Plastic article or earthenware shaping or treating: apparatus – With foraminous or absorbent means for removal of vehicle or...
Reexamination Certificate
1999-03-11
2001-03-06
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
With foraminous or absorbent means for removal of vehicle or...
C210S184000, C210S186000, C210S236000, C210S447000, C425S197000, C425S199000
Reexamination Certificate
active
06196820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a process and a corresponding device for filtering plastics in an injection molding machine in which a holding device receiving a filter element is arranged between a plasticizing unit and a mold cavity.
2. Description of the Related Art
Kunststoffe [Plastics] 87 (1997), pages 154-159, discloses a screen system (page 156) in which the screening locations are arranged in a rectangular slide (cassette) or a round bolt. Changing is initiated manually or automatically via a hydraulic drive when a defined pressure limit is reached by displacing the screen surface carrier.
Screen changing systems of the above-mentioned type are used in plastics processing and, in this case, especially in extrusion. Problems occur in this respect precisely in changing systems which are not expressly constant with respect to pressure, since the continuous insertion and exchange of the screen surface involves sometimes enormous pressure fluctuations in front of the filter.
German reference DE 44 19 284 C1 discloses a filter device for plastic melts in which screen inserts are arranged in a power-operated displaceable slide. Seals are arranged at both sides of the slide, wherein at least one of the seals has a sealing body made of metal which encloses a hollow space that is filled with a substance whose thermal expansion coefficient exceeds that of the material of the sealing body. When the seal is inserted, its sealing body which is made of metal, for example, high-grade steel, is relaxed in practice. As a result of heating by the plastic melt flowing through, the sealing body, including the material with which it is filled, expands thermally so that the end face of the seal lies firmly against the slide in a sealing manner during operation after the thermal expansion or deformation.
A disadvantage in this type of seal is its dependence on the pressure and on the temperature of the processed plastic substance such that at low pressure and low temperature leaks occur and at high pressure and high temperature undesirably high area pressing occurs in the support surfaces.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process and a corresponding device for filtering plastic in an injection molding machine having a plasticizing unit and a mold cavity in which it is ensured that extraneous materials are reliably removed from the plastic substance at high substance pressures by a filter element changeable by means of a simple construction.
According to an embodiment of the present invention, a preheated filter element is used when changing filters, wherein the preheated filter element is acted upon by the plastic substance which is kept away from the mold cavity until the cast substance is determined as suitable and is accordingly supplied without defects for processing.
For this purpose, there is provided in a connection line, between the plasticizing unit and a nozzle connected with the mold cavity, a 3-way cock with the following operating positions:
through to the mold cavity located in a die or tool;
blocking position; and
flushing position with outward substance flow, preferably downward.
In the blocking position a blocking member prevents any influencing of the filter and of the screw out of the tool or distributor system, e.g., hot channel in the case of multiple components, and the like.
The flushing position sprays out air volume and old material after changing the filter units, particularly when starting the injection molding machine and when changing filters.
Moreover, according to the present invention, a preheating device is provided so as to preheat fresh filter elements. For this purpose, a filter holder is provided as a slide in which the active filter is mounted. The slide is displaceable and movable into a position in which its receptacle for the filter element corresponds with a piston-shaped displacing unit by means of which a spent filter element is ejected and a fresh filter element simultaneously inserted.
The displacing unit has, in the region of the filter holder, the preheating device by means of which the filter elements are preheated to operating temperature. The preheating advantageously prevents the plastic substance from solidifying in the fresh filter at a next injection stroke, which would cause an interruption in production.
To change filters, the slide is arranged as a carrier plate by which the spent filter is pulled out of the filter holder from the top. The preheated filter element is slid into the carrier plate by means of the piston of the displacing unit. In so doing, the spent filter element is ejected away from the displacing unit into a collection channel or gutter.
In an advantageous further embodiment of the invention, the filter element is also thermally influenced with respect to its operating position. For this purpose, a filter heater is provided in the slide in a region in which the filter element is received.
Although it is desirable that the slide receiving the filter element be easily movable for changing, it is also desirable that the slide be held in a tightly closing manner during operation so as not to allow leakage. For this purpose, it is known to provide sealing rings on both sides of the slide.
In another embodiment of the present invention, a sealing ring which comprises at least two parts is provided between the slide and the housing on a side of the slide directed toward the plasticizing unit. The sealing ring is either free of play or is pressed against the slide depending on substance pressure present in the plasticizing unit channel. For this purpose, one seal part of the sealing ring is roof-shaped, while another seal part has a triangular shape, wherein both seal parts contact one another along an inclined surface. Both seal parts are made exclusively of metal, wherein at least the roof-shaped sealing ring is preferably manufactured from a highly-elastic material. In a pressureless state, both sealing rings are sprung back and lean lightly against one another in a pretensioned manner. As substance pressure increases, the diameter increases with respect to the roof-shaped sealing ring. As the roof-shaped seal part expands radially outward the sloping surface which is inclined toward the triangular sealing ring moves the triangular sealing ring axially and presses it against the slide. The angle of the contacting inclined surfaces of the two seal parts is selected in such a way that these seal parts do not jam and they spring back into their initial position in the pressureless state.
In a preferred embodiment of the present invention a metal with a low modulus of elasticity is used so as to promote the required deformation.
In a further advantageous embodiment of the present invention, the blocking member provided in the connection line is a 3-way cock that can be connected with an accumulator. The injection molding substance that has been found to be of good quality is additionally influenced with respect to its pressure and its quantity by this accumulator. For this purpose, the accumulator is a piston-cylinder unit which is hydraulically or electrically driven. The piston-cylinder unit has a piston rod and which is thermally separated from the injection molding substance, so that the injection molding substance is not negatively influenced.
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, its operating advantages, and 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: 3962092 (1976-06-01), Newman, Jr.
patent: 4167384 (1979-09-01), Shirato et al.
patent: 4814186 (1989-03-01), Trott
patent: 5090887 (1992-02-01), Gneuss
patent: 6010625 (1976-06-01), Whitman
patent: 4419284 (1995-10-01), None
Cohen & Pontani, Lieberman & Pavane
Heitbrink Tim
Mannesmann AG
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