A plastic extruder comprising a rotating helical screw in a heated cylinder, said screw having a core with a helical flight on the surface of said core, means for feeding plastic at the rearward end of said cylinder and discharge port means at the forward end of said cylinder for the discharge of molten plastic, an automatic shut-off valve at the forward end of said helical screw, said valve having a valve body and a poppet at the forward end of said valve body, said poppet axially movable and rotatable relative to said valve body, a facing surface on said poppet and a complementary seating surface on said valve body defining a valve opening, an axial bore in the forward end of said core, said valve body having a rearward projection extending into said axial bore and secured therein so that said entire valve body is integral with and rotates with said helical screw, a rearwardly extending axial stem on said poppet, a longitudinal bore in said valve body, said stem extending through said longitudinal bore into said axial bore, a compression spring mounted around the rear of said stem and out of contact with molten plastic, said spring operating cooperatively with respect to the poppet to maintain the poppet in a normally retracted position so that said facing and seating surfaces are normally in contact with each other and the valve is normally closed, opening means in said valve body for passing molten plastic from said shell into said valve body and towards said poppet, rotation of the screw and flow of molten plastic towards the poppet exerting pressure against the poppet to force the poppet away from the facing surface of the valve body and open the valve.

An automatic shut-off valve for a plastic extruder including a helical screw within a cylinder, said valve comprising a unitary valve body secured to said helical screw and a poppet at the forward end of and axially movable with respect to said valve body, a facing surface on said poppet and a complementary seating surface on said valve body defining a valve opening, flow passageway means through said valve body for the passage of molten plastic through said valve body, said flow passageway means including said valve opening, spring means cooperatively positioned with respect to said poppet to urge said poppet towards said valve body to maintain said valve opening in a normally closed position, said spring means positioned at the exterior of said valve and out of contact with molten plastic, flow of molten plastic forcing said poppet away from said valve body to open said valve against the force of said spring, said poppet both axially movable and rotatable with respect to said valve body.

Screw root attaching means are necessarily provided for interconnecting the inventive screw tip with a plastic extruder screw. Preferably, such means comprises a circular cylinder formed wholly with the forward cone, such cylinder extending rearwardly from the rearward end of the melt converging surface, such cylinder preferably having helical threads which are fitted for mating helically threaded mounting upon mounting threads of the downstream end of the root of an extruder screw. Where the root of such extruder screw comprises an interior oil conduit, the preferred helically threaded cylinder preferably further functions as a leak preventing plug or cap. The interior of such cylinder also preferably comprises an oil return conduit.

 

Where the inventive plastic extruder screw tip comprises an oil returning plug or cap, "O" ring receiving channels are preferably milled within the outer peripheral surface of the rearwardly extending cylinder, such channels receiving "O" rings for preventing oil leakage.

Accordingly, it is an object of the present invention to provide a plastic extruder screw tip having melt stagnation preventing dashers extending laterally therefrom.

It is a further object of the present invention to provide such a screw tip having dashers which are further adapted and configured for rotation through extruder die areas posing high risks of plastic melt stagnation.

It is a further object of the present invention to provide a plastic extruder screw tip having dashers which are further adapted for reduction of sheer forces applied to plastic melt flow.

Other and further objects, benefits, and advantages of the present invention will become known to those skilled in the art upon review of the Detailed Description which follows, and upon review of the appended drawings.

An injection molding machine has a two-part mold comprising a back mold half 22 and front mold half 24. Elastomeric material is injected into a cavity 26 formed by the two mold halves having a shape desired for the base member 12. After theplastic is injected into the cavity 26 forming the base member 12, the front mold half 24 is pulled away from the back mold half 22 leaving the base member 12 in place in the back mold half 22. The back mold half 22 and base member 12 are then rotatedand a second front mold half 28 is brought into engagement with the base member 12. A second elastomeric material is injected through the second front mold half 28 into cavities 30, 32 having the shapes desired for the contrast members 16. It ispossible to use multiple injection screws to fill the separate cavities 30, 32. This allows use of a third or even a fourth material to add colors or textures to the mat as desired.

The elastomeric material to form the base member 12 and the elastomeric material to form the contrast members 16 are very similar in molding characteristics and melting points. The injection molding of the contrast members 16 directly againstbase member 12 causes the contrast members 16 to weld to the base member 12 and then create a unitary bath mat 10. While the contrast members 16 may have different characteristics such as color, surface texture, surface skin feel, and Shore A hardness,the contrast members 16 are welded to and unitary with the base member 12.

After the injection molding of the contrast member 16 through the second front mold half 28, the second front mold half 28 is separated from the back mold half 22 and finished bath mat 10 ejected. Thus, an integrated two-step molding processstarts with two resin compounds and produces a finished bath mat. A base member is molded with a back mold half and a first mold half, then contrast members are integrated into the base member and molded with the same back mold half and a second frontmold half or over-mold half.

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