US3380243A - Plastic cordage - Google Patents

Description

April 30, 1968 R. L. STANTON PLASTIC CORDAGE Filed July 26, 1965 INVENTOR. 1908577 Z. fT/I/VTO/V Klmmfilwmjamwm United ts ABSTRACT OF THE DISCLOSURE A strand of a rope has a core which comprises highly elongated plastic bands which have been tightly compressed against one another and lie essentially parallel to one another. These bands are not twisted prior to the compression; the only twist they exhibit is due to the twist imparted to the strand as a whole.

This invention relates to cordage and in particular to a novel rope made at least in part of synthetic materials.

Synthetic ropes previously used in industries such as maritime industries, for example, include all nylon, all polypropylene, all polyethylene and all polyester types. In my US. Patent 3,026,669, issued on Mar. 27, 1962, there is disclosed and claimed a rope whose outer layer yarns include selected thermoplastic materials with selected melting points to prevent the ropes sticking on the bitts of vessels such as tugboats. This rope, like other previously known synthetic plastic ropes, had a core made up of a number of pre-twisted yarns of selected thermoplastic materials. While this rope has been commercially successful, research has gone on in an effort to produce other ropes with greater strength for a given cross-section, lower stretch properties for use by tugboats, ships, etc., and lower cost of production.

It is therefore one object of the present invention to provide a rope made at least in part of synthetic materials which has greater strength per cross-section than previous competitive ropes.

Another object of the invention is to provide a rope made at least in part of synthetic materials which has extremely low elongation or stretch properties.

Still another object of the invention is toprovide a novel rope made at least in part of synthetic plastic materials which can be produced more inexpensively than competitive ropes.

Yet another object of the invention is to provide a rope having less weight for a given strength.

A further object of this invention is to provide a rope with improved dimensional stability.

Another object of the invention is to provide a rope in which the total void space is very small.

Other objects of the invention will occur to one skilled in the art upon perusal of the specification, drawings and claims herein.

In accordance with the present invention, I provide a strand of a rope made at least in part of synthetic mate rials and having a core which includes highly elongated plastic bands, filaments or tapes that have been compressed. These bands, filaments, etc. have not been twisted to any appreciable extent before compression. As a result, the rope achieves the aforementioned objects for reasons which will be explained more fully below.

FIGURE 1 is a side elevation view of a rope constructed according to my invention.

FIGURE 2 is a crossscction of the rope shown in Fl URE l, and,

FIGURE 3 is a perspective view of part of the apparatus employed in maxing the rope shown in FIGURE 1.

Referring to FIGURE 1 there is shown a novel rope '7 according to one form of this invention. It comprises three atet 3,380,243 Patented Apr. 30, 1968 strands 8, 9 and 10 which have been twisted together. Each strand consists of a number of outer yarns 12. As illustrated in FIGURE 2, there is only one layer of such yarns although it should be appreciated that any number of outer layers are possible if desired. As shown, the outer yarns have been given a Z-twist, but this is purely a matter of design. These outer yarns may be composed of pretwisted polypropylene yarns or polyethylene yarns, or may be made of any other desired material. A typical marine rope may include twenty-seven of such. pre-twisted outer yarns 12, by Way of example.

The outer yarns of each strand of the rope shown in FIGURE 1, regardless of what material they are made of, or of the number of layers of them, or the number of yarns in the layers, or their general structure, surround a core which includes at least some highly-elongated bands of plastic material which have been compressed or crushed inwardly. In any conventional rope, its stretchability is due to the inherent stretchability of the materials used and to the particular fabrication characteristics imparted to those materials. It is the core which chielfly determines the overall stretchability of the rope. In the case of the novel rope illustrated, the core constituents, being made from highly-elongated materials, limit the stretchability of the rope. Since these core constituents are practically untwisted, they do not add appreciably to the fabrication stretchability of the overall rope either. Consequently, the resultant rope has very low stretchability which makes it very valuable in many maritime and industrial applications. Furthermore, as may be appreciated after reading the following description of one successful process for making such ropes, a numberof conventional rope-making steps can be by-passed with resultant lower costs of production.

To make the novel rope according to the form of this invention shown in FIGURE 1, a number of reels 14 of pre twisted yarns 12 are disposed on rods 13. As stated previously, a typical marine rope may include twentyseven outer yarns 12 for each strand so there would be twenty-seven sue-h reels. As shown in FIGURE 3, the pretwisted yarns 12 are fed into a forming die 17 having a tapered axial aperture therein surrounding the core from die 16. To form the core (or at least part of it) a number of reels 18 are provided on which bands 15 of elongated polypropylene, for example, are disposed. Each band, for example, may be approximately two inches wide and consist principally of linear isotactic polypropylene which has been stretched eight or ten times its initial extruded length. The thickness of such bands may be 23 mils, for example. It should be appreciated, however, that the width, thickness and elongation ratio of these bands may be varied, within limits, as desired, but the bands must be oriented to achieve a certain fibrousness and greater tensile strength. At elongation ratios of eight or ten to one, for example, the bands 15 will be highly oriented or fibrous and will have the requisite splittability. When such highlyoriented bands are viewed, the internal axial strains are visible and, in this condition, it is easily split by transverse forces, in a longitudinal direction. In fact, the bands, as they come from the reels 18, may already have perceptible slits.

These bands 15 are fed through a die 16 which has a tapered axial aperture. Since the exit aperture of the die 1'5 is quite small, the many bands 15 are fed through the die at one time, they will be crushed inwardly by the gradually tapering inner wall thereof. As stated before, these bands, before entry into the die 16, had longitudinal strains and the inwardly-crushing or compressing action of the die causes considerable longitudinal splitting of the bands. The diameter of the exit aperture is at least 5 percent smaller than the dia actor of the core in the finished rope.

The crushed or compressed bands are applied through the die 17 centrally with respect to the pre-twisted yarns 12. As the bands and pre-twisted yarns pass through die 17, the two capstan reels 19 and 21 which are mounted upon rods and 22 respectively are rotated in a counterclockwise direction (as viewed by the reader hereof). This will produce a strand such as strand 8, 9 or 10 with a Z-twist. The strand is taken upon reel 23 which is mounted upon the rod 24 which also rotates in the same direction as the capstan reels 19 and 21. Three or more of such strands are then laid up into the completed rope 7 in conventional fashion.

As may be seen, one rope that may be made according to the present invention has a core which is predominantly made of crushed and twisted highly-elongated bands of plastic material. These bands supplant the customary large numbers of individually pre-twisted yarns that conventionally constitute the core of a strand. It is the individual twisting of each conventional core yarn before the core is formed which makes conventional ropes more costly to produce than ropes made according to the Present invention wherein the pre-twisting of individual yarns of the core is completely obviated.

As a result of this method of production, the rope 7 has a greater strength for a given cross-section since there is only a small amount of void space in the core. The rope also has greater strength since strength loss due to yarn twisting has been eliminated. The original bands 15 were flat and thin before the crushing action and then they were made into narrow strips of fiat plastic which lie substantially parallel to one another even after they are twisted. Thus, they do not have the undulatory contours of twisted yarns with the inevitable numerous spaces between adjacent yarns. Hence they may be more compactly compressed by the action of the dies as compared with the usual aggregation of pretwisted core yarns. Moreover, since the core strips are disposed substantially parallel to one another and do not lie athwart one another, movement of the rope during use does not cause the internal nicking" or abrading effects that conventionally shorten the useful life of prior art ropes. The core elements move against one another in a longitudinally sliding way, not accross one another transversely.

Since the bands 15 have already been stretched quite a bit prior to incorporation in the core and are not pretwisted, no fabrication stretch is introduced into the core in making the finished rope. The resultant rope is thus characterized by low stretch properties making it highly suitable for tugboats, for example.

The form of the invention just described used as its core constituents highly elongated strips from originally broader bands of plastic material. However, the present invention is not limited to the use of strips or bands in the formation of the compressed, low void-space core. Alternatively, it is possible to make the cord from highly oriented monofilaments of linear isotactic polypropylene. For example, the core might be composed in large part of .013" polypropylene monofilaments which have been stretched to at least 6 and preferably at least 8 times their original extruded length.

The method of making each strand with this alternative core construction would be substantially similar to that illustrated in FIGURE 3. However, those reels containing the bands 15 would be supplanted by reels containing the highly-oriented monofilaments. In all other aspects, the process would be the same as illustrated.

Alternatively, the core constituents need not be monoiilaments but can be substantially untwisted multifilaments of elongated plastic material. Whether the core constituents are monoor multi-filamentary, their cross-section needs not be round. As a matter of fact, to obtain the minimum void space in the core, their cross-sections might be substantially square or triangular, for example.

While the invention has been explained in terms of a marine rope consisting of three twisted strands, the invention is not limited thereto, There may be a y as eight or nine strands, for example, any selected strand having a novel core as described and claimed herein. There can be any desired number of cover yarns, or outer layer yarns, or other yarns disposed around the core, the constitution, arrangement and number of such outer yarns not constituting part of the present invention. It is not necessary that the outer yarns, regardless of their number, present a smooth surface as they can be so made as to have different diameters or different positions as desired. By the same token, ropes employing the present invention may be plaited or square braided in construction, or be of so-called plied yarn construction or cable laid. Furthermore, it is not necessary that the novel core explained herein have a homogeneous construction. In other words, there may be one or more plastic materials in the core, each having different stretch ratios. Additionally, nonsynthetic materials may be interspersed among the fibrous synthetic materials, or disposed in any desired part of the core to achieve desired design objectives.

The plastic materials that can be used for the novel core can be of the nylon, polypropylene, polyethylene, polyester chemical families, or can be made of other synthetic materials such as elongated cellulosic fibers such as rayon, or synthetic materials derived from polyvinyl alcohol, or of other plastic materials. One important requirement for these materials in the first form of the invention explained above is that they be quite fibrous so that the bands will split into narrow strips when subjected to the compressing action of the dies.

If desired, the finished rope or the constituent core bands may be lubricated according to conventional cordage practices.

Since many variations of the invention as disclosed herein, which do not depart from the essence thereof, will occur to those skilled in the art on reading this specification and perusing the drawings, the present invention should be limited only by the claims herein, as follows:

I claim:

1. On a rope, a core for at least one strand thereof comprising: a plurality of compressed and elongated members made of a highly oriented pastic material, sa-id members having a twist substantially determined only by the twist of the strand in which it is disposed, adjacent ones of said compressed members lying substantially parallel to one another.

2. The core according to claim 1 wherein said highly oriented members are made from an extruded thermoplastic material which has been stretched to a minimum of about six times its length after extrusion.

3. In a rope, a core for at least one strand thereof comprising: a plurality of compressed highly oriented plastic bands whose twist characteristic is substantially determined only by the twist imparted to said strand, adjacent ones of said compressed bands lying substantially parallel to one another.

4. In a rope, a core for at least one strand thereof, which core comprises: a plurality of compressed, highly oriented plastic monofilaments whose twist characteristic is substantially determined only by the twist imparted to said strand, adjacent ones of said compressed filaments lying substantially parallel to one another.

5. A rope which comprises:

(a) a core which includes a plurality of highly compressed elongated members made of a plastic material, adjacent ones of said members lying substantially parallel to one another, and

(b) a plurality of yarns disposed around said core.

6. The rope according to claim 5 wherein said plastic members have a draw ratio of at least about six.

'7. The rope according to claim 6 wherein said members have a twist characteristic determined substantially by the twist imparted to the strand.

3. The rope according to claim 7 wherein said plastic members are made from an extruded thermoplastic material which has a draw ratio of at least about six.

9. A rope which comprises:

(a) a core which includes a plurality of bands of a highly oriented thermoplastic material which have been compressed, adjacent ones of said bands lying parallel to one another, and

(b) a plurality of yarns disposed around said core.

10. A rope which comprises:

(a) a core which includes a plurality of filaments made from a highly oriented plastic material, adjacent ones of said filaments lying parallel to one another, said filaments having been compressed together, and

(b) a plurality of yarns disposed around said core.

11. A method for making cordage which comprises:

(a) forming a core by passing a plurality of substantially parallel elongated elements of a highly oriented plastic material through an opening smaller than the aggregate cross-section of said elements, thereby causing said elements to be compressed inwardly upon one another, and

(b) applying a plurality of yarns about said core.

12. The method according to claim 11 wherein said elements are bands of a thermoplastic material said material having been stretched at least about six times in length to render it fibrous and wherein said bands and said yarns are both subjected to a low twist operation.

13. A method for making cordage which comprises:

(a) passing a plurality of parallel filaments of a highly oriented plastic material through an opening smaller than the aggregate cross-section of said filaments tion of the step of subjecting said compressed filaments and said yarns to a low twist operation.

References Cited UNITED STATES PATENTS 1,752,115 3/1930 Sliter 57-138 XR 2,944,379 7/1960 Davis 5731 2,981,052 4/1961 MacHenry 57-31 XR 3,001,354 9/1961 Davis 57-31 3,332,228 7/1967 Chill 57--151 XR 2,217,826 10/1940 Van Laer 57--144 X 2,239,601 4/1941 Forster 57144 2,852,834 9/1958 Englehard 57152 X 2,979,982 4/1961 Weitzel 57144 X 3,089,379 5/1963 Finor et al.

3,090,277 5/1963 Schmittmahn 57144 X 3,129,631 4/1964 Hill et al 57152 X 3,166,885 1/1965 Bridgeman et al. 57-152. 3,287,892 11/ 1966 Rapoza 57-152 FRANK I. COHEN, Primary Examiner. D. WATKINS, Assistant Examiner.

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