Bowstring

Description

[0001] The invention relates to a bowstring made wholly or mainly of synthetic filaments, whether or not bundled into threads.

[0002] Synthetic bowstrings are known and are often applied in archery. Examples are bowstrings on the basis of polyesters, such as a polyethylene terephthalate marketed by Du Pont under the name Dacron, and bowstrings on the basis of aromatic polyamides, such as an aramide product marketed by Du Pont under the name Kevlar.

[0003] It has been found that bowstrings from Dacron have a long life, but exhibit the disadvantages of a high elongation and low arrow velocity. Bowstrings from Kevlar, on the contrary, are found to break rather quickly, for instance after 1000-1500 shots, while, on the other hand, the elongation still is substantial and the arrow velocity not yet really high.

[0004] The present invention provides a bowstring that, on the one hand, exhibits an extremely low elongation and a very high arrow velocity, while on the other hand, it has an extraordinarily long life.

[0005] The invention therefore relates to a bowstring comprising a number of synthetic filaments, whether or not bundled into threads, that is characterized in that use is made of filaments having a tensile strength of at least 2 GPa and a modulus of at least 20 GPa on the basis of polyethylene having a weight-average molecular weight of at least 4 ^x 10⁵ kg/Kmol.

[0006] In the present invention use can be made in particular of filaments obtained by converting a solution of linear polyethylene having a weight-average molecular weight of at least 4 ^x 10⁵ kg/Kmol by thermoreversible gelation into a homogeneous polyethylene gel of virtually the same composition as the solution started from, and stretching this gel at a stretch ratio of at least 10.

[0007] The preparation of such filaments is disclosed in, for instance, US-A-4,344,908; US-A-4,422,993; US-A-4,430,383; US-A-4,411,854 and US-A-4,436,689.

[0008] In the present invention a number of filaments is often bundled into threads, upon which a number of threads is wound into a string, for instance on a string board. The number of threads for the string is determined by the desired drawing force of the bow and generally amounts to 8-20, the number of filaments used generally being 1000-3000, depending on filament thickness. The length of the string is determined by the bow length and is generally chosen to be 5-10 cm smaller than the bow length.

[0009] The string is in the usual way provided with servings and a middle serving, for instance on a string board, and is often treated with a wax, such as beeswax, to ,keep the threads together.

Example

[0010] A bowstring on the basis of polyethylene filaments according to the invention was tested on a longbow during some months. After more than 5000 shots the string exhibited no deterioration in strength or increase in elongation, while the original, very high arrow velocity was fully retained.

Claims

1. Bowstring comprising a number of synthetic filaments, whether or not bundled into threads, characterized in that use is made of filaments having a tensile strength of at least 2 GPa and a modulus of at least 20 GPa on the basis of polyethylene having a weight-average molecular weight of at least 4 ^X 10⁵ kg/Kmol.

2. Bowstring according to claim 1, characterized in that use is made of polyethylene filaments obtained by converting a solution of a linear polyethylene having a weight-average molecular weight of at least 4 ^x 10⁵ kg/Kmol by thermoreversible gelation into a homogeneous polyethylene gel of virtually the same composition as the solution started from and stretching this gel at a stretch ratio of at least 10.

3. Bowstring substantially as described.