US2335307A - Cork extrusion apparatus - Google Patents

Description

NOV- 30, 1943. A. H. PENDERGRAST 2,335,307 com( ExTRUsIoN APPARATUS Filed Feb. 1, 1940 INVENTOR conductivity, such as brass.

Patented Nov. 30, 1943 conx Ex'rm-JsloN ArPAnA'rUs Ambrose Il. Pendegrast, Wilmington, Del., as-

signor to Bond Manufacturing Corporation, Inc., a corporation of Delaware Application Febrary 1, 1940, serial No. $18,121, (ci. 18-12) 9 Claims.

'I'his invention relates to an improvement in apparatus for extruding composition cork and similar products.

In the manufacture of composition cork by the extrusion process as heretofore practised, comminuted cork in admixture with an adhesive or binder is forced through a tube or die and bonded together by the action of heat and pres- -heating section of the "tube or die.

The binder is usually of a thermo-setting type, for example, urea, phenolic, or alkyd resinous materials or albumens or proteins treated with a material to insolubilize them upon heat# ing, or it may be of other types which will impart adhesive properties. In practice it has been customary to apply to the heating zone suf- Iicient heat to liquefy and set oi the binder, i. e., bring about chemical changes in the binder `to render it insoluble andinfusible, and' at the same time maintain a low enough temperature lin the forming section so that such changes do not take place until the comminuted cork par- -ticles have been brought together in a body of the desired shape and compactness. Accordingly, in practice, it has been customary to surround the extrusion passage with a coling jacket adjacent to the feed end to retard the transfer of heat through the walls of the tube from the heating 'zone to the fresh material being introduced at the feed end.

In order to maintain a more uniform temperature in the heating zone and to improve the emciency of heat transfer, ithas come to be a commercial practice to use a metal for the extrusion tube or die of high heat conductivity such as copper. But when such a material is used, although the thoroughness of heating is greatly improved, the high heat conductivity allows the transfer of heat back into the forming zone at a much higher rate than was the case with the type of tube material used in the older practice and having a moderatethermal This heat, penetrating the forming section, prevented the satisfactory formation of the cork body or plug. Only by the use of a. high rate of ilow of cold water through the jacket surrounding the forming zone could the undesirable/temperature rise be prevented. Not only was this method uneconomical but often impossible when a low temperature water supply was not available. Also variations in rate of iiow, temperature, amount of scale formed, and diiierences in water entrance and exit temperatures gave objectionable variations in the type of formed body or plug which governs to a great extent the size, density, pattern, and strength of the composition cork.

One of the most important properties of composition cork is tensile strength, both wet and dry, which is a measure of the ability of the coinposition cork to function effectively for the uses to which it is put, such, for example, as sealing discs for crown caps, gaskets, expansion joints in concrete roadways, etc. One of the important factors which iniluence the tensile strength of an extruded composition cork bar is the amount of heattreatment or curing given to the cork while in the process of extrusion or supplemented by an after-curing heat treatment. In other words, it is not only necessary in the extrusion operation to bring the cork to a temperature suicient to promote the thermal setting reactions in the binder, but it is also necessary, after the binder has been set off, to continue the heat treatment to effect a soaking or curing of the cork.

Due to the nature of the extrusion process,

` the'period during which the cork can be subjected to a curing heat treatment in its passage through the extrusion tube or die is limited.

l If the rate of extrusion is reduced, this tends to render the cork bar too dense. At the same time the output is lowered. It is also to be remembered that friction is set up between the cork bar and tl'ie side walls of the tube. While this is desired tothe extent that it promotes the compression of the cork particles and binder into a body of the desired shape and density, there are, nevertheless, definite limits beyond which the. cork composition should not be compressed. Also,`there are limits on the extent to which the temperature can be raised to control the friction.` Accordingly, the length of the extrusion tube is limited and formerly when brass tubes were used in association with 'a cooling jacket between the feeding and heating zones, the extrusion tube was rather short. Because of these limiting conditions, it has been the practice to further cure the composition cork either by allowing it to age at room temperature for a week or more or by heating at an elevated temperature, say TIO-200 F., for at least several hours. As so conducted the curing is not entirely satisfactory because it is not feasible to confine the composition cork under pressure as in the extrusion die.

This invention has then, for one object, to

sure more posi-tively against setting off of the binder in the feeding and forming zone as well as to prevent undesired transfer of heat tothe feeding mechanism and the cork as it is fed to theforming tube or die. In the earlier formsof apparatus the transfer of heat through the tube was often sufficient to cause tackiness of the admixture of comminuted cork and resin in the feeding mechanism and thus causing clogging.

A still further object of the invention is to bring about savings in power consumption and cost of water dueto elimination or decrease of the amount of water heretofore required to be circulated in a cooling jacket about the forming section of the tube or die, and also due to the elimination or shortening of I the additional operation of further curing that was heretofore required.

It is still a further object o'f the invention to obtain an increased output of product with an apparatus of a given size.

The above objects and advantages are brought about according to the present'inventlon by introducing in advance of and contiguous to the heating section, that is, at the feed end, a tube or Wall, section composed of a material of low heat conductivity. This section' may extend through the feeding and forming zone, or may be merely a short section or coupling joining a tube or die of relatively high heat conductivity forming the heatingv section to a tube or die forming the walls of the feeding zone or section.

According to one advantageous embodiment of the invention the short tube or' wall section of low heat conductivity is inserted between and joined to a tube or `die of ,high heat conductivity forming the heatingV section, such as copper, silver orl aluminum, and to a tube or die of similar high heat conductivityor to a tube of ,somewhat lower but nevertheless considerable heat conductivity such as brass, forming the wallslof the feeding zone or section. According to another embodiment of the invention the heating section of the tube or die may consist of brass or other material of intermediate heat conductivity, and this section may be insulated from a forming section of similar or higher or lower heat conductivity by meansof an interposed coupling or section of low heat conductivity. Instead of interposing aninsulating section -of low' heat conductivity between the forming and heating sections, the'tube or wall'section of low heat conductivity may extend through and comprise the feeding and forming section.'

Further features and advantages of the invention will be disclosed as the description proceeds.

In the drawing:

Fig. 1 is a vertical section view of a typical form of apparatus embodying the present invention; and

Fig. 2 is a vertical longitudinal section through a. modification of the extrusion tube or die shown in Fig. 1.

The form of the invention chosen for purposes of illustration in Fig. lof the drawing is shown as embodied in an extrusion machine of the type disclosed andclaimed in U. S. Patent No. 1,453,617, and consisting of an open-ended forming tube or die 2, a feeding hopper 4, a distributor 6, and a plunger 8. An opening I8 is provided in the `upper wall of the tube 2 adjacent the hopper 4 through which the admixed comminuted cork and binder are fed from the hopper. The plunger 8 reciprocates in that portion of the forming tube adjacent and beneath the hopper 4 through a length of stroke that alternately, brings the head of the plunger forward past the opening I8 and; in the rearward half of the stroke, withj draws the head of the plunger to the left of the opening I0, thereby permitting a. fresh charge of cork to fall into the tube 2. In this way, the increments of freshly deposited cork are advanced and compressed against the previously formed cork body, at the same time advancing the cork body for a short distance.

, is shown in Fig. 1, the extrusion die 2 is tubular in shape and consists of a feeding and forming section I2 and a heating and curing section I 4. The forming section` I2 is made of reinforced Bakelite and is joined to the heating section I4 by a coupling I6 made of the same material. AThe heating section is made of copper,

- brass or other metal of high or intermediate heat conductivity. Surrounding and in contact with the metal tube there is shown a steam jacket I8. It will be understood that any other suitable means of transmitting heat to the heating section may be employed, such as an electrically heated jacket.

In Fig. 2 the insulation of the feeding and forming section I2 from the heating and curing section I4 is effected by means of a short tubular insert 20 joined to and continuous with the tubular sections I2 and I4 by means of couplings I6. The insert 20 and the couplings I6 are made of reinforced Bakelite, or some other material having a thermal conductivity comparable to Bakelite, whereas the other sections are made of copper, brass or any other suitable material having a high or intermediate thermal conductivity. If desired, when using an insulating insert 20, the feeding section may be made of a metal, e. g., copper or brass, or of another material of high or intermediate thermal conductivity. When so made the feeding and forming section I2 may be surrounded by a cooling jacket, as at.22, provided ing section that is obtained by the constructions yabove described, it is made possible to operate at a higher hot Jacket temperature and, at the same time, use a longer heating and curing tube section since a higher temperature inthe heating and curing zone decreases friction; At the same time, the rate of .extrusion can be increased and heat that was formerly carried oil in the cooling water circulationmay be utilized in curing the cork. Because of the greater heat input that is made possible in the heating and curing zone, it

. is possible to produce a lighter and stronger bar.

or in the form of strips of varying widths and thicknesses, it may be necessary to introduce other materials to hold together the section o material of'low heat conductivity.

A reinforced Bakelite that has been found to work well for the purposes of the present invention is that formed from a Bakeliteimpregnated laminated fabric molded and finished to the' desired dimensions. While reinforced Bakelite has been specified, it will be understood thatvarious other materials may be used provided they have a low thermal conductivity and the requisite strength and, at the same time, may be threaded and coupled or otherwise secured to a tube section of copper or other highly heat conductive material. Examples of such other materials are various plastics, e. g., pyroxylin, and urea resins, laminated for increased strength and low heat conductivity purposes with asbestos, cloth, paper or various other fibrous materials. These materials give exceptionally low values for heat conductivity, varying from K=0.05 to 0.30.

In addition to materials of extremely low ther- I am aware that gaskets of insulating material Ahave been interposed between abutting ends of fend of the mold or substantially decrease the power loss due to the absorption of 'heat units by the cooling water. In contradistinction to such prior proposals, my invention involves the use of a tubular section of low heat conductivity of a length and thermal conductivity so regulated as to eiect a sharp blocking off of heat transferv along the -walls of the forming tube from the heating section to the cork composition material disposed in the forming section. As shown in the drawing, this tube section may be relatively short but nevertheless. of substantial length usually greater than the diameter of the forming tube, as

. shown in' Fig. 2, or may extend entirely through mal conductivity such as above mentioned, there are various metals and alloys Vthat possess .low thermal conductivity and which are deemed to be included within the class of materials having low thermal conductivity as defined herein.

Among these are the type of stainless steel known as "1B-8 (18% Cr, 8% Ni), various nickel-chromium-iron alloys, e. g., the alloy containing 68% Ni, 12% Cr and 26% Fe, and Const-antan (60% Cu, 40% Ni), all with thermal conductivity values for the constant K of from 10 to 15.

Materials of high thermal conductivity, as

this term is used herein, are copper, K=218;` sil.

able materials having a thermal conductivity' of around K=90 or more.

The constant Vvalues,`K, for thermal conductivity of the various materials referred to herein. are expressed in B Vt. u. per hour for one 'square foot and temperature difference per foot of one degree F. l

It is to be understood that the invention is not predicated upon the use of a particular material but rather involves the use in the association described of two materials of such differing thermal conductivities as to make itpossible to secure a high rate of heat input and prolongation of the heat treatment, with the desired advantages hereinbefore stated, while maintaining the temperature in the feeding and preliminaryforming zone below the point Where setting off of the binder will take place and, at the same time, within a range that will promote the molding of the freshly fed material into the desired form and density.

and denne the entire forming section of the die as shown in Fig. l. A

Various changes in the form and mode of application of the invention will suggest themselves to the worker skilled in the art, and, therefore,

the invention is not to be deemed as limited except as indicatedby the language of the appended claims.

I claim:

1. In an apparatus for extruding composition cork, a forming tube or die through which comminuted cork and a binder are forced and bonded together by the action of heat and pressure comprising a forming section and a heating section, said forming section consisting at least in part of a tube section disposed contiguous to and -continuous with the walls of said heating section and dening at least in part the path of travel of the cork, vsaid tube section being of such a length greater-than the diameter thereof and of such low thermal conductivity` as to substantially prevent transfer of heat from the heating section to material in the forming section in the course of a normal extrusion operation.

z. In an apparatus for extruding composition cork, a forming tube or-die through which cornminuted cork and a binder are forced and bonded together by the action of heat and pressure comprising a forming section and a heating section, the walls of said heating section being cornf posed of a material having high thermal conductivity, said `forming section consisting at least in part of a tube section disposed contiguous to and continuous with the walls of said heating section and ldefining at least in part Athe path of travel of the cork, said tube section being of such a length greater than the diameter thereof and of such low thermal conductivity as to substantially prevent transfer of heat from the heating section to material in the' forming section in the course of a normal extrusion operation. y

3. Inl an apparatus for extruding composition cork, a forming tube or die through which comminuted cork andra binder are forced and bonded together by the action of heat and pressure comprising a forming section and a heating section, the Walls of said heating section being com- -posed of a material having a high thermal conductivity, and the walls of said forming section y being composed substantially of a material havtube section interposed in the walls of said formthrough the walls oi' said forming section to the material disposed therein during normal operation of said apparatus is substantially prevented.

4. In an apparatus for extruding composition cork, a forming tube or die through which comminted cork and laibinder areforced and bonded together bythe :action of heat and pressure comprising a forming-'section and a "heating section positioned contiguous to and continuous with the walls oi?- said forming section, the walls Vlof said heating section :being composed of copper, and the'walls of said forming section being corn-` posed of laminated Bakelite, whereby transfer of heat from the walls of said heating section throughthe walls of said forming section to the material disposed therein in normal operation of said apparatus is substantially prevented,v

5. In an apparatus for extruding composition cork, a forming tube lor diel through which comminuted cork and a binder are forced and bonded together b y the action of heat and pressure comprising a forming section and a heating section, the Walls of said heating section being composed of a material having a heat conductivity at least as high as that of brass and the walls of said forming section being composed substantially of a materialpossessing such low heat conducti'vity and of such lengthv as to prevent transfer of heat from the heating section to said forming section suicient to cause premature setting-- oii of the binder'in the course of a normal extrusion operation,

6. In an apparatus for extruding composition cork, a forming tube or die through which comminuted cork and a Abinder are forced and bonded 'together by the action of -heat and pressure comprising a forming section and a heating section, the walls in said heating section being composed of copper, said forming section consisting in part of a tube section interposed in the walls of said forming tube contiguous to and continuous with the walls of said heating section and intermediate the heating section and the point of feed of cork to said forming section, said tube section being` of such a length greater than the 4diameter thereof and of such low thermal conductivity that the transfer of heat from the heating section along the Walls of said die to material disposed in said forming section is maintained suiliciently low to avoid interference with proper forming of a cork body in said forming section in the course of a normal extrusion operation.`

7. In an apparatus f or extruding composition cork, a forming tube or die through which comminuted cork and a binder are forced and bonded together by the action of heat and pressure comprising a forming section and a heating secing tube intermediate the heating section and the point of feed of cork to said forming section, said tube section being of such a length greater than the diameter thereof and of such low thermal conductivity that the transfer ofheat from the heating lsection along the walls of said `die to material disposed in said .forming 'section is maintained :sufficiently low to .avoid interference ywith proper forming of a cork body in said form-` ing section in the course of a normal extrusion operation.

' vil'. In an apparatus for extruding composition cork, a forming tube or die through which comminntedcork and a binder are forced and bonded together by the action of heat and pressure comprising a forming section and a heating section,

. the walls of lsaid heating section being composed tion, said forming section consisting in part of a f loi? a material having high thermal conductivity,"

said forming section consisting in part of a tube O.

section interposed in the walls of the forming die between the heating section and the point of feed of cork to said forming section, said tube section being of such a length greater than the diameter thereof and of such low thermal conductivity that the transfer of heat along the walls of said forming tube to material disposed in said forming section is maintained suiliciently low to a'void interference with proper forming of a cork body in said forming section during normal operation of said apparatus.

9. In an apparatus for extruding compositionl cork, a forming tube or die through'which comminuted cork and a binder are forced and bonded together by the action of heat andpressure comprising a forming section and a heating section, the walls of said heating section being composed of material of high thermal conductivity, and said forming section consisting of a tube section composed of material of high thermal conductivity and a. tube section composed of materialof low 'thermal conductivity, said tube section of low thermal conductivity being interposed between said tube section of high thermal conductivity and said heating section and in contiguous relation thereto, and said tube section of llow thermal conductivity being of such a length greater than the diameter'thereof and of such low thermal conductivity that the transfer of heat along the wallsof the extrusion passage defined by said forming and heating sections from the heating section to the forming section in the course of a normal extrusion operation is maintained sufficiently low to avoid interference with proper forming of a cork body in said forming section during normal operation 'of said apparatus. i

AMBROSE H. PENDERGRAST. 4

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