METHOD FOR PRODUCING SEAMS ON WEBBINGS FOR TECHNICAL PURPOSES

Abstract

In a method for producing seams on webbings for technical purposes, in particular on lifting straps or lashing straps for securing cargo during transport, a sewing thread is used to produce the seam, the fine strength of said sewing thread being significantly greater than the fine strength of the fibrous material or yam from which the webbing is produced. In this way, the binding load of a webbing having a seam is increased.

Description

This invention relates to a method for producing seams on webbings for technical purposes, more particularly on lifting belts or lashing straps for cargo securement in transit.

Webbings for technical purposes are generally produced from yarns formed from manufactured fibers. The usual choice is for filament yarns composed of polyamide (PA 66), polyester (PES) or polypropylene (PP) which are heat stabilized and light- and aging-resistant and which have a tenacity of at least 60 cN/tex. Connection points, for example at end loops to enclose fitting parts, are stitched by using multiple longitudinal and/or transverse seams to connect together a sheetlike portion in which the webbing parts to be connected together lie on top of each other. The sewing yarn used for this is typically made of the same fiber material as the webbing in order to ensure the same physical and chemical stability. In fact, for particularly demanding applications, such as lifting belts for example, the same tenacity is prescribed for the webbing material and the sewing yarn.

Tensile tests on webbings with seams have shown that the loading limit is determined by the breaking load of the seam, since it is appreciably smaller than the breaking load of the webbings.

It is an object of the present invention to provide a method for producing seams on webbings which provides an increase in the strength and hence the breaking load of the seam.

I have found that this object is achieved according to the present invention by producing the seam using a sewing yarn having a tenacity which is appreciably greater than the tenacity of the fiber material or yarn of which the webbing is made.

The invention is based on the insight that using sewing yarn having a tenacity which is significantly higher, for example twice as high, than the tenacity of the yarn of the webbing provides a significant increase in the load-bearing capacity of the seam, effectively also significantly increasing the loading limit for the webbing provided with seams. It has further been found that the significantly higher tenacity of the sewing yarn has no adverse effects on the strength and also the remaining performance characteristics of the webbing. Tests have further shown that the use of sewing yarn of particularly high tenacity compared with the tenacity of the webbing yarn provides a seam strength which is equal to or greater than the strength of the webbing.

Particularly favorable results in the case of polyester webbings were obtained with a sewing yarn consisting of Dyneema fiber material. Dyneema fiber material is a fiber material of high tensile strength, which includes highly oriented fibers composed of high molar mass linear polyethylene. High molar mass here is to be understood as an average molar mass of at least 400 000 g per mole. Linear polyethylene is to be understood as meaning polyethylene having less than one side chain per 100 carbon atoms, preferably less than one side chain per 300 carbon atoms. The polyethylene may additionally contain up to 5 mol % of one or more other alkenes copolymerizable therewith, such as propylene, butene, pentene, 4-methylpentene, octane.

It is particularly advantageous when the sewing yarn is made of polyethylene fibers consisting of filaments obtained in a gel-spinning process as described in GB-A-2042414 and in GB-A-2051667 for example. This process comprises essentially preparing a solution of a polyolefin of high intrinsic viscosity, spinning the solution into filaments at a temperature above the dissolving temperature, cooling the filaments to below the temperature at which the gel state is attained, and stretching the filaments before, during or after removing the solvent.

To evidence the attainable strength of a seam produced by the method of the present invention on a webbing of polyester multifil yarn having a tenacity of at least 60 cN/tex for the fibers, a thickness of 1.8 mm and a width of 45 mm, the webbing was formed into a loop and the free webbing end of the loop was stitched to the webbing along a length of 80 mm, using seams extending in a zigzag pattern at an angle to the longitudinal direction of the webbing. The sewing yarn used was, in the case of a first sample, polyester multifil yarn having a tenacity of 60 cN/tex and, in the case of a second sample, yarn formed from fibers bearing the trade name Dyneema from DSM High Performance Fibers B.V. having a tenacity of 236 cN/tex. The subsequent tensile tests revealed a breaking load of 19 602 N for the first sample and of 27 291 N for the second sample.

Two further tests were performed using the same webbing and the same sewing yarns, except that the loop was stitched to the webbing only along a length of 40 mm using 12 zigzag seams. In this case, the breaking load was 24 226 N in the case of the sample stitched with the polyester sewing yarn and 28 647 N in the case of the sample stitched with Dyneema sewing yarn.

The results show that breaking load of seams on webbings can be increased appreciably provided that, in accordance with the present invention, the seams consist of a sewing yarn having a tenacity that is multiple times higher than that of the webbing yarn. The load-bearing capacity of the webbing is better utilized as a result. Accordingly, thinner and hence lighter webbings can be used for given load scenarios.

Claims

1. A method for producing seams on webbings for technical purposes, characterized in that the stitching is effected using a sewing yarn having a tenacity which is significantly greater than the tenacity of the fiber material of which the webbing is made, more particularly is at least twice the tenacity of the fiber material of which the webbing is made.

2. The method according to claim 1, characterized in that the tenacity of the sewing yarn is at least four times the tenacity of the fiber material of the webbing.

3. The method according to either of the preceding claims, characterized in that the sewing yarn consists of highly oriented fibers composed of high molar mass linear polyethylene.