GB2058280A

GB2058280A - Reinforced Tubular Articles

Info

Publication number: GB2058280A
Application number: GB8020923A
Authority: GB
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1979-07-17
Filing date: 1980-06-26
Publication date: 1981-04-08
Also published as: IT8023427A0; GB2058280B; IT1149841B

Abstract

A method of making a hose comprises applying to a polymeric inner liner, e.g. of rubber or plastics, at least one reinforcement layer, and then fully impregnating the layer or layers with a liquid elastomer-forming reaction mixture. The method may be suitable for use in the production of hydraulic hose. The liner may be a nitrile, chlorinated polythene, silicone, or polyester/polyether block rubber or nylon. The reinforcement layer may be polymeric glass or metal. The elastomer-forming reaction mixture may be polyurethane, silicone or an epoxy combined with an amine-tipped butadiene/acrylonitrile copolymer rubber.

Description

SPECIFICATION Reinforced Tubular Articles This invention relates to an improved method for making a reinforced tubular articles such as a hose.

According to the present invention, a method of making a reinforced tubular article comprises applying to a tube of polymeric material which will form the inner liner of the article at least one layer of material to provide reinforcement in the article and then fully impregnating the layer or layers with a liquid elastomer-forming reaction mixture.

The method of the present invention is particularly applicable where an inner liner is provided with a plurality (at least two) of reinforcement layers and these reinforcement layers are then impregnated in a single operation. "Fully-impregnating" means that the interstices of the reinforcement are substantially filled with impregnant and "fully impregnated" is to be construed accordingly.

One application of the method is in the manufacture of substantially flexible heavy duty hose, e.g.

hydraulic hose, which may have a burst pressure of 10.341 MN/m2 (1500 psi) or higher. (Ref: Society of Automotive Engineers publication "Tube, Pipe, Hose and Lubrication Fittings-Standards, Recommended Practices, Information Reports". Handbook Supplement HS 150, 1977 Edition). In such a construction the density of the reinforcement is usually relatively high, e.g. at least 60% and preferably, at least 75% coverage. Previously known methods of making this type of hose where a plurality of reinforcement layers has been used have necessitated a non-porous polymeric insulation layer between the layers of reinforcement, mainly to prevent chafing. The need for such an insulation layer may be obviated if the method of the present invention is adopted since the complete impregnation of the interstices may substantially reduce or even prevent this chafing.

One way to make a cheaper hose could be to reduce the wall thickness of the inner liner to a minimum. Unfortunately, in hoses produced by known methods there is often air in the interstices of the reinforcement and if the inner liner is too thin the hose may fail due to the inner liner expanding into these interstices. This disadvantage may be overcome by use of the method of the present invention in that, because full impregnation can be achieved, it is feasible to reduce the thickness of the inner liner.

The inner liner is impervious to the impregnant and may be of an elastomeric material (e.g. a vulcanised rubber such as nitrile rubber, chlorinated polyethylene rubber or silicone rubber, or a thermoplastic rubber such as a polar elastoplastic linear block copolymer containing polyester and polyether blocks available as 'Hytrel' from Du Pont) or a thermoplastic plastics material (e.g. a nylon such as Nylon 11).

The reinforcement may be of a textile material such as nylon, a homo- or co-polymer of propylene, rayon, an aromatic polyamide (e.g. as available under the trade name Kevlar) or a polyester, or of glass or of a metal such as brass-coated steel wire. The reinforcement may comprise axial and spiral components which may be layered, woven, knitted or braided to produce a balanced construction. Alternatively, the reinforcement may be applied by spiral winding.

If desired, a material e.g. a textile scrim, permeable to the liquid elastomer-forming impregnant used may be provided between layers of reinforcement and/or between the inner liner and the reinforcement layer or layers.

The impregnant is an elastomer-forming reaction mixture which is liquid at the temperature of impregnation and comprises ingredients which will chemically react and set to form an elastomer. The impregnant may be one which will produce a polyurethane elastomer or a silicone rubber or it may be a functional-group-tipped liquid polymer e.g. an amine-tipped butadiene/acrylonitrile copolymer rubber (e.g. as available under the trade name Hycar from B. F. Goodrich) in combination with a suitable coreactant such as an epoxy resin. The impregnant may contain other additives e.g. at least one additive selected from plasticisers, extenders, pigments and surface tension modifiers.An example of a polyurethane-forming reaction mixture is one comprising a relatively high molecular weight polyol, a relatively low molecular weight diol, an isocyanate and optionally a catalyst, which will react to form a polyurethane e.g. those quick-cure polyurethane-forming compositions described in the specification of our co-pending British Patent Application No. 35493/76 which comprise a liquid poly(propylene glycol) polyol having a molecular weight of more than 400, a liquid low molecular weight diol having a molecular weight less than 250, a liquid di(isocyanatophenyl) methane and a catalyst selected from stannous salts of carboxylic or mineral acids that are either in liquid form or are soluble in the polyols.

The viscosity of the impregnant at the temperature of impregnation should not be too high, otherwise a substantially complete impregnation will prove difficult to achieve. Preferably the viscosity will be less than 10 Ns/m2 (10,000 centipoise), more preferably less than 5 Ns/m2 and advantageously less than 1 Ns/m2, at the impregnating temperature. In determining a suitable viscosity for the impregnant the texture of the reinforcement will usually be taken into account as an open-textured reinforcement will obviously accept an impregnant of higher viscosity than will a close-textured one. One advantage of the method of the present invention is that it is not usually necessary to apply external pressure (e.g.

by evacuating the vessel containing the impregnated article), other than any pressure due to the presence of the impregnant itself, in order to ensure complete impregnation.

After application to the reinforcement material, the liquid impregnant reacts and sets, this will usually be aided by the application of heat. Heat may be applied before, during and/or after the impregnation. If desired a further reinforcement layer can then be applied to the assembly and the impregnation repeated.

Preferably the impregnation is carried out by passing the inner liner/reinforcement assembly through an impregnation vessel. One way to obtain the desired degree of impregnation of the reinforcement material is to apply at least one reinforcement material layer, e.g. as a braid, to a tube of inner liner material and then to pass the resulting tubular article vertically down through an impregnation vessel and out through an orifice in the vessel beneath the impregnant level, which may also serve to remove excess impregnant from the assembly. If desired the impregnant can be set and then the assembly passed up through the impregnation vessel so as to apply a coating either of the same or of a different material to the impregnant.

The inner liner/reinforcement assembly may be substantially self-supporting i.e. will substantially retain its cross-sectional shape during impregnation without the use of a mandrel. Alternatively it may be desirable to use a mandrel or to pressurise the article from within in order to support it e.g. where the end product may be a "lay flat" hose.

One embodiment of the present invention will now be described by way of example only with reference to the accompanying Figure which is an elevational cross-section of the impregnation of an inner liner/reinforcement assembly.

An impregnation vessel 1 has an orifice 2 provided with a rubber seal 3 sized so as to allow passage of a tubular assembly 4 whilst preventing escape of impregnant 5 from the vessel. The tubular assembly 4 comprises an inner liner 6 encased in one or more reinforcement layers 7. In use, the tubular assembly 4 is pulled down through the impregnant and out of the vessel 1 through the seal 3 which also serves to remove excess impregnant from the assembly 4. If desired the assembly 4 may be provided with a coating or coatings either of the same or different material to the impregnant e.g. by pulling the assembly vertically up through the impregnation vessel 1. The impregnant may be heat-set by means of hot air applied to the assembly before, during and/or after impregnation.

After impregnation of the reinforcement and either before or after the setting of the impregnant and outer cover, e.g. of an elastomeric material, may be applied to the assembly e.g. by the technique of the preceding paragraph or by the extrusion technique.

One aspect of the present invention is illustrated by the following Examples in which the impregnation was carried out in the apparatus shown in the accompanying Figure.

Example I A nylon tube having an internal diameter of 6.3 mm and external diameter of 9.4 mm was covered with two layers of braided brass-plated steel wire to give an assembly having an internal diameter of 5.5 mm. The wire, which has a diameter of 0.305 mm, was applied from a conventional braiding machine.

A 1.3 m length of this product was washed by immersion in dichloromethane and, after drying, was threaded through a rubber seal in the bottom of an open-topped 300 ml capacity metal container so that 40 mm protruded below the seal. The temperature of the tube was raised to 40-450C by passing hot air through it.

The following polyurethane-forming composition was mixed and poured into the container, around the braided nylon tube:- Propylan D-2122 (ex Lankro)2 75.0 g Ethane diol' 9.3 Anhydrous stannous chloride1 0.75 Pigment dispersion 3373 ex Chemical Products (Cheshire) Ltd. 3.0 Liquid silicone (available as Silicone DC 200, 50 Centistokes from Dow Corning) 0.3 Isonate 1 43L (ex Upjohn)3 60.0 1The stannous chloride was dissolved in the ethane diol before mixing with the other ingredients.

2Ethylene oxide-tipped poly(propylene glycol) diol of molecular weight 2000.

3Liquid mixture of pure M.D.I. and a carbodiimide adduct of M.D.I.

This composition has an initial viscosity of 0.239 Ns/m2 at 21 C measured with a Brookfield viscometer, Model LVF, using Spindle No. 1 at 12 r.p.m. None of the ingredients were dried and therefore the Propylan and ethane diol would be expected to contain a small proportion of water.

The hose was then pulled down, through the seal, at a speed of about 14.2 mm/sec while the mixture was being stirred, until only approximately 150 mm remained above the seal. After 20 minutes the liquid composition had reacted and set to a solid elastomer and the container and residue were cut away from the hose.

This process was repeated but in the reverse direction, i.e. pulling the hose upwards, to apply a further thin coat of polyurethane on the outside of the construction. This coating procedure was repeated twice more to build up a coating thickness of approximately 0.5 mm.

After being left to stand for 7 days, suitable connections were fitted to sections of the resulting hose. A sample was subjected to impulse testing using a square wave impulse pressure of 43.98 MN/m2 at a frequency of 60 impulses/minute with hydraulic fluid at 930C.

The sample had not failed after 333,300 impulse cycles and had a burst pressure of 227.5 MN/m2.

Example II A braided nylon tube as described in Example I was washed by immersion in dichloromethane, dried, and then threaded through a rubber seal in the bottom of an open topped 1 -litre container so that about a 40 mm length protruded below the seal. The temperature of the tube was raised to about 500C by the passage of hot air through it.

The following 3-part composition was prepared and the three components were then mixed together at 600 C.

Epoxy resin (available 100 g mixed at 1200C as Epikote 815 from Shell) 9 and cooled 2,2-di(4-hydrnxy-phenyl) 24 at 600C Component A propane (available as Bisphenol-A from BDH Chemicals Ltd.) di-iso-octyl sebacate 100 9 mixed and amine-terminated butadiene/ 300 9 } heated to 600C Component B acrylonitrile copolymer (available as Hycar 1300X16 from B. F. Goodrich) Component C silicone liquid (available 0.8 g as Silicone DC 200, 50 Centistokes from Dow Corning The mixture (which had a viscosity at 600C of about 5Ns/m2 measured on a Brookfield viscometer, model LVF, spindle 4, speed 60 r.p.m.) was poured into the 1-litre container, around the braided nylon tube. The tube was pulled down through the seal at a speed of about 8.3 mm/sec until approximately 1 50 mm remained above the seal. The temperature of the assembly was maintained at about 500C for a further 13 hours. When the hose was examined after this, the braid was found to be substantially fully impregnated.

Claims

1. A method of making a reinforced tubular article comprises applying to a tube of polymeric material which will form the inner liner of the article at least one layer of material to provide reinforcement in the article and then fully impregnating the layer or layers with a liquid elastomerforming reaction mixture.

2. A method according to Claim 1 in which a plurality of layers of material to provide reinforcement in the article is applied to the tube of polymeric material and the layers are then impregnated in a single operation.

3. A method according to Claim 1 or 2 in which the liquid elastomer-forming reaction mixture comprises ingredients which will react and set to form a polyurethane.

4. A method according to Claim 1 or 2 in which the liquid elastomer-forming reaction mixture comprises a functional group-tipped liquid butadiene/acrylonitrile copolymer rubber and an epoxy resin.

5. A method according to any preceding claim in which the viscosity of the liquid elastomerforming reaction mixture is less than 10 Ns/m2 at the impregnating temperature.

6. A method according to any of Claims 1 to 4 in which the viscosity of the liquid elastomerforming reaction mixture is less than 5 Ns/m2 at the impregnating temperature.

7. A method according to any of Claims 1 to 4 in which the viscosity of the liquid elastomerforming reaction mixture is less than 1 Ns/m2 at the impregnating temperature.

8. A method according to any preceding Claim in which the or each reinforcement layer comprises metal.

9. A method according to any of Claims 1 to 7 in which the or each reinforcement layer comprises an aromatic polyamide.

10. A method according to any preceding Claim in which the or each reinforcement layer comprises a braid.

11. A method according to any of Claims 1 to 9 in which the or each reinforcement layer is spirally wound onto the inner liner.

12. A method according to any preceding Claim in which the or each reinforcement layer has an at least 60% coverage.

13. A method according to any of Claims 1 to 11 in which the or each reinforcement layer has an at least 75% coverage.

14. A method according to any preceding Claim in which there is a plurality of reinforcement layers and no non-porous polymeric insulation is applied between them.

15. A method according to any preceding Claim in which a material permeable to the liquid elastomer-forming reaction mixture is provided between the inner liner and the reinforcement layer or layers and/or, where there is a plurality of reinforcement layers, between the reinforcement layers.

16. A method according to any preceding claim in which no external pressure is applied to the reinforced tubular article during the impregnating step.

17. A method according to any preceding Claim in which the reaction and set of the reaction mixture is aided by the application of heat.

18. A method according to any preceding Claim in which the inner liner/reinforcement layer or layers assembly is passed down through an impregnating vessel containing the liquid elastomerforming reaction mixture,

19. A method of making a reinforced tubular article according to Claim 1 and substantially as described in Example I or II.

20. A method of making a reinforced tubular article according to Claim 1 and substantially as herein described with reference to the accompanying drawing.

21. A reinforced tubular article made by the method according to any of the preceding Claims.

22. A reinforced tubular article according to Claim 21 which is a hose.