Patent Application
20170148541
The present invention relates to a molten Al plated steel wire that is improved particularly in resistance to deformation associated with “torsion”. The invention also relates to a strand wire containing the molten Al plated steel wire as an element wire.
A copper wire has been used as various conductive wires including a conductive wire for a wire harness of an automobile. However, contamination with a copper material is not preferred on recycling with iron scrap. Accordingly, from the standpoint of the recycling efficiency, an aluminum wire, which can be melted with iron scrap and has relatively good conductivity, is advantageously applied.
A strand wire is often used as a signal wire or the like used in a wire harness. As a strand wire for a wire harness formed of an aluminum wire, for example, a strand wire containing approximately 10 Al element wires each having a diameter of from 0.25 to 0.30 mm stranded has been subjected to practical use. Although such a large cross sectional area is not necessary from the standpoint of the conductivity for transmitting a signal electric current, an Al element wire is inferior in strength to a Cu element wire and the like, and this level of thickness becomes necessary in consideration of the strength of the strand wire formed only of Al element wires.
As a measure for enhancing the strength of the signal strand wire using Al element wires, it is effective that a steel wire having a larger strength than aluminum is used as a core element wire, around which Al element wires are stranded. The enhancement of the strength of the strand wire enables reduction of the cross sectional area, and lead to reduction in size of a wire harness. As the steel wire for the core element wire, an Al plated steel wire is considered to be promising. The use of an Al plated steel wire avoids bimetallic corrosion, which becomes a problem, for example, in the case using a naked steel wire or a Zn plated steel wire. Furthermore, the material cost is largely decreased as compared to the case using a stainless steel wire.
For the mass production of an Al plated steel wire, a molten Al plating method is effective. It has been considered that it is not easy to form a molten Al plated layer stably on a steel wire having a core wire diameter of 1 mm or less. However, in recent years, molten Al plated steel wires with various depositing amounts can be produced with a continuous line (PTLs 1 to 3).
A molten Al plated steel wire having a small depositing amount suitable for a signal element wire can be produced by the techniques described in PTL 3 and the like. However, in the case where the conventional molten Al plated steel wire is used as it is as a core element wire of a strand wire, there arises a problem that a phenomenon that the element wire is broken in the production process of the strand wire is liable to occur. It has been clarified that the cause of the phenomenon is that the conventional molten Al plated steel wire has a defect of weakness against a “torsional process”.
On the other hand, various techniques for producing a strand wire with no torsion applied to the element wires have been developed and subjected to practical use.
An object of the invention is to provide a molten Al plated steel wire excellent in torsional resistance that does not cause the aforementioned problem of breakage due to torsion in application to an ordinary production equipment for a strand wire, in which element wires are applied with torsion.
The object is achieved by a molten Al plated steel wire containing a steel core wire having a diameter of from 0.05 to 0.50 mm as a core material, having thereon molten Al plating with a depositing amount thereof that is uniformized to satisfy the following expression (1) for an average diameter DA (mm) and a minimum diameter DMIN (mm) in the longitudinal direction of the wire:
(DA−DMIN)/DA≦0.10 (1)
The average diameter DA (mm) and the minimum diameter DMIN (mm) can be obtained by measuring the wire diameter of one Al plated steel wire for a length L of a portion thereof to be applied continuously to a stranding process. Assuming that the two directions that are orthogonal to each other and each are perpendicular to the longitudinal direction of the wire material are designated as an x direction and a y direction respectively, the average value of the diameter DX (mm) in the x direction and the diameter DY (mm) in the y direction at one position in the longitudinal direction, i.e., (DX+DY)/2, is designated as the wire diameter at the position in the longitudinal direction. The diameters DX and DY can be obtained, for example, by a method of measuring the projected diameter on viewing the wire material in one direction by irradiating with laser light. The average diameter DA and the minimum diameter DMIN are the average value and the minimum value respectively of the wire diameter D within the range of the length L. On obtaining the average diameter DA and the minimum diameter DMIN, the distance between the measurement points adjacent to each other in the longitudinal direction (i.e., the measurement pitch of the wire diameter D) is 0.2 mm or less.
The molten Al plated steel wire having a depositing amount of the molten Al plating that is uniformized is preferably not subjected to a wire drawing process after applying to the molten Al plating.
The material steel wire applied to molten Al plating may be a naked steel wire, and also may be a plated steel wire, such as a Zn plated steel wire and an Ni plated steel wire. In the description herein, the plating that is preliminarily applied to the surface of the material steel wire to be applied to molten Al plating is referred to as “preliminary plating”. The “steel core wire” described above means the steel portion occupied on the cross section of the molten Al plated steel wire. In the molten Al plated steel wire that is not subjected to a wire drawing process after applying to the molten Al plating, the diameter of the steel portion constituting the material steel wire applied to molten Al plating corresponds to the diameter of the steel core wire. The thickness of the preliminary plating layer is not included in the diameter of the steel core wire.
The invention also provides a strand wire containing the aforementioned molten Al plated steel wire as an element wire that is stranded with other element wires in a state where the molten Al plated steel wire is applied with torsion. The invention also provides a method for producing a strand wire, containing twisting the aforementioned molten Al plated steel wire with other element wires in a state where the molten Al plated steel wire is applied with torsion.
The molten Al plated steel wire of the invention is notably improved in resistance to torsion. Accordingly, as an element wire of a strand wire in application thereof to an ordinary method of a wire stranding process with torsion applied thereto, the breakage thereof, which has been a problem, can be avoided. In particular, the wire can be subjected to a wire stranding process with torsion applied thereto without subjecting to a wire drawing process after applying to the molten Al plating, and therefore the use of the wire as a core element wire of a strand wire can enhance the strength of the strand wire at low cost. Accordingly, the invention is useful particularly for achieving both the high strength and the low cost of the strand wire for wire harness.
As the molten Al plated steel wire that assumes a role of reinforcing a strand wire for a wire harness, a steel core wire having a diameter in a range of from 0.05 to 0.50 mm is useful. When the steel core wire is too thin, the strength enhancing effect of the strand wire may be small, and when the steel core wire is too thick, not only the strength may be excessive, but also the total diameter of the strand wire may be larger, which is contrary to the needs of a thin wire and a light weight of a wire harness.
According to the investigations made by the present inventors, it has been found that the molten Al plated steel wire having a steel core wire having such a small diameter as above tends to have a wire diameter that is uneven in the longitudinal direction in the production thereof, which is a cause of the reduction of the durability to a “torsional process” (which may be hereinafter referred to as “torsional resistance”) in a state untouched after the molten Al plating. However, it has been difficult to find a condition for providing good torsional resistance stably only by evaluating the torsional characteristics with the difference between the maximum diameter and the minimum diameter in the longitudinal direction as the parameter. As a result of the further investigations under the circumstances, it has been clarified that in the fluctuation of the wire diameter in the longitudinal direction, the portion having an increased wire diameter has no particular adverse effect on the torsional resistance of the molten Al plated steel wire. Accordingly, such a parameter is necessarily determined that excludes the effect of the increased wire diameter. As a result of the detailed studies, it has been confirmed that the torsional resistance of the molten Al plated steel wire can be favorably evaluated by the expression (DA−DMIN)/DA, which is a function of the average diameter DA (mm) and the minimum diameter DMIN (mm) in the longitudinal direction of the molten Al plated steel wire.
As a torsional test method of a wire material, for example, there has been the rule for a hard drawn steel wire in JIS G3521. However, the method targets a material having a wire diameter of 0.70 mm or more, and there is no general standard for evaluating the torsional resistance of a wire material that is thinner than that. Under the circumstances, the inventors referring to the JIS document have investigated the torsional resistance of various molten Al plated steel wires (that are not subjected to a wire drawing process after applying to the Al plating) by using a torsional test equipment shown schematically in
It is understood from
(DA−DMIN)/DA≦0.10 (1)
While the minimum diameter DMIN used herein is a value over the distance between the chucks, i.e., 100 mm, as described above, the portion that is most liable to be broken in the production of a strand wire is a portion having the smallest diameter over the entire length in the longitudinal direction. Accordingly, in the case where DA and DMIN based on the measurement data of the wire diameter over the entire length in the longitudinal direction satisfy the expression (1), it can be evaluated that the molten Al plated steel wire has a capability that is capable of avoiding breakage in the production of a strand wire over the entire length.
The molten Al plated steel wire that satisfies the expression (1) can be produced directly through a molten Al plating process by applying a measure for uniformizing the depositing amount of the Al plating on molten Al plating, without performing a wire drawing process thereafter. For example, it has been confirmed that the molten Al plated steel wire can be produced by the following method.
The molten Al plated steel wire can be produced in such a manner that a material steel wire formed of a steel core wire having a diameter of from 0.05 to 0.50 mm or a material steel wire formed of a plated steel wire containing the steel core wire having on the surface thereof a Zn plated layer or an Ni plated layer having an average thickness of 5 μm or less is immersed in a molten Al plating bath and then continuously withdrawing to a gas phase space.
In the gas phase space 8 inside the shield 4, a nozzle 61 for blowing an inert gas to the position on the bath surface, at which the steel wire 3 is withdrawn, (i.e., the plating bath rising portion 5) is disposed. The inert gas is supplied to the nozzle 61 from an inert gas supplying device 57 via a pipe line 56. A gas flow rate controlling mechanism (which is not shown in the figure) is provided in the course of the pipe line 56 or inside the inert gas supplying device 57, with which the flow rate of the inert gas discharged from the nozzle 61 can be controlled. The nozzle 61 is adjusted in the inert gas discharge direction to prevent the inert gas discharge stream from the nozzle 61 from striking on the portion of the withdrawn steel wire at a height of 20 mm or more from the average bath height. Accordingly, the inert gas discharged from the nozzle 61 directly strikes a part of the plating bath surface 6 including the plating bath rising portion 5 and a part of the region of the steel wire 3 withdrawn from the plating bath rising portion 5 at a height of less than 20 mm from the average bath height, and thereby the oxygen concentrations in these parts are kept lower. The nozzle 61, the pipe line 56, the inert gas supplying device 57, and the gas flow rate controlling mechanism (which is not shown in the figure) constitute an inert gas supplying system. Examples of the inert gas include nitrogen gas, argon gas, and helium gas. In the gas phase space 8 inside the shield 4, a pipe line 63 having a discharge port 62 for introducing an oxygen-containing gas, and thereby the oxygen concentration inside the shield 4 is controlled depending on necessity.
The steel wire 3 withdrawn through the gas phase space 8 inside the shield 4 is cooled during the process of withdrawing, and thereby the plated layer is solidified. In the withdrawing process, a cooling device 53 may be provided depending on necessity, with which the steel wire can be forcibly cooled by blowing gas or liquid mist. A heat treatment device may be inserted between the supplying device 51 and the plating bath 1. The heat treatment atmosphere used may be, for example, a reductive gas atmosphere (such as an H2—N2 mixed gas). In the region from the heat treatment device to the position where the wire is immersed in the plating bath 1, a snout for shielding from the air may be provided in some cases. In the case where preliminary plating or wire drawing is performed as a preceding step, the equipment for the preceding step and the plating equipment may be disposed in series to constitute a continuous line.
For uniformizing the depositing amount of the molten Al plating to satisfy the above expression (1) by using the equipment shown in
The material steel wire subjected to the molten Al plating may be a wire having preliminary plating, such as a Zn plated steel wire and an Ni plated steel wire, as described above. In the case where a naked steel wire having no preliminary plating is subjected to the molten Al plating, it is preferred that the steel wire is subjected to a reductive heat treatment, and then continuously charged in the molten Al plating bath without exposure to the air by passing through a snout. The steel core wire may also be a stainless steel wire depending on necessity, in addition to a steel types having been used as a Zn plated steel wire and an Ni plated steel wire. A stainless steel is an alloy steel containing Cr in an amount of 10% by mass or more. Examples thereof include the stainless steel types of an austenite series, a ferrite series, a martensite series and the like, defined in JIS G4309:2013. Specific examples thereof include a stainless steel where an austenite phase is said to be metastable, such as SUS301 and SUS304, a stable austenitic stainless steel, such as SUS305, SUS310, and SUS316, a ferritic stainless steel, such as SUS405, SUS410, SUS429, SUS430, SUS434, SUS436, SUS444, and SUS447, a martensitic stainless steel, such as SUS403, SUS410, SUS416, SUS420, SUS431, and SUS440, and also include a chromium-nickel-manganese based stainless steel classified into the SUS200 series, but the stainless steel is not limited thereto. The stainless steel that is applied to the core wire is preferably subjected to Ni plating as preliminary plating.
The molten Al plating bath may have a Si content of from 0 to 12% by mass. In other words, a pure Al plating bath having no Si added may be used, and an Al plating bath containing Si in a range of 12% by mass or less may also be used. The addition of Si can suppress the growth of the brittle Fe—Al based alloy layer formed between the steel core wire and the Al plated layer. The addition of Si also lowers the melting point to facilitate the production. However, the increase of the Si content may deteriorate the workability of the Al plated layer itself, and also may lead reduction of the conductivity. Accordingly, in the case where Si is contained in the Al plating bath 1, the content thereof is preferably in a range of 12% by mass or less. The bath may unavoidably have impurity elements, such as Fe, Cr, Ni, Zn, and Cu, mixed therein in some cases.
The depositing amount of the Al plating is preferably from 5 to 50 μm in terms of the average thickness of the molten Al plated layer in the longitudinal direction. When the depositing amount of the Al plating is too small, there is a possibility that the steel base is exposed in the stranding process and a subsequent crimping process or the like, which may be a cause of deterioration of the corrosion resistance. When the depositing amount of the Al plating is excessive, on the other hand, the proportion of the steel core wire in the cross section is relatively lowered, and the strength per unit wire diameter may be lowered.
A molten Al plated steel wire was produced by using a production equipment of a molten Al plated steel wire having the structure shown in
The material steel wires subjected to the molten Al plating were a Zn plated steel wire, an Ni plated steel wire, and a naked steel wire, each containing a hard drawn steel wire according to JIS G3560 as the core material. Among these, the Zn plated steel wire was obtained by subjecting a molten Zn plated hard drawn steel wire having a diameter of 1.0 mm to a wire drawing process to make the prescribed diameter. The Ni plated steel wire and the naked steel wire were also adjusted to have the prescribed diameter by a wire drawing process. The thickness of the Zn plating or Ni plating (preliminary plating) of the material core wire can be found by (outer diameter D1 of material core wire−diameter D0 of steel core wire)/2.
The resulting molten Al plated steel wires were measured for the breaking number of torsion by the aforementioned method (chuck distance: 100 mm, load: 50 g) with the torsional test equipment shown in
For the diameters of the resulting molten Al plated steel wires, as described above, the average diameter DA was a value based on the measurement data of the entire length of approximately from 100 to 8,000 m of the molten Al plated steel wire, and the minimum diameter DMIN was a value based on the measurement data of the chuck distance of 100 mm of the wire material that was actually subjected to the torsional test.
It was understood from Table 1 that in the case where the steel wire was withdrawn from the bath surface without the use of the contact member, the uniformization of the depositing amount of the molten plating satisfying the expression (1) was not realized. As a result, the torsional resistance was deteriorated.
On the other hand, in the examples of the invention using the contact member, the depositing amount of the molten Al plating was uniformized to satisfy the expression (1). The examples exhibited a breaking number of torsion exceeding 50, and thus evaluated to have torsional resistance capable of resisting to a stranding process with torsion applied thereto in a state untouched after the molten Al plating.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/067766 | 7/3/2014 | WO | 00 |
