Abstract: The mixing apparatus, which is constructed like a known mixing apparatus with return grooves (18, 19) in the control piston (2), has return grooves (18, 19) of a length which is equal to the distance between the inlet and return openings (4to 7) to be connected by it, the control piston (2) being able to be moved into an intermediate position (B), in which the return grooves (18, 19) connect the inlet openings (4, 5) to the assigned return openings (6, 7), and into a further advanced clearing position (C), in which the return grooves are no longer connected to the return openings. Due to the short return grooves, the length of which is no longer dependent o the length of the mixing chamber or of the outlet pipe of the mixing chamber, the overall length of the mixing apparatus is shortened. It is then only twice the stroke of the control piston. The neck region of the control piston is shortened, as a result of which the area of adhesion is reduced.

Abstract: A method of producing inside linings with a skin of polyurethane material and a polyurethane support reinforced with fiberglass pour-behind foamed together in a mold. The method operates in such a fashion that the support is first produced separately from a fiberglass mat, cut to size with exact contours and dimensions relative to the finished inside lining, and saturated with polyurethane material to form a support with a protruding edge section consisting only of the polyurethane material. The polyurethane skin is inserted into a lower mold with an edge that protrudes in the separation plane of the lower mold. The separately produced polyurethane support is then inserted into the upper mold with the edge section, made only of polyurethane material, lying in the separation plane. The support and the skin are pour-behind foamed by filling the polyurethane material into the open mold.

Abstract: A method and apparatus for metering and mixing multi-component plastics, in particular polyurethane, in which two or more hydraulic piston and cylinder units (A.sub.1 and A.sub.2) for each component, operate periodically by a balanced procedure. The pressure for the second piston and cylinder unit which takes over metering is equilibrated, before the beginning of the metering procedure, with the pressure of the first piston and cylinder unit which is in the process of metering. Switching from one piston and cylinder unit to the other (e.g. from A.sub.1 to A.sub.2) takes place in such a way that metering is taken over by the second piston and cylinder units at the same time as the first piston and cylinder unit is switched off. This is achieved by providing a pilot valve which has zero overlap and inevitably releases the component stream from the first piston and cylinder unit at the same time as the other piston and cylinder unit is switched off.