Patent Application
20080072985
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.
With reference to
The thickness, t, of the sidewall 20 is measured as a radial dimension between an interior or inner surface 22 of the inner diameter and an exterior or outer surface 24 of the outer diameter. The inner and outer surfaces 22, 24 define the boundaries of the sidewall 20. The inner surface 22, which borders and defines the lumen 16, is exposed to the fluid conveyed through the lumen 16 and is typically substantially smooth. The outer surface 24 is exposed to the working environment of the hose 10. Opposite ends 26, 28 of the flexible hose 10 are terminated by conventional hose fittings 30, 32, respectively, used for coupling the flexible hose 10 to a fluid source, a fluid drain, a fluid dispenser, or even another hose or conduit. The inner surface 22 of the tubular member 12 may have an inner diameter of, for example, ¼″, ⅜″, ½″, ⅝″, ¾″, or 1″.
The reinforcement strip 14 includes a plurality of continuous coils or turns, such as representative turns 34, 36, 38 (
The cross-sectional area of the turns 34, 36, 38, as well as the helical pitch of the reinforcement strip 14, may influence the flexibility of the hose 10 and its strength against flattening and against pressure to resist bursting. Increasing the helical pitch of the reinforcement strip 14 in the axial direction increases the centerline spacing, s, which increases the flexibility of the hose, but may decrease the strength against flattening and pressure resistance against bursting. Increasing the cross-sectional area of the turns 34, 36, 38 increases the crush resistance against flattening but may reduce flexibility.
As best shown in
An optional sheath layer 42 may be applied about the outer surface 24 of the tubular member 12 for the purpose of imparting abrasion resistance or chemical resistance. The construction material for the optional outer sheath 42 may comprise thermoplastic elastomer (TPE) or PVC added to hose 10 by, for example, a sequential extrusion process. In addition, an optional liner layer 44 may be applied on the inner surface 22 of the tubular member 12 by, for example, a sequential extrusion process. The liner layer 44 may be composed of a chemical-resistant material, such as rubber, that is chemically inert and resistant to permeation by the conveyed fluid in the lumen 16.
In one aspect, the reinforcement strip 14 comprises a high modulus material having a greater initial modulus than a low modulus material forming the tubular member 12. Because of the higher initial modulus, the high modulus material forming the reinforcement strip 14 has a greater rigidity (or lower flexibility) than the low modulus material forming the tubular member 12. As understood by a person having ordinary skill in the art, the initial modulus is a physical property of a material measured from the slope of an engineering stress-strain curve at low strain levels near zero strain. An engineering stress-strain curve is a graph representing an experimental measurement derived from measuring load (i.e., stress) versus extension (i.e., strain) for a sample of a material. The shape and characteristics of the stress-strain curve vary with the type of material. The stress-strain curve features an initial elastic region over an initial range of relatively low applied stresses, followed by a plastic region over another range of moderate applied stresses, and ultimately fracture at a sufficiently high applied stress.
The high modulus material of reinforcement strip 14 may be a TPE, a blend of two or more TPE's, a blend of TPE with polyethylene, or a blend of TPE with polypropylene. In particular, the high modulus material of reinforcement strip 14 may comprise a blend of a TPE and polypropylene having a composition ranging from about 80 percent by weight (wt. %) TPE to about 20 percent by weight TPE. A particularly useful polymer blend is believed to comprise a composition of about 50 percent by weight TPE and about 50 percent by weight polypropylene. Increasing the percentage by weight of polypropylene in the blend relative to percentage by weight of TPE is believed to increase the kink resistance of the hose 10, but reduce the flexibility. High modulus materials suitable for constructing the reinforcement strip 14 may comprise a blend of polypropylene and a TPE selected from the ENGAGE® family of TPE's commercially available from Dow Chemical Company (Midland, Mich.). A particularly useful polymer blend comprises ENGAGE® ENR™ 7256 ethylene-butene copolymer and polypropylene combined in a ratio of about 50 wt. % TPE to about 50 wt. % polypropylene, which has an initial modulus of about 40,000 psi. ENGAGE® ENR™ 7256 is characterized by a density of 0.885 grams per cubic centimeter (ASTM D792) and a melt mass flow rate of 0.80 grams per ten minutes (190° C./2.16 kg, ASTM D1238).
The high modulus material of reinforcement strip 14 is selected with a composition that exhibits a minimum initial modulus of about 5,000 pounds per square inch (psi). The high modulus material constituting reinforcement strip 14 may also exhibit a minimum tensile strength of about 1000 psi, or greater. The selected composition of the high modulus material of reinforcement strip 14 may also exhibit a zero or positive value of tangent modulus on the engineering stress-strain curve through a strain level of at least 20 percent as measured with a variation of ASTM standard D412 at crosshead speed of about two inches per minute. The tangent modulus is the slope of the engineering stress-strain curve at a given level of stress or strain. The tensile strength represents the stress at the inflection point or maximum on the engineering stress-strain curve, which corresponds to the maximum stress that can be sustained by a structure in tension. For applied stresses exceeding the tensile strength, the tangent modulus becomes negative because of permanent and non-recoverable deformation as the tested specimen extends. In one embodiment, the high modulus material of reinforcement strip 14 is characterized by an initial modulus of about 40,000 psi or more, a tensile strength of about 1600 psi or more, and a zero or positive value of tangent modulus on an engineering stress-strain curve through a strain level of at least 20 percent.
Although not wishing to be limited by theory, the relatively high initial modulus of the high modulus material of reinforcement strip 14 is believed to impart appreciable kink resistance to the hose 10. Although not wishing to be limited by theory, the minimum tensile strength of the high modulus material of reinforcement strip 14 is believed to impart appreciable burst strength to the hose 10. Although not wishing to be limited by theory, the positive tangent modulus of the high modulus material of reinforcement strip 14 is believed to impart appreciable crush resistance to the hose 10 by limiting the permanent deformation of the strip 14 in response to a crushing force tending to flatten the coils 34, 36, 38.
The low modulus material constituting the tubular member 12 is significantly more flexible than the high modulus material constituting the reinforcement strip 14. In one aspect, the low modulus material constituting the tubular member 12 exhibits a maximum initial modulus of about 3000 psi and, typically, an initial modulus between about 200 psi and about 3000 psi. In one embodiment, the initial modulus of the low modulus material may range from about 600 psi to about 1,000 psi. The minimum stress at 250 percent strain of the low modulus material may be about 400 psi and, in certain embodiments, the stress at 250 percent strain may range from about 750 psi to about 1250 psi.
The low modulus material constituting the tubular member 12 may be a polymer such as TPE, a blend of two or more TPE's, or polyvinylchloride (PVC), although the invention is not so limited. Low modulus materials suitable for constructing the tubular member 12 may be a TPE selected from the family of polyolefin elastomers commercially available under the trade name ENGAGE® from Dow Chemical Company (Midland, Mich.). A particularly useful TPE for forming tubular member 12 is ENGAGE® 8180 polyolefin elastomer, which is an ethylene-octene copolymer characterized by a density of 0.863 grams per cubic centimeter (ASTM D792) and a melt mass flow rate of 0.50 grams per ten minutes (190° C./2.16 kg, ASTM D1238).
In certain embodiments, one or more conventional additives, such as a crosslinking agent, may be added to either the low modulus material of tubular member 12 or the high modulus material of the reinforcement strip 14. For example, silane may be added as a crosslinking agent to the low modulus material constituting the tubular member 12. In particular, the low modulus material of tubular member 12 may comprise a blend of ENGAGE® 8180 with the crosslinking agent SILCAT® RHE silane, which is a crosslinking vinylsilane agent commercially available from General Electric Advanced Materials (Wilton, Conn.). Depending upon the composition, the addition of SILCAT® RHE silane provides an initial modulus of approximately 600 psi to 1000 psi and a stress at 250 percent strain of 750 psi to 1250 psi.
In an alternative embodiment, the low modulus material of the tubular member 12 may be foamed to reduce the weight and increase the flexibility of the hose 10. The blowing agent works by expanding the low modulus material of the tubular member 12 to produce a cellular structure having significantly less density than the polymer itself. The foamed structure may be achieved by introducing a conventional blowing agent into the low modulus material of tubular member 12 during extrusion. The blowing agent may be any chemical agent that liberates gas when heated above a characteristic decomposition temperature (e.g., sodium bicarbonate that liberates CO2 when heated above its decomposition temperature), any physical agent such as any gas (e.g., gaseous nitrogen or carbon dioxide), or any other known type of blowing agent. As the low modulus material of the tubular member 12 cools and hardens, gas-filled bubbles originating from the blowing agent define a closed cellular structure of a given density throughout the tubular member 12.
The combination of a low modulus material for the tubular member 12 and a high modulus material for the reinforcement strip 14 is selected to construct a hose 10 that, in comparison with conventional hose constructions, exhibits acceptable flexibility, kink resistance, and crush resistance under zero- and low-fluid pressure conditions without sacrificing strength that resists bursting. In certain embodiments of the invention, the materials for the tubular member 12 and reinforcement strip 14 may be selected to operate under internal working fluid pressures ranging from about 15 psi to about 500 psi.
The hose 10 may be manufactured or fabricated using extrusion techniques known to a person having ordinary skill in the art. For example, one extrusion technique involves feeding a continuous extruded body of molten material tangentially relative to a rotating cylindrical mandrel. The molten extruded body, before contacting the rotating mandrel, consists of an outer shell of the low modulus material of the tubular body 12 and an inner core of the high modulus material of the reinforcement strip 14. As the extruded body contacts the rotating mandrel, the molten extruded body coils in a multiplicity of successive loops about the circumference of the mandrel. Confronting edges of adjacent loops merge or fuse together in the molten state to form a continuous and integral tubular body or mass in which the inner core remains segregated from the outer shell. When cooled, the tubular body 12 and reinforcement strip 14 are defined from the outer shell and the inner core, respectively, as a continuous length of tubing defining hose 10 without additional processing steps. The tubing is cut to length and the hose fittings 30, 32 are attached.
The high modulus and low modulus materials constituting the reinforcement strip 14 and tubular member 12, respectively, are compatible in that they mutually adhere together to create a cohesive, strongly bonded integral composite structure. An intermediate tie or bonding layer (not shown), which may be co-extruded between the outer shell and inner core, may be formed of a material that is adhesion bond compatible with both the materials of reinforcement strip 14 and tubular member 12.
Hose 10 may be adapted for use in a wide variety of industrial or household applications. One commercial application for hose 10 is a garden or water hose for household or industrial use. Another commercial application for hose 10 is a drop hose mainly used for the transfer of various fluids including, but not limited to, gasoline, petroleum based products, chemicals, petrochemicals, and fluid food products. Hose 10 may be also used to make pneumatic hoses for pneumatic tools and the like.
With reference to
In the hose construction of hose 50, the yarn layer 54 and inner tubular member 52 are disposed radially inside of the inner surface 22 of tubular layer 12. The yarn layer 54 is disposed radially between the tubular member 12 and inner tubular member 52. After the tubular member 52 is formed, the yarn layer 54 is applied about tubular member 52 before the extrusion forming hose 10 is applied about the exterior of the yarn layer 54.
With reference to
With reference to
References herein to terms such as “inner” or “interior” and “outer” or “exterior” refer, respectively, to directions toward and away from the center of the referenced element, and the terms “radial” and “axial” refer, respectively, to directions perpendicular and parallel to the longitudinal central axis of the referenced element are made by way of example, and not by way of limitation, to establish a frame of reference. It is understood that various other reference frames may be employed for describing the invention.
The embodiments described above may be further appreciated with consideration of the following example.
The properties of candidate high modulus and low modulus materials for a flexible hose as described herein were tested. The candidate high modulus material for the reinforcement strip 14 was selected to be ENGAGE® ENR™ 7256 and polypropylene blended in a nominal ratio of about 50 percent by weight TPE to about 50 percent by weight PP. As indicated in
To generate the engineering stress-strain curves of
While the invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants' general inventive concept. The scope of the invention itself should only be defined by the appended claims, wherein we claim:
