Agitating – With specified discharge means
Reexamination Certificate
2001-03-28
2003-07-15
Soohoo, Tony G. (Department: 1723)
Agitating
With specified discharge means
C366S192000, C366S195000, C366S289000, C366S286000
Reexamination Certificate
active
06592249
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a device for producing and/or for processing mixtures having several components, in particular plastic mixtures, the device comprising a mixing head with at least one inlet for the mixture or its components, with a rotatably driven mixer in the mixing head for mixing the mixture or its components and with an outlet for the mixture, whereas the mixer is arranged axially displaceable in the mixing head by means of a drive unit and releases or closes the outlet according to its axial position.
When processing plastic mixtures, for example for producing a seal moulded directly onto a valve lid, the individual components of the plastic mixture are to be mixed with one another, if possible, only immediately before the processing of the plastic material consisting of the several components. For the production and the processing of mixtures with several components, a typical device is known from DE-OS 42 35 850, in which the individual components of the plastic mixture to be processed are fed to a mixing head and are mixed therein by means of a rotating mixer. The final mixed mixture can leave the mixing head by means of an outflow and can be injected directly into a die or moulded onto a part, for example as a seal. With the known mixing device, the mixer serves also as a closing means for the outflow and can be axially displaced in the mixing head by means of a pneumatic cylinder which engages the mixer shaft, whereby the mixer closes the outflow in a valve needle-like manner in a first, lower position with an approximately conical point, and opens the outflow in a second, raised position so that the mixed plastics can be ejected.
This known device has proved to be very successful in practice, as the mixer does justice to its dual function on one hand as a mixing element, and on the other hand as a closing means, so that operation disturbances occur only rarely, and high qualities are achieved with the injected parts, in particular also with moulded-on seals. But it has been found that the sudden opening or closing movement of the mixer in the axial direction, when using the pneumatic cylinder acting immediately on the mixer shaft, results in a quality loss of the tools, seals or the like, which are produced from the mixture, when sensitive materials are processed. In consequence of the sudden starting and the very fast lifting of the mixer for opening the outlet, the volume in the mixing region of the mixing head is increased in a very short time to such an extent that, depending on the rheology of the produced mixture, or its components, these cannot flow fast enough from their inlet along the mixer side walls through the mixing region in the direction of the outlet, so as to fill the suddenly enlarged volume in this region. A low pressure can result from the sudden lifting of the mixer in the mixing head, in particular when the outlet is still filled with remainders of the mixture ejected from the previous processing. The low pressure in the mixing head can result, even though only for a short time, in an exhaling of the produced and processed plastic mixture in the mixing head, which results in a quality loss of the material to be processed or it does not have even processing qualities during the processing procedure. It can result that a part of a seal which is moulded onto a part by means of the device is foamed in a different way than the rest of the seal so that the complete seal does not obtain an even thickness and a reliable closure cannot be guaranteed with the seal which is being produced.
SUMMARY OF THE INVENTION
It is an object of the invention to improve a device of the above-mentioned type in such a way that a sudden opening or closing of the outlet opening by means of the mixer is avoided, and to thereby prevent the disadvantageous influences on sensitive materials which are to be processed. This object is achieved by means of the invention, in that the drive unit comprises a mechanical cam drive having at least one actuating cam which cooperates with a lifting element engaging the mixer or its shaft.
By the use of the cam gear, in which the actuating cam(s) lifts or lift the lifting element and therewith the mixer for opening the outlet, it is possible to increase the speed of the mixer during the opening from a very small value at the beginning of the lifting movement during the further course of the axial movement of the mixer. The cam drive permits the use of actuating cams with different cam areas, which can be adapted to the material and the flow behaviour of the material which is being processed in an optimal manner. As the opening speed of the mixer which closes the outlet in the manner of a needle valve is only small at the beginning of the opening movement, the mixture in the mixing head can readily fill the increasing volume in the mixing head during the critical opening movement, so that the mixer does not produce any low pressure by means of its displacement in the mixing chamber of the mixing head and the mixed mixture of several components which is to be processed cannot exhale and experience a quality loss. During the further course of the opening movement, in which the influence of the opening speed of the material which flows in the mixing head to the outlet is reduced noticeably and the danger of quality loss due to fast opening is not present, the opening speed will be increased considerably by correspondingly the formed actuating cam(s), so that the total time in which the outlet for the mixture with several components is released completely does not have to be larger than with the known devices, and a processing of the mixture can occur after the start of the opening movement of the mixer within the shortest time.
The cam drive has preferably at least one camshaft comprising an actuating cam, which shaft is mounted rotatably in a bearing housing at the side next to the mixer shaft. It is particularly suitable to provide a cam drive with two parallel camshafts each having an actuating cam, which camshafts are mounted rotatably in a common bearing housing on both sides of the mixer shaft. With this embodiment, the lifting element preferably engages the mixer shaft, so that the entire drive unit for the displacement of the mixture in its axial direction can be arranged away from the actual mixing head. Therefore, there is no danger that the drive unit contacts the mixture of the several components which is to be processed with its partially very precisely manufactured parts, which could lead to faults or inaccuracies when opening and closing the outlet. By the use of two parallel camshafts, which are preferably driven in a counter-rotating manner in the housing, it is ensured that the axial movement, which is produced when the cams during their rotation are hobbing at the lifting element, is introduced exactly axially into the mixer shaft so that this will not be cocked when the mixer is displaced. The camshafts suitably have a common drive element which ensures that the cams of both camshafts are always rotated by exactly the same amount and act evenly on the lifting element so as to lift the mixer in the mixing head or lower it when closing.
A particularly advantageous type of drive for the camshafts results when these are provided with a drive gear which can be rotated by a gear rack drive element which is driven in the axially displaceable direction. The gear rack drive element can be provided with a dual or peripheral gearing for both drive gears at the two camshafts which are preferably arranged in parallel. By the displacement of the gear rack drive element in its axial direction, the two drive gears of the camshafts and the actuating cams which are arranged thereon are preferably rotated in a counter-rotating manner, whereby the cams hob along the lifting element with their cam areas, and lift this or draw it back or lower it or move it forward, depending on the direction of the displacement of the gear rack drive element. A most advantageous design is that, in which the drive element
Baldauf Günter
Hausbichler Hannes
EDF Polymer-Applikation Maschinenfabrik GmbH
Fay Sharpe Fagan Minnich & McKee
Soohoo Tony G.
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