Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Forming plural articles
Reexamination Certificate
2001-06-28
2003-01-07
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Forming plural articles
C264S297200, C264S328800, C264S328120, C366S336000, C366S076800, C425S572000, C425S588000, C425S464000
Reexamination Certificate
active
06503438
ABSTRACT:
BACKGROUND
This invention relates to a method and apparatus for affecting the formation of a product made from laminar flowing material flowing in a molding tool by producing significantly balanced conditions of concentric laminates of that material.
Various manufacturing processes and apparatus use laminar flowing material flowing through one or more tools, such as dies or molds, in the formation of products. These tools have various part forming geometries used to shape the laminar flowing materials into desired products. As used hereinafter, the term “tool” includes all of the components within the body of an entire mold or die used to produce one or more products. Normally, tools of these types are constructed of high strength materials, such as tool steels or aluminum alloys having a very high compression yield strength, so as to withstand the pressure which forces the laminar flowing material through flow paths within the tools. These flow paths are commonly referred to by terms such as channels or runners, depending on the actual manufacturing process or tool being used. The terms “runner” and “runner system” will be used hereinafter to mean a flow path through a tool for laminar flowing material.
Runners used to deliver laminar flowing material may be machined or formed directly into the surface of one or more matched plates in one or more halves of a tool such that when combined form a runner or runners. Runners may also be machined into a block or blocks of steel or other high strength materials. Blocks of high strength materials are typically used as hot manifold systems, which are parts of tools used in injection molding processes. Runners may also be machined into one or more inserts, which can be added to a portion of the plate(s) or the block(s) of a tool. These inserts are also sometimes referred to as runner bars or runner inserts. Inserts may contain only a portion of the runner system or the entire runner system. Some tools also use items normally referred to as plugs which are typically inserted into runners in blocks of steel or other high strength materials to terminate a portion of a machined runner or otherwise affect the flow of material in the tools. These plugs will also be included hereinafter in the term “insert.” Inserts may include runners used for new tools or may be used to retrofit existing tools to alleviate problems in the manufacture of products.
Typical cross sectional shapes of runners include, but are not limited to, full round, half round, trapezoidal, modified trapezoidal or parabolic, and rectangular. Runners maybe solidifying or non-solidifying. For example, in thermoplastic injection molding processes, laminar flowing material in cold runners solidifies during the manufacture of products and is ejected from the tool during each cycle of the process. Whereas, hot runners are typically machined inside a block of high strength material and heated within the block so that the laminar flowing material within the hot runners remains fluid and is not ejected. Some tools may contain both hot runners and cold runners.
Manufacturing processes using tools and runner systems of the types described above include, but are not limited to, injection molding, transfer molding, blow molding and extrusion molding. The materials typically used in these processes include thermoplastics, thermosets, powdered metal and ceramics employing laminar flowing carriers, such as polymers. While this invention is useful for manufacturing methods and for apparatus which use the materials described above, this invention can be used to correct imbalances occurring in any tool in which imbalances occur in runners carrying a fluid exhibiting laminar flow and having a viscosity which is affected by shear rate (as with a non-Newtonian fluid) and/or by temperature, that is a fluid exhibiting variations in its characteristics as a result of variations in shear or flow velocity across the cross section of a runner.
Molding processes produce products by flowing laminar flowing material from a material source and through a runner system in a tool to an area or areas where the material is used to form the product. Molding processes include injection and transfer molding, in which laminar flowing material is injected under high pressure into a tool and through the runner system to a cavity or cavities in the tool (called a mold). The mold may have a single parting plane which separates two mold halves for forming molded items, or the mold may be a stack mold which has more than one parting plane, each separating a pair of mold halves. The material flows in concentric laminates through runners of whichever shape is used for a tool by following the center of the path of the runners.
Another manufacturing process using laminar flowing materials flowing in a runner system through a tool is extrusion blow molding. In the extrusion blow molding process, laminar flowing material is fed from a material source through a tool which includes a single runner or a branched runner system. After the material is fed through the runner system, it passes around a normally torpedo shaped insert near the end of the runner system which is used to form the solid stream of laminar flowing material into a tube, or profile, of material exiting the die. This tube of material is normally referred to as a parison. As the parison continues to lengthen to its desired length, it is clamped between two halves of a tool closing around it, and the tool then normally pinches off the bottom of the parison. Next, air is injected inside the tube of material, causing the material to expand against part forming walls of the tool. The material inside the tool is then cooled, solidifies, and is ejected after the tool is opened at the end of each production cycle. The tool then returns into position to grab another parison.
Yet another process using laminar flowing material flowing in a runner system through a tool is extrusion. In extrusion processes the laminar flowing material is normally, continuously fed from a material source through a die having a single runner or a branched runner system to be delivered to a part forming geometry which shapes the material as it exits at the end of the die. The extrusion process is normally referred to as a steady-state process and produces continuous shapes, or profiles, such as pipes or the coatings on electrical wires. As the laminar flowing material exits the part forming die, the material is normally drawn through a coolant, such as water, where it takes on its final shape as it solidifies.
Regardless of process and the type of tool used, as a laminar flowing material flows through a runner, the material near the perimeter of the runner experiences high shear conditions, whereas the material near the center experiences low shear conditions. These shear conditions are developed from the relative velocity of the flowing material to the stationary boundary of the flow channel and the relative velocity of the laminates of material flowing through the channel. The relative velocity of these laminates is usually referred to as the shear rate of the material.
FIG. 1
illustrates a characteristic shear rate distribution across the diameter “d” of a runner, where the magnitude of the shear rate is shown on the horizontal axis and the diameter is shown on the vertical axis. As seen in
FIG. 1
, shear rate is normally at or near zero at the outermost perimeter of a runner, is at its maximum level near the perimeter of the runner, and is then reduced to a level at or near zero in the center of the runner.
The result is that the laminar flowing material near the perimeter of the runner is dominated by high sheared material, and the center of the runner is dominated by low sheared material. The high sheared material will gain heat from friction caused by the relative velocity of the laminates as the laminar flowing material flows through the runner. This heat, and the effects of the shear on the non-Newtonian characteristics of polymers and other laminar flowing materials, will normally
Beaumont John P.
Hoffman David A.
Beaumont Runner Technologies, Inc.
Goebel, Jr. Edward W.
Heitbrink Jill L.
MacDonald, Illig, Jones and Britton LLP
Woodard Jon L.
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