CONTINUOUS SURFACE TREATMENT METHOD FOR STEEL WIRE

Abstract

A method to form a phosphate coating on a steel wire, the method including: continuously forming a phosphate coating on a steel wire before being subjected to cold forming; and a descaling of jetting slurry including grit-like abrasive particles onto the steel wire before forming the phosphate coating, thereby producing a new surface on the steel wire. The method can further include a preheating of the steel wire after the descaling and before the coating treatment. The method makes it possible to form a phosphate coating on a steel wire in a short time with high productivity without causing significant forming deterioration on the surface of the steel wire.

Claims

1: A continuous surface treatment method for a steel wire, which is for continuously treating a surface of a steel wire before subjecting the wire to cold forming, the method comprising: continuously forming a phosphate coating on the steel wire; and a descaling of jetting slurry including grit-like abrasive particles onto the surface of the steel wire before forming the phosphate coating, thereby producing a new surface on the surface of the steel wire.

2: The continuous surface treatment method for a steel wire according to claim 1, further comprising a preheating which is performed after the descaling and before the coating treatment, to preheat the steel wire.

3: The continuous surface treatment method for a steel wire according to claim 1, wherein, in the descaling the slurry is jetted at a jetting pressure of 0.2 MPa or more and 0.6 MPa or less.

4: The continuous surface treatment method for a steel wire according to claim 2, wherein, in the descaling, the slurry is jetted at a jetting pressure of 0.2 MPa or more and 0.6 MPa or less.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0018] FIG. 1 is a diagram showing a process of a continuous surface treatment method according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

[0019] An embodiment of a continuous surface treatment method of the present invention is explained in detail below with reference to the drawings.

[0020] As shown in FIG. 1, the continuous surface treatment method of the present invention is performed in a manufacturing line 1 (a wire drawing line and a heading line) in which cold forming such as wire drawing is performed on a steel wire (a steel wire rod) W. Specifically, the continuous surface treatment method in this embodiment includes a coating step P5 for forming a phosphate coating, which is a base of a lubricant on the surface of the steel wire W in order to secure lubrication between a die 5 and the steel wire W in wire drawing and a lubrication treatment step P6 for applying a lubricant including metallic soap to the phosphate coating to coat the phosphate coating with the lubricant in order to increase lubricity.

[0021] More specifically, as shown in FIG. 1, the continuous surface treatment method in this embodiment includes a winding-off step P1, a straightening step P2, a descaling step P3, a preheating (wire preheating) step P4, the coating treatment P5, the lubrication treatment step P6, a drying step P7, a wire drawing step P8, and a coiling step P9. In the winding-off step P1, the steel wire W is wound off from a coil of a supply stand 2. In the straightening step P2, the steel wire W wound off in the winding-off step P1 is straightened into a linear shape by a straightening machine 3. In the descaling step P3, scale adhering to the surface of the steel wire W is removed. In the wire preheating step P4, preheating of the steel wire W after the descaling is performed. In the coating treatment P5, the steel wire W after the preheating is immersed in a coating solution tank. A phosphate coating is formed on the surface of the steel wire in the coating treatment P5. In the lubrication treatment step P6, a lubricant such as metallic soap is applied to the steel wire after the coating treatment to coat the steel wire with the coating. The lubricant forms a necessary lubrication state between the surface of the steel wire W and the die when cold forming is performed in the wire drawing step P8 in a later stage of the lubrication treatment step P6. In the coiling step P9, the steel wire W after being subjected to the cold forming such as the wire drawing in this way is coiled.

[0022] The preheating step P4 between the descaling step P3 and the coating treatment step P5 may be omitted according to specifications. When the lubricant used in the lubrication treatment step P6 is liquid, for example, a drying step P7 for drying the lubricant may be performed between the lubrication treatment step P6 and the wire drawing step P8.

[0023] The steel wire surface-treated by the continuous surface treatment method and contents of the steps configuring the continuous surface treatment method are explained.

[0024] The steel wire W treated by the continuous surface treatment method in this embodiment is obtained by rolling steel, stainless steel, or the like into a long linear shape with a hot rolling mill. The steel wire W has a diameter of 5.0 mm to 55 mm. The steel wire W is coiled after the rolling. After the rolling, in order to adjust the structure, mechanical characteristics, and the like of the steel wire W, heat treatment such as annealing is sometimes applied to the steel wire W in a batch furnace or a continuous furnace.

[0025] In the winding-off step P1, the steel wire W is wound off, in a line shape, from the coil of the steel wire W disposed in the supply stand 2. The supply stand 2 is a facility that supports the coil of the steel wire after the hot rolling such that the axis of the coil faces the up-down direction or the horizontal direction. The winding-off of the steel wire W is performed by, for example, unwinding the steel wire W to be pulled out toward the upper direction of the coil or the downstream side of the manufacturing line or winding off the steel wire W while rotating the coil itself within a horizontal plane.

[0026] In the straightening step P3, a curl of the steel wire W is straightened using a straightening machine 3. The straightening machine 3 includes a plurality of straightening rolls 4. The straightening rolls 4 eliminate the curl of the steel wire W wound off from the supply stand 2. Specifically, the steel wire W coiled shape after the hot rolling passes through the plurality of straightening rolls 4 in order, whereby the curl of the steel wire W is eliminated. The steel wire straightened into the linear shape by the straightening machine 3 is supplied to the next descaling step P3.

[0027] In the descaling step P3, scale is removed from the surface of the steel wire W straightened into the linear shape by the straightening machine 3. In this embodiment, the removal of the scale on the surface is performed by wet blast for jetting slurry including grit-like abrasive particles onto the surface of the steel wire W. Details of the descaling step P3 are explained below.

[0028] In the preheating step P4, the steel wire W after being descaled is preheated before the phosphate coating treatment. The preheating is performed by, for example, spraying heated water or steam on the steel wire W from which the scale is removed or directly heating the steel wire with high-frequency induction heating or the like. Consequently, the steel material W is preheated to temperature substantially the same as temperature for the phosphate coating treatment. The preheating promotes a chemical conversion reaction in forming a phosphate coating after the preheating and enables an increase in formation speed of the phosphate coating. Details of the preheating are also explained below.

[0029] In the coating treatment step P5, a phosphate coating is formed on the surface of the steel wire W by immersion of the steel wire W in phosphate coating solution. The coating is formed as a base layer of lime soap, metallic soap, or the like that plays a role of a carrier for drawing the lubricant into the die in the cold forming such as the wire drawing and is used as the lubricant.

[0030] The phosphate coating is formed by a chemical reaction. As a treatment temperature is higher, the chemical reaction is promoted more. Therefore, not only the steel wire W but also the coating treatment solution is desirably preheated to approximately 60 C. to 80 C., which is temperature substantially the same as the temperature of the wire preheating. An etching reaction is promoted by increasing total acidity. Therefore, the coating reaction is considered to be also promoted. Therefore, the increasing the total acidity is effective as means for reducing a coating treatment time.

[0031] In the lubrication treatment step P6, a lubricant including metallic soap such as lime soap is applied to the surface of the steel wire W coated with the phosphate coating in the coating treatment step P5 to cover the coating. When the lubricant is liquid, drying of the lubricant is desirably performed in the next drying step P7. Cold forming represented by the wire drawing step P8 is performed by a forming machine (in the wire drawing step P8, a wire drawing machine 5) on the steel wire W coated with the lubricant. The coating of the steel wire W by the lubricant enables the cold forming while lubricating the steel wire W and makes it possible to smoothly perform forming of the steel wire.

[0032] The continuous surface treatment method is characterized in that the continuous surface treatment method includes the descaling step P3 as pretreatment of the coating treatment step P5 and, in the descaling step P3, slurry including grit-like abrasive particles is jetted onto the surface of the steel wire W. The preheating step P4 is desirably performed before the coating treatment step P5 as explained above. The descaling step P3 and the preheating step P4 make it possible to form a phosphate coating on the surface of the steel wire W in a short time and with high productivity while suppressing forming deterioration of the surface of the steel wire W. Details of the descaling step P3 and the preheating step P4 are explained below.

[0033] As explained above, the descaling step P3 includes removing scale using wet blast for jetting slurry including grit-like abrasive particles. The wet blast is a method of jetting slurry, which is a mixture of water and hard particles, from a plurality of nozzles toward a target object with high-pressure air to thereby cause the slurry to collide with the surface of the steel wire W and scrape off scale on the surface of the steel wire W.

[0034] The plurality of nozzles are respectively disposed in a plurality of positions, desirably, three or more positions arranged in the circumferential direction. Desirably, the plurality of nozzles are disposed at substantially equal angle intervals in the circumferential direction around the axis of the steel wire and disposed such that the surface of the steel wire can be covered over the entire circumference by a plurality of jetting regions by the plurality of nozzles. The positions of the nozzles are desirably distributed in a conveying direction of the steel wire such that the jetting regions of the nozzles do not interfere with one another. Specifically, the plurality of nozzles are desirably disposed in a zigzag shape along the conveying direction extending along the axis of the steel wire (such that the nozzles are apportioned alternately to the left and the right along the circumferential direction when viewed along the axis of the steel wire) or disposed in a spiral shape.

[0035] In the wet blast, it is possible to reduce an impact on a target object by a jetted polishing material by keeping a jetting pressure of the slurry within an appropriate range. In this case, the target object is less easily damaged compared with shot blast and water jet (a jetting pressure is approximately 100 MPa). Specifically, when dry shot blast not using liquid is performed or when the water jet is performed at extremely high air pressure even if water is used, a forming deterioration layer produced on the surface of the steel wire tends to be thick. It is likely that forming defects such as a crack of the steel wire and seizure of the die are caused during cold forming. On the other hand, when the wet blast for spraying slurry, which is a mixture of water and hard particles, on the steel wire at an appropriate jetting pressure is performed, it is possible to reduce the thickness of the forming deterioration layer produced on the surface of the steel wire compared with the shot blast and the water jet. It is possible to reduce a working hardening amount and a working hardening depth of the steel wire surface hardened by collision of the polishing material. Therefore, in cold forming after treatment of a phosphate coating explained below, it is possible to significantly reduce the likelihood that forming defects such as a crack of the steel wire and seizure of the die are caused.

[0036] Specifically, the slurry is desirably jetted at a jetting pressure of, for example, 0.2 MPa or more and 0.6 MPa or less. The jetting pressure of 0.2 MPa or more enables production of a new surface explained below. The jetting pressure of 0.6 MPa or less makes the suppression of forming defects such as a crack of the steel wire and seizure of the die more conspicuous compared with treatment at a jetting pressure higher than 0.6 MPa.

[0037] This method has a characteristic that the slurry includes grit-like abrasive particles. The grit-like abrasive particles means a grit defined as a metallic polishing material for blast treatment in JIS Z 0311. The grit-like abrasive particles indicate particles that are formed in a square shape having line angles in a state before use and in which a ratio of round portions of the surfaces of the particles to the entire surface of the particles is smaller than a half. Therefore, the grit-like abrasive particles are greatly different in shape from the metallic polishing material for shot treatment defined in JIS Z 0311, that is, particles that do not have line angles, crushed surfaces, or other sharp surface defects in a state before use and the long diameter of which is within a double of the short diameter.

[0038] When such grit-like abrasive particles are used, even in the wet blast for jetting the slurry at the jetting pressure lower than the jetting pressure of the water jet as explained above, it is possible to form a large number of concaves and convexes on the surface of the steel wire. Further, since a new surface is obtained on the surface of the steel wire by fine surface cutting by the corners of the grit-like abrasive particles, a chemical conversion reaction is promoted in the following phosphate coating treatment. It is possible to obtain a phosphate coating in a short time. In other words, a content of the grit-like abrasive particles in the slurry only has to be set to a degree for making it possible to produce the new surface on the surface by jetting the slurry onto the surface of the metal wire W. The new surface means a surface where the scale and an old surface layer of the metal wire W are shaved by the jetting of the slurry and a new portion of the metal wire W on the lower side of the surface layer appears.

[0039] A type of metal configuring the grit-like abrasive particles is not limited. From the viewpoint of forming efficiency of the descaling, the metal is desirably selected to configure particles having higher hardness than the hardness of the steel wire to be treated. Specifically, as the grit-like abrasive particles, from the viewpoint of, for example, preventing post-pierce remaining particles in the steel wire surface, steel or stainless steel excellent in toughness is desirably used.

[0040] On the other hand, in the preheating process, by preheating the steel wire to temperature close to the temperature of the phosphate coating solution used in the phosphate coating treatment, the chemical conversion reaction in forming a phosphate coating is promoted. Therefore, a treatment condition of the preheating also greatly affects efficiency of continuous surface treatment.

[0041] For example, when the temperature for heating the steel wire in the preheating is less than 60 C., the effect of the preheating decreases and the formation of the phosphate coating becomes insufficient. Conversely, the preheating at temperature exceeding 80 C. excessively raises the solution temperature of the phosphate coating solution to cause hydrolysis or deteriorate the coating treatment solution. Therefore, the preheating is undesirable from the viewpoint of productivity and cost to the contrary.

[0042] Note that, when the steel wire put in a wet state by the wet blast is dried for the preheating, it is likely that an oxide film is formed on the surface of the steel wire during the preheating and a reaction in the formation treatment of the phosphate coating is hindered. However, when the preheating at a low temperature of 80 C. or less is performed only for less than 60 seconds, the oxide film is hardly formed to have large thickness during the preheating. Therefore, the oxide film formed during the preheating does not cause hindrance due to the reaction in the formation of the phosphate film after that. Therefore, it is possible to obtain an excellent effect that the chemical conversion reaction is promoted by the preheating.

[0043] As explained above, there is provided the continuous surface treatment method for the steel wire that can form the phosphate coating on the steel wire in a short time at low cost and with high productivity without causing significant forming deterioration on the surface of the steel wire. This method is a method of continuously treating the surface of a steel wire before being subjected to cold forming and includes a step of continuously forming a phosphate coating on the steel wire and a step of jetting slurry including grit-like abrasive particles on the surface of the steel wire before the formation of the phosphate coating, thereby producing a new surface on the surface of the steel wire.

[0044] The use of the grit-like abrasive particles makes it possible to promote a chemical conversion reaction in the following phosphate coating treatment through production of a new surface on the surface of the steel wire by fine surface cutting by corners of the grit-like abrasive particles and obtain a phosphate coating in a short time.

[0045] Therefore, in the continuous surface treatment method, it is also possible to perform the wet blast while keeping the jetting pressure of the slurry in an appropriate range, for example, a range of 0.2 MPa or more and 0.6 MPa or less to promote the formation of the phosphate coating. Consequently, it is possible to reduce a forming deterioration layer produced on the surface of the steel wire and a working hardening amount, a working hardening depth, and the like of the steel wire surface.

[0046] Further, when a preheating process for heating the steel wire performed after the descaling process and before the coating treatment process is included, the temperature of the steel wire can be brought close to temperature near the temperature of the phosphate coating solution, for example, temperature of 60 C. or more and 80 C. or less by the preheating process. Consequently, it is possible to promote a chemical conversion reaction in forming the phosphate coating. Therefore, it is possible to form the phosphate coating on the steel wire in a short time and with high productivity.

EXAMPLES

[0047] Effects of the continuous surface treatment method are explained more in detail with reference to examples and comparative examples.

[0048] Both of the examples and the comparative examples are based on an experiment in which spheroidizing annealing, continuous surface treatment, wire drawing, and heading for a steel wire (11.0 mm) made of steel (SUJ2) are performed in this order. The continuous surface treatment includes descaling by wet blast, preheating, phosphate coating treatment, lubrication using lime soap, and drying.

[0049] Details of conditions of the experiment are as described below.

(1) Scale that should be Removed by the Descaling
Chemical composition: Fe.sub.3O.sub.4 (60%), Fe.sub.2O.sub.3 (40%)

Thickness: 2 m

(2) Wet Blast

[0050] Apparatus in use: General-purpose wet blast apparatus manufactured by MACOHO Co., Ltd.
Polishing material: GRITTAL GH10 manufactured by VULKAN INOX GmbH.
Average abrasive particle radius: 0.113 m
Air pressure: 0.4 MPa
Angle of wire and nozzle: near 90
Distance between the wire and the nozzle: 100 mm
Abrasive particle concentration in slurry: 15%

(3) Preheating

[0051] Heat medium in use: Hot water (40 to 80 C.)
Treatment time: 60 s

(4) Phosphate Coating

[0052] Phosphate treatment agent in use: Nihon Parkerizing PB-3670X
Total acidity: 90 pt* * pt used for the total acidity is a concentration unit of phosphate coating treatment solution and means a mol number of NaOH of 0.1N required for neutralizing 10 ml of the phosphate coating treatment solution
Coating solution temperature: 40 C. to 80 C.
Treatment time: 10 s

(5) Lubrication

[0053] Lime soap in use: Inoue Calcium Corporation MAC-A20
Treatment temperature: 40 C. to 80 C.
Treatment time: 10 s

(6) Others

[0054] Reduction of area of wire drawing: 12% (11 mm.fwdarw.10.3 mm)
Heading: Forward extrusion, reduction of area 50%

[0055] A result of the experiment is shown in Table 1. In Table 1, among signs indicating a wire drawing result and a heading result, indicates that seizure and a crack immediately occurred, .Math. indicates that seizure and a crack did not occur and cold forming was possible, and indicates that seizure did not occur but the life of the die was slightly short, and a sign of seizure was observed. The inventors confirmed that the steel wire had sufficient performance when there is no in both of the wire drawing result and the heading result in the experiment and regarded this example as a preferred example. The inventors regarded an example, in which there is no in only one of the wire drawing result and the heading result, as an example equivalent to the preferred example.

TABLE-US-00001 TABLE 1 Descaling Coating Experiment result Particle Particle Wire Total adhesion Wire drawing Heading Method shape material speed Preheating Acidity amount result result Example WB Sphere Steel 20 m/min No 90 pt 2.7 (g/m.sup.2) X 01 (seizure occurred) Example SB Sphere Steel 20 m/min No 90 pt 2.8 (g/m.sup.2) X 02 (seizure occurred) Example WJ Sphere Steel 20 m/min No 90 pt 3.2 (g/m.sup.2) X 03 (seizure occurred) Example WJ Grit Steel 20 m/min No 90 pt 5.0 (g/m.sup.2) X 04 (life of die was (crack occurred) short) Example WB Grit Steel 20 m/min No 90 pt 5.2 (g/m.sup.2) .Math. .Math. 05 (No seizure) (No seizure) Example WB Grit Steel 40 m/min Yes 90 pt 4.2 (g/m.sup.2) .Math. 06 (40 C.) (No seizure) (Surfaces gloss) Example WB Grit Steel 40 m/min Yes 90 pt 5.0 (g/m.sup.2) .Math. .Math. 07 (60 C.) (No seizure) (No seizure) Example WB Grit Steel 40 m/min Yes 90 pt 6.4 (g/m.sup.2) .Math. .Math. 08 (80 C.) (No seizure) (No seizure) Example WB Gird Alumina 40 m/min Yes 90 pt 6.2 (g/m.sup.2) 09 (80 C.) (life of die was (life of die was short) short)

[0056] Focusing on the experiment example 1 to the experiment example 5 of Table 1, whereas coating adhesion amounts of the experiment examples 1 to 3 in which spherical abrasive particles were used for the descaling are 2.7 g/m.sup.2 to 3.2 g/m.sup.2, in the experiment examples 4 and 5 in which grit-like abrasive particles were used, coating adhesion amounts are 5.0 g/m.sup.2 and 5.2 g/m.sup.2. It is seen that the coating adhesion amounts greatly increased. Therefore, it is seen that productively can be greatly improved by using the grid-like abrasive grains (abrasive particles) for the descaling.

[0057] Focusing on the experiment example 4 and the experiment example 5 of Table 1, coating adhesion amounts are substantially the same in the experiment example 4 in which the descaling was performed using water jet (WJ) and the experiment example 5 in which the descaling was performed using wet blast (WB). However, in the wire drawing result and the heading result, the wet blast (WB) indicates a wire drawing property and a heading property more excellent than the water jet (WJ). Specifically, in the experiment example 4, the wire drawing is possible but the heading is difficult. However, in the experiment examples, satisfactory results can be obtained concerning both of the wire drawing and the heading. Therefore, it is seen that the descaling by the wet blast at an appropriate jetting pressure makes the effect of suppressing forming deterioration on the surface of the steel wire and improving formability such as the wire drawing and the heading more conspicuous.

[0058] On the other hand, focusing on the experiment example 6 to the experiment example 8 of Table 1, it is seen that the coating adhesion amounts increased and the wire drawing property and the formability were improved as the preheating temperatures were higher. Whereas the coating adhesion amount is 4.2 g/m.sup.2 and gloss indicating a sign of seizure is observed in a sample after the heading in the experiment example 6 in which the preheating temperature is 40 C., the coating adhesion amounts are 5.0 g/m.sup.2 to 6.4 g/m.sup.2 and the surface after the heading is in a more desirable state in the experiment example 8 and the experiment example 9 in which the preheating temperatures are respectively 60 C. and 80 C. Therefore, it is seen that it is possible to improve treatment wire speed and greatly improve productivity by performing preheating prior to the coating treatment and, desirably, performing preheating at 60 C. or more and 80 C. or less.

[0059] In addition, as opposed to the experiment example 8 in which the material of the grit-like abrasive grains is steel, in the experiment example 9 in which the material of the abrasive grains is alumina, although the coating adhesion amounts are substantially the same, the life of the dice is slightly shorter. Therefore, the evaluations of the wire drawing result and the heading result are . This is considered to be because, since the alumna is inferior to the steel in toughness, the alumina pierced and remained in the wire during the descaling and caused seizure during the wire drawing and the heading. Therefore, the material of the grit-like abrasive grains is considered to be more desirably the steel having high toughness.

[0060] Note that the embodiment disclosed herein should be considered as illustrative in all aspects and not limiting. In particular, matters not explicitly disclosed in the embodiment disclosed herein, for example, operation conditions and running conditions, various parameters, and dimensions, weights, volumes, and the like of components do not deviate from a range of normal implementation by those skilled in the art. Values that those skilled in the art can easily assume are adopted.