Metallic tubes coated internally with plastics layer - using double walled lance with radial spigot to blow plastics at heated wall and remove excess

A lance composed of an inner tube and a concentric outer tube is introduced in the metallic tube. The lance tubes have a bent frusto-conical end portion such that the pneumatically conveyed particulate plastics material in the inner tube impinges on the heated inner wall of the metallic tube and excess material is exhausted through the outer tube. Large dia. tubes can be coated economically without loss of material, its excessive use to ensure uniform coating and the coating may be carried out in a horizontal disposition. Coating is carried out by rotating the metallic tube and displacing all the tubes relative to one another.