the interior of a pipe is coated with a uniform thickness of plastic . a fluidized bed of heat - meltable plastic material in particular form is connected to the inlet end of the pipe , while the opposed end of the pipe is made attachable to a source of reduced pressure . a source of compressible fluid is also connected to the inlet end of the pipe . the pipe is preheated and then rotated axially while the compressible fluid flows therethrough . the compressible fluid flowing to the inlet is suddenly terminated while a flow from the fluidized bed is immediately established so that the vacuum at the outlet end of the pipe causes uninterrupted mass flow and pulls a finite pocket of the finely divided plastic into the pipe . the flow of particular plastic material is terminated , while the flow of compressed gas is immediately re - established , thereby pushing the pocket of plastic material into and through the pipe .