Apparatus for the extrusion molding of foamable plastics

Claim 2

Apparatus for the extrusion molding of a foamable plastic material, comprising in combination: a hollow extrusion die having an elongated central chamber with an outlet at one end thereof; an induction tube disposed within said central chamber, said tube having an inner passage extending therethrough, said passage being of progressively larger cross-sectional area toward said outlet of said extrusion die, the outer surface of said induction tube being spaced from the wall of said central chamber to define a narrow circumferential passage therebetween for dividing a Flow of plastic material into an inner and an outer portion and for inhibiting foaming in said circumferential passage, said circumferential passage and said inner passage being joined together before said outlet of said die for joining said inner and outer portions of said plastic material; communicating means for providing communication of the ends of said inner passage and said circumferential passage remote from said outlet with a source of foamable thermoplastic material.

Claim 3

Apparatus for the extrusion molding of a foamable plastic material, comprising in combination: a hollow extrusion die having an elongated central chamber with an outlet at one end thereof; an induction tube disposed within said central chamber, said tube having an inner passage extending therethrough, said passage being of progressively larger cross-sectional area toward said outlet of said extrusion die, the outer surface of said induction tube being spaced from the wall of said central chamber to define a narrow circumferential passage therebetween for dividing a Flow of plastic material into an inner and an outer portion and for inhibiting foaming in said circumferential passage, said circumferential passage and said inner passage being joined together before said outlet of said die for joining said inner and outer portions of said plastic material; communicating means for providing communication of the ends of said inner passage and said circumferential passage remote from said outlet with a source of foamable thermoplastic material.

Claim 4

Apparatus for the extrusion molding of a foamable plastic material, comprising in combination: a hollow extrusion die having an elongated central chamber with an outlet at one end thereof; an induction tube disposed within said central chamber, said tube having an inner passage extending therethrough, said passage being of progressively larger cross-sectional area toward said outlet of said extrusion die, the outer surface of said induction tube being spaced from the wall of said central chamber to define a narrow circumferential passage therebetween for dividing a Flow of plastic material into an inner and an outer portion and for inhibiting foaming in said circumferential passage, said circumferential passage and said inner passage being joined together before said outlet of said die for joining said inner and outer portions of said plastic material; communicating means for providing communication of the ends of said inner passage and said circumferential passage remote from said outlet with a source of foamable thermoplastic material.

Claim 5

The device defined in claim 1 in which said circumferential passage completely encompasses said tube and is of substantially constant cross-sectional area throughout its length.

Claim 6

The device defined in claim 1 in which said communicating means includes means interposed between said tube and the wall of said chamber and located axially along said tube adjacent the input end thereof for defining a plurality of small orifices communicating between said source of material and the input end of said circumferential passage.

Claim 7

The device defined in claim 3 in which said orifices constitute four generally L-shaped cross-section openings and said circumferential passage has the cross-sectional shape of substantially a hollow square, said orifices being located adjacent the corners of said circumferential passage.

Claim 8

The device defined in claim 3 in which said circumferential passage is of substantially hollow square cross-section and said orifices comprise a plurality of axially extending holes communicating with each of the four sides of said circumferential passage.

Claim 9

The device defined in claim 1 in which the thickness of said circumferential passage is selected to resist the flow of the plastic material therethrough sufficiently to suppress the foaming pressure thereof and so restrain such material from foaming while passing through said circumferential passage.

Claim 10

The device defined in claim 1 including a multiperforate breaker plate spaced by means defining an intervening chamber from the inlet ends of said circumferential passage and said inner passage, said breaker plate being interposed between said source of material supply and said induction tube.

Claim 11

The device defined in claim 1 in which said inner passage has a first, material input portion which is elongated and of substantially constant cross-section and a further and elongated output portion which is of substantially uniformly increasing cross-section to allow uniform expansion of material passing therethrough due to foaming of such material, the output end of said increasing cross-section portion of said inner passage lying closely adjacent the output end of said circumferential passage for allowing smooth and rapid contact of foamed material from said inner passage with substantially unfoamed material leaving said circumferential passage.

Claim 12

The device defined in claim 1 including a radial flange extending outwardly from said tube adjacent the material input end thereof and a hollow adaptor ring coaxially located with respect to said tube and said die, said flange being axially disposed between said ring and said die and being provided with a plurality of substantially evenly circumferentially spaced small orifices extending axially therethrough and communicating between the interior of said hollow ring and said input end of said circumferential passage, a shell-like holder surrounding said die, said flange and said adapter ring for holding same in coaxially aligned relationship, said source of material comprising an extrusion screw substantially axially aligned with said tube and disposed within a hollow housing, means for rigidly connecting said shell-like holder to the output end of said screw housing and a multiperforate breaker plate interposed between said screw housing and said adapter ring whereby said screw extrudes foamable plastic material through said multiperforate breaker plate and through said hollow ring, one portion of said flow of material passing through said orifices and circumferential pAssage and the remainder of said material passing through said inner passage, the material flowing in said circumferential passage being constrained from foaming and the material in said inner passage being allowed to foam as it exits therefrom, the two portions of material combining to flow out of said extrusion die to form a product having an unfoamed or less completely foamed exterior portion and a more completely foamed interior portion.