FAILURE ANALYSIS OF SHOT BLAST SYSTEM

(FRAME FACTORY,TML JAMSHEDPUR)

AVISHEK GHOSH

JADAVPUR UNIVERSITY KOLKATA

ACKNOWLEDGEMENT

We would like to deeply thank our project supervisor Mr Ashok Kumar for his unconditional support, guidance and understanding, continuous support throughout our work which will be infinitely profitable for the rest of our life.

We would like to thank Tata Motors Jamshedpur workers especially Mr Rajeev Ranjan(Manager) for his support in the case study while pursuing my project.

We are indebted to our fellow students, staffs and friends for their continuous support and the brainstorming discussions and I strongly believe that what we have leaned from them during the study period is worthy to articulate for problem solving.

Our thanks also goes to MTC Department of Tata Motors especially to Mr Johnson Mathews for providing every possible help during the course of our training period.

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CONTENTS

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SL. No. TOPIC Pg. No.

1 ACKNOWLEDGEMENT 1

2 INTRODUCTION TO TATA MOTORS 5i)Major milestones in Tata Motors 6

3 INTRODUCTION TO FRAME FACTORY 84 PROCESSES INVOLVED IN PTCED 95 PAINT PRE TREATMENT 106 WHAT IS SHOT BLASTING 11

7 MAJOR COMPONENTS OF SBM 12

i) Cabin 13

ii) Bucket elevator 14

iii) Air separator 15

iv) Abrasive Hopper 16

v) Abrasive Gates 17

vi) Blast units 18

vii) Screw conveyer 19

viii) Roller conveyer 20

ix) Abrasive removal device 21

x) Specifications of abrasives 22

8 REPRESENTATIVE BREAKDOWN DATA ANALYSIS OF SBM FOR ONE MONTH 23

9 REPRESENTATIVE CUMULATIVE SBM BREAKDOWN DATA FOR ONE MONTH 24

10 BREAKDOWN DATA ANALYSIS OF PTCED (APR'15-MAR'16) 25

11 SBM BREAKDOWN DATA ANALYSIS (APR'15-MAR'16) 26

12 ANALYSIS OF SBM BREAKDOWN DATA (APR'15-MAR'16) 27

13 FISHBONE DIAGRAM OF SHOTS ON LM 28

14 ANALYSIS OF FISHBONE DIAGRAM OF SHOTS ON LM 29

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SL. No. TOPIC Pg. No.15 SUGGESTIONS AND RECOMMENDATIONS 3416 AIR AMPLIFIER 37

i)Working Principle 38ii)Coanda Effect 39iii)Amplifier to increase efficiency and intensity 40iv)Maintaining the integrity of amplifier air 41v)Performance parameters of Air amplifiers 42vi)Determination of total output and air consumption of air amplifiers 44

17 IMPROVEMENT OVER AIR AMPLIFIER 45i)Air jets 46ii)Star profile air nozzles 47

18 FORCE DELIVERY COMPARISION FOR DIFFERENT AIR NOZZLES 4819 APPLICABILITY IN PRESENT SCENARIO 4920 REPRESENTATIVE CALCULATIONS 5021 IMPLEMENTATION OF THE IDEA 5322 FISHBONE DIAGRAM OF BLAST WHEEL BLADE WEAR 5523 ANALYSIS OF FISHBONE DIAGRAM OF BLAST WHEEL BLADE WEAR 5624 SUGGESTIONS AND RECOMMENDATIONS 6125 WEAR REDUCTION 6426 COMPONENT DESIGN 6627 REPRESENTATIVE CALCULATIONS 6828 POSSIBLE MODIFICATION 6929 ADVANTAGES 7130 MECHANICS OF CONTROL CAGE SHOT TRANSFER 7231 DISCUSSIONS 7432 REFERENCES 75

INTRODUCTION TO TATA MOTORS

Tata Engineering & Locomotives Company (TELCO) now TATA MOTORS is the automobile front-runner of India. The company’s Head office is in Mumbai while its works operates at Jamshedpur, Pantnagar, Lucknow, Ahmedabad, Sanand, Dharwad and Pune in India, as well as in Argentina, South Africa and Thailand. Since first rolled out in 1954, Tata Motors has produced and sold over 4 million vehicles in India.

Tata Motors' principal subsidiaries purchased the British premium car maker Jaguar Land Rover (the maker of Jaguar, Land Rover, and Range Rover cars) and the South Korean commercial vehicle manufacturer Tata Daewoo. Tata Motors has a bus-manufacturing joint venture with Marcopolo (Tata Marcopolo), a construction-equipment manufacturing joint venture with Hitachi (Tata Hitachi Construction Machinery), and a joint venture with FiatChrysler which manufactures automotive components and Fiat Chrysler and Tata branded vehicles.

The company is the world's fourth largest truck manufacturer, the world's second largest bus manufacturer, Tata Motors in 2005 was ranked among the top 10 corporations in India with an annual revenue exceeding INR 320 billion. In 2010, Tata Motors surpassed Reliance to win the coveted title of 'India's most valuable brand' in an annual survey conducted by Brand Finance and The Economic Times.

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The major milestones in TATA MOTORSYEAR MILESTONES ACHIEVED

2000 • Axle division of Jamshedpur plant becomes HV Axle Ltd., a 100% subsidiary of Telco. Gear Box division of Jamshedpur plant becomes HVTL, 100% subsidiary of Telco.

• Growth Division of Pune plant becomes Telco Automation Ltd., a100% subsidiary of Telco.• 50,000 Tata Indica sold out in 12 months since commencement of deliveries.

2008 • Tata Motors unveils Tata Nano, the People’s Car, at the 9th Auto Expo in Delhi on January 10, 2008.

• Tata Motors acquires the Jaguar and Land Rover brands from the Ford Motor Company.

2009 • Tata Motors announces commercial launch of the Tata Nano; Tata Nano draws over 2.03 lakh bookings; first 100,000 owners of the Tata Nano chosen; delivers first Tata Nano in the country in Mumbai.

• Tata Motors ushers new era in Indian auto industry with its new, world-standard truck range.

• Jaguar Land Rover introduces its premium range of vehicles in India.• Tata Motors acquires remaining 79 per cent shares in Hispano Carrocera, one of the largest

manufacturers of bus and coach cabins in Europe.

2010 • New plant for Tata Nano at Sanand inaugurated.

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The company has following Joint Venture to improve the range and the quality of products.TATA CUMMINS LTD (TCL)MERCEDES BENZ INDIA LTD. (MBIL)TATA HOLSET LTD (THL) Among the venture abroad are the Tata Precision Industries (TPI), Singapore and Nita Company Ltd., Bangladesh.

PRODUCTS AND SERVICESThe product range of TATA MOTOR is quite large to account for all in this report. Just a small list of vehicles is given here:

1. Medium and heavy vehicles:

a. Rigid truck: LPTA 713, LPT1109&1112, SE1613, etc

b. Tractor trailer: LPS3516, LPS4018, LPS4923

c. TIPPERS: SK1613, LPK1615, LPK2516&1618 etc.

d. World Trucks - PRIMA

2. Light trucks:

a. Rigid truck: SFC407, LPT407, LPT709 etc.

b. Tippers: SFC407, LPK407&709 etc.

3. Small vehicles: Super Ace, Ace EX, 207DI EX etc.

4. Buses:

a. Public transport: LP1109, LPO918, etc

b. Intercity transport: LPO1316&1318

c. Charter buses: SFC407,LP4075. Tata Motors Defence Solutions

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INTRODUCTION TO FRAME FACTORY

Steel Rolls supplied by TATA Steel & SAIL

Coils are decoiled and cut by decoiler and then straightened

Sheets are piled by magnetic stacker

5000T press is used for punching , cutting & bending using separate dies and stacked

C section frames are sent to Vehicle Factory I & II for manual inspection of defects (Burrs in holes, Taper and height of flanges) which are rectified using hand and

spot grinding

PROCESSES INVOLVED IN PTCED

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Long Member (LM) prewashed using Ridoline at 40ºc to remove grease,oil and dirt

LM sent to Shot Blasting Machine(SBM) using roller conveyers for removal of mill scale

LM are subjected to Paint pre treatment

LM loaded on hangars using Robotic Arms

LM are finally sent to baking oven (Temp 170-220ºC, Time cycle – 36 min) and sent to Assembly Line

PAINT PRE TREATMENT

DIP DEGREASING: The LM are dipped in a tank of Ridoline to further wash away the dirt which may have accumulated on it’s surface during shot blasting.

RAW WATER RINSE

DEMINARALISED WATER (DM) RINSE (Conductivity < 50µs/cm)

NANO COATING: The LM are dipped in a tank of TEC TALIS for pre paint coating to increase corrosion life of LM (Conductivity < 2500µs/cm, pH: 3.8-4.5)

DM WATER RINSE 2 (Conductivity < 100µs/cm)

DM WATER RINSE 3 (Conductivity < 50µs/cm)

Cathodic Electrode Deposition(CED) BATH: Painting of LM is done in this chamber and a conductivity of 1000-1700 µs/cm and a pH of 5.3-5.8 is maintained (NVM < 15%)

ULTRA FILTRATION 1 RINSE (Conductivity < 800-1500µs/cm, pH: 5.0-5.7, NVM < 1%)

ULTRA FILTRATION 1 RINSE (Conductivity < 800-1500µs/cm, pH: 5.0-5.7, NVM < 0.7%)

RECIRCULATED DM WATER RINSE (Conductivity < 100µs/cm, pH: 6.0-7.0)

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WHAT IS SHOT BLASTING?Shotblasting is a method used to clean, strengthen (peen) or polish metal. Shot blasting is used in almost every industry that uses metal, including aerospace, automotive, construction , foundry, shipbuilding rail, and many others. There are two technologies used: wheelblasting or airblasting.

Wheelblasting

Wheelblasting directly converts electric motor energy into kinetic abrasive energy by rotating a turbine wheel. The capacity of each wheel goes from approximately 60 kg per minute up to 1200kg/min. With these large amounts of accelerated abrasive, wheelblastmachines are used where big parts or large areas of parts have to be derusted, descaled, deburred, desanded or cleaned in some form.

Airblasting

Airblast machines can take the form of a blastroom or a blast cabinet, the blast media is pneumatically accelerated by compressed air and projected by nozzles onto the component. For special applications a media-water mix can be used, this is called wet blasting.In both air and wet blasting the blast nozzles can be installed in fixed positions or can be operated manually or by automatic nozzle manipulators or robots.The blasting task determines the choice of the abrasive media, in most cases any type of dry or free running abrasive media can be used.

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MAJOR COMPONENTS OF SBM

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1. Abrasive Gates 2. Blast Wheel3. Cabin 4. Workpiece5. Roller conveyer 6. Longitudinal screw conveyer7. Lower transversal screw conveyer 8. Bucket Elevator9. Upper transversal screw conveyer 10. Air separator11. Main Hopper 12. Replenisher Hopper13.Replenisher Screw conveyer 14. Expansion chamber

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SHOT BLAST MACHINE

CABINThe machine’s blast cabin is made of manganese steel to prevent wear. The interior wall opposite to blast units is also provided with replaceable manganese covering plates.

Inside the cabin there is a V- shaped metal sheet with holes(to catch rough impurities).through the holes and the space between the sheet and the cabin wall the abrasive passes together with small impurities, to the hopper under the cabin. The mixture is transported from the cabin hopper to the longitudinal screw conveyer and then the transverse screw conveyer, at last the mixture will be transported to the bucket elevator.

Cabin has a interface connected to the dust collector, the adjusted air pipe throttle valve controls de-dusting extraction amount and creates minus pressure in the cabin to prevent dust overflowing.

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Blast unit

Abrasive collecting hopper

Interface to filter

BUCKET ELEVATOR

The elevator transports the mixture of abrasive and impurities to the air separator.

Bucket elevator belt: The elevator belt equipped with buckets is made of fabric reinforces rubber. The buckets are made of wear resistant tempered cast iron. The belt is connected by means of clamp and screws.

Belt drum, control of belt movement, drive: The elevator belt moves between two drums. The upper drum is provided with tensioning system and elevator drive.

In order to prevent backward start of the bucket belt due to weight of filled buckets ,the motor is provided with brakes for backward running.

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AIR SEPARATORThe separator separates the mixture of abrasive, sand and dust by transporting this mixture by a system of cascades.

While the mixture blows over the cascades, the sucked air separates in counter flow the abrasive from impurities and dust.

Air separator Flap: The flap separator balances the non-uniform feed of mixture. It ensures the uniform layer thickness of abrasive, impurities and dust,

Expansion Chamber, Throttle Valve: After passing the cascades, the sucked air enters the expansion chamber. The rough impurities and dust and too fine abrasives are separated.

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1.Air separator flap2.Screen 3.Abrasive outlet4.Abrasive distributor5.Door6.Abrasive inlet

OUTLET

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ABRASIVE HOPPER Only clean abrasive after separated from mixture of air separator can fall into storage hopper. It is installed above the blast units with two lever switches. At the bottom of hopper there are four interfaces connected to the abrasive valves.

There are two lever switches equipped on the hopper, if the high lever switch inspects there are no abrasives , control panel will show warning “MISSING ABRASIVE” to inform the operators to add abrasive. If the low lever switch insects there are no abrasives ,blast machine will stop automatically

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ABRASIVE GATES

The abrasives flows through a pneumatically operated abrasive feed valve to the corresponding blast wheel. The abrasive flow is regulated by an end stop, which can be adjusted by means of a stop bolt.

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Inlet tube insertion

Pneumatic cylinder

Proximity switch

Stop Bolt

Indicator lever

BLAST UNITS

The blast machine has 4 blast units installed. The abrasive is fed through the feed spout casing to the centre of the blast wheel, to the impeller, where the abrasive gains the radial acceleration, from the impeller, the abrasive is led through the rectangular opening in the control cage to the blades of the blast wheel.

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Blast wheel

BLAST UNIT WITH MOTOR Control Cage

AcceleratorNotch

SCREW CONVEYER

There are two screw conveyers (longitudinal and transversal) under shot blast cabin. Transversal screw conveyer transports abrasive from longitudinal screw conveyer to bucket elevator and then into separator. At the end of the screw shaft is equipped with driving motor.

There is another screw conveyer used to transport abrasive from abrasive replenisher to bucket elevator.

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SCREW CONVEYER

ROLLER CONVEYER

The roller conveyer consists of 10 pieces of rollers. Three of them which direct installed on blast hot pot are made of special wear resist material. It is chain driven. The driving parts outside the cabin and speed of roller can be adjusted by frequency changer. Roller conveyer can also rotate clockwise and anticlockwise. Distance ring is used to prevent workpieces deviating, encoder is equipped on the shaft end of transport roller near the entrance of blast cabin to inspect position of workpieces.

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ROLLER CONVEYER

ABRASIVE REMOVAL DEVICE

Abrasive removal device is used to remove abrasive from workpieces coming from blast cabin, it is composed of three system:

High pressure blower- to remove most of abrasive

Low pressure blower- to remove residual abrasive

Compressed air removal device- to further and fully remove abrasive, using of compressed air removal system depends on the real situation, pressure air supply done by customer.

Inside the abrasive removal cabin, there are nozzles which are manually adjustable according to the height of the workpieces by means of a threaded bar. The angle of nozzle can be manually adjustable to the range 10º-50º.

There are some rubber curtains inside the removal cabin and a silencer to reduce noise on high pressure blower.

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1.High pressure removal system2.Low pressure removal system3.Compressed air removal system4.Silencer5.Rubber curtains6.Nozzle

SPECIFICATIONS OF ABRASIVES

Abrasive: For ordinary usage, the resilient abrasives made of cast steel or grains of steel wire are suitable. The granules of hard cast are not recommended. It has shorter life times and it causes high wear.

Operating mixture: The operating mixture consists of rounded grains of various size. The rough grains must remove the covering layers. The medium sized grains clean the surface. The fine sized grains make the final cleaning and smooth the surface.

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SS 230 SHOTS

REPRESENTATIVE BREAKDOWN DATA ANALYSIS OF SBM FOR ONE MONTH (OCTOBER-2015)

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21%

16%

15%13%

13%

12%

10%

BREAKDOWN TREND FOR OCT-2015

BUCKET ELEVETOR

OUT FEED P/C

LONGITUDINAL

CONVEYOR

CLEANING ROLLER

LM SLIP

BLAST WHEEL

PROBLEMTIME IN

MINUTES

BUCKET ELEVETOR 215

OUT FEED P/C 160

LONGITUDINAL CONVEYOR 150

CLEANING ROLLER 130

LM SLIP 130

BLAST WHEEL 120

SHOTS LEAKGE 105

REASON FOR DOWNTIMEDOWNTIME IN

MINUTES

SBM LEAKAGE 105

MANUALLY SHOTS CLEANING 0

OUT FEED P/C 160

SHOTS ON LM 30

CLEANING ROLLER 130

PREWASH CONVEYOR 25

IN FEED P/C 85

LONGITUDINAL CONVEYOR COVER 150

BLAST WHEEL 120

BUCKET ELEVETOR 215

UNLOADING HOIST 20

OUT FEED ROLLER CONVEYOR FAULT 30

LOADING SLAT CONVEYOR 15

TOTAL 1035

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REPRESENTATIVE CUMULATIVE SBM BREAKDOWN DATA FOR ONE MONTH (OCTOBER-2015)

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BREAKDOWN OF SBM OCT-2015

BREAKDOWN DATA ANALYSIS OF PTCED (APR’15-MAR’16)

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BREAKDOWN DATA ANALYSIS OF PTCED (APR’15-MAR’16)

SBM BREAKDOWN ANALYSIS (APR’15-MAR’16)

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SBM BREAKDOWN ANALYSIS (APR’15-MAR’16)

ANALYSIS OF THE SBM BREAKDOWN DATA (APR’15-MAR’16)

On analysing the data of SBM breakdown data over a period of 1 year (APR’15-MAR’16), the following problems pertaining to the SBM breakdown were found to be occurring frequently and consumed a significant of the total downtime which was 11987 minutes.

SHOTS ON LM (Total downtime-1540 minutes)

BLAST WHEEL FAILURE (Total downtime-2254 minutes)

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13%

19%

68% SHOTS ON LM

BLAST WHEEL

FAILURE

OTHER PROBLEMS

FISHBONE DIAGRAM FOR SHOTS ON LM

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SHOTS ON LM

MANENVIRONMENT METHOD

MATERIAL MACHINE

Checking and cleaning of LM not done by operator

Improper nozzle orientation

LM having less number of holes and improper orientation

Improper size of shots and incompatible

material

Conditions inside SBM is too dusty due to malfunctioning dust collector

Faulty rubber curtain Nozzle choked

due to dust particles

Air blowers not working properly

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ANALYSIS OF THE FISHBONE DIAGRAM

On analysing the data and going through the findings the following points were highlighted:1.Low abrasive warning ignored by the operator leading to uneven firing resulting in residual shots on LM.2.At times when LM is stuck inside the machine of if there is a problem with the centring of the LM SBM has to be tuned to manual mode during which the automatic nozzle is dysfunctional during which the LM is to be thoroughly cleaned manually because after switching to automatic mode the conveyer and the nozzle do not start simultaneously which leads to some uncleaned patches on LM.

MANChecking and cleaning of LM not done by operator

Nozzle cleaned by wire

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METHOD

Improper nozzle orientation

For effective removal of the shots on LM the nozzle angle needs to be set at an angle of 50-55º failing to do so will lead to residual shots on LM.

Nozzle not inclined properly

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MACHINE

Nozzle choked due to dust particles

Air blowers not working properly

Despite having a dehumidifier installed in the compressor plant water droplets still come along with the compressed air and due to the absence of any device to check the water content at the outlet of the nozzle the dust particles adhere to the nozzle outlet during the period when the nozzle is idle i.e., air is not coming out of the nozzle because it is automatically controlled by a sensor which works during the presence of LM.

Air Knife ioniser for dust removal

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MATERIAL

LM having less number of holes and improper orientation

Improper size of shots and incompatible material

Faulty rubber curtain

Some LM like LPT 2518/62, LPT 1613/62, LPT 3718/62 have comparatively lesser number of holes due to which sometimes the shots could not be completely removed. Other problems include worn out rubber curtains and problems in centring of LM or due to bent LM due to which the LM gets struck on the roller conveyer leading to manual switching of the machine which again leads to manual cleaning.

Patches having less holes

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ENVIRONMENT

Conditions inside SBM is too dusty due to leakage of shots

A malfunctioning dust collector unit or a leaking blast unit may lead to a very dusty condition inside the LM which may leading to blocking of the nozzle. The blast machine unit needs to be cleaned failing, to do so may lead to dust accumulating on the nozzle.

SUGGESTIONS AND RECOMMENDATIONS

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A Regulator, Filter (RF) Unit has been fitted to limit the supply of compressed air to a pressure of 5-5.2 bar from the main header pipe which feeds to three pipes which are respectively 2 in. , 1 in. and 1.5 in. in diameter. The innermost 2 in. pipe presently operates by bleeding out the air at a pressure of around 4.8-5 bar by a series of holes drilled on the pipe itself proceeding further towards the exit of the machine comes a deioniser air knife with a 1 in. pipe which only removes minute dust particles using ionised air and at last a 1.5 in. pipe does the final cleaning. RF UNIT 1.5 in. drilled pipe

The following accessories have already been added to the machine to eliminate the problem of shots coming on LM :

Rubber curtains are provided which somewhat remove the residual shots on the LM.

The innermost 2 in. pipe has nine holes (3 for each LM) drilled in it each having a diameter of 6mm providing a blast of air at a velocity of 35-40 m/sec.

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Air Knife with ioniser to remove minute dust Inner 2 in. pipe for blowing off shots

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The table below compiles the losses due to the leakage of air from the open pipes with drilled holes in it:

SIZE OF HOLE (mm) AIR LOSS (SCFM)POWER REQUIRED

(kW)ANNUAL COST

(INR)

0.75 1 0.2 6745

1.5 4 0.8 26890

3 17 3 101180

6 70 12 404750

10 150 25 843150

12 270 45 1517670

This shows that although the present systems in the machine cleans the shots but the effectiveness is low primarily due to the 1)Air loss2)Lack velocity and volume regulation of the air flow. Therefore an adjustable device must be incorporated to deliver a high velocity, high volume flow as per requirement consuming the least amount of compressed air.

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AIR AMPLIFIER

WHAT ARE AIR AMPLIFIERS?A simple, low cost way to move air, smoke, fumes, and light materials. Air Amplifiers utilize the Coanda effect, a basic principle of fluidics, to create air motion in their surroundings. Using a small amount of compressed air as their power source, Air Amplifiers pull in large volumes of surrounding air to produce high volume, high velocity outlet flows. Quiet, efficient AirAmplifiers will create output flows u p to 25 times their consumption rate.Air Amplifiers have no moving parts, assuring maintenance free operation. No electricity is required. Flow, vacuum and velocity are easy to control. Outlet flows are easily increased by opening the air gap. Supply air pressure can be regulated to decrease outlet flow. Both the vacuum and discharge ends of the Air Amplifier can be ducted, making them ideal for drawing fresh air from another location, or moving smoke and fumes away. Cycle time is dramatically reduced when aluminumcastings are cooled with the high volume airflow of two Air Amplifiers.

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WORKING PRINCIPLE:

Compressed air flows through the inlet (1 ) into an annular chamber (2). It is then throttled through a small ring nozzle (3) at high velocity. This primary airstream adheres to the Coanda profile (4), which directs it toward the outlet. A low pressure area is created at the center (5) inducing a high volume flow of surrounding air into the primary airstream. The combined flow of primary and surrounding air exhausts from the Air Amplifier in a high volume, high velocity flow.

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THE COANDA EFFECT:Coanda Effect: A moving stream of fluid in contact with a curved surface will tend to follow the curvature of the surface rather than continue traveling in a straight line.

DEMONSTRATION OF THE COANDA EFFECT:

To perform a simple demonstration of this effect, grab a spoon and find a sink. You can easily demonstrate the Coanda effect for yourself. Conveniently, these are often found together in the kitchen, no need for highly technical lab. Get a small stream of water coming down from the sink, and then place the bottom of the spoon next to the stream. Dangle the spoon next to the stream coming from the tap.

What is unusual about the Coanda effect is the fact that the fluid or gas flow is pulled so strongly by a curved surface. With a tap, the water will be projected out at a remarkable distance. The degree to which the water and the curved surface remain attached goes beyond the expected. A concave curve will naturally push the flow, but the fact that a convex one would react so strongly to fluid or gas is unusual.

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AIR AMPLIFIERS TO INCREASE INTENSITY AND EFFICIENCY

A variable air amplifier is another option when using compressed air. Air amplifiers produce a constant, high velocity air stream for very targeted drying and blow-off applications. Efficiency is maximized because additional free air is pulled through the unit along with the compressed air. Variable air amplifiers typically provide coverage in the ¾ to 4” (19.1 to 101.6 mm) range at a distance of 6” (152.4 mm). Commonly used for spot drying, blow-off and exhaust operations, variable air amplifiers are ideally suited to robotic applications as well. Benefits of using variable air amplifiers include:

Extremely efficient use of compressed air – up to 90% less than open pipes and 60% less than air nozzles.

Delivers higher volumes of air and operates at higher pressures than air nozzles for fast drying and blow-off.

Low noise.

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MAINTAINING THE INTEGRITY OF THE AMPLIFIED AIRSome air amplifiers feature a protruding leading edge design that directs the airflow out of the knife in a straight stream, producing an air stream that retains its integrity better than other air amplifier. This design also takes advantage of the Coanda effect and air entrainment to economically produce a uniform and constant air stream. The Coanda effect induces the supplied air to attach itself to the surface of the air amplifier and helps maintain the integrity of the air stream further downstream. This effect also creates a condition conducive to entraining ambient air to increase the total volume of air.

Another advantage of the leading edge design is that it provides a visual guide for positioning the air stream, pointing out the direction of the flow. This allows easy positioning of the amplifier to ensure maximum target coverage.

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PERFORMANCE PARAMETERS OF AIR AMPLIFIERS

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*Data provided by Spraying Systems Co. and is based on AA727 and AA707 WindJet® air nozzles. Assumes a 16 hour work day, 5 days a week

Open Pipe Equivalent impact Using Air Amplifiers

Air Consumption reduction %Size in.

(mm)Air Consumption SCFM

(Nl/min)

5/32 (4) 19 (538) 1 25

¼ (6) 41 (1161) 2 28

5/16 (8) 94 (2662) 4 33

½ (12) 177 (5012) 7 35

5/8 (16) 309 (8750) 12 36

The following tables will represent the significant amount of saving of compressed air consumption as well as show the amount of amplification that can be provided which will lead high velocity blast of air.

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Model Air Consumption Amplification Air Vol. at

Outlet

Air Vol. at 6”

(125mm)

Sound Level

SCFM SLPM Ratio SCFM SLPM SCFM SLPM dBA

120020 6.1 173 12 73 2066 219 6198 69

120021 8.1 229 18 146 4132 436 12339 72

120022 15.5 439 22 341 9650 1023 28951 72

120024 29.9 826 25 730 20659 2190 61977 73

120028 120 3396 25 3000 84900 9000 254700 88

Super Air Amplifier Performance at 80 PSIG (5.5 BAR)

DETERMINATION OF TOTAL OUTPUT FLOW AND AIR CONSUMPTION OF AIR AMPLIFIERS

Total Airflow:From the performance curves (above), determine total output flow for any Super Air Amplifier at any pressure.Example: A Model 120021 at 60 PSIG (4.1 BAR) supply air pressure has a total output flow of 120 SCFM (3398 SLPM).

Air Consumption:Divide the total output flow by the amplification ratio (shown in the chart above) to determine air consumption for any Super Air Amplifierat any air pressure.In the example above, the Model 120021 at 60 PSIG (4.1 BAR) supply air pressure has a total output flow of 120 SCFM (3398 SLPM).Dividing this total output flow by its amplification ratio of 18 gives an air consumption of 6.7 SCFM (189 SLPM)

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IMPROVEMENT OVER AIR AMPLIFIERS

One fundamental problem of air amplifiers is the drop in pressure while ensuring a high velocity, high volume flow although not a problem but by maintaining the exact same performance characteristics the pressure drop can be appreciably reduced by using accessories such as:

1) Air Jets

2) Star profile Air nozzles

These can provide a greater amount of force by using the amplified air and work on the principle similar to that of air amplifiers.

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AIR JETS

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Air Jets are larger than nozzles and used when a wider area needs to be hit with the amplified air. They are significantly more efficient than nozzles although often use as much compressed air. Their best use is to replace pairs of nozzles that are used for part ejection or for blow-off applications that require greater force than that provided by air knives or air movers. Nozzles are for point use while air jets can fan out somewhat for better continuous blow-off when a row of them are made. Air jets are all made adjustable with a lock ring to assure the security of any gap setting.

Air Jets pull large volumes of surrounding "free" air throughthe jet to create a directed airflow. The two styles includethe High Velocity Air Jet with high thrust for chip removal,part ejection and drying; and the Adjustable Air Jet wherethe airflow can be adjusted from a "blast" to a "breeze".

STAR PROFILE AIR NOZZLES

The air amplifying nozzle has the best force/air consumption ratio known. Ideal when higher force required in blow off applications.

It provides a high thrust, concentrated stream of high velocity airflow for blow off, cooling, drying and cleaning applications. The sound level is extremely low and air consumption is minimal. The compressed air is ejected through holes located in recessed grooves that can not be blocked or dead ended.

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A) Incoming Air B) Amplified AirC) Entrained ambient Air

FORCE DELIVERY COMPARISON FOR DIFFERENT AIR NOZZLES

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Force at 12" ( 305mm) from targetAll sound levels measured at 3' ( 914mm)All measurements taken at 80 PSIG ( 5. 5 BAR)

INLET (FNPT) AIR CONSUMPTION AT 80 PSIG (5.5

BAR)

FORCE SOUND LEVEL (dBA)

SCFM SCLM Lbs GRAMS

1/8 17.5 495 1 462 82

1/4 32 906 1.8 792 87

3/8 35 991 1.9 850 82

1/2 60 1699 3.3 1497 87

3/4 91 2577 4.5 2041 96

1/2 98 2773 5.7 2585 85

1 168 4754 9.8 4445 89

APPLICABILITY IN THE PRESENT SCENARIO

After comparing performance, force delivery and air consumption data across a wide range of manufacturers we can easily conclude that the above mentioned solution is one of the most efficient and effective solution which can be easily incorporated into the present system with minimal cost. But if there is any need for such modifications can be predicted by some calculations based on assumptions listed below:

1. All of the supplied shots are completely spherical.

2. The material of the shots are homogenous and isotropic.

3. The shots occupy 50 % of the total volume of the long member after shot blasting is completed.

4. A C-Section of uniform section is considered.

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The shots supplied are of the following specifications SS 170 (Dia 0.4-0.7 mm) & SS 230 (Dia. 0.8-1 mm). Considering SS 230 shots of dia 1mm.

Density of stainless steel, ρ= 7.8g/cm3

Volume of shots = 4

3Πr3 =

4

3Π(0.5)3 =4.18x10-3 cm3

Mass of shots = ρ×4

3Πr3 = 7.8g/cm3×4.18x10-3 cm3 = 0.0326 gms.

REPRESENTATIVE CALCULATIONS

Representative C-Section as per given dimensions

Considering a LM with uniform C-Section having the following dimensions Length = 600cmBreadth = 28.5 cmFlange height = 6.5 cm

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Volume of the LM= 600×28.5×6.5 cm3 =111150 cm3

Considering half of the total volume effectively filled with shots,Volume occupied = 0.5×111150 = 55575 cm3

Total no. of shots over the entire length of the LM = 55575 cm3

4.18x10−3 cm3 = 13.29x106

Total weight of the shots = 13.29x106×0.0326 =433430 gms =433.43 kgs.

Considering a length of 1 ft of the C- section,Volume of LM= 30.48×28.5×6.5 cm3 =5646.42 cm3

Considering half of the total volume effectively filled with shots,Volume occupied = 0.5×5646.42 = 2823.21 cm3

Total no. of shots over the entire length of the LM = 2823.21 cm3

4.18x10−3 cm3 = 679.41x103

Total weight of the shots = 679.41x103×0.0326 =22.15 kgs

In order to blow off the weight of shots according to the above calculations three air nozzles (Star type or Air jet type) per LM of a force delivery capacity of 6804 gms can be used which will give a combined capacity of 20412 gms which is enough to blow the residual shots eliminating the need of any further pipes or manual cleaning.

DISCUSSION:

Since a C-Section without the presence of any holes is considered the weight of the shots is overestimated .

A part of the shots falls off from the LM and the nozzle does not have to bear the whole load as estimated.

There is gap between the packing of shots in real life but in the analysis we have considered solid section leading to overestimation of the total load.

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IMPLEMENTATION OF THE IDEA

Presently pipes approximately of total length 1.5 meters with 9 holes (3 for each LM) are being used. Each holes are 6 mm in diameter and the area covered by the blast of air from each nozzle is not presently determined. Using EXAIR SUPER AIR NOZZLE of 6 FNPT (Catalogue available from manufacturer website on request) the width of the effective blast air is shown below as per various models available:

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Super Air Amplifier Airflow Pattern

MODEL # A B C D

120020 inch 1.25 2.2 4.4 6

mm 32 56 104 152

120021 inch 2 2.9 4.7 6.5

mm 51 74 119 165

120022 inch 2.75 3.55 5.15 6.75

Mm 70 90 131 171

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The figure shows the width of the blast at different distances of the nozzle from the workpiece is shown presently the workpieces are placed at 6” from the opening and this nozzle provides a blast of 152 mm. The maximum width of a LM is 285 mm so two super air nozzles placed at a distance of 160 mm can be used to clean out all of the shots.

FISHBONE DIAGRAM FOR BLAST WHEEL BLADE WEAR

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BLAST WHEEL BLADE WEAR

MANENVIRONMENT METHOD

MATERIAL MACHINE

Throttle valve not set at correct opening

The compressed air supply valve to pneumatic cylinder not opened

Blade wear not checked as specified

Improper material of shots and blast wheel blade

Humid conditions leading to coalescing of shots.

V belt broken leading to improper loading Puncturing of

compressed air pipe to pneumatic cylinder

Throttle valve broken or worn

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ANALYSIS OF THE FISHBONE DIAGRAM

On analysing the data and going through the findings the following points were highlighted:

MANThrottle valve not set at correct opening

The compressed air supply valve to pneumatic cylinder not opened

1. If the throttle valve opening is not at a correct opening angle initially during starting the machine then improper amount of blasting media will be fired leading to uneven wearing.

2. The valve supplying compressed air to the pneumatic cylinder might not be opened by the workers leading to absence of blasting media on the wheels.

1. The blades are to be inspected mainly by visual inspection and this is to be done manually and the thickness reduction is to be determined manually and failure to abide by guidelines may lead to excessive wear and breaking of blast wheel.

2. The V-Belt driving the impeller must be checked , failing to do so will lead to vibrations and wear

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METHOD

Blade wear not checked as specified

Correctly operating wheel

A Misbalanced worn-out wheel

1. If the throttle valve is worn or broken then excessive amount of shots will be supplied to the wheels leading to the excessive wear of the blades.

2. A worn out control cage or the accelerator can also damage the wheels.

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MACHINE

V belt broken leading to improper loading Puncturing of compressed

air pipe to pneumatic cylinder

Throttle valve broken or worn

WORN OUT BLADE NEW BLADE

The material being used presently for the blast wheel blade is steel strengthened and hardened with Manganese and shots are made of Stainless Steel. If the blades are not properly alloyed and improper abrasives are used pre mature wearing may occur.

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MATERIAL

Improper material of shots and blast wheel blade

Schematic representation of hot-spot

Presence of humidity on shots may lead them to coalesce together to form rock hard ball like structure which if permitted to enter the blast wheel unit may severely damage the blades. A wire mesh has been incorporated at the entry of the air separator to prevent any such particles entering into the unit.

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ENVIRONMENT

Humid conditions leading to coalescing of shots.

Wire mesh to prevent entry of coalesced shots to blast unit

“A centrifugal blast machine is probably the most self-destructive of all modern mechanical machines.” Enormous numbers of hard particles are pressed against unlubricated rotating surfaces, hence generating fiendish wear problems.

These mechanisms are called “Adhesive wear” and “Abrasive wear”. For both mechanisms we have either “two body” or “three body” situations. These alternatives are illustrated in fig.1.

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SUGGESTIONS AND RECOMMENDATIONS

ADHESIVE WEAR: As the name implies, adhesive wear occurs when two surfaces physically adhere to one another. This type of wear is often called “galling.” Adhesion takes the form of micro-welds formed between the two surfaces. Two nascent metal surfaces pressed together will micro-weld to one another at points of contact. “Nascent” means newborn and implies a surface completely free from oxide protection. Relative movement of the two surfaces breaks apart the tiny points of adhesion, causing wear.

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ABRASIVE WEAR: Abrasive wear mainly occurs when a harder material rubs against a softer material. Emery paper contains particles that are harder than metals—hence its usefulness for rust removal. That is an example of two-body wear. Metallurgists use diamond-impregnated polishing wheels to produce ultrasmoothsurfaces. That is three-body wear. Both two- and three-body wear occurs in shot blasting situations. Abrasive wear characteristically occurs when an asperity on the harder surface strikes an asperity of the softer surface. This is illustrated in fig.4. As an asperity on the harder surface strikes an asperity on the softer surface something has to give! In this case it is the asperity on the softer surface which is work-hardened until it fractures.

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WEAR REDUCTION

Material selection and component design are the two major factors in wear reduction.

Material Selection: Material selection has benefited from the enormous advances made in developing wear-resistant materials. The choice is now so large that it is easy to over-simplify selection. Consider, for example, using just hardness as a wear resistance criterion. The assumption then is that the higher the hardness the greater will be the wear resistance. This assumption is only valid when comparing materials that have similar microstructures. Fig.5 illustrates schematically two types of wear-resistant alloys having the same measured hardness but with quite different microstructures. Each grain of the single-phase material has a similar hardness.

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Component Design: All components that are in a wear environment must be designed to withstand wear to a specified extent. Commercial considerations are of paramount importance for both supplier and user. A balance has to be obtained between cost and useful life. If, for example, it was possible to design a component that had an infinite life then suppliers would soon go out of business. On the other hand if a component had to be replaced frequently then users would be prepared to pay a premium. A universal example is that of light bulbs. The classic shot peening design problem is that of blast wheels whose performance is adversely affected by substantial wear.

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COMPONENT DESIGN

With a blast-wheel we have both high pressures and high speeds. Both accelerator and throwing blades normally rotate at the same angular velocity.

Two-body wear of a blast wheel will occur when shot particles are moving along the blades—shot as one body and the blade as the second body. Another example is when shot particles strike a component’s surface to produce a dent. Three-body wear will occur, for example, when shot particles are trapped between the accelerator and the control cage as infig.9.

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Wear rate increases with both force and sliding speed. One way to reduce the wear rate would be to reduce the diameter of the accelerator—hence reducing both sliding speed and centrifugal force. That approach, however, induces several problems. One is that the throwing blade length must then be a large fraction of the wheel radius. Long blades generate a relatively-large spread angle for the thrown shot stream. Another problem is that exiting the shot through the control cage opening becomes more difficult because the centrifugal force on the shot—pushing it out of the control cage—is lower and also because the outlet slot has to occupy a greater angular proportion of the control cage. The maximum number of throwing blades that can be accommodated without interfering with the shot stream also decreases with increase in blade length. Wear reduction might, however, be effected by component design modification. Such a modification would need to reduce the sliding speed without reducing the accelerator diameter. A modification is presented here which could offer substantial advantages in terms of wear reduction, increased shot stream concentration and reduction of component number.

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REPRESENTATIVE CALCULATIONSIf, for example, the blade tips sweep a circumference of 1.0 m at 60 r.p.s. then the thrown shot will have a velocity of at least 60ms-1. If, for the same example, the accelerator has a circumference of ⅓m (radius 53mm) then shot is scouring the control cage at a sliding speed of 20ms-1. This shot is also being pressed into the accelerator/ control cage interface with an acceleration of some 770 times that of gravity!

That figure comes from dividing the square of the circumferential velocity by the radius of rotation [(20ms-1)2/0.053m = 7540m.s-2 = 770g, where g = 9.8m.s-2].

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POSSIBLE MODIFICATION

Wear reduction might, however, be effected by component design modification. Such a modification would need to reduce the sliding speed without reducing the accelerator diameter. A modification is presented here which could offer substantial advantages in terms of wear reduction, increased shot stream concentration and reduction of component number.

This modification involves:

(a) Not having a separate, static, control cage. Instead every throwing blade has an outlet slot

(b) Having one fewer slot in the accelerator than there are blade outlet slots (and hence blades)

(c) Rotating the accelerator at a specified faster rate than the throwing wheel. This rate synchronizes the accelerator and outlet slots - so that they always coincide at only one point on the circumference

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The accelerator’s angular rotation rate has to be faster than that of the throwing blade wheel by the ratio of the number of throwing blades to the number of accelerator slots. In fig.10 there are eight throwing blades and seven accelerator slots. Hence the accelerator rotation rate has to be 8/7 times that of the throwing blade wheel. The reason for the matched, but different, rotation speeds is that an accelerator slot and a blade slot must only coincide at the same, fixed, angular position – such as P in fig.10. Coincidence is achieved when the product of angular rotation speed and number of slots is the same for both accelerator and blade wheel.

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ADVANTAGES

There are several advantages that can be attributed to the suggested system:

The most important advantage is that the relative surface speeds between the moving parts are greatly reduced for given diameters of accelerator and blade wheel.

For example, a relative surface speed of 35 m.s-1 for an eight bladed wheel would be reduced to 5 m.s-1. This would lead to reduced shot breakage and wear, together with reduced accelerator cage and blade wheel wear.

A second advantage is the number of basic components is reduced from three to two—from accelerator, control cage and blade wheel to simply accelerator and blade wheel. That means that there are now only two major sources of wear and breakage.

With the reduced overall wear it is possible to increase the wheel blade and accelerator diameters so as to accommodate a greater number of blades on a given wheel. That, in turn, leads to a more concentrated thrown shot stream.

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MECHANICS OF CONTROL CAGE SHOT TRANSFER

Conventional blast wheels have two stages of shot transfer:

(i) Shot has to emerge from a slot and cross over the static slot

(ii) To be collected by a moving blade. With the suggested system, shot transfers directly onto a moving blade.

The differences in the respective movements are illustrated. The exit slot for a conventional wheel has to be several times the width of the cage slot. That is to allow time for the surface layers of the shot in the accelerator slot to be transferred to the exit slot. Once in the exit slot the shot is travelling across a “no man’s land” until it crosses into the path of the moving blade. The forward face of the exit slot may be sharply angled to bounce shot into the path of the blade. Once shot is collected by the blade it is propelled outwards by centrifugal force until it reaches the blade tip.

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With the suggested modification, shot is transferred directly to the root of a moving blade as soon as the accelerator slot starts to coincide with an exit slot. It is important to note that the relative speed of the slots is much less than that for a conventional wheel. For an “8/7” modified wheel, the relative motion is seven times slower than that for a conventional wheel. That means that the exit slot does not need to be much wider than the accelerator slot – there is seven times as much time for exiting of shot per degree of wheel rotation. Shot transfer, being direct to the blade, is much more orderly than that with a conventional wheel.

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DISCUSSION

The suggested modification of blast wheel design is purely an academic exercise designed to illustrate the types of thought processes and calculations that might be encountered in product re-design.

Improvement of wear performance is a constant factor for equipment manufacturers. A balance has to be struck between cost and longevity.

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REFERENCEShttp://www.exair.com/en-US/Primary%20Navigation/Products/Air%20Amplifiers/Pages/Super%20Air%20Amplifier.aspx?tab=Specs

http://www.spray.com/popup/how_air_amplifiers_work.html?iframe=true&width=750&height=520

http://www.spray.com/popup/coanda_effect.html?iframe=true&width=750&height=400

https://www.electronics-inc.com/wp-content/uploads/WearAndItsReduction.pdf

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