1

Restructuring of a Parabolic Rolling Production Line of Frauenthal to

Improve its Energy and Production Efficiency

GUILHERME DE CAMPOS MATIAS VENDEIRINHO

Under supervision of Prof. Viriato Sérgio de Almeida Semião

Mechanical Departmenent, IST, Lisbon, Portugal

November, 2014

ABSTRACT

This paper focused on the identification and analysis of three main measures to reduce the energy

consumption of Frauenthal factory, with significant impacts on the improvement of its energy and production

efficiency.

The first suggested measure aims to conceive a more efficient forging procedure by changing the parabolic hot

rolling process. To achieve this, a numerical simulation was performed using ANSYS® commercial code to

characterize the thermomechanical phenomena during rolling of steel bars, in order to enable the design of a

new rolling mill capable of processing simultaneously both ends of the steel bars.

The second measure is intended to achieve the direct use of the energy contained in the exhaust gases of an

annealing furnace for subsequent injection into the inlet of a tempering furnace.

The third measure is related to the recovery of thermal energy contained in the hot quenching oil and

tempering furnace exhaust gases to meet the heat demand in different parts of the plant.

With the assistance of an application software developed in MATLAB®, which allows the characterization and

monitoring of different energy and productivity aspects, it is concluded that the three measures are

economically viable, enabling an effective final energy saving of 30% and an energy bill reduction of 25%.

Computational modelling of the rolling process has shown the main factors influencing the heat exchange and

temperature distribution on the billet, as well as the major forces that occur during rolling.

KEYWORDS: Final energy saving, Energy efficiency, Hot rolling mill, Finite element method, Temperature

distribution, Energy management software

1. Introduction It is essential to create favorable conditions for automotive companies to be competitive, so they can

anticipate the challenges of competition and respond to them in a socially responsible and innovative way.

Thereby, the main objective of this work is the energetic and economic assessment of the implementation of

three measures that promote energy and productive efficiency of the Frauenthal factory, after the

restructuring of one of its parabolic rolling lines. The purpose of this work includes the development of a

software that estimates the of costs associated with the energy consumption of the factory. On the other hand,

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it is also intended to carry out a numerical simulating of the hot rolling process, in order to evaluate the

benefits provided by the first measure, which is the largest one.

The Finite Element Method (FEM) simulates the rolling process of steel bars with a high level of certainty and

proved to be a useful tool in the study of severall hot rolling parameters, improving not only industrial planning

but also the design of new rolling lines with the increasing productivity in perspective [1].

It is known that the geometrical parameters are directly associated with the rolling forces, while the

thermomechanical and structural parameters are related also to the temperature distribution on the bar after

the passage of the roll [2]. The influence of those parameters on the modelling of the rolling process will be

presented in detail on chapter three.

The factory studied in the present work, Frauenthal Automotive Azambuja, produces parabolic leaf springs for

the automotive industry. The primary energy consumption of the factory in 2012 reached 4306 TEP, which for

that year corresponded to a consumption of 2566 kWh/ton of produced stock, resulting in a production cost of

124,8 €/ton.

Figure 1.1 - Flowchart of the productive process in the forging area, where 1-Bar cutting lines, 2,3 – Parabolic rolling lines,

4,5 – Eye forming lines and with the heat treatment lines at the end [3]

As shown on the figure 1.1, the processing of steel bars starts at the cutting lines (1 in figure 1.1), followed by

the individual rolling on each side of the blade. Subsequently, each eye is formed individually (4 e 5 in figure

1.1) and finally the heat treatment of the parts is carried out. Each process requires partial heating of the bar

followed by a forced cooling before entering in the next line.

2. Energy Efficiency Measures 2.1. Dimensioning of the New Hot Rolling Single Line – Hot Zone

A MATLAB® application was conceived allowing the analysis of energy data collected manually, and the

correlation of these elements with the production data. The table 2.1 shows some energy data obtained with

this software for the production lines that will be covered by this first measure, among which it should be

noted the low efficiency and high annual cost of the furnaces for each production line.

Table 2.1 - Production and energy data of the lines that will be merged into the new PR single line

The huge waste of energy that occurs in some furnaces, the fact that there is a forced cooling of hot steel bars

between each of 5 forging processes and both the slowness and the complexity of the forging process reveals a

high potential for improving energy and productive efficiency.

Production

Line

Monthly

Production (ton)

Monthly Natural Gas

Consumption (m3)

Specific Consumption

(Wh/kg)η

Average working

days (days)

Natural Gas

Annual Cost (€)

Weighted

Consumption (%)

Average efficiency

of furnaces (%)

325 601 11110 3550 5% 20 97322 7% 20,9%

405 527 9992 728 25% 20 87529 7%

406 623 16595 1023 18% 20 145369 11%

407 109 3905 1378 13% 11 34211 3%

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The proposed solution intends to the reduce energy waste and the above mentioned productive inefficiencies

by designing a single production line where the entire forging process of the steel, with the exception to the

eye forming lines, is done in a continuous line. So, the main goal is to merge the cutting line 325, and the

parabolic rolling lines 405, 406 and 407, shown in the figure 2.1(a), into one single line as shown in the figure

2.1(b).

Figure 2.1 - Forging area with light springs processing lines (blue) and heavy springs processing lines (red), as well as

some of the possible routes for light springs (blue arrows) (a) and location shown in blue for the new single line without 405, 406, 407 and 325 lines (b)

The biggest barrier to implementing this measure lies in the design of a mill capable of processing both sides of

the bar simultaneously. The equations 2.1, 2.2 e 2.3, developed in accordance with the Slab Method [4], are

the starting point for the chosen bar profile (or thickness) that will be used in the numerical simulation of the

rolling process, whose results will be presented in chapter 4.

Figure 2.2 - Schematic representation of the variables involved in the sizing of a rolling process

Table 2.2 – Equations used to calculate the rolling load, P, in accordance with Slab Method

𝑃 =2

√3𝜎0 [

𝑏

𝑄(𝑒𝑄 − 1)√𝑅𝛥ℎ] (2.1) 𝑃[𝑁] is the rolling load, σ0 [MPa] is the steel flow stress, b [m] is the width of the bar, μ

is the friction coefficient between the bar and the roll, R [m] is the roll radius, Δh [m] is

the absolute thickness reduction, ℎ̅ [m] is the average thickness in each roll passage and

T [N.m] is the torque in the rolls.

𝑄 =𝜇𝐿𝑝

ℎ̅ (2.2)

𝑇 = 𝑃𝐿𝑝 (2.3)

After performing the calculation of the daily productive capacity of the new line it turned out that this single

line will have a capacity that is 25% greater than the lines 325, 405, 406 and 407 altogether, summing up a total

of 2646 springs/day. In order for this to be achieved, a 1024 kW induction heating furnace was dimensioned.

2.2. Recovering of the thermal energy in the furnace 537 exhaust gas to inject in the 541 tempering furnace

This measure intends to directly forward the exhaust gases from the furnace 537 to the fresh air inlet of

furnace 541, which will be achieved through the installation of an air duct that will capture the hot exhaust

gases in the entrance of furnace 537. Figure 2.3 illustrates how to achieve this benefit.

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Figure 2.3 - Representation of the reutilization of the exhaust gases from furnace 537 (left) to furnace 541 (right)

The available power, 𝑃𝑜𝑡𝑒𝑥ℎ𝑎𝑢𝑠𝑡_537, to inject in furnace 541 can be calculated with an ordinary energy balance.

Thus, after finding the flow rate of the exhaust gases available at the inlet of the furnace 537, the following

parameters were calculated: the heat received by the new air duct for passing near the hot surface of the

furnace 537; the heat loss from the duct to the environment; and the main inlet’s (figure 2.3) fresh air flow,

�̇�𝑓𝑟𝑒𝑠ℎ 𝑎𝑖𝑟, shown in table 2.3, that ensures a temperature inside the furnace 541 slightly above 300 ° C.

Table 2.3 - Power available in the exhaust gases and fresh air admitted in the main inlet

𝑃𝑜𝑡𝑒𝑥ℎ𝑎𝑢𝑠𝑡_537 (kW) 474,8

�̇�𝑓𝑟𝑒𝑠ℎ 𝑎𝑖𝑟 (kg/s) 0,7

2.3. Quenching Oil and Furnace 538 Heat Recovery In this measure will be analysed two solutions to recover the heat contained both in the exhaust gases of the

538 tempering furnace and in the quenching oil of the heat treatment lines.

In the first solution the use of air-fluid heat exchangers (i.e. finned tubes) will be studied, while in the second

the use of radiant panels will be studied only in the paint ovens. In both measures the heat will be transported

to the cold zone of the factory with a thermal fluid.

The heat exchange between the thermal fluid and the exhaust gases of 538 furnace will be made using a coil

formed by tube banks, while the heat exchange with the quenching oil is made with a plate heat exchanger

2.3.1. Liquid-to-Air Heat Exchangers The purpose of this measure is to transform the current circuit, shown on the left side of figure 2.4, in the

circuit of the right side of the same figure.

Figure 2.4 - Schematic representation of the initial circuit (left) and the circuit to be installed (right)

Three circuits will be designed, where the first transports the heat to the paint ovens, the second one to

electrical heaters in the warehouse and showers, while the third circuit transports the heat to the domestic hot

water central (DHW).

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First, the heat requirements of each paint oven, �̇�𝑎𝑖𝑟_𝑑𝑟𝑦𝑖𝑛𝑔, were evaluated by an energy balance, taking into

account the desired temperature inside each oven. Subsequently, it was evaluated the temperature at which

the thermal fluid needs to reach the paint ovens, 𝑇𝑛𝑒𝑐𝑒𝑠𝑠𝑎𝑟𝑦_𝑖𝑛𝑙𝑒𝑡, with equation (2.4):

𝜀 =

(𝑡𝑜 − 𝑡𝑖)

(𝑇𝑛𝑒𝑐𝑒𝑠𝑠𝑎𝑟𝑦_𝑖𝑛𝑙𝑒𝑡 − 𝑡𝑖) (2.4)

On the previous equation, 𝜀 refers to the design efficiency of the heat exchangers to be installed in the paint

ovens and the DHW central (𝜺 = 𝟎, 𝟕𝟓), 𝑡𝑜 [K] is the outlet temperature of the fluid with the lower heat

capacity rate, �̇�𝐶𝑝 (Air and Water, in the paint ovens and DHW central, respectively), 𝑡𝑖 [K] is the inlet

temperature of the fluid with the lower �̇�𝐶𝑝, 𝑇𝑛𝑒𝑐𝑒𝑠𝑠𝑎𝑟𝑦_𝑖𝑛𝑙𝑒𝑡 [K] is the temperature of the fluid with the higher

�̇�𝐶𝑝, in order to satisfy the heat required, �̇�𝑎𝑖𝑟_𝑑𝑟𝑦𝑖𝑛𝑔 (Thermal fluid).

Through an iterative method, knowing the available energy by radiation and convection in the exhaust gases of

538 furnace and quenching oil, discounting the heat losses from the thermal fluid that come from the heat

treatment area until it reaches every heat exchange point in the cold zone of the factory, and knowing the

mass flow in the piping, it is possible to calculate the total length of the tube bank to be installed in 538 furnace

(84m) and the heat recovered in the furnace 538 and in the quenching oil (table 2.4)

Table 2.4 - Summary of energy recovered in the 538 furnace and in the quenching oil

448 kW to Pain ovens, 60kW to DHW and 52 kW to Electric heaters

Total needs

Circuit 1 (kW)

Total needs

Circuit 2 (kW)

Total needs

Circuit 3 (kW)

�̇�𝑐𝑖𝑟𝑐𝑢𝑖𝑡 1 (𝑘𝑔

𝑠) �̇�𝑐𝑖𝑟𝑐𝑢𝑖𝑡 2 (

𝑘𝑔

𝑠) �̇�𝑐𝑖𝑟𝑐𝑢𝑖𝑡 3 (

𝑘𝑔

𝑠)

Heat recovered in the Furnace

(kW)

Heat recovered in the

Quenching oil (kW)

448,0 60,0 63,4 2,59 0,426 1,169 347,6 168,0

2.3.2. Radiant Panels Solution The solution proposed in this section is similar to the previous one, since it was considered the use of radiant

panels instead of air-fluid heat exchangers. Equation (2.5) shows the used method to compute the energy

required to dry the ink in the steel bar, which was then used to design the radiant panels to be installed.

𝐸𝑣𝑎𝑝 = 𝑚𝑝𝑎𝑖𝑛𝑡ℎ𝑓𝑔 + 𝑚𝑝𝑎𝑖𝑛𝑡𝐶𝑝𝑤𝑎𝑡𝑒𝑟(𝑇𝑓 − 𝑇𝑖) (2.5)

Where, 𝐸𝑣𝑎𝑝 [J] is the necessary energy to evaporate the water in the bar surface, 𝑚𝑝𝑎𝑖𝑛𝑡 [kg] is the mass of ink

applied on the bar surface, ℎ𝑓𝑔 [kJ/kg] is the latent heat of vaporization of water and 𝑇𝑖 and 𝑇𝑓 [K] are the initial

and final temperature of the bar, respectively. The heat recovered in the furnace 538 with this second solution

is, approximately, 248 kW and the necessary length of the tube bank is significantly reduced to 46m.

It should be noted that this solution provides a significant reduction in the insulation and piping, since it is

possible to suppress the circuit 2 (DHW) because there is still enough energy available in the thermal fluid after

all thermal exchanges that occur at the end of the circuit 1.

3. Modelling of the Rolling’s Thermo-Mechanical Process The hot rolling process was simulated using ANSYS® code, based on the finite element method (FEM).

To simplify the mathematical and physical modelling of the rolling process, the following assumptions were

taken into account: (i) the simulation was considered two-dimensional (2D); (ii) the temperature in the roll axis

direction is assumed to be constant; (iii) the rolling load, P, in both rolls, upper and lower, as well as the

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geometry of the steel bar, are symmetrical relative to its center plane (as shown in figure 3.1); (iv)

Thermoplasticity effects and the heat generated by the friction force were ignored. [1,2,5]

Figure 3.1 - Symmetry plane representation, rolling load, P, initial, hi, final, hf, and absolute thickness reduction, Δh

3.1. Mathematical Rolling Mill Modelling The behaviour of the steel was assumed to be elastic-plastic after being assumed that the strain-rate of the

steel during its parabolic rolling is reduced and, therefore, negligible. The thermal and mechanical properties of

the steel bar and the roller are defined as temperature dependent functions. Figure 3.2 (b) shows the

temperature dependency of the 0,2% tensile yield strength for a similar steel to that to be used in this

modelling (51CrV4).

Table 3.1 summarizes the constitutive and thermal equations employed in this model.

Table 3.1 - Summary of thermal and constitutive equations used in the model

Constitutive Equations

Elastic Plastic

Symbol Equation Symbol Equation

{𝜀𝑒𝑙} {𝜀𝑒𝑙} = {𝜀} − {𝜀𝑡ℎ} (3.1) 𝜀̃ 𝜀̃ = 1.15ln (ℎ𝑖

ℎ𝑓) (3.3) [6]

{𝜎} {𝜎} = [𝐷]{𝜀} (3.2) {𝜎𝑦} [3

2𝑠𝑖𝑗𝑠𝑖𝑗]

1

2 − 𝜎𝑦=0 (3.4)

Heat Equation 𝜕

𝜕𝑥(𝑘𝑥

𝜕𝑇

𝜕𝑥) +

𝜕

𝜕𝑦(𝑘𝑦

𝜕𝑇

𝜕𝑦) +

𝜕

𝜕𝑧(𝑘𝑧

𝜕𝑇

𝜕𝑧) = 𝜌𝑐𝑝

𝜕𝑇

𝜕𝑡 (3.5)

In table 3.1, {𝜀𝑒𝑙} is the elastic strain vector, {𝜀} is the total strain vector,{𝜀𝑡ℎ} is the thermal strain vector,

{𝜎} is the stress vector, {𝜎𝑦} is the yield stress, [3

2𝑠𝑖𝑗𝑠𝑖𝑗]

1

2 is the equivalent yield stress, according von Mises

yield criteria, [𝐷] is the elasticity matrix, and 𝜀̃ is the effective strain in the deformation zone during hot rolling.

Figure 3.2(a) shows the bilinear isotropic (BISO) hardening criteria used in ANSYS® which illustrates the Young's

modulus, E, and tangent modulus, ET. In the plastic deformation, 𝜎 is determined directly from the equivalent

plastic strain vector {𝜀̃𝑝𝑙} as shown in figure 3.2 (a).

Figure 3.2 - Bilinear hardening (a) [7] and 0,2% yield strength as function of temperature (b) [8]

The thermal-mechanical simulation was made with a strong (or fully) coupled analysis. In this strong solution

approach, the distribution of temperature is obtained simultaneously with the temperature field [2,7]. The

model proposed in this work follows this approach; it couples the vectors of structural load {F} and thermal

load {Q}, according to the matrix equation (3.6).

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[[𝐶] [0]

[𝐶𝑡𝑢] [𝐶𝑡]] {

{�̇�}

{�̇�}} + [

[𝐾] [𝐾𝑢𝑡]

[0] [𝐾𝑡]] {

{𝑢}

{𝑇}} = {

{𝐹}

{𝑄}} (3.6)

In the previous equation, {T} is the vector of the temperatures, {Q} is the vector of the total heat flow (given by

the sum of the contributions due to the convection, to the surface loads and to the heat generated internally),

{u} is the vector of the displacements, [K] is the stiffness matrix, [Kt] and [C

t] are the total conductivity and the

specific heat matrix, respectively, and [𝐾𝑢𝑡] and [𝐶𝑡𝑢] are thermoelastic stiffness and damping matrices,

respectively.

3.2. Numerical Modelling Due to the high width/thickness ratio, the simulation model performs a transient analysis in plane stress of a

2D bar profile, whose representation is made in figure 3.3. This profile was chosen because it maximizes the

horizontal forces, which depend mostly on the absolute thickness reduction, Δh (figure 3.1), as will be seen in

chapter 4.

Figure 3.3 – Upper roll and upper bar dimensions (in mm)

It should be noted that this rolling process involves a traction car that applies a horizontal force on the bar,

while rolls apply only vertical forces. In this process there is no torque applied to the rolls, unlike the traditional

rolling processes. The X and Y rolling profiles are given in figure 3.4.

Figure 3.4 - Y (green) and X (red) rolling profiles (in m)

For the discretization of the geometry it was defined a computational mesh that divides the two-dimensional

geometry into finite elements. A mesh with 3186 quadrilateral elements was chosen to perform the thermal-

mechanical strong coupled simulation. The bar geometry has 1800 elements, whilst the roll has 3186 elements.

Figure 3.5 shows the arrangement of the cells in the discretization domain.

Figure 3.5 – Mesh with 3186 elements

The table 3.2 shows the thermal and structural boundary conditions (BCs) used in the simulation, according to

the referential of figure 3.5, where u and v (m/s) are the velocity components in X and Y directions,

respectively.

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Table 3.2 – Boundary conditions used in the numerical simulation

4. Results and Discussion The bar profile shown in the figure 3.3 was chosen taking into account that, according to Equations 2.1, 2.2 and

2.3, the profile 4 shown in table 4.1, whose Δh is equal to 5 mm, requires the greatest horizontal force

compared with the remaining profiles of table 4.1.

Table 4.1 – Relevant parameters to choose the bar profile

Figure 4.1 shows the time evolution of the horizontal and vertical force, Fh an Fv, respectively, obtained with

the numerical simulation performed with the mesh displayed in figure 3.5.

Figure 4.1 - Time evolution of force Fh e Fv

As would be expected, the time evolution of Fh along the roll passage follows, qualitatively, the Y profile of the

roll (figure 3.4). The moment of greatest solicitation of force Fh (734,9 N), and Fv (5216,4 N), occurs precisely

at the instant of greatest vertical penetration of the roll. An important remark is the possibility of applying

torque on the rolls, which effectively reduces the horizontal force required at least by half.

Figure 4.2 shows the temperature distribution in the bar after the passage of the roll.

Figure 4.2 - Isothermal curves in the bar after roll passage (Instant: 3s)

The minimum temperature in the bar takes place at the surface and near its right end after the roll passage.

Also, the region near the symmetry plane, over its entire length, has the highest temperature in a region where

the heat transfer occurs only by conduction in the material.

hi (mm) hf (mm) Δh (mm) b (mm)Redução espessura

relativa (%)hmed na passagem (mm)

Carga de

separação P (kN)

Angulo α

(rad)

Componente

horizontal Fh (kN)

Perfil 1 13,2 10,3 2,9 70 22% 11,75 284 545 0,092 26 167

Perfil 2 11,75 8 3,75 70 32% 9,875 424 599 0,119 50 444

Perfil 3 12 8 4 70 33% 10 433 283 0,127 54 890

Perfil 4 25 20 5 70 20% 22,5 355 193 0,159 56 161

Steel Bar: 𝑇𝑡=0 = 𝑇(𝑋, 𝑌)0 = 830 °𝐶 Roll: 𝑇𝑡=0 = 𝑇(𝑟, 𝜃)0 = 400 °𝐶

Structural BCs X=-450 mm X=450 mm Y=-50 mm

Y=-62,5 mm

r=0 mm r=R=50 mm r=27,5 mm

u=- 1/6 𝑚

𝑠 - - v=0 Figure 3.3 Rigid -

Thermal BCs

Radiation -

𝑞𝑟𝑎𝑑′′[

𝑤

𝑚2] −𝑘𝑥

𝜕𝑇(𝑥, 𝑦, 𝑡)

𝜕𝑥− 𝑘𝑦

𝜕𝑇(𝑥, 𝑦, 𝑡)

𝜕𝑦= 𝜎𝜀(𝑇(𝑥, 𝑦, 𝑡)4

− 𝑇∞4 ) + ℎ(𝑇 − 𝑇∞)

- - −𝑘𝑥𝜕𝑇(𝑟,𝜃,𝑡)

𝜕𝑥−

𝑘𝑦𝜕𝑇(𝑟,𝜃,𝑡)

𝜕𝑦=

ℎ𝑒𝑥𝑡(𝑇 − 𝑇∞) + 𝜎𝜀(𝑇(𝑥, 𝑦, 𝑡)4 − 𝑇∞

4 )

−𝑘𝑥

𝜕𝑇(𝑟, 𝜃, 𝑡)

𝜕𝑥

− 𝑘𝑦

𝜕𝑇(𝑟, 𝜃, 𝑡)

𝜕𝑦= ℎ𝑖𝑛𝑡(𝑇 − 𝑇∞)

Convection -

𝑞𝑐𝑜𝑛𝑣′′[

𝑤

𝑚2] - -

Thermal Contact Heat Flux : 𝑞′′𝑏𝑎𝑟 = − 𝑞′′𝑟𝑜𝑙𝑙 = ℎ𝑐 (𝑇𝑏𝑎𝑟 − 𝑇𝑟𝑜𝑙𝑙) , 𝑡 > 0, r= 𝑅,

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The figures 4.2 and 4.3 show that the conduction occurring inside the bar due to the thermal gradient

generated in the bar surface after the roll passage is much more significant than the heat transfer solely by

convection and radiation. There is also the perpendicularity of the isothermal curves on the symmetry plan.

Figure 4.3 – Temperature distribution in the bar at the maximum penetration point (Instant: 2,5 s)

Figure 4.4(a) reveals a sudden change of temperature in the bar surface after the passage of the roll, from

616°C, right after the 2,5 s instant, until 771°C at 3s, compared to the smooth change that occurs from the first

moment up to 2,5 s. Figure 4.4(b) confirms that for the same X coordinate, but on the symmetry surface, the

evolution of the temperature remains practically unchanged, except some asymmetries occurring at 2,5 s,

when the roll passes by.

Figure 4.4– Temperature evolution at maximum penetration Instant (2,5s)

Regarding the economic valuation of the three suggested measures, the main results are shown in table 4.2.

For this study it was considered an investment period of 10 years, an energy price increase of 4%/year and a

discount rate of 9% (Inflation: 3%, real income: 3%, 3% risk premium, VAT: 0%).

Table 4.2 - Summary of the economic results of the 3 suggested measures

In the first measure, which is the dimensioning of the new hot rolling single line, the economic feasibility study

results in a payback period (PP) of 2 years and 1 month, an internal rate of return (IRR) of 57,1% and net

present value (NPV) of 4 190 169 €. This is the worst case scenario, in which the new rolling mill, capable of

processing both sides of the steel bar simultaneously, has a cost of 900 000 €.

In the second suggested measure, which is the forwarding of the exhaust gas of furnace 537 to the tempering

furnace 541 inlet, the PP is around 6 months, the IRR is 199,3 % and the NPV is 527 554 €.

Year 1 (€)Final Energy

(kWh)

Primary Energy

(TEP)

GHG Emissions

(tonCO2e)

1 - Single Line 755 468,6 8 702 982,2 657,2 1 846,3 - 1 150 000,0 1,7

2 - Recovering of furnace 537 exhaust

gas to inject in 541 tempering furnace 77 878,5 2 002 070,0 169,8 383,3 - 39 600,0 0,6

3 - Quenching Oil and 538 Furnace Heat

Recovery 87 351,9 1 336 124,2 168,3 423,3 - 105 107,2 1,3

Total 920 699,0 12 041 176,4 995,3 2 652,9 - 1 294 707,2

Savings

Investment (€)Payback Period

(Years)

10

In the last measure, the quenching oil and furnace 538 exhaust gas heat recovery, the solution with liquid-to-

air heat exchangers has a PP of 1 year and 11 months, an IRR of 61,7 % and NPV of 429 689 €. The second

solution with radiant panels has a PP of 1 year and 4 months, an IRR of 85,4 % and a NPV of 525 634 €.

5. Conclusions Although there is a reduction in energy consumed per ton produced by the factory over the past years, from

2691 kWh/ton in 2008 to 2566 kWh/ton in 2012, energy costs per ton produced (€/ton) tends to increase, from

96,6 €/ton in 2008 to 124,8 €/ton in 2012. Such situation reinforces the need for continuous implementation of

energy efficiency measures in order to invert this trend of increasing energy costs.

With the assistance of the developed application software, it is demonstrated that the three presented

measures enable a saving of 30% of the final energy and a 25% savings of energy costs. The total savings

exceed 920 000 €, which represents a very interesting value since it shows that there are indeed improvements

that can be undertaken to reduce costs associated with energy. Moreover, the developed software allowed the

company's managers to conclude that the average efficiency of the factory’s furnaces is 20,9%.

Along with the numerical simulation it was also obtained some qualitatively relevant information, such as the

evaluation of the existing efforts during the rolling of the steel bar, the temperature distribution during and

after the passage of the roll, the variation of the forces as a function of rolling parameters, and the required

torque on the rolls in order to reduce the horizontal force limitations of current rolling mills. Indeed, it can be

seen that the major temperature reduction in the bar during rolling is due to the passage of the roll and the

application of torque is an essential factor to design the new rolling mill that can handle both sides of the bar

simultaneously.

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vol. 134, pp. 338-351, 2003.

[2] Galantucci, L. M. e Tricarico, L. “Thermo-mechanical simulation of a rolling process,” Journal of Materials

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[3] Continuous Improvement, Energy Workshop_Report, Frauenthal Group, 2010.

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[5] W.B. Lai, T.C. Chen e C.I. Weng, “Transient thermal stresses of work roll by coupled thermoelasticity”,

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[6] Kumar, D. e Dixit, U.S. “A slab method study of strain hardening and friction effects in cold foil rolling

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[7] ANSYS® Academic Research, Release 14.5, Mechanical APDL Theory Reference, 2012.

[8] Chen, J, Young, B. e Uy, B., “Behaviour of High Strength Structural Steel at Elevated Temperatures”, Journal

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