US Patent 7585103 Mixing head with creep barrier on the cleaning piston

A mixing head includes a mixing device which is secured to a housing and has a mixing chamber for mixing at least two plastic components to form a material mixture. Received in a recess of the housing is a cleaning device which has a cleaning piston for back-and-forth movement in relation to the mixing chamber between a first position in which the cleaning piston is retracted from the mixing chamber and a second position in which the cleaning piston extends into the mixing chamber. The cleaning device has a barrier which interacts with a housing wall for pushing the material mixture radially outside. The barrier has a flank which has an incline which is steeper than an incline of the housing wall.