US 3078755 A
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Feb. 26, 1963 A. F. CHACE, JR
BRAIDED CORDAGE Filed Jan. 27, 1961 United States Patent sachusetts Filed Jan. 27, 1961, Ser. No. 85,309 3 Claims. (Cl. 87-9) This invention relates generally to cordage, and more particularly it concerns a cordage construction especially useful for marine usage. This application is a continuation-in-part of my copending application Serial No. 2,188, filed January 13, 1960, now abandoned, which is a continuation-in-part of my prior application Serial No. 785,834, filed January 9, 1959, now abandoned.
It is a general object of the invention to provide cordage which incorporates the best features of two different materials but has none of their disadvantages.
It is another object to provide a stronger and longer wearing cord or rope of the above-mentioned character which does not have undesirable properties such as excessive elongation under load and poor wear resistance.
A still further object is to provide a braided cord or rope of the above-mentioned character which is spliceable.
Cordage must meet several different requirements. First of all, the cord, rope or line (herein called cord) must have good handling qualities so that, for example, it can be coiled easily without kinking and will work well over pulleys. Secondly, it should have good resistance to the elements especially sunlight and moisture since it may be left out in the open and in the water a good deal of the time. Elongation under load is another important factor especially where the cord is to be used for halyards, sheets and stays, just to name a few applications. Finally, the stronger and longer wearing is the cord, the better, and to this end it must have good resistance to abrasion.
Hitherto common materials used for the manufacture of cordage have been cotton, manila and hemp. Cotton has a good hand and is relatively cheap but it is not very strong. Also, repeated wetting and drying of cotton cord tends to weaken it, and ultimately causes it to rot out. Cordage made from manila fiber or hemp has fairly good strength but does not have a very desirable hand because of its hairy surface. A related defect is that it is subject to deterioration through abrasion. Finally, it is subject to rotting which, as in the case of cotton cord, is accelerated considerably by repeated wettings. Orlon, a synthetic fiber manufactured by E. I. du Pont de Nemours & Company, has been used aboard boats but it has proven completely unsatisfactory. The reason is that it has very poor resistance to abrasion although it is very strong otherwise.
The materials that have proven most successful are nylon and Dacron which, as is well known, are synthetic fibers also manufactured by E. I. du Pont de Nernours & Company. Of the two, Dacron is used much more extensively because it is less elastic than nylon and has appreciably greater resistance to abrasion and sunlight. However, it is not as strong as nylon and costs appreciably more.
One Dacron construction that has been widely used embodies a core of parallel strands for strength, together with a covering of braided strands which affords a desirable hand. A disadvantage of cord with a parallel strand core is that the strain on the individual elements is not at all evenly distributed when the cord is used over pulleys and the like. More particularly, the filaments that are more remote from the center of the pulley must traverse a longer path length and consequently 3,078,755 Patented Feb. 26, 1963 they are strained a good deal more than the filaments that pass close to the pulley. For this reason it has been a common practice to provide sash cord, for example, with twisted core strands which, on the average, are located equidistant from the center of the radius of curvature of any pulley over which they may be passed. However, a twisted cord has internal torsional stresses which produce a noticeable effect when the cord itself is twisted, for example in coiling.
A braided construction has neither of the aforementioned disadvantages of a parallel or spiral construction. Except for covers, braided constructions have not been used extensively, however, because of strength considerations. That is to say, in any construction where individual filaments are arrayed at an angle to the direction of stress, it has been assumed that they do not act to bear load nearly so well as when they are stressed axially. I have found a way, however, to construct a braided cord that is equally as strong as or stronger than any other type of cord or rope known to me which is suitable for marine use. In addition to its being extremely easy to coil and handle generally, the cord according to my invention has. much better wearing qualities than other cord fit for this usage and also, in a preferred form, it is spliceable.
The novel features of my invention together with further objects and advantages thereof will become apparent from the following detailed description and the drawing to which it refers.
In the drawing:
FIG. 1 is a view in elevation of the cord construction according to my invention with the cover broken away in part to show the inner or core portion more clearly; and
FIG. 2 is a sectional view taken on line 2-2 of FIG. 1.
As shown in the drawing, I make use of a plurality of core strands 11 that are loosely braided together, and a plurality of cover strands 12' that are more tightly braided. In the preferred embodiment illustrated, both the core element 11 and the cover element 12 have eight strands although this is by no means a critical requirement. What is of crucial importance, however, is the fact that the material used for the core strands is nylon or other higher elongation filaments having similar characteristics, such as poly-vinyl alcohol and polyolefins, while the material used for the cover strands is filaments of lower elongation than those of the core, such as Dacron or other similar polyester filaments. The explanation is as follows. Nylon is much more elastic (i.e., more readily elongated) than Dacron, however, owing to the fact that the nylon core strands according to the invention are relatively loosely braided so that their constituent filaments run more nearly parallel to the axis of the cord, the core considered as a whole is much less elastic (i.e., less readily elongated) than it would be otherwise. Conversely, the relatively tight braid of the cover strand-s causes the cover to exhibit a markedly more pronounced elastic (i.e. elongation) quality than would a loosely braided cover. This is a for-tuitous situation because the tightness of braid of the cover is primarily responsible for the desirable hand of the cord, while the looseness of braid of the core permits the natural strength of the individual core filaments to be more nearly realized. In fact, I have found that a loosely braided arrangement of stranded filaments is actually stronger than a parallel arrangement even for straight runs. The reason appears to be that as a pra tical matter it is impossible to achieve a perfectly parallel alignment of a bunch of filaments, with the result that some are stressed disproportionately unless they are free to align themselves longitudinally in the same direction 3 as the others. A braided construction affords this freedom of action of the individual make up a strand.
What is meant by a tight braid for the cover is a braid having a pick ratio in the range two to five, and what is meant by a loose braid for the core is a pick ratio in the range six to fifteen, with the cover strands contributing approximately half the bulk of the cord, that is half the volume of filaments per unit of length. With such dimensional criteria as these, both core and cover work together under load and there is realized from the cover a substantial portion of the cords total load-bearing capacity. This is in addition to the tightly desirable prop erties which the cover affords with respect to hand and resistance to abrasion and the elements, especially sunlight. When the cover has a pick ratio within the range of 2.7 to 5 and the core has a pick ratio in the range 6-8, still another highly desirable feature of cord constructed in accordance with the invention is that it can be spliced.
The term pick ratio of a braided element as used herein means the number of picks per revolution of the braider divided by (the number of picks per inch times the diameter in inches of the braid). For a hollow braid of eight strands as used herein, each revolution of the braider or cycle produces four picks lengthwise of the braid. Hence, the pick ratio for an eight-strand braid may be written where F is the pick ratio, P is the number of picks per inch measured lengthwise of the braid, and D is the braid diameter in inches. As is well known to those skilled in the art, all measurements are to be taken with the cord under the standard tension of 200' D pounds, where D is the diameter of the cord in inches. In FIG. 1 of the drawing, D indicates the diameter of the cover, d the diameter of the core, P indicates the length of a single pick in the cover and p the length of a single pick in the core, all as is well understood in the art.
By way of example, a one-quarter inch cord according to the invention may comprise a core of eight strands, each strand being made up of two twisted ends of 840 denier, 6 ply nylon. In the cover, where a corresponding number of strands are provided, each strand preferably comprises two twisted ends of 1100 denier, 6 ply Dacron. Both the core and cover strands are manufilaments that go to factured in the usual way, namely the yarns are plied once in a twisting machine to form the ends which are then wound parallel in a winding operation to make up the strands. Such a cord has a breaking strength of at least 2000 pounds, which value is only slightly less than that of an all-nylon cord. The former will last appreciably longer under field conditions, however, and as aforementioned, it will not suffer the disadvantage of elongating excessively under load as does conventional all-nylon cord. Rather, it has elongation characteristics roughly equivalent to a cord made from manila fiber or hemp. As compared with an all-Dacron cord, my cord is thirty to forty percent stronger as well as being substantially longer wearing.
Therefore, what is claimed is:
l. A braided cord comprising a braided core and a more tightly braided cover surrounding the core, said cover and said core each consisting of filaments arranged in separate strands braided together to form an interlocked bundle, the elongation of the filaments of said core being greater than the elongation of the filaments of said cover, said core braid having a pick ratio in the range of 6 to 8, and said cover braid having a pick ratio in the range provides approximately half of the bulk of said core and cover.
2. The braided cord of claim I wherein the filaments of said cover are polyester filaments.
3. The braided core of claim 2 wherein the filaments of said core are nylon filaments.
References Cited in the file of this patent UNITED STATES PATENTS 2.7 to 5, and wherein the cover braid UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,078,755 February 26, 1963 Arthur F Chace, Jr.
It is hereby certified that error appears in the above-numbered patent requiring correction and that the said Letters Patent should read as corrected below.
Column 3, line 13, for "tightly" read highly same column 3, lines 29 to 30, the equation shoul' appear as shown below instead of as in the patent:
Signed and sealed this 24th day of September 1963.
ERNEST w. SWIDER DAVID LA Attesting Officer Commissioner of Patents