Abrasion protection

Details Abrasion protection Abrasion protection

1998-12-18

2001-07-24

Cole, Elizabeth M. (Department: 1771)

Stock material or miscellaneous articles

Hollow or container type article

Polymer or resin containing

Reexamination Certificate

active

06265039

ABSTRACT:

The present invention relates to the use of a fabric sheath, or other article, on a conduit, for example a pipe or flexible hose, to provide abrasion resistance or other forms of protection, for example impact protection or cut-through protection, thereto, and relates to fabric sheaths suitable for such use. One aspect of the invention relates to circumferentially-heat-shrinkable sheaths of woven fabric for use in providing abrasion protection to conduits. The conduits may be fluid or electrical conduits, or other elongate guiding forms, such as electrical wiring bundles or harnesses, or electrical or optical cables.
Mechanical protection of hoses etc. is often found to be necessary because it is difficult to provide all of the desired properties in a single material. For example, a hose must in general be impermeable to fluids, flexible and heat-resistant. The preferred materials for providing those properties often have poor abrasion and cut-through resistance.
U.S. Pat. No. 5,413,149 (Bentley Harris) discloses a flexible, kink-resistant shaped fabric product for protecting and/or covering cables, conduits and wiring etc. The shaped fabric has a wall portion comprising a filament resiliently set in a spiral configuration with respect to the longitudinal axis of the shaped product. The wall portion may also comprise a filament in the form of circumferential hoops substantially conforming in shape and size to the cross-sectional configuration of the shaped product. To achieve the resilient set, thermoplastic filaments are heated to a temperature above their glass transition point and are then cooled to cause recrystalization or “set” of the filaments. The resulting product then has the desired spiral resilient bias. This is stated to be an “elastic memory”. Whilst the products disclosed in U.S. Pat. No. 5,413,149 are satisfactory for many purposes, we have found that it may be difficult to locate the products on the conduit to be protected. In general some fixing means such as a small length of heat-shrinkable tubing will be required at each end of the product.
A further prior art product, known as “Expando”, is also disclosed in U.S. Pat. No. 5,413,149. This product is an open braid that when compressed longitudinally expands radially, and vice versa. It is therefore longitudinally compressed, pushed over a hose to be protected, and then longitudinally stretched. The ends must, however, be secured in position by some additional means.
I have now discovered an alternative approach to abrasion resistance which makes use of heat-shrinkage of a fabric product, and one aspect of the present invention accordingly provides the use of a heat-shrinkable fabric sheath to provide abrasion resistance or impact resistance or cut-through resistance to a conduit, for example a pipe or flexible hose.
It should be noted that, although “heat-shrinkage” makes use of the property of “elastic memory”, the resilient set disclosed in U.S. Pat. No. 5,413,149 does not result in a heat-shrinkable sheath. In fact, since it is a spiral configuration that is locked in by the process of setting, the effect of heat on the prior art product would, if anything, result in its radial expansion. In this respect, and in others, the prior art clearly teaches away from the present invention.
Various fabric designs may be employed in the present invention, but I prefer to use a weave, in particular a plain weave, although other weaves such as a 2/2 twill would be suitable. When using a weave, I prefer that one set of fibres runs substantially parallel to the length of the sheath, and another set of fibres runs substantially circumferentially of the sheath. If the sheath is to be made continuously in line, it will be desirable (at least when using a narrow fabric loom) for the warp fibres to become the longitudinal fibres of the sheath, and the weft fibres to become the circumferential fibres of the sheath.
By using a fabric for abrasion resistance, it is possible to select as circumferential fibres those that are ideal for the provision of heat-shrink properties, and to select for the longitudinal fibres those which are ideal for provision of abrasion-resistance, for example toughness, resistance to notch propagation, low coefficient of friction, impact resistance, and high temperature performance. Such fibres preferably predominate on an external surface of the sheath. Thus, I prefer to use high density polyethylene (HDPE) as the circumferential fibres and to use a polyester, such as polyethylene terephthalate, or a nylon in the warp direction. Other suitable circumferential fibres include polyolefins such as low density polyethylene, medium density polyethylene, polypropylene/polyethylene copolymers and fluoropolymers such as polyvinylidene difluoride (PVDF) and ethylene chlorotrifluoroethylene (E-CTFE). Other suitable longitudinal fibres include polyacryonitrile and copolymers thereof, polyphenylene sulphide, cellulose acetate, aromatic polyamides, eg Kevlar, natural fibres and fluoro polymers. The longitudinal abrasion-resistant fibres are preferably able to flatten-out and/or to move under the influence of an adjacent surface. This ability to flatten-out or to move results in that surface causing less damage to the fibres. To this end I prefer that the longitudinal fibres comprise multi-filament bundles since the filaments within each bundle will be able to move slightly with respect to one another. At present I prefer to use a co-mingled yarn. A further advantage of multifilament bundles is that cut-through of any filament results in less overall damage to the product. The circumferential, heat-shrinkable, fibres may comprise simple monofilaments.
Various preferred characteristics of the product can be achieved by suitable selection of the weave density, weave design, and weaving process. For example, in order to protect the underlying hose against abrasion or cut-through by sharp objects, I prefer that a high-density weave, or weave using fibres of high tex value, be used to achieve a high optical coverage. Optical coverage is a well-known term that simply relates the percentage of a plan view of a fabric that is taken up by the fibres themselves, rather than by the interstices between then. The optical coverage, at least after shrinkage is preferably at least 75%, more preferably at least 95%, most preferably substantially 100%.
A second preferred characteristic of a fabric is that it be ribbed, preferably warp ribbed. This means that the fabric will have a surface relief comprising a series of parallel ribs. If the hose is to be protected from abrasion caused by an adjacent surface moving longitudinally with respect to the hose, it will generally be preferable for ribs to be provided that run circumferentially of the hose. Ribbed fabrics are well understood in the weaving art, and warp ribbed fabrics may be constructed by inserting several weft picks in succession into the same shed of an ordinary plain weave. A warp ribbed fabric will in general be woven with a larger number of ends than picks. The weft yarn generally has less twist than the warp yarn and is of heavier linear density, and if it is a single monofilament it will have zero twist.
Crimp is another characteristic of the fabric that may be considered. Preferably the crimp is predominantly in the longitudinal direction of the sheath.
Although it will depend on the tex value of the fibres, for most purposes the following weave densities will be suitable. 25-60, particularly 35-45 warp ends per cm, and 3-20, particularly 10-15 weft picks per cm. As mentioned above, the circumferential fibres are preferably monofilaments, and the longitudinal fibres preferably comprise multifilament bundles. More particularly, the longitudinal fibres comprise five to ten fold (particularly about seven fold) bundles, each of the fibres within each bundle again comprising a bundle of very fine filaments. Each of the folds is preferably 10-20 tex, (preferably about 17 tex (tex being the ISO standard for linear density of textile strands and is the weight in grams of

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