US2367394A - Extrusion machine - Google Patents

Description

F.- T. GRIFFITHS EXTRUSION MACHI NE Jan. 16,1945.

7 Sheets-Sheet 1 Filed June 30, 1943 r. w w

I G T.

Inventor Hi8 A ltorneyS Jan; 1945- F. T. GRIFFITHS 9 r v EXTRUSION MACHINE Filed June 30, 1943 7 Sheets-Sheet 2 Frann Z GriffiT/z:

Inventor H is Attorneys Jan. 16,1945;

' F. T. GRIFFITHS 2,367,394

EXTRUSION MACHINE Fi led June so, 1943 '7 Sheets-Sheet 3 Francis ZGriffifhs l I Inventor 8 Attorney;

1945- F. T. GRIFFITHS 2,367,394

' EXTRUSION MACHINE Filed June so, 1943 7 sheets-sheet 4 Inventor B MMLM H is Attorneys Jan. 16, 1945- F. 'r. GRIFFITHS Exmws'lon- MACHINE 7 Sheets-Sheet 5 Filed June. 30 1943 E Wwt a,

H 8 Attorney Jan. 16, 1945. GRIFFlTHs 7 2,367,394

EX'I'RUSION MACHINE Filed June 30, 1943 '7 Sheets-Sheet 6 Francis 7. CriF-fif/M Inventor Hi5 Attorneys Jan. 16, 1945.

F. 1'.' GRIFFITHS EXTRUSION MACHINE Filed Jime so, 1943 7 Sheets-Sheet 'r Wm No GMT/i772;

Inventor Hi8 A ttofney;

Patented Jan. 16, 1945 EXTRUSION MAC Francis 'lladman Grifliths, Gravesend, Kent, England, assignor to W. T.

Henleys Telegraph Works Company Limited, Dorking, Surrey, England, a British company Application June 30, 1943, Serial No. 492.8 50,

in Great Britain July 31, 1942 (Chm-12) 11 Claims.

tending projections and/orrecesses, that relative rotary movement of the two members causes material fed into one end of the annular space between them to be fed forward. Continuous relative rotary movement of the two concentric members, combined with continuous feeding of the material to the impelling device, results in the continuous delivery of the material in the plastic state to the extrusionchamber and in extrusion of it through the die or between the inner and outer die, as the case may be, by the pressure exerted on it by the following material. It is the practice to arrange the die or, where there is an inner die or point, the two dies, co-axlally with the impelling device with the object of pelling devices may ensuring a perfectly uniform pressure at the" mouth of the die throughout the circumference thereof.

In machines of thistype at least one of the members constituting the impelling device must rotate relative to the main supporting structure. Since a considerable pressure (of the order of ten to twelve tons per square inch where the ma= terial to be extruded is a metal, such as lead) must be produced in the material in-the extrusion chamber in order to extrude it. it follows that there will be exerted a correspondingly great reaction on the member (or members) that carries the screw thread projections and/or recesses.

which reaction will have a considerab e component in a direction parallel to the axis of the imp'elling device.

of a thrust bearing which generally requires to be of large dimensions and of special construction. It is an object of the present invention to provide an improved form of construction of extrusion machine which avoids the necessity for such thrust bearings but does not entail the sacrifice to any substantial degree of the qualities as regards uniform extrusion pressure possessed by the existing type of machine in which the extrusion orifice is co-axial with the impelling device.

When this member is a rotary member, the thrust must be taken up by means In the improved form of construction, the material to be extruded is delivered to the extrusion chamber by a number of screw thread impelling devices. These are arranged in pairs, the two de-.

vices of each pair being disposed in axial alignment with each other and with their delivery ends together. The rotating parts of the two devices are integral with one another or coupled together at the delivery ends, whereby the thrust on the rotating part of one impelling device of a pair opposes thethrust on the corresponding part of the other device of the pair, so that, under normal working conditions, the resultant thrust is negligible, and the two or more pairs of devices are distributed round the axis of the extrusion chamber, whereby the material is fed into the chamber from a number of points distributed around the wall of the chamber, so that a substantially uniform feed of material can be obtained throughout the circumference of the extrusion orifice.

The pairs of impelling devices may be distributed around the extrusion chamber axis with their respective axes parallel thereto. Alternatively, the respective axes of the several imbe disposed transversely of the extrusion chamber axis, preferably at right angles thereto. Where the machine has only two pairs of impelling devices, the axes of the two pairs may lie parallel to one another in a plane at right angles to the axis of the extrusion chamber. Where three pairs of impelling devices are used, their axes may lie at an angle of to one another and in three separate planes at right angles to the axis of the chamber. Where four pairs are present two pairs may have their axes parallel to each other two may have their axes parallel to one another in another plane, for instance, a plane parallel to the first plane; the axes of the first two pairs for instance, lying at an angle, for instance an angle oi 45", to those of the other two pairs. In cases where it is necessary to locate the pairs of extrusion devices in diflerent planes the delivery characteristics of the several pairs may b moditied to compensate for the varying distance from the extrusion orifice.

In. the case of a machine having two pairs of impelling devices disposed on diametrically opposite sides ofthe extrusion chamber with their axes parallel with one another and at right angles to 'that of the extrusion chamber, it is sometimes preferable for the impelling devices and extrusion chamber to be housed in, 'or in part formed by, a machine body or casing built up of a pair of end 56 blocks, a pair of cylinders and a' central 'block.

in one plane and the other ures 1 and 2,

Such cylinders each house, or preferably form, the outer parts of one of the two pairs of impelling devices, and their ends form spigot and socket joints with the end blocks in which feed ports are provided which register with feed openings in the spigot ends of the cylinders The central block fits between the central parts of the two cylinders and forms or houses the extrusion chamber which is fed from the delivery ends of the impelling devices by ports in its walls which register with delivery openings in the walls of the cylinders. The assembly is maintained by tie bolts which draw the two end blocks together.

We also prefer, in some cases, to employ a removable extrusion chamber which is externally of cylindrical or substantially cylindrical form, for instance, tapered, and is'arranged to slide axially into a position in a correspondingly shaped recess o-r'bore in the central part of the machine housing, in which openings in the circumferential wall of the chamber register with ports in the machine housing leading from the delivery ends of the four or more impelling devices. This removable -extrusion chamber comprises a pair of sleeves which telescope one within the other to a limited extent and of which one supports a matrix holder (or a number of such holders) and the other of which has a transverse wall carrying a point holder (or a number oi. such holders) for supporting an inner die or point which may or may not be of tubular form. Preferably, the two sleeves are held together and the complete extrusion chamber secured in place in the recess or bore in the machine casing by the same clamping means. The chamber may incorporate, between the openings in the circumferent al wall thereof and the matrix, a screen the bearing 9 formed by the end of the other comprising a support grid carrying a layer of wire gauze or other suitable screening material. This grid is clamped between a'projecting surface on the outer sleeve and the inner end of the inner sleeve when the. two parts are locked in position in a recess'in the machine housing. This grid may serve as an additional support for the point holder or as the main support.

The invention, which is applicable not only to metal extrusion machines but also to machines trusion machine comprising two parallel pairs of impelling jdevices, disposed on diametrically opposite sides'of an extrusion chamber and at right angles to the axis thereof. the section being taken in a plane containing the axes of the said impelling devices,

- Figure 218 a section. taken on the line II- -II of Fi ure 1 of the machine shown therein,

Figure 3 is a sectional elevation of a second form of construction of lead extrusion machine.

7 Figure 4 is to the left of the centre line a rear elevation and totheright of the line a front. elevation of a plastics extrusion machine comprising two pairs or impelling devices arranged gain the lead extrusion machine-shown in Fig- Figu're 51s a sectional-elevation of the machine shown in Figure. 4,

Fi ur 6 is a section taken'on the unevr-vr of Figure .5,

Figure 7 is a section, on an'enlarged scale, taken onthe line VII-VII of Figure 5, and

Figure 8 is a fragmental section, on a still larger scale, on the line VIII-VIII of figure 5 showing the machine fitted with a multiple die extrusion chamber in place of the single die chamber shown in Figures 4, 5 and 7.

The machine shown, somewhat diagrammatically, in Figures 1 and 2 of the drawings is intended for the'production of tubing of lead or lead alloy or for the sheathing of electric cable with such metal. It comprises a machine casing l in the form of a pair of barrels integral with a central part having an aperture which extends from the front to the rear face thereof and at right angles to the two barrels. The central part of this aperture is of increased diameter to form an extrusion chamber 2. An outer extrusion die or matrix 3 is fitted in one of the portions adjacent the enlarged portion 2 of the aperture and is held in .place by a tubular nut 4 screwing into the wall of the aperture. The other or rear end of the aperture receives a tubular nut 5 constituting a holder for an inner die or pointfl which passes centrally through the extrusion chamber 2. The barrels 1 are parallel to one another symmetrical about a vertical plane containing the axis of the extrusion chamber, and are located oneabove and one below the central aperture and directly above and below the extrusion chamber 2, but they may, alternatively, lie to the rear of that chamber. Each barrel 1 is counterbored at each end to receive a bush 8, the outer end of which forms a bearing 9. Each hushed barrel houses-a shaft in extending from the bearing 9 formed by one bush to and beyond .bush. The overhanging end of each shaft l0 carries a gear wheel H by which a drive may be imparted to it. Additional hearings to support this end of each shaft may be provided. Portions of each shaft that lie one on each side of a central portion of the barrel I are provided with a screw thread II, the thread on one portion being of opposite hand to that on the other portion. -T'hese threads, which may be single-start or multi-start threads, (the former being shown) co-operate with the adjacent surfaces of the tubular barrel linings 8 to form-screwthread impelling devices. The threads are-preferably of the buttress form shown in Figure 1 and lie at an angle of about 85 to the axis of the shaft, and the surfaces co-operating with them have projections or recesses, for instance, a screw thread l3 of opposite hand'to that on the adjacent part of the shaft, or are rifled or grooved longitudinally. Alternatively, the barrel linings 8 may be screw threaded and the co-operating surface of the shaft be splined.

At the outer end of each bush 8 an annular feed chamber I4 is formed by increasing the clearance between the shaft in and the bush, and provision is made for feeding the chamberwith molten metal. The feed chamber I4 is heated by means of electric'heaters in the wall of the barrel,

located as shown diagrammatically at ii, to maintain the metal in the chamber in the mblten condition. In the central region of each impelling device circumferential channels i8 are provided in and around the wall ,of thebarrel through whicha cooling medium, for instance.

air, steam or water, may be jcirculated'to cool machine, it is not so convenient.

. 2,867,894 end of the device. Between the-feed chamber ing and the adjacent end of each internally screw threaded bush,'the wall of the barrel is smooth and the clearance between it and the screw threaded shaft forms an annular,delivery chamber I9. Each of these four annular delivery chambers I9 is placed in communication with the extrusion chamber 2 by a separate port 20, the ports from the four chambers entering the IB of each shaft separating details from the lead extrusion machine described above with reference to incorporates certain novel features of construction' which are not present in the lead machine shown in Figures 1 and 2 but may, nevertheless, in some cases, be incorporated in such a machine.

- Referring now more particularly to Figures 4, 5

and 6, it will be seen that the casing'is built up of a pair of end blocks 3!, a pair of cylinders 32 and a central block 33. The ends of the cylinders enter recesses 34 in the end blocks and are held therein by four tie bolts 35 which draw the two end blocks together. The central block common extrusion chamber at points more or less uniformly distributed around the circumferential wall thereof. -At each end of the central bearing surface on each shaft it is preferred to provide a screw'thread gland 2| for building up a counterpressure; in any metal entering the bearing, which will prevent transfer of plastic metal across the bearing. Alternatively, this central hearing may be omitted and the shaft be locally reduced in diameter to provide one delivery chamber for each pair of axially aligned impelling devices which can be placed in communication with the transversely extending extrusion chamber by a single port. With such an arrangement; plastic metal would be fed into the extrusion chamber at diametrically opposite sides thereof.

. It will generally be necessaryv to apply heat in the region of the delivery ends of the impelling 83 is of general rectangular form and is located between parallel surfaces 36 on the central portion of the cylinders 32. These surfaces are flat except for recesses 31 in which enter correspondingly shaped projections 38 in the co-operating surfaces of the block and serve Positively to restrain the central bloc]; from moving relatively to the cylinders. Alternatively, of course, the projections may be on the cylinders and the recesses in the wall of the block. In addition, the

. central block 3| may be held between the two devices and that of the extrusion chamber. This may be effected'very conveniently by inserting tubular electric heaters 22 in the necessarily massive walls of the barrels I and those of the extrusion chamber 2. I

The lead extrusion machine shown diagrammatically in Figure 3 of the drawings resembles that described with reference to and shown in Figures 1 and ,2, save as regards the disposition of the extrusion chamber. Consequently, the same reference numerals have been used to in-. dicate corre ponding parts in the two machines; In the machine shown in Figure 3, the axes of the two pairs of impelling devices are parallel with, and lie one on each side of, that of the extrusion chamber. The machine body in this case, however, is in the form of a triple barrelled block. As regards the elimination of heavy thrust bearings and symmetry of feed into the extrusion chamber, the machine is the equivalent of that shown in Figures 1 and 2, but, as regards control of the temperature of the various parts of the The machine shown in Figures 4 to '7 of the drawings is of the same general form as that shown in Figures 1 and 2, that is to say, it has two pairs of screw thread impelling devices, each of atype in which the inner of the two longitudinally extending concentric members is rotatably driven, the two devices of each pair being in axial alignment and having their respec tive rotating parts integral with one another atthe delivery ends, the two pairs'being disposed on diametrically opposite sides of the extrusion chamber with their axes parallel with one another and at right angles to that of the extrusion chamber. However, it has been developed for the extrusion of syntheticplastics such as, for instance, polyvinyl chloride compositions, and differs in cylinders by transverse tie bolts extending from cylinder to cylinder. These may or may not pass through the centre block. Alternatively, the flat surfaces 36 on the cylinder may be slightly inclined to one another and the central blockbe given in a correspondingly slight tapered form so that it may be wedged in position to ensure a tight joint between the co-operating surfaces. These precautions to. obtain a tight joint between the co-operating surfaces of the block and cylinders are not necessary where the machine is to be used on rubber or plastics but may be advisable in the case of lead machines in whichthe extrusion pressures required are very much higher.

The cylinders 32 of of the barrels I and their linings 8 of the lead machine described above and form the outer concentric members of the impelling devices. -Where the material to be extruded is rubberor a synthetic plastic, the bore of the cylinders may be smooth as shown and of the same diameter throughout the length thereof, but naturally, if this built up machine casing construction is adopted for a lead extrusion machine, the bore will have, except possibly at its centre, a broken surface of a kind described above with reference to Figures 1 to 3 of the drawings. The inner concentric member of each pair of axially aligned impelling devices is, as in the case of the lead machine previously described, constituted by a shaft, 40, of which the portions lying within the cylinder and to each side of a central portion 4| serving as a central bearing carry each a screw thread 42, the thread on one portion being of opposite hand to that on the other. As

the machine shown in Figures 4 to 7' is for plastics, the angle of the thread is advantageously about 75 to Each end of each shaft 4il'projects through a bushed opening 43 in the bottom wall of the recess 34 receiving, the spigot end of its cylinder 32 and is rotatably supported by a ball bearing 44 housed in a bracket 45 extending from the end block 3!. This is preferable to housing thebearing in the block itself as it reduces the flow of heat to the bearing.

In each end block M are provided a, pair .of feed ports 46, one for each impelling device, which register with feed openings 41 in the spigot ends of the cylinders 32. Delivery openings 48 are provided in the walls of the cylinders Figures 1 and 2. It also 1 this machine take the place :2 which register with delivery ports 49 a the wall of the central block 85 and serveto place the four annular delivery chambers 58 in communication with a removable extrusion chamber 5| housed in the central block. This extrusion chamber, as will be seen most clearly from Figure 7 of the drawings, is built up of a pair of sleeves 52, 53 which telescope one within the other to a limited extent. The sleeves are of cir cular cross-section and the outer, 52, is a push-in fit in a cylindrical bore 54 of corresponding crosssectional shape which extends through the central block 33 in a direction at right angles to the axes of the cylinders 32 and their impeller shafts 40. At one end the outer sleeve 52 has an outwardly turned flange 55 which bears against the front face'55 of the block 33. At its other end it has an inwardly extending flange which is integral with a tubular part 51, concentric with,

but of considerably smaller diameter than, the sleeve, and extending axially towards the flanged end to form a support for an inner die or point 58 which is a sliding fit in the end of the holder 51. At its end carrying the flange 55 the outer sleeve is counter-bored to a larger diameter and to a depth extending just to the rear of the front end of the point holder 51 to provide an annular seating 59. The inner sleeve 53 is a sliding fit in the counter-bored part of the outer sleeve 52, projects outwards beyond the flanged end of the outer sleeveand also carries an external flange 50 which overlies the flange 55. The wall thickness of the sleeve 53 first increases rapidly as the outer end of the sleeve is approached, to provide a conical surface 5|, and then gradually diminishes to provide a conversely tapering surface 52 which forms a seating for an outer die or matrix 53 which is held in place by an annular cap 54 screwed on the ring shaped projection 55 formed by cutting an annular groove in the front end face of the sleeve. The inner end face of this matrix forms a continuation of the conical surface 5| of the inner sleeve. Four openings 55 are provided in the wall of the outer sleeve.

These are located between the inwardly extend- I engaging the front face 55 thereof. Between the inner end of the inner sleeve and the annular seating 59 i the outer sleeve is located a screen consisting of .a foraminous disc 51 with an external diameter equal to that of the inner sleeve, and of a gauze disc 58 of slightly less diameter housed in a recess in the disc. Both disc and gauze have central apertures in which the front end of the point holder, which in this region is cylindrical, is a sliding fit. The inner sleeve 53 is pressed inwardly to clamp the screen between it and the seating 59 and to hold the outer sleeve 52 in theblock, by means of a number of hand clamps 59 mounted on studs projecting from bosses on the front face 55 of the block, one

1 in each corner thereof. These have cam faced jaws which normally engage the front face of the flange 50 on the inner sleeve, but can readily be swung clear to permit removal of the inner sleeve and the screen, or, if required, of the entire extruslon chamber. To provide for longitudinal adjustment of the point 58 it is screw threaded internally and receives a tube which extends rearwardly beyond the rear end wall of the outer sleeve 52 and is restrained from moving axially .of the point holder by means of its collar 1i and the retaining ring 12. By rotating the sleeve and preventing the point from rotating relative to its holder by means of a feather key or the like, the latter may be moved longitudinally whilst the machine is working, thereby permitting the wall thickness of the extruded product to be corrected without delay. V

In a modified form of construction of removable extrusion chamber, the matrix holder is adjustably positioned in one end of the outer sleeve and the point holder is integral with the inner sleeve. In this form the overlapping parts of the sleeves lie on the opposite side of the screen to the matrix -holder and, consequently, the apertures which register with the delivery ports in the wall of the block housing the sleeves are in this double walled portion of the extrusion chamber. Also the external flanges on the outer and inner sleeves lie at the rear, so that the chamber is inserted from the opposite direction to that in which the chamber shown in Figure 7 is inserted.

The provision of a central bearing M for the two impeller shafts 40 which separates the neighbouring delivery chambers 5!] permits of the production of a partiscoloured rubber or plastic product by charging each impelling device with stock of an appropriate colour. To this end the annular extrusion chamber may be divided into four compartments by radially extending partition walls which maintain the stock delivered by each port 49 separate from that delivered by the others. These partitions may be permanent or removable. Partitions of the latter form are shown in the upper half of Figure '7, but are omitted from the lower half for the sake of clearness. They comprise a pair of flat plates. One plate, 13, of each pair is located to the rear of the screen and midway between two neighbouring ports by engaging in grooves in the wall of the outer sleeve 52 and in the surface of the point holder 51. The other plate, 14, is located between the screen and the matrix and is located in alignment with the plate 13 by engaging in grooves in the conical surface of the inner sleeve'53 and in the surfaces of the point 58 and point holder 51, thus also serving to restrain the point from rotating relative to its holder. The plastic material delivered to the extrusion chamber thus progresses therethrough in four separate streams of arcuate section separated only by the thickness of the partition walls (which can be small, since there is no appreciable pressure difference across them) until just before they reach the extrusion orifice, between which point and the oriflce they unite without appreciable interpenetration.

The single oriflce extrusion chamber shown in Figures 4, 5 and '1 of the drawings may be modifled, as shown in Fig. 8, to provide for two or more extrusion orifices. The form of the inner telescoping sleeve is similar to that shown in Figure '1 save that it is fitted with a removable front wall which provides for the mounting of a pair of dies 53. The method of mounting them, however, is precisely the same. The internal form of the outer sleeve 52 is rather difierent in that massive point holders which extend from the rear end wall are dispensed with and the foraminous disc 51 is provided with a pairof tubular projections 15 which serve the same purpose. This has the advantage of reducing to a minimum the obstruction presented to the stock as it issues from the openings 55 in the circumferential wall of the chamber. To ensure correct alignment of point and die, a projection is provided on the end of which engages in a recess in the and a key 18 on the flange 55 of the outer sleeve to engage in a slot in the flange 60 of the inner sleeve. Naturally, the interior of this modified form of removable extrusion chamber may be furnished with removable division plates to confine the stock from each impelling device to a particular extrusion orifice or, where more than two sets of dies are present, to a particular orifice or group of orifices. One pair of such plates is shown at 16 and II in Figure '8. It will beappreciated that the provision, of more than one die will entail some sacrifice as regards uniformity of extrusion pressure, particularly when division plates are present.

Withdrawal of the removable extrusion chamthe inner sleeve rim of the grid 67 tion of the need for heavy her is facilitated by an extractor comprising a four legged table 80 with a screw threaded aperture in which works a screw threaded rod 8| carrying a rotatable cup 82 of which the rim is rear face of the outer sleeve 'chamber- The feet 83 of the adapted to fit the 52 of the extrusion extractor seat on sleeves 84 on'the tie bolts 35 and are held there by a handle 85 secured to the bush and having areduced portion 86 which enters a circumferentially extending slot 81 in the foot, as is most clearly shown in Figure 8. By screwing down the rod by rotating the hand wheel 88, the inner and outer sleeves are pushed out of the bore in the central block and the four streams of plastic material in the delivery ports 49 and 66 are sheared through.

For the satisfactory extrusion of a plastic such as a polyvinyl chloride composition, it is generally necessary to apply heat to the delivery end of the impelling device and in the region of the extrusion chamber. In the machine shown in Figures anced pairs of impelling devices, .possesses a number of advantages in addition to the elminathrust bearings without sacrifice of uniform extrusion pressure. The rotating member of each impelling device can,

if required; be supported at its delivery end with-- out introducing -a bearing of which the ends are subject to large pressure difierences. This is particularly important in the case of lead extrusion machines where the pressure at the delivery end is 10 to 12 tons per square inch. In the case of a lead extrusion machine, the improved form of construction eliminates trouble arising from oil lubrication of moving parts subject to high temperature, for, as all gearing is extraneous to the machine, the only moving parts subject to high temperature are the three bearings for each rotating member, and each of these is effectively lead lubricated. The inner part of each impellingdevice can be cooled internally; if necessary, as no provision has to be made for the passage through it of a cable or other core to which a covering of the extruded material is 4 to 8 of the drawings, the parts of each'cylinder between the end blocks 3| and the central block 33 are externally of-octagonal cross-section to provide flat surfaces 90 on which electric resist- I anoe heating elements 9| are clamped, and tubular electric heaters 92 are inserted in the wall of the central block in which'the removable extrusion chamber is housed. Naturally these heated parts of the machine casing are encased in heat insulating material. to reduce loss by radi ation. Provision is made to measure the ternperature of the stock at the feed ports 46 by thermostats 94 and at the extrusion chamber by a thermostat 95. For the extrusion of natural rubber mixes by a machine ofv the form shown in Figures 4 to 8, the heating arrangements there shown would be replaced by suitable cooling arrangements, for instance, a water jacket or channels for the circulation of a cooling liquid, generally water.

It will be noticedthat, at one end, each shaft 40 is supported in the bearing 4| through an intermediary consisting of the socketed end of a driving shaft 96. This shaft 96 is supported at its other end by a second bearing 81 mounted on a pedestal 98 and carries a driving wheel 99 on its overhanging end. The end of the shaft 40 fits into the socket of the shaft 96 with a morse taper fit and is held in driving engagement by means of the screwed bolt I00 whichalso provides a means of disengaging the two shafts. When disengaged, the impeller shaft 40 may be withdrawn from the opposite end of the machine casing without having to dismantle the gear drive thereto. s

From the preceding description, it will be appreciated that the improved construction of extrusion machine, comprising two or more balto be applied. Where an inner die or point is used, this can be mounted more rigidly as its support is isolated from all moving parts and is not required to be lengthened for the purpose of providing an impelling surface, or a surface cooperating with an impelling surface, as in many existing types of machines, The use of a short support for the point permitsof bridge pieces extending from the support to the wall of the extrusion chamber to be dispensed with and has the additional advantage that the length of cable in the machine at any time is a minimum. This latter is of importance in the lead sheathing of impregnated paper insulated cables, for there is then no danger of the cable being damaged by over heating. In the usual forms of construction of extrusion machine for the production of lead tube or cable sheathing, Provision has to be made for adjustment of the outer die or matrix with respect to the inner die in order to secure control of the wall thickness of the product. With the improved machine constructed in accordance with the present invention, the wall thickness may be controlled by adjusting the flow of lead from the several impelling devices into the extruson chamber,- rendering unnecessary the provision of die adjusting means.

What I claim as my invention is:

1. A,machine-for the extrusion of material in a highly viscous or plastic state, comprising to feed in material through a number of openings distributed around the wall thereof.

2. A machine for the extrusion of material in a highly viscous or plastic state, comprising an extrusion chamber with an extrusion oxifice and two pairs of screw thread impelling devices for delivering material to the chamber, each device comprising two longitudinally extending and relatively rotatable concentric parts, the two dev'ces of each pair being in axial alignment with their delivery ends together and having their respective rotating parts united at their deliiery ends, and the two .pairs of devices being disposed on opposite sides of the extrusion cham-, her with their axes parallel to one another and at right angles to that of the extrusion chamber,

relatively rotatable concentric parts, the two devices of each pair being in axial alignment with their delivery ends together and having their respective rotating parts united atthe delivery ends, and the two pairs of devices being disposed on opposite sides of the extrusion chamber with their axes parallel with that of the extrusion chamber, whereby to feed in material-through a number of openings distributed around the wall thereof.

4; A machine for the extrusion of material in a highly viscous or plastic state, comprising a pair of end blocks, a pair of cylinders disposed in spaced parallel relationship and extending between said end blocks and making spigot joints therewith, a central block fitting between the central parts of said cylinders and making joint therewith, an extrusion chamber in said central block having an extrusion orifice in an end wall thereof, a pair of axially aligned screw thread impelling devices in each of said cylinders, the feed ends of said devices being at the ends of said cylinders and the delivery ends at the middle thereof, the end blocks having feed openings which register with lateral feed openings in the spigot ends of said cylinders, and the central block having ports which register with delivery openings in the walls of said cylinders and place said extrusion chamber in commumcation withthe delivery ends of said impelling devices.

r 5. A machine for the extrusion of material in a highly viscous or plastic state comprising an extrusion chamber with an extrusion orifice, at least two pairs of screw thread impelling devices distributed round the said chamber, each device having its own separate delivery chamber and comprising two longitudinally extending and relatively rotatable concentric parts, the

wall of the surrounding barrel, located one of each side of the central bearing, a separate por between each delivery chamber andthe said extrusion chamber, the said ports from the deliver: chambers entering the extrusion chamber a1 points distributed around the circumferential wall thereof, and means for driving each of sale impeller shafts 'in rotation within its barrel ir. a direction to impel plastic material in the barrel into each delivery chamber and thence through said ports into the said extrusion chamber.

7; An extrusion machine comprising a machine body including a central portion and a pair of barrels disposed symmetrically on opposite sides two devices of each pair being in axial alignment with their delivery ends together and having their respective rotating parts "united at their delivery ends, and a separate port from each delivery chamber to the extrusion chamber, the ports from all the delivery chambers entering the common extrusion chamber at points distributed round the circumferential wall thereof.

6. An extrusion machine comprising a machine body including a central portion and a pair of barrels disposed symmetrically on opposite sides of said central portion with their axes parallel to one another, an extrusion chamber in said central portion, a pair of impeller shafts, one in of said central portion with their axes parallel to one another, an extrusion chamber in said central portion, a pair of impeller shafts, one in each barrel, a pair of screw threads on each of said shafts, the screw threads of each pair being of opposite hands and disposed one on each side of a central portion of the surrounding barrel, which portion forms a central bearing for the shaft therein, surfaces on the internal wall of each barrel which co-operate with the screw threads on the shaft therein to form a pair of screw thread impelling devices, annular delivery chambers between each of said shafts and the wall of the surrounding barrel, located one on each side of the central bearing, a plurality of separate ports, one between each delivery chamber and the said extrusion chamber, the said ports enter ing the said extrusion chamber at points distributed around the circumferential wall thereof, means for driving each of said impeller shafts in a direction to impel plastic material in the barrels into the delivery chambers and thence through said ports into said extrusion chamber, and at each end of the centrallysupported portion of each impeller shaft a screw thread of opposite hand to thatof the adjacent impelling thread on that shaft and of relatively short pitch, for building up a counterpressure in material entering the bearing from the delivery chamber adjacent to it.

8. In an extrusion machine comprisin a machine body housing a number of pairs of screw I thread devices for impelling material in a highly each barrel, a pair of screw threads on each of said shafts, the screw threads of each pair being of opposite hands and disposed one on each side "of a central. portion of the surrounding barrel,

- which portion forms a central-bearing for the shaft therein, surfaces on the internal wall of each'barrel which co-operate. with the screw threads on the shaft therein to form a pair of screw thread impelling devices, annular delivery chambers between each of said shafts and the viscous or plastic state, each device comprising two longitudinally extending and relatively rotatable concentric parts and the two devices of each pair being in axial alignment with their delivery ends together and having their respective rotating parts integral with one another or coupled together at the delivery ends, an extru sion chamber comprising a pair of sleeves which telescope one within the other to a limited extent, an end wall on one of said sleeves for supporting a matrix, an end wall on the other of said sleeves supporting a holder for an inner die, the outer of said sleeves being of substantially cylindrical form and a sliding fit in a correspondingly shaped hole in a central part of said machine body and the circumferential wall of said chamber having a plurality of openings which register with ports in the machine body leading from the delivery ends of the said screw thread impelling devices.-

tatable concentric parts. and the two devices of each pair being in axial alignment with their delivery ends together .and having their respective rotating parts united at the .delivery ends thereof, an extrusion chamber having openings in its circumferential wall, removably positioned in the central part of said machine body with said openings registering with ports in the machine body leading from the delivery ends of the said screw thread impelling devices, said chamber comprising a pair of sleeves which telescope one within the other to a limited extent, one of said sleeves having an end wall for supporting a matrix and the other of said sleeves having an viscous or plastic state, each device comprising two longitudinally extending and relatively rocircumferential extrusion chamber into at least two segmental parts, said dividing means comprising a corresponding number of partition walls which are preferably removable and which each extend between the inner die and its holder and the wall or the chamber, the said being so located with respect to partition walls the circumferential wall of the the opfinings in chamber that each delivery port feeds only one segmental part of the partitioned chamber.

11. in an extrusion machine comprising a machine body housing a number or pairs oi screw thread devices i'or impelling material in a highly viscous or plastic state, each device comprising two longitudinally extending and relatively rotatable concentric parts and the two devices of each pair being in axial alignment with their delivery ends together and having their respective rotating parts unitedat the delivery ends tatable concentric parts and the two devices of each pair being in axial alignment with their delivery ends together and having their respective rotating parts united at the delivery ends thereof, an extrusion chamber having openings in its circumferential wall, removably positioned in the central part of said machine'body with said openings registering with ports in the machine body leading trom the delivery ends of the said screw thread impelling devices, said chamber comprising a pair of sleeves which telescope one within the other to a limited extent, one or said sleeves having an end wall supporting a matrix and the other an end wall supporting a holder thereof, an extrusion chamber having openings in its'circumferential wall, removably positioned in the central part of said machine body with said openings registering with ports in the machine body leading from the delivery ends or the said screw thread impelling devices, said chamber comprising a pairoi sleeves which telescope one within the other to a limited extent, one of said sleeves having an end wall supporting two mat- ,rices and the other an end wall supporting a pair 0! holders for inner dies eo-operating with the matrices, and means comprising a partition wall,

which is preferably removable and which passes across the chamber between the two holders, for dividing the chamber into two parts each having for an inner die, and means for dividing said the same number or the registering openings as the other.

FRANCIS TADMAN GRIFFITHS.

- I Disclaimer 7 ,394.Franaz's Tadman Grifliths, Gravesend, Kent, England. Ex'rRUsmN MACHINE. Patent dated Jan. 16, 1945. Disclaimer filed Dec. 12, 1949, I by the assignee, W. T.- Henleys Telegraph Works Company Limited.

Hereb enters this disclaimer to claims 1 and 2 of said patent. cial Gazette January 3, 1950.]

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