Metal founding – Means to shape metallic material – Pressure shaping means
Reexamination Certificate
2001-02-17
2002-07-30
Lin, Kuang Y. (Department: 1725)
Metal founding
Means to shape metallic material
Pressure shaping means
C164S065000, C164S113000, C425S812000
Reexamination Certificate
active
06425433
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO COMPACT DISC(S)
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to injection molding apparatus, and in particular, to means for evacuating gasses from the mold cavity of injection molding apparatus.
2. Information Disclosure Statement
The die casting process is well-known for making parts by injecting a specific amount of molten material into a mold cavity having a specific area and shape. The problem with the die-casting process is that any air trapped in the mold cavity during the injection process will cause voids or porosity in the molded part, thereby reducing the structural integrity of the final product.
Well known solutions to this problem include attaching a vacuum pump to the mold by means of a valving system as described in Ozeki, U.S. Pat. No. 4,997,026. The invention disclosed by Ozeki and other similar devices create a constant uncontrolled vacuum throughout the injection sequence and rely on a mechanical device, such as a valve, to control the repeated application of the vacuum. There are many shortcomings associated with this method of gas evacuation. One such problem occurs when the valve is opened too soon, causing the vacuum to draw the molten material into the mold cavity. If this happens and the material solidifies prior to completion of the injection sequence, the part produced will lack the required structural integrity. Another problem with the prior art is that the rate of evacuation of the vacuum-evacuated air is uncorrelated with the rate of injection of molten material injected into the mold cavity.
Still another problem exists in the prior art due to the lack of coordination between the operation of the vacuum breaking valve and the injection sequence. Over a period of time and after a large number of repetitions, molten material may be pulled into the mechanical workings of the valve and impede its performance unless the opening and closing of the valve is perfectly coordinated with the injection sequence.
It is therefore desirable to have an injection molding apparatus that controls the amount of vacuum present in the system and coordinates the operation of the valve with the steps in the injection sequence.
A preliminary patentability search in Class 425, subclasses 546, 812, and 420, produced the following patents, some of which may be relevant to the present invention: Siggers, U.S. Pat. No. 5,277,570, issued Jan. 11, 1994; Ozeki et al., U.S. Pat. No. 4,997,026, issued Mar. 5, 1991; Hoschele et al., U.S. Pat. No. 3,804,570, issued Apr. 16, 1974; Fritsch, U.S. Pat. No. 3,477,101, issued Nov. 11, 1969; Hodler, U.S. Pat. No. 3,433,291, issued Mar. 18, 1969; Crandall, U.S. Pat. No. 2,991,506, issued Jul. 11, 1961; Cherry et al. U.S. Pat. No. 2,415,462, issued Feb. 11, 1947; and Brunner et al., U.S. Pat. No. 2,243,835, issued Jun. 3, 1941.
None of these references, either singly or in combination, discloses or suggests the present invention.
BRIEF SUMMARY OF THE INVENTION
The present invention is a vacuum device for removing gas from the mold cavity of a injection molding apparatus such as a die-casting machine. Like the prior art, the invention has a mold consisting of first and second mold portions, and, when the first and second mold portions are pressed together, they form the mold cavity where the molded part is formed. Different from the prior art, the rate of gas evacuation from the mold cavity is directly proportional to the rate of injection of molten material into the mold cavity, accomplished by a pair of ganged pistons, both in communication with the interior of the mold cavity, that are linked together for simultaneous operation. One of the ganged pistons is an injection piston that injects molten material from an injection piston cylinder into the mold cavity. The other of the ganged pistons is a vacuum piston that pulls a vacuum in the mold cavity to eliminate gases which, if present, would cause porosity of the final product. This vacuum is created through a vacuum line that is connected on one end to the mold cavity and on the other end to the vacuum cylinder. The vacuum line contains a filter interposed between the mold and the vacuum cylinder to prevent any molten material that has escaped into the vacuum lines from going into the valve of the regulator and clogging the valve mechanism.
The injection sequence is divided into two phases. During the first phase, the injection and vacuum pistons concurrently move at a slow pace with the injection piston of the injection cylinder slowly moving the molten material toward the mold cavity and with the ganged vacuum piston pulling a vacuum in the mold cavity at a rate proportional to the reciprocation speed of the injection piston. When the ganged pistons pass a certain point in their stroke, an electrical signal from the die-casting apparatus triggers the high-velocity second phase of the injection sequence. During this second phase, both the injection and vacuum pistons move at a high rate of speed with the injection piston rapidly forcing the molten material into the mold cavity. The electrical signal that triggers the second phase also opens a vacuum break in the vacuum cylinder. The vacuum break has a diaphragm that can be adjusted to control the amount of vacuum in the vacuum line, thus allowing a pre-selected constant vacuum during the second phase of the injection sequence.
It is an object of the present invention to provide a gas-evacuating device that, during the first stage of injection, develops a vacuum at a rate proportional to the rate molten material is injected into the mold cavity.
It is a further object of the invention to provide such a device that requires no additional energy for operation over already existing devices.
It is an object of the invention to provide a vacuum device with very few moving parts, none of which come into contact with the molten material, thereby decreasing repair time and increasing efficiency.
REFERENCES:
patent: 2243835 (1941-06-01), Brunner et al.
patent: 2415462 (1947-02-01), Cherry et al.
patent: 2991506 (1961-04-01), Crandall
patent: 3433291 (1969-03-01), Hodler
patent: 3477101 (1969-11-01), Fritsch
patent: 3804570 (1974-04-01), Höschele et al.
patent: 4997026 (1991-03-01), Ozeki et al.
patent: 5277570 (1994-01-01), Siggers
IMI Cash Valve, Inc., D-51, D-52 Vacuum Regulating or Breaker Valves (1997), p. 22.
Lin Kuang Y.
Walker, McKenzie & Walker PC
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