Under the title ‚20000 ° Celsius cool controlled‘ megalink magazine reports in it’s current issue about products manufactured by Medicoat AG as well as Siemens components used for control and drive technology.

Coating specialist Medicoat built a plasma coating system for a university institute in China in order to study new coatings. The special operation requirements of the university environment made necessary a customized WinCC Scada surface.

Coatings provide surfaces specific properties, which the substrate does not have. The surface treatment is characterized by a variety of coating processes. In the high-end sector, there are complex coating systems, such as ceramic multilayer, deposited from the plasma-assisted gas phase. In this area Medicoat AG is specialized. As a job coater the company developes and applies coatings primarily for medical applications such as implants. Based on vacuum plasma spraying (VPS) biocompatible coatings can be produced that offer the best conditions for the bone ingrowth process.

A view through the sight glass of the vacuum chamber, showing the nozzle outlet of the plasma jet at low power (Photos: Siemens)

Plasma coating system for research

Medicoat uses its coating know-how also in the field of engineering. The company designs and builds coating systems based on VPS and related technologies. With the latest plasma coating system, developed for a university research institute in China, the company pushes technologically forward toward the border area of ​​the VPS method. «The plant is being used for the study of a new type of layer with good thermal insulation and highly protective properties», explains Rolf Kuhn, Head of Thermal Spray Systems. «Although it is a ceramic coating, it has exceptionally good thermal stretching properties and is less prone to cracks.» The method is being used especially for the coating of gas turbine blades, thereby obtaining a higher resistance to gas corrosion at high temperatures. The coating process is technologically very demanding. In a double-walled, water-cooled vacuum chamber, an arc is generated by special gas mixtures, and an electric current of 3000 A. The spray powder is mixed into the gas jet, forming small liquid droplets at temperatures above 20,000 ° C  – being accelerated, compacted and applied onto the workpiece surface. The whole process takes place in a controlled vacuum of 1 to 2 mbar. In order to keep this vacuum and to compensate for the pressure rise through the gas entry, vacuum pumps with a capacity of 6000 m 3 / h are necessary.

Control unit integrated recipe and trend management 

The entire control and drive technology has been implemented with Siemens components including the main functions of pressure and vacuum control, control of the gas mixture, control of the plasma, dosage of the spray powders, as well as manipulation of the burner and the parts to be coated. Other features include the cooling the vessel and a filter cleaning systen to avoid explosions. Integrated into the control system are the main operation as well as a recipe and trend management. „The operation concept of the educational background of the university environment was given special consideration,“ says Christian Specht, who is responsible for the overall engineering of the plant.«Apart from the pure plant operation, the goal is to promote the students‘ understanding of the process.» Most process data such as temperature, pressure, current / voltage et cetera can be logged and retrieved for analysis and reports. An ease of use was achieved with a customized WinCC Scada surface with 3D images. The system documentation and operating instructions have been translated to Chinese by the company representative office in Beijing and incorporated in the WinCC.

Innovative motor protection switch

Medicoat works in the control and drive area almost exclusively with Siemens products. Only some special functions, such as mass flow controller or pyro measurements are performed with „foreign components“, their integration into the Siemens control, however, is easily possible. After six months of development and construction, the VPS-system was completed in Mägenwil, ready packed in 13 wooden crates and shipped  to China.

Again, an innovative development by Siemens helps to avoid problems. „Formerly during commissioning repeatedly failures occured with the motor circuit breakers because of loose contacts caused by the frequency of ship diesel engine during transport,“ explains Rolf Kuhn: «With the motor protection switches of the latest generation with spring-loaded contact these problems no longer occur.»