Thin walled metal pipe coated with plastics - applied by turbulent air in sub-atmospheric duct preventing powder escape

摘要

The parent patent describes a method of coating a continuously moving, thin-walled metal pipe with plastics powder by high-speed, turbulent air entrainment of the powder into the coating chamber: the temp. of th pipe entering the chamber being sufficient only to cause preliminary fritting of the powder; the frit being melted in an immediately following stage to form the coating. The addn. describes an appts. for the process, comprising a cylindrical chamber, maintained at sub-atmospheric pressure by a suction chamber and blower, an inlet pipe for powder-air mixt. adjacent to the nozzle-shaped mouth, and a cyclone for sepg. powder from the extracted air and recycling it to a fluidising chamber with injector. No powder escapes to atmosphere; fully automatic operation is possible and it is much faster and safer tahn electrostatic coating.