Agitating – Having specified feed means – Impinging jets
Patent
1996-12-17
1998-07-28
Cooley, Charles E.
Agitating
Having specified feed means
Impinging jets
422133, B01F 504, B29B 776
Patent
active
057854220
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a device for mixing at least two chemically reactive plastic components, and in particular to a mixing device of a type having a cylindrical mixing chamber for receiving injected plastic components and having disposed therein a reversible piston for removing remaining plastic mixture, and a cylindrical stabilizing chamber adjoining the mixing chamber and positioned at an angle of preferably 90.degree. relative to the longitudinal axis of the mixing chamber, with a reversible cleaning piston disposed inside the stabilizing chamber for removing the reactive plastic mixture from the stabilizing chamber.
A device of this type is known from the German utility model G 89 15 329 where the cleaning piston has a sealing ring disposed in a circular channel. With this sealing ring, the surface of the stabilizing chamber can be cleaned well, but it cannot be ruled out that fully reacted plastic material enters between the surface of the stabilizing chamber and the surface of the cleaning piston and leads to sticking of the cleaning piston. In the same manner, especially an uneven distribution of the reacted plastic material may lead to a dangerous situation where the piston and the cylinder tube come into metallic contact and seize.
It is already known from DE-AS 28 38 798 to place indentations on the piston controlling the supply of the plastic components in order to prevent seizing of the control piston, wherein fully reacted material in the indentations is supposed to prevent metallic contact between the piston and the cylinder wall. It is, however, difficult to dislodge the piston by this method alone when it is stuck in the cylinder wall, so that, in this case, strong tear-off forces may be required which could lead to damage or breaking or tearing of the cleaning piston.
SUMMARY OF THE INVENTION
It is the object of the invention to reduce the tendency of a cleaning piston of the aforedescribed type to become stuck and to reduce the tear-off forces.
The invention is based on the realization that when spacer material is applied to the cleaning piston in a spiral-shaped pattern, the potentially stuck surface is, on one hand, reduced and the gap between the piston and the cylinder tube, on the other hand, is not capable of being unevenly coated with sticking fully reacted plastic material. This eliminates the danger that the piston comes into metallic contact with the cylinder tube as a result of one-sided radial pushing. Especially, however, the introduction of a rotational motion results in a shear force component which is oriented transversely to the axial piston stroke, whereby sticky materials remaining between the piston and the cylinder tube can be particularly effectively dislodged. The additional advantage is that new surface areas of the piston and the cylinder face each other every time as a result of the rotation of the cleaning piston, so that the formation of striations and deposits extending in a axial direction is positively eliminated.
Fully reacted plastic material is preferably employed as spacer material. This material is formed when the not yet fully reacted plastic mixture seeps into the gap between the piston and the cylinder tube. The plastic mixture settles in the indentations and provides--as the result of the swelling associated with the complete reaction--a securely maintained gap which prevents metallic contact between a piston and the cylinder surface.
In principle, it is also possible to introduce other materials into the indentations other than a fully reacted plastic mixture, before the cleaning piston is installed. Suitable for this purpose may be sealing materials which not only do not tend to stick with respect to the plastic mixture to be processed, but--because of their strongly repellent effect--also rule out sticking in the regions immediately adjacent to the sealing material.
In a preferred embodiment, the cleaning piston is freely rotatably secured to the piston rod of the hydraulic piston, whereby the torque created b
REFERENCES:
patent: 3189325 (1965-06-01), Levy
patent: 4279517 (1981-07-01), Wallner et al.
patent: 4497579 (1985-02-01), Schmitz et al.
patent: 4503014 (1985-03-01), Bauer
patent: 4510120 (1985-04-01), Bauer
patent: 4592657 (1986-06-01), Taubenmann
Cooley Charles E.
Feiereisen Henry M.
Krauss-Maffei AG
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