US 2736897 A
Description (OCR text may contain errors)
Feb. 28, 1956 Filed Sept. 2, 1955 J. A. PARSONS METHOD OF COVERING ROD-LIKE MATERIAL 2 Sheets-Sheet l INVENTOR John Q Prsons 'alw, fw/
ATTORNEY Feb. 28, 1956 J. A. PARsoNs 2,736,897
METHOD OF COVERING ROD-LIKE MATERIAL Filed Sept. 2, 1953 2 Sheets-Sheet 2 INVENTOR John, J1?. Parsons ATTORNEY United States Patent O 2,736,897 METHOD F COVERING ROD-LIKE MATERIAL John A. Parsons, Bainbridge, N. Y., assignor to American Plastics Corporation, New York, N. Y., a corporation of New York Application September 2, 1953, Serial No. 378,154 3 Claims. (Cl. 18-59) This invention vrelates to plastic coatings and, more particularly, to the continuous application of ridged blisterfree coatings of extrudable plastic materials on rods of varied cross-sectional shape and design.
The appearance and physical properties of fibrous and cellulose-containing articles, such as wood, paper, etc., can be inherently improved by depositing a covering of a suitable plastic material thereon. For example, plastic coatings can provide a permanent finish ranging from a high gloss to a matte surface. Another advantage associated with the use of these coatings is the obtainment of a `surface that is suiliciently water-resistant and also relatively unaifected by contact with substances that are alkaline or acid in nature. Likewise, by incorporating various decorative coloring bodies or pigments in these coatings, articles possessing a wide variety of colors and shapes l are secured.
A conventional method for the preparation of a plastic covering for wood, paper tubes and substances of a similar nature, involves dipping these materials into a molten solution of a thermoplastic or thermosetting plastic and then drying the resulting product either (1) for an extended period of time at a low temperature or (2) baking at a high temperature. To insure an adequate coating, the article must be successively dipped and dried a number of times.
This process is highly unsatisfactory as it is not only time-consuming, but also uneconomical, necessitating the use of expensive drying equipment and requiring large areas of drying space as well. Furthermore, this dipping process is not suitable for applying coatings having a ribbed or ridged exterior surface.
This invention comprises forcing thermoplastic plastic material through a grooved or serrated die or other suitable shaping structure thereby vforming a grooved or ridged coating in tubular form and then pressing this tubular coating onto the article or section to be covered without completely flattening the ridges, thereby shaping the tube to the contour of the article so that the coating will adhere to the article, The air is expelled so that the coating is free of blisters. A ridged surface of this type provides numerous advantages in that it is sufficiently rough to be applicable as a covering for clothes driers, towel racks, etc. Where the fabrics cannot slip olf easily. Likewise, handles for brushes, luggage, hand-tools, etc. can be covered with a ridged coating of this type thereby furnishing a firm though comfortable grip.
While it should be noted that any extrudable plastic material either thermoplastic or thermosetting in nature or any plastic materials possessing properties intermediate thereto such as casein, is utilizable in the process embodied in this invention, it is preferable to employ thermoplastic materials such as cellulose acetate butyrate, polyethylene, vinyl resins, etc., instead of thermosetting materials such as phenol-formaldehyde resins, etc.
The invention is illustrated by way of example in the accompanying drawings in which ice Figure I is an end view of one form of extrusion apparatus which may be used in carrying out this invention showing conveying means for the article to'be coated;
Figure II is a horizontal view of a section taken on line 2 2 of Figure I;
Figure III is a cross section of a portion of the crosshead taken along line 3 3 of Figure I;
Figure IV is an enlarged fragmentary sectional view taken along line 4 4 of Figure I, and
Figure V is a fragmentary sectional View taken along line 5 5 of Figure IV on an enlarged scale.
Referring to the drawings, an extrudable plastic material in powder, pellet or any other suitable form, is fed through the rear end of a cylinder 1 of an extruder. Means are provided for heating or cooling cylinder 1 by chambers or jackets 2 located within the cylinder wall. Positioned within the cylinder 1 is a motor-driven screw 3 which forces the plastic material through the cylinder. By the application of heat throughout the entire length of the cylinder 1, together with a pressure created by motordriven screw 3, the plastic material is melted, forced through a breaker-plate or sieve 4 into a tapered opening 6 leading to the channel 7 in the body of the crosshead 5. The plasticized material continues on through an annular channel 8 formed by the hollow core pin 10 and the surface 17 of the vdie 5. The material is then forced through passages 18 in the element 9 which serves partly as an additional breaker-plate and also as an aligning bushing for hollow core pin 10 through which the article V19 to be coated passes. From passages 18, the melted material is forced along and is then extruded in tubular form through a constricted opening 15 between the smooth outer surface of core pin 10 and the grooved inner surface of adjustable bushing 11 and then out of the crosshead 5. Numeral 16 designates the aligning shoulder of bushing 11. Cover plate 12 may be removed to facilitate the cleaning of the crosshead.
The article 19 to be coated is fed forwardly into the rear opening 13 of the hollow cylindrical core pin 10 by roller conveyor 25 or other suitable feeding means as illustrated in Figure I and then into the inside of the tube 27 formed by the plastic material coming out of the constricted opening 15. Lugs 22, or other suitable devices, are positioned within the hollow core pin 10 to insure centralization of the article 19 to be covered.
At the output end 14 of the hollow core pin 10, the extrudable plastic in tubular form is considerably larger than the material to be covered. On leaving the output end 14 of the hollow core pin 10, the plastic tube 27 is cooled by conventional means as, for example, cool air jets 20, and then the intermediate product comprising both tube 27 and the article 19 are drawn through means 23 for pressing the tube 27 against article 19. The inner portion of means 23 includes a flexible sleeve 23 of rubber or similar material and preferably possessing the shape lof the article and which is small enough to apply uniform pressure to the exterior. On passing through the sleeve 28, the extruded plastic tube 27 is shaped to the contour of the. article 19 and is pressed thereon. Where the article to be coatedis irregular in cross-sectional shape, the swedging sleeve 28 in addition to being composed of material capable of stretching, preferably has a cross-sectional shape similar to that of the article.
On the passage of the extrudable plastic tube through the swedging die 23, any air or other vapor present in the tube is forced back through the hollow core pin 10 and then expelled through the rear opening 13 of the core pin 10. The structure of the lugs 22 located in the hollow core pin 10 which are used to center the object 19 to be coated as it passes therethrough, is of such a nature that it does not interfere with the passage of the vapors being ejected through this hollow cylindrical chamber or obstruct the passage of the sections through the aforementioned chamber. By the expulsion of air or other vapors present between the article to be coated and the plastic covering, a bubble-free or blister-free coating is obtained.
An important feature of the present process is that the pressure applying sleeve 28 does not apply suliicient pressure to completely fiatten the ridges 29. The plastic flowing out through annular passage is quite soft and owable. As the tube moves toward the pressure applying means 23, the plastic partially hardens so that while the tube 27 -is pliable and soft enough to be pressed against rod 19 as it passes through sleeve 28, the tube 27 has sufficient stiffness so that ridges 29 are not completely flattened. The ridges 29 will at first have relatively sharp outer edges corresponding to the grooves 3i) in bushing 11. Normally, the sleeve 28 will slightly flatten or round the peaks of ridges 29 so that they will assume the shape shown in Figure V. The stiffness of the plastic and the resistance of the ridges to flattening is influenced by a number of factors including the type of plastic ma'- terial, the temperature, the speed of extrusion, and the amount of cooling effected by 2li. As the ridges are not completely flattened, the finished product presents a ridged exterior surface which prevents slippage.
While the ridges 29 are shown as extending in straight lines parallel with the longitudinal axis of rod 19, the ridges may extend about the finished article in spirals. If the rod 19 is turned about its longitudinal axis, either by hand or mechanical means (not shown), as the rod is moved forwardly, the forward portion of the plastic tube 27 will turn with rod 19 while the portion of the tube at the outlet of passage 15 is held against rotating movement. This will cause the ridges 29 toA extend in spirals about the outer surface. When the rod 19 is turned, the sleeve 2S may be omitted if the rod 19 is moved forward- 1y at a speed slightly in excess of the speed of extrusion of the tube as under these conditions the plastic tube will tightly lit the rod 19 without utilization of the pressure applying means.
The interior and exterior portions of the core pin 10 and the adjustable bushing 11 may be shaped to correspond to the contour of the article 19 or section to be covered. Normally itis of no advantage to have the core pin 10 and bushing 11 shaped similar to the cross-section of the article 19 if said section is irregular in shape longitudinally.
As in conventional apparatus of this design, the article 19 on which a coating will be applied is led into and forced through core pin 10 by a suitable device such as a power driven roll-fed mechanism as shown in Figure I. After the coated section leaves the swedging die 23 it is carried over a series of free-running rolls or roller conveyors 24 and is further cooled by suitable cooling devices such as air jets 26, etc. Care must be exercised at this point so that the material is subjected to a cooling action in a fairly even manner to minimize or avoid distortion and lack of uniformity in the finished product. The plastic material sets and hardens. The coated material 21 proceeds from the rolls or roller conveyors 24 onto a belt, not shown. The roller and belt conveyor are moved at a speed at least equal to that of the feed roller 25 so that the section 19 to be covered and the finally covered section 21 are moved forward at a uniform and predetermined rate of speed. The speed of the feed rollers and conveyor rollers may be determined to suit the article being coated and may be adjusted relative to each other to feed this article through the machine at the proper rate.
The present invention embodies the coating of either a short yor continuous length of the base material by the use of. an extrusion press which may be either of `the screw operated or of the hydraulic-ram type or any other suitable extrusion device. A screw operated press such as the one illustrated is more desirable because of the continuous flow of materials through the press afforded by this means, whereas the ow of materials through a hydraulic press is intermittent. Although the drawing and the description in the specification illustrate an extrusion press of the screw type, it is not to be construed Ias limitative to a press of this type.
Having thus described kthe invention and the preferred embodiments thereof in which certain of the improved features and advantages have been particularly stressed, it is to 'oe understood that other forms and modification will become apparent to those skilled in the art upon examining Ithe specification, drawings and claims. yIt is to be understood, however, that this invention is not to be `limited to the specific disclosure las obviously other embodiments thereof may he devised within the scope of the appended claims.
l. The method of applying a substantially blister-free, homogeneous, single-layered coating possessing frictional gripping qualities to rod-shaped material which comprises feeding thermoplastic material in a heated and liowable condition through a grooved extrusion die orifice to form a continuous extruded tube larger than said rod-shaped material and having an exterior longitudinally-ridged surface, continuously introducing said rod-shaped material to be coated directly into said extruded tube Ithus providing an intermediate structure, passing said intermediate structure through a constriction chamber possessing expansible walls thereby applying uniform pressure to the exterior contours of said intermediate structure without completely tia-Mening the exterior ridges of the tube of thermoplastic material to shape the form -of said lthermoplastic material to the contour of said rod-shaped material while simultaneously ejecting the vapors present within said intermediate structure, followed by cooling thereof, `whereby the rod-'shaped material is covered with an extruded tube of thermoplastic material presenting a longitudinally-ridged exterior surface.
2. A method of applying a closely fitting ltubular coating of plastic material to an elongated rod which comprises the steps of extruding plastic material through an orifice having a gro'oved outer surface at a controlled rate of how to progressively extrude at a controlled speed an elongated plastic tube larger than said rod and having ridges extending longitudinally of the outer surface of the tube, simultaneously introducing an elongated rod into said tube and progressively moving the rod forwardly at a speed in excess of the speed at which said tube is extruded, thereby stretching 'the 'tube into engagement with the exterior of the rod, and turning the rod as it is moved forwardly to twist the Itube as it is extruded whereby the ridges also extend aro-und the tube on the rod.
3. A method of applying a closely fitting plastic coating to an elongated rod which comprises the steps of extruding thermoplastic material through an orifice having a grooved outer surface 'and thereby progressively extruding an elongated tube larger than said rod and having longitudinally-extending outer ridges, introducing an elongated rod into said tube and progressively moving the rod and the tube longitudinally through a chamber and applying therein uniform pressure to the exterior of lthe Itube to shape the tube to the contour of the rod without completely attening the exterior ridges, and turning the rod as it is move-d forwardly to twist the tube as it is extruded whereby the ridges extend around the tube on the rod as well as lengthwise of the tube.
References Cited in the file of this patent UNITED STATES PATENTS 1,834,554 Briggs ocr. 25, 1932 1,943,867 Hume Ian. 16, 1934 1,957,212 Hinsky May l, 1934