Hose construction

Abstract: Hoses (10) for transporting or otherwise handling refrigerant and oil fluids are disclosed which are comprised of an inner tube (20), an outer cover (40) and a reinforcing layer (30) interposed therebetween. The inner tube includes at least two walls, one being an inner resinous wall (20a) and the other being an outer rubbery wall (20b) having specified moduli at 100%. The outer cover is formed by a selected class of rubbers having a higher modulus at 100% than the outer wall of the inner tube. The resulting hose is securely interconnectable with metal fittings, highly impermeable to gaseous and oily fluids, sufficiently resistant to stress cracking and adequately flexible.

Description: This invention relates to hoses suitable for use in transporting or otherwise handling refrigerant and oily fluids. Known hoses of this type are comprised of an inner tube and an outer cover, the inner tube being of a two-layered structure having a thermoplastic, resinous wall and a rubbery wall so as to improve impermeation to gaseous and oily fluids. An inner wall of the hose is usually formed by a thermoplastic material having regard to chemical and heat resistance. In US-E-32230, there is described a hose comprising an inner tube 12, 14, a reinforcing layer 16 and an outer cover 18 superimposed in the order mentioned. The inner tube of this reference has a double-layered structure in which the tube 12 is constituted as an inner wall and the tube 14 as an outer wall. This construction is intended to produce a hose resistant to chemical attack from gasolines. In US 4510974, a multi-layer hose for refrigerants is disclosed, wherein the problems of permeation of gas out of the hose and the inward permeation of water are addressed. In these prior constructions, however, the inner tube is difficult to tightly Interconnect with a metal fitting under clamping force because the inner resinous wall of the tube is great in modulus, generally about 10 to 500 times the outer cover and the outer wall. Excessive clamping would deform or eventually impair the outer cover and even the outer wall, leading to hazardous leakage of a refrigerant or oil from the hose portion so affected. Insufficient clamping would make the hose ready to slip out of the metal fitting and hence susceptible to cutting. To cope with the foregoing problems, it has been proposed to apply an adhesive or a rubber coating onto the fitting. This is literally tedious but with little success. Certain resins are known in common use as materials for the inner tube, and they include nylon-6, a copolymer of nylon-6 and nylon-66 (nylon-6-66), nylon-11 and nylon-12. Nylon-6 and nylon-6-66 have been found satisfactory with respect to gas impermeation but susceptible to stress cracking and rigidity, while nylon-11 and nylon-12 are not sufficiently impermeable to gas. It has also been found that if pin holes or minute scars occur on an inner resinous wall of the inner tube during tube processing as by extrusion molding or during fabrication of the hose, then they tend to grow into cracks due to repeated compression of the hose in service, or into stress cracks particularly on contact with metal chlorides such as zinc chloride. This type of cracking would in most instances extend to and break an outer rubbery wall as is usually called crack propagation and thus leak a fluid in transit, resulting in bursted hose and hence reduced service life. It is therefore the primary object of the present invention to provide an improved hose which excels in attachment to metal fittings, impermeation to gaseous and oily fluids, and flexibility and has freedom from crack propagation, thus ensuring safe and reliable piping work. Many other objects and advantages of the invention will be better understood from the following description taken in connection with the accompanying drawings. According to the invention, there is provided a hose comprising an inner tube, a reinforcing layer and an outer cover superimposed one on another, said outer cover having a one hundred per cent modulus in the range of 20-50 kgf/cm², said inner tube including at least two walls, one being an inner wall and the other being an outer rubbery wall having a one hundred per cent modulus of 15-40 kgf/cm² and characterised in that said inner wall is formed by a polyamide resin and in that said outer cover has a one hundred per cent modulus higher than that of said outer rubbery wall. In the drawings, Figure 1 is a segmentary perspective view, partly broken, of the hose embodying the present invention; and Figure 2 is a partial cross-sectional view of the hose with a metal fitting assembled. A hose constructed in accordance with the present invention and shown at 10 in Figure 1, comprises an inner tube 20, an outer cover 40 and a layer of reinforcement 30 interposed therebetween. The inner tube 20 includes at least two walls, one of which is an inner wall 20 a formed by a selected class of polyamide resins and disposed for direct contact with gaseous fluids such as refrigerants, and oily fluids such as gasoline, light gas oil, lubricating oil, hydraulic oil and the like. The other wall is an outer wall 20 b formed by a selected class of rubbers and laminated over the inner wall 20 a . Polyamide resins useful for the purpose of the invention include for example nylon-6, nylon-11, nylon-12, nylon-6-66, a blend of nylon-6, nylon-11 and a polyolefin (nylon-6/nylon-11/polyolefin) and the like. Ternary blends are preferably composed of 40 to 80 parts by weight of nylon-6, 5 to 30 parts by weight of nylon-11 and 10 to 40 parts by weight of a polyolefin. The polyolefin may suitably be selected from polyethylene, polypropylene and an ethylene/propylene copolymer. The inner wall 20 a has a thickness of 0.05 to 0.80 mm, preferably 0.08 to 0.50 mm, and 5 to 25%, preferably 5 to 10%, of the total thickness of the inner tube 20. Importantly, the outer wall 20 b should have a modulus at 100% in the range of 15 to 40 kgf/cm². Smaller moduli would render the outer wall 20 b too deformable on clamping, leading to bulging at the end of a metal fitting 50 made up of a socket 50 a and a nipple 50 b as seen in Figure 2. Greater moduli would not be effective in pressing the outer wall 20 b in an extent to give adequate strain with the result that the inner wall 20 a fails to make an exact fit to the inside recesses of the fitting 50 and thus leaves therebetween a clearance from which a fluid readily leaks. Suitable rubbers for use in the outer wall 20 b include for example flexibility-imparting rubbers such as acrylonitrile/butadiene copolymer rubber (NBR), chlorosulfonated polyethylene (CSM), ethylene/propylene/diene terpolymer rubber (EPDM), butyl rubber (IIR), chlorinated butyl rubber (Cl-IIR), brominated butyl rubber (Br-IIR), acrylic rubber (ACM), chloroprene rubber (CR) and the like. Particularly preferred are IIR, CI-IIR, Br-IIR, CSM, EPDM, CHR and CHC as they are highly impermeable to moisture. The outer wall 20 b ranges in thickness from 0.5 to 3 mm. The outer cover 40 should be formed by a selected class of rubbers having a modulus at 100% of 20 to 50 kgf/cm². Further importantly, the 100% modulus of the outer cover 40 should be higher up to 20 kgf/cm² than that of the outer rubbery wall 20 b . Departures from this range would fail to produce adequate strain on the outer wall 20 b and also on the inner wall 20 a , causing similar problems noted in connection with the outer wall 20 b . Specific examples of the rubbers of such higher moduli include ethylene/propylene/diene terpolymer rubber (EPDM), chloroprene rubber (CSM), epichlorohydrin rubber (CHR and CHC), butyl rubber (IIR), chlorinated butyl rubber (Cl-IIR), brominated butyl rubber (Br-IIR) and the like. The thickness of the outer cover 40 is between 0.5 and 3 mm. To attain improved resistance to crack propagation which would arise out of pin holes or scars on the inner resinous wall, the outer wall of the inner tube should importantly have a 100% modulus of 15 to 40 kgf/cm² and a tear strength of not less than 15 kgf/cm², preferably 15 to 50 kgf/cm², at 120°C at which to use the hose according to the invention. To this end, butyl rubber (IIR), chlorinated butyl rubber (Cl-IIR), brominated butyl rubber (Br-IIR) and the like are preferred. Suitable bonding adhesives may be applied, where desired, onto and inbetween the inner and outer walls of the inner tube. No particular restriction is imposed upon the reinforcing layer 30. This layer may conveniently be formed for instance by braiding rayon, or polyester. The hose according to the invention may be fabricated by any suitable known methods. One such method involves passing a release-treated mandrel through an extruder equipped with a head from which a resin is extruded peripherally on the mandrel and thus forms an inner plastic tube. The tube-carrying mandrel is allowed to successively enter a rubber extruder at which time an outer wall of rubbery material is laminated over the plastic tube to thereby form an outer rubbery tube. To facilitate bonding between the plastic and rubbery walls, it is convenient to coat the plastic tube as by spraying with a chlorinated rubber, or phenolicresin. A layer of reinforcement is laminated by braiding suitable textile yarns over the outer rubbery wall of the core tube. An outer cover is disposed outwardly about the braided layer by extrusion of a predetermined The resulting hose body is vulcanised under pressure at 130° to 170°C, preferably 140° to 160°C, and subsequently cooled. The mandrel is afterwards pulled out of the vulcanized hose body, whereby a desired hose product is obtained. The following examples are given to further illustrate the invention. Examples 1 - 9 and Comparative Examples 1 - 6 Different hoses were prepared according to the formulation shown in Table 1. The hoses representing the invention had an outer cover formed by butyl rubber-1 (IIR-1) having a 100% modulus (M-100) of 35 kgf/cm² or by chloroprene (CR) of 43 kgf/cm2. Butyl rubber-2 (IIR-2) of 21 kgf/cm², chlorosulfonated polyethylene rubber (CSM) of 27 kgf/cm² and chlorinated butyl rubber (CI-IIR) of 24 kgf/cm² were used as the outer covers in the comparative hoses. A rayon braid was used as the reinforcing layer. Metal fitting attachment of the hoses was examined under the conditions given below and with the results shown in Table 1. IIR-1 IIR (Exxon Butyl 268, Esso Chemical Co.) 100 carbon black (Show Black N220, Showa Cabot Co.) 65 AC polyethylene 7 stearic acid 3 antioxidant (Antage OD, Kawaguchi Kagaku Co.) 2 zinc oxide 5 brominated phenol resin (Tackiroll 250-1, Taoka Kagaku Kogyo Co.) 12 IIR-2 IIR (Exxon Butyl 268, Esso Chemical Co.) 100 carbon black (Show Black N220, Showa Cabot Co.) 65 AC polyethylene 7 stearic acid 3 antioxidant (Antage OD, Kawaguchi Kagaku Co.) 2 softener (Machine Oil 22, Fuji Kosan Co.) 8 zinc oxide 3 brominated phenol resin (Tackiroll 250-1, Taoka Kagaku Kogyo Co.) 12 Cl-IIR Cl-IIR (Chlorobutyl 1066, Esso Chemical Co.) 100 carbon black (Show Black N220, Showa Cabot Co.) 60 AC polyethylene 7 stearic acid 2 magnesium oxide 1 antioxidant (Antage OD, Kawaguchi Kagaku Co.) 2 softener (Machine Oil 22, Fuji Kosan Co.) 5 accelerator TT (Sunceller TT, Sanshin Kagaku Kogyo Co.) 2 accelerator R (Actor MS-R, Kawaguchi Kagaku Co.) 2 NBR-1 NBR (Nipol 1042, Nippon Zeon C o.) 100 carbon black (Asahi 50, Asahi Carbon Co.) 80 stearic acid 2 zinc oxide 5 antioxidant (Antage OD, Kawaguchi Kagaku Co.) 2 plasticizer (DOP, Chisso Chemical Co.) 10 sulfur 2 accelerator TS (Sunceller MS, Sanshin Kagaku Kogyo Co.) 1 CSM CSM (Hypalon 40, Dupont) 100 carbon black (Asahi 50, Asahi Carbon Co.) 60 paraffin wax (Sunnoc, Ohuchi Shinko Kagaku Co.) 1.5 magnesium oxide 4 stearic acid 1 softener (Fuccol 1000, Fuji Kosan Co.) 30 pentaerythritol (Noylizer P, Nippon Kagaku Kogyo Co.) 3 accelerator TRA (Sunceller TRA, Sanshin Kagaku Kogyo Co.) 2 CR CR (Neoprene W, Showa Neoprene Co.) 100 carbon black (Asahi 50, Asahi Carbon Co.) 100 magnesium oxide 4 stearic acid 3 antioxidant (Ozonon 3C, Seiko Kagaku Co.) 3 softener (Fuccol 1150N, Fuji Kosan Co.) 10 sulfur 1 accelerator TS (Sunceller TS, Sanshin Kagaku Kogyo Co.) 1 accelerator D (Sunceller D, Sanshin Kagaku Kogyo Co.) 1 zinc oxide 5 Metal Fitting Attachment As shown in Figure 2, a hose was interconnected with a socket-nipple metal fitting with the outer cover abutted against the socket and with the inner wall of the inner tube abutted against the nipple. The metal fitting was clamped at a clamping ratio of 30 to 50%, followed by aging of the hose in an aerial atmosphere at 120°C for 168 hours and by subsequent charging with nitrogen gas at 30 kgf/cm². Metal fitting attachment was determined by gas leakage (airtightness) on lapse of 5 minutes after gas charging. Examples 10 - 17 and Comparative Examples 7 - 12 Different hoses were formulated and prepared as shown in Table 2. Performance test was made for crack propagation, flon gas permeation and flexibility under the conditions given below and with the results shown in Table 2. IIR-3 IIR (Exxon Butyl 268, Esso Chemical Co.) 100 carbon black HAF (Show Black N330T, Showa Cabot Co.) 80 AC polyethylene 7 stearic acid 3 zinc oxide 5 softener (Machine Oil 22, Fuji Kosan Co.) 10 brominated phenol resin (Tackiroll 250-1, Taoka Kagaku Kogyo Co.) 10 NBR-2 NBR (Nipol 1042, Nippon Zeon Co.) 100 carbon black (Asahi 50, Asahi Carbon Co.) 80 zinc oxide 5 stearic acid 1 antioxidant (Antage OD, Kawaguchi Kagaku Co.) 1 plasticizer (DOP, Chisso Chemical Co.) 10 sulfur 2 accelerator TS (Sunceller MSPO, Sanshin Kagaku Kogyo Co.) 1 NBR-3 NBR (Nipol 1042, Nippon Zeon Co.) 100 carbon black (Asahi 50, Asahi Carbon Co.) 70 white carbon (Nipseal AQ, Nippon Silica Co.) 20 zinc oxide 5 stearic acid 1 antioxidant (Antage OD, Kawaguchi Kagaku Co.) 1 plasticizer (DOP, Chisso Chemical Co.) 15 sulfur 2 accelerator TS (Sunceller MSPO, Sanshin Kagaku Kogyo Co.) 1 Crack Propagation An inner resinous wall of the inner tube of a hose was cut to a length of 1 mm by knife and secured onto an impulse tester, followed by filling of the hose with hydraulic oil (Autoloop SAE 30). The hose was exposed to repeated stress at an oil temperature of 120°C and at a pressure of 30 kgf/cm² (rectangular wave 100%) for a total cycle of 300,000 runs. When crack propagation took place, resulting in cracked outer wall of the inner tube and eventually bursted hose prior to the total cycle of runs, the number of impulses was counted. In the case of no bursting even after the total run, crack propagation was adjudged by cracking on the outer wall of the inner tube. Freon Gas Permeation (Freon: Dupont's trademark) JRA 2001 of the Japan Refrigerating and Air-Conditioning Association was followed. A 45 cm long test hose having a metal fitting was charged with a refrigerant (Freon R-12) in an amount of 0.6 ± 0.1 g per cubic centimeter, followed by disposition at 100°C for 96 hours. Gas permeation resistance was determined by gas leak after a lapse of from 24 to 96 hours and indicated in terms of g/m/72 hr. Flexibility A test hose was arcutely bent at a bend radius of 10 times its outer diameter, followed by measurement of bending stresses (n=2) ranging in bend radius from 10 to 3 times. Flexibility was determined by bending strength (kgt) read at a bend radius of 4 times from the stress-radius curve.

Claims: A hose comprising an inner tube (20), a reinforcing layer (30) and an outer cover (40) superimposed one on another, said outer cover (40) having a one hundred per cent modulus in the range of 20-50 kgf/cm², said inner tube (20) including at least two walls, one being an inner wall (20a) and the other being an outer rubbery wall (20b) having a one hundred per cent modulus of 15-40 kgf/cm² and characterised in that said inner wall (20a) is formed by a polyamide resin and in that said outer cover (40) has a one hundred per cent modulus higher than that of said outer rubbery wall (20a). The hose according to Claim 1, characterised by said outer wall (20b) having a tear strength of not less than 15 kgf/cm. The hose according to Claim 1, characterised by said inner wall (20a) being formed by nylon-6, nylon-11, nylon-12, nylon-6/66 or nylon-6/nylon-11/polyolefin. The hose according to Claim 1, characterised by said outer wall (20b) being formed by acrylonitrile/butadiene rubber, chlorosulphonated polyethylene rubber, ethylene/propylene/diene rubber, butyl rubber, chlorinated butyl rubber, brominated butyl rubber, chorosulphonated polyethylene, butyl rubber, chlorinated butyl rubber or brominated butyl rubber. The hose according to Claim 1, characterised by said outer cover (40) being formed by ethylene/propylene/diene rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, chlorinated butyl rubber or brominated butyl rubber. The hose according to Claim 1, characterised in that the 100% modulus of the outer cover (40) is up to 20 kgf/cm² higher than the 100% modulus of the outer rubbery wall (20b).

Inventors: KITAMI TETSU, MITO JUN, NARITA TOYOTAKA, KITAMI, TETSU, MITO, JUN, NARITA, TOYOTAKA
Applicants: YOKOHAMA RUBBER CO LTD, THE YOKOHAMA RUBBER CO., LTD.
Application year: 1988
Main classification: F16L11
IPC codes: F16L11, F16L33