https://www.mdu.se/

The thesis focuses on an estimation of investment potential in alternative equipment for the deposition of a thin film on the ends of Kanthal Super heating elements. The film serves as an electrical contact when the elements are installed in an industrial furnace for heat generation and control. Currently, an arc spraying process involving aluminium film deposition is used. Aluminium in the form of powder is explosive and reactive. Therefore, the arc spraying equip­ment is impos­sible to integrate into the heating element production line. Thus, various conduc­tive material groups were investigated in terms of electrical conductivity, melting point, oxida­tion resistance and cost as an alternative to aluminium. The result of the material study is four deposition ma­terial options including aluminium- and copper-based alloys to be studied further with alterna­tive deposition methods. The deposition method study allowed selecting un­balanced DC mag­netron sputtering with rotating substrate holders to perform deposition tests with. Pure aluminium was selected as deposition material as alloys may sputter non-uniformly, and copper, in particular, is not compatible with the Kanthal Super material chemically.

Further investigation based on the recommended magnetron sputtering machine proved that the machine improves product quality by coating film lengths within the standard range of 25-100 mm to fit electrical connection braids. Minimum sputtered film thicknesses are 10 times lower the maximum expected value, which points at lower film porosity. Lastly, improved sputtered film adhesion compared to arc sprayed films is achieved through sig­nifi­cantly longer heating element pre-cleaning with RF plasma in high vacuum. Thus, heating ele­ments are expected to be more durable in operation. Furthermore, it is undefined whether the sputtering machine improves deposition process efficiency. The number of machines, the amount of coated element sizes in one machine and personnel involved, the number of manual operations and the coating capacity per working day are comparable with the set values. How­ever, coating capacity is estimated based on the assumption that the minimum sputtered thick­ness is enough to provide the same electrical contact as the arc sprayed thickness. The number of sputtering process parameters to control is approximately twice as high compared to the set value based on the arc spraying process. This proves the unnecessary complexity of the sputtering process. On the other hand, sputtering contributes to increased safety of the deposi­tion process by eliminating the number of hazardous aluminium particles in the air due to process isolation in a high vacuum. The noise levels are kept within the officially set limit of 80 dB at a workplace. From the cost efficiency perspective, the sputtering machine is within the set limit of maximum 110 % when it comes to pure economical investment while yearly operating costs were found to be 5 % higher than the set limit. Thus, magnetron sput­tering is a suitable method to perform metallization of electrical contacts on Kanthal Super heating ele­ments. It can be recommended as an alternative deposition method if physical tests are per­formed to confirm the film thickness assumptions.