Injection-molding dimension-control and clamp-reduction

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 re 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 steps of

• (a) forming said mold cavity in which within a portion of the mold cavity, 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;
• and
• (b) 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 material temperature and mold cavity wall temperature 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.

A method of reducing a separative force exerted against mold sections when injection molding a hollow plastic product that is injected by using a first mold section and a second 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 and flow channels extending through a region of the cavity, wherein plastic material injected into the mold cavity exerts said separative force against the mold sections while said injected plastic remains in a fluid state, 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 material 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 prior to the mold cavity being filled with the injected plastic material to thereby reduce said separative force.