GB2096658A

GB2096658A - Glass fibre yarns

Info

Publication number: GB2096658A
Application number: GB8111360A
Authority: GB
Original assignee: TBA Industrial Products Ltd
Current assignee: TBA Industrial Products Ltd
Priority date: 1981-04-10
Filing date: 1981-04-10
Publication date: 1982-10-20

Abstract

A yarn comprises a textured continuous filament glass fibre yarn with at least 1.5% retained overfeed and one or more metal and/or organic filaments. The metal wires may be added to the glass fibre strands as they pass into the texturing jet, or they may be added during the twisting operation given to the yarn. The wires may be added either as a core to the yarn or as a wrapper lying in a helical path around the twisted glass yarn. The organic fibres may be added by passing them as continuous filaments with the glass fibres through the texturing jet, or one may ply or double one or more ends of organic fibre yarns with one or more ends of textured glass yarn (staple organic fibres may be added in this method). Particular applications mentioned are as clutch facings and as friction linings.

Description

SPECIFICATION Improvements in or relating to glass fibre yarns This invention relates to glass yarns, and in particular to glass fibre yarns which are especially suitable for use in clutch facings and in friction linings incorporating woven fabrics made from such yarns.

It is known to make clutch facings from conventional glass fibre yarns produced by textile twisting and plying operations from either continuous glass fibre filaments or from staple glass fibre filaments. Yarns containing continuous glass fibre filaments have relatively tight compact structures with little space between individual filaments and between the twisted bundles of filaments comprising the ply structure of the yarn.

Such yarns cannot absorb and retain large quantities of impregnant solutions, and, unless the impregnant has a low viscosity, very little penetration of the impregnant into the bundles of filaments occurs. Clutch facings manufactured from such continuous filament based yarns show many loose unimpregnated fibres projecting from the surfaces which have been ground or turned thus making dimensional tolerances difficult to maintain. However, continuous filament glass fibre yarns possess much greater strength than staple glass fibre yarns and enable the production of clutch facings of high burst strength (the speed at which the facing may be rotated before disintegrating under the action of centrifugal forces).

Yarns containing staple glass fibres have bulky structures with relatively large spaces between individual fibres and many fibre ends protrude from the yarn surface. Such yarns can absorb relatively large quantities of impregnant solutions and excessively dilute solutions are not required for penetration into the centre of the yarn.

Adhesion between adjacent yarns is excellent and the facings may be satisfactorily ground or machined. Clutch facings containing staple filament glass fibre yarns are generally of lower strengths than facings containing continuous glass fibre yarns. A further disadvantage of staple glass fibre yarns is that broken fibres fall out of the yarn during impregnation resulting in contamination of the impregnant bath which increases the viscosity of the impregnant and reduces its penetration into the yarn. The atmosphere surrounding the impregnation apparatus also becomes contaminated with these broken fibres, commonly known as 'fly'. Staple glass fibres are normally tapered and, if broken, short fibres of respirable diameter may be produced thus causing a potential hazard to health.Clutch facings incorporating improved glass yarns with rough or "open" surfaces comprising continuous glass fibre filaments, staple glass fibre filaments or combinations of the two are described for example in published UK patent specification No. 2039 557 A.

One such yarn has projecting loops where one group of strands is wrapped around another group of strands and the whole yarn is overwrapped with a fine thead, loops being produced by overfeeding the wrapping group of strands.

Loop structure yarns are made wholly from continuous filaments and have high strength whilst retaining relatively large quantities of impregnant solutions. Strong clutch facings may be manufactured from such yarns but viscous impregnant solutions are retained in the relatively large loops and surface interstices without penetrating between the closely packed filaments in each strand of the yarn.Two stage impregnation, as described in published UK Patent specification No. 2,033,443. where the yarn is first impregnated in a dilute solution of thermosetting resin which can penetrate between individual glass filaments, dried to remove solvent and then reimpregnated with a more viscous solution or dispersion of thermosetting binder cement, is'desirable with these yarns, to prevent bundles of unimpregnated glass filaments remaining in the yarn and projecting from ground or machined surfaces of facings made from them.

We have found that improved yarns may be manufactured from textured continuous filament glass fibres and that such yarns possess improved properties for certain purposes such as the reinforcement of friction materials.

Thus, according to the present invention a yarn comprises a textured continuous filament glass yarn into which at least 1.5% of retained overfeed has been introduced during texturing, together with one or more metal filaments and/or organic filaments.

Continuous filament glass yarns may be textured, for example, by the action of a turbulent air jet to produce yarns of increased bulk which posses the relatively high bulk of staple fibre yarns but with higher strength and at reduced cost. In the texturing process one or more strands, each comprising a multitude of parallel, fine continuous glass filaments coated with a size which holds the bundle of filaments together are passed through a turbulent air jet in which the size coating is broken, allowing the individual filaments to separate from the strand and then become tangled together to produce a relatively open, bulky structure in which individual filaments are no longer parallel to each other.The strands are fed into the texturing jet at a higher speed than that at which they are withdrawn from the jet, the excess material being converted by the turbulent air stream to loops and waves, which become entangled with each other to create the desired bulk. The amount of texture introduced into a yarn may be measured by comparing the weight of a given length of yarn before texturing with the same length of yarn after texturing, the percentage increase in weight of the given length of yarn being called the 'percentage retained overfeed'. A lightly textured yarn, in which the glass filaments are separated from the original strand but remain relatively straight would have a retained overfeed of about 0.5% whereas a heavily textured yarn, in which the filaments lie in wavy paths and are highly entangled to produce a bulky yarn, would have a retained overfeed of over 10%.The retained overfeed can be varied by changing the overfeed applied, air pressure, windup tension, in a known manner.

Yarns with relatively large amounts of retained overfeed tend to exhibit excessive liquid retention when impregnated during futher processing into friction materials. It is thus preferred that the yarns used in the present invention have a retained overfeed of no more than 9% and preferably no more than 6%. If desired, the stands may be twisted, individually or together, before being subjected to texturing.

Impregnant pick-up in further processing may be reduced to a lower desired level for a particular yarn by consolidating the yarn by twisting prior to impregnating. The twist required is determined by the bulk and tex of the original textured yarn. As the cost of a twisting operation increases with the twist level and the twist levels required to reduce the pick-up of higher-bulk yarns to acceptable levels tend to render the yarn 'twist lively', necessitating doubling to obtain stability, a further expensive step, it is preferred to operate at lower levels of bulk and twist.

A commonly used concept in the textile industry is that of 'Twist Factor'. This is defined as the product of the twist level (usually in turns per metre) and the square root of the tex. Yarns of different tex having the same twist factor tend to have very similar properties in respect to bulk, liveliness, specific strength etc, and thus tend to behave similarly during impregnation. For airtextured glass yarns with approximately 3% retained overfeed we prefer to operate at twist factors within the range 1000-3000.

It has been found that the presence of one or more metal filaments in air textured yarns improves the friction and wear characteristics of clutch facings produced from such yarns, suitable wires being those which have been used in conventional asbestos based clutch yarns e.g.

copper, brass, bronze and zinc, but wires made of other metals may be used if desired. Metal wires of very small diameters may be added to the glass fibre strands as they pass into the texturing jet but it is more convenient to add the usual thicknesses of wire e.g. about 36 swg as employed in asbestos yarns, during the twisting operation given to the yarn. One or more wires may be added, either as a core to the yarn with the glass distributed around the wire or as a wrapper lying in a helical path around the twisted glass yarn. Impregnant pickup and penetration may be reduced by wrapping the wire around the glass, pickup depending upon the amount of twist in the final yarn and on the tension in the wire: if maximum pickup of penetration is required, wrapper wire tension and yarn twist should be kept to a minimum.Two or more fine wires may be used as wrappers instead of one thicker wire and may be placed side by side or spaced apart, spaced wrappers reduce impregnant pickup compared to side by side wrappers but friction facings made from spaced wrapper yarn shown a more uniform distribution of wire in their surfaces.

Wire may also be wrapped around a textured glass strand by using a conventional wrapping machine to produce a bound strand comprising an untwisted core of textured glass fibre filaments helically wrapped with one or more wires. The glass core is again consolidated by the action of wrapping it with wire and yarns with satisfactory impregnation characteristics may be manufactured by this process.The wrap frequency of the wire may be higher using this process than by twisting the glass and wire together whilst still maintaining satisfactory impregnation properties e.g. in one experiment, the use of one end of 1 800 tex textured glass yarn wrapped at 120 turns per metre gave an impregnant pickup of 135% by weight whereas a satisfactory twisted yarn could not be made at 120 turns per metre because it was too twist lively and too tightly consolidated to process properly. Bound strand yarns with opposed helical wire wrappers have been made but impregnant pick-up is lower than when only one wire is used.

Organic fibres may be incorporated into these yarns, if desired, to modify friction, wear and density characteristics of friction facings by (a) passing continuous filament organic fibres and glass fibre strands through the texturing jet to produce a textured yarn in which the fibres are intimately mixed or (b) plying or doubling one or more ends of organic fibre yarns with one or more ends of textured glass fibre yarn, the fibres in the resulting yarn not being as well mixed together as in (a) although staple organic fibres may be added by this method. Organic fibres which decompose without melting are preferred.

Suitable infusible organic fibres are natural or regenerated celluldse fibres e.g. cotton, jute, hemp, sisal, rayon, phenolic resin fibres and aromatic polyamide or aramid fibres. If the infusible fibre is to be textured with the glass fibre then it must be available as continuous filaments, thus excluding natural staple cellulose fibres which may only be added as yarns during a doubling or plying operation or during the impregnation stage.

The inclusion of organic fibres in textured glass fibre yarn based friction facings can be advantageous because it enables the facing density to be reduced and hence the inertia of the clutch friction plate to be minimized. The friction levels and fade performance of friction materials made from these yarns may be modified by the inclusion of suitable quantities of either fusible or infusible organic fibres in the yarn. The addition of fusible organic fibres appears to be a useful method of improving the fade resistance of clutch facings containing glass fibres.

Textured glass fibre yarns containing glass fibres alone, glass fibres and metal wires or glass fibres and organic fibres with or without the addition of metal wires may be used to weave fabrics which, after impregnating with binders, are suitable for use as friction elements in clutches or brake mechanisms. Typical impregnants include solutions of thermosetting resins, elastomers and asphalt or similar pitch like materials and also drying oils.

The proportion of metal filament(s) incorporated into the textured glass yarn may be from 0 to 40% of the total weight of the yarn although we prefer to use proprortions of between 5% and 30% of the yarn weight. The incorporation of high proportions of dense metal wires such as copper or brass results in the production of excessively high density facings unless large amounts of organic fibre are also incorporated into the yarn. The proportion of organic fibres incorporated into the textured glass yarn may be from 0 to 100% of the weight of glass present in the yarn, the preferred proportion of heat fusible organic fibres being 1-1 5% of the weight of glass present in the yarn and the preferred proportion of infusible organic fibres being 1 0%-67% of the weight of glass present in the yarn.

In order that it be better understood, the invention will now be described by way of example only, with reference to the following Examples: Example 1 One end of 1800 tex air jet textured glass yarn with a retained overfeed of 3% was twisted with one end of 36 swg copper wire as a wrapper to give a twist of 68 turns per metre in the final yarn.

Three ends of this yarn were impregnated with a conventional styrene butadiene rubber/phenolic resin impregnant to give an impregnant pickup of 101% by weight of dry solids. Clutch facings were manufactured from the impregnated yarn, using a random winding pattern and press curing.

The finished facing density was 2.09-2.16 g/ml The burst strength of 8"x5i" drilled facings at 2000C was 12000-14000 rpm.

Example 2 1600 tex glass fibre strand and 250 tex viscose rayon were passed together through an air texturing jet to produce a textured yarn with a retained overfeed of 3% one end of which was twisted with one end of 36 swg brass wire as a wrapper to produce a yarn with a twist of 68 turns per metre. Three ends of yarn were impregnated together as in Example 1, resulting in an impregnant pickup of 103% by weight.

Clutch facings were then manufactured from this yarn as described in Example 1.

The finished facing density was 1.95-2.0 g/ml.

The burst strength of 8"x5i" drilled facings at 2000C was 1 1500--12600 rpm.

Example 3 One end of a 1650 tex air jet textured glass yarn with a retained overfeed of 3% was twisted with three ends of 109 tex continuous filament polyester yarn and one end of 36 swg brass wire as a wrapper to produce a yarn with a twist of 50 turns per metre. Three ends of yarn were impregnated together as in Example 1, resulting in an impregnant pickup of 122% by weight and made into clutch facings, also in Example 1.

The finished facing density was 1.87-1.94 g/ml.

The burst strength of 8"x5i" drilled facings at 2000was 12,200-13,400 rpm.

Example 4 One end of 1800 tex air jet textured glass yarn with a retained overfeed of 3% was twisted with four ends of 54 tex 'Kynol' (R.T.M.) phenolic resin staple fibre yarn and one end of 36 swg brass wire as a wrapper to produce a yarn with a twist of 68 turns per metre. Three ends of this yarn were impregnated together as in Example 1, resulting in an impregnant pickup of 106% by weight, clutch facings being manufactured from this yarn, as in Example 1.

The finished facing density was 2.00-2.03 g/ml.

The burst strength of 8"x5i" drilled facing at 2000was 1 1500--12100 rpm.

Example 5 One end of 1860 tex air jet textured yarn comprising 7 ? 71% glass fibre and 29% viscose fibre was twisted at 40 tpm, a 36 swg, copper wire being applied as a wrapper at the twisting stage.

Three ends of this yarn were impregnated together as described in Example 1 to give an impregnant pickup of 110% by weight. The yarn was then made into clutch facings, also as in Example 1.

The finished facing density was 1.9-i 1.98 g/ml.

The burst strength of 8"x5+" drilled facings at 2000C was 10,500-11,500 rpm.

Claims

1. A yarn comprising a textured continuous filament glass yarntinto which at least 1.5% of retained overfeed has been introduced during texturing, together with one or more metal filaments and/or organic filaments.

2. A yarn according to claim 1 wherein the retained overfeed is in the range of 1-5 to 6%.

3. A yarn according to claim 1 or 2 in which the metal filament constitutes from 0 to 40% by total weight of the yarn.

4. A yarn according to any of claims 1 to 3 wherein the metal filament constitutes from 5 to 30% the total weight of the yarn.

5. A yarn according to any preceding claim containing organic fibres in the range 0 to 100% by weight of the glass fibre component.

6. A yarn according to any preceding claim containing from 1 to 1 596 of heat fusible organic fibres and from 10 to 67% of infusible organic fibres, both referred to the weight of the glass fibre component of the yarn.

7. a yarn substantially as described with reference to any of the examples.