Dry screw vacuum pump in plasma spray coating system

Dry screw vacuum pump in plasma spraying coating system of application

We offer a wide range of vacuum solutions for coating processes. Apart from independent vacuum pumps, we also supply complete vacuum systems. Dry screw vacuum pump is especially suitable for coating process. Practice proves that punnock screw vacuum pump combined with roots vacuum pump is the standard solution for medium vacuum coating application. The strength of punnock lies in the ability to meet the specific requirements of each customer to build customized coating system vacuum solutions. This paper introduces the application of dry screw vacuum pump in plasma spraying coating system.

Vacuum plasma spraying (VPS) is a process in which a plasma-enhanced coating can be applied to the surface in a vacuum. This process can give certain properties to the surface without changing the carrier material. With a vacuum chamber volume of 19,000 liters, this system is not only the largest vacuum plasma spraying system, but also an attempt to use the dry vacuum technology, dry screw vacuum pump, provided by pronock.

The technically required vacuum plasma spraying system coating process requires a double-walled water-cooled vacuum chamber. The parts to be coated are placed inside and the processing room is closed. The vacuum system discharges the chamber at a pressure of 0.08 millibar. This ensures that oxygen in the atmosphere and water vapor attached to the parts are completely evacuated without adversely affecting the parts. It also creates conditions for extremely pure gas. The pressure of the treatment chamber and argon is then refreshed to 100 mbar and further evacuated to 1 mbar.

The actual coating will only begin when the process gas mixture is entered 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 individual process steps.

In the case of a high current, the plasma creates an arc that transfers energy to the coating. The spray powder is mixed in a gas jet, where the liquid droplets form at a temperature range of 20,000 degrees Celsius and are accelerated, compressed and sprayed onto the surface of the workpiece. A processing robot in the vacuum chamber moves the plasma burner during this process and ensures that all components are sprayed evenly. The whole process takes about 30 minutes.

The screw vacuum pump serves as the backup pump of the vacuum system. A vacuum system has three stages. In each case, it consists of two vacuum boosters that precompress the evacuated air and flush or process gas and then transmit it to two additional vacuum boosters that are working in parallel. Thus, before the gas mixture or gas is further compressed in the downstream screw vacuum pump, additional compression is generated to reach the final pressure of the system. The size of the thrusters used is coordinated to achieve a pumping speed of 12,000 cubic meters per hour. The vacuum system can quickly reach the pressure required for the initial evacuation of 0.08 mbar in the vacuum chamber, but can work within all pressure ranges to 900 mbar, and accurately maintain the set point required for the process.

In addition to frequency-controlled drives, the punnock dry screw vacuum pumps have other advantages, namely that they are water-cooled. This means that the operating temperature can be set or set to a temperature range to prevent the process gas from condensing in the vacuum pump. Both vacuum pumps are connected to the cooling water system of the vacuum plasma spraying coating system. This also provides ionized cooling water for the entire system. As the water cools, no heat is released. The practical application of dry screw vacuum pump in plasma spraying coating system is to run completely dry process. This means that they do not need to operate the fluid in a compression chamber and can mix with the process gas.