The injection moulding of elastomers takes place on snail injection moulding machines. Elastomers can be drawn in in the form of powders or band-shaped by a special snail, which brings little shearing into the plastifizierte mass. The cylinder is usually kept at a moderate temperature with a liquid, in order to avoid overheatings. The processing temperature is with approx. 70"°C, in order to prevent a vulcanization in the cylinder. Apart from the characteristics mentioned, the spraying casting procedure runs similarly in principle with the thermoplastic injection moulding. The snail kneads and mixes the molding material, which is prepared homogeneous thereby. Thus a quality improvement of the manufactured shaped parts leaves itself obtains e.g. in relation to pressing, with which from the heat supply an inhomogenous temperature distribution results from the outside. The procedure runs also relatively fast. When flowing in the nozzle and in the runners frictional heat develops. This shortens the vulcanization time. Thus the injection moulding process becomes particularly economical. Some mechanical characteristics can lie up to 30% more highly than with pressed elastomers. The high material viscosity makes relatively large dead head cross sections necessary. Very economically cold runner tools so mentioned work. The runner in the tool is cooled. One can through-squirt again and again by the not vulcanizing mass in the channel. One often uses injection moulding machines with several closing units for several tools with the elastomer injection moulding and different parts, since the vulcanization time is substantially larger than the preparation time in the spraying unit. That makes the elastomer injection moulding particularly economical.
The fundamental difference between the processing of elastomers (e.g. natural rubber) and thermoplastics (e.g. Polyproplylen) to injection moulding machines shows the temperature distribution in machine with thermoplastics is the snail relatively hot around material to be melted. The tool however is to be cooled down relatively coldly around the straight developed shaped part. The inherent stability is given the softening temperature by falling below. With elastomers the snail is relatively cold. To make possible the tool however hotter around the Vulkanisation (cross-linking/shaping). The thermoplastic elastomers form an exception.
We found here 5 articles.
|Elastomer injection moulding|
» Electron beam melting
» Extruding (finishing technique)
» Extrusion blow moulding