Process for molding of plastic structural web articles

A process for the product of a molded plastic structural web article comprising:

• introducing a volume less than the volume of the mold of a molten plastic material, having a high shear viscosity and elasticity, into a mold cavity having a contour which provides the desired flow length-to-thickness ratio;
• injecting low viscosity pressurizing fluid into said molten plastic material in said mold cavity through at least one injection opening and at a fluid flow rate and fluid pressure to cause (i) said pressurizing fluid to penetrate into said molten plastic material so that the fluid-plastic interface is first deformed into a wave-like corrugation of finite lengths and (ii) the formation of a generally continuously hollow center with sufficient fluid-plastic interface distortion(s) to produce at least one skin-connecting web therein for each distortion and capable of growth with time whereby the outer portion of said plastic material is forced to assume the contour of said mold cavity, thereby forming a molten structural web article without causing said low viscosity pressurizing fluid to break through the plastic material flow front and prevent the plastic material from substantially completely assuming the contour of said mold cavity;
• and maintaining said pressure of said pressurizing fluid in said article in said mold until said article is self-supporting.