Hot sprue assembly for an injection molding machine

Claim 2

In an injection molding machine for producing centrally apertured record discs, apparatus for controlling flow of molten disc-forming material into a disc-shaped mold cavity, comprising: a sprue assembly forming an open and relatively narrow gate for passage of the molten disc-forming material into the mold cavity, said gate being disposed in a plane recessed slightly from the general plane of the disc to be formed within the mold cavity; said sprue assembly including a sprue bushing having a central bore formed therein for passage of the molten disc-forming material toward the mold cavity, and dispersion means having a plurality of relatively small extrusion passages formed therein, said dispersion means being mounted generally within the end of said bore adjacent said mold cavity for passage of the molten disc-forming material through said extrusion passages prior to passage through said gate; and heater means for controlled elevation of the temperature of said sprue assembly to create a preselected temperature gradient between said sprue assembly and the mold cavity for permitting solidification of the disc-forming material within the mold cavity up to the gate without substantial solidification of disc-forming material within said sprue assembly.

Claim 3

The apparatus of claim 1 wherein said gate is generally annular in shape.

Claim 4

The appartus of claim 2 wherein said annular gate has a radial width of on the order of from about 0.005 inch to about 0.020 inch.

Claim 5

The apparatus of claim 2 wherein said gate is defined by an annular space between said sprue bushing and said dispersion means adjacent the mold cavity.

Claim 6

The apparatus of claim 1 wherein said sprue assembly further includes means positioned within the mold cavity for molding a central aperture into the disc prior to solidification of the disc-forming material.

Claim 7

The apparatus of claim 1 wherein said dispersion means cooperates with said sprue bushing to define a first annular chamber for receiving the molten disc-forming material, and a second annular chamber communicating with said gate, said extrusion passages permitting flow of the material from said first annular chamber into said second annular chamber.

Claim 8

The apparatus of claim 6 wherein said dispersion means comprises a generally cylindrical sleeve having said plurality of extrusion passages formed therein.

Claim 9

The apparatus of claim 7 wherein each of said extrusion passages has an opening diameter on the order of from about 0.020 to about 0.060 inch.

Claim 10

The apparatus of claim 7 wherein said sleeve comprises a radial boundary between said first and second annular chambers, and wherein said second annular chamber is relatively narrow and has an axial length sufficient to permit rehomogenization of the material into a single annular flow stream prior to passage through said gate.

Claim 11

The apparatus of claim 1 wherein said sprue bushing is oriented with its central bore extending generally along a central axis of the mold cavity.

Claim 12

The apparatus of claim 1 wherein said heater means is mounted for supplying heat energy to the end of said sprue bushing generally opposite the mold cavity.

Claim 13

The apparatus of claim 1 wherein said heater means comprises a heating element carried within said dispersion means.

Claim 14

The apparatus of claim 1 including a first mold half and a second mold half movable with respect to each other between a closed position to define the mold cavity and an open position to permit a molded disc to be removed from the machine, said sprue assembly being mounted on said first mold half for movement therewith, and including a die plug mounted on said second mold half to extend through the mold cavity when said mold halves are closed for cooperation with said disepersion means to mold a central aperture into the disc prior to solidification of the disc-forming material.

Claim 15

The apparatus of claim 13 wherein said die plug has a generally cylindrical shape for close reception of its distal end into a matingly-shaped recess formed in said dispersion means when said mold halves are closed.

Claim 16

The apparatus of claim 1 wherein said bore in said sprue bushing has a first portion of relatively narrow cross section opening toward the mold cavity into a second portion of increased cross section, said dispersion means being mounted generally within said second portion and including means for dividing the molten material into an annular flow stream prior to passage through said extrusion passages and for recombining the molten material downstream of said extrusion passages into a homogeneous flow stream prior to passage through said gate.

Claim 17

In an injection molding machine for producing centrally apertured record discs, a sprue assembly for controlling flow of molten disc-forming material into a disc-shaped mold cavity, comprising: a sprue bushing having a central bore for passage of the molten disc-forming material toward the mold cavity, said bore opening into a chamber of enlarged cross section extending in a direction toward the mold cavity; dispersion means positioned generally within said chamber and cooperating with said sprue bushing to define an open and relatively narrow annular gate for passage of molten disc-forming material into the mold cavity, said dispersion means having a plurality of relatively small extrusion passages formed therein for passage of the material prior to passage of the material through said gate; and heater means for creating a preselected temperature gradient between said dispersion means and the mold cavity for permitting solidification of the disc-forming material within the mold cavity substantially up to said gate without substantial solidification of disc-forming material within the sprue assembly.

Claim 18

In an injection molding machine for producing centrally apertured record discs, a sprue assembly for controlling flow of molten disc-forming material into a disc-shaped mold cavity, comprising: a sprue bushing having a central bore for passage of the molten disc-forming material toward the mold cavity, said bore opening into a chamber of enlarged cross section extending in a direction toward the mold cavity; dispersion means positioned generally within said chamber and cooperating with said sprue bushing to define an open and relatively narrow annular gate for passage of molten disc-forming material into the mold cavity, said dispersion means having a plurality of relatively small extrusion passages formed therein for passage of the material prior to passage of the material through said gate; and heater means for creating a preselected temperature gradient between said dispersion means and the mold cavity for permitting solidification of the disc-forming material within the mold cavity substantially up to said gate without substantial solidification of disc-forming material within the sprue assembly.

Claim 19

The sprue assembly of claim 16 wherein said sprue bushing and said dispersion means cooperate to form said gate in a plane recessed slightly from the general plane of the disc to be formed within the mold cavity.

Claim 20

The sprue assembly of claim 16 wherein said sprue bushing is oriented within its bore aligned generally along a central axis of the mold cavity, and including means positioned within the mold cavity for molding a central aperture into the disc prior to solidification of the disc-forming material, said gate being positioned concentrically about and relatively close to said aperture-molding means.

Claim 21

The sprue assembly of claim 16 wherein said annular gate has a radial width of on the order of from about 0.005 inch to about 0.020 inch.

Claim 22

The sprue assembly of claim 16 wherein said gate is formed within a relatively shallow annular boss defined by said sprue bushing and said dispersion means to extend slightly into the mold cavity.

Claim 23

The sprue assembly of claim 16 wherein said heater means comprises a heat generation device mounted at the end of said sprue bushing generally opposite the mold cavity.

Claim 24

The sprue assembly of claim 21 wherein said heat generation device comprises an electrical resistance coil.

Claim 25

The sprue assembly of claim 16 wherein said heater means includes a heating element carried within said dispersion means.

Claim 26

The sprue assembly of claim 16 wherein said dispersion means includes means for dividing the molten disc-forming material into an annular flow stream upstream of said extrusion passages and means for recombining the material into a homogeneous annular flow stream downstream of said extrusion passages.

Claim 27

The sprue assembly of claim 24 wherein said dividing means comprises means forming a relatively narrow annular chamber for receiving molten disc-forming material from said bore for passage into communication with said extrusion passages, and wherein said recombining means comprises means forming a relatively narrow annular chamber for receiving molten disc-forming material from said extrusion passages into communication with said gate.

Claim 28

The sprue assembly of claim 16 wherein said dispersion means comprises a generally cylindrical sleeve having one end secured to said sprue bushing generally within said chamber and extending axially toward the mold cavity, said sleeve and said sprue bushing cooperating to define said gate and a relatively narrow annular flow path opening toward said gate, said extrusion passages being formed in said sleeve.

Claim 29

The sprue assembly of claim 26 wherein said dispersion means further includes a generally cylindrical dispersion head disposed within said sleeve and projecting in radially spaced relation therewith toward said bore whereby said head and sleeve cooperate to define a relatively narrow annular flow path communicating between said bore and said extrusion passages.

Claim 30

The sprue assembly of claim 27 wherein said sleeve includes a radially inwardly projecting flange for supporting said head.

Claim 31

The sprue assembly of claim 27 wherein said chamber formed in said sprue bushing has a generally conical surface expanding from said bore in a direction toward the mold cavity, said conical surface merging with a generally cylindrical surface extending toward the mold cavity with a substantially uniform cross section, said dispersion head including a generally conical portion disposed in spaced relation with said conical surface and a generally cylindrical portion disposed in spaced relation with said cylindrical surface.

Claim 32

The sprue assembly of claim 26 wherein said one end of said sleeve is threadably secured to said sprue bushing.

Claim 33

In an injection molding machine for producing centrally apertured record discs, a sprue assembly for controlling flow of molten disc-forming material into a disc-shaped mold cavity, comprising: a sprue bushing having a central bore for passage of the molten disc-forming material toward the mold cavity; means forming a relatively narrow annular gate for passage of the material into the mold cavity, said gate being disposed in a plane recessed slightly from the general plane of the disc to be formed within the mold cavity; means for dividing the material passing from said bore into a first annular flow stream; means for extruding said first annular flow stream through an annularly-arranged plurality of relatively small extrusion passages; means for recombining the extruded material into a substantially homogeneous second annular flow stream and for coupling said second annular flow stream for passage through said gate; and heater means for creating a preselected temperature gradient between said bore and the mold cavity for permitting solidification of the disc-forming material within the mold cavity substantially up to said gate without substantial solidification of disc-forming material upstream of said gate.

Claim 34

In an injection molding machine for producing centrally apertured record discs, a sprue assembly for controlling flow of molten disc-forming material into a disc-shaped mold cavity, comprising: a sprue bushing having a central bore for passage of the molten disc-forming material toward the mold cavity; means forming a relatively narrow annular gate for passage of the material into the mold cavity, said gate being disposed in a plane recessed slightly from the general plane of the disc to be formed within the mold cavity; means for dividing the material passing from said bore into a first annular flow stream; means for extruding said first annular flow stream through an annularly-arranged plurality of relatively small extrusion passages; means for recombining the extruded material into a substantially homogeneous second annular flow stream and for coupling said second annular flow stream for passage through said gate; and heater means for creating a preselected temperature gradient between said bore and the mold cavity for permitting solidification of the disc-forming material within the mold cavity substantially up to said gate without substantial solidification of disc-forming material upstream of said gate.

Claim 35

The sprue assembly of claim 31 including means positioned within the mold cavity for molding a central aperture into the disc prior to solidification of the disc-forming material.

Claim 36

In an injection molding machine for producing centrally apertured record discs, a sprue assembly for controlling flow of molten disc-forming material into a disc-shaped mold cavity, comprising: a sprue bushing having a central bore for passage of the molten disc-forming material toward the mold cavity; means forming a relatively narrow annular gate for passage of the material into the mold cavity, said gate being disposed in a plane slightly recessed from the general plane of the disc to be formed within the mold cavity; means forming a relatively narrow and generally axially extending flow path communicating between said bore and said gate; means forming an annularly arranged plurality of relatively small extrusion passages disposed along the axial length of said flow path, whereby material flowing through said flow path is extruded through said extrusion passages and is recombined into a substantially homogeneous annular flow stream downstream of said extrusion passages; and heater means for creating a preselected temperature gradient between said bore and the mold cavity for permitting solidification of the disc-forming material within the mold cavity substantially up to said gate without substantial solidification of disc-forming material upstream of said gate.

Claim 37

In an injection molding machine for producing centrally apertured record discs, a sprue assembly for controlling flow of molten disc-forming material into a disc-shaped mold cavity, comprising: a sprue bushing having a central bore for passage of the molten disc-forming material toward the mold cavity; means forming a relatively narrow annular gate for passage of the material into the mold cavity, said gate being disposed in a plane slightly recessed from the general plane of the disc to be formed within the mold cavity; means forming a relatively narrow and generally axially extending flow path communicating between said bore and said gate; means forming an annularly arranged plurality of relatively small extrusion passages disposed along the axial length of said flow path, whereby material flowing through said flow path is extruded through said extrusion passages and is recombined into a substantially homogeneous annular flow stream downstream of said extrusion passages; and heater means for creating a preselected temperature gradient between said bore and the mold cavity for permitting solidification of the disc-forming material within the mold cavity substantially up to said gate without substantial solidification of disc-forming material upstream of said gate.

Claim 38

The sprue assembly of claim 33 including means positioned within the mold cavity for molding a central aperture into the disc prior to solidification of the disc-forming material.

Claim 39

In an injection molding machine for producing centrally apertured record discs, a sprue assembly for controlling the flow of molten disc-forming material into a disc-shaped mold cavity, comprising: a sprue bushing having a central bore formed therein for passage of the molten disc-forming material toward the mold cavity, said bore including a first portion of relatively narrow cross section opening into a second portion having a cross section expanding in an axial direction toward the mold cavity, said second portion merging with a third portion of generally uniform cross section opening axially toward the mold cavity; a dispersion head assembly positioned generally within said second and third portions of said bore, said dispersion head assembly including a generally cylindrical sleeve having one end secured to said sprue bushing and extending within said third portion axially toward the mold cavity, said sleeve cooperating with said sprue bushing to define therebetween an axially extending and relatively narrow annular flow path opening toward the mold cavity and terminating in an annularly open gate disposed in a plane recessed slightly from the general plane of the disc to be formed within the mold cavity; said dispersion head assembly further including a dispersion head disposed within said sleeve and projecting in a direction away from the mold cavity, said dispersion head having a cylindrical portion radially spaced from said sleeve and a conical portion radially spaced from said second portion of said bore for defining a relatively narrow annular flow path communicating between said first portion of said bore and said sleeve, said sleeve having a plurality of relatively small extrusion passages formed therein for passage of the material therethrough; and heater means for creating a preselected temperature gradient between said bore and the mold cavity for permitting solidification of the disc-forming material within the mold cavity substantially up to said gate without substantial solidification of disc-forming material upstream of said gate.

Claim 40

In an injection molding machine for producing centrally apertured record discs, a sprue assembly for controlling the flow of molten disc-forming material into a disc-shaped mold cavity, comprising: a sprue bushing having a central bore formed therein for passage of the molten disc-forming material toward the mold cavity, said bore including a first portion of relatively narrow cross section opening into a second portion having a cross section expanding in an axial direction toward the mold cavity, said second portion merging with a third portion of generally uniform cross section opening axially toward the mold cavity; a dispersion head assembly positioned generally within said second and third portions of said bore, said dispersion head assembly including a generally cylindrical sleeve having one end secured to said sprue bushing and extending within said third portion axially toward the mold cavity, said sleeve cooperating with said sprue bushing to define therebetween an axially extending and relatively narrow annular flow path opening toward the mold cavity and terminating in an annularly open gate disposed in a plane recessed slightly from the general plane of the disc to be formed within the mold cavity; said dispersion head assembly further including a dispersion head disposed within said sleeve and projecting in a direction away from the mold cavity, said dispersion head having a cylindrical portion radially spaced from said sleeve and a conical portion radially spaced from said second portion of said bore for defining a relatively narrow annular flow path communicating between said first portion of said bore and said sleeve, said sleeve having a plurality of relatively small extrusion passages formed therein for passage of the material therethrough; and heater means for creating a preselected temperature gradient between said bore and the mold cavity for permitting solidification of the disc-forming material within the mold cavity substantially up to said gate without substantial solidification of disc-forming material upstream of said gate.

Claim 41

The sprue assembly of claim 35 including a first mold half and a second mold half movable with respect to each other between a closed position to define the mold cavity and an open position to permit a molded disc to be removed from the machine, said sprue assembly being mounted on said first mold half for movement therewith, and including a die plug mounted on said second mold half to extend through the mold cavity when said mold halves are closed for reception into a matingly shaped recess formed in said dispersion head assembly to mold a central aperture into the disc prior to solidification of the disc-forming material.