential of surface treatment

industry and new product development.

SUMMARY

Design and development of pen-shaped plasma torch.

Keywords: Plasma, Plasma-troch, Pen-shaped, Surface treatment, Hydrophilic


RK University’s First International Conference on Research & Entrepreneurship (ICRE 2016) 2

INTRODUCTION

Plasma is called as 4th state of matter, unlike from the gaseous states, liquid and solid which is a high

temperature ionized gas. Processing at atmospheric pressure is favored on industrial scales due to the

simplicity and viability (1).

So, Plasma is a gas wherein electrons, ions, and neutral gas species co-exist. The mixture of charged and

neutral gas species is unique and responds to electromagnetic forces (2).

Plasmas can be classified in different ways according to its many characteristics, such as approximations

of the model which defines them, density, degree of ionization and temperature.

Hot plasma (thermal plasma) is that which approaches a state of local thermodynamic equilibrium. A hot

plasma is also known a thermal plasma. This plasmas can be formed by flames, electric sparks and

atmospheric arcs.

Cold plasma (non-thermal plasma) is that which ignores the ions thermal motion. As a result, only the

electric force is considered to act on the particles. The pressure force and the magnetic force can be

ignored in case of non-thermal plasmas. Examples of cold plasmas includes the fluorescent tube flow

discharge and ionosphere.

Plasma State Example

Thermal plasma

(Quasi-equilibrium)

Telectron ≈ Tion ≈ Tgas < 2 x 104 K

nelements > 1020 m-3

Arc plasma, Plasma torches,

RF inductively coupled discharges

Non thermal plasma

(Non-equilibrium)

Telectron >> Tion ≈ Tgas = 300 to 108 K

nelements ≈ 1010 m-3

Glow discharge, Corona,

Atmospheric pressure plasma jet torch

Table 1. Classification of plasma.

Thermal plasmas are described by proximate equality between neutrals, ions and electrons or by an

equilibrium. These plasma sources gives a high flux of heat and are predominantly used in areas such as

waste material treatment by plasma and plasma material processing. By using microwave devices and

plasma torches, the commonly used thermal plasmas can be generated. Due to high temperature thermal

plasma can process even the most noncompliant wastes including nuclear elemental waste, industrial

waste, medical waste, municipal solid waste, toxic waste, bio-hazard etc. in due course reducing

environmental pollution caused due to them. But there are several technical applications wherein the high

temperature characteristic of thermal plasmas neither anticipated nor necessary. Thermal plasmas in

certain cases even becomes prohibitive. In such application, cold plasmas become more appropriate (3).

Non-thermal plasmas (cold plasmas) are those in which the neutral elements and plasma ions maintains

approximate room temperature. Cold plasma produces active (energy full) electrons instead of heating the

whole stream of gas because the most of the coupled electrical energy is predominantly controlled to the

electron elements of the cold plasma. The approximate room temperature characteristics of the neutral

elements and ions of the cold plasma provides the opportunity of using non-thermal plasmas for low

temperature plasma application and for the treatment of bio-logical tissues and polymers that are very


heat sensitive. There are remarkable potential to employ these cold plasma sources in a wide range of

applications (3) and this is possible due to its extraordinary characteristic features of cold plasma that

includes high selectivity, presence of reactive species, a strong thermo dynamic non-equilibrium nature

and of course low temperature of gas.

INDUSTRIAL NEED OF PLASMA

Plasma arc torches are being applied today as unique heating tools in industrial surface treatment

processes. The many benefits of using plasma torches are being demonstrated in different production

plants and prototype equipment around the world. And the successful demonstration of this versatile, low-

mass, controlled high-enthalpy, selective-atmosphere, heat source is generating new applications.

Industry today is benefiting from plasma heating and will in the future derive more benefits from this

proven heating technology. There are many different types of plasma arc torches available. Single torch

power ratings range from 2 kilowatts to 60 megawatts. The plasma heaters at the low and high ends of the

power range are employed in the universities and in the national research laboratories for basic scientific

studies. The industrial sector, with its emphasis on durability and economy, has adapted only the plasma

torches in the range from 0.25 kW to 8 mW depending upon the application. The operating life of plasma

systems is very important in industry for economic reasons. Industrial processes that use plasma torches

must be capable of many hours or weeks of continuous operating life, unlike the several minutes of

operating life demanded of the 60-mW plasma heater that is used for re-entry heating simulation (2). This

paper presents the state-of-the-art of the plasma torch and discuss their industrial uses. But, the paper will

place emphasis on non-thermal plasma torch only due to research scope of the author.

ENTREPRENEURIAL POTENTIAL OF NON-THERMAL PLASMA TECHNOLOGIES

Recently, there has been a marked tendency to use non-traditional technologies for the material

production, surface treatment and waste utilization of different origin. Using the energy of plasma flows

in industry has allowed us to modify old and develop new technologies. In particular, this concerns

surface treatment and chemical industry. Operated and controlled plasma heating allows us to obtain an

efficient mode of the technological process, ensuring the maximum useful output under minimum specific

expenses or cost of material and energy. Besides, high-temperature heating plasma by flows creates

conditions of strong disbalanced, when high energy particles participate under the moderate middle-mass

temperature in the working process. New knowledge of these processes has allowed the researchers to

create a new technologies in the field of surface treatment industry (4).

The cold plasma technique uses cold gases to disinfect the surfaces of packaging or food products. The

technique has the potential to inactivate micro-organisms on the surface of products and packaging

materials at low temperatures. Non-thermal plasma is drawing a lot of consideration from the industry

belonging to food. Hardly a surprise, because many cleaning options are not heat-resistant, cleaning with

water is expensive and chemicals are often out of the question. But gas reaches every nook and cranny.

Food and bio-based research has many years of experience in cold plasma processing, including

microbiology, product research, technology development and process impact. Plasma technologies have

gained a new base in surface and coating industries. The main essential uses of these technologies are;

– Theoretical generalization of research results in the field of plasma chemistry, building material

processes and surface treatment with the aim of processing materials with the help of low-temperature

plasma or cold plasma.


– Packaging materials dis-infection: Packaging materials and vegetable microorganism can be inactivate

by using non-thermal plasmas. Particularly for temperature sensitive products, this can have a clear

benefit compared to heat treatments.

– Food products dis-infection: non-thermal plasmas can be used for inactivation of both bacteria and

vegetative cells that are located at the surface of a food product. The appearance and quality of the food

does not effected as a result of low temperature treatment. Research and development is vital for scaling

up and implementation of cold plasma since non-availability of an industrial equipment at the present.

CURRENT STATUS AND APPLICATION OF PEN-SHAPED PLASMA TORCH

The atmospheric pressure plasma has various applications in surface treatment and coating technologies,

including the pre coating adsorbates removal (5, 6), anti-bacteria (7) and the hydrophilic property

improvement of the polymer materials (8). The hydrophilic properties of plastic strip and polyethylene

can be enhanced by surface treatment done by pen-shaped plasma torch. This device has simple

construction and has been efficaciously used for it in past. Conversely, the present status of the device is

still not feasible for practical applications because of its limited effective surface treating area (9).

The reported uses of pen-shaped plasma torch are as follows:

– Surface treatment of polymers like polyethylene and plastics to increase hydrophilic properties.

– Improve printing ability of polyethylene film (10).

– De-coloration of dye solution of textile industries.

MOTIVATION BEHIND RESEARCH ON PEN-SHAPED PLASMA TORCH

Literature review itself shows that the non-thermal plasma technology has various industrial applications

as mentioned above. These technologies to become gradually commercially worthwhile in the upcoming

days. But, it is also reported that the present status of the plasma torch is still not feasible for practical

applications, hence in this vision it is necessary to develop novel design of the pen shaped plasma torch.

MATERIAL AND METHOD FOR NEW CONCEPT OF PEN-SHAPED PLASMA TORCH

It is expected that some modifications in the existing design parameters of the pen-shaped atmospheric

plasma torch system would enhance the effective treating area and thus would fulfill the prerequisite of

practical industrial applications. The subsequent discussion shows new research methodology and

materials for efficient design of the pen-shaped atmospheric plasma troch. The major focus are on feed

stoke gas from monatomic to diatomic because the diatomic gases have higher specific heats than

monatomic gases; the cathode material from SS to tungsten because of its low thermionic work function

and higher free electron emission capacity which leads to perfect ionization process the goal of any

plasma generation method (11) and the anode material from SS to copper because of its higher thermal

conductivity. The major change in construction of the pen shaped plasma torch is introduction of arc

stabilization method. The existing design has straight flow of driving gas but in new design the swirling

effect to the flow pattern of the driving gas shall be introduced for stabilization of the plasma arc. The

erosion of the anode can significantly reduce by application of swirl flow of the gas because it keeps the

arc plum in the center of the nozzle and rotates the arc and anode attachment point (12). This shall lead to

prolonged torch operation for better surface treatment of the component.


Fig. 1. New concept of pen-shaped plasma torch.

RESULTS AND DISCUSSION

Based on state of the art report, it can be concluded that the non-thermal plasma technology has various

industrial applications and this technology to become gradually commercially worthwhile in the

upcoming days for surface treatment and coating industries. Due to the simple configuration and

respectable treating performance of the pen shaped plasma troch the entrepreneurial potential of the

device to become powerful equipment for surface treatment in future is highly expected. Nonetheless, the

development of the pen shaped plasma torch at the present stage is not feasible for practical applications

because of its limited effective surface treating area. Therefore, further investigation to improve the

effective treating area of the pen shaped atmospheric plasma torch system is very crucial. Through the

study of influence by new design parameters and materials the effective treating area could be increased.

Nowadays industries requires cost effective and prolonged torch operation in this competitive market. It is

anticipated that newer design will be able to satisfy this industrial requirements. The literature also reports

that entrepreneurial potential is huge in terms of enhancing the existing potential of surface treatment

industry and new product development.

CONCLUSION

The literature supports that entrepreneurial potential is huge in terms of enhancing the existing potential

of pen-shaped plasma torch device in surface treatment industry and as a new product development. For

that reason it is worthwhile to do research on pen-shaped plasma torch.

ACKNOWLEDGEMENT

The author would like to acknowledge Dr. Ajitkumar N. Shukla (Director), RK University, Rajkot,

Gujarat, India, for providing the valuable support and guidance during the research.


COPYRIGHT TRANSFER

The authors of this manuscript hereby transfer all the copyrights and publishing rights to RK University

(Rajkot, India). As per the copyright transfer agreement, RK University reserves the right to publish,

distribute, upload, or advertise the contents of this manuscript as and when required, without any

restrictions. The authors further acknowledge that the content presented in this manuscript is entirely

original in nature and not published anywhere else.

REFERENCES

1. Boulos, M. I. and Fauchais, P., “Thermal Plasmas: Fundamentals and Applications”, vol. 1, pp. 1,

New York, United States of America, (1994).

2. Camacho, S. L., “Industrial-worthy Plasma Torches: State-of-the-art”, Plasma Energy Corporation,

Raleigh, North Carolina, 27612, pp. 619-620, United States of America, (1988).

3. Nehra, V., Ashok Kumar and Dwivedi, H. k., “Atmospheric Non-Thermal Plasma Sources”,

International Journal of engineering, vol. 2, pp. 55, India, (2012).

4. Solonenko, O. P., “Thermal Plasma Torches and Technologies: Basic Studies and Design”, vol. 1,

pp. 112, Novosibirsk, Russia, (2003).

5. Chapman, B. N., “Glow Discharge Process Sputtering and Plasma Etching”, Wiley, New York,

(1980).

6. Pochner, K., Neff, W., and Lebert, R., Atmospheric pressure gas discharges for surface treatment,

“Surface and Coatings Technology”, 74 – 75, pp. 394 – 398, (1995).

7. Akitsu, T., Ohkawa, H., Ohnishi, M., Tsuji, M., and Kogoma, M., A study on anti-bacterial effect of

non-thermal oxygen plasma and bio-medical application, “Proceedings of the 3rd Asia-Pacific

International Symposium on the Basic and Application of Plasma Technology”, pp. 139 – 144,

Taiwan, (2003).

8. Takayama, S., Ono, S., and Teii, S., Surface treatment of plastics by an atmospheric pressure corona

torch, “Transactions of IEE of Japan”, 122-A (8), pp. 722 – 728, (2002).

9. Ko. T. H. and Syu, J. C., Numerical investigation on thermo-fluid fields induced by pen-like

atmospheric non-thermal plasma torch with array type: A preliminary study, “International

Communications in Heat and Mass Transfer”, vol. 36, pp. 148-154, (2009).

10. Phuong, H. T. and Ting, K., “Atmospheric Pressure Pen-like Plasma treatment of PE film”, Journal

of Science and Technology, 72-A, pp. 57, Vietnam, (2009).

11. Gallimore, S. D., “The Virginia Tech Plasma Torch Design”, Section 4.0, pp. 41, Virginia

University, Charlottesville, United States of America, (1998).

12. Gallimore, S. D., “Operation of a High-Pressure Uncooled Plasma Torch with Hydrocarbon Feed

stokes”, pp. 82, Virginia University, Charlottesville, United States of America, (1998).

Annexure – IV

Int. Conf. on Industrial, Mechanical and Production Engineering: Advancements and Current Trends Department of Mechanical Engineering, MANIT, Bhopal

November 27-29, 2014

*Presenting author: Amit R. Patel

PEN-LIKE PLASMA TORCH: STATE-OF-THE-ART

Amit R. Patel1*, Dr. Ajitkumar N. Shukla2

1Mechanical Engineering, Gujarat Technological University, Ahmedabad, India, [email protected] 2Mechanical Engineering, Pandit Deendayal Petroleum University, Gandhinagar, India, [email protected]

Abstract: The paper describes a state of the art of the non-thermal pen-like plasma torch. Plasmas have found applications in a variety of areas such as plasma welding, melting, cutting, treatment of surfaces – nitriding and treatment of polymers, textiles, and many more. It is being used extensively nowadays for a variety of industrial applications. The pen-like plasma torch device has simple structure and has been successfully applied for the surface treatment to improve hydrophilic properties of plastic film and polyethylene, in past. However, due to the effective treating area of an existing pen-like atmospheric plasma torch is still very limited, the current status of the device is still far from the practical applications. In view of this, the development of the new design of the “pen-like atmospheric plasma torch”, which is efficient, is necessary. It is anticipated that some modifications in design parameters of the plasma torch system could increase the effective treating area and satisfy the need of practical applications. The major interest is to develop the different feed stoke gas, different flow pattern, different anode material and different cathode material to improve effective treating area. Keywords: plasma; plasma torch; pen-like; feed stoke; anode; cathode.

1. Introduction A familiarity with plasma phenomena is essential to understanding the bases for the design and operation of plasma torches, so a brief review of some plasma phenomena is presented. There are ample evidence of the phenomena of the plasma state, the fourth state of matter. As examples, it is observed as electrical discharges during lightning storms. Or it is observed an electrical discharge when home appliance is switched off or when accidentally the wires of car battery get “shorted”. These are all visual observations of the phenomena of the plasma state as explicitly reported by Camacho (1988). Soon after a lightning storm, the sky get cleared as if by some magic. Perhaps magic cannot explain everything. Another explanation is: the upward motions of air masses that were initiated by the heat of the lightning bolt plasma discharge "clear" the air. After the spark on the switch of the appliance it is sensed that the switch get warm. The source of heat is the plasma arc discharge that has initiated when the contacts of the switch opened. So Plasma is a gas wherein electrons, ions, and neutral gas species co-exist. The mixture of charged and neutral gas species is unique and responds to electromagnetic forces defined by Camacho way back in (1988). Boulos and Fauchais (1994) stated plasma is called as the fourth state of matter, distinct from the solid, liquid and gaseous states. Processing at atmospheric pressure is favored on industrial scales due to the simplicity and viability.

Plasma torch is one such device which operates at atmospheric pressure and has high rate of heat transfer because of presence of high temperature and chemical reactivity because of availability of large no of free radicals. It is being used increasingly extensively nowadays for a variety of applications such as surface treatment, metal cutting etc. In fact plasma technology has given new limits to many industrial processes by opening a new range of mechanical, chemical and metallurgical processing techniques. In a plasma torch, flowing gas is ionized to produce plasma. The plasma torch is a device used to control and stabilize an arc to efficiently convert the electrical energy into thermal energy of the plasma. There has been a very significant growth in the employment plasma torches in last decade mentioned by Boulos and Fauchais (1994). 2. Literature Review

The pen-like plasma torch device, which was developed in 2002, has very simple structure and has been successfully applied for the surface treatment to improve hydrophilic properties of plastic film and polyethylene. However, the literature review says that due to the effective treating area of a single pen-like atmospheric plasma torch is still very limited, the current status of the device is still far from the practical applications as mentioned by Ko and Syu (2009). In view of this, Ko and Syu (2009) has developed the new design of the “pen-like atmospheric plasma torch array”, which is composed of multiple pen-like atmospheric plasma torches. By that study, it was expected the array design of the plasma-torch system could increase the effective treating area and satisfy the need of practical applications. The referred paper carried out the numerical simulations of the thermo fluid fields induced by the devices with dual and four pen-like plasma torches. The major interest was to exploit the different flow features of single dual- and four-plasma torch system. The results revealed in the past study provided fundamental understanding of the thermo fluid fields induced by the multiple pen-like plasma torches only, which were worthwhile for the design work of the array-type devices as concluded by Ko and Syu (2009). The figure shows the existing design of a single pen-like atmospheric plasma torch. This design is arrayed by Ko and Syu (2009) to increase the effective treating area.

Figure 1 Configuration of the pen-like atmospheric plasma torch device.




3. Research Issues The literature shows following research issues are there in the existing design of the pen-like atmospheric plasma torch.

The literature review discussed only about argon gas as a driving gas in pen-like plasma torch. It doesn’t mention anything about how the driving gas affects the plasma temperature and thus effective treating area, which is very important factor as well. Research papers demonstrate the use of stainless steel as a cathode material for plasma generation. But, the cathode material which provides more free electrons for better ionization process is the best material for plasma generation. Therefore it is to be expected to use cathode material with higher electron emission capacity, to get a perfect ionization of the driving gas and thus to get proper surface treatment of the component. The literature review confirms the use of stainless steel as an anode material for plasma generation. But, the anode material has to withstand maximum heat flux during the operation of the plasma torch. Hence the material with the higher thermal conductivity is the best option for anode material that carries away the heat from anode surface. The researcher used ceramic tube as an insulating outer body of the plasma torch but it is not lend itself for quick machining for various design iterations like geometrical changes. Therefore it is to be expected to use material with better insulating properties as well as easy to machined out to perform design iterations in case of requirement. The existing pen-like plasma torch system has not any plasma arc stabilization method to get higher plasma temperature and to lower anode erosion. There are various arc stabilization methods to get prolonged torch operation for better surface treatment of the component.

4. New Research Methodology and Materials

It is expected that some modifications in the existing design parameters of the pen-like atmospheric plasma torch system could increase the effective treating area and satisfy the need of practical applications without increasing the number of plasma torches. The following discussion shows new research methodology and materials for efficient design of the pen-like atmospheric plasma troch. As an improvement is first concern, the nitrogen gas which is a diatomic gas should be used as a driving gas for plasma generation by non-thermal pen-like plasma torch. When designing a plasma torch, the feedstock gas with which the torch operate is an important consideration. The specific heats of diatomic and monatomic gases vary widely and behave differently over temperature ranges. Diatomic gases have higher specific heats than monatomic gases. The specific heat of diatomic nitrogen gas is 1.04 kJ/kg K and the specific heat of monatomic argon gas is 0.52 kJ/kg K. The thermal conductivity of a gas is directly proportional to its specific heat. Therefore, a diatomic gas shall be more efficient in extracting thermal energy from an electric arc.

As an improvement is second concern, the 2% thoriated tungsten shall be used as a cathode material to obtain greater life, and again modified for the present torch to maximize effective treating area. 2% thoriated tungsten shall be chosen for the cathode because of its low thermionic work function and higher free electron emission capacity which leads to perfect ionization process the goal of any plasma generation method as stated by Gallimore (1998).

The third improvement as a concern is that the ETP copper shall be used as an anode material to obtain greater life of anode. ETP copper is recommended for the anode because of its higher thermal conductivity. The anode material has to withstand maximum heat flux during the operation of the plasma torch. Hence copper is the best option for anode material that carries away the heat from anode surface for continuous torch operation. The author has experienced the use of stainless steel material as an anode. The thermal conductivity of copper is 401 W/m K and the thermal conductivity of stainless steel 304 is 16 W/m K which is very low compared to copper.

As a next improvement the Perspex (i.e. it is a casted acrylic) shall be used as an insulating outer body of the plasma torch. Perspex is suggested for an insulating outer body of the plasma torch because of its better insulating properties and it is easy to machining casted acrylic for various design iterations like geometrical changes during development of the plasma torch. Ceramic outer body cannot be machined out in case of requirement during development of the plasma torch. The Perspex is a transparent material which enables the researchers to see the gas flow pattern inside the body of the plasma torch.

As a last improvement the swirling effect of flow pattern of the driving gas shall be introduced for stabilization of the plasma arc. The author has used straight flow of the driving argon gas where arc stability is of utmost important in maintaining smooth reliable operation of a plasma torch. However, various other methods is proposed to be employed to increase the efficiency of stable arc operation. For stabilizing the plasma arc, the main driving gas is often introduced in the torch tangentially. The swirling of the flow causes the arc column to remain in the center of the nozzle and rotates the anode arc attachment point and thus greatly decreases erosion of the anode as mentioned by Gallimore (1998). This shall lead to prolonged torch operation for better surface treatment of the component.

5. Summary

Based on state of art report, it can be concluded that there are specific designs of plasma torch for specific purpose in a various fields. But only a few pen-like plasma torch is reported in the literature. It has been observed that few researchers around the world aim to investigate on pen-like plasma torch for surface treatment of plastic material. Because of the simple configuration and good treating performance, the potential of the device to become powerful equipment for surface treatment in future is highly expected. Nonetheless, the development of the single pen-like plasma torch at the current stage is still far from the practical application. Therefore, further investigation to improve the effective treating area of the pen-like atmospheric plasma torch system is very essential. Through the study of influence by new design parameters as discussed above the effective treating area could be increased without increasing number of the pen-like atmospheric plasma troch systems. Nowadays industries requires cost effective and prolonged torch operation in this competitive market. It is anticipated that newer design will be able to satisfy this industrial requirements.




Acknowledgements

The authors would like to acknowledge Dr. G. Ravi (Scientist) FCIPT division, Institute for Plasma Research, Gandhinagar, Gujarat, India for providing the valuable support and guidance during the research.

References

Boulos, M. I. and Fauchais, P., (1994), Thermal Plasmas: Fundamentals and Applications, Volume 1,

Page 1, New York, United States.

Camacho, S. L., (1988), Industrial-worthy plasma torches: State-of-the-art, Page 620, Plasma Energy Corporation, Raleigh, North Carolina, 27612, USA.

Gallimore, S. D., (1998), Section 4.0: The Virginia Tech Plasma Torch Design, Page 41, Virginia University, Charlottesville, VA, United States.

Gallimore, S. D., (1998), Operation of a High-Pressure Uncooled Plasma Torch with Hydrocarbon Feedstokes, Page 82, Virginia University, Charlottesville, VA, United States.

Ko, T. H. and Syu, J. C., (2009), Numerical investigation on thermofluid fields induced by pen-like atmospheric non-thermal plasma torch with array type: A preliminary study, International Communications in Heat and Mass Transfer, Volume 36, Page 148-154.

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