Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Patent
1991-02-01
1992-09-22
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
264268, 26432812, 26432816, 425577, B29C 4514
Patent
active
051494825
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention generally pertains to injection molding of plastic products and is particularly directed to improvement in methods of controlling the wall thickness of a plastic product while being injection-molded and improvement in methods of reducing the clamping force requirements of a plastic product while being injection molded.
Prior art methods for controlling the wall thickness of a plastic product while being injection molded and for reducing the clamping force requirements of a plastic product while being injection molded are described in U.S. Pat. No. 3,375,554 to Blumer, U.S. Pat. No. 3,737,272 to Segmuller, U.S. Pat. No. 3,995,007 to Spiegelberg, U.S. Pat. No. 4,264,295 to Hingley and U.S. Pat. Nos. 4,381,275; 4,467,994; 4,508,676 and 4,789,326 all to Sorensen.
SUMMARY OF THE INVENTION
The present invention provides a method of controlling the dimensions of a hollow plastic product that is injection molded within the cavity of a mold having a core section and a cavity section defining the mold cavity therebetween and separated by a parting line, by stabilizing the core section in relation to the cavity section. The method includes the steps of: part of the mold cavity is filled; plastic material into the mold cavity so that the cooled injected first plastic material in said section extending between the core section and the cavity section of the mold cavity is sufficiently solidified to stabilize the core section in relation to the cavity section by impeding movement of the core section in relation to the cavity section caused by injecting the second plastic material, whereby the injected second plastic material fills the mold cavity; and solidify the product; plastic material without intermission; partially solidified and so that another portion of the first plastic material remains fluid; material displaces some of the fluid first plastic material to thereby provide at least one flow path for the second plastic material to fill the mold cavity and so that some of the at least partially solidified first plastic material stabilizes the core section in relation to the cavity section.
In another aspect, the present invention provides a method of controlling dimensions of a hollow plastic product having perimetric side walls that is injection molded by using a core mold section and a cavity mold section that are combined to define a mold cavity for the product therebetween, and which mold sections, when so combined, are separated by a parting line, wherein the mold cavity includes a gate in a base region and flow channels extending from the base region through a region of the cavity that defines the side walls of the product, the method comprising the step of injecting plastic material continuously into the mold cavity from the gate until the mold cavity is filled with said injected plastic material, with said injection being under such conditions of injection pressure, injected plastic temperature, mold cavity wall temperature, flow channel length, distance between flow channels, flow channel thickness and wall thickness in a thin-cavity region between flow channels that initially injected plastic material solidifies in the thin-cavity regions to stabilize the core mold section in relation to the cavity mold section prior to the mold cavity being filled with the injected plastic material.
I have ascertained that under the right combination of conditions of injection pressure, injected plastic material temperature and mold cavity wall temperature, the product dimensions can be controlled by this method when within a portion of the mold cavity in which dimension control is desired, the quotient of a ratio of flow channel length to distance between flow channels divided by the square of a ratio of flow channel thickness to wall thickness in a thin-cavity region between flow channels is less than two. These ratios are applicable for that portion of the mold cavity in which dimension control is desired.
The present invention also provides a method of reducing th
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Callan Edward W.
Heitbrink Jill L.
Primtec
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