Description

Technical Field

[0001 ] The invention relates to a hose reinforcement steel wire for reinforcing elastomeric flexible hoses with a working pressure up to 7 000 kPa (70 bar) known as low to medium pressure hoses.

Background Art

[0002] Flexible hoses are omnipresent in equipment where fluids have to be

transported and/or power has to be transmitted. Flexible hoses at least comprise an inner liner that is fluid tight but not strong and one or more reinforcement layers that are strong yet flexible.

[0003] The type of reinforcement chosen is depending on the pressure rating of the hose. Therefore for low pressure hoses (hoses with a working pressure below 20 bar) cheap reinforcement materials such a cotton, nylon or polypropylene are used. Medium pressure hoses are normally reinforced with polyester or rayon. High pressure hoses (hoses with a working pressure of above 7 000 kPa) are practically solely reinforced with high tensile steel wires. High tensile steel wires generally have a tensile strength in excess of 2100 N/mm ² . The steel wires are coated with a bronze or brass layer in order to facilitate adhesion to rubber. In applications where weight, but not price, is of importance high tenacity fibres such as carbon, aramid, or glass can be considered.

[0004] There are low and medium pressure hose applications where other

properties of steel wire, besides strength, may have beneficial effects. For example, low or medium pressure gas hoses for domestic use may be armoured with steel wire in order to prevent rodents gnawing the elastomer wall thereby generating gas leaks. Alternatively gasoline fuel dispenser hoses may benefit from the electrical conductivity of the steel wires to prevent static charge build-up.

[0005] In these low to medium pressure hoses the use of the known high tensile steel wires only adds to the costs. The following features of the high tensile wire particularly add to the cost of the wire: • The use of plain high carbon steel wire rod (pearlitic steel with a carbon content larger than 0.60 wt%) necessitates the regular patenting of the steel wire in order to restore the metallographic structure to a drawable pearlitic steel.

• The application of a brass coating necessitates the electrolytical deposition of a copper and zinc layer that are subsequently diffused into one another.

Although prior art publications on low carbon steel wires for reinforcement of rubber goods are available, they focus on reaching as high as possible tensile strengths per wire. Moreover, the brass coating is maintained in order to keep the drawability of the wire. Reference is made to JP

05/105951 , EP 0429094, US 5338380.

Disclosure of Invention

[0006] In order to provide a hose reinforcement steel wire that is fit for its purpose in terms of performance and price for low and medium pressure hoses, the inventors suggest a hose reinforcement wire that can be manufactured at a lower cost but still has the additional benefits associated with the use of steel.

[0007] According a first aspect of the invention a hose reinforcement wire defined by the terms of claim 1 is claimed.

[0008] The hose reinforcement wire is suitable for reinforcement of low to medium pressure hoses i.e. hoses with a working pressure below 70 bar. The hose reinforcement wire has a carbon content of between 0.02 percent by weight (abbreviated to "wt%" in all that follows) to 0.25 wt%, a silicon content of between 0.05 to 0.30 wt%, a manganese content of between 0.20 to 1 .0 wt%, any other intentionally or unintentionally added element other than iron being present in an amount of less than 0.5 wt%, the balance being iron.

[0009] Particularly preferred compositions have a carbon content between 0.10 to 0.22 wt% of carbon, between 0.05 and 0.18 wt% of silicon and between 0.2 and 0.5 wt% of manganese, any other intentionally or unintentionally added element other than iron being present in an amount of less than 0.3 wt%, the balance being iron. [0010] With 'any other intentionally or unintentionally added element' are meant metal elements like - but not limited thereto - chromium, nickel,

molybdenum, copper and also non-metal elements like - but not limited thereto - oxygen, nitrogen, sulphur, phosphorus.

[001 1 ] Such steels have what is generally known as a 'plain carbon steel

composition'. Stainless steel compositions also typically have a low carbon content but there the presence of metals like nickel or chromium is appreciable and fall outside the scope of this application.

[0012] The plain carbon composition has mainly a ferrite or pearlite matrix and is predominantly of a single phase. There are no martensite or bainite phases or mixed phases of martensite and bainite phases present, not in the wire rod nor in the final product.

[0013] The hose reinforcement wire is free of any metallic coating. By this is

meant that the steel surface of the wire is not intentionally coated with another metal or metal alloy coating like brass, bronze, zinc, zinc alloys like zinc aluminium or ternary alloys or quaternary alloys that consist only out of metallic elements.

[0014] The proof strength at 0.2% plastic extension is the stress (expressed in N/mm ² ) at which the plastic extension is equal to 0.2% of the

extensometer gauge length in a tensile test. See paragraph 3.10.3 and Figure 3 of ISO 6892-1 :2009(E). It is abbreviated as R _p0 . ₂ . The plastic extension is the permanent elongation induced on the wire after a proof stress has been applied and subsequently removed. If the applied stress is equal to the proof strength at 0.2% plastic extension, the tested wire length will be 0.2% longer compared to the original length after that stress has been removed.

[0015] For the hose reinforcement wire of interest the proof strength at 0.2%

plastic extension is lower than 1700 N/mm ² . Even more preferred is if it is lower than 1600 N/mm ² .

[0016] In a further preferred embodiment the proof strength at 0.2% plastic

extension is larger than 1000 N/mm ² , for example larger than 1300 N/mm ² .

[0017] The proof strength at 0.2% plastic extension is a measure for the ductility and bendability of the wire. For the specific hose reinforcement wire it brings the following advantages with it: • As a hose reinforcement wire is incorporated in a braided structure, different ribbons of hose reinforcement wires cross each other over and under each other. This short bending generates a stress concentration when the hose is pressurised. Conventional hose reinforcement wires - with an R _p0 .2 value above the values of the inventive wire - are very sensitive to these transversal stresses.

• When a hose reinforcement wire is incorporated in a braided or

spiralled structure it is preformed in order to obtain a helix shape compatible with the diameter of the hose. When the proof strength at 0.2% plastic extension is between the limits claimed, it is easier to give a permanent curvature to the wire compared with the known high tensile hose reinforcement wires.

• Due to the improved ductility and bendability, hoses comprising the inventive reinforcement wire are easier to bend and do not spring back so much as hoses comprising the conventional high tensile steel reinforcement wires.

[0018] According a further preferred embodiment, the reinforcement wire has a tensile strength of between 1200 to 2000 N/mm ² . Although this is lower than the known high tensile hose reinforcement wires, a strength level of above 2000 N/mm ² is not needed for the particular use in a low to medium pressure hose. Typically the hose reinforcement wires of the invention have a diameter of between 0.15 to 0.80 mm, such as 0.15, 0.20, 0.25, 0.28, 0.30, 0.35, 0.38, 0.40, 0.45, 0.50, 0.56, 0.60, 0.65, 0.71 , or 0.80 mm.

[0019] The hose reinforcement wire according the invention is cold drawn from the wire rod without any intermediate heat treatment. With 'heat treatment' is meant any treatment that intentionally brings the wire at a temperature above about 500°C. The skilled person understands under 'heat treatment' treatments such as patenting (bringing the steel above 1000°C to austenise the steel and subsequently cooling the steel to a temperature of about 600°C to 650°C), annealing (bringing the wire above 700°C) followed or not followed by quenching, stress relieving (bringing the wire above 500°C followed by slow cooling).

[0020] Cold drawing is the action whereby the diameter of the steel wire is

reduced by drawing it through a sequence of circular dies on wire drawing machines. At each die the wire obtains a reduction in diameter from an entrance diameter 'D' to an exit diameter 'd'. The 'true elongation ε' due to the die is then equal to ε = 2 ln(D/d). The true elongation of each die can be added resulting in a total true elongation 'ετ'. This total true elongation is in a preferred embodiment larger than 5.0.

[0021 ] The surface of the hose reinforcement wire is free from any intentionally applied metallic coating. Therefore it may be necessary to coat the surface of the hose reinforcement wire with a non-metallic coating in order to prevent corrosion and/or induce adhesion to the elastomer of the hose.

[0022] In a first preferred embodiment, the wire is coated with one out of the

group consisting of an organo functional silane, an organo functional titanate, or an organo functional zirconate or mixtures thereof. These compounds are known for the purpose of improving adhesion between elastomers and metals. The compounds have at least one endgroup - containing the silicon, titanium or zirconium atom - that provides the binding to the iron surface and a backbone that reacts with the elastomeric material such as for example the vulcanisable rubber elastomer.

[0023] A preferred organo functional silane has the following structure:

Y-(CH ₂ ) _n -SiX ₃

wherein :

Ύ' represents an organo functional group selected from

NH ₂ , CH ₂ =CH-, CH ₂ =C(CH ₃ )COO-, 2,3-epoxypropoxy, HS- and, Cl-

'X' represents a silicon functional group selected from

-OR, -OC(=O)R', -CI wherein R and R' are independently selected from C1 to C4 alkyl, preferably -CH ₃ , and -C ₂ H ₅ ; and 'n' is an integer from 0 to 10 and preferably from 0 to 3.

[0024] Such compounds can easily be dissolved in a mixture of alcohol and

water. Application to the wire can occur by means of dipping, spraying, painting, guiding through a fluid curtain or any other known way to apply a liquid to a wire. Care must be taken to thoroughly dry the wire to prevent corrosion.

[0025] An alternative coating is an organic coating based on a hydrocarbon or phenolic resin. Hydrocarbon resin includes coumarone-indene resins, petroleum resins, terpene resins, bitumens, tar and copolymers, e.g., high styrene reinforcement polymers and rosins, their salts, esters and other derivatives. Most preferred are coumarone (benzofuran) or indene or mixtures thereof. Phenolic resin includes various kinds like

alkylphenol/formaldehyde resins, alkylphenol and acetylene condensation products, lignin and modifications thereof to name a few.

[0026] The resin coating is prepared by dissolving the above mentioned

hydrocarbon or phenolic resins in a solvent. Suitable solvents can be acetone, gasoline, xylene, diethylene glycol diethyl ether, butyl acetate, ethyl acetate or a mixture of one or two of the above. Between 5 and 300 grams of resin or more preferred between 5 to 50 grams of resin or added to one litre of the solvent. The resin coating can be applied by means of dipping and subsequent stripping, painting, spraying or through a coat curtain. After coating the solvent is evaporated.

[0027] In another preferred embodiment the resin coating further comprises a corrosion inhibiting reagent that is one out of the group consisting of benzimidazole, benzotriazole, organic borates, organic phosphates, organic metaphosphates, or organic nitrides.

[0028] Benzimidazale and benzotriazole are compounds known per se.

[0029] Examples of organic borates are organic alkyl, cycloalkyl and aryl

derivates of m-boric acid, o-boric acid, and pyro boric acid. Examples of organic phosphates and metaphosphates are organic alkyl, cycloalkyl and aryl derivates of m-, o-, pyro- and hypo-phosporic acid.

[0030] An alternative inorganic coating is obtained by forming a phosphate layer on the steel surface of the hose reinforcement wire. Such phosphate layer can be iron, manganese or zinc based. Most preferred is iron based phosphate.

[0031 ] An alternative organic coating is a liquid coating comprising a mineral oil such as an alkane or naphthenic mineral oil or liquid paraffin oils. Even more preferred is if the oil applied on the hose reinforcement wire is compatible with the oil used in the mixing of the rubber for example is the same oil as used in the mixing of the rubber.

[0032] According a second aspect of the invention a braided hose is presented.

The hose comprises at least one braided reinforcement layer, for example one braided reinforcement layer. In a braided reinforcement layer, the reinforcement wires are grouped into ribbons containing between 4 to 10, more preferred between 6 to 8 for example 7 hose reinforcement wires. Two sets each comprising between 6 and 18 ribbons for example 12 ribbons are interwoven according the maypole weave. The first set turns in a first direction and the second set turns in the direction opposite to the first direction around the inner liner of the hose. The two sets are interwoven meaning that - when following one ribbon - this ribbon will go above and below the ribbons of the other set and vice versa. For example the one ribbon can go below one ribbon of the second and then above the next ribbon of the first set resulting in a plain weave. Alternatively the interweaving can be according a twill or satin weave. The at least one braided reinforcement layer comprises the hose reinforcement wire according the invention. Alternatively the at least one braided

reinforcement layer consists of the hose reinforcement wire according the invention.

[0033] The inventive wire is particularly suitable for braiding as:

• The inventive wire is easily formable;

• The inventive wire is less susceptible to transverse stresses than high tensile wire;

[0034] In a particularly preferred embodiment of the braided hose the coverage degree of any one of said reinforcement layers is less than 93%. With 'coverage degree' is meant the ratio - expressed in percentage - between the area of the hose that is covered by the reinforcement wires to the total area of the hose when braided on the inner liner of the hose. More preferred is if the coverage degree is larger than 50% for example between 70% and 90%. With decreasing coverage degree, the amount of surface not covered by the reinforcement layer increases.

[0035] If the coverage degree becomes too low the risk exists that the inner tube is no longer sufficiently supported by the reinforcement layer. If the coverage degree becomes too high the cost benefit is lost.

[0036] According third aspect of the invention a spiralled hose comprising at least one reinforcement layer is presented. The at least one reinforcement layer comprises the described inventive hose reinforcement wire. Alternatively the at least one reinforcement layer consists only of the inventive hose reinforcement wire. In a spiralled hose all filaments in one reinforcement layer are wound side by side in a spiral shaped fashion. The winding angle is close or equal to the neutral angle Atan{yp∑). Preferably an even number of reinforcement layers are present to preserve that the hose does not rotate when pressurised.

Brief Description of Figures in the Drawings

[0037] Figure 1 shows the prior art process for making high tensile hose

reinforcement wire.

[0038] Figure 2 shows the process for making the high tensile hose reinforcement wire according the invention.

[0039] Figure 3 shows the load elongation diagram of the inventive wire

[0040] Figure 4 shows the remaining bending after applying a certain degree of bending to the wire for the known high tensile wires and the inventive wire.

[0041 ] Figure 5 shows a twill 2x2 weave with the inventive wires.

Mode(s) for Carrying Out the Invention

[0042] Figure 1 shows the conventional routing for high carbon hose

reinforcement wire. Coil 10 with wire rod of 5.5 mm is cold drawn to a diameter of between 3.0 to 3.5 in dry drawing step 12. In order to restore the pearlite steel structure to enable further drawing, a first intermediate patenting step 14 is performed. After patenting the wire is further cold drawn in dry drawing step 16 resulting in an intermediate diameter of between 1 .0 to 2.5 mm. Again the pearlite steel structure must be restored in patenting step 18. This patenting is normally followed by a plating step 20 wherein the pearlite steel structure is restored. In a final cold drawing step 22 the wire is reduced to its final diameter of between 0.15 to 0.75 mm. The resulting spool 24 contains a hose reinforcement wire with a tensile strength higher than 2100 N/mm ² .

[0043] Figure 2 shows the inventive route with no heating steps involved. Wire rod 30 is a low carbon wire rod with an exemplary composition of 0.037 wt% carbon, 0.290 wt% manganese, 0.030 wt% silicon, 0.010 wt% sulphur, 0.01 1 wt% phosphorus, 0.015 wt% chromium. The wire rod has a diameter of 5.5 mm. For larger size hose reinforcement wire a wire rod diameter of 6.5 mm can be considered. In a first cold drawing 32 the wire is dry drawn to diameter of between 3.0 to 3.5 mm for instance 3.25 mm. The true elongation applied is 1 .052. In a second cold drawing 34 the wire is dry drawn to a diameter of 1 .5 mm. The true elongation applied is 1 .546. In a third cold drawing 36 the wire is wet drawn in a watery soap emulsion to a diameter of 0.55. The true elongation applied is 2.007. In a fourth cold drawing 38 the wire is oil drawn to a final diameter of 0.30 mm. True elongation is here 1 .212. The total true elongation is then 5.817.

[0044] In an alternative processing, thicker intermediate wires can be directly used as final wires 42', thereby eliminating the fourth drawing step 38. This is particularly suitable for wires with diameters above 0.50 mm.

Possibly a wire rod of 6.5 mm can be used in case the total true elongation must be larger than 5.00.

[0045] Possibly the wire is coated by means of a coating applicator 40. For

example the wire can be dipped in a mineral oil and subsequently slightly wiped. A suitable mineral oil is for example RPO 501 naphthenic oil obtainable from Gulf Petrochem.

[0046] Figure 3 shows the load elongation curve of the inventive wire. The tensile strength 'Rm' is only 1739 N/mm ² . The proof strength at 0.2% plastic extension 'R _p0 .2' is 1432 N/mm ² . This is much lower than the conventional high tensile wire that is normally used as hose reinforcement wire. On a conventional wire an 'Rm' of 2631 N/mm ² and an 'R _p0 .2' of 2329 N/mm ² was found.

[0047] The effect of this is twofold: when the wire is braided, the contact points between wires from crossing ribbons are less susceptible to transversal stresses as the wire is clearly more ductile.

[0048] Secondly the wire can be easily given a permanent bending. Hoses made with the inventive wire as reinforcement layer can be easily given a permanent bend too as the reinforcement of the hose overcomes the stiffness of the rubber.

[0049] Figure 4 illustrates this bending behaviour of a prior art wire 404 and an inventive wire. When a steel wire is bent over a roll with a radius 'r _a ' (in mm) a curvature of 1/r _a is applied onto the wire: the 'Applied Curvature k _a ' (in 1/mm). After the release of the bending moment (i.e. removal of the bending force) a 'Remaining curvature k _r ' (in 1/mm) remains on the wire i.e. the wire has obtained a permanent deformation. From plastic bending theory it follows that:

wherein E is the modulus of steel, D is the diameter of the wire and η is a form factor that for a round wire is equal to 1 .70. As the proof strength at 0.2% plastic extension is much lower for the inventive wire 404, the wire will bend easier and the 'springback' k _a -k _r is smaller. The wire is easier to bend and the wire will take any deformation applied.

[0050] The plasticity of the wire has also effect on the hose produced. The hose can be easily give a permanent shape and will not spring back. Prior art hoses comprising high tensile wires are very difficult to deform and spring back to their original shape when no longer held.

[0051 ] Figure 5 shows The 2x2 twill weave of a single layer braided hose prior to embedment into the outer layer hose. In a 2x2 twill weave, the ribbons 502 and 504 of different sets cross one another two up two down with an offset of 1 . The degree of coverage is equal to the surface covered by the wires (corresponding to the difference in area between the white lined diamond 506 and the grey area 508) over the total area (the area delineated by the white lined diamond 506). In this case the coverage degree is 92%. The presence of the windows 510 has the additional advantage that the covering rubber connects, adheres, is vulcanised to the inner liner. This improves the overall integrity of the hose. Moreover, the presence of windows allows the two sets of ribbons to move in a scissor way relative to one another thereby easing the bending of the hose.