Dies extending beyond the head should be heated. The mandrel through which the product to be sheathed is passed should be adjustable in the axial direction to allow the surface quality of the sheath to be influenced. The actual sheathing process is carried out by the pressure or tubular process (Fig. 3).

Fig. 3: Sheathing dies

With the pressure technique, a noncircular substrate can be topped up to produce a circular cross section.

With the tubular process, a coating of even thickness is applied, which largely adjusts to the given cross section.

Adhesion of the Desmopan® or Texin™ extrudate to the carrier material essentially depends on which sheathing process is used. Good adhesive strength can generally be achieved by the pressure method. On the other hand, the tube/pipe extrusion method allows easy peeling off of the sheathing. By applying a vacuum to the mandrel, adhesion can be adjusted to suit requirements. It is important to have a dry, grease-free substrate, otherwise blistering and adhesion problems may occur.