Application of the C-test methodology for the validitation of boundary condition for oil quenching process.
Adamcikova, Andrea ; Taraba, Bohumil
1. INTRODUCTION
The aim of this paper is the presentation of partial results of the
heat transfer phenomena research by cooling of parts in choosen coolants
used in industrial production. Knowledge of parameters of cooling
medium, physical, mechanical material properties and geometry of a
quenched part allows to predict behavior of a part during cooling
process. The quantification of the combined heat transfer coefficient (CHTC) by the cooling process in quenching oil and verification of its
validity are presented. The obtained boundary condition for convection
heat transfer was based on the Wolfson's test. Combining the
experimental temperature measurement and numerical analysis, the cooling
condition usable for vertical wall was determined. The validity of CHTC
obtained was verified at the same experimental conditions as in
Wolfson's test. Isomax 166 quenching oil in unagitated state at the
temperature of 60[degrees]C was used as a cooling medium for the
C-shaped tested part. The Wolfson's probe and the tested part were
made of DIN 1.4541 material. ANSYS interpretation computer code was used
and solution procedures were transient and nonlinear.
2. EXPERIMENTAL
The oil Isomax 166 belongs to intensive quenching oils of low
viscosity (v= 12.5 [10-.sup.6] [m.sup.2]. x [s.sup.-1] at 40[degrees]C)
and is generally applied for quenching non-alloyed, low-alloyed, alloyed
and carbonized steels. It is resistant to evaporation. The recommended
working temperatures of Isomax 166 range from 40[degrees]C to
70[degrees]C (www.petrofer.com.ua 2008). The experimental equipment
consisted of an electrical resistance furnace of LM 212.10 type,
cylinder-shaped experimental Wolfson's probe (www.extra.ivf.se
2008), Isomax 166 oil and NI USB 9211 for digital record of the
temperatures measured. Before quenching, the probe was heated up to the
initial temperature of 850[degrees]C. The temperatures were measured by
the encapsulated 304 SS thermocouple of K type by the diameter of 1.53
mm situated in the center of the probe. The tested "C" part
(tube) had a longitudinal slot in the tube body by the initial width of
1.72 mm. In the process of cooling the probe and the tested part, the
oil temperature was kept constant at 60[degrees]C, where the cooling
ability of Isomax 166 is maximum (Taraba & Lascek 2006).
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
3. THEORETICAL BACKGROUND
Thermal problem. For the presented problem, temperature fields are
transient and they can be described by the Fourier-Kirchoff differential
equation of heat conduction in cylindrical coordinate system (probe) and
the Cartesian coordinate system (tube), respectively. Material is
considered to be isotropic. Thermal and mechanical properties were given
by functions of temperature for the temperature interval from
20[degrees]C to 900[degrees]C (Tab. 1). Thermal load represented the
boundary condition of the 3rd type, i. e. the heat transfer by
convection (Incropera). Structural problem. The temperature field, tube
shape, thermal expansion and mechanical properties (elastic modulus,
Poisson's ratio and yield stress) generate thermal stress-strain
states. Stress fields are described by the equation for temperature
stress state (Trebuna at al. 2002). An elastic-plastic material model
with bilinear isotropic hardening (Fig. 3) was used. Generation of
plastic strains was evaluated by the Huber-Mises-Hencky's
hypothesis (Trebuna at al. 2002). The reference temperature for
structural task was 60[degrees]C. The geometric models and generated
meshes were generated for one half of the probe (Fig. 1b) and a quarter
of the tube (Fig. 2b).
For probe meshing, 2D elements PLANE77 with the option axisymmetric were used.
[FIGURE 3 OMITTED]
The tube model was meshed by the element of BRICK90 (thermal
problem) and BRICK 186 (structural problem) types (ANSYS 10.0 2005). For
structural analysis, symmetry conditions according to the Fig. 2b were
used. The "C" model was gripped in the point 1 considering the
displacement in the direction of x axis.
4. RESULTS
Fig. 4 shows the measured cooling curve from the Wolfson's
test. The solution was searched via fitting the curves (measured vs.
computed temperatures) and applying the iterative approach to the CHTC,
as the function of surface temperature. The correlation coefficient by
value of 0.995 was achieved by the fitting of curves. The CHTC curve is
shown in the Fig. 5 and it can be considered the boundary condition for
the vertical walls cooling.
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
The tested part. Fig. 6 illustrates the comparison of the
temperature field in the time of 3.2 s after immersing the tube into the
oil, as well as the real photo taken at the same time. Each of the three
types of cooling process is evident: vapor blanked (A), boiling oil zone
(B), convection after ending of boiling (C). There is a reference
temperature field from numerical simulation in Fig. 6b. Distribution of
residual stresses after cooling the part to the temperature of
60[degrees]C is shown in Fig. 7b. It is evident from the Fig. 7b that in
the process of cooling, the stresses reach and exceed the yield stress
of material. The existing residual stresses resulted in the contraction
of the slot width. Time history of the slot width can be seen in Fig.
7a. The maximum change of the slot width was observed during the cooling
in the phase of oil boiling. The final slot width after cooling was 1.43
mm.
[FIGURE 6 OMITTED]
[FIGURE 7 OMITTED]
5. CONCLUSIONS
The relation between the experiment and numerical simulation allows
us to obtain the knowledge and better understanding of the relationships
of cooling parameters in the process of oil quenching.
Loading boundary condition of cooling, obtained by combination of
the Wolfson's test and numerical analysis, was proved acceptable
for vertical walls cooling.
The influence of particular parameters on the stress-strain state
of a tested part during cooling can be determined by the indirect
measurement of the change in the slot width. The slot width after
experimental cooling on one hand, and the computed slot width on the
other hand, exhibited the difference of 0.08 mm.
The research was supported by the projects No. 1/0721/08, 1/0837/08
and 2/7167/27 within VEGA Ministry of Education and the Slovak Academy
of Science, Slovak Republic.
6. REFERENCES
Ansys Theoretical Manual, Release 10.0. (2005). Available from:
http://www.tsne.co.kr/intra/data_center/ansy s/theory. pdf Accessed
2008-06-23
Available from: www.extra.ivf.se/smartquench/dokument/down
load.asp?id=21 Accessed 2008-06-23
Available from:www.petrofer.com.ua/content/hardening_comp
ound/2_1.htm Accessed 2008-06-23 Incropera, F., P. (1996). Fundamentals
of Heat and Mass Transfer, John Wiley Sons, ISBN 0-471-30460-3, New York
Taraba, B. & Lascek, M. (2006). The influence of Isomax 166
quenching oil temperature on its cooling properties. Acta Mechanica
Slovaca, 10, 01, (01 2006) ISSN 1335-2393, 567-572
Trebuna, F.; Simcak, F. & Jurica, V. (2002). Elasticity and
strenght II, Vienala, ISBN 80-7165-364-0, Presov
Tab. 1. Material DIN 1.4541, thermal & mechanical properties.
Temperature Thermal Specific Density
T conductivity heat [rho]
[[degrees] [lambda] c [kg.[m.sup.-3]
C] [W. [J.
[m.sup.-1]. [kg.sup.-1]
[K.sup.-1] .[K.sup.-1]
0 14.8 455 7940
100 15.8 475 7911
200 17.0 495 7871
300 18.4 508 7830
400 20.0 525 7787
500 22.0 550 7745
600 24.0 572 7703
700 25.7 602 7662
800 27.5 620 7620
900 29.4 630 7578
Temperature Elasticity Thermal Yield
modulus expansion stress
E coefficient R.[MPa]
[GPa] [[alpha]
.sub.1].
[10.sup.6]
[K.sup.-1]
0 200 16.8 235
100 195 17.2 233
200 188 17.6 230
300 181 17.8 222
400 172 1S.0 206
500 165 1S.3 174
600 157 1S.5 137
700 147 1S.8 94
800 135 19.0 55
900 100 19.2 36
Temperature Poison's Tangent
ratio modulus
v [E.sub.1]
[-] [MPa]
0 0.3 1185
100 0.3 1175
200 0.3 1160
300 0.3 1080
400 0.3 950
500 0.3 812
600 0.3 660
700 0.3 470
800 0.3 250
900 0.3 185