USRE23240E

USRE23240E - Apparatus for extruding thermo

Info

Publication number: USRE23240E
Authority: US
Publication date: 1950-06-13

Description

June 13, 1950 w. A. MAGERKURTH l-:TAL Re. 23,240

APPARATUS FOR EXTRUDINC THERMOPLASTLC MATERIALS 2 SheetsFSheet 1 original Filed Jan. 21, 1941 H .mm RK m5,. www WN. H E mw EH MH W June 13, 1950 W. A. MAGERKURTH ETAL APPARATUS FOR EXTRUDING THERMoPnAsTIc MATERIALS Original Filed Jan. 2l, 1941 2 Sheets-Sheet 2 INVENTORS WMA/ELM A. nunka/PTH /mvs E'. Bufc KEN Ressued June 13, 1950 APPARATUS FOR EXTRUDING THERMO- PLASTIC MATERIALS WilheimA. Magerkurth and Bans E. B uecken, Akron, Ohio, assigner: to National Rubber Machinery Company, Akron, Ohio, acorporation of Ohio Original No. 2,407,503, dated September 10, 1948,

Serial No. 375,124, January 2l, 1941. Application i'or reissue October 19, 1949, Serial No.

5 Claims. (Cl. 18-12) Matter enclosed in heavy brackets I: l appears in the original patent but forms no part o! this reissue specication; matter printed in italics indicates the additions made by reissue 'I'his invention relates to a method and apparatus for plasticizing and extruding powdered, granular, ilaked, or like thermoplastic materials.

Heretofore, plasticizing and extruding machines having various types of extruding screws therein have been used, for example, in the rubber art, the extruding screws usually having had a single thread extending the length of the screw, and the screw threads having been designed in various ways for elimination of air bubbles from the plastic material and for the purpose of maintaining proper pressure at the extrusion head of the machine.

None oi the known prior art extrusion devices, however, are entirely satisfactory for use in plasticizing thermoplastic materials, such as ethyl cellulose, vinyl chloride, vinyl acetate, cellulose acetate, cellulose acetate butyrate, cellulose nitrate, methyl methacrylate resins, and possibly many others, which when fed into the extruder are in powdered, granular, ilaked form. One reason for this is that the physical characteristics of materials of the type enumerated are such that the plasticizing process tends to reduce the bulk of the material, sometimes to as much as one third of its original volume. Thus, there was a tendency for the agitation by the plasticizing screw to become less and less effective, with consequent proportionate reduction in the pressure toward the extrusion end of the screw. It has been found that the reducing oi' the effective screw. pressure in this manner causes the material to be masticated too long, whereby it becomes overheated and discolored, the resulting extruded product frequently being semi-plastic, lumpy, or of non-uniform consistency because of the overtreated condition. Moreover, the stock issues from such devices in a pulsatory non-uniiorm manner causing variations in the cross-section of the issuing stock.

Because of certain characteristics of materials of the types mentioned above, it has been a practice in the vpast to form the same into'articles by injection molding, which method, of course. has disadvantages and limitations.

An object of this invention is to provide a machine oi' the character described, including an improved plasticizingand extruding screw, by.

means of which desired pressure on the treated material will be maintained throughout the length of the screw, regardless of variations in the bulk of the material as it is plasticized from powdered or like form to a desired plastic condition, whereby the stock will be kept flowing uniformly to the extruding die and the resulting. extruded product will be of uniform desired consistency and appearance.

Another object of the invention is to provide an improved apparatus for plasticizing and continuously extruding powdered, granular, flaky, or like thermoplastic material.

Another object of the invention is to provide apparatus of the character described having means for producing and uniformly maintaining the desired consistency of the plasticized thermoplastic material at a point just prior to its being forced through the extrusion kdie of the machine.

Still another object of the invention is to. provide apparatus of the character described in which the screw is operable to plasticize the thermoplastic material without substantial pulsatory movement, whereby the material is extruded at a uniform rate of speed to produce continuous material of uniform cross-section.

A further object of the invention is to provide a device of the character described which can be readily cleaned.

These and other objects' of the invention will be manifest from the following brief description and the accompanying drawings.

Of the accompanying drawings:

Figure 1 is a vertical cross-section, longitudinally of a machine embodying the invention.

Figure 2 is a cross-section taken on line 2--2 of Figure 1.

Figure 3 is a cross-section taken on line 3 3 oi' Figure l.

Figure 4 is a cross-section taken on line I-I of Figure 1, J

Figure 5 is a fragmentary cross-section, greatly enlarged, of the extrusion end oi' the machine shown in Figure 1.

Figure 6 is an enlarged fragmentary, crosssectional-view of a modined form oi construction at the extrusion end of the machine.

Figure 'I is a fragmentary cross-sectional view, I

on a reduced scale, taken at the other end of th`e machine shown in Figure 6, illustrating the inlet and outlet connections for supplying heated fluid to the interior of the plasticizing screw.

Referringinparticulartoll'lgures1to5,inclu sive, the numeral I. designates a supporting homing, within which is suitably Journalled at I I, Il a sleeve I2 within which is keyed the shank I8 of a horizontally extending plasticizing and extruding screw shaft I4, said screw shaftbeing rotatable within a bushing Il removably mounted in a casing II secured'to the housing Il, as by bolts II. I1. The screw shaft may be continuously rotated through a gear il keyed, within housing Ii, on rotatable sleeve l2, by means of a suitable motor and reduction gearing (not shown). y

f For removably mounting bushing Il in casing Il, an enlarged portion 2l on the outer end of the casing is counterbored to receive, flush with the outer face'2lla thereof, an annular ange 2| on the outer end of the bushing, the inner end of said bushing being tightly received in a bore 22 in an enlarged portion 2l at th shank 4ond of 'casing Il. The bushing is secured in place by means of countersunk 'screws 2l, 24 as shown in Figure 1. An laperture lla in bushing li 'communicates the shank end of the screw il with a feed hopper 23a in the enlarged portion 2l of casing Il.

Removably secured to the end face 20a of the enlarged portion 20 of casing II may be an ex- The screwishaft Il may have a continuous f thread 2l which extends from the hopper end of the shaft ,tovx approximately the end of cylinder or bushing Ii I, the pitch `of this thread for about half its length, at the hopper end of the screw, being substantiall, uniform, and the remainder of the thread being of gradually diminishing pitch `toward the extrusion or head end of the screw. Starting from a point P, half way along the length of the screw shaft, from the feed hopper end, thereof or substantially at the point where the pitch of thread 2l'starts to diminish, there may be a second thread 29 lying within or co-extensive with the remainder of said thread 2l, and having correspondingly diminishing pitch. Thus, the screw shaft is so designed that granular, powdered, aky, or like thermoplastic material of the types heretofore mentioned, may be fed through the hopper 22a to be first worked along the single-threaded portion of the' screw, under the influence of a requisite degree of external heat for starting the breaking down or plasticizing process without the powdered material substantially adhering to the surfaces of the screw and cylinder. To this end, a chamber 3l in casing i6 surrounding a major portion of the single threaded portion of screw I4 may be suitably heated as by having hot oil, or other heated uid, circulated therein, through piping ll, I2 from asuitable source of supply (not shown). An electrically heated Jacket or other suitable electrical heating means may be used at this pint, 1.

As the niaterial moving along thescrew becomes more and more plasticized, its volume decreases proportionately, and hence the mass tends to remaintoo long in prior types of machines and to issue in a pulsatory manner. Ihiahowever, in the present machine, is prevented by the j 4 material entering the double threaded. diminishing pitched portion of the screw which increasingly confines the material to keep it moving -forward under requisite pressure, the diminishing pitches of the threads 2l and 29 being-Such as to compensate for the decreasing volume of the materiales it becomes completely plasticized toward the extrusion end of the `screw. Proper plasticizing temperature may be maintained' around the double threaded portion of .the screw as by circulating hot fluid, such as hot oil or the like, within an annular chamber 3l in casing IB, such oil being supplied through piping 34, 3S from a suitable source of supply (not shown). An

electrical heating element may be substituted lhere also. y

In order to prevent the powdered or likethermoplastic material from becoming sticky in the --hopper 23a and around the portion of the screw adjacent the same, which stickiness might hinder the plasticizing process, a cooling iluid, such as water from a suitable source (not shown), may

Abe supplied, through piping 36, 31 to an annular chamber 3s in the enlarged portion 23 of casing It adjacent the hopper.

After the thermoplastic material has been plasticized, under the in'uence of heat and pressure, by means of the screw Il, it is finally subjected to uniform working under heat andpressure before extrusion of the material through a suitably apertured forming die.

To this end, a hollow extension Il is4 provided on the extrusion end of screw shaft I4, to rotate therewith, this extension Il projecting into a cavity 42 in the head 25. tension," preferably is greater than the diameter of the hub of the screw I4, this-enlarged extension being Joined to the `screw shaft by smoothly blended curves. AThe outer end of the extension is rounded and in spaced relation to the outer end of cavity 42. Cavity l2 may be the same shape as the extension, but larger in-proportion to permit passage of a relatively thin uniform stream of plastic material from'the end of the screw proper as compared with the stream as it leaves the extension end of the screw. The enlarged diameter of extension 4I, compared with the diameter ofthe hub of screw Il, provides maximum surface areas for further uniform working and heating of the material, as will be described. the length of the extension. of course, also being an important factor in this `connection. In other words, the now of plasticized material passing along the extension toward the extrusion orifice is relatively thin for the purposes described, but is substantially the same as the flow of the material as it passes from the extension end of the screw shaft so that the material will move smoothly toward said extrusion orince. The revolving extension Il has an additional advantage in that it is more readily cleaned than would be a fixed extension at this point which would require a supporting spider having arms extending across the path of the stock and fixed to or integral with the head 25. It will be seen that upon removal of head 26 extension 4I and cavity 42 both may be readily cleaned.

This additional working and heating of the plasticlzed material is necessary to make it of proper consistency for smooth continuous passage thereof through the forming, aperture in the die Il. Heat may be supplied by a suitable

electrical heating element

4,5 fixed within a cavity or bore a in the extension 4I, as shown in Figures 1 and 5, said element being connected to a source The diameter of exof an electrical supply (not shown) through wiring extending through a bore in screw Il and the shank Il thereof and through a slip-ring device l of known type, and in addition, the head 25 may have therein an annular chamber Il surrounding extension Il wit-hin which hot oil is circulated, through piping I8, l! connected to a source of supply. Bailles or

vanes

50, 55 serve to facilitate uniform circulation of the heating fluid. Thus, the material passing through cavity I2 may be uniformly worked between the screw extension 4| and the inner surface of head 25 while thoroughly and eect-ively heated to the desired uniform plasticity for the purposes described. An electrical jacket or other suitable electrical heating means may be used instead of the circulating fluid heating means.

As best shown in Figure 5, the forming or extruslon orifice 40a of die 40 is located beyond the end of the extension 41 and may be enlarged inwardly at Mb toward chamber l2. Held within a recess 5I in block 25 by die I0, to be between enlarged aperture ,40h and chamber 42, may be one or more relatively fine mesh screens 52, 5l. and a perforate strainer plate 5I, the meshes of the respective screens, preferably becoming increasingly coarse toward the plate. Plate 54 and the

screens

52, 53 not only strain foreign matter from the extruded material but strain out any lumps therein so that these will be reworked between the `extension ll and the head 25 to the same degree of plasticity as the rest of the stock.

In the operation of the machine shown in Figures l to 5, inclusive, powdered, granular, flaky, or like thermoplastic material, of the types previously mentioned, is fed into hopper 23a at the shank end of screw Il. It may be said that there are three distinct zones in the apparatus described above. One zone is located along the single-threaded portion of screw I4, in which the material is mixed and broken down from powdered, granular, or flaky form to a partly plasticized mass. The second zone is along the doublethreaded portion of the screw, in which zone the plasticizing process is completed, the double thread increasing the action on the material, and the diminishing pitch of the threads not only tending further to increase the pressure but also compensating for the ever decreasing volume or bulk of the'material due to the breaking down process thereby maintaining uniform flow. The third zone is located in chamber 42, wherethe material is not only heated as desired to make it of requisite consistency or plasticity for extrudlng it through the die lll but in addition is uniformly worked. The material after thus being uniformly heated and worked is then converted from a relatively thin annular form to a desired compacted form in which .latter condition the material issues from the extrusion orifice 40a. In this connection it is to be observed that the extension 41 terminates short of the extrusion orifice 40a whereby the material is not worked by relatively rotating surfaces at the time of extrusion, thus assuring a uniform extruded product. It is understood that the temperatures in chamber 30, J3 and 50, adjacent the respective zones mentioned above, as well as the temperature of heatving element l5, may be regulated as required to suit the particular material in use in the machine.

Figures 6 and 'I illustrate a modified form of the invention. This construction differs in one respect from the apparatus described in connection with Figures 1 to 5 in that one thread 25a of the double threaded screw Ila, similar to screw I4 previously described, extends around the extension lla along a substantial straight portion thereof, the extended thread 29c engaging the inner surface of the cavity 42a into which extension 4| projects. The extended thread 29e preferably has a Vrelatively large pitch for urging the material toward the extruding die "c without unduly increasing the pressure thereon after it leaves the screw I la. The thread extension or helical rib 29e, by engaging the surface of cavity Iza, along a substantial portion of the length thereof, provides a bearing surface for the extension l la to center the same and prevent whipping which might cause the extruded material to be non-uniform in cross-section.

For internally heating the enlarged extension Ma, a relatively fixed conduit 55 may be coaxially extended through a bore 55 extending from the outer end of shank lila of screw shaft Ila (see Figure 6) and through the screw shaft, and substantially to the end of said enlarged extension thereon (Figure 6). As shown in Figure 7, there may be provided a device 51, of type commonly called a mill-T, including a packing sleeve or gland 5B, secured in the end of shank |32. to rotate therewith, and a relatively fixed fitting 59 secured on the outer end of conduit 55. A sleeve 58a, co--axially mounted on conduit 55, is secured at one end to fitting 59 and is in fluid sealed connection with the rotatable packing gland 58 at the other end, to provide a. passage from bore 55 to fitting 59 exteriorly of the conduit. Heating fluid, such as hot oil from a suitable source (not shown) may be circulated, through a pipe rlill connecting fitting 59, and through conduit to the other end thereof, where the fluid is returned on the outside of the conduit, and through the passage between conduit 55 and sleeve 58a, fitting 55, and a return pipe 5l, to said source of supply. 'I'his arrangement is such that hot oil, owing from the extrusion end of conduit 55 will be hottest where most desirable, in the region of the enlarged extension, the effective temperature of the oil gradually decreasing along the screw shaft Ila toward the shank thereof. I'he temperatures in the regions of the different zones may be controlled, however, by

.varying the externally supplied heat as described in connection with Figures 1 to 5.

By means of the forms of the invention described above, it is possible uniformly to extrude plastics of the types previously mentioned, for example, into continuous strip materials having desired cross-sectional shape, for numerous purposes, and in certain instances to make finished products which, heretofore, have not been thought possible or practical.

Modifications of the invention may be resorted to Without departing from the spirit thereof, or the scope of the appended claims.

What is claimed is:

1. A machine for plasticizing and extruding thermoplastic materials of the character described, comprising a casing having a bore therein, [and] a screw shaft rotatable in said bore, said screw shaft having a hub with a feeding rib extending outwardly therefrom', said casing having a cavity communicating with said bore at the extrusion end of the machine, and a die at one end of said casing formed with an extrusion orifice communicating with sach cavity, said shaft having a substantially cylindrical extension projecting into said cavity but terminating short of the extrusion orijice in said die, said extension aaaeo l I being rotatable with said shaft. the diameter .of the extension being greater than that of said hub. the surface of said extension being in closely and uniformly spaced relation to the surface of said cavity, said extension having a helical rib' v8 an elongated substantially cylindrical extension projecting into said cavity but terminating short of the extrusion orijlce, said extension being rotatable with said shaft, said extension being of thereon projecting outwardly therefromand engagingthe surface of said cavity.

2. A` machine ,for plasticizing and extruding thermoplastic materials of the character described, comprising a casing having a bore therein, a screw shaft rotatable in said bore, said screw shaft having a hub with a feeding rib extending outwardly therefrom, said casing having a cavity communicating with said bore at the extrusion end of the machine. a die at one end of said casing formed with an extrusion orifice communicating with-such cavity, said shaft hav- .ing a substantially cylindrical extension projecting into said cavity but terminating short of the extrusion orifice in said die, said extension being rotatable with said/shaft, the diametery of the extension being greater than that of said hub, the surface of said extension being in closely and uniformly spaced'relation to the surface of said cavity, and means on said extension movable with the surface thereof for urging forwardly piasticized material received from said screw, and means for heating said material as it is urged over the surface of said extension. l

3. A machine for plasticizing and extruding. thermoplastic imaterials of the character` de` scribed, comp in, a screw sh shaft having lhub provided with a feeding rib extending outwardly therefrom, a head on said v g a casing having a bore theret rotatable in said bore, said screw greater diameter than said hub of the screw shaft andbeingofsuchdiameterwithrespecttothe diameter of-said cavity that the flow of plasticized material passing along the extension toward said extrusion orifice will be relatively thin but substantialLv the same as the flow of-'the material as it passes from the extension end' of the screw shaft. l

5..A machine for plasticizing and extruding thermoplastic materials of the character described, comprising a casing having a bore and an extension cavity in communication with said bore at an extrusion end of the casing. saidcasing having an extrusion orifice at the' extrusion end thereof communicating with said cavity, and a screw shaft rotatable in said bore and having a hub, said shaft having a continuous thread extending substantially the length thereof outwardly of said hub, n substantial portion of said thread adjacent said cavity being of diminishing pitch, said shaft having a second thread also outwardly of said hub and coextensive with a substantial proportion of the length of said first named thread at the end of the shaft adjacent said cavity, said screw shaft having an extensionend and an elongated extension pr'ojecting into said cavity but terminating short of the extrusion orifice, said extension being rotatable with the screw shaft, said extension being casing having an extrusion orice at an extrusion fend of 'the casing and having an extension cavity communicating said bore with said extrusion orice, said shaft havingan elongated substantially cylindrical extension thereon projecting into said cavity batterminating short of the extrusion orifice, said eitension being rotatable with said shaft, said extension being of greater diameter than said hub of the screw shaft and being of sucli diameter with respect to the diameter of said cavity that the flow of plasticized material passing along the extension toward said extrusion orifice will be relatively thin but substantially the same as the ow of the material as it passes from the extension end of the screw'shaft.

4. A machine for plasticizing and extruding thermoplastic materials of the character described, comprising a casing having a bore .therein, a plasticlzihg screw shaft rotatable in said bore, said screw shaft having a hub provided with a. feeding rib extending outwardly therefrom, a head on said casing having an extrusion orice at-anvextrusion end of the casing and having an extension cavity communicating said bore with said extrusion orifice-said screw having thereon of greater diameter than said hub of the screw shaft and being of such diameter with respect to the diameter of'said cavity that the flow of plasticized material passing along the extension toward said extrusion orifice will be relatively thin but substantially the s ame as the Aow of the material as it passes from the extension end o f the screw shaft.

WILHELM A. MAGERKURTH. HANS E. BUECKEN.

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

UNITED STATES PATENTS Number Name Date 1,445,724 Skorkorsky Feb. 20, 1923 1,608,980 Gordon L Nov. 30, 1926 1,902,295 Shook Mar. 21, 1933 1,904,884 Royle Apr. 18, 1933 1,935,050 Gordon Nov. 14, 1933 1,959,628 Jacobson May 22,-1934 f 2,177.g33 Blackard Oct. 31,` 1939 2,177, 58 Kimble, et al. Oct. 31, 1939 2,286,405 Gordon June 16, 1942