Ruri Agung W Et Al (2012, A CFD Study of Annealing Treatment ...)

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EECCIS 2012

Abstract — Annealing is the last stage of aluminum foil

production process which often causes undesired condition

of foil. It is mostly caused by improper annealing

treatment. In this paper, annealing treatment for

aluminum alloy AA 1235 in foil annealing furnace (FAF)

has been analyzed. A combined study was conducted by

means of Computational Fluid Dynamic (CFD) to evaluate

thermal distribution inside the two FAF A and FAF B

during heating. Furnace performance from the

temperature control response and conduction time for

heating of aluminum are also analyzed. The FAF A has a

better temperature distribution than that of FAF B, but

there is saturated airflow between the aluminum roll in the

second stage. Based on temperature control response,

settling time of evaporation temperature is achieved about

4 hours for FAF B and can’t be reached in FAF A whereas

it is desired to be reached in 1 hour. It is suggested tochange the proportional mode control to higher value in

order to get fast settling time since the furnace employs

PID controller. There is large different between theoretical

and actual conduction time of aluminum foil that indicates

improper work of insulating material of furnace so that

there is much heat losses.

Keywords — CFD, Annealing treatment, FAF, AA1235.

I. I NTRODUCTION

very rolling mill company especially aluminum foil

production possess many kind of defect and

undesired quality of aluminum foil. They are caused byimproper conditions and treatments of two main

production processes which consist of rolling and

finishing [1] – [2]. It employs a set of cold works in

rolling process that include some passes through rolling

to obtain the desired thickness of aluminum foil. At the

next process, finishing, aluminum foil is also passed

through some steps. They are separating, slitting,

rewinding, annealing and packaging [3].

Rolling process that usually employed in aluminum

company is categorized to cold work. It reduces

thickness of aluminum coil to particular thickness of

aluminum foil by external force from work rolls. It isoperated below the re-crystallization temperature ofaluminum alloy. There is also coolant oil that sprayed

along the surfaces of aluminum coil and work rolls

during rolling process. This coolant oil is added to avoid

direct surface friction between work rolls and coil ofaluminum which caused many defects [3] – [4].

The consequent of rolling process is carrying coolant

oil which embedded inside the rolled aluminum. The

carrying oil needs to be removed from the rolled

aluminum. Therefore, annealing is employed. Basically,annealing is a heat treatment given to soften the metal

due to cold work [1] – [5]. It removes physical stress of

the metal so that some of the mechanical properties are

back to normal. Annealing in aluminum foil production

is a part of finishing process. It is employed to remove

both physical stress and carrying coolant oil ofaluminum foil [2], [3].

It is often found that the aluminum foils still have

worse wet-ability (usually called as weta) and some of

them are too sticky. It is induced by non-evaporated

coolant oil trapped inside the roll of aluminum.

Improper heat treatment of annealing process may becaused by insufficient heat in the furnace or temperature

control in the furnace. In this study we collaborate with

PT. Supra Aluminium Industri (SAI), one of growing

aluminum industries in Indonesia, which mostly work

with AA 1235 (non heat treatable alloy). As the problem

remains, data of quality control of SAI show that there isstill undesired quality of final product after pass through

annealing process.

Foil annealing furnaces (FAF) employed in SAI are

two kind of sided blow inlet-outlet furnace. They havespecific structure and dimension, thermal distributioncharacteristic, and also response to the temperature

control. However, the treatment of annealing process

given to roll of aluminum foil is same to the all of

furnace [2]. The aim of this study is to evaluate the

overall annealing treatment including temperature

control, thermal distribution, and furnace’s performancesince AA 1235 must be treated in proper heat treatment

to get high quality product.

II. THEORETICAL APPROACH AND REAL

PROCESS

Annealing is an additional heat treatment to soften themetal. It removes physical stress resulting from cold

working (cold rolling) given during overall production

process of rolled aluminum foil [1] – [3]. Annealing

A Computational Fluid Dynamics Study of 6.5

Micron AA 1235 Annealing Treatment in Sided

Blow Inlet – Outlet FurnaceRuri A. Wahyuonoa), Wiratno A. Asmoro b), Edy Sugiantoro c), and Muhamad Faisal d)

a,b,d) Department of Engineering Physics, Institut Teknologi Sepuluh Nopember Surabayac) PT. Supra Aluminium Industri (SAI), Jalan raya Kasrie 146 Pandaan - Pasuruan

E-mail address: [email protected], [email protected], [email protected],[email protected]

E



EECCIS 2012

applies heat by convection through the atmosphere

inside an annealing furnace. To avoid oxidizing any

un-evaporated lubricant residues or forming magnesium

oxide on magnesium-bearing alloys, annealing may be

carried out in a dry, inert (low O2) atmosphere such as

nitrogen gas. A large integrated aluminum rolling plantmay have its own nitrogen generating plant for this

purpose [2], [6].

Non-heat-treatable aluminum alloy, commonly

heated for 1.5 – 2 hours in the range of operating

temperature 635 – 765oF or equivalent to 335 – 445oC

[6], [7]. The heat released to the rolled aluminum hasanother objective. It also evaporates the carrying coolant

oil inside rolled aluminum. So that’s why, annealing

chamber must be dry (very low oxygen intensity) to

avoid oxidizing of coolant oil in the surfaces.

Annealing process in SAI is batch annealing. It

means loading a furnace with a batch of metal, roll ofaluminum foil, and holding it there until the annealing

process is complete. Rolls of aluminum foil are annealed

as a single batch, depending on the size of the foils andthe size and shape of the furnace [2]. In batch annealing,

heat conveyed by the furnace atmosphere to the outsidesurfaces of the foils must be conducted through the

metal to the innermost layers, and sufficient time must

be allowed for all parts of each foil to absorb enough

heat to achieve the planned anneal [1], [3]. Batch

annealing is an efficient approach and is the most

commonly used method in high-production aluminumfoil mills.

Fig. 1. Heat treatment scheme of batch annealing in SAI

The annealing scheme is describe as three stages of

thermal treatments (See Fig. 1). They are heating,

soaking and cooling. In heating stage, aluminum foil is

heated to particular temperature up to 5 hours.

Temperature setting depends on the thickness of

aluminum foil. Soaking stage holds annealing chambertemperature to particular value for 15 – 20 hours. This

step also includes evaporating and drying. The last

stage, cooling, chills amount of rolled aluminum for two

hours inside the annealing chamber. It’ll be pulled out

later if the temperature reaches 70oC [2].

Evaporation of carrying coolant oil of 6.5 micronaluminum foil is estimated to occupy 15 hours of

heating with temperature setting 225

o

C. Since the presence of receding fold (RF) on aluminum foil after

annealing, it is identified that the mechanism of

preheating (big temperature different) induces thermal

shock. The thermal shock effect can be reduced by

applying graded pre-heating.

III. METHOD

First analysis of the annealing problem is temperature

and airflow distribution since decrease in temperature in

some volume of chamber can induce incomplete

evaporation. This has caused to some rolls of aluminumfoil is still in worse wet-ability and/or sticky. This

analysis is conducted based on the simulation results of

Computational Fluid Dynamics (CFD) simulation

intended to analyze temperature and air flow

distribution in the empty and filled chamber of Foil

Annealing Furnace (FAF). The furnace is distinguished

as FAF A and FAF B which the aluminum is in specific

orientation inside the chamber.

A. Computational Fluid Dynamics

The computational fluid dynamics, usually

abbreviated as CFD, is a branch of fluid mechanics

using numerical methods to analyze and solve problemsthat involve flows of fluid. CFD has also been used as

powerful tool for thermal analysis in incubator [8], [9].

Numerical method is built by employs the governing

equations such as conservation of energy, momentum

and continuity. Energy conservation is determined as

equation shown below [10].

heff

eff

S

T k p E E t

..

.. (1)

where k eff is effective conductivity which the value is

equal to sum of k and k t (thermal conductivity for the

presence of turbulence). The two terms on the right siderepresent the energy transfer by conduction and

viscosity dissipation.For the solid region (i.e. newborn body), energy

transfer is calculated by employing equation as follow

[8], [9]:

hS T k hvht

).().()(

(2)

where is solid density, h is sensible enthalpy, k isconductivity constant of newborn, T is newborn skin

temperature, and S h is volumetric heat source.

The equation (1) and (2) are complemented by

continuity and conservation of momentum defined below:

0. u (3)

u p F dt

du 2 (4)

where p is normal pressure (N/m2), F is body force on

solid region.

B. Thermodynamic Analysis

The analysis of conduction rate has been developed.

The heat transfer and thermodynamic (control volume)

approach is used to determine how long the aluminumfoil steadily reaches the setting temperature furnace. The

first assumption is the type of material must be solid or

rigid body so that the roll of aluminum foil is same as

0 10 20 30 40 50 60 70 80 9040

60

80

100

120

140

160

180

200

220

240

Time (hours)

Temperatur(oC)

Pre-heating 1 (130 oC ~ 8 hr)

Drying (180 oC ~ 60 hr)

Pre-heating 2 (160oC ~ 8 hr)

Evaporating (225 oC ~ 15 hr)

http://en.wikipedia.org/wiki/Fluid_mechanics

http://en.wikipedia.org/wiki/Numerical_methods

http://en.wikipedia.org/wiki/Numerical_methods

http://en.wikipedia.org/wiki/Fluid_mechanics



EECCIS 2012

rigid cylinder. The Fourier equation that represent

conduction rate is given below [11].

dx

dT k

A

q (6)

Since the aluminum foil is assumed to be cylindrical, the

cross-section area become a circle. The equation (6) can

be written:

dr

dT rLk

dr

dT kAqr 2 (7)

Integrating (7) for r 1 to r 2 in left side and T 1 to T 2 in right

side, so that we obtain:

1

2

21

ln

2

r

r

T T kLqr

(8)

In evaporating phase, the temperature different is 65oC.

The aluminum foil on evaporation temperature (225

o

C)has conductivity coefficient 222 W/m K. In this study,

specification of aluminum roll is 82 cm width, 34 cmOD (Outer Diameter) and ID (Inner Diameter) 8 cm. By

using (8), the heat needed for aluminum foil roll is 5.413

kW. As the time setting for transient response during

pre-heating to evaporating is 1 hour, the released heat

which needed is approximately 51,356 kWh .

The energy balance on a control volume is given asequation below.

ee

e

q

q

e

ii

i

p

p

icvcvcv

gz V

hm

gz V

hmW Qdt

dE

n

n

2

2

2

1

2

1

(9)

There are no work applied in the control volume so that

the value ofcvW equals to zero. Potential energy

difference of inlet and outlet can be neglected since the

value is too small. Steady state analysis results as

follow:

ip

ip

ip

p

p

ip

eq

eq

eq

q

q

qecv

gz V

hm

gz V

hmQ

n

n

2

22

1

2

1

(10)

Since AV m , (10) can be rewritten as,

ip

ip

ip

p

p

ipip

eq

eq

eq

q

qqeeqcv

gz V

hV A

gz V

hV AQ

n

n

2

2

2

1

2

1

(11)

The calculation of energy in control volume (furnace)

provides the data of heat accumulated inside the

chamber. From this value, it can be determined the

theoretical settling time of air chamber and annealed

aluminum in the FAF.

IV. RESULT AND DISCUSSION

A. Thermal Distribution

FAF A has the setting basket to hang the roll of

aluminum foil in front-rear direction. The heat is blown

to spherical surface of aluminum roll. The orientation of

aluminum rolls inside the chamber makes the capacity

of FAF A is only 32 rolls. The CFD simulation result of

temperature and airflow distribution is given as follow.

Fig. 2. Temperature distribution of FAF A in (a) right-

left view and (b) front-rear view

This Fig. 2 expresses temperature distribution of FAF

A chamber. It shows that the chamber has better

temperature distribution in bottom to half of chamber

height. The upper stage reaches temperature setting inthe center.

Fig. 3. Airflow distribution of FAF A in (a) right- left

view and (b) front-rear view

Based on Fig. 3, lower velocity magnitude of air is

distributed in upper side. However, it won’t affect much

to annealing in FAF A since the upper side of chamber

isn’t fully filled by rolls of aluminum foil. It shows that

the airflow distribution is almost well (average airflow

magnitude is about 2.09 ms-1). The higher airflowmagnitude (3.35 – 4.19 ms-1) is only distributed in

bottom of chamber.



EECCIS 2012

Fig. 4. Temperature distribution on roll of aluminum foil

inside FAF A

The distributed heat in the roll of aluminum annealed

in FAF A is shown as Fig. 4. In the figure shows that

almost all of aluminum is well treated by the proper

heat, especially in the side closed to inlet flow. This

condition can minimize the weta and/or sticky of

aluminum foil.

Fig. 5. Temperature distribution of FAF B in (a) right-

left view and (b) front-rear view

Fig. 6. Airflow distribution of FAF B in (a) right- left

view and (b) front-rear view

Based on the result on Fig. 5, temperature of FAF B

chamber can’t reach the set point in almost all of area.

Only several rolls of aluminum in the upper side get air

temperature 1 – 2 oC lower than the set point

temperature. The highest airflow magnitude (2.66 – 3.2ms-1) in FAF B is achieved in bottom to half of chamber

then it drops until 0.38 ms-1 on the upper side. Fig. 6

clearly shows that the fourth stage of aluminum rollsisn’t supplied adequate airflow to blow up the vaporized

carrying oil.

Fig. 7. Temperature distribution on roll of aluminum foil

inside FAF B

Comparing to FAF A, the distributed heat in the roll

of aluminum annealed in FAF B isn’t better as shown as

Fig. 7. In the figure above shows that the second row of

aluminum foil inside the chamber isn’t get the proper

heat. Only half of aluminum foil rolls in first row is

heated in the desired temperature. It probably induces

some weta condition of aluminum rolls.

B. Evaluation of Temperature Control and Furnace’s

Performance

The temperature control on both FAF A and FAF B is

recorded in overall annealing time which consumes 93 –

95 hours. Notice that the FAF A and FAF B employ PID

controller to control the temperature of annealing.

Transient and steady response of temperature control in

FAF A is given in the figure below.

Fig. 8. Response of temperature control of annealiang

process in FAF A

The steady conduction time of aluminum foil rolls in

FAF A is theoretically obtain by dividing conductive

heat transfer by accumulative evaporation heat. Based

on thermodynamic calculation, the conduction time of

aluminum foil in FAF A is 0.152 hour. This value is

lower than the actual conduction time which needs 1 – 4

hours to settle. The detail data of settling/conduction

time of aluminum foil in FAF A is as in Table 1.

Table 1. Settling time for evaporation temperature

set point of FAF A

Zone T Set 0.5oC Tinit evap.

1 1 0.96

0 10 20 30 40 50 60 70 80 900

50

100

150

200

250

Time (hours)

Temperature(K)

Air Temperature at Zone 1



Metal Temperature



EECCIS 2012

2 1 0.96

3 1 0.96

Metal Temp. ~ 4

The recorded temperature response of annealing in

FAF B is follow.

Fig. 9. Response of temperature control of annealiang

process in FAF B

The evaporation settling time based on control

response in FAF B (see Table 2) is about 1 hour foraluminum in zone 1 and can’t be reached for aluminum

in zone 2 (see Fig. 9). The conduction time for annealing

aluminum foil in FAF B is 0,042 hour theoretically.

Table 2. Settling time for evaporation temperature

set point of FAF B

Zone T Set 0.5oC Tinit evap.

1 1 0.97

2 1 0.93

Metal Z1 1 0.97

Metal Z2 ~ ~

Both of FAF A and FAF B have a quite big different

of conduction time theoretically and actual, taken from

response of temperature control. As usual, this data

analysis indicates that improper heat treatment is

occurred while annealing. Two conditions that might become the cause of this condition are undesired heat

process/heat transfer and inappropriate control mode for

temperature annealing.

C. Discussion

Considering the result of temperature and airflow

distribution from CFD simulation, FAF A has good

thermal distribution than FAF B. However, the settling

time to evaporating phase in FAF A is about 1 – 4 hours.

The FAF B has average settling time to evaporation phase about 1 hour. It fit to transition setting time of

pre-heating and evaporating. The temperature andairflow distribution for FAF B is worse than FAF A.

That is caused by the profile of airflow inside the

chamber is different. Comparing to furnace that has

inlet-outlet in the side of chamber, the airflow of FAF B

is worse than the FAF A. This condition is caused by the

geometry of blade sticked in the inlet and outlet zone is

different to FAF A. The orientation of aluminum foil roll

is also affect to airflow distribution. It is recommended

to change the blade of FAF B as the FAF A has orchange the orientation of aluminum roll annealed in the

chamber to get better het treatment.

Comparing settling time of metal/aluminum in to

conduction time of aluminum oil rolls in each FAF,

there is big different value. Theoretically in FAF A, it

only need about 0,016 – 0,152 hour to reach the set pointtemperature. However in fact, aluminum foils need 4 to

reach the set point temperature. Moreover aluminum foil

in FAF B can’t achieve the set point temperature. It is

probably caused by two problems explained in the

previous point. They are improper tuning controller and

the condition of insulating material. Due the FAF A andB still using PID controller, it should be check that the

value of proportional constant, time derivative and time

integral setting is based on transient response. Since thesettling time is too much longer then the proportional

constant should be substituted to higher value to get fastresponse. The other problem may be caused by the

insulating material (e.g. glass wool, grafite, gypsum,

etc) inside the annealing chamber doesn’t work properly

so that there is so much heat losses during the annealing

process. In order to reduce the heat losses, it is

recommended to check the condition or thermalconductivity of the insulating material.

V. CONCLUSIONS

Annealing treatment of AA 1235 in foil annealing

furnace has been analyzed. FAF A has quite bettertemperature and airflow distribution which is set point

temperature and higher airflow magnitude is distributed

in upper side of chamber. The worst temperature and

airflow distribution is possessed by FAF B. The

upper-right side of chamber gets lower temperature so

that it may induce weta. There is heating problem due

the big difference between conduction time of real

process and theoretical calculation. It is probably caused

by improper control tuning of PID controller in the

furnace and heat losses by under works of insulation

material.

ACKNOWLEDGMENT

Thanks to Dr.-Ing. Doty D. Risanti and Dyah Sawitri,

M.T. for the helpful comments on the analysis of

annealing treatment. This study was supported by PT.

Supra Aluminium Industri Pasuruan for giving

measurement data of FAF and Indonesia-Germany Fast

Track Scholarship from Directorate of Higher Education

for the grant.

R EFERENCES

[1] The Aluminum Association. 2007. Rolling Aluminum: From the

Mine Through the Mill . The Aluminum Association, Inc.[2] Visual Quality Characteristic of Aluminum Sheet and Plate, the

Aluminum Association Inc., 4th Edition February 2002

[3] Annisa Kesy Garside, “Penentuan Setting Parameter ProsesFinishing Rolling untuk Aluminium Foil dengan Thickness Exit

0 10 20 30 40 50 60 70 80 90

0

50

100

150

200

250

Time (hours)

Temperature(K)



Metal Temperature at Zone 1

Metal Temperature at Zone 2



EECCIS 2012

7 Mikron di PT. Supra Aluminium Industri.” Laporan Magang

Dosen, Program Hibah A1, Jurusan Teknik Industri – FT,

Universitas Muhammadiyah Malang, 2005.[4] Smith, W. F. 1990. Principle of Materials Science and

Engineering 2nd Edition. New York: McGraw-Hill Publishing

Company.[5] Jing Zhang, Fusheng Pan, Rulin Zuo, Chenguang Bai. The low

temperature precipitation in commercial-purity aluminium

sheets for foils. Journal of Materials Processing Technology.2008; 206: 382 – 387.

[6]

Ozgul Keles, Murat Dundar. Aluminum foil: Its typical quality

problems and their causes. Journal of Materials ProcessingTechnology. 2007; 186: 125 – 137.

[7] R. J. Vidmar. (1992, August). On the use of atmospheric plasmas

as electromagnetic reflectors. IEEE Trans. Plasma Sci. [Online].21(3). pp. 876 — 880. Available:

http://www.halcyon.com/pub/journals/21ps03-vidmar

[8] Ruri Agung Wahyuono. Analisis Distribusi Temperatur dan

Aliran Udara Pada Inkubator Bayi dengan Variasi Tipe Dinding

dan Overhead Screen. Undergraduate Thesis Department of

Enginering Physics. Institut Teknologi Sepuluh Nopember.2012.

[9] R. A. Wahyuono, R. Hantoro, G. Nugroho. Study on Dry Heat

Loss of a Very Low Birth Weight (VLBW) Newborn Nursed inan Infant Incubator with Overhead Screen. Proceeding of SITIA

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J. Blazek. Computational Fluid Dynamics: Principle andApplications. ELSEVIER SCIENCE ltd. 2001.

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and Mass Transfer 4th Edition. U.S.A.: John Wiley & Sons, Inc.

Ruri Agung Wahyuono was born in Pasuruan, 21 February 1990. His

B.Eng degree was gotten from Engineering Physics Institut Teknologi

Sepuluh Nopember (ITS), Surabaya - Indonesia majoring ininstrumentation & control and energy – environmental engineering.

Recently, he takes graduate program in the same department of

Engineering Physics through Fast Track Grant Indonesia – Germany.He actively do some research in the field of heat process using CFD

and currently develop research of dye-sensitized solar cell (DSCs).

Wiratno Argo Asmoro was born 29 February 1960. He graduated

from Engineering Physics Institut Teknologi Bandung (ITB),

Surabaya - Indoensia majoring in instrumentation and his M.Sc degreewas get from Electrical Engineering ITB. Recently, he responsible as

lecturer in Department of engineering Physics ITS in the field of

acoustic and electronics. His research interest is about acoustic andvibration.

Edy Sugiantoro recently responsible as PPIC manager in Supra

Aluminium Industri Pasuruan. He graduated from Material

Engineering Institut Teknologi Bandung (ITB) – Indonesia. He is well

known as expert in aluminum process in high-production aluminummills in several aluminum industries mostly as manager in quality

control department.

Muhamad Faisal was born in Jakarta, 23 November 1992. Recently,

he takes undergraduate program in Engineering Physics Institut

Teknologi Sepuluh Nopember (ITS), Surabaya - Indoensia majoring inenergy – environmental engineering. His research interest is about

developing technology of renewable energy.



Ruri Agung W Et Al (2012, A CFD Study of Annealing Treatment ...)

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