Vacuum systems in plasma spraying

The vacuum system for plasma spraying is a process in which the surface can be coated with plasma enhanced coating in vacuum. This vacuum plasma spraying process can change some characteristics of the surface, but the carrier material will not change. When the volume of vacuum chamber is 19000l, the vacuum system is applied to plasma spraying. Why use vacuum system in plasma spraying?

Plasma spraying is a technology of material surface strengthening and surface modification, which can make the substrate surface have the properties of wear resistance, corrosion resistance, high temperature oxidation resistance, electrical insulation, heat insulation, radiation protection, wear reduction and sealing. Plasma spraying technology is a method which uses the plasma arc driven by DC as the heat source to heat ceramics, alloys, metals and other materials to the melting or semi melting state, and spray high-speed to the surface of the pre-treated workpiece to form a solid surface layer. Plasma spraying is also used for medical purposes. A coating of tens of microns is sprayed on the surface of artificial bone as a method to strengthen artificial bone and its affinity.

What is plasma spraying?

Vacuum plasma spraying is a technology of spraying in a sealed room with controllable atmosphere and 4 ~ 40kpa. Because the working gas is ejected in a low-pressure atmosphere while expanding the volume, the jet velocity is supersonic, and it is very suitable for materials which are highly sensitive to oxidation.

The coating process of plasma spraying system requires a double wall water-cooled vacuum chamber. The parts to be coated are placed inside and the treatment chamber is then closed. The vacuum system will discharge the chamber at a pressure of 0.08 mbar. This ensures that the oxygen in the atmosphere and the water vapor attached to the components are completely evacuated without negative effects on the components. This also creates conditions for the production of extremely pure gas environment. Then, the pressure of the treatment room and argon will be refreshed to 100 mbar, and then further evacuated to 1 mbar.

The actual coating will only start when the process gas mixture enters and the plasma burner is turned on. This is customized for individual coatings and materials. The coating is mainly affected by energy input, gas and gas mixture used, temperature, coating time and pressure level of a single process step.

Plasma spraying process

Plasma spraying process is a need for careful work, and in this process, there are many factors that can affect the quality of large coating. Then the main processes are:

1. Choose plasma gas. According to the availability and economy of gas, N2 is more suitable. It is not only cheap, but also has high flame heat ratio and fast heat transfer. However, it is not available for some materials prone to nitriding reaction. At this time, a slightly more expensive ar will be used.

2. Arc power. In the process, the arc power requirement is very strict, neither too high nor too low. If the arc power is too high, the arc temperature will rise, and the gas will be converted into plasma, and the plasma flame temperature will also increase, which may lead to the change of coating properties. If the arc power is too low, the plasma temperature will be too low and the properties of the coating will be changed.

At present, vacuum system is mainly used in the field of medical technology, and vacuum plasma spraying process is used to create a biocompatible coating for implants, which provides the best conditions for the growth of bone cells. In this process, the process provides high corrosion resistance at high temperature. The application of vacuum system in plasma spraying can create the best production conditions and environment for many industries.