EXTRUSION

The silicone compounds then undergo the extrusion process, in which the tool
(die) creates the actual contour. Vulcanisation follows in a heating section without external pressure (pressureless vulcanisation) with platinum catalyst for addition curing or with peroxide curing.

At BIW, the extrudate is scanned in contactless control procedures between the extruder head, which is constantly cooled together with the screw and cylinder of the extruder, and the heating section. Laser gauges are used not only for permanent quality data registration and evaluation but also for direct process control. The use of stateof- the-art control technology together with the wealth of know-how of BIW's experts has resulted in a self-regulating control loop in which the measured data from the laser scanning process are used directly as control parameters for the running speed of the extrusion screw. In turn, this ensures that the profiles have exactly the right shape and hoses the right dimensions, even in long series.

Together with classical elastomer extrusion, BIW also uses special processing methods for individual customised solutions:

• - Vertical extrusion: the vertical process is used to produce large-volume special hoses with diameters of up to 200 mm or profiles with a high dead weight and complicated contours, without belt impressions
• Foam extrusion: appropriate machinery and technology for multi- imensional material expansion together with suitable blowing agent are used to produce silicone foam profiles in differing densities and compressibility classes
• Crosshead extrusion: screw and cylinder are arranged in a 90° angle to integrate textiles, metals or other materials as functional elements in silicone profiles
• Co-extrusion: up to 3 extruders can be combined to produce combinations of hard/soft profiles, multi-coloured profiles and combined foam/solid profiles The in-house development team in BIW Technology Centre adopts the customer's own characteristic features insofar as corresponding solutions do not already exist. The standard programme for example includes wearproof "in-line" marking, together with in-process extrudate shaping (e.g. hose manifolds) or finished profiles (e.g. corner- vulcanised frames or profiles with notches or ventilation punchings).