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A method and apparatus for making a twin-wall internally corrugated plastic structural part provided with a smooth, dense, solid, thin walled, non-cellular skin comprising injecting a thermoplastic or resin material into a pair of closed mold members which define a sealed cavity. A small amount of p

A method and apparatus for making a twin-wall internally corrugated plastic structural part provided with a smooth, dense, solid, thin walled, non-cellular skin comprising injecting a thermoplastic or resin material into a pair of closed mold members which define a sealed cavity. A small amount of plastic material is initially injected into the cavity with the material impinging upon and being dispersed over the mold members thereby forming a generally continuous thin skin substantially the mold surfaces. Thereafter, successively and intermittently injecting an inert gas under pressure through one mold member during continued injection of the plastic material into the cavity thereby pressurizing the skin against the walls of the mold cavity and progressively commingling the inert gas under pressure and the inwardly flowing plastic material as both enter the cavity until the cavity is filled with an internal corrugated body integral with and bonded to the skin. Further steps include cooling the twin-wall internally corrugated structural part to permit the same to solidify as an integral unit and venting the mold cavity to atmosphere to relieve pressure from the corrugated plastic structural part. The intermittent injection of the inert gas introduces minute amounts of pressurized gas into the continuously injected plastic material.

대표청구항 ▼

1. Apparatus for making a twin-wall, internally corrugated plastic structural part having a smooth, dense, solid, thin walled, non-cellular skin comprising a pair of mold members defining, when closed, a sealed cavity; one of said mold members including an opening means through which plastic mate

1. Apparatus for making a twin-wall, internally corrugated plastic structural part having a smooth, dense, solid, thin walled, non-cellular skin comprising a pair of mold members defining, when closed, a sealed cavity; one of said mold members including an opening means through which plastic material is adapted to be injected into said cavity; and probe means having a bore projected therethrough and mounted upon the other of said mold members, said probe means having one end located outwardly of said other mold member and adapted to be connected to a source of pressurized inert gas; and said probe means having its other end located opposite from and facing said opening means and communicating with the mold cavity for injecting the gas under pressure into the mold cavity, first means for causing introduction of plastic material into said opening means; second means for causing the introduction of gas into said probe means whereby a small amount of the plastic material first introduced into said cavity by said first means is pressurized by the gas introduced by said second means, thereby forming the skin against the walls of said mold cavity and thereafter the progressive commingling of the inert gas under pressure from said second means with additional plastic material from said first means filling the cavity and forming an internal corrugated body integral with and bonded to said skin. 2. In the apparatus of claim 1, said probe means having a head at said other end thereof, said head being located in said mold cavity when the inert gas is directed through said probe means and head into said mold cavity. 3. In the apparatus of claim 2, including valve means within said probe means for controlling the flow of the inert gas. 4. In the apparatus of claim 1, wherein at least one sprue is provided for injecting the plastic material; and at least one probe is provided for injecting the pressurized gas into the cavity. 5. In the apparatus of claim 1, said probe means having a head upon its other end; there being a plurality of radially directed orifices within said head communicating with the probe means bore for uniformly dispersing the gas in a transverse plane laterally outward towards the interior walls of the mold members throughout 360°. 6. In the apparatus of claim 5, said orifices being right angularly related. 7. In the apparatus of claim 5, said orifices having a diameter of in the range of 0.003 to 0.010 inches, approximately. 8. In the apparatus of claim 5, the head of said probe means having; an orifice communicating with the bore of said probe means for dispensing the gas towards an interior wall of the mold members. 9. In the apparatus of claim 1, the connection of said probe means to said gas source including a conduit; a vent valve means in said conduit normally closed to atmosphere; and a gas control valve means in said conduit adapted to be closed on filling the mold with plastic material; said vent valve means being successively opened to vent the mold cavity to atmosphere to relieve gas pressure from the plastic structural part. 10. In the apparatus of claim 5, including valve means within said probe means, at one end normally closing said orifices and with its other end projecting from said probe means; and a power operated reciprocal actuator means mounted upon said other mold member and connected to the other end of said valve means for intermittently reciprocating said valve means successively opening and closing said orifices whereby said gases are injected intermittently into said cavity introducing minute amounts of pressurized gas into the continuously injected plastic material. 11. In the apparatus of claim 8, valve means within said probe means at one end normally closing said orifice and with its other end projecting from said probe means; and a power operated reciprocal actuator means mounted upon said other mold member and connected to the other end of said valve means for intermittently reciprocating said valve means successively opening and closing said orifice. 12. In the apparatus of claim 10, said actuator means reciprocating in the range of 4 to 100 cycles per second. 13. In the apparatus of claim 10, said valve means being an elongated rod loosely nested within said probe means, at one end alternately registerable with said orifices, said gas adapted to move past said rod outwardly thereof along its length, said actuator means being connected to said rod. 14. In the apparatus of claim 13, said head having a tapered valve seat in registry with said orifices, said rod having a tapered valve element normally registerable with said seat. 15. In the apparatus of claim 13, a fitting mounted upon and depending from said probe means, having a bore guidably receiving said rod, and a counterbore receiving said rod and in communication with said probe means bore; the connection of said probe means to said gas source including a conduit at one end connected to said gas source and at its other end connected to said fitting for communication with said probe means bore. 16. In the apparatus of claim 15, a first control valve connected to said gas conduit; a vent pipe connected to said fitting in communication with its counterbore; and a second control valve on said vent pipe openable on closure of said first control valve. 17. In the apparatus of claim 13, said probe means having an apertured base mounted upon said other mold member, and having an interiorly threaded bore; said actuator means having a threaded boss projected into said threaded bore. 18. In the apparatus of claim 13, said actuator means having reciprocal oscillator connected to said rod and normally biased outwardly, said rod normally closing said orifices. 19. In the apparatus of claim 1, the connection of said probe means to said gas source including a conduit, a normally closed control valve connected to said conduit venting said probe means to atmosphere, said control vavle when opened directing pressurized gas to said probe means. 20. In the apparatus of claim 19, a normally open gas injection timer and a normally open gas flow delay timer connected into said conduit upstream of said flow control valve. 21. In the apparatus of claim 10, a probe support slide mounted upon said probe means and slidably mounted upon said other mold member for limited reciprocal movements; and an intermittently operable cam lifter means connected to said slide; said probe means head and orifices being retracted from said cavity closing said orifices when said lifter means is retracted, and said probe means head and orifices being moved into said cavity on advancing of said cam lifter means. 22. In the apparatus of claim 21, a bushing mounted upon said other mold member coaxial of said probe means slidably receiving said probe support slide; a stop fastener on one end of said slide registerable with said bushing limiting movement of said slide in one direction; a shoulder on said slide normally spaced from said bushing limiting movement of said slide in the opposite direction. 23. In the apparatus of claim 22, the reciprocal movement of said probe support slide being about one-eighth of an inch, approximately. 24. In the apparatus of claim 21, said cam lifter means including a double acting cylinder assembly mounted upon said one mold member and having a piston rod; and an elongated cam arm at one end axially connected to said piston rod and at its other end engaging a cam surface upon said probe support slide.