IONITECH Ltd. Furnaces for Plasma (Ion) Nitriding are fully automated. After loading the parts in the working chamber the technological program begins. It allows – vacuuming and change of the working atmosphere, ion bombardment that creates a sputtering effect and final cleansing of the parts, heating and nitriding (nitrocarburizing). There is a possibility for later oxidation, cooling in plasma, in vacuum or faster with nitrogen or argon.
Scavenging: After vacuuming to 0.5 mbar the chamber is filled up with working gas to a predetermined pressure for a predetermined time in order to remove any, if left, air inside.
Cleansing: This step is used for preheating and additional cleaning of the treated parts. Before loading the parts in the chamber, they must be cleaned of oil, grease, wax, salt, metallic and mechanical scraps, aluminum, brass etc. Usually the cleaning isn’t perfect and there are some dirties left. The purpose of the cleaning step of the process is to remove all these left dirties. During the cleaning, the plasma current is constant, usually 10-20 % of the maximum value, the electric pulses duty factor is 50 % and the pressure is constant - 0.5-0.8 mbar. The low current and small duty factor prevent arc development, while the parts are cold and yet dirty. The cleaning step lasts from 5 to 30 minutes.
1 to 14 - heat and treatment steps: Here, depending of the type of steel and the results that must be achieved, are applied the heating rate, speed of heating, pressure, duty factor, the working gases and the delay time at a predetermined temperature. During these steps, the parts are heated to reach the nitriding temperature. The current is determined by the temperature regulator. The duty factor is increased from step to step, to become 80 to 95 %. The pressure is increased as well, being constant throughout the step, or going up in conjunction with the temperature.
After the appropriate temperature is reached, the treatment step begins. The temperature, duty factor and pressure stay constant, being respectively 400 - 600 оC, 80-95 % and 2.0 - 8.0 mbar. The Plasma (Ion) Nitriding is carried out with ammonia or with a mixture of hydrogen and nitrogen. When working with hydrogen and nitrogen, the gas ratio can vary from 1:1 to 10:1.
When Plasma (Ion) Nitrocarburizing is carried out - carbon-containing gas is added. It can be methane, propane or natural gas. Its content is from 2 to 10 % of the gas mixture.
The treatment step lasts from several minutes to 20 hours, depending on the parts type and material, and the layer depth technological demands.
The frequency of the electric pulses is constant throughout all the steps. Normally, it is 10 kHz.
The technological process is totally automated. The parameters control, temperature and pressure curves, duty factor changes and gas composition variations are executed by the main controller. If it detects a failure - short circuit in the chamber, high temperature of the chamber walls, gas exhaustion etc.- the controller will stop the process and turn on alarm signals.
Oxidation: In order of achieving better corrosion resistance, our installations allow post-process oxidation.
Cooling: After the end of the Plasma Nitriding process, begins the last part – cooling. In order to prevent unwanted oxidation of the nitrided parts, the cooling could be carried out in plasma, in vacuum neutral gas atmosphere. To decrease the time of cooling - the chamber could be filled with nitrogen or argon.
