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Vacuum Carburizing
Low Pressure Carburizing or LPC
Fast Carbon Transfer
No Surface Oxidation
Good Case Depth Uniformity
Integration into Manufacturing
Little Consumption of Carburizing Gas
No Formation of Furnace Atmosphere
High Carburizing Temperatures possible
Advantages of Vacuum Carburizing
Material Temperature ECD Treatment Treatment (0.35 % C) time* time* vacuum gas carburize carburize
16 MnCr 5 930°C 0.6 mm 2.00 hours 2.75 hours
~ SAE 5115 (1700°F)
17 CrNiMo 6 960°C 1.6 mm 7.50 hours 9.50 hours
~ SAE 9310 (1760°F)
* treatment time = carburizing + diffusion + lowering to quenching temperature
Cycle Time Comparison LPC vs. Batch Atmosphere
Time
Convective Heating
Carburizing Diffusioning
Quenching
1
10-1
10-3
10-5
20
940
850
20
Pressure (bar)
Temperature (°C)
Time
LPC Cycle
Process - LPC Exhaust Contents
100%
5 %
90 %*) Approx. 5% other
Hydrocarbons
part of it
< 0.03 Vol.-% Benzene
10 %
45 %
40%
10 %*)
End of
pause
Average over
boost cycle
End of
boost cycle
N2
N2
HC
H2 No thermal off gas
incinerator necessary 5 %
N2
C2Hx
*) depends on Gas ballast flow rate
H2
24/7, 50 weeks per year, 6 hour cycles, 2250 net pounds per load, 3050 gross pounds per load, 4,100,625 pounds per year.
Electrically heated atmosphere furnace process gas figures:
2,810,813 ft3 of CH4 = 2,810,813 ft3 of CO2 x 0.117 lbs per ft3 = 328,865 lbs CO2 or
149.5 Metric tons of CO2 per year per furnace
Vacuum Carburizing (ModulTherm LPC):
95,886 ft3 C2H2 x .05 C2H2 up the stack <5% C2H2 in Exhaust 4794.3 ft3 C2H2 will oxidize to 9,588.6 ft3 CO2 = 1121.9 lbs CO2 or
0.51 metric tons CO2 per year
Naturally, all of these calculations are theoretical and assume properly adjusted systems. The LPC system assumes C2H2 disassociation
>95%. >75% C absorbed by the steel. A known stack discharge of 0-5% C2H2 during boost. The majority of carbon not absorbed by the
load is recovered as particulates in the pump oil filtering system.
Process – Greenhouse Gas Exhaust Volume LPC vs. Batch Atmosphere
A very
“green”
process
Bright and shiny parts after heat treatment
due to
Clean, vacuum process with inert gases.
Highest repeatability / reproducibility
due to
precision of the process.
(ECD uniformity of +/- 0.05 mm or 0.002”
@ CD 0.5 – 0.9 mm or 0.02 – 0.035”)
Significant Characteristics Product Quality
Clean Parts
Significant Characteristics Product Quality
Higher fatigue strength and wear resistance
due to
NO intergranular oxidation at the surface,
higher consistency of case depth between tooth root
and tooth flank,
ECD @ tooth root/tooth flank*
VC + Gas Quench: 80 – 90 %
VC + Oil Quench: 70 – 75 %
Gas Carb. + Oil Quench: < 70 %
*depending on the part size.
greater depth of hardness > 58 HRC in tooth root and
tooth flank (SAE 8620).
Significant Characteristics Product Quality
• No surface or subsurface (intergranular) oxidation (No IGO)
– Atmosphere carburizing typically produces both surface oxidation (dealloying)
and an intergranular oxidation (IGO) layer of 7.5 – 12.5 micron.
Gas-Carburized Vacuum-Carburized
Significant Characteristics Product Quality
Significant Characteristics Product Quality
• Case Depth Consistency
• Carbon Profile Uniformity
Atmosphere Carburize (Oil Quench):
Pitch Line & Root Comparison
180
220
240
260
280
.010
300
200
.020 .030 .040 .050 .060 .070 .080.000
58 HRC
AC @ pitch line
AC @ root50 HRC
50 HRC
58 HRC
Depth (inches)
Hard
nes
s (m
icro
ns)
Root case depth is
significantly lower than Pitch-line case depth
Significant Characteristics Product Quality
Vacuum Carburize (HPGQ):
Pitch Line & Root Comparison
180
220
240
260
280
.010
300
200
.020 .030 .040 .050 .060 .070 .080.000
58 HRC
VC @ pitch lineVC @ root
50 HRC
50 HRC
58 HRC
Depth (inches)
Hard
nes
s (m
icro
ns)
Root case depth is in
the same level as Pitch-line case depth
Significant Characteristics Product Quality
Less distortion and Less variation
due to
Optimal controllability of the quenching process by
• Single-phase “uniform” heat transfer during quenching
• Controllable quenching intensity:
- Free choice of gas pressure (from 1 to 20 bar).
- Free choice of gas speed (2 speeds of the quenching fan).
- Using different gases (Helium, Nitrogen).
(Optimized quenching achieves desirable hardness & minimal distortion)
Significant Characteristics Product Quality
Operational cost advantages:
Environmentally and workplace friendly.
Flexible in operation
Potential to eliminate post HT press quenching or straightening
Significant Characteristics Operation
For more information contact us at:
ALD Vacuum Systems, Inc.
50477 Pontiac Trail
Wixom MI 48393
(248) 956-7610
www.ALDVac.com