Shot piston for molten plastic material

Details Shot piston for molten plastic material Shot piston for molten plastic material

1999-07-22

2001-01-02

Walberg, Teresa (Department: 3742)

Pumps

Expansible chamber type

Valved piston

C164S315000, C264S299000

Utility Patent

active

06168399

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shot piston for molten plastic material with a force-operated piston guided in a cylinder provided with an inlet and an outlet, wherein valve arrangements ensure that the cylinder is filled during the return stroke of the piston and the cylinder content is discharged during the work stroke of the piston.
2. Description of the Related Art
Shot pistons of the above-described type are known, for example from DE 35 20 454 A1. They can be used for a variety of applications. The best known application is the injection molding of articles. In many cases, such arrangements are also used for cleaning plastic filters by backwashing. In both cases, the shot volume should remain constant in a predeterminable manner and it should not be necessary to use conventional valve arrangements with angles because they constitute dead spaces or corners in which molten plastic material can remain for uncontrollable periods of time. Because of the high temperature of the molten material, when molten material remains in the valves there is the danger of uncontrollable chemical changes of the plastic material. In the conventional shot pistons for molten plastic material, these valves make it possible to adjust the shot volumes, the flow velocity and frequently also the pressure required for the shot.
SUMMARY OF THE INVENTION
Therefore, it is the primary object of the present invention to provide a shot piston for molten plastic material of the above-described type in which unintentional transfers from the inlet to the outlet and from the outlet to the inlet are prevented, in which dead spaces in which quantities of molten plastic material could remain are avoided, and in which the shot volume, the flow velocity and the pressure of the material and the pressure pattern are adjustable in a reproducible manner, wherein a degree of filling of the cylinder is to be achieved which is proportional to the return stroke of the piston.
In accordance with the present invention, the piston is fixedly connected by means of a drive bolt to a differential piston arranged upstream or in front of the piston. At least in its rearward extreme position, the differential piston covers and closes the outlet arranged in the corresponding differential cylinder. The circumference of the piston has at least one groove located underneath the inlet and extending from the end face of the piston facing the differential piston. The length of the groove is shorter than the length of the piston. A closing ring is arranged so as to be axially slidable on a cylindrical portion of the drive bolt arranged in front of the end face of the piston facing the differential piston. The closing ring is capable of closing the groove relative to the pressure space.
As a result of the configuration of the present invention, the differential piston can be used to block or close the outlet after filling up to the beggining of the shot, and the cylinder can receive molten material during the return stroke along distances which can be absolutely blocked during the work stroke.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.


REFERENCES:
patent: 3964537 (1976-06-01), Koch et al.
patent: 5052468 (1991-10-01), Koenig
patent: 5205969 (1993-04-01), Nett, Jr. et al.
patent: 5299623 (1994-04-01), Yaffe et al.
patent: 5632321 (1997-05-01), Hegel et al.
patent: 5660223 (1997-08-01), Thieman et al.
patent: 3520454 (1986-12-01), None

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