WO2012111291A1

WO2012111291A1 - Method for straightening

Info

Publication number: WO2012111291A1
Application number: PCT/JP2012/000896
Authority: WO
Inventors: 内田　和宏; 忠司河上
Original assignee: 住友金属工業株式会社
Priority date: 2011-02-14
Filing date: 2012-02-10
Publication date: 2012-08-23
Also published as: JP5462202B2; EP2676746B1; CN103370149A; BR112013017469B1; TW201302337A; MX2013008855A; KR20130118960A; EP2676746A4; BR112013017469B8; MX363214B; US20130327110A1; BR112013017469A2; EP2676746A1; TWI538751B; JP2012166233A

Abstract

A method for straightening a steel material, the method comprising using superhard straightening rolls, the material of which is a tungsten carbide-cobalt (WC-Co)-based sintered object (superhard alloy). The method for straightening is characterized in that the superhard rolls have a hardness of HRA85-87. According to this straightening method, when a steel material is straightened, the rolls are inhibited from wearing and the surface of the material being straightened is prevented from suffering a flaw due to wear. In addition, the period required for roll replacement can be shortened to improve the operating ratio of the straightener and to attain an improvement in the efficiency of precise finishing and hence in productivity. The method is especially effective in the case where the material to be straightened is a high-strength material, e.g., a steel pipe for automotive air bags.

Description

Bending correction method

The present invention relates to a method for correcting the bending of a steel material such as a pipe or a rod, and in particular, suppresses the wear of a roll of a straightening machine, prevents the transfer of unevenness of the roll due to the wear to the steel material, etc. It is related with the bending correction method which can aim at the improvement of a precision efficiency by shortening.

Unless otherwise stated, the definitions of terms in this specification are as follows.
“Carbide straightening roll”: A straightening roll whose roll material is a tungsten carbide-cobalt (WC—Co) based sintered body (superhard alloy). Also simply referred to as “carbide roll”.
“Hardness”: The hardness of a roll or a material to be straightened means the Rockwell hardness (scale A) measured by the Rockwell hardness test specified in JIS Z 2245, and expressed as, for example, “HRA86” To do.

Steel materials such as tubes and rods are manufactured through hot or cold processing, but bending occurs during processing or during heat treatment in the process. This bending is usually corrected by a bending straightener using a roll such as an inclined roll type straightening machine (straightener) in which a plurality of drum-shaped rolls are combined.

However, especially when correcting the bending of high strength materials such as steel pipes for automobile airbags, the roll tends to wear away (uneven wear), and the deviation from the design roll profile is likely to occur. In some cases, unevenness may cause spiral wrinkles in the material to be corrected, or the unevenness may be transferred to the material to be corrected. In addition, it is necessary to change the roll position setting (setup) during bend correction, which is called crash and offset, and the operation rate of the bend straightening machine decreases due to the extension of the set-up time, resulting in a decrease in the efficiency and hence productivity. In addition, the accuracy of bending correction is reduced.

As a pipe straightening method, for example, in Patent Document 1, in order to prevent stress corrosion cracking that occurs in a product due to residual stress that occurs during straightening, the amount of crash required during straightening of the pipe is kept constant, and excessive residual stress is maintained. A method of straightening a tube without causing erosion is disclosed. However, there is no description about the suppression of roll wear, and the method described in the patent document cannot be a solution to the above problem.

Further, in Patent Document 2, in a straightening method in which a bend is made by applying a bend by an offset roll set and the bend is made, the offset direction of the offset roll set is changed to the opposite direction for each predetermined pipe passing amount. A correction method is disclosed. By applying this method, it is possible to make the wear of the upper roll and the lower roll uniform and eliminate the work of rearranging the upper and lower rolls. However, the wear itself cannot be reduced.

JP-A-55-128318 JP-A-8-47722

As described above, when correcting bending of steel materials such as pipes and rods, especially bending of high-strength materials such as steel pipes for automobile airbags, the roll is worn and the material to be corrected is caused by the wear. There are cases where wrinkles occur on the surface and it takes time to change the setup. This problem is difficult to deal with by the prior art.

The present invention has been made in view of such problems, and corrects bending in steel materials such as pipes and rods, particularly high strength materials such as steel pipes for airbags, using a straightening machine using a roll such as a straightener. In doing so, the wear of the roll is suppressed, the unevenness of the roll due to the wear is prevented from being transferred to the material to be corrected, and the occurrence of wrinkles is shortened. It aims to provide a method for correcting bending.

The gist of the present invention is as follows.

(1) A bending correction method for steel using a cemented carbide straightening roll, wherein the hardness of the cemented carbide roll is HRA 85 to 87.
(2) The bending correction method according to claim 1, wherein the material to be corrected is a steel pipe for an automobile airbag.
Here, the "bending correction method using a roll" is a correction method using a roll type straightening machine that corrects bending while advancing the correction material by placing rolls above and below the correction material. This refers to a straightening method using an inclined roll type straightening machine (straightener). Further, the “steel material” refers to a steel material such as a tube or a rod that can correct the bending by this correction method regardless of the material.

The bending straightening method of the present invention is a straightening method using a cemented carbide straightening roll having a hardness of HRA85 to 87. According to this method, when correcting the bending of a steel material such as a pipe or a rod using a roll such as a straightener, the wear of the roll is suppressed and the generation of wrinkles on the surface of the material to be corrected due to the wear is prevented. By shortening the setup change time, it is possible to improve the operation rate of the bending straightening machine, and to improve the finishing efficiency rate and thus the productivity.

FIG. 1 is an explanatory diagram of a method for evaluating the wear resistance of a roll material. FIG. 2 is a diagram showing the results of examining the wear resistance of the roll material. FIG. 3 is a diagram schematically showing a schematic configuration of a straightener used for straightening a steel pipe and an application location of a cemented carbide roll. FIG. 4 is a diagram showing a result of investigating the amount of wear of the roll when the bending correction method of the present invention is applied, in comparison with the case where a conventional roll is used. FIG. 5 is a diagram showing the investigation results of the surface roughness of the roll when the bending correction method of the present invention is applied. FIG. 6 is a diagram showing the transition of the setup change time when the airbag pipe is straightened by applying the bending straightening method of the present invention in comparison with the case where a conventional roll is used. FIG. 7 is a diagram showing the operation rate of the straightener when the steel pipe for an airbag is straightened by applying the bending straightening method of the present invention in comparison with the case where a conventional roll is used.

In order to solve the above problems, the present inventors have attempted to suppress the wear of the roll by optimizing the roll material, and tried to apply a WC-Co based sintered body as the roll material. It was. WC-Co sintered body is a composite material made by adding Co as a binder to fine powder of WC to make a sintered body, which is called cemented carbide and has high hardness and excellent wear resistance. Therefore, it is frequently used as a material for cutting tools.

As a result of investigating the wear resistance and heat crack resistance of this cemented carbide, the cemented carbide is a tool steel (specified in JIS G 4404) used as a material for conventional rolls, as shown in the examples described later. SKD1: 2.1C-12Cr (hereinafter, simply referred to as “SKD”) was confirmed to have about 100 times the wear resistance. In addition, it has been found that the cemented carbide has heat crack resistance (evaluated by the number of repetitions until the occurrence of cracks after repeated heating and water cooling) that can withstand use as a roll material.

Furthermore, as a result of applying a cemented carbide roll as a straightener roll to the actual machine, no wear was observed, and it was confirmed that the operation rate of the straightener could be improved by shortening the setup change time.

The present invention has been made on the basis of such findings, and as described above, is a method for correcting the bending of a steel material using a cemented carbide roll, and the hardness of the cemented carbide roll is HRA 85 to 87. It is a characteristic bending correction method.

In the present invention, it is assumed that a cemented carbide straightening roll is used. The cemented carbide, which is a composite material of ceramics and metal, is hard and has excellent wear resistance and also has heat crack resistance. This is because it is suitable as a roll material. That is, as a material of the straightener roll, hardness, wear resistance, and heat resistance (withstand heat generation during correction by the roll) are necessary, but cemented carbide is excellent in any of them.

In the present invention, the hardness of the straightening roll is HRA 85 to 87 in order to keep both wear resistance and heat resistance high. When the hardness of the roll is less than HRA85, the difference from the hardness of the material to be corrected becomes small, and the wear resistance becomes insufficient. Moreover, when the hardness of a roll exceeds HRA87, although abrasion resistance will increase, heat resistance will fall and the tendency for heat crack resistance to fall will be seen.

The bending correction method of the present invention is particularly effective when the material to be corrected is a steel pipe for an automobile airbag.

A steel pipe for an automobile airbag is made of a high strength steel having a tensile strength of approximately 800 to 1100 MPa. When the tensile strength is 1100 MPa, the hardness is approximately HRA68.5. When correcting such bending of a steel pipe for airbag with high strength and high hardness, a roll made of ordinary tool steel (SKD, for example, SKD11: 1.5C-12Cr-1.0Mo, etc.) is used. , Roll wear is likely to occur, wrinkles occur on the surface of the material to be straightened, and it takes time to change the setup as the wear progresses (increase in reduction allowance due to wear). Often, the rate drops and the accuracy rate drops.
In such a case, if the bending straightening method of the present invention using the carbide straightening roll is applied, as shown in the examples described later, the wear of the roll is virtually completely suppressed, and the surface roughness is not greatly changed. (In other words, no generation of wrinkles is recognized), and the setup change time is shortened.

Example 1
The wear resistance and heat crack resistance of a cemented carbide, which is a material of a cemented carbide roll used in the bending correction method of the present invention, were investigated. In addition, about abrasion resistance, the same investigation was done for the tool steel SKD (it used for sub-zero processing and was used) which is the raw material of the conventional roll for the comparison.

Table 1 shows the materials and properties of the test materials. In Table 1, “particle size” is the particle size of the cemented carbide.

As shown in Table 1, cemented carbides A, B, and C are materials whose Co addition amount to WC is about 15%, 16%, and 17% (all by mass%), respectively, and the increase in Co addition amount As a result, the hardness has changed from HRA88.0 to HRA85.0.

FIG. 1 is an explanatory diagram of a method for evaluating the wear resistance of a roll material.

As shown in FIG. 1, a ball 1 (material: SUJ, diameter: 15 mm) to which a load was applied was repeatedly slid on the test piece 2, and the wear amount (wear volume) of the test piece 2 at that time was measured. . This wear amount is converted into specific wear amount (wear volume per unit sliding distance / unit load [mm ³ / (mm · N)] = [mm ² / N]), and tool steel SKD (conventional roll material) The wear resistance was evaluated by comparing with the specific wear amount at.

FIG. 2 is a diagram showing the results of investigation of wear resistance. As shown in FIG. 2, the specific wear amounts of cemented carbides A, B, and C are all 1/100 or less compared to tool steel SKD, and the cemented carbide is much less than conventional roll materials. It was confirmed that the film had about 100 times the wear resistance. Further, when compared between the cemented carbides A, B and C, the cemented carbide A having the hardest hardness of HRA88.0 has the least specific wear and the best wear resistance.

The heat crack resistance of the cemented carbide was evaluated by repeating the process of “heating (700 ° C.)” → “water cooling” on the test piece until the test piece was cracked. The greater the number of repetitions, the better the heat crack resistance.

Table 2 shows the evaluation results of heat crack resistance. In Table 2, the symbol “◯” indicates that no crack was observed, and the symbol “X” indicates that a crack occurred. The presence or absence of cracks was determined by visual observation.

As shown in Table 2, in the cemented carbides B and C, no cracks were observed even when the heating / water cooling cycle number was 20, but in the cemented carbide A, cracks occurred when the cycle number was 10 times. did.

Table 3 shows the results of comprehensive evaluation of the wear resistance, heat crack resistance and hardness of the cemented carbides A, B and C. The wear resistance was all good and marked with ◯. In particular, when the specific wear amount was less than 100 × 10 ⁻¹² mm ² / N (Cemented Carbide A), it was marked with ◎ (see FIG. 2).

Heat crack resistance is based on 10 repetitions of heating / water cooling. When cracks are not observed after 10 times, the mark is good. Marked. In addition, the hardness of the cemented carbide is marked as ◯ because it has sufficient hardness. However, in particular, when it is HRA88.0 or more (carbide A), it is indicated as ◎. .

As shown in Table 3, cemented carbide A (hardness: HRA88.0) is the hardest material in the investigation and has excellent wear resistance, but the heat crack resistance is cemented carbide B. , It was lower than C, and it was Δ in the overall evaluation (relatively low heat crack resistance). On the other hand, cemented carbide B (hardness: HRA86.5) and cemented carbide C (hardness: HRA85.0) are both good in wear resistance and heat crack resistance. The mark was good.

From the above investigation results, the cemented carbide as the material of the cemented carbide roll used in the bending correction method of the present invention has extremely high wear resistance, and the hardness of the cemented carbide is limited to the range of HRA85 to 87. Was confirmed to be appropriate.

(Example 2)
The bend straightening method of the present invention is applied to straightening a steel pipe with a straightener to investigate the amount of wear and surface roughness of the roll, and shorten the setup change time when the steel pipe for an automobile airbag is targeted for straightening. The effect was confirmed. For comparison, the same investigation was performed when a conventional roll (material: tool steel SKD11) was used.

Table 4 summarizes the characteristics of the straightener roll materials used. The material of the cemented carbide roll used in the bending correction method of the present invention is the cemented carbide B used in Example 1.

FIG. 3 is a diagram schematically showing a schematic configuration of a straightener used for straightening a steel pipe for an air bag and an application location of a carbide roll. The straightener is 2-2-2-1 type. Carbide rolls are applied to the # 2 and # 3 upper and lower rolls with a large amount of wear (in FIG. 3, the rolls are indicated by hatching), and the guide roll # 1 roll and the final # 4 roll are conventional. A roll made of SKD11 was used. The roll dimensions are roll center (minimum) diameter: 190 mm, roll width: 180 mm.

The steel pipe to be straightened is a steel pipe having an outer diameter in the range of 15.90 to 42.7 mm.

Table 5 summarizes the rolls to be measured for the wear amount and the surface roughness, the measurement points, and the measurement method.

FIG. 4 is a diagram showing the result of investigation of the amount of wear of the roll when the bending straightening method of the present invention is applied, in comparison with the case where a conventional roll is used. The vertical axis in FIG. 4 represents the wear rate (mm / km) obtained by dividing the wear amount (reduction margin due to wear: mm) by the correction total length (km).

As shown in FIG. 4, when a roll made of tool steel SKD11 is used, the wear rate when using up to the conventional roll life (the use limit due to wear, and the total length of correction is 2500 km) is 1.6 ×. 10 ⁻³ mm / km, but when the bending straightening method of the present invention using a carbide roll is applied, the straightening total length reaches 4300 km (1.7 times the conventional roll life). The wear rate was 0 mm / km and no wear was observed.

FIG. 5 is a diagram showing the investigation results of the surface roughness of the roll when the bending correction method of the present invention is applied. The surface roughness is indicated by the maximum height (Rz).

As shown in FIG. 5, immediately after the start of correction, minute irregularities on the roll surface are smoothed to improve the surface roughness (Rz decreases), and thereafter there is no significant change. Changed within the indicated range. There was no significant change after the total correction length exceeded 4300 km.

FIG. 6 is a diagram showing the transition of the setup change time when the air pipe steel pipe (outer diameter: 25 mm) is corrected by applying the bending correction method of the present invention in comparison with the case where a conventional roll is used. .

As apparent from FIG. 6, when the conventional roll (made of tool steel SKD11) is used, the set-up time becomes 30 minutes per time as the straightening total length increases and the wear of the roll increases. (Indicated by a thick arrow in the figure), but when the bending correction method of the present invention using a carbide roll is applied, wear does not occur, so the setup change time is extended. Therefore, the changeover within the target time could be continued.

FIG. 7 shows the operation rate of the straightener when the air pipe steel pipe (outer diameter: 20 mm, 25 mm or 30 mm) is corrected by applying the bending correction method of the present invention, as compared with the case where a conventional roll is used. FIG.

As can be seen from FIG. 7, the straightener operation rate improved regardless of the outer diameter of the steel pipe for the airbag to be corrected. This is due to the shortening of the setup change time due to the application of the bending correction method of the present invention. The efficiency of the refining process largely depends on the operating rate of the straightener, and the operating efficiency of the refining process has been improved by improving the operating rate of the straightener.

From the above investigation results, it is possible to completely suppress the wear of the roll by applying the bending correction method of the present invention, and the correction method of the present invention is particularly suitable for the bending correction of the steel pipe for airbag, and the setup change time is reduced. It was confirmed that the operating rate of the straightener could be improved by shortening.

The bending correction method of the present invention can be effectively used to correct bending that occurs in steel materials such as pipes and rods, particularly bending of high strength materials such as steel pipes for automobile airbags.

1: Ball, 2: Test piece

Claims

A method for correcting the bending of a steel material using a carbide straightening roll,
A bending correction method, wherein the hardness of the cemented carbide roll is HRA 85 to 87.
2. The bending correction method according to claim 1, wherein the material to be corrected is a steel pipe for an automobile airbag.