Method to mold round polyurethane rollers free of injection gates, parting lines and bubbles

摘要

Solid rollers of a urethane material are formed in closed mold formed by a tube and two end plugs spaced by a shaft, the latter becoming the shaft for the roller. The closed mold avoids rough grinding to a cylindrical shape, as well as avoiding the resulting waste of material and introduction of defects that arise from rough grinding. The formation of bubbles during injection of the urethane material is avoided by filling the closed mold with carbon dioxide gas prior to injection. The formation of gate marks in the urethane material is avoided by repositioning the end caps after injection to separate the injection gate from the cylindrical cavity. The need to trim the ends of the roller is avoided by providing an annular cavity between the top end cap and the tube that receives excess urethane material to be drawn into the cylindrical cavity as the urethane shrinks during curing.