US2591508A

US2591508A - Extrusion apparatus

Info

Publication number: US2591508A
Application number: US141541A
Authority: US
Inventors: Grant S Brown
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1950-01-31
Filing date: 1950-01-31
Publication date: 1952-04-01
Anticipated expiration: 1969-04-01

Description

April 1, 1952 G. 5. BROWN EXTRUSION APPARATUS Filed Jan. 31, 1950 #vvnvrm 6'. 6: 1980 WA/ Afro/awn Patented Apr. 1, 1952 EXTRUSION APPARATUS Grant S. Brown, Downers Grove, Ill., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application January 31, 1950, Serial No. 141,541

6 Claims.

This invention relates to extruding apparatus and more particularly to apparatus for platicizing and straining plastic material.

In the manufacture of electrically conducting cables and the like wherein it is desired to cover a core consisting of one or more cable conductors with a protective or insulating cover of thermoplastic material by extrusion, it is necessary that the thermoplastic material be worked prior to the extrusion. It is further necessary that the extrudable material be maintained at all times free of air bubbles in order to prevent blisters up in the material being worked and fed by the feed screw. This back pressure is controlled by the number of screens employed and by the mesh of the screens, and the function of the breaker plate is primarily to support the screen or screens. Back pressure is highly desirable with most plastic materials used for extruding, since such pressure tends not only to drive out undesirable entrapped air or other gases, but also tends to increase the temperature of the plastic material to a certain extent, thereby afi'ording more efficient and easier extrusion thereof.

As has been explained before, the breaker plates now in use in plastic extrusion apparatus are employed primarily to support relatively fine mesh screens, which screens actually provide the necessary back pressure. The breaker plates thus employed are provided with a large number of holes of relatively large diameter. For example, in the ordinary breaker plate used with a feed screw working in a cylinder bore having a diameter of 10'', the total area of the breaker plate holes is on the order of 35 square inches. Due to the high fluidity of many plastic materials, the number of screens necessary with conventional breaker plates becomes quite large, making their use undesirable or impossible.

It is an object of this invention to provide an improved breaker plate which may be employed to produce the desired back pressure in extrudable plastic material.

One embodiment of the invention may comprise a breaker plate so constructed that it provides not only for adequate back pressure, but also for the necessary streamlining of flow which must be maintained in order to preserve the quality of the plastic material as well as the efficiency of the equipment. A breaker plate embodying these desirable features may comprise a plate having a perforated central area surrounded by a dished imperforate area. It is significant that the total cross-sectional area of the holes in the perforated area is on the order of 1% square inches in a breaker plate used with a cylinder of diameter. It is thus obvious that the reduced area of the holes greatly improves the back pressure, regardless of, whether or not a screen or screens precede the holes. In order to increase the back pressure even further, the dished imperforate an- I nular portion is provided, which not only produces increased back pressure, but also insures smooth flow of the plastic material through the breaker plate by virtue of its dished configuration. Other objects and advantages of the invention will appear from a consideration of the following detailed description when taken in conjunction with the accompanying single figure drawing illustrating one embodiment of the invention.

Referring to the drawing, the extruding mechanism consists of a cylinder l0 having a cylindrical liner 1 I suitably positioned therein to provide a bore 12 into which extrudable plastic material may be fed by any suitable means (not shown). The diameter of the bore 12 is substantially equal to the major diameter of the threads on a feed screw 13 which is rotatably mounted within the bore l2 to work the plastic material and feed it into an extruding head M.

The extruding head I 4 consists of a housing 15 which is suitably hinged to the cylinder Ill by a hinge IS. The housing l5 on the extruding head l4 has a centrally located bore extending therethrough, which serves to position a cylindrical core tube holder 20. The core tube holder is suitably threaded on its outer (left) end 2| to receive an adjusting nut 22, which serves to position the core tube holder 20 longitudinally within the bore formed in the housing IS. The adjusting nut 22 is adapted to be locked in position by a locking nut 23 having an inwardly extending annular shoulder 24 formed thereon, which shoulder is adapted to engage an outwardly extending annular shoulder 25 on the adjusting nut 22. The locking nut 23 is suitably threaded so that it threadedly engages cooperating threads formed on the housing l5, whereby tightening of the locking nut 23 causes the adjusting nut 22 to be firmly seated against the housing 15 and thereby prevent axial movement of the core tube holder 20. A key 30 which is formed integral with the core tube holder 20 rides in a longitudinal keyway 3| formed in the housing l5, and consequently, rotation of the adjusting nut 22, when the locking nut 23 is released, causes the core tube holder 20 to be moved longitudinally with respect to the housing IS without relative rotation between the core tube holder 20 and the housing IS.

The core tube holder 20 is interiorly threaded at its inner (right) end with threads 32 which threadedly engage a core tube 33 having a bore 34 in axial alignment with a bore 35 formed in the core tube holder 20. A die 40 having" a cylindrical bore All is suitably secured in axial relation with the

bores

34 and 35 to provide an annular orifice through which extrudable plastic material may flow around a core passing through the

bores

34, 35 and ll. The die 40 is adapted to be secured to the housing l by means of cooperating annular shoulders formed on the die 40 and on a die holder 56. The die holder 50 is in turn locked in position by means of a locking nut 5| which is threadedly engaged with the housing 15. The die 46 is adapted to be laterally positioned with respect to the core tube by means of a plurality of set screws 52 which are threaded into the housing l5, so that their inner ends bear against the die holder 50.

The annular orifice which is formed by the cooperation of the core tube 33 and the die 40 is in communication with and is adapted to receive plastic extrudable material from a cavity 69 formed Within the housing I5. The cavity 60 in turn receives properly worked extrudable plastic material from the feed screw Hi. In order to insure that the plastic material being worked by the feed screw 13 is at all times maintained under a sufficient pressure to insure proper'plasticity, a breaker plate 6| is suitably secured between the feed screw 13 and the cavity 60. The breaker plate 6! consists of an annular imperforate dished portion 62, which surrounds a circular area provided with a plurality of apertures 63 which serve to permit passage of the plastic material from the feed screw 3 to the cavity 69. The diameter of the circular area which is provided with the apertures 63 is substantially one-half the diameter of the bore l2 and furthermore, the total cross-sectional area of the apertures 53 is on the order of one-fiftieth of the total cross-sectional area of the bore. The proportions just stated have proven highly satisfactory in extruding some polyethylene compounds, but with other compounds which have different consistencies, the area of the apertures may be increased to as much as one twenty-fifth of the total cross-sectional area of the bore. A compound which may be eificiently extruded by use of the last named proportions is polyvinyl chloride. It will be observed that the restriction of flow of plastic material caused by the greatly reduced size of the apertures 53 produces a considerable back pressure within the bore 12. Furthermore, it is to be noted that the dished imperforate area 62 surroundingjhe apertures 63 not only provides for further back pressure around the feed screw 13, but also, due to its dished configuration, the portion 62 serves to direct the material toward the apertures 63. Smooth fiow is thereby provided, and no dead spots are present in which plastic material may become stagnant or clogged.

Although such is not absolutely necessary, it is usually desirable to provide one or more screens 64 over the apertures 63 for the purpose of more completely straining the plastic material prior to its extrusion. A recess 65 is, therefore, provided within the breaker plate 6! for the purpose of accommodating the screen 64. It is to be observed, however, that such screens 64 used in conjunction with a breaker plate such as that disclosed and described herein have no appreciable effect on the back pressure within the bore 12.

The apparatus disclosed and described herein has been confined to extruding mechanism wherein a cover is continuously extruded on a moving core. It is to be understood that the invention is not limited to the specific apparatus shown herein. The breaker plate construction of this invention may be employed in any type of continuous extrusion apparatus wherein a back pressure Within a feeding cylinder is necessary or desirable.

It is to be understood that the above-described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

1'. Apparatus of the character described for providing back pressure Within a plastic material feeding and working chamber comprising a breaker plate, an annular imperforate surface on the plate gradually sloping toward its center, and a flat central area on said plate containing a plurality of relatively small apertures, the total cross-sectional area of the apertures being less than about one twenty-fifth of the cross-sectional area of the plate.

2. In a continuous extrusion apparatus including an extrusion cylinder having an extrusion bore therein, an extrusion head and means for forcing plastic material through the extrusion bore to the extrusion head, a working and straining device positioned between the extrusion cylinder and the extrusion head comprising a plate having a perforated area in the center thereof, the diameter of which is substantially one-half the diameter of said bore, and an annular dished imperforate surface surrounding said perforated area, said dished imperforate surface terminating at its juncture with the inner periphery of the extrusion bore, the total cross-sectional area of the perforations being not greater than about one twenty-fifth of the cross-sectional area of the bore.

3. In a continuous extrusion apparatus including an extrusion cylinder having an extrusion bore therein, an extrusion head and means for forcing plastic material through the extrusion bore to the extrusion head, a working and straining device positioned between the extrusion cylinder and the extrusion head comprising a plate having a perforated area in the center thereof, the diameter of which is substantially one-half the diameter of said bore, the total cross-sectional area of the perforations in said perforated area being in the order of one-fiftieth of the total cross-sectional area of said bore, and an annular dished imperforate surface surrounding said perforated area, said dished imperforate surface terminating at its juncture with the inner periphery of said bore.

4. In a continuous extrusion apparatus including an extrusion cylinder having an extrusion bore therein, an extrusion head and means for forcing plastic material through the extrusion bore to the extrusion head, a working and straining'device positioned between the extrusion cylinder and the extrusion head comprising a plate having a perforated area in the center thereof, the diameter of which is substantially one-half the diameter of said bore, the total cross-sectional area of the perforations in said perforated area being between one-twenty-fifth and one-fiftieth the total cross-sectional area of said bore, and an annular dished imperforate surfac surround-1 ing said perforated area, said dished imperforate surface terminating at its juncture with the inner periphery of said bore.

5. A continuous extrusion apparatus for extruding polyethylene, which comprises an extrusion cylinder having an extrusion bore of predetermined cross-sectional area therein, an extrusion head secured to the extrusion cylinder, means for forcing polyethylene material from the extrusion bore into the extrusion head, and a breaker plate having a perforated area in the central portion thereof and a dished imperforate surface surrounding the perforated area extending from the periphery of the bore to the perforated area, the total cross-sectional area of the perforations in the perforated area being in the order of one-fiftieth of the total cross-sectional area of the bore.

6. A continuous extrusion apparatus for extruding polyvinyl chloride plastic material, which comprises an extrusion cylinder having an extrusion bore therein of a predetermined cross- -sectional area, an extrusion head, means for forcof the bore, said breaker plate being provided with sloping surfaces on the forward face thereof from the periphery thereof to the perforated area.

GRANT S. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,022,895 Morrell Dec. 3, 1935 2,090,404 Parkhurst Aug. 17, 1937 2,135,325 Burt et al Nov. 1, 1938 2,262,989 Conklin et a1. Nov. 18, 1941 2,331,139 Safiord Oct. 5, 1943