Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – With means to heat or cool
Reexamination Certificate
2000-12-21
2003-02-25
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
With means to heat or cool
C425S564000
Reexamination Certificate
active
06524093
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus and method for converting the circular flow inside a melt channel to a uniform annular flow. More specifically, this invention relates to an apparatus and method for improving uniform melt flow and elimination of stagnation points as it passes through an injection molding system and/or hot runner system.
2. Summary of the Prior Art
The large number of variables in the injection molding process creates serious challenges to creating a uniform and high quality part. These variables are significantly compounded within multi-cavity molds. Here we have the problem of not only shot to shot variations but also variations existing between individual cavities within a given shot. Shear induced flow imbalances occur in all multi-cavity molds that use the industry standard multiple cavity “naturally balanced” runner system whereby the shear and thermal history within each mold is thought to be kept equal regardless of which hot-runner path is taken by the molten material as it flows to the mold cavities. These flow imbalances have been found to be significant and may be the largest contributor to product variation in multicavity molds.
Despite the geometrical balance, in what has traditionally been referred to as “naturally balanced” runner systems, it has been found that these runner systems can induce a significant variation in the melt conditions delivered to the various cavities within a multi-cavity mold. These variations can include melt temperature, pressure, and material properties. Within a multi-cavity mold, this will result in variations in the size, shape and mechanical properties of the product.
It is well known that providing for smooth flow of pressurized melt is critical to successful molding of certain materials. Sharp bends, corners or dead spots in the melt passage results in unacceptable residence time for some portion of the melt being processed which can cause too much delay on color changes and/or result in decomposition of some materials or pigments of some materials such as polyvinyl chloride and some polyesters or other high temperature crystalline materials. In most multi-cavity valve gated injection molding systems it is necessary for the melt flow passage to change direction by 90° and to join the bore around the reciprocating valve stem as it extends from the manifold to each nozzle.
These problems necessarily require fine tolerance machining to overcome and it is well known to facilitate this by providing a separate bushing seated in the nozzle as disclosed in U.S. Pat. No. 4,026,518 to Gellert. A similar arrangement for multi-cavity molding is shown in U.S. Pat. No. 4,521,179 to Gellert. U.S. Pat. No. 4,433,969 to Gellert also shows a multi-cavity arrangement in which the bushing is located between the manifold and the nozzle. Also shown in U.S. Pat. No. 4,705,473 to Schmidt, provides a bushing in which the melt duct in the bushing splits into two smoothly curved arms which connect to opposite sides of the valve member bore. U.S. Pat. No. 4,740,151 to Schmidt, et al. shows a multi-cavity system with a different sealing and retaining bushing having a flanged portion mounted between the manifold and the back plate.
U.S. Pat. No. 4,443,178 to Fujita discloses a simple chamfered surface located behind the valve stem for promoting the elimination of the stagnation point which would otherwise form.
U.S. Pat. No. 4,932,858 to Gellert shows a separate bushing seated between the manifold and the injection nozzle in the melt stream which comprises a melt duct with two smoothly curved arms which connect between the melt passage in the manifold and the melt passage around the valve stem in an effort to eliminate the stagnation points.
Reference should also be made to the following reference: “Extrusion Dies for Plastics and Rubber” by W. Michaeli, Carl Hanser Verlag, Munich, ISBN 3-446-16190-2 (1992).
There exists a need for a method and apparatus that substantially reduces the flow imbalances and stagnation points in an injection molding system and/or hot runner system that occurs as a result of the flow being diverted around a melt flow obstruction such as a valve stem, a nozzle, a nozzle tip, a valve stem guide, a torpedo, etc.
SUMMARY OF THE INVENTION
A flow deflector in a melt channel is provided, preferably around a valve stem or other flow obstruction, where the melt flow is converted from circular flow to annular flow. One preferred embodiment comprises a cylindrical body with a gradually constricting channel disposed on its outer surface. The channel is formed to be decreasing in depth and width, so as the melt flows into the channel, it gradually spills out of the channel. The gradual restriction of the channel helps direct the melt around the back of the cylindrical body which helps to eliminate stagnation points behind the flow obstruction while also providing uniform annular flow of the melt.
Further objections and advantages of the present invention will appear hereinbelow.
REFERENCES:
patent: 4026518 (1977-05-01), Gellert
patent: 4268240 (1981-05-01), Rees et al.
patent: 4303382 (1981-12-01), Gellert
patent: 4433969 (1984-02-01), Gellert
patent: 4443178 (1984-04-01), Fujita
patent: 4705473 (1987-11-01), Schmidt
patent: 4932858 (1990-06-01), Gellert
patent: 5334010 (1994-08-01), Teng
patent: 5518393 (1996-05-01), Gessner
patent: 5545028 (1996-08-01), Hume
patent: 5834041 (1998-11-01), Sekine et al.
patent: 5849343 (1998-12-01), Gellert et al.
patent: 5891381 (1999-04-01), Bemis et al.
patent: 2259818 (1974-07-01), None
Heitbrink Tim
Husky Injection Molding Systems Ltd.
Katten Muchin Zavis & Rosenman
LandOfFree
Flow deflector in an injection molding system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Flow deflector in an injection molding system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flow deflector in an injection molding system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3154857