Extrusion of complicated inner profiles of glass

Abstract

While extrusion today is a frequently applied and approved shaping method for metals and plastics for the production of rods, tubes and any inner and outer profiles, it is still in a state of development for the processing of glass melts. One particular advantage of this method of glass shaping is the fact that the working temperature is lower and thus the viscosity of the glass melt is higher compared with the usual forming procedures. Therefore, the corner radiusing effect of surface tension is largely suppressed. Especially in the production of hollow sections, it is now possible to manufacture sharp-edged inner profiles and even complicatedly shaped capillary cross sections at a close tolerance of the external diameter. At present, such profiles cannot be produced by any other method of glass shaping. In addition to the various extruded hollow sections, the corresponding pressing tools are described as well. For the accuracy of shape and the precision of size the die swell phenomenon is of special importance. It causes differences between the cross sections of extruded material and the profiles both of the channel and the mandrel. The reasons for this phenomenon, the difficulty of its theoretical analysis, and possible preventive measures will be dealt with.