Extended mandrel technique

The extended mandrel technique, illustrated in Fig. 6.22b, is highly desirable for fluoropol5miers because it provides internal cooling and support to the tube. The shrinkage of the plastic as a result of cooling causes a tight contact between the tube and the metal mandrel that can extend up to 30 cm beyond the die. Longer mandrels have been difficult to use due to mechanical difficulties. Surfaces will eventually cor-... 

The most common method of fabricating tubing with outside diameters of 12-30 mm and wall thickness in the range of 0.3 to 0.8 mm is the extended mandrel technique.Aside from corrosion concerns, brass is the best choice of construction material for the mandrel and Vespel for the insulation gasket between the guide and the mandrel. The guide is heated electrically to prevent melt fracture. Mandrel temperature is controlled to allow solidification of the melt and avoid sticking. 

A special extrusion technique that is occasionally used is the extended mandrel. This is particularly used for thin wall tubing. In this technique the tip extends beyond the die by a considerable distance. The purpose of the extended mandrel is to obtain better shaper definition. Another use of the extended mandrel is to provide localized heating of the tip using an induction coil at the die exit. This is a variation of the G-Process discussed under special features. It is a suitable method to eliminate internal melt fracture or internal die drool. The mandrel extension should be made of a ferro-magnetic material to obtain an efficient temperature increase under the influence of the alternating magnetic field of the induction coil. 

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