The Model 921 is a computer-controlled cryogenic processor. It comes with proven processing cooling curves programmed into the computer. Any other desired cooling curves can be easily programmed into the processor. To run the Model 921 Cryo Processor, one icon is clicked and the program will run automatically.
It is a dry process. Liquid nitrogen is converted to a gas before it enters the chamber so that at no time does liquid nitrogen come in to contact with the parts assuring that the dangers of cracking from too rapid cooling are eliminated.
The model 921 uses conventional electrical cooling to reduce the temperature to -100°F, making it the most economical processor on the market. At -100°F, the liquid nitrogen system cuts in, and the dry vapors of liquid nitrogen are used to cool to the desired cycle.
The electric cooling has another advantage. At the end of the run the processor is set to hold a temperature below freezing and not return to room temperature where condensation and rusting can be a problem.
The standard Model 921 Processor uses 220 volt, single phase 11.2 amp service. For a small fee, any other power requirements can be built into the processor.
We list the capacity of the processor at 1500 lbs. We customarily run at 1800 to 2000 lbs. when we make our runs. We have run loads in excess of that although this practice is not recommended. When the processor is loaded about half full while running a normal load of ferrous tools, it uses about one pound of liquid nitrogen for every pound of material processed. Loads less then this are somewhat less efficient, while loads more the half are significantly more efficient. In general, this model provides excellent ease of operation with economical performance and great reliability. There are several older models still in operation worldwide.
The question is often raised if the (heat) tempering should be performed inside the Cryo Processor or if it should be done in a separate tempering oven. We here at 300 Below Inc. considered that question very early in our existence. It certainly would make for a smoother running operation if the material did not have to be transferred from one vessel to another. We found that there are certain considerations that did not make tempering in the cryo processor a good idea:
First: different materials get different (heat) tempering cycles.
Second: different cross sectional areas need different tempering times. Therefore how would it ever be possible to run loads of mixed materials or sizes. If you do, it is a compromise at best.
Next: we pack our processor quite tightly – in our case about 2000 pounds. We do this to make the cooling operation more efficient meaning that we will use less nitrogen. We cool this mass very slowly so there is plenty of time for the cold nitrogen gas to penetrate the mass to achieve the desired temperature. The opposite is required during (heat) tempering, by heating the material rapidly and uniformly. This is just not possible when one attempts to heat a large mass with heaters either on the top or on the bottom of that mass. The outside of the mass will tend to be overheated, while the center may never get to the desired temperature. Thus some of the material may be way over tempered, while some may be barely tempered at all.