High-area reduction ratio stretching device for steel wire rods

Abstract

To provide a device for producing a wire rod with a smaller diameter with a commercially available hot rolled wire rod as a material.SOLUTION: A wire rod feeder draws one end of a wire rod coil and runs the wire rod straight at a constant speed. A pull-out device for pulling out the wire rod is made to follow, and meanwhile, a workpiece is heated to about 1000°C by direct electrification. At a pull-out inlet part, the temperature is highest, the yield force is lowest and the pull-out stress due to drawing / area reduction is largest, and therefore, drawing continues. A drawing ratio (area reduction ratio) corresponding to a front / rear speed ratio can be obtained. The pull-out device is composed of a multistage pinch roll for holding elastic reduction as a process stabilization condition, and a pull-out force of each stage is accumulated to prevent abnormal deformation. A pull-out speed can be adjusted to obtain the wire rod without stopping and with an arbitrarily small diameter.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an apparatus for manufacturing a wire rod with a smaller diameter using a steel wire rod manufactured by hot rolling as a raw material.

Background Art

[0002] In the production of steel wires, a hot-rolled wire rod that has been appropriately controlled-cooled as a material is used, and drawing is performed by a multi-stage continuous wire drawing machine to provide a predetermined diameter and predetermined mechanical properties. When the steel wire diameter is about 2 mm or more, it is directly manufactured from the wire rod. However, in the following cases, since wire rods with a desired small diameter are not commercially available, the wire rod is first drawn and then heat-treated to obtain a secondary wire rod, which is used as a material. This is usually referred to as a bare wire. Naturally, not only does the cost increase significantly from the wire rod, but it is also dispersed into small quantities of multiple varieties, and there are significant problems in production efficiency.

[0003] Examine a method for efficiently manufacturing a wire rod with a smaller diameter than before. Patent Document 1 is an example of die-less wire drawing, and its principle has been studied for a long time. According to it, while applying tension to a straight-running steel wire, it is rapidly heated by induction heating to soften the outside, immediately followed by water cooling for rapid cooling to strengthen the part, and local stretching is performed at the part immediately before rapid cooling by the tensile force of the winding bobbin. Three features can be obtained: a high reduction ratio can be obtained, the cross-sectional shape is a similar deformation of the material, and the wire diameter can be freely changed corresponding to the ratio of the running speed and the winding speed. It seems that it can be utilized for small-lot production of multiple varieties.

[0004] The problem with this method is that in order not to cause drawing breakage, rapid cooling immediately after heating is indispensable, and appropriate controlled cooling (heat treatment) necessary for wire drawing in subsequent processes cannot be applied. If controlled cooling is incorporated anyway, a subsequent reheating process is required. The difficulty of overall control becomes a problem.

[0005] Patent Document 2 discloses a method for manufacturing secondary wire rods by adding hot rolling and controlled cooling immediately afterward to a wire rod. According to this method, the wire rod is driven in a straight line, heated by electric current, rolled to a predetermined diameter using a tandem mill (multi-head continuous rolling mill), a vertical spiral ring row is formed using a laing-type winding machine, the ring row is regularly stacked, and controlled cooling is added. In essence, this can be seen as a downsizing of the conventional wire manufacturing method. Compared to existing secondary wires (drawn + heat treatment), a considerable cost reduction is possible.

[0006] The problem is that, as with rolling and wire drawing, various dimensional changes require rearranging the roll or die rows, which is complicated, inefficient, and burdensome in terms of the number of parts required, making it unsuitable for handling small-batch, high-mix production.

[0007] As previously described, die-less wire drawing, a type of drawing process, can achieve a high reduction ratio and flexible dimensional changes in a single pass. The following method aims to replace this principle with hot rolling while maintaining high temperatures. Patent Document 3 discloses a rolling method for wire rods with a high reduction ratio (high elongation ratio). According to this method, the wire is driven in a straight line by pinch rolls and supplied to a rolling mill, heated between the pinch rolls and the rolling mill, the peripheral speed of the rolling mill is set to be excessively high compared to the feed speed, and the roll diameter ratio (= roll diameter / material diameter) is made excessively large to increase the frictional pulling force and suppress slippage on the roll surface, causing large hot stretching and rolling to occur simultaneously under excessive tension, and inducing processing with a high reduction ratio in a single pass of rolling. This is called overtension rolling. An elongation ratio of 10 (reduction ratio of 90%) is theoretically possible. Its features include a high speed ratio supported by high frictional force, resulting in a high reduction ratio. Furthermore, any desired cross-sectional area can be obtained in proportion to the speed ratio.

[0008] The problems with this method are that, although the processing principle is robust, it has not been sufficiently demonstrated, and the cross-sectional shape of the wire processed from a circular cross-section becomes oval due to the rolling process, which causes the circle to be reduced.

[0009] Patent Document 4 discloses an improvement to the rolling method for the aforementioned wire rod with a high reduction ratio (high elongation ratio). According to this, in a trial run using a pilot plant, slight fluctuations in processing conditions caused the wire to be drawn out between the front and rear rolls, and also induced buckling and kinking at the entrance of the rolling mill due to insufficient pulling, often resulting in rolling stoppages. To address this problem, 1) direct electric heating is added to guide the rolling engagement point to the highest temperature, drawing the wire into the rolling mill and preventing drawing out, and 2) auxiliary pinch rolls are provided downstream of the rolling mill to prevent rolling slippage and suppress the occurrence of kinking.

[0010] The problem with this method is that although the process is stable, the resulting cross-sectional shape is no longer circular as in conventional methods, leading to practical inconveniences. This is an unavoidable problem since rolling is applied to enhance the tensile force. To prevent this weakness, a straightening rolling mill must be used afterward. This would require double dimensional adjustment, making it cumbersome and discouraging implementation. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Published Patent Application No. 61-88916 [Patent Document 2] Published Patent Application 2005-246401 [Patent Document 3] Japanese Patent Publication No. 4284396 [Patent Document 4] Japanese Patent Publication 6084817 [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] The object of the present invention is to provide an apparatus for manufacturing smaller diameter hot-rolled wire rods using ordinary steel wire rods as material in an equipment- and operationally advantageous manner, and to manufacture secondary wire rods that can replace conventional primary wire drawing and secondary heat treatment. To this end, the following four functions are provided: 1) High surface reduction ratio machining in a single pass (simplification of equipment and operation) 2) Similar deformation of the cross-section (maintaining the circular shape) 3) Uninterrupted and flexible changes to wire diameter (improvement of operational efficiency) 4) Maintaining high temperature (followed by controlled cooling) The challenge to be solved is to achieve both simultaneously. All previous examples lack at least one of these elements. [Means for solving the problem]

[0013] To solve the above problems, the inventor cleverly combined "stabilized hot drawing and rolling," which enables a high reduction ratio and high temperature retention as in Prior Example 4, and "die-less wire drawing," which enables similar deformation as in Prior Example 1, thereby constructing a device that eliminates the drawbacks of each and possesses the advantages of both.

[0014] The first invention is a device for manufacturing smaller diameter hot-worked wire rods using hot-rolled steel wire rods as a material, and is mainly composed of three parts: a wire rod supply device that moves the wire rod in a straight line at a constant speed, a drawing device that pulls in the wire rod at a speed greater than the constant speed, and a heating device that directly energizes the wire rod between the wire rod supply device and the drawing device to induce the maximum temperature at the inlet of the drawing device, characterized in that 1) the drawing device is equipped with multiple stages of gripping parts that grip and pull the workpiece, 2) each stage of gripping part elastically presses the workpiece with a predetermined reduction force, 3) the reduction force of each stage is greater than or equal to the reduction force of the previous stage, and 4) the travel speed of each stage is greater than or equal to the previous stage, and the wire rod is stretched by similar deformation corresponding to the speed difference between supply and drawing, and the stretch ratio is expressed in proportion to the speed ratio.

[0015] The second invention is based on the following five conditions: 1) The gripping portion consists of pinch rolls or upper and lower caterpillar-type infinite belt conveyor tracks that grip the workpiece. 2) The power supply for the heating device is single-phase AC, with one end of the power supply connected to the midpoint of the wire between the wire supply device and the extraction device, and the other end connected to a busbar that electrically couples the wire supply device and the extraction device, and the potential of the entire device outside of the above section being the same and at ground potential. 3) The reduction of the multi-stage gripping section shall be performed by a pneumatic cylinder. 4) Provide at least one leveling roll with a pressing direction perpendicular to the entrance of the supply device and the exit of the pulling device. 5) Provide a laser wire diameter measuring device, a cutting diverter, a winding route, and a waste route on the downstream side of the pulling device. The manufacturing apparatus for thin wire according to the first invention, characterized by incorporating any one or more of the above.

[0016] Here, as the definition of the predicate, "constant speed" means that a constant speed is maintained without slippage occurring on the roll contact surface even when forward or backward tension acts. The "gripping part" is a working part that presses and pulls the traveling wire from above and below. A track shoe is a plate-shaped component that is continuously joined to form a track (track link, caterpillar belt).

Advantages of the Invention

[0017] The wire is subjected to a tensile action between the wire supply device with a constant speed and the pulling device that pulls the wire at a speed higher than the constant speed, and the space between the two devices is heated. Therefore, the high-temperature part of the wire stretches corresponding to the speed ratio between the front and rear. The speed ratio and the cross-sectional area ratio are inversely proportional, enabling high reduction rate processing. This principle has been known for a long time, and while exerting this ability, the present invention has solved the problems inherent in Citation 1 (die-less wire drawing) and Citations 3 and 4 (over-tension rolling).

[0018] Due to direct electric heating, the front end of the pulling device (which becomes an electrical contact) reaches the maximum heating temperature, resulting in the localization of stretching and the pulling in of the drawing part. The strengthening of the yield strength by the conventional rapid cooling treatment after heating becomes unnecessary, and the high temperature is maintained even after processing, enabling subsequent controlled cooling.

[0019] As a pulling method, a multi-stage gripping part is adopted, and since the rolling in Citations 3 and 4 is eliminated, the deformation becomes only simple stretching and undergoes similar deformation. The subsequent rolling for correcting the deformed shape caused by rolling becomes unnecessary. A thin wire with a circular cross-section can be directly obtained from a wire with a circular cross-section.

[0020] Since the drawing speed can be freely changed in relation to the supply speed, the wire diameter can be freely changed in accordance with the speed ratio. By continuously increasing or decreasing the latter, the wire diameter changes continuously and transitions to a predetermined wire diameter, and offline processing is performed during this time, so the wire diameter can be changed without interruption.

[0021] Since the drawing process is distributed across multiple stages, excessive reduction force in a single stage is unnecessary, and deformation associated with reduction is almost nonexistent. At least one stage is designed for orthogonal reduction, anticipating the worst-case scenario, making fine adjustments for achieving a perfectly round shape easy. Each section of the pinch roll compresses elastically, so even if the dimensions of the workpiece change, a constant compressive force is maintained, allowing for easy extraction. Similarly, the reduction force and extraction speed in each stage are increased from the later stages, so that even with slight fluctuations, the extraction remains stable, the stability of the extension conditions is enhanced, and this works effectively during high-speed extension.

[0022] In the case of direct current supply, leakage current to the equipment becomes a problem. In the present invention, one electrode is placed approximately in the center of the heating section, and the other is connected to the nearest roll. Both rolls are electrically coupled with a busbar, and the entire device is at ground potential, resulting in high safety. Furthermore, the circuit changes from series to parallel, halving the operating voltage for the same output, which is advantageous in terms of safety. [Brief explanation of the drawing]

[0023] [Figure 1] This is a schematic diagram of the small-diameter secondary wire manufacturing apparatus of the present invention. [Figure 2] This is a schematic diagram of the heating device portion of the small-diameter secondary wire manufacturing apparatus of the present invention. [Figure 3] This is a comparative diagram of leakage current countermeasures for various heating devices. [Figure 4] This is a schematic diagram of the drawing device portion of the small-diameter secondary wire manufacturing apparatus of the present invention. [Figure 5] The drawing stabilization conditions for the small-diameter secondary wire manufacturing apparatus of the present invention are shown. [Figure 6] This is a schematic diagram of another example of the extraction device of the present invention. [Modes for carrying out the invention]

[0024] The manufacturing apparatus for small-diameter steel wire rods according to the present invention will be explained with reference to Figure 1. 1 is a commercially available hot-rolled wire coil that will be used as the material. The wire diameter should preferably be the standard minimum diameter of 5.5 mm. The type of steel is not particularly limited. The wire coil 1 is extended at its tip and becomes a workpiece 2 that moves in a straight line by a wire supply device 3 at a constant speed. Constant means that the wire speed does not fluctuate even when forward or backward tension is applied, and remains constant.

[0025] The workpiece 2 enters the drawing device 5, which operates at a speed faster than the constant speed mentioned above. The workpiece 2, located between the wire supply device 3 and the drawing device 5, is directly heated by the electric heating device 4. Since the electric heating is applied to a moving workpiece, the energizing time increases as it moves downstream, resulting in gradient heating, and the maximum temperature at the electrode contacts at the entrance of the drawing device reaches approximately 1000°C.

[0026] Due to the speed difference between the wire feeding device 3 and the drawing device 5, tension is generated in the workpiece 2, and when the yield stress is exceeded at the highest temperature, stretching occurs. To prevent slippage due to tension, the drawing device 5 is configured with multiple stages of gripping devices, such as pinch rolls, providing multiple gripping points, and each stage having an appropriate reduction force. Appropriate means a range in which no slippage occurs and no deformation occurs due to reduction.

[0027] When the speed ratio is increased fourfold, the material is stretched fourfold. The small-diameter workpiece 2 moves towards the winding device (not shown) at four times the speed. During this time, the wire diameter is measured by a laser-type dimension measuring instrument 6, and the drawing speed is adjusted to achieve the predetermined diameter. When the wire diameter is changed, the cutting switch 7 switches the workpiece 2 from the winding route 9 to the scrap route 8, and scrap is processed while changing the drawing speed until the desired diameter is reached. Once the desired diameter is reached, the cutting switch 7 returns the workpiece to the winding route 9 and normal production continues.

[0028] The direct current heating device 4 will be explained with reference to Figure 2. The material to be heated 21 passes through the lowest roll 22 of the wire supply device, and then passes through the uppermost roll 25 of the drawing device while the pressing roll 24 comes into contact with the electrode roll 23 that is attached to it. The upper and lower rolls 22 and 25 described above are electrically coupled by a busbar 28 via contacts 26 and 27, and there is no resistance between them, resulting in the same potential. One end of a single-phase AC power supply 29 is coupled to the busbar 28, and the other end is coupled to the electrode roll 23. The busbar 28 is also coupled to the earth 30.

[0029] The method of wiring the circuit is related to preventing electrical leakage. As shown in Figure 3, if current is simply passed between the two rolls as in A, preventing electrical leakage from the heated material becomes extremely complicated. A highly safe energizing method, as shown in B, is being implemented in some cases. In this method, a ring transformer 31 is installed surrounding the material to be heated. The ring transformer is energized by an AC power supply 32 to the primary coil, and the secondary coil is a single-turn circuit consisting of a busbar 33 that electrically couples the material to be heated and both rolls. The potential rises within the iron core, the potential falls before and after the iron core, and the potential of both rolls becomes approximately ground potential, resulting in high safety. If there is any problem, it is that a double transformer is required, including one for output adjustment.

[0030] In the present invention C, a power supply roll 34 is provided in the middle of both rolls, and a busbar 35 is provided connecting the two rolls, thus forming a parallel circuit extending forward and backward. The potential of both rolls becomes the ground potential, similar to B described above, and the leakage current problem is greatly improved. Furthermore, when the same power is applied, the load voltage in the present method is halved compared to method B due to the parallel circuit. This offers a greater advantage in terms of safety. Because the cross-sectional area of ​​a busbar is excessively large, it has almost no resistance, and therefore no potential difference is generated.

[0031] The mechanism of the extraction device will be explained with reference to Figure 4. The drawing device for drawing the workpiece 41 consists of multiple pinch rolls, for example, PR1, PR5. All of the stages and upper and lower rolls 44 are driven at the same rotational speed (rpm) from a drive source 42 via gears 43, 45. The upper rolls elastically press down on the workpiece 41, and grip it with the same pressing force even when the gap between the rolls changes due to a change in wire diameter. For this reason, each stage is equipped with a pneumatic cylinder 46. One or more of the pinch rolls, for example, 47, are positioned perpendicular to the others. This allows for correction of the cross-sectional shape, which may have been slightly deformed by the compression. The ideal placement is in the middle of the structure, where tension is acting both before and after the final roll. Although only one example of a drive source (e.g., electric motor) is shown, it is also possible to provide individual drive sources for each roll and control them synchronously.

[0032] The control method for the extraction device will be explained with reference to Figure 5. For production efficiency, high-speed drawing, for example 400 m / min, is assumed. Therefore, even slight fluctuations in processing conditions can cause cutting, buckling, or kinking, leading to a halt in processing. The occurrence of both defects must be reliably prevented. As we learned in previous example 4, with only one pinch roll, simple reduction alone results in slippage when the stretching ratio becomes large. When reduction is performed until rolling occurs, friction increases, and the stretching becomes almost stable. The larger the roll diameter ratio, the more stable the friction becomes. Unfortunately, the cross-sectional shape changes from circular to oval due to rolling.

[0033] To achieve both slip prevention and deformation prevention, the extraction points should be distributed across multiple stages. 1) While suppressing abnormal deformation, 2) Increase the reducing force (∽ frictional force), 3) Accumulate the pulling force so that each stage acts effectively in the pulling process. It will become necessary. The workpiece 51 is pulled out by the first-stage pinch roll 53 and travels forward while forming a stretched portion 52 at the entrance where the temperature is highest. The following conditions are set between the multi-stage pinch rolls to stabilize this process even at high speeds. The reduction force P of each stage must be greater than or equal to that of the previous stage. P1 ≤ P2 ≤ P3 ≤ P4 ... The peripheral speed V of each stage must be greater than or equal to that of the previous stage. V1 ≤ V2 ≤ V3 ≤ V4... Assume the rotational speed N is the same for each stage. N1 = N2 = N3 = N4... The roll diameter D of each stage should be greater than or equal to that of the previous stage. D1 ≤ D2 ≤ D3 ≤ D4...

[0034] Another example of the structure of a drawing device is shown in Figure 6. The workpiece 61 is gripped and pulled out by upper and lower caterpillar-type conveyors 62 and 63. The conveyors 62 and 63 consist of track links 64 and 65 and driving wheels 66 and 67 that drive the tracks, and the tracks 64 and 65 consist of a series of track shoes 68 and 69. Each track shoe 68 or 69 serves as a gripping part of the extraction device. Each track shoe also functions as an electrode contact. A fixed sliding guide 70 is provided on the inside of the track 64, and an elastically compressed sliding guide 71 is provided on the track 67. The elastically compressed sliding guide 71 is provided with an appropriate compression force by pneumatic cylinders 72 and 73. By adjusting the pressure settings of both cylinders, inclined compression is possible. The gripping portion is a plate-shaped footplate, and the contact point expands from a point in the case of a roll to a line, and since it is configured in multiple layers, the stability of the extraction is greatly improved. The electrical contacts will be handled by the fixed sliding guide 70. [Examples]

[0035] The following is a schematic of the manufacturing equipment used to produce thin wires up to approximately 2.5 mm in diameter. Production capacity: 1000 kg / h Material; 5.5mm wire rod Wire feeding speed; 0~100m / min Heating device output: 200kW (=40V × 2500A × 2) Number of gripping parts: 5(4H+1V) Extraction speed: 0-500 m / min Small wire diameter; 4.4~2.5mm [Explanation of Symbols]

[0036] 1; Wire coil 2; Workpiece material 3; Wire supply device 4; Direct current heating device 5; Extraction device 6; Dimensional measuring instrument 7; Cutting and turning machine 8; Scrap route 9; Winding route 21; Workpiece 22; Bottom roll 23; Power supply roll 24; Pressing roll 25; Top roll 26; Highest temperature section 27; Electrical contact 28; Busbar 29; Power supply 30; Ground 31; Ring transformer 32; Single-phase AC power supply 33; Busbar 34; Electrode roll 35; Busbar 41; Workpiece 42; Drive source 43; Gear 44; Rolling roll 45; Gears 46; Pneumatic cylinders 47; Vertical pinch rolls 51; Workpiece 52; Extension section 53, 55; Reduction roll 54, 56; Pneumatic cylinder 61; Workpiece 62,63; Conveyor 64,65; Track 66, 67; Driving wheels 68, 69; Track plates 70; Fixed sliding guides 71; Elastic pressure sliding guide 72,73; Pneumatic cylinder

Claims

[Claim 1] A device for manufacturing smaller diameter hot-worked wire rods using hot-rolled steel wire rods as a material, A wire supply device that moves the wire in a straight line at a constant speed, and a device that pulls the wire at a speed greater than the constant speed The extraction device and the wire supply device and the wire between the extraction device are directly energized at the inlet of the extraction device. It consists of three parts: a heating device that induces the temperature to the maximum, The following five conditions, 1) The gripping portion of the extraction device consists of multi-stage pinch rolls or upper and lower caterpillar-type infinite belt conveyor tracks that grip the workpiece. 2) The power supply for the heating device is single-phase AC, and one end of the power supply is between the wire supply device and the wire extraction device. The wire is connected at its midpoint, with the other end connected to a busbar that electrically connects the wire supply device and the extraction device. The entire device outside the above-mentioned section must have the same potential and be at ground potential. 3) The downward force of each gripping section is elastic, provided by a pneumatic cylinder. 4) At least one straightening roll with a reduction direction perpendicular to the direction of the supply device shall be provided between the inlet of the supply device and the outlet of the extraction device. 5) A laser-type wire diameter measuring device, a cutting switch, a winding route, and a waste route shall be provided downstream of the extraction device. A manufacturing apparatus for small-diameter wires, characterized by incorporating one or more of the following.

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