The Benefits and Limitations
Oxygen in the furnace forms a scale on the surface of knife blades and other parts during heat treating. To avoid surface scale, wrap the parts in heat treating foil or inject an inert gas into the furnace. The gas displaces the oxygen.
Please note that the gas may reduce heating element life. Also, gas injection does not offer better results than heat treating foil nor does gas injection prevent all scaling. The main benefit of gas injection is the savings in time over wrapping the steel in foil.
The Flow Meter Solenoid Kit
The flow meter can be ordered with an optional solenoid kit, which enables you to turn the gas on or off for each segment, or stage, of the firing. (Please add $101.00 for the solenoid kit to the price shown below.) Paragon knifemaking furnaces are available with the 12-key Sentry controller and the compact, less expensive 3-key Sentry Xpress. The solenoid kit must be ordered with the 12-key controller. Program the controller to turn on the gas at temperatures where carbon begins to form on the tool steel.
The Flow Meter Pressure Regulator
In addition to the flow meter, you will also need a regulator to reduce the pressure from the gas tank. The gas pressure to the flow meter should be less than 20 psig (psig = pounds per square inch, gauge). (Paragon does not sell the pressure regulator.)
Flow Meter Operation
The gas will leak out through the furnace bricks and sheet metal seams, because the furnaces are not air tight. This is why you will need a steady flow of gas at high temperatures. However, gas at room temperature will expand to over ten times its volume when injected into a firing chamber at 1000°F and above. This is why a low setting on the flow meter is adequate to prevent most scaling.
Argon gas is popular for heat treating because of its price. Please note that the gas will not support life and is heavier than air. Therefore, your shop must be well ventilated when using gas injection.