This presentation reviews the features of ALD ModulTherm® and DualTherm® systems and the corresponding advantages of High Pressure Gas Quenching.

1. Process Principles of
High Pressure Gas Quenching
In ModulTherm® and DualTherm®

2.  Reduction of hardening distortion and/or variation of distortion
 Quenching intensity adjustable by of gas pressure and gas velocity
 Process flexibility
 Clean, non-toxic working conditions
 Integration into manufacturing lines
 Reproducible quenching results
 Clean and dry parts, no washing
 Simple process control
High Pressure Gas Quenching (HPGQ) Advantages

3. Bubble Boiling
Film Boiling
Convection
t = 10 s
750°C
700°C
700°C
600°C
500°C
400°C
300°C
200°C
Temperature distribution
t = 10 s
Heat transfer coefficient 
5000 10000 15000 20000
Öl
oil Wasser
water
[W/m K]
2
ref.: Stick, Tensi, HTM 50, 1995
Heat Transfer & Temperature Distribution
Immersion Quenching

4. Heat transfer coefficient 
1000 2000 3000 4000 [W/m K]
2
Temperature distribution
750°C
650°C
550°C
450°C
350°C
250°C
Gas direction
Only convection
Heat Transfer & Temperature Distribution
High Pressure Gas Quenching (HPGQ)

5. Heat Transfer Coeffizient  (W / m2 K)
0 500 1000 1500 2000 2500 3000 3500 4000
Water (15-25 °C)
Agitated oil (70-180 °F)
Air 1 bar
He 20 bar (hot chamber)
He 20 bar (cold Chamber)
Saltbath quench (1020 °F)
N2 6-10 bar (hot chamber)
Still oil (70-180 °F)
Fluidised bed
N2 / He 1 - (10) / 20 bar
Heat Transfer Coefficient  different quenching media

6. Chemical symbol
Density at 15 oC
and 1 bar
Density relative to air
Molar mass
(kg / kmol)
Specific heat capacity
Cp (kJ / kg K)
Dynamic viscosity
 (N s / m 2)
Thermal conductivity
 (W / m K)
Argon Nitrogen Helium Hydrogen
Ar
1,6687
1,3797
39,948
0,5024
177x10- 4
22,6x10- 6
N 2
1,170
0,967
28,0
1,041
259x10- 4
17,74x10- 6
He
0,167
0,138
4,0026
5,1931
1500x10- 4
19,68x10- 6
H 2
0,0841
0,0695
2,0158
14,3
1869x10- 4
8,92x10- 6
(at 25 oC und 1 bar)
Gas Properties
High Pressure Gas Quench

7. 0
2
4
6
8
10
12
14
16
0 2 4 6 8 10 12 14 16 18 20
0
2
4
6
8
10
12
14
16
0 2 4 6 8 10 12 14 16 18 20
Relative Motorpower for
cooling gas fans
Relative
Heat Transfer Coefficient
Gas pressure (bar) Gas pressure (bar)
HPGQ Influencing Parameters

8. Multi Chamber Vacuum Furnace
(Cold Chamber)
Backfill time to
final pressure >> 10 sec
Backfill time to
final pressure << 10 sec
Gas flows
through the
charge and inpart
around the charge
Hot wall
and hot
graphite elements
Gas must
flow through
the charge
Cold Wall
Single Chamber Vacuum Furnace
(Hot Chamber)
HPGQ Quenching Chamber Influences

9. Reversing Gas Flow Increased Quenching Uniformity
Modular Design Flexible and Expandable
Compact Chamber Design Short Gas Recycling Cycles
High Pressure Gas Quenching (HPGQ)
Quenching Chamber

10. Cooling curves in the tooth root of Truck- Gear Wheels (GW)
0
100
200
300
400
500
600
700
800
900
-50 0 50 100 150 200 250
Time /sec.
Temp./°C
GW bottom, no rev.
GW, top, no rev.
gas-temp. bottom, no rev.
GW bottom, with rev.
GW, top, with rev.
gas-temp. bottom, with rev.
Quench behavior in the tooth root of heavy truck gears
HPGQ Quench Chamber
Reverse Gas Flow Quenching

11. 300
320
340
360
380
400
420
440
460
No reversing With reversing
CorehardnessatMid-tooth/HV30
Bottom min
Bottom average
Bottom max
Top min
Top average
Top max
Gas flow Gas flow
300
310
320
330
340
350
360
370
380
390
400
No reversing With reversing
CorehardnessatToothroot/HV30
Bottom min
Bottom average
Bottom max
Top min
Top average
Top max
Gas flow Gas flow
Tooth
root
Mid-
tooth
Core hardness influence in the tooth root of heavy truck gears
HPGQ Quench Chamber
Reverse Gas Flow Quenching

12. High Pressure Gas Quench Chamber
Cold Chamber, 20 Bar with Reverse Gas Flow Quenching

13. 20
25
30
35
40
45
50
0 5 10 15 20 25 30 35 40 45
Jominy Distance (mm)
Hardness(HRC)
20NiCrMo2 (SAE8620)
20MoCr4 (SAE4118)
16MnCr5 (SAE5115)
20MnCr5 (SAE5120)
20NiCrMoS6-4
18CrNiMo7-6
20
bar
He
20
bar
N2
Jominy Curves of steel grades with
high hardenability acc. to EN
10084
Core Hardness Influences
Case Hardened Steel

14. D Ovality of Outer Diameter (mm)
Oil A : Houghton
Quench A
Oil B : Bellini FN
10 bar He
20 bar He
Cold Chamber
0
0,01
0,02
0,03
0,04
0,05
0,06
10 bar
He
20 bar
He
Oil A Oil B
Average and
Standard Deviation
n=12
7
12
6
Material: SAE 52100, (D=70 mm, H=15 mm, S=5 mm)
Dimensional Changes
Bearing Rings

15. Process Comparison
Drive Shafts
Shaft Length up to 750 mm (29.5 inches)
Material 17CrNiMo6 (similar SAE 9310)
Past H. T. Process
Gas Carburizing
Quench in Salt Bath
Distortion over Length of Shaft
Average 3 mm (0.12 inches)
Straightening Scrap 20 %
New H. T. Process
Vacuum Carburizing with
High Pressure Gas Quench with 8 bar
Helium
No Washing – Clean and Dry Parts
Distortion over Length of Shaft Average
1.0 mm (0.039 inches)
Less Straightening Work
No Scrap
Significant Characteristics
Product Quality

16. High Pressure Gas Quenching
500 kg gross Load of Pinions, 20 bar Helium, SAE 8620

17. 0
2
4
6
8
10
12
14
16
18
20
1 2 3 4 5 6
Runout (1/1000 in)
Gas carburizing & Oil quench
Vacuum Carburizing & High Pressure Gas quench
HPGQ versus Oil Quench
Distortion Analysis
Frec

18. Summary
• High pressure Gas quenching can significantly reduce distortion
and/or variation of distortion
• Microstructure, Hardness and Distortion are strongly influenced by:
- Part
- Quenching Parameters
- Cold Chamber Design
• 20 bar Helium Quenching Technology is capable of successfully
hardening low alloyed case hardening steels if material
hardenability can be controlled
• Alloy modification offers the chance to reduce gas
pressure/velocity thereby reducing distortion and/or investment
costs

19. For more information contact us at:
ALD Vacuum Systems, Inc.
50477 Pontiac Trail
Wixom MI 48393
(248) 956-7610
www.ALDVac.com