US3348581A

US3348581A - Plastic lug strap

Info

Publication number: US3348581A
Application number: US450918A
Authority: US
Inventors: Coyt E Murray
Original assignee: FUTURE PLASTICS Inc
Current assignee: FUTURE PLASTICS Inc
Priority date: 1965-04-26
Filing date: 1965-04-26
Publication date: 1967-10-24
Anticipated expiration: 1984-10-24

Description

Filed A ril 26, 1965 Oct. 24, 196? c. E; MURRAY 3,348,581-

' PLASTIQ Lue STRAP I a sheets-sheet 1 I U "7 v I 20A 203' INVENTOR ATTORNEY Oct. 24,

Filed April 26, v1.965-

C. E. MURRAY PLASTIC LUG STRAP v 5 Sheets-Sheet 2 I BY v ATTORNEY INVENTOR United States Patent 3,348,581 PLASTIC LUG STRAP Coyt E. Murray, Gastonia, N;C., assignor to Future Plasfics, Incorporated, Gastonia, N.C., a corporation of North Carolina Filed Apr. 26, 1965, Ser. No. 450,918 2 (Ilaims. (Cl. 139-153) This invention relates generally to the method of manufacturing lug straps used in textile and other machinery. More particularly, my invention relates to lug straps made of a plastic such as a high molecular weight polyethylene and to the method for forming same.

It has long been known in the art of making lug straps that a U-shaped lug strap will wear longer in use on todays high-speed looms if the bowed, impact-receiving web portion of the strap is thicker than the sides. Thickening of the Web has previously been accomplished by fixing an impact-absorbing plug to the inner surface of the web.

Traditionally, lug straps have been formed from lengths of a suitable material by bending said lengths into U- shapes and treating or mechanically fixing the formed strap so that the said U-shape is retained during use. United States Letters Patent No. 2,216,999 to Bacon discloses a method of making lug straps with a thickened web from a fiat, woven webbing impregnated with an excess quantity of rubber or other thermo-setting materials by so molding the impregnated webbing as to force additional impregnant from the side portions of the lug strap into the web and to shape the excess impregnant in the web of the strap to provide the desired thickened area or cushion.

The known methods of manufacturing lug straps from polyethylene of a high molecular weight or from other suitable plastic materials either have involved the provisionof a separate plug and the subsequent aflixing of the plug to the inner surface of the web by suitable means, or have involved the formation of the lug strap from a blank stock having a medial portion which is thicker than the end portions which are to become the sides of the formed strap.

The use of separate plugs necessitates the extra manufacturing step of mechanically affixing the plug to the formed lug strap blank or of forming the strap about the plug under pressure and temperature conditions conducive to some polymerization between the molecules of the plug and the molecules of the blank. Unless there has been suflicient polymerization between the molecules of the wtih the web. I

The use of non-uniformly thick lengths of plastic has been unsatisfactory in that complicated and costly machinery for forming same may be required or else expensive and time consuming machining of uniformly thick pieces into desired shapes is necessary. In either eventthere is a consequential waste of material.

Unsuccessful attempts have been made to manufacture lug straps with an integral plug by injection molding of high molecular weight polyethylene. The resultant product has proven unsatisfactory in use because of a high form thickness throughout its length, which method has the attendant advantages of avoiding the use of separateice 1y formed plugs or cushions; and of avoiding the necessity of providing lengths of stock having portions of varying thicknesses with a consequent waste of material.

It is a still further object of this invention to provide a method of manufacturing plastic lug straps wherein substantial economies in machinery, labor, and materials can be effected. i

It is another object of this invention to provide an improved lug strap which includes an integral plug and wherein the entire lug strap and plug are formed from a length of high molecular weight polyethylene which is of substantially the same uniform width and thickness throughout its length as the legs of the finished lug strap.

It is a more specific object 'of the invention to provide an improved method of making an improved lug strap with an integral plug from high molecular weight polyethylene of the type described wherein the improved method of defining the integral plug results in a substantial increase in tensile strength of the plug due to the orientation of the molecular chain in the direction ofthe impact to which the plug is subjected in use. The increased tensile strength of the plug greatly improves the wear and abrasion properties of the lug strap and significantly increases the useful life of the strap.

Some of the objects of the invention having been stated, other objects will appear as the description proceeds, when taken in connection with the accompanying drawings, in

- which:

FIGURE 1 is a perspective view of a length of plastic stock of substantially uniform width and thickness throughout its length from which the improved lug strap is formed;

FIGURE 2 is a perspective view illustrating the initial step of bending the stock into a U-shaped configuration;

FIGURE 3 is a plan view of the U-shaped strap loosely positioned within a schematically illustrated mold;

FIGURES 4 and 5 are plan views of the strap within the schematically illustrated mold at sequential stages during the molding operation;

FIGURE 6 is a perspective view of the completed lug strap removed from the mold;

FIGURE 7 is a sectional view with parts broken away taken substantially along the line 7-7 in FIGURE 3 and omitting the .lug strap blank;

FIGURE 8 is a somewhat schematic perspective view of a mold used in practicing the invention; and

FIGURE 9 is a sectional plan view taken substantially along the line 9-9 in FIGURE 8.

According to the preferred form of the present invention a'charge of powdered high molecular weight polyethylene having a molecular weight in excess of one million is placed in an extruder and heated above the fusion point. Bar stock is extruded under a sufficiently high temperature to polymerize the polyethylene. While the bar stock is at a temperature within its fusion range of 200- 500 F., wherein the plastic stock is sufliciently softened to be bonded or welded, it is cut into desired lengths to define blanks 10, each 'blank being of substantially uniform width and thickness throughout its length, and from which the lug straps are to be formed according to the invention. While it is preferred, in an integrated operation, to shape and define the lug straps from bar stock which still retains the heat from the extruder, it is to be understood that it is within the spirit of the invention to form the lug straps from inventories of extruded bar stock which has been allowed to cool and reheated subsequent to its extrusion, or to cut stock of the desired dimensions from slab material to define a blank 10 and reheat it.

In any event, the method and product of the invention are obtained while the blank 10 is at a temperature within the said fusion range of the high molecular weight poly- 3 ethylene, preferably at a temperature between 289 to 350 F.

While the blank is still within the said fushion range, it is manually bent into generally U-shaped configuration as shown in FIGURE 2. Upon being bent into U-shaped configuration, the blank 10 com-prises legs or sides 11 and 12 interconnected by a web 13. The blank 10, while still at a temperature above its fusion point is loosely placed in an open mold 14 comprising a fixed core 15, a pair of

movable side plates

16 and 17 and a movable end plate 18.

The other end of the mold is closed by a'fixed end plate 19 which abuts the corresponding end of the core 15. The mold 14 additionally includes a base 30 to which the core and fixed end plate 19 are fixed. The

movable side plates

16 and 17 and the movable end plate 18 may be reciprocated by respective hydraulic cylinders 31a, 31b, and 310 and hydraulic pistons 32a, 32b, and 320. The cylinders 31a, 31b, and 310 are fixed against movement relative to the base 30 as by stops or

abutments

33a, 33b, and 330.

The mold also includes a top plate 35 fixed to the lower end of a ram or piston 32d (FIGURE 8). The piston 32d is reciprocable within a hydraulic cylinder 31d, the upper end of which depends from a stationary supporting plate 36. The support plate 36 is held in fixed spaced relation to the base 30 by a plurality of tubular leg-s 37 (FIG- URE 8), each of which loosely penetrate the movable top plate 35 of the mold 14, and are fixed at their respective ends to the base 30 and the support plate 36.

After the U-shaped blank 10 is loosely placed in the open mold 14, the top plate 35 is moved downwardly under hydraulic pressure to close the top of the mold. The hydraulic rams 32a and 32c are then actuated to move their

respective side plates

16 and 17 inwardly to clamp the legs of the U-shaped blank 10 against the core 15. Next, the end plate 18 is moved inwardly under hydraulic pressure imparted to the ram 32b to shape the web of the lug strap.

The inner limit of the inward movement of the

side plates

16 and 17 and the movable end plate 18 is predetermined to coincide with the desired thickness of the legs and web of the finished lug strap. In general, the thickness of the legs of the finished lug strap corresponds to the thickness of the initial bar stock and the thickness of the web in the finished lug strap is in the order of one and one-half to two and a half times the thickness of the legs.

As most clearly seen in FIGURE 3, the inner surface 20 of the web 13 is deformed into alternate transverse projections and depressions 20A and 20B as a result of the compression to which the surface 20 is subjected during bending of the blank into U-shaped configuration. The end of the core 15 adjacent the end plate 18 has a concave surface 21 (FIGURE 7) with which the inner surface 20 of the web 13 is adapted to engage under inward pressure of the mold end plate 18.

When loosely placed in the mold, the outer surface of the web 13 is located at a point spaced beyond the concave surface 21 on the core, the location of the outer surface of the web being designated by the line A in FIG- URE 3. Arranged in this manner, the inner surface 20 of the web 13 is likewise spaced from the end 21 of the core 15 to define a cavity C between the core and the inner surface 20 when the blank 10 is initially positioned in the mold as shown in FIGURE 3.

Continued inward pressure of the end plate 18 moves the outer surface of the web 13 away from the line A and toward the end surface 21 of the core 15 (FIGURES 4 and 5). It is apparent from the sequential steps illustrated in FIGURES 3, 4, and 5 that the continued inward movement of the end plate 18 collapses and reorients the web causing it to move into the cavity C until the projections 20A on the inner surface of the web enlarge under inward movement of the end plate 18 and engage the concave surface 21 of the core 15 (FIGURE 5). The cavity C is gradually filled in and closed by the thickening web as the molecular structure of the plastic is reoriented in the mold. Meanwhile, the sides or legs 11 and 12 have been subjected to pressure sufficient to serrate the inner end surfaces of the legs 11 and 12, but the pressure is not sufficient to significantly change the dimensions of the legs as in flow molding. Thus, when removed from the mold the lug strap as shown in FIGURE 6 has legs of substantially the same dimensions as the thickness and width of the bar stock from which the blank 10 was formed, while the web 13 with its integral plug is much thicker.

In order to help in maintaining the plastic at a temperature which will permit reorientation of the web under pressure of the mold, and to improve the surface appearance of the strap, the mold is desirably heated to a temperature within the range of to 230 F., preferably at about 180 F., for controlled cooling of the blank while in the mold. The mold can be used at room temperature, if desired, but experience has shown that the surface appearance of the lug strap is improved by heating the mold as indicated.

In practice, the blank is molded under a molding pressure of from about 200 to 300 psi. for one to four minutes. If desired, the molding pressure can be incresed as high as practical, such as 5000 psi, and the molding time can be lengthened indefinitely; but an increase in pressure and time does not improve the product and the invention is not limited to a top range of molding pressure and time.

The slots 40a. and 40b in the serrated end portions of the legs 11 and 12 (FIGURE 6) may be cut after the lug strap is removed from the mold. Alternatively, if desired, the mold may be equipped with suitable punches or dyes to form the

slots

40a and 40b during the postforming molding operation.

The completed lug strap has exhibited unusual wearresistant properties in use and these properties are attributed in part to the reorientation of the molecular structure during the post-forming molding operation at which time the web is reoriented and thickened in the manner described and illustrated.

The term plastic as used throughout the specification and claims refers to high molecular weight polyethylene and/ or to any material which is its equivalent, and the invention is not limited specifically to the use of high molecular Weight polyethylene.

In the drawings and specification there have been set forth preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the claims.

I claim:

1. A lug strap comprising a pair of spaced legs and an enthi-ckened web interconnecting corresponding ends of the legs and formed from high molecular weight polyethylene having a molecular weight of at least 1,000,000, and the molecular chains in said high molecular weight polyethylene web extending in a direction parallel to said legs, thus increasing the strength of said web.

2. A lug strap according to claim 1 wherein the enthickened web is integral with the legs.

References Cited UNITED STATES PATENTS 2,216,999 10/1940 Bacon 139l53 2,325,060 7/1943 Ingersoll. 3,019,486 2/ 1962 Stinson 264-291 (Other references on following page) 5 FOREIGN PATENTS 567,192 10/1958 Belgium. 978,052 12/1964 Great Britain.

OTHER REFERENCES Textile Industries: Vol. 125, No. 12, November 1961, Smith Pub. Co., Atlanta, Ga., p. 59.

6 Textile Industries: Vol. 127, N0. 6, June 1963, Smith Pub. Co., Atlanta, Ga., pp. 48-49.

Textile Industries: Vol. 127, N0. 2, February 1963, Smith Pub. 00., Atlanta, Ga., pp. 36-37.

MERVIN STEIN, Primary Examiner.

J. KEE CHI, Assistant Examiner.

Claims

1. A LUG STRAP COMPRISING A PAIR OF SPACED LEGS AND AN ENTHICKENED WEB INTERCONNECTING CORRESPONDING ENDS OF THE LEGS AND FORMED FROM HIGH MOLECULAR WEIGHT POLYETHYLENE HAVING A MOLECULAR WEIGHT OF AT LEAST 1,000,000, AND THE MOLECULAR CHAINS IN SAID HIGH MOLECULAR WEIGHT POLYETHYLENE WEB EXTENDING IN A DIRECTION PARALLEL TO SAID LEGS, THUS INCREASING THE STRENGTH OF SAID WEB.