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Ask The Expert Metals

For our vacuum furnace, how can we get adequate gas pressure to quench at pressures up to 20 bar?

Steve Ruoff
Commercial Technology Manager, Metals Processing

There are a number of ways to address the challenge of high pressure gas quench in vacuum furnaces – and a variety of factors to consider in order to achieve the most economical high pressure gas supply solution.

First, you need to know the furnace gas volume required for backfilling. Then, the corresponding surge tank must be properly sized, which requires a balance between the maximum tank operating pressure and its internal volume. This surge tank pressure is one of the key factors that influences the type of gas supply system that is best suited to your operation. Another factor to think about is the estimated monthly volume of gas you’ll use, which is dependent on the number of times all of the furnaces will require a backfill.

Next, is a consideration of the cryogenic gas supply options. Cryogenic systems using high pressure liquid tanks generally result in the least amount of vented gas, but are capital intensive and are somewhat limited in pressure due to the critical point of the cryogen (i.e. liquid nitrogen is 473 psia, approximately 32 bar). High pressure liquid tanks generally are standardized at 400 and 600 psig. Switching batch-type high pressure systems utilize less costly standard pressure liquid supply tanks (250 psig), but can have high vent losses as the batch vessels vent down each time. These systems are also typically limited to about 450 psig (31 bar). High pressure liquid pumping systems also use standard pressure liquid tanks, with a cryogenic pump filling high pressure cylinder banks or hydril tubes. These systems have a much higher pressure range (up to as much as 2,300 psig) and if properly specified, have relatively low vent losses, however they often have the highest overall capital cost. Additional factors to consider as part of a complete evaluation include the maintenance costs for each type of system, along with the unit price for the gas.

Air Products applications engineers can work with you to thoroughly understand your parameters. Then, they can help you evaluate the benefits and considerations to each type of supply, in order to deliver a system optimized to your operation.

To contact us about your heat treating challenge, send us an e-mail or call 800-654-4567 (press 1 and mention code 749).

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