Abstract:
Flexible reinforced rubber hose adapted for conveying fluids under low temperatures and high pressures. The hose includes a inner tube formed of an acrylonitrile butadiene rubber (NBR) or other low temperature rubber compound having an elastic modulus of not greater than about 8.4 MPa (1200 psi), and an outer jacket formed of a chloroprene rubber (CR) or other low temperature rubber compound having a durometer of not greater than about 75 Shore A.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 61/116/926, filed Nov. 21, 2008, the disclosure of which is expressly incorporated herein by reference 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates broadly to flexible rubber hoses for low, medium, and, particularly, high pressure applications, and more particularly to a construction therefor for use at low service temperatures. 
     Flexible rubber hose is used in a variety of hydraulic and other fluid transfer applications for conveying fluid pressures which for “high” pressure applications may range up to about 8000 psi (55 MPa) or more. In basic construction, hoses of the type herein involved typically are formed as having an inner tube or core surrounded by one or more outer layers of a braided or spiral-wound reinforcement material which may be a metal or metal-alloy wire or a natural or synthetic fiber. The reinforcement layers, in turn, are protected by a surrounding outermost jacket or cover which may be of the same or different material as the inner tube. The cover provides the hose with increased abrasion resistance and also helps to protect the hose from being damaged by external forces. 
     In the case of “rubber,” as opposed to thermoplastic, hose constructions, the inner tube, may be provided as formed of a vulcanizable natural or, more typically, a synthetic rubber material such as Buna-N or Neoprene. Such material or blend may be conventionally extruded and cooled or cured to form the inner tube. As is detailed in U.S. Pat. Nos. 3,116,760; 3,159,183; 3,966,238; and 4,952,262, if necessary, the tube may be cross-head extruded over a mandrel for support, or otherwise supported in later forming operations using air pressure and/or reduced processing temperatures. 
     From the extruder, the inner tube may be delivered through a braider and/or a spiral winder for its reinforcement with one or more surrounding layers of a wire and/or fibrous material or blend such as a monofilament, yarn, cord, or yarn-wire composite. As is described in Japanese (Kokai) Publ. No. 10-169854 A2, Canadian Patent No. 973,074, and U.S. Pat. Nos. 3,654,967; 3,682,201; 3,790,419; 3,861,973; 3,905,398; 4,007,070; 4,064,913; 4,343,333; and 4,898,212, these reinforcement layers are applied under tension and typically may be formed of an interwoven braid or a spiral winding of a nylon, polyester, polyphenylene benzobisoxazole, polyvinyl acetate, liquid crystal polymer (LCP), or para-, meta-, or other aramid yarn, or a high tensile steel or other metal wire. A bonding or other interlayer of a vulcanizable rubber may be extruded or otherwise applied between each of the reinforcement layers to bond each successive layer to the next layer. 
     Following the braiding, winding, or other application of the reinforcement layers and the interlayers, an outer cover or sheath optionally may be applied. Such cover, which may be formed as a cross-head extrusion, a moisture-cured or solvent-based dipped coating, or a spiral-wound wrapping, typically comprises an abrasion-resistant synthetic rubber or a thermoplastic such as a polyurethane. Following the application of the cover, the hose construction so-formed is heated to vulcanize the rubber layers and thereby consolidate the construction into an integral hose structure. Representative hose constructions, as well as manufacturing methods and materials therefor, are shown in U.S. Pat. Nos. 3,921,674; 3,953,270; 3,994,761; 4,104,098; 4,238,260; 4,759,388; 6,037,025; 6,474,366 and 7,143,789. 
     In normal use, such as in mobile or industrial hydraulic applications, hoses of the type herein involved may be exposed to a variety of environmental factors and mechanical stresses which cannot always be predicted. Of utmost importance to the integrity and performance of the hose is that a strong bond is achieved between the constituent parts thereof. However, while it is important to bond these parts together, it is also important that the hose not be made overly stiff so as to make it prone to kinking or fatigue or otherwise unusable for certain applications. 
     In view of the foregoing, it will be appreciated that hose constructions must exhibit a demanding balance of chemical and physical properties. Indeed, industry standards such as Society of Automotive Engineers (SAE) 100R12, 100R13, and 100R15, International Organization for Standardization (ISO) 3862 Types R12, R13, R15, 4SH, and 4SP, and European Standard EN 856 Types R12, R13, 4SH and 4SP specify a service temperature ranging from −40° C. (−40° F.) to +125° C. (+257° F.). The service pressure for hoses of such types vary by specification and hose diameter, but typically range from 17.5 MPa (2500 psi) to 42.0 MPa (6000 psi). 
     As commercial applications for hoses continue to increase, it is believed that improvements in hose constructions would be well-received by numerous industries for a variety of mobile and industrial application. Especially desired would be a construction which is flexible and light-weight, and which is resistant to low temperatures so as to meet various industrial standards. 
     BROAD STATEMENT OF THE INVENTION 
     The present invention is directed to flexible rubber hoses, and particularly to a construction therefor which results in a hose which is resistant to low temperatures, but which is still flexible. Such construction may be adapted for use in a variety of applications such as mobile or industrial hydraulic installations specifying service temperatures ranging from about −57° C. (−70° F.) to +100° C. (+212° F.) and maximum service pressures exceeding about 28.0 MPa (4000 psi) and up to about 56.0 MPa (8000 psi). 
     The hose of the present invention is constructed as having an inner tube or core formed of a nitrile butadiene rubber (NBR) or other such rubber compound formulated for low temperature use such as having an elastic modulus (at 100% elongation) of not greater than about 1200 psi (8.4 MPa) and, preferably, not less than about 500 psi (3.4 MPa), and a durometer of not greater than about 80 Shore A and, preferably, not less than about 70 Shore A. The hose further is constructed as having an outer cover or jacket formed of chloroprene rubber (CR) or other such rubber compound similarly formulated for low temperature use such as having a durometer of not greater than about 75 Shore A and, preferably, not less than about 60 Shore A, an elongation at break of not less than about 160% and, preferably, not greater than about 500%, and a tensile strength of not greater than about 2500 psi (17.2 MPa) and, preferably, not less than about 1600 psi (11.0 MPa). Such construction results in a hose which remains flexible enough to be serviceable at temperatures as low as −57° C. (−70° F.), but which also has enough abrasion resistance to withstand normal usage in a variety of hydraulic and other applications. Such construction also allows for the hose to be wire spiral reinforced so as to meet maximum service pressure requirements of up to about 56.0 MPa (8000 psi). 
     In an illustrated embodiment, the hose construction of the present invention includes the aforementioned inner core over which, for example, at least a pair of metal or metal alloy wire reinforcement layers are spiral wound to provide resistance to internal working pressures of 4000 psi (28 MPa) or more. The aforementioned jacket is provided over the reinforcement layers. Each reinforcement layer may be bonded to the next adjacent reinforcement layer by a rubber or other interlayer interposed therebetween, with the inner tube being bonded to the innermost reinforcement layer, and the cover being bonded to the outermost reinforcement layer. That is, the rubber layers of the hose as so formed may be vulcanized to bond each layer in the hose wall to the next adjacent layer to thereby consolidate the layers into an integral hose wall structure. 
     The present invention, accordingly, comprises the construction, combination of elements, and/or arrangement of parts and steps which are exemplified in the detailed disclosure to follow. Advantages of the present invention include a hose construction which is economical to manufacture, and which may be spiral wire reinforced as otherwise adapted for use in a variety of mobile or industrial hydraulic or other applications requiring maximum service pressures exceeding about 28.0 MPa (4000 psi) and up to about 56.0 MPa (8000 psi). Additional advantage include a hose which retains a bend radius or other flexibility at service temperatures as low as about −57° C. (−70° F.). These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein: 
         FIG. 1  is a side elevation, cut-away view of a representative low temperature, high pressure rubber hose construction according to the present invention; and 
         FIG. 2  is a radial cross-sectional view of the hose of  FIG. 1  taken through line  2 - 2  of  FIG. 1 . 
     
    
    
     The drawings will be described further in connection with the following Detailed Description of the Invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain terminology may be employed in the following description for convenience rather than for any limiting purpose. For example, the terms “forward” and “rearward,” “front” and “rear,” “right” and “left,” “upper” and “lower,” and “top” and “bottom” designate directions in the drawings to which reference is made, with the terms “inward,” “inner,” “interior,” or “inboard” and “outward,” “outer,” “exterior,” or “outboard” referring, respectively, to directions toward and away from the center of the referenced element, the terms “radial” or “horizontal” and “axial” or “vertical” referring, respectively, to directions or planes which are perpendicular, in the case of radial or horizontal, or parallel, in the case of axial or vertical, to the longitudinal central axis of the referenced element, and the terms “downstream” and “upstream” referring, respectively, to directions in and opposite that of fluid flow. Terminology of similar import other than the words specifically mentioned above likewise is to be considered as being used for purposes of convenience rather than in any limiting sense. 
     In the figures, elements having an alphanumeric designation may be referenced herein collectively or in the alternative, as will be apparent from context, by the numeric portion of the designation only. Further, the constituent parts of various elements in the figures may be designated with separate reference numerals which shall be understood to refer to that constituent part of the element and not the element as a whole. General references, along with references to spaces, surfaces, dimensions, and extents, may be designated with arrows. Angles may be designated as “included” as measured relative to surfaces or axes of an element and as defining a space bounded internally within such element therebetween, or otherwise without such designation as being measured relative to surfaces or axes of an element and as defining a space bounded externally by or outside of such element therebetween. Generally, the measures of the angles stated are as determined relative to a common axis, which axis may be transposed in the figures for purposes of convenience in projecting the vertex of an angle defined between the axis and a surface which otherwise does not extend to the axis. The term “axis” may refer to a line or to a transverse plane through such line as will be apparent from context. 
     For illustration purposes, the precepts of the low temperature rubber hose construction herein involved are described in connection with its configuration as particularly adapted for use in high pressure, i.e., between about 4000-8000 psi (28-56 MPa) mobile or industrial hydraulic applications. It will be appreciated, however, that aspects of the present invention may find use in other hose constructions for a variety or general hydraulic or other fluid transfer applications. Use within those such other applications therefore should be considered to be expressly within the scope of the present invention. 
     Referring then to the figures wherein corresponding reference characters are used to designate corresponding elements throughout the several views with equivalent elements being referenced with prime or sequential alphanumeric designations, a representative hose construction according to the present invention is shown generally at  10  in the cut-away view of  FIG. 1  and in the radial cross-sectional view of  FIG. 2 . In basic dimensions, hose  10  extends axially to an indefinite length along a central longitudinal axis,  12 , and has a select inner and outer diameter referenced, respectively, at “D i ” and “D o ” in the radial cross-sectional view of  FIG. 2 . The inner and outer diameter dimensions may vary depending upon the particular fluid conveying application involved, but generally for many high pressure hydraulic applications will be between about 0.25-2 inch (6-51 mm) for inner diameter D i , and about 0.5-3 inch (13-76 mm) for outer diameter D o , with an overall wall thickness, “T,” therebetween which will depend on the hose size and pressure rating. 
     As may be seen in the different views of  FIGS. 1 and 2 , hose  10  is constructed as being formed about a tubular innermost layer, i.e., inner tube or core,  14 , which may be of a single or multi-layer construction. In either construction, inner tube  14  has a circumferential outer core tube surface,  16 , and a circumferential inner core tube surface,  18 , which defines the inner diameter D i  of the hose  10 . A wall thickness is defined between the outer and inner core tube surfaces  16  and  18 , as referenced at “t” in the cross-sectional view of  FIG. 2 . Such thickness t will depend on the hose size and otherwise on the desired pressure rating and liquid and/or gas permeation resistance. 
     Inner tube  14  may be provided as extruded or otherwise formed of a vulcanizable, chemically-resistant, synthetic rubber material. As used herein, “chemical resistance” should be understood to mean the ability to resist swelling, crazing, stress cracking, corrosion, or otherwise to withstand attack from organic fluids such as solvents and hydraulic fluids. Suitable materials include acrylonitrile butadiene rubbers (NBR) and modified NBR&#39;s such as hydrogenated NBR (HNBR) and cross-linked NBR (XNBR), as well as copolymers and blends, thereof. Such blends may be, for example, XNBR or HNBR blended with one or more of a chlorinated polyethylene (CPE), polyvinyl chloride (PVC), or polychloroprene (CR). 
     The NBR or other rubber material may be formulated to have the properties listed in Table 1 below: 
                         TABLE 1                   Durometer (Shore A), pts   70-80       Elongation @ Break (%)   150-500       Elastic Modulus @ 100% Strain (MPa)   4.4-8.4       Tensile Strength @ break (MPa)   10.3-14.9       Mooney Viscosity (ML 1 + 4) @ 100° C. (212° F.)   62-82       Mooney Scorch @ 121° C. (250° F.) Ts5 (mins)   &gt;30       Specific Gravity (kg/m3)   1.25-1.31                    
Such properties of the rubber material provide the inner tube  14  with flexibility at low temperatures, while allowing for sufficient impulse pressure resistance. Such properties also provide the inner tube with sufficient crush resistance so as to be useable in conventional processes in the manufacture of the hose  10 . Thus, the rubber material as so formulated provides the desired degree of low temperature flexibility without unduly compromising the manufacturability of hose  10 , or its serviceability under high pressure conditions.
 
     The rubber material as so provided may be compounded with between about 15-66% by total weight of the compound of one or more reinforcing fillers. Each of such fillers may be provided, independently, as a powder or as flakes, fibers, or other particulate form, or as a mixture of such forms. Typical of such reinforcing fillers include carbon blacks, clays, and pulp fibers. For powders, the mean average particle size of the filler, which may be a diameter, imputed diameter, screen, mesh, length, or other dimension of the particulate, may range between about 10-500 nm. 
     Additional fillers and additives may be included in the formulation of the rubber compound depending upon the requirements of the particular application envisioned. Such fillers and additives, which may be functional or inert, may include curing agents or systems, wetting agents or surfactants, plasticizers, processing oils and other aids, pigments, dispersants, dyes, and other colorants, opacifying agents, foaming or anti-foaming agents, anti-static agents, coupling agents such as titanates, chain extending oils, tackifiers, flow modifiers, pigments, lubricants, silanes, and other agents, stabilizers, emulsifiers, antioxidants, thickeners, and/or flame retardants. The formulation of the material may be compounded in a conventional mixing apparatus as an admixture of the rubber and filler components, and any additional fillers or additives. 
     With respect to the spiral-wound construction shown in  FIGS. 1 and 2 , at least two, and typically four (as shown) or up to six or more, reinforcement layers,  30   a - d , are provided over the inner tube  14 . Each of the reinforcement layers  30  may be conventionally formed as spiral, i.e., helically, wound of, for example, from 1 to about 180 ends of monofilament, continuous multi-filament, i.e., yarn, stranded, cord, thread, tape, or ply, or short “staple” strands of a fiber material. The fiber material, which may be the same or different in layers  30   a - d , may be a natural or synthetic polymeric material such as a nylon, cotton, polyester, polyamide, aramid, polyolefin, polyvinyl alcohol (PVA), polyvinyl acetate, or polyphenylene benzobisoxazole (PBO), or blend, a steel, which may be stainless or galvanized, brass, zinc or zinc-plated, or other metal wire, or a blend thereof. 
     In the illustrated spiral wound construction  10  of  FIGS. 1 and 2 , which also may contain additional extruded, spiral, braided, and/or knitted layers (not shown), the reinforcement layers  30  are oppositely wound in pairs so as to counterbalance torsional twisting effects. For each of the spiral wound layers  30   a - d , from 1 to about 180 parallel ends of, preferably, a monofilament metal or metal alloy wire, may be helically wound under tension in one direction, i.e., either left or right hand, with the next immediately succeeding layer  30  being wound in the opposite direction. The innermost reinforcement layer  30   a  may be wound as is shown in  FIG. 1  directly over the outer surface  16  of inner tube  14 , or over an intermediate textile, foil, or film or other layer. 
     As successively wound in the hose  10 , the layers  30   a - d  each may have a predetermined pitched angle, referenced at −θ in  FIG. 1  for layers  30   a  and  30   c , and at θ for layers  30   b  and  30   d , measured relative to the longitudinal axis  12  of the hose  10 . For typical applications, the pitch angle θ will be selected to be between about 45-63°, but particularly may be selected depending upon the desired convergence of strength, elongation, weight, and volumetric expansion characteristics of hose  10 . In general, higher pitch angles above about 54.7° exhibit decreased radial expansion of the hose under pressure, but increased axial elongation. For high pressure applications, a “neutral” pitch angle of about 54.7° generally is preferred as minimizing elongation to about ±3% of the original hose length. Each of the layers  30  may be wound at the same or different absolute pitch angle, and it is known that the pitch angles of respective reinforcement layers may be varied to affect the physical properties of the hose. In a preferred construction, however, the pitch angles of reinforcement layers  30   a - d  are provided to about the same, but as reversed in successive layers. 
     The tension and area coverage at which the reinforcement layers  30  are wound may be varied to achieve the desired flexibility. Such flexibility may be measured by bend radius, flexural forces, or the like, of the hose  10 . In the illustrated construction which may be particularly adapted for high pressure hydraulic applications, each of the reinforcement layers  30   a - d  may be spiral wound from one end of a monofilament carbon or stainless steel wire having a generally circular cross-section. As so formed, each of the layers  30   a - d  thus may have a thickness of that of the wire diameter. Although a circular wire is shown, a “flat-wire” construction alternatively may be employed using wires having a rectangular, square, or other polygonal cross-section. Low profile oval or elliptical wires also may be used. To better control the elongation and contraction of hose  10 , and for improved impulse fatigue life, the innermost reinforcement layer  30   a  may be bonded, by means of fusion, i.e., vulcanization of the inner tube  14 , mechanical, chemical, or adhesive bonding, or a combination thereof or otherwise, to the outer surface  16  of the core tube  14 . 
     The outermost reinforcement layer  30   d  may be sheathed within one or more layers of a coaxially-surrounding protective cover or jacket, referenced at  40 , having a circumferential interior surface,  42 , and an opposing circumferential exterior surface,  44 , which defines the hose outer diameter D o . Depending upon its construction, cover  40  may be spray-applied, dip coated, cross-head or co-extruded, or otherwise conventionally extruded, spiral or longitudinally, i.e., “cigarette,” wrapped, or braided over the reinforcement layer  30   d  as, for example, a 0.02-0.15 inch (0.5-3.8 mm) thick layer of an fiber, glass, ceramic, or metal-filled, or unfilled, abrasion-resistant thermoplastic, i.e., melt-processible synthetic rubber such as chloroprene rubber (CR), or a CR copolymer or blend. By “abrasion-resistant,” it is meant that such material for forming cover  40  may have a hardness of at least about 60 Shore A durometer. 
     The CR or other rubber material may be formulated to have the properties listed in Table 2 below: 
     
       
         
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
             
             
               
                 Durometer (Shore A), pts 
                 60-75 
               
               
                 Elongation @ Break (%) 
                 270-370 
               
               
                 Elastic Modulus @ 100% Strain (MPa) 
                 2.0-4.4 
               
               
                 Tensile Strength @ break (MPa) 
                 10.9-15.9 
               
               
                 Mooney Viscosity (ML 1 + 4) @ 100° C. (212° F.) 
                 66-86 
               
               
                 Mooney Scorch @ 121° C. (250° F.) Ts5 (mins) 
                 &gt;30 
               
               
                 Specific Gravity (kg/m 3 ) 
                 1.40-1.46 
               
               
                   
               
             
          
         
       
     
     Such properties of the rubber material provide the jacket with flexibility at low temperatures, while still having enough abrasion resistance to withstand normal usage conditions. 
     Any of the materials forming the cover  40  may be loaded with metal particles, carbon black, or other electrically-conductive particulate, flake, or fiber filler so as to render hose  10  electrically-conductive for static dissipation or other applications. Separate electrically-conductive fiber or resin layers (not shown), which may be in the form of spiral or “cigarette-wrapped” tapes or otherwise provided, also may be included in the hose construction  10  between the core  14  and the innermost reinforcement layer  30   a , between the reinforcement layers  30 , or between the outermost reinforcement layer  30   d  and cover  40 . 
     Similar to the bonding of core  14  to the innermost reinforcement layer  30   a , or to a textile or other layer therebetween, the interior surface  42  of cover  40  may be bonded to the outermost reinforcement layer  30   d . Such bond, again, may be by fusion, chemical, mechanical, or adhesive means, or a combination thereof or other means. 
     Each of the reinforcement layers  30   a - d  within hose  10  may be bonded, such as chemically and/or mechanically, to its immediately succeeding layer  30  so as to provide for the more efficient transfer of induced internal or external stresses. Such bonding may be effected via the provision of a bonding agent in the form of an intermediate adhesive, resin, or other interlayer,  50   a - c . In an illustrative embodiment, such bonding agent may be provided as an adhesive in the form of a melt-processible or vulcanizable material which is extruded or otherwise applied in a molten, softened, uncured or partially uncured, or otherwise flowable phase over each of the reinforcement layers  30   a - d  to form the respective interlayers  50   a - c . Each such interlayer  50  may have a thickness of between about 1-25 mils (0.025-0.64 mm). The corresponding reinforcement layer  30  then may be wound over the corresponding interlayer  50  while it is still in its softened phase. Alternatively in the case of a thermoplastic interlayer  50 , the layer may be reheated to effect its re-softening prior to the winding of reinforcement layer  30 . 
     The material forming interlayers  50  specifically may be selected for low temperature performance, flexibility, or otherwise for compatibility with the reinforcement layers  30  and/or the inner tube  14  and cover  40 . Suitable materials include natural and synthetic rubbers, as well as thermoplastic, i.e., melt-processible, or thermosetting, i.e., vulcanizable, resins which should be understood to also include, broadly, materials which may be classified as elastomers or hot-melts. Representative of such resins include plasticized or unplasticized polyamides such as nylon 6, 66, 11 and 12, polyesters, copolyesters, ethylene vinyl acetates, ethylene terpolymers, polybutylene or polyethylene terephthalates, polyvinyl chlorides, polyolefins, fluoropolymers, thermoplastic elastomers, engineering thermoplastic vulcanizates, thermoplastic hot-melts, copolymer rubbers, blends such as ethylene or propylene-EPDM, EPR, or NBR, polyurethanes, and silicones. In the case of thermoplastic resins, such resins typically will exhibit softening or melting points, i.e., Vicat temperatures, of between about 77-250° C. For amorphous or other thermoplastic resins not having a clearly defined melting peak, the term melting point also is used interchangeably with glass transition point. 
     With each of the respective layers  14 ,  30   a ,  50   a ,  30   b ,  50   b ,  30   c ,  50   c ,  30   d , and  40  being extruded, wound, or otherwise formed sequentially in such order, following the application of the cover  40 , the hose  10  may be heated to vulcanize the rubber layers and thereby consolidate the construction into an integral hose structure. 
     Thus, an illustrative rubber hose construction is described which is resistant to low temperatures while maintaining its flexibility. Such construction may be adapted to meet a variety of industrial standards specifying service temperatures ranging from about −57° C. (−70° F.) to +100° C. (+212° F.) and maximum service pressures exceeding about 28.0 MPa (4,000 psi) and up to about 56.0 MPa (8,000 psi). As such, the hose construction may be used in a variety of mobile or industrial hydraulic installations, or otherwise in a variety of pneumatic, vacuum, shop air, general industrial, maintenance, and automotive applications such as for air, oil, antifreeze, and fuel. 
     As it is anticipated that certain changes may be made in the present invention without departing from the precepts herein involved, it is intended that all matter contained in the foregoing description shall be interpreted as illustrative and not in a limiting sense. All references including any priority documents cited herein are expressly incorporated by reference.