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Ionitech Ltd.
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  5. Ionitech - Hot-Wall Plasma Nitriding ...

Ionitech - Hot-Wall Plasma Nitriding and Low Temperature Nitrocarburising Equipment

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Ionitech's Hot-Wall plasma nitriding and low-temperature nitrocarburising equipment combines advanced heating methods using both heaters and pulsed plasma within a vacuum chamber. These systems are particularly effective for treating components of various shapes and sizes in a single batch. They adhere to the AEROSPACE MATERIAL SPECIFICATION - AMS 2759/8A and are ideal for aerospace industry applications, providing consistent temperature uniformity across all parts. The vacuum chambers, built from stainless steel, house 2 to 3 separate heating and cooling zones depending on their size, and require no water cooling. Components are placed on metal plates inside the chamber, which rest on support insulators connected to the plasma generator’s cathode. Real-time temperature measurements are possible using embedded K-type thermocouples. The plasma generator is safeguarded by a comprehensive defense mechanism and operates within an IP54 rated metal cabinet cooled by air conditioning. The integrated gas vacuum system, composed of a vacuum pump, valves, filters, pressure gauges, and controllers, facilitates chamber evacuation and gas filling, enabling the use of hydrogen and nitrogen for nitriding, and propane or natural gas for nitrocarburising. Accelerated cooling post-treatment is achieved using argon. Each unit is managed via a user-friendly PC Control Panel, ensuring precise process control. Ionitech offers a range of Hot-Wall plasma nitriding models catering to different load capacities and working volumes, from the ION-25HWI model to the ION-200HWI.

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In the Hot-Wall type plasma nitriding installations, the heating of the parts in the vacuum chamber is done by both heaters and pulsed plasma. This type of installations are especially suitable for nitriding different shaped and sized parts in one batch. The main advantages of this type of equipment are:

  • The installations fully comply with the AEROSPACE MATERIAL SPECIFICATION - AMS 2759/8A
  • Can plasma nitride parts for the aerospace industries
  • Absolute temperature uniformity in all parts
  • The chambers could be equipped with their own lifting mechanism
  • No water cooling of the vacuum chamber

The vacuum chambers are manufactured from stainless steel. Depending on their size they have 2 or 3 separate zones of heating and cooling. The parts are loaded on metal plates. These plates lie on support insulators, and are connected to cathode of the plasma generator. The process of plasma nitriding could be viewed through a sight glass. The temperature during the process is measured directly in the parts using one or two thermocouples K-type.

The plasma generator and its defense mechanism - a power transformer, a three phase thyristor rectifier, a power choke, a power IGBT switch and a number of circuit breakers, filters and contactors, assembled for different supply voltages and mains frequencies. They are mounted in metal cabinet IP 54 that is cooled with and air conditioning.

The gas vacuum system evacuates the chambers and fills them with treatment gases. It includes a vacuum pump, electro-pneumatic and electromagnetic valves, reducing valves with filters and manometers, mass flow controllers, gas mixer, manual valves, two absolute pressure gauges and vacuum connections.

The pressure gauges are mounted on the chambers bodies. The rest of the components are placed in a ventilated metal enclosure IP54. The process is carried out with a mixture of hydrogen and nitrogen. Propane or natural gas are used for nitrocarburising. After the end of the treatment, the chambers can be filled with argon for accelerated cooling. Pressed air is used for the operation of the electro-pneumatic valves.

The control system consists of a PC controller, main system controller and subsystems (transmitters and drivers) that are connected in a communication network. The Panel PC is equiped with a 15” touchscreen display and uses Windows Embedded Standard 7 operating system.

The technological process is completely automatic. All of the main parameters are controlled by the system controller:
                          

•    Pressure in the working chamber
•    Temperature of the processed parts
•    Heat rate
•    Ratio and consumption of working gases
•    Process time length
•    Pulsed Plasma Current
•    Frequency of pulses
•    Duty-cycle of pulses
•    Temperature of cooling water

Specifically designed application, called IonView, implements the operator interface of the ion nitriding installation. It has the following capabilities:

•    Visualization of the technological process parameters
•    Review and editing of technological programs, even while the installation is working
•    Archive of the technological processes
•    Remote access to the archive
•    Visualization of the installation alarms
•    Alarm notification through e-mail and sms
•    Possibility to send process data to Ionitech as attached zip-file through email.

Typical feature of plasma nitriding is the active participation of the treated parts in the glow discharge - the parts act as a cathode, while the chamber acts as an anode. There are many advantages of this method over conventional gas nitriding:

Cost effectiveness
  • 3 to 10 times reduced duration of treatment;
  • 50% - 100 % less energy consumption;
  • 50 to 100 times less working gas consumption;
  • Distortion - none or negligible distortions, because ion nitriding is performed at lower temperature and under vacuum;
  • Higher surface, case and core hardness;
  • Excellent wear resistance - the ion nitriding process produces a compound zone which is dense, nonporous, very hard, not brittle, and has a low coefficient of friction;
  • Reproducible results and better control - the technological process of ion nitriding is fully automated and computer controlled. The parts are heated by the ion bombardment on their surface and therefore the parts are heated uniformly;
  • Surface finish - due to minimum deformations no additional mechanical treatments are necessary;
  • Necessity of predepassivation of stainless steel is eliminated;
  • Masking - surfaces which require masking are easily masked with reusable mechanical masking devices or special paint for masking - 100 % effective;
  • Excellent hygiene and working conditions - the process is not toxic and corresponds to all modern requirements for environmental control.
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 ?C, 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.