Gas injection process for molding plastic pipes or hollow products involves mechanical smoothing of plastic in the gas injection area after molten plastic in the center has been blown out under pressure

摘要

Molten plastic is introduced into a molding tool(4) and solidifies from the wall inwards. Plastic remaining in a molten state in the center area is blown out under pressure and plastic around the area in which the pressurized gas is introduced is smoothed or held smooth. On completion of tool(4) filling with plastic the smoothing tool(5) is drawn out of the gas injection area and remaining molten plastic blown out. The smoothing tool is then re-inserted. The area through which a pressurizing gas is blown in may be kept free of plastic by a sleeve and the medium blown through the sleeve. The sleeve is then retracted from the tool after blowing out the plastic. An Independent claim is included for process equipment for producing a pipe(1) or hollow product which comprises a gas injection system and a molding tool with a smoothing tool in the gas injection area for removing irregularities in the wall thickness.