Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Reexamination Certificate
2000-07-31
2004-05-18
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
C264S328800, C425S145000
Reexamination Certificate
active
06737001
ABSTRACT:
This invention relates generally to molding an article with material, and more particularly concerns an injection control gate for controlling the flow of moldable material into a mold for molding an article.
The use of plastic components in machines, equipment and generally in commercial products is wide, extensive and continually growing. Plastic components afford low cost, lightweight corrosion resistance and many other significant advantages.
The manufacture of plastic components is typically accomplished through a molding process. The molding process includes injecting plastic material in the form of small pellets into a machine which includes a mold having a cavity with the shape of the plastic component. The plastic pellets are conveyed into a cavity or chamber and are advanced toward the cavity of the mold by a screw or ram. The screw or ram is housed in an electrically heated enclosure which melts the pellets into a liquid which readily fills the cavity within the mold.
The mold typically includes a fixed and movable portion with the cavity being formed therebetween. The movable portion of the cavity is separated from the fixed portion after the cavity is filled with the plastic fluid and allowed to cool. The cooled plastic,material thus forms the molded plastic part.
The plastic liquid within the screw or ram is introduced into the mold cavity through channels or runners in communication between the screw of ram and the mold cavity. To regulate the flow of the plastic material through the channels or runners, valves typically called gates are positioned within the channels or runners and are opened to permit flow of the plastic fluid therethrough and closed to prohibit the flow of the fluid.
The opening and closing of the gates within the channels or runners is an important part of the development of a proper process for molding plastic parts. This is particularly true for large and flat complex components which may have a large number of channels or runners and consequently a plurality of gates.
Typical problems in the filling of the plastic fluid within the mold cavity are fill balancing and clamp tonnage optimization. In fill balancing, it may be necessary to have more fluid pass through a channel in a area within the mold cavity which has a large area or mass and to permit only a much smaller amount of plastic fluid to flow through a channel related to a portion of the mold cavity where the mass or cross section is quite small.
Further, in order to optimize, i.e. minimize, the clamp tonnage which is the pressure or force required to clamp the mold or cavity halves together against injection pressure. Clamp tonnage is best minimized when the flow of the plastic material through the channels or runners corresponding to portions of the cavity are evenly balanced and much higher amounts of material are not necessary to be filled within only one particular gate which corresponds to that area of high volume. Thus optimum flow of material through the proper channels or runners for the proper period of time may minimize the amount of injection pressure or force required to fill the mold cavity with liquid plastic, and thus reduce clamp tonnage requirements.
Furthermore, as the liquid plastic enters the mold cavity from different channels or runners, the molded material meets at a transition zone within the cavity. The integrity and appearance of the plastic material at this transition zone may be inferior to other portions of the plastic material within the mold cavity. For example, the transition zones may occur at highly visible areas where the appearance of the molded article is more important or in areas of greater stress within the molded article where material integrity is more critical. Thus, it is important that the flow of material into the mold be accurately and precisely controlled.
While generally it may be sufficient to open and close a gate within a channel or runner only once during the molding cycle, at times it may be desirable to open and close different gates at different times within the molding cycle, or a particular gate more than once. In situations where material is passed through a first channel with a first gate into an area of small cross section while additional material is permitted to flow through a second channel and a second gate into a area of large cross section, the area of greater cross section typically requires a much large amount of time to fill the large cavity. Thus, the first channel with the small cavity area has its gate shut before the second gate of the large area is shut.
The material flowing through the first channel then tends to cool after it has flowed and may cause a problem since the gate, which is now shut cannot transmit hold, or pack pressure to the minor area. The material in this area will shrink away from the cavity wall during the hold phase of the molding cycle if hold pressure cannot be applied. This will render the molded article unusable dimensionally and cosmetically. If, however, the first gate which regulates the first channel is permitted to be opened again for a short period of time immediately preceding the end of the molding cycle, pressure through the first channel may cause the molded material through the first channel to transmit hold pressure through the molded article and avoid an unacceptable article.
Typically, molding machines either have no capability whatsoever to regulate gates within a mold of the plastic molding machine, or include only the ability of opening all the gates and closing all the gates simultaneously. Other newer machines may have some limited ability to sequence gates but may be limited to a time variable singular sequence for each injection gate within the molding cycle.
Newer, modern, more expensive machines such as those manufactured by Engel Manufacturing Company, Guelph, Canada, Model No. 600/200 VHRO, have the ability to sequence the opening and closing of gates within a molding machine. These machines are able to open and close a particular gate once during the molding cycle. Recently, Incoe Corporation has offered a gate sequencing control system for opening and closing the valves of a mold for a molding machine. The Incoe system is portable computer based system and is very complicated and expensive.
The following disclosures nay be relevant to various aspects of the present invention:
U.S. Pat. No. 5,523,045
Patentee: Kudert et al.
Issue Date: Jun. 4, 1996
U.S. Pat. No. 5,149,547
Patentee: Gill
Issue Date: Sep. 22, 1992
U.S. Pat. No. 5,141,696
Patentee: Osuna-Diaz
Issue Date: Aug. 25, 1992
U.S. Pat. No. 5,078,589
Patentee: Osuna-Diaz
Issue Date: Jan. 7, 1992
U.S. Pat. No. 4,592,711
Patentee: Capy
Issue Date: Jun. 3, 1986
U.S. Pat. No. 4,279,582
Patentee: Osuna-Diaz et al.
Issue Date: Jul. 21, 1981
U.S. Pat. No. 4,140,238
Patentee: Dawson et al.
Issue Date: Feb. 20, 1979
U.S. Pat. No. 3,902,665
Patentee: Hendry
Issue Date: Sep. 2, 1975
Control Cavity Filling with Melt ‘Throttles’ in the Mold
Plastic Technology Magazine
June 1998
Internet printout
Incoe Corporation
Jul. 5, 1998
The relevant portions of the foregoing disclosures may be briefly summarized as follows:
U.S. Pat. No. 5,523,045 discloses methods for injection molding and injection blow-molding multi-layer plastic articles, including containers and partisans for forming containers, which include providing a plurality of co-injection nozzle means for injecting plastic materials into associated injection cavities to form each article, providing streams of polymeric materials to form corresponding layers of the articles, moving each stream separately to plural nozzle means, separately receiving the streams in the plural nozzle means, and injecting the streams to form the multi-layer plastic articles. Preferably, each stream of material which is to form a corresponding layer of the articles is provided with substantially the same polymer flow, preferably from where each stream is split and moved to each nozzle means. Valve means can be employed in each nozzle means for positively controlling preferably substan
Heitbrink Jill L.
Ryan Andrew D.
Xerox Corporation
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