Evaluation of Bubblers and Baffles for Cooling of Die Casting Dies
John F. WallaceDavid Schwam
Sun FengSebastian Birceanu
Case Western Reserve University
Cleveland, OH - March 5, 2003
NADCA Die Materials Committee
Introduction
Background:
F Thermal fatigue cracking of die inserts is a constant problem in die casting industry.
F High temperature of die surface is the most frequent cause of thermal fatigue cracking, because it promotes higher thermal stress and accelerates softening.
F A temperature threshold exists, below which the thermal fatigue damage is minimal.
F Bubblers and baffles are typical water cooling devices for dieinserts, slides and cores.
Effect of Overheating to H13 Die Steel
• Specimen: Ø1”×0.5”, Premium Grade H13 Steel, quenched and tempered to 46 HRC.
No.20(20h)No.16No.12No.8No.4100 hours
No.19 (15h)No.15No.11No.7No.350 hoursNo.18No.14No.10No.6No.210 hours
No.17No.13No.9No.5No.11 hour1200 °F1150 °F1100 °F1050 °F1000 °F
Temperature-Time Effect on Softening of H13
25
30
35
40
45
50
0 20 40 60 80 100 120
Tempering Time [hour]
Har
dn
ess
[HR
C]
1000 F
1050 F
1200 F
1100 F
1150 F
• Discussion: Critical temperature is between 1050oF and 1100oF. If the die insert surface temperature can be kept below 1050oF, the service lifeof the die insert will be prolonged.
The Effect of Temperature on Thermal Fatigue CrackingDifferent Immersion Times
0
20
40
60
80
100
120
140
160
180
200
900 950 1000 1050 1100 1150 1200
Temperature [F]
Tota
l Cra
ck A
rea
[x10
6 m
2 ]
5 sec
9 sec
12 sec
7 secThe Effect of Immersion Time
15, 000 cycles
The Effect of Thermal Cycling on Thermal Fatigue CrackingDifferent Immersion Times
0
20
40
60
80
100
120
140
160
180
5000 10000 15000
Number of Cycles
Tota
l Cra
ck A
rea
[x 1
06
m2 ]
5 sec 7 sec
9 sec 12 sec
all below 0.2 5 sec
12 sec
9 sec
7 sec
The Effect of Immersion Time
The Effect of Temperature on Thermal Fatigue CrackingDifferent Cooling Line Diameters
0
20
40
60
80
100
120
900 950 1000 1050 1100
Temperature [F]
Tota
l Cra
ck A
rea
[x10
6 m
2 ]
1.6"
1.7"
1.8"
1.5"
The Effect of Cooling Line Diameter
15,000 cycles
Illustration of Bubblers and Baffles Used in the Experiment
Bubbler
Baffle
Schematic of Water Flows Directed by Bubbler and Baffle
Bubbler
Water Flow
Specimen
T/C Hole
Water Inlet
Water Outlet
T/C Hole
Specimen
Water Flow
Baffle
Water Inlet
Water Outlet
• Water Flow Directed by Bubbler • Water Flow Directed by Baffle
Geometry Details of Bubbler Cooled Specimen
Bottom T/C
Gap BetweenBubbler and Specimen
Bubbler
φ1.5”φ 9/16”
1”0.
2”O.D.I.D..
Specimen
0.06
”
A A
A-A Section
Geometry Details of Bubbler Cooled Specimen (continued)
0.0980.1720.199Bubbler/Specimen Annular Area [inch^2]
0.0630.1250.156Bubbler/Specimen Gap [inch]
0.0740.0360.023Inner Section Area of Bubbler [inch^2]
0.0650.0490.040Wall Thickness of Bubbler [inch]
0.4370.3120.250Outer Diameter of Bubbler [inch]
0.3070.2140.170Inner Diameter of Bubbler [inch]
Geometry Details of Baffle Cooled Specimen
φ 1.5”φ 9/16”
1”0.06
”
Controlled Gap Size
Baffle
H
Specimen
A A
A-A Section
Cooling Efficiency Evaluation of Bubblers and Baffles in Molten Aluminum
Dip In-Dip Out Experimental Setup
Furnace
Molten A356:1350 ºF (600lb)
Water Outlet
Water Inlet Flow Meter
Thermocouple
Specimen(Cycle time: 25s in/25s out)
The Specimen Used in Dip In- Dip Out Experiment
3/8”NPT
3/8 ”
NPT
φ 9/16”
0.06
”
0.07
5”
3/8”
8.75
”
0.4”
10”
Data Processing for Dip In-Dip Out Experiment
1000400
500
600
700
800
900
1000
1100
0 200 400 600 800
Time [second]
Bo
tto
m T
/C T
emp
erat
ure
[F
]
T1T2
T3 T4T5
T6 T7 T8 T9 T10 T11 T12T13 T14 T15 T16
T17T18 T19
∑=
=n
iiT
nT
1
1
800
900
1000
1100
1200
1300
1400
0 0.41 0.83 1.38 2.15 3 3.7Flow Rate of Cooling Water through 0.17” Bubbler [gallon/minute]
Ave
rag
e P
eak
Tem
per
atu
re [
F] 1312
915 900 892 882 875 874
Difference of Specimen Surface Temperatures with/without Water Cooling
(Dip In-Dip Out Experiment; 1” Immersion)
Cooling Effect of Bubblers and Baffles on “Hot Spot”(Dip In-Dip Out Experiment; 1” Immersion)
860
880
900
920
940
960
980
1000
1020
0 1 2 3 4 5
Flow Rate of Cooling Water [gallon/minute]
Ave
rag
e P
eak
Tem
per
atu
re [F
]
0.214 Bubbler
0.17” Bubbler
0.307” Bubbler
Baffle: Gap Area=0.09 inch^2
Baffle: Gap Area=0.17 inch^2
Effect of Bubbler Size and Water Jet Velocity on the Efficiency of “Hot Spot” Cooling
(Dip In-Dip Out Experiment; 1” Immersion)
870
880
890
900
910
920
930
0 10 20 30 40 50 60
Water Jet Velocity [feet/second]
Ave
rag
e P
eak
Tem
per
atu
re [
F]
0.17” Bubbler
0.307” Bubbler
0.214” Bubbler
Water Jet Velocity
where Flow Rate
Section Area
I.D. of Bubbler
A
2
4dF
AF
Vπ
==
F
d
Effect of Water Velocity on Baffles’ CoolingEfficiency on “Hot Spot”
(Dip In-Dip Out Experiment; 1” Immersion)
940
950
960
970
980
990
1000
1010
1020
1030
0 5 10 15 20
Velocity through Gap [feet/second]
Ave
rag
e P
eak
Tem
per
atu
re [F
]
Gap Area=0.17 inch^2Gap Area=0.09 inch^2
Velocity of Cooling Water:
where: Flow rate; Gap Area
AF
V =
F A
Position of Thermocouples for 4.5” Immersion Experiment
0.06
”
1”
3.5”
T1, T1’
T2, T2’
T3, T3’
0.23”
0.23”
700
750
800
850
900
950
1000
1050
1100
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Flow Rate of Cooling Water [gallon/minute]
Ave
rag
e P
eak
Tem
per
atu
re [
F] T1
T1'
T2
T2'
T3
T3'
Immersion Depth: 4.5”: Bubbler; I.D=0.17”: Baffle; Gap Area=0.09 inch^2
Cooling Efficiencies of a Bubbler and a Baffle for a Large Area(Dip In-Dip Out Experiment; 4.5” Immersion)
Conclusions
F The surface temperature of a die casting die plays an important role in the failure of the die. Overheating to die steel results in degradation of themicrostructure and softening of the steel.
F The use of a bubbler or a baffle can be very effective in lowering the surfacetemperature of a die insert, core or slide.
F A baffle is more suitable to cool a certain area, while a bubbler is better for cooling a specific “hot spot”.
F For a given insert and cooling mode, higher flow rates improve cooling leading to lower surface temperature.
Conclusions (continued)
F For a given cooling line and flow rate a bubbler with a smaller inner diameter has a better cooling efficiency at the “hot spot” than a bubbler with a larger inner diameter.
F At same flow rate, high velocity of cooling water enhances the heat transfer between the cooling water and the sidewall of a cooling line. For design and application purposes it is preferable to set up a high velocity of cooling waterin a cooling line in order to lower surface temperatures.
