Reiloy Metall: Armoured Flights
As the flights are the parts of the screw most exposed to abrasion and wear, screws supplied by Reiloy Metall, Germany, are coated with an armouring layer. The thickness of the layer is between 1.5 and 2 mm, and is applied by means of the plasma powder arc weld process, during which the armouring layer, and the base material of the screw are inseparably bonded together. The alloy composition, structural state, hot hardness, and the sliding properties are the decisive factors for the abrasion resistance of a screw armouring. Regardless of the screw diameter, the most suitable base material for the screw is 31CrMoV9. To ensure that the screw root and the flight flanks are adequately protected against wear, the complete screw surface is ion-nitrided. In case of a risk of corrosion caused by certain additives or plastics, X35CrMo17 can be used. As an alternative a hard-chrome layer with a thickness of 0.03 mm can also be used.