JP6106814B2 - Continuous wire drawing method - Google Patents

Description

  The present invention relates to a continuous wire drawing method when a steel wire is drawn out into a steel wire.

Steel wire is usually a wire rod drawn with a hole die and processed to the desired diameter and desired mechanical properties. In many cases, however, many passes are required. A continuous wire drawing machine (hereinafter referred to as a continuous drawing machine) is frequently used.
One of the problems in the stretcher is as follows. The temperature of the steel wire rises due to the processing heat accompanying drawing. The steel wire is gradually cooled by contact with the drawn drawing pot, but in the continuous stretcher, it is guided to the next pass in the cooling process, the pre-processing temperature rises from the previous stage, and the post-processing temperature also increases accordingly. . The temperature rise is repeatedly accumulated, resulting in hardening and embrittlement (called age hardening) of the steel wire different from work hardening. In particular, a high tensile strength steel wire has a high yielding force, and thus heat generation and temperature rise are large, and embrittlement easily proceeds. Measures are taken against the quality problem from the viewpoints of enhancing cooling and suppressing heat generation.

For cooling enhancement, for example, a method of directly cooling the steel wire at the die outlet is effective, but since the adhered water hinders the lubricity of the next drawing, it is difficult to apply only the final kettle.
Usually, water cooling strengthening of the extraction pot and cooling time gain by increasing the number of dredging to the pot are adopted. There are two types of winding to the pulling pot. One is a storage type, which is superposed and spreads in a kettle to have a sufficient amount of accumulation. As a result, the cooling time is long and it is easy to cope with the wire drawing temperature control. Also, speed adjustment between the hooks is easy. Often used for products that are not strict to quality.

  The other is straight, and the steel wire is lined up in the hook and walks between the hooks under constant tension. The reverse tension acts, the die surface pressure is reduced, the die life is good, the twisting is difficult to enter, the wire wrinkles are good, the scratches are hard, the lubrication is stable, etc. On the other hand, disconnection due to inadequate tension control (therefore, the reverse tension ratio is not relatively large), and cooling tends to be insufficient (as a countermeasure, the wire drawing speed is controlled and the equipment is enlarged). There is a problem that the mechanism for accurately adjusting the speed between the hooks becomes complicated. The present invention is directed to the straight type that is advantageous in terms of quality.

On the other hand, for suppressing heat generation, the degree of processing (area reduction) per pass is suppressed, but the number of hooks may be insufficient due to an increase in the number of passes. Since increasing the tensile strength of the product requires an increase in the degree of processing, the number of passes must be increased. For this reason, recently, new machines have a tendency to increase the number of hooks connected, and the burden of equipment costs is extremely high.
Adoption of a high-performance lubricant (reduction of heat generation due to low friction) has a certain effect, but there are problems such as insufficient and high cost. Therefore, the actual situation is that there is no effective measure. Although the wire drawing speed can be reduced by misunderstanding, even if it is effective for cooling, it is ineffective for increasing the temperature.

  Patent Document 1 discloses that embrittlement of a steel wire is prevented by controlling the wire drawing temperature below a certain level. As a method for controlling to a predetermined temperature, in addition to suppressing the temperature rise by reducing the area reduction rate, the enhancement of cooling, the reduction of the wire drawing speed, and the like are raised, but all are publicly known means.

  Patent Document 2 discloses a new mechanism that facilitates tension adjustment and speed adjustment in a straight-line stretcher. Although the workability of wire drawing is excellent due to the stability of reverse tension, nothing has been suggested that exceeds the conventional knowledge about the significance of reverse tension.

  In Patent Document 3, in order to suppress embrittlement due to strain aging in a linear stretcher, a steel wire and a steel wire can be formed by appropriately setting the axial inclination of the pulling pot diameter (the hook shape is a truncated cone shape). It is disclosed to improve the cooling performance by improving the contact with the kettle. This method is effective for cooling but is not related to temperature rise.

JP2007-29965 JP-A-8-24939 JP 7-12628

  When drawing high-strength steel wires such as piano wire and PC steel wire, straight-line continuous stretchers that are advantageous in terms of quality are usually used. However, because of the high tensile strength, the temperature rise of the steel wire is large, resulting in strain aging embrittlement. It is easy to generate. Although the wire drawing temperature must be controlled to a predetermined value or less, measures for improving the cooling performance of the wire drawing machine and suppressing heat generation due to drawing are necessary. When the cooling capacity is insufficient, the drawing speed has to be reduced, resulting in a decrease in productivity. On the other hand, measures are taken to reduce the area reduction rate on the heat generation side, but the number of hooks becomes insufficient, and special measures (for example, new installation / addition of facilities, double wire drawing, etc.) are required. High tensile strength of products in recent years makes this problem even more difficult.

  It is an object of the present invention to solve the above-mentioned problems by controlling the wire drawing temperature within an allowable level both at normal cooling capacity and at a normal area reduction rate. It aims at providing the method which can be suppressed.

  In order to solve the problem, a detailed investigation of changes in the wire drawing temperature revealed that reverse tension was related to the temperature rise. On the other hand, when the plastic processing theory was arranged, the reverse tension lowered the die surface pressure and the temperature increased. It was found to reduce the amount. After examining the prior literature for such a simple result, we found that a similar view was not found and it was speculated that this was a phenomenon not yet noticed in the industry, and made the following invention.

In the first invention of the present application, in the method of drawing a steel wire by a linear continuous wire drawing machine on which reverse tension acts, the magnitude of reverse tension is set to 40% or more of the yield strength of the steel wire before drawing, It is a continuous wire drawing method characterized in that the temperature of the subsequent steel wire is suppressed to 145 ° C. or lower.
However, the above temperature is the lowest temperature of the steel wire train wound on the drawing pot.

  The second invention is characterized in that a signal obtained by measuring a steel wire temperature is input to a reverse tension adjusting mechanism, and when the temperature is 145 ° C. or higher, the reverse tension is increased and induced below the temperature. It is the continuous wire drawing method described in the invention.

The first effect of the present invention is that the wire drawing temperature of the steel wire is controlled to a predetermined value (for example, 150 ° C.) or less, strain age hardening is suppressed, and a tough high tensile strength steel wire is easily obtained.
The second effect is that it is not necessary to set the surface reduction rate, which is a conventional method, to a low level in order to suppress the temperature of the steel wire below a predetermined value, and the total surface reduction rate is considerably increased even with existing wire drawing machines. Can do.
Third, the tension control method is relatively simple and can be easily attached by adjusting the drive mechanism by electronic control using a temperature sensor as an input.
Fourth, the temperature history is recorded and used effectively for quality assurance.

It is the schematic of the continuous drawing machine which implements the continuous wire drawing method of this invention. It is a figure which compares the actual condition and calculation of the wire drawing temperature in a continuous drawing machine.

Hereinafter, embodiments will be described with reference to the drawings.
FIG. 1 is a schematic view of a straight-line continuous wire drawing machine embodying the present invention. Usually, 6 to 12 pulling pots are in series, but only 3 are required for explanation.
The wire 1 is supplied to the continuous stretcher 2, passes through the first die 3 having a predetermined area reduction rate, is wound around the first hook 4 and pulled out. The intermediate steel wire 5 that has been drawn is instantaneously heated by the processing heat. The steel wire 5 receives contact cooling from the hook 4. The length of time required for cooling to a predetermined temperature or less is wound. Next, the steel wire 5 bypasses the dancer roller 6, passes through the second die 7, and is similarly wound around the second hook 8. The speed of the second hook 8 is set under the condition of “cross-sectional area × speed = constant” corresponding to the area reduction rate with the speed of the first hook 4 as a reference.

The dancer roller 6 has two functions. One acts as a pulling resistance, and generates reverse tension between the first hook and the second die downstream thereof.
Other than that, the trajectory / tension of the steel wire is basically constant due to the proportional relationship between the area reduction rate and the speed ratio, but if slight differences are accumulated, the tension balance between the hooks will shift. Subtle speed control is performed by detecting the position of the dancer roller.
The dancer roller 6 has a structure in which the reverse tension increases as the pushing amount increases. The steel wire wound on the kettle is measured with a radiation thermometer 9 and the reverse tension is adjusted by pressing the dancer roller 10 via the controller 10 corresponding to the temperature. When the temperature is 145 ° C. or higher, embrittlement of the steel wire is recognized. Therefore, the pressing amount is increased, and it is confirmed that the temperature is lowered, and the position is maintained. Here, the steel wire temperature is a value that changes from moment to moment, and the temperature measurement region is kept constant. The first contact with the drawing kettle, that is, the lowermost stage of the wound steel wire row.

The temperature rise by drawing will be described.
Most of the drawing power is consumed to raise the temperature of the steel wire. The frictional heat on the surface of the steel wire is divided into conduction heat transfer toward the inside of the steel wire and heat transfer toward the die, but the amount of heat toward the die may be ignored from the difference in temperature gradient and thermal conductivity. The amount of temperature rise is as follows by developing the Kobel pull-out type.
Temperature rise ΔT (° C) = exothermic Q (kcal / h) / heat capacity (= specific heat x production efficiency P) (kcal / ° C / h)
Heat generation Q ≒ Pulling power E = Load x Speed = σ ・ A ・ V
On the other hand, the drawing power is decomposed into the following from the theory of plastic working.
Drawing power E = Deformation power W + Internal friction Fi + Surface friction Fs
Deformation power W = yield stress k × distance / time = k ・ A ・ V ・ ln [Ao / Ai]
Internal friction Fi = k ・ A ・ V ・ 4 / 3√3 ・ α
Surface friction Fs = k ・ A ・ V ・ μ / α ・ ln [Ao / Ai]

From the above, the following five equations are derived.
E = k ・ A ・ V ・ [ln (Ao / Ai) + 4 / 3√3 ・ α + μ / α ・ ln (Ao / Ai)] ----- (1)
P = ρ ・ A ・ V ---- (2)
ΔT = E / cρAV = k ・ [ln (Ao / Ai) + 4 / 3√3 ・ α + μ / α ・ ln (Ao / Ai)] / cρ −− (3)
= σ / cρ ----- (4)
σ / k = ln (Ao / Ai) + 4 / 3√3 ・ α + μ / α ・ ln (Ao / Ai) −−−− (5)
Here, the symbols are as follows.
k: Yield stress Ao: Cross section before processing Ai: Cross section after processing α: Die half angle μ: Friction coefficient c: Specific heat ρ: Density V: Drawing speed σ: Pulling stress

From the formula (3), it is arranged as follows.
The temperature rise is proportional to the calorific value / production efficiency, but the factor is simply proportional to the product of the yield stress k and the wire drawing conditions (reduction ratio Ao / Ai, die angle α, friction coefficient μ). The drawing speed, the wire diameter (cross-sectional area), etc. are irrelevant. It can be seen that the high tensile strength steel wire has a high yield stress k value, so that the temperature rises and becomes a problem.

Consider how reverse tension affects the temperature rise. As described above, the calorific value Q is the drawing power E, and the drawing power E is proportional to the drawing stress σ. The left side of the equation (5) represents the ratio of the pulling stress σ to the yield stress k (pulling stress ratio), and is usually 0.4 to 0.5. In the case of a high tensile strength steel wire, the amount of reduction in the area reduction and the amount of increase in friction are offset in the latter-stage hook, and the ratio is close to 0.5 in all passes. As is understood from the equation, the stress ratio is related only to the aforementioned wire drawing conditions. The yield stress k value is about 80% of the tensile strength in the case of a drawn material.
The drawing stress σ corresponds to a component force in the drawing direction of the die surface pressure, and the component force is directed rearward (upstream). Therefore, the die surface pressure is reduced by the corresponding amount when reverse tension is applied. That is, the calorific value Q decreases. Normally, in reverse tension drawing, the tension between the hooks increases, but the drawing stress (load on the die) decreases by 20 to 30%. The following document describes the reduction of the pulling stress σ due to reverse tension and the calculation method.
Cited Reference: Plastic Processing: Hiroshi Suzuki, Peng Hua, P80 ~ 81

  With regard to the natural theoretical consequence that reverse tension reduces heat generation due to drawing, the reasons that have been hardly noticed and have not been discussed in the past are as follows: 1) usually not very high strength, 2) thin wire if high strength (Example: Steel tires and steel wires), and because of wet drawing, the cooling was strong and did not cause any problems. 3) Furthermore, in the case of large diameter and high tensile strength such as PC steel wires, reverse tension continuous For example, a stretcher was used and was not conscious, but the temperature rise was suppressed to some extent.

Consider the magnitude of reverse tension. Reverse tension drawing has the weak point that there are many disconnections. Therefore, excessive reverse tension has been avoided. Attention has been paid to stabilization, and various structures ( eg, Patent Document 2) have been devised. Although the structure is not limited in the present invention, the larger the reverse tension is, the more effective the purpose is. Therefore, if the reverse tension is not present, 30% or more of the front tension (= drawing stress × cross-sectional area) is sufficient. In general, it seems to be operating at around 30% or less. As shown in the examples, under the conventionally applied conditions, the magnitude of the reverse tension was about 30% of the forward tension (yield force × about 0.5 as described above). Therefore, in the present invention, it is 40% or more (that is, 20% or more of the yield force) at which a further effect is obtained. This is the core of the present invention.
It is desirable that the magnitude of the reverse tension be accurately grasped, but even if it is not, the problem is small in terms of quality control. It is only necessary that the wire drawing temperature can be reliably grasped and the tension can be adjusted.

  The effects of the wire drawing conditions (particularly the area reduction ratio Ao / Ai), the tensile strength and reverse tension of the steel wire on the temperature rise can be easily calculated from the equations (3) and (4). The reverse tension may be a ratio to the pulling stress. The amount of temperature increase is proportional to the pulling force including reverse tension. When the pulling stress is reduced by reverse tension, the temperature rise corresponding to the decreasing rate is obtained.

  The reason why reverse tension control and speed control are performed via temperature in the present invention is superimposed on the reverse tension control or speed control system that is naturally incorporated in conventional linear stretchers. The level is higher than before and more precise control is required, and the maximum temperature of wire drawing is always detected and maintained in the proper range, which has a direct effect on embrittlement due to strain aging of high tensile strength steel wire. This is because it can be applied to quality assurance.

The result of having conducted a drawing test of a high tensile strength PC steel wire using a straight type 9-head large continuous drawing machine is shown.
The test material is a hypereutectoid low alloy steel, a wire diameter of 12.5 mm, a tensile strength of 1400 KPa, and a finished diameter of 5.2 mm. In each pass, the temperature of the steel wire was measured at the part wound around the kettle after drawing. The temperature immediately before drawing is stable at 30 ° C. or less for each pass. On the other hand, the temperature rise by drawing was calculated according to the equation (3), and the temperature at the relevant part was calculated.

FIG. 2 shows a comparison of temperatures in each pass. The calculated value 1 is when the reverse tension is 30% of the drawing stress, and the calculated value 2 is when there is no reverse tension. Since reverse tension does not act in the first pass, using the calculated value 2 approximates to the actually measured value, and the calculation formula can be regarded as valid first. Reverse tension acts after the second pass. In the calculated value 2 of no tension, the temperature rise is greatly different from the actual measurement. The magnitude of the reverse tension is a rough measured value, but it is regarded as about 30% of the pulling force , and if it is 30% in all subsequent passes, the calculated value 1 approximates the measured value. About 30% of this is an unintentionally implemented range, but the effect of reverse tension on temperature rise was proved. If the reverse tension is further increased, further temperature rise suppression can be expected. In the present invention, the reverse tension is set to 40% or more of the pulling stress.

1: Wire rod 2: Continuous stretcher 3: First die 4: First hook 5: Steel wire 6: Dancer roller 7: Second die 8: Second hook 9: Radiation thermometer 10: Controller

Claims (2)

In a method of drawing a steel wire with a straight-line continuous wire drawing machine on which reverse tension acts, a reverse tension adjusting mechanism that reinforces the reverse tension in the wire drawing machine, and a steel after drawing wound on a drawing pot and attaching a thermometer for measuring the lowest temperature of the line column, the size of back tension is 20% or more of the yield strength of the steel wire after drawing, to suppress the temperature of the steel wire after drawing to 145 ° C. or less A continuous wire drawing method characterized by that.   The continuous signal according to claim 1, wherein a signal obtained by measuring the steel wire temperature is input to a reverse tension adjusting mechanism, and when the temperature is 145 ° C or higher, the reverse tension is increased and induced below the temperature. Drawing method.

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