RFI Screening Ltd., England, has selected Metallisation MK61 Flamespray equipment from Metallisation Ltd., England, to metal spray a 40-metric-ton generator rotor with fine silver. It was first sprayed with a 25-micron coating of molybdenum, to optimize the adhesion of the top coat of silver. A final coating of silver was then added to achieve the specified outside diameter on the shaft. In a typical application, a coating 250 microns thick of silver would be sprayed. Prior to spraying the rotor, the surface was grit blasted to Standard SA 2.5, to clean and prepare the shaft. The shaft was also pre-heated by induction to prevent coating shrinkage issues and to enhance the adhesion of the metal spray.
The flamespray system was chosen instead of arcspray due to the higher efficiency that can be achieved with a more controllable application process. The flamespray system with small diameter wire also produces a fine, close structured coating that maximizes the conductivity of the applied silver, which is the main purpose of the coating.
The Metallisation MK61 is an oxygen-acetylene fuelled flamespray system, primarily for spraying engineering coatings of steels, bronzes, copper, and molybdenum. The lightweight, robust pistol offers the possibility to reclaim damaged parts for small to medium-sized applications, as it has a continuous nozzle setup, ideal for engineering coatings. Molybdenum can also be sprayed with the MK61 as a soft bond coat through to a very hard, wear-resistant coating.
The MK61 is also ideal for use with RFI Screening’s mobile metal spraying unit, as the pistol is lightweight, robust, sturdy, and well balanced. Requiring only gases and compressed air, it also lends itself to site applications where three-phase electricity may not be available.
