Hose with optimized steel wire reinforcement layers

Abstract

A high pressure hose having steel wires with different load elongation properties, which are introduced into the subsequent reinforcement layers of the hose. The difference in load elongation is quantified by the E-ratio of the wire that is equal to the tensile strength divided by the elongation at break. The steel wires of the radially outermost steel wire reinforcement layer have the highest E-ratio, while the radially innermost steel wire reinforcement layer has the lowest E-ratio. The E-ratio of any steel wire reinforcement layer is not lower than the E-ratio of any inner laying steel wire reinforcement layer. The E-ratio of the steel wires can be influenced by either a thermal treatment or by a mechanical treatment. In the mechanical treatment crimps or bends can be introduced into the wire by guiding them through a preforming device.

Claims

1. A hose for conveying fluids under pressure comprising an elastomer core tube, at least two reinforcement layers at distinct reinforcement layer radii, said reinforcement layers being radially separated by intermediate elastomer material layers and an outer protective layer covering the outermost reinforcement layer, wherein at least two of said reinforcement layers comprise steel wires helically wound around the axis of said hose, wherein the steel wires of the radially outermost steel wire reinforcement layer have the highest E-ratio of the at least two reinforcement layers, the steel wires of the innermost steel wire reinforcement layer have the lowest E-ratio of the at least two reinforcement layers differing from said highest E-ratio, whereby the E-ratio of any steel wire reinforcement layer is not lower than the E-ratio of any inner laying steel wire reinforcement layer, said E-ratio being equal to the ratio of the tensile strength over the elongation at break of said steel wire, wherein said E-ratio is between 70,000 N/mm.sup.2 up to 200,000 N/mm.sup.2 for the radially outermost steel wire reinforcement layer and between 30,000 N/mm.sup.2 and 120,000 N/mm.sup.2 for the radially innermost steel wire reinforcement layer, wherein said steel wires of at least the innermost steel wire reinforcement layer have crimps or bends for altering said E-ratio, while said steel wires of at least the outermost steel wire reinforcement layer are free of bends or crimps, wherein said steel wires of at least the innermost and outermost steel wire reinforcement layer are of the same diameter.

2. The hose according to claim 1, wherein the elongation at break of said steel wires of at least said innermost steel wire reinforcement layer is higher by the crimps or bends in said steel wire compared to the steel wire that is free of crimps or bends by at least 0.3% and at most 4%.

3. The hose according to claim 1, wherein said steel wires of at least the innermost and outermost steel wire reinforcement layer are of the same tensile class, said tensile class being one out of the group consisting of: Low tensile class with steel wires having a tensile strength from 2150 to below 2450 N/mm.sup.2; Normal tensile class with steel wires having a tensile strength from 2450 to below 2750 N/mm.sup.2; High tensile class with steel wires having a tensile strength from 2750 N/mm.sup.2 to below 3050 N/mm.sup.2; Super tensile class with steel wires having a tensile strength from 3050 to 3350 N/mm.sup.2.

4. The hose according to claim 1, wherein said steel wires in at least the innermost steel wire reinforcement layer are periodically unidirectionally bent for reducing the E-ratio of said steel wire reinforcement layer.

5. The hose according to claim 1, wherein said steel wires in at least the innermost steel wire reinforcement layer are periodically bidirectionally crimped for reducing the E-ratio of said steel wire reinforcement layer.

6. The hose according to claim 2, wherein said steel wires of at least the innermost and outermost steel wire reinforcement layer are of the same tensile class, said tensile class being one out of the group consisting of: Low tensile class with steel wires having a tensile strength from 2150 to below 2450 N/mm.sup.2; Normal tensile class with steel wires having a tensile strength from 2450 to below 2750 N/mm.sup.2; High tensile class with steel wires having a tensile strength from 2750 N/mm.sup.2 to below 3050 N/mm.sup.2; Super tensile class with steel wires having a tensile strength from 3050 to 3350 N/mm.sup.2.

7. The hose according to claim 2, wherein said steel wires in at least the innermost steel wire reinforcement layer are periodically unidirectionally bent for reducing the E-ratio of said steel wire reinforcement layer.

8. The hose according to claim 2, wherein said steel wires in at least the innermost steel wire reinforcement layer are periodically bidirectionally crimped for reducing the E-ratio of said steel wire reinforcement layer.

9. A method to produce a hose for conveying fluids under high pressure according to claim 1 comprising the steps of providing an elastomer core tube; winding steel wires around said elastomer core tube in a spiralled or braided innermost steel wire reinforcement layer; applying an intermediate elastomer material layer on said innermost steel wire reinforcement layer; winding one more spiralled or braided steel wire reinforcement layer on said intermediate elastomer material layer; optionally applying an intermediate elastomer material layer on said then outermost steel wire reinforcement layer; optionally applying another spiralled or braided steel wire reinforcement layer on said intermediate elastomer material layer; optionally repeating the two previous steps one or more times; applying an outer protective layer covering the outermost reinforcement layer; wherein the steel wires of said innermost steel wire reinforcement layer have an E-ratio that is lower than the E-ratio of the steel wires of said radially outermost steel wire reinforcement layer, whereby the E-ratio of any steel wire reinforcement layer is not lower than the E-ratio of any inner laying steel wire reinforcement layer, wherein said E-ratio is between 70,000 N/mm.sup.2 up to 200,000 N/mm.sup.2 for the radially outermost steel wire reinforcement layer and between 30,000 N/mm.sup.2 and 120,000 N/mm.sup.2 for the radially innermost steel wire reinforcement layer, wherein said steel wires of at least the innermost steel wire reinforcement layer have crimps or bends for altering said E-ratio, while said steel wires of at least the outermost steel wire reinforcement layer are free of bends or crimps, wherein said steel wires of at least the innermost and outermost steel wire reinforcement layer are of the same diameter.

10. The method according to claim 9, wherein said steel wires of at least said innermost steel wire reinforcement layer are thermally treated to an E-ratio between 30,000 and 120,000 N/mm.sup.2 while said E-ratio of said steel wires of at least the outermost steel wire reinforcement layer is between 70,000 N/mm.sup.2 and 200,000 N/mm.sup.2.

11. The method according to claim 9, wherein said steel wires of at least said innermost steel wire reinforcement layer are preformed with a preforming device that induces crimps or bends into said steel wires.

12. The method according to claim 11, wherein said steel wires are preformed with a preforming device prior to the step of winding steel wires in at least said innermost spiralled or braided steel wire reinforcement layer.

13. The method according to claim 11, wherein said steel wires are preformed with a preforming device concurrently with the step of winding steel wires in at least said innermost steel wire reinforcement layer.

14. The method according to claim 11, wherein said preforming device comprises a rotatable pin of substantially polygonal shape where over said steel wires are led under tension thereby inducing periodical unidirectional bends on said steel wires.

15. The method according to claim 11, wherein said preforming device comprises a pair of intermeshing gears where between said steel wires are led thereby inducing periodical bidirectionial crimps in said wires.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1a describes the load elongation curve of a conventional hose reinforcement wire of diameter 0.295, 1b shows the load elongation curve of a heat treated hose reinforcement wire, 1c shows the load elongation curve of a wire having crimps.

(2) FIG. 2 describes tensile load on the steel wires in the inner and outer layer reinforcement layer in a conventional braided hose as a function of hose pressure.

(3) FIG. 3 describes the tensile load on the steel wires of the different reinforcement layers in function of hose pressure according a first braided hose embodiment of the invention.

(4) FIG. 4 shows the tensile load on the steel wires of the different reinforcement layers in function of hose pressure according a second braided hose embodiment of the invention.

(5) FIG. 5 shows a preforming device to induce bends to the steel wires.

(6) FIG. 6 shows a preforming device to induce crimps into the steel wires.

(7) FIG. 7a describes the load elongation curve of a conventional hose reinforcement wire of diameter 0.60 mm, 7b shows the load elongation curve of a heat treated hose reinforcement wire, 7c shows the load elongation curve of a wire having bends.

(8) FIG. 8 describes the tensile load on the steel wires of the different reinforcement layers of a conventional spiralled hose as a function of the pressure inside the hose.

(9) FIG. 9 show the tensile load on the steel wires of the different reinforcement layers as a function of internal pressure of a first spiralled hose embodiment according the invention.

(10) FIG. 10 displays the force on the steel wires of the different reinforcement layers as a function of internal pressure of a second spiralled hose embodiment according the invention.

DETAILED DESCRIPTION OF THE INVENTION

(11) While for a thick walled isotropic tube under high pressure the hoop, radial and axial stresses can be calculated by the laws of continuum mechanics, a steel wire reinforced hose is a more intricate system due to the non-isotropy of the load carrying membersthe steel wiresand the large differences in material behaviour of the steel and the elastomer material. Therefore the inventors resorted to finite element modelling in order to corroborate their ideas.

(12) In a first embodiment a braided hose of following build was analysed:

(13) TABLE-US-00001 TABLE I Braided hose Inner diameter of core tube 9.52 mm Diameter of first steel wire reinforcement layer 16.12 mm Braided layer of 12 7 steel wires in S and 12 7 steel wires in Z Winding angle 53.5 Diameter of steel wire 0.295 mm Thickness of intermediate elastomer material layer 0.99 mm Diameter of second steel wire reinforcement layer 18.10 mm Braided layer of 12 7 steel wires in S and 12 7 steel wires in Z Winding angle 55.5 Diameter of steel wire 0.295 mm Thickness outer protective layer 2.79 mm Intended work pressure 35 MPa

(14) In order to evaluate the model the tensile properties of a conventional steel wire was used for both reinforcement layers. The force (F (in N)) Elongation (in %) curve of the wire is depicted in FIG. 1a. The wire has a diameter of 0.295 mm, a breaking load of 184 Nhence a tensile strength of 2692 N/mm.sup.2 i.e. Normal Tensile classand shows an elongation at break of 2.5%. It follows that the E-ratios of both reinforcement layers are equal to 107 689 N/mm.sup.2.

(15) FIG. 2 shows the resulting force (F (in N) in ordinate) on the wires of the inner layer (full line) and outer layer (dashed line) when the hose is pressurised (P (in MPa) in abscissa). It is clear that the first layer is first loaded as pressure rises thereby taking all the load and screening off the second layer. It is not until the inner layer wires start to yieldwhich occurs at about 100 MPabefore the outer layer takes up more load. Hence the tensile strength of the inner layer is reached well before the outer layer wires attain their ultimate tensile strength. Burst therefore occurs due to the collapse of the inner layer at about 140 MPa. At that moment, the outer layer steel wires are only loaded up to 66% of their capability.

(16) According a first preferred braided hose embodiment of the invention the steel wires of the innermost reinforcement layer have been thermally treated while the steel wires of the outermost reinforcement layer are left unaltered i.e. as drawn with the same force elongation diagram as of FIG. 1a. By heating the wire for seconds above a temperature of 400 C. in a protective atmosphere the plastic region of the wire is greatly increased together with a loss in tensile strength. In order to obtain a wire with a tensile strength of about 2700 N/mm.sup.2 one must therefore depart from a wire having a tensile strength of about 3100 N/mm.sup.2. The forceelongation diagram of a thermally altered steel wire is shown in FIG. 1b. The wire has an elongation at break of 4% while it attains a tensile strength of 2700 N/mm.sup.2. Hence its E-ratio is 67500 MPa i.e. much lower than that of the unaltered wire. This wire is used for the innermost reinforcement layer.

(17) FIG. 3 shows again the forces occurring in the wires of the reinforcement layers (F (in N)) as a function of the pressure P (in MPa). The full line is for the wires in the innermost reinforcement layer while the dashed line refers to the forces occurring in the outermost reinforcement layer. Due to the much higher elongation at break of the first layer it does not break prematurely and maintains it strength till much higher pressures. The burst pressure now occurs at 160 MPa and all wires are practically loaded to their tensile strength. Compared to the conventional hose, the burst pressure has increased with 14%. However, when comparing the forces occurring in the wires at about one fourth of the burst pressure i.e. the working pressure, there is quite a big discrepancy between the forces acting on the steel wires of the different layers. And it is just in this region, impulse testing is performed. Hence, although the design is optimal for burst pressure, it is unlikely that it will perform also well in impulse life testing.

(18) In a second preferred braided hose embodiment, the steel wires of the innermost reinforcement layer were subjected to a crimping treatment. The untreated wire (with the loadelongation according FIG. 1a) was drawn through a pair of crimping wheels thereby giving the wire a wave-like shape with an amplitude a and a wavelength . Within the context of this application with double amplitude 2a is meant the distance between parallel planes touching the extreme tops of the crimped wire minus the diameter of the wire. It can be shown that the extra elongation due to the structure of the wire i.e. the deformation of the wire .sub.structural scales according:
.sub.structural(a/).sup.2

(19) For this particular case the wire had received a crimp of wavelength 5.3 mm with amplitude a of 0.238 mm. This resulted in an extra elongation of about 2% giving a total elongation at break of 4.5%. The breaking load only slightly decreased to 178 N. The tensile strength was 2600 MPa resulting in an E-ratio of 57 873 MPa which is well below the original 107 689 MPa value of the original wire by a factor of 0.537.

(20) A second steel wire of 0.30 mm diameter originally had a breaking load of 183 N resulting in a tensile strength of 2590 N/mm.sup.2 (Normal Tensile strength). The elongation at break was 2.3%. After crimping the steel wire showed an amplitude a of 0.115 mm and a wavelength of 5.2 mm. The breaking load was 172 N at an elongation of break of 3.0% i.e. an increase of elongation of 0.7%. Hence the original E-ratio of 113 000 N/mm.sup.2 decreased to 81 000 N/mm.sup.2 or a factor of 0.717 by the crimping. These two examples illustrate that crimping allows to control the E-ratio very well.

(21) When now considering a hose of equal build as the conventional one wherein the steel wires of the innermost reinforcement layer are replaced with crimped wires and the outermost reinforcement layers with the same wire but free of crimps the loading of the filaments is remarkably equal for all wires. This is depicted in FIG. 4 wherein the full line depicts the loading of the innermost layer and the dashed line the loading of the outermost layer. Both load lines remain close to one another over the complete pressure range up to burst pressure. As a result, the loading of steel wires will be equal also at the working pressure (about 35 MPa) and also during impulse testing. An improved impulse life is therefore expected. Also an increase in flexibility is observed.

(22) FIGS. 5 and 6 show devices 500, 600 with which unidirectional bends or bidirectional crimps can be imposed on the wire. Such a device can be easily mounted on the spool carrier of the braiding machine or on the winding head of a spiralling machine. In a braiding or spiralling machine a preforming pin 506, 606 is already present in order to give the steel wires a helical deformation that fits the winding angle of the reinforcement layer. The preforming device can be used off-line i.e. during rewinding of the steel wires on the braiding or spiralling machine bobbins, or can be used in-line i.e. the wires are deformed concurrently with the winding of the wires around the hose body.

(23) In FIG. 5, wires 504 coming from the pay-off spool in parallel are first guided over the preforming pin 506. Preforming pin 506 can either be fixedly or rotatably connected to mounting plate 502. The imposed radius of curvature willamongst othersdepend on diameter and tensile strength of the wires and the diameter and friction properties (if non-rotatable) of the preforming pin 506. The wires are thereafter guided over a polygonal shaped wheel 508 that is mounted rotatable on axis 512. For example, the wheel can be provided with teeth 510. If sufficient tension is maintained on the steel wires, the steel wires 504 leaving the preforming device will show very local and very small bends 514. The bends are always in the same direction (unidirectional). Bends of different wires are in phase when leaving the polygonal shaped wheel i.e. the bends occur at equal positions along parallel wires. The wires are subsequently wound around the intermediate hose body (not shown).

(24) In FIG. 6, wires 604 coming from the pay-off spool in parallel are again first guided over a performer pin 606 that may be rotating or fixed. The wires are subsequently led between two preforming wheels 608 and 618 that are provided with intermeshing teeth 616, 610. The wheels are mounted rotatable on axes 620, 612 to the mounting plate 602. The wheels are sufficiently far apart that the wires 604 can pass without damage. Subsequently the deformed wires 604 are wound around the then already formed intermediate hose body (not shown). The passage through the forming wheels gives the wires a bidirectional, zig-zag like crimp 614. The amplitude of the crimp can be set by the distance between the preforming wheels and the wavelength of the crimp can be set by changing the pitch module of the teeth. Again the crimps are in phase.

(25) FIGS. 7 to 10 illustrate what happens when the inventive concept is applied to a high pressure hose of spiralled build-up with four reinforcement layers that are numbered L1 to L4 from radially most inner to most outer layer as summarised in Table II. The inner diameter of the hose (32 mm) is considerably larger than for the braided hose (9.52 mm) and therefore the reinforcement wall must be much stronger to guarantee about the same working pressure of 36 MPa.

(26) The spiralled hose has four steel wire reinforcement layers, situated at four discrete radii. The steel wires are wound in alternating directions (S, Z, S, Z) under slightly increasing winding anglesall close to the neutral anglewhen progressing from the inner reinforcement layer to the outer reinforcement layer as is customarily in the field. The wires are of diameter 0.60 mm in all embodiments following:

(27) In a conventional embodiment all wires are straight and not thermally treated. They have a tensile strength of 2900 N/mm.sup.2 (HT class) and an elongation at break of 2.5%. The E-ratio of all the steel wires is thus 116000 N/mm.sup.2. The LoadElongation curve of the Conventional Wire (CW) is illustrated in FIG. 7a. The forces occurring in the steel wires of the different reinforcement layers as a function of the pressure applied to the hose is shown in FIG. 8. The curves learn that in a conventional hose, the inner layers are first loaded followed by the radially outer layers. At the burst pressure of 130 MPa the steel wires of the outer two reinforcement layer L3 and L4 have been loaded only to about half of their load bearing capacity.

(28) When now the steel wires of the two innermost layers L1 and L2 are replaced with thermally treated wires (designated HE a (High Elongation)) a first preferred spiralled hose embodiment is obtained. The heat treatment of the wires results in an increase of the elongation at break to about 4% with only a little loss in tensile strength. The E-ratio of the steel wire of which the loadelongation curve is illustrated in FIG. 7b is 72504 N/mm.sup.2. The steel wires of the two outer layers L3 and L4 remain of the conventional type (CW) with the curve as depicted in FIG. 7a. The number of filaments in each layer and the winding angles remain the same as in the conventional embodiment.

(29) The forces acting on the steel wires of the different reinforcement layers as a function of pressure in this first preferred spiralled hose embodiment are illustrated in FIG. 9. Although there is still quite a difference in loading between the wire of the various layers at intermediate pressures, the pressure at burst has much improved to 145 MPa due to the elongation of the inner layers L1 and L2.

(30) In a second preferred spiralled hose embodiment the steel wires of the inner layers L1 and L2 are replaced with steel wires with bends by guiding conventional 0.60 mm wires under tension over a polygonal wheel. The bends increase the elongation at break of the wire from 2.5% up to 4.5% with only a small decrease in breaking load: from 820 N to 778 N. The E-ratio of the steel wire reduces from 116 000 N/mm.sup.2 (conventional wires) to 61147 N/mm.sup.2. The bends are outwardly oriented relative to the axis of the hose. The outer two layers L3 and L4 are made of conventional wires.

(31) The force per wire of the wires in the different layers as a function of the pressure is presented in FIG. 10. The forces acting on the filaments remain in a relatively narrow band and the loading of all wires is close to equal at all pressures. This is expected to result in a major improvement of impulse life. Moreover, the burst pressure has increased further to 155 MPa.

(32) TABLE-US-00002 TABLE II Spiralled hose Inner diameter of core tube 32 mm Diameter of first steel wire reinforcement layer L1 36.6 mm Number of filaments in layer 110 Winding angle 52.5 S Diameter of steel wire 0.60 mm Thickness of intermediate elastomer material layer 0.3 mm Diameter of second steel wire reinforcement layer L2 38.4 mm Number of filaments in layer 112 Winding angle 53.8 Z Diameter of steel wire 0.60 mm Thickness of intermediate elastomer material layer 0.30 mm Diameter of third steel wire reinforcement layer L3 40.2 mm Number of filaments in layer 114 Winding angle 55 S Diameter of steel wire 0.60 mm Thickness of intermediate elastomer material layer 0.30 mm Diameter of fourth steel wire reinforcement layer L4 42.0 mm Number of filaments in layer 116 Winding angle 56.2 Z Diameter of steel wire 0.60 mm Thickness outer protective layer 1.80 mm Intended work pressure 35 MPa