Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – With means between charger and mold to cut off flow of...
Reexamination Certificate
1998-12-16
2001-08-28
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
With means between charger and mold to cut off flow of...
C425S566000
Reexamination Certificate
active
06280177
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority on German Application No. 197 57 412.2, filed Dec. 23, 1997.
The present invention refers to an injection moulding tool comprising a hot-runner manifold plate, at least one nozzle holder resting on said hot-runner manifold plate, a shut-off needle which is movably guided in said nozzle holder, and a piston arranged in a piston chamber and adapted to be actuated by a fluid, said piston being connected to the shut-off needle and moving said shut-off needle to its various positions, and said hot-runner manifold plate comprising at least one distributor channel, said nozzle holder comprising at least one supply channel which is associated with said shut-off needle, and said at least one distributor channel being connected to said at least one supply channel.
BACKGROUND OF THE INVENTION
An injection moulding tool of this type is known e.g. from U.S. Pat. No. 5,533,882. In this device, a nozzle holder rests directly on the hot-runner manifold plate, a distributor channel being directly connected to a supply channel in the nozzle holder. The nozzle is arranged at the nozzle holder end facing away from the hot-runner manifold plate. The supply channel merges at this point with the nozzle opening, said nozzle opening being adapted to be opened and closed by a valve stem. The valve stem is supported in the nozzle holder such that it is axially displaceable therein. The movement of the valve stem is produced by a sleevelike piston which is coaxially arranged around the nozzle holder. The piston chamber is defined by a sleeve surrounding the nozzle holder and by a closure plate. In order to establish a connection between the valve stem and the piston, a comparatively complicated yoke structure has to be used for connecting said needle and said piston through a lateral opening. It is true that this kind of structural design already provides a valve-stem closure means on the side of the cavity, but this closure means is comparatively complicated as far as its structural design is concerned so that improvements are desirable.
In the case of nozzle holders resting on the hot-runner manifold plate, needle closure means including a shut-off needle which extends through the hot-runner manifold plate have normally always been used up to now. The piston used for controlling the shut-off needle was then provided in a separate means at the back of the hot-runner manifold plate. However, such a structural design always necessitated a comparatively long shut-off needle, and this rendered the structural design comparatively complicated and expensive. A structural design of this type is known e.g. from EP 0647514A1.
In the case of another structural design, the hot-runner manifold plate has been subdivided into a main hot-runner manifold plate and into cooler individual plates. Although the piston units could-there be accommodated in the cooler individual plates, a connection channel which could be heated less strongly was necessary between the main hot-runner manifold plate and the nozzle holder resting on the individual plate. Also this structural design is comparatively complicated and expensive, since additional components are required. Furthermore, temperature control problems may arise in the case of this kind of embodiment. Such a device is known e.g. from EP0374353A2.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to provide an injection moulding tool of the type mentioned at the start, which has a compact and economy-priced structural design.
According to the present invention, this object is achieved by the features that the piston chamber is integrated in the nozzle holder in such a way that the piston is arranged between the shut-off needle and the hot-runner manifold plate.
Hence, the great advantage of the present invention is to be seen in the measures of implementing the piston as a movable component of the nozzle holder and arranging it directly in the hot area. Apparently, a prejudice against arranging the piston in the direct vicinity of the hot-runner manifold plate has hitherto existed in the prior art. On the basis of the present solution, it is possible to use extremely short shut-off needle lengths. In addition, the structural designs of the shut-off needle and of the piston are less complicated than in the case of known needle closure means located on the side of the cavity. This also results in a substantial advantage with regard to the assembly and disassembly of the injection moulding tool according to the present invention, since a disassembly operation can be carried out from the outer side towards the inner side, without direct access to the hot-runner manifold plate. The present solution also provides a structural design which requires a much smaller number of components than prior art designs. Last but not least, the overall height of the whole tool and the entire amount of space required are essentially reduced. The nozzle holder can easily be a multi-part component and rest on the hot-runner manifold plate via intermediate connecting pieces.
In the case of one embodiment, an essential simplification of the assembly and disassembly of the injection moulding tool is given on the basis of the features that the nozzle holder has a rear area with which it rests on the hot-runner manifold plate, that the piston chamber is open at said rear area of the nozzle holder, and that the piston chamber is closed by the hot-runner manifold plate at said rear area. Insertion and removal of the piston including the needle can therefore be carried out from the back of the nozzle holder. It is not necessary to provide an additional closure means, since one wall of the piston chamber is defined by the surface of the hot-runner manifold plate.
A further improvement of the compactness of the whole device can be achieved in that the at least one supply channel extends through the piston chamber and the piston, said piston being provided with at least one corresponding opening. Hence, it is not necessary to enlarge the cross-section of the nozzle holder for transferring the liquid plastic material from the distributor channel to the supply channel. The measure of positioning the at least one supply channel such that it extends directly through the piston chamber has not been known in the prior art up to now.
A preferred embodiment can be so conceived that, displaced relative to the shut-off needle, at least one thick-walled connection piece projects into the piston chamber, said connection piece being connected to the nozzle holder and projecting into the piston chamber substantially parallel to the axis of said shut-off needle, that the supply channel extends through the connection piece, and that the connection piece has an end face through which it communicates with the hot-runner manifold plate in such a way that the supply channel is connected to a distributor channel. In view of the fact that the connection pieces are directly placed on the hot-runner manifold plate, the at least one supply channel is sufficiently heated as well. Due to the thick-walled nature of the connection piece, this heat is also sufficiently maintained and the fluid flowing into the piston chamber has only an insignificant influence in this respect. It is, however, also possible to preheat the fluid in a suitable manner.
In addition, the connection piece can also serve as a piston guide means. For this purpose, the at least one corresponding opening in the piston is adapted to the outer contour of the connection piece in positive engagement therewith in such a way that the piston slides on said connection piece. A positive adaptation is also necessary to prevent a leakage flow of fluid from one side of the piston to the other. The openings in the piston can also be provided with suitable sealing rings sliding along the outer contour of the connection piece.
In order to achieve for most cases of use an arrangement in which the heat radiated from the hot-runner manifold plate has the least possible influence on th
Heitbrink Tim
Seed Intellectual Property Law Group PLLC
System Engineering Knauer GmbH & Co. KG
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