JPS5935688B2 - Method for forming ERW steel pipes - Google Patents

Description

Detailed Description of the Invention The present invention involves forming a strip into a cylindrical shape while lowering the center portion of the strip as forming progresses, and then rolling it down in the tube circumferential direction with tandem fin bath rolls to finish it into a blank tube. This method relates to a method for forming a base pipe of an ERW steel pipe to be formed, and in particular, it is suitable for applying to the process of forming a base pipe of a base pipe using a cage roll, and is suitable for the generation of edge waves at the joint edge portion of a base pipe. The present invention relates to a method for forming an electric resistance welded steel pipe, which can simultaneously prevent warping in the longitudinal direction of the pipe.

Generally, electric resistance welded steel pipes by cage roll forming are manufactured as follows.

That is, as shown in FIGS. 1 and 2, the strip 10 is sequentially formed into a cylindrical shape by a plague down roll 12, an edge forming roll 14, an outside cage roll 16, and an inside cage roll 18 in the early and middle stages of forming. After that, the top rolls 20a, 2, which are finish forming rolls, are
2a, 24a) Side rolls 20b, 22b, 24b)
By being rolled down in the pipe circumferential direction by tandem-type fin bath rolls 20, 22, and 24 consisting of bottom rolls 20c, 22c, and 24c, the blank pipe is formed into a predetermined pipe shape and size while stably forming the edge portion 10a. 26 is finished and molded. FIG. 3 schematically shows the state of forming the raw tube in the first fin bath roll 20. Tandem type fin bath roll 20
, 22, 24 in the tube circumferential direction,
Both edges 26a of the seam are heated by high frequency and are upset welded by a squeeze roll 28 consisting of a top roll 28a, a side roll 28b, and a bottom roll 28c to form an electric resistance welded steel pipe 29. In addition, in this cage roll forming, normally, in the early and middle stages of forming,
As shown in Figures A and B, so-called down-build molding is performed in which the central portion 10b of the strip 10 is lowered to the baseline BL as molding progresses, and the edge portion 1 of the strip 10 is lowered down to the baseline BL.
By reducing the difference in the length of the trajectory traced between 0a and the central portion 10b,
The elongation of the edge portion 10b in the longitudinal direction is suppressed. Furthermore,
Smooth bending is performed by continuously restraining and supporting the edge portion 10a by a large number of continuous outside gauge rolls 16. According to cage roll forming accompanied by such down building forming, as shown in Fig. 5,
Using conventional breakdown rolls 30, side cluster rolls 32, and fin pass rolls 34, the strip 10 is
Compared to step roll molding, which molds the raw pipe 26 from
It is characterized by almost no edge waves 10c occurring during the early and middle stages of molding.

However, even in this cage roll forming, in the final stage of forming, that is, in the fine pass forming area corresponding to the final forming process, a longitudinal compressive force may act on the strip edge portion 10a that has been stretched during the early and middle forming stages. If this compressive force exceeds the buckling stress limit of the strip edge portion 10a, edge waves may occur. In general, the forming condition of the edge of the raw pipe has a large influence on the shape quality of the weld, and therefore, in particular, the decline in the shape quality of the weld caused by edge waves, as well as the decline in material yield and productivity, is an important problem. It was becoming. Therefore, in the cage roll forming as described above, the down build amount DH) of the strip 10 is
Total reduction R of tandem type fine pass roll
Combinations such as reduction distribution and reduction distribution are extremely important molding conditions, but these combinations are not uniquely defined and there are an infinite number of them, and in the past, various molding conditions have been adopted empirically. It is. However, quantitative understanding is insufficient, and it is difficult to select the appropriate combination of forming conditions.In actual operations, edge waves may still occur due to incorrect selection of forming conditions, especially when manufacturing pipes of an unexperienced size. When forming pipes, it was difficult to select the molding conditions, and edge waves tended to occur frequently. In addition, in the above-mentioned method for forming a blank tube, depending on the selection of the downbuild conditions and the fine pass forming conditions in the forming area, the condition of the blank tube 26 after the fine pass forming is as shown in FIG. 6A or B. Warpage occurred in the longitudinal direction in some cases.

In the figure, S is a seam portion. Conventionally, the warpage of this raw pipe was shaped and corrected using a sizing roll in the post-process, but the selection of the sizing roll setting conditions for this shaping and correction is important because this roll is the final forming roll and the pipe It has become extremely difficult to determine the shape and size accuracy of the product. As described above, in the past, forming control such as selecting fin pass forming conditions and down building conditions to prevent warpage in the longitudinal direction of the raw pipe has not been carried out.
The warpage that occurred in the raw pipe was corrected using sizing rolls in the subsequent process, which caused a decrease in productivity due to an increase in the time required for straightening, as well as a decrease in shape and dimension accuracy due to poor correction, which became a major problem. Ta. In addition, in order to prevent the occurrence of edge waves at the joint edges of the raw pipes or warpage in the longitudinal direction of the raw pipes as described above, it is possible to select appropriate forming condition ranges suitable for each. There is a fear that one of these occurrences cannot be prevented, or that the range of appropriate molding conditions becomes complicated and it becomes difficult to select the appropriate molding conditions. The present invention
This was made to eliminate the above-mentioned drawbacks of the conventional method, and by using a relatively simple range of appropriate forming conditions that makes it easy to select the appropriate forming conditions, it is possible to prevent the occurrence of edge waves at the joint edge of the raw pipe and the occurrence of warpage in the longitudinal direction of the raw pipe. Provided is a method for forming an ERW steel pipe, which can simultaneously and reliably prevent the above-mentioned problems, thereby stably producing an ERW steel pipe with excellent welded part shape quality and shape and dimensional accuracy. The purpose is to In the present invention, the strip plate is formed into a cylindrical shape while the center part of the strip plate is lowered as forming progresses, and then rolled down in the tube circumferential direction by tandem type fin pass rolls to finish form the blank pipe. In the tube forming method, the downbuild coefficient η
is within the range of 0.3 to 1.25, the fin path total reduction R is within the range of 0.55 to 1.25%, and the value of η is approximately equal to η= The lower limit rises almost linearly with 1.05 as the lowest point and η=0.5 as the intermediate refraction point, and approximately η=0.6 as the highest point, η=1.
2 is the intermediate refraction point, and the upper limit falls almost linearly within the allowable range, and furthermore, the first fin pass reduction distribution ratio δ is 75% or more and, depending on the value of η, approximately η The above object has been achieved by molding the raw pipe to a value within the allowable range in which the lower limit increases almost linearly with the lowest line being 0.45 to 1.2.

The present invention will be described in detail below with reference to the drawings. The edge waves generated at the edge portion 26a of the raw pipe and the warpage in the longitudinal direction of the raw pipe are determined by the down-build amount DH of the strip plate 10 and the fine pass forming conditions (fin pass total reduction R).
) reduction distribution), and it is known from experience that it is important to select an appropriate combination of these molding conditions in actual operations. The present invention
This was done based on the results of numerous experiments and studies conducted by the inventors in order to obtain an appropriate range of forming conditions in which edge waves and warpage do not occur in cage roll forming, and the down-build amount DH of the strip ) Total reduction of tandem type fin pass rolls R) fin pass reduction distribution Appropriate forming condition range without edge waves and warpage is clarified by three forming condition factors. The range of appropriate molding conditions obtained as a result of experiments and research by the inventors is as follows.

That is, first, the down build amount (here, the down build amount DH
downbuil coefficient η = DH/D divided by the product tube outer diameter D) and the fin pass total reduction R (the sum of the reduction Ri of each stand with a fin pass roll for all stands Σ Ri stand output Using the side tube outer circumference length 1ii=1, rl=1001n(1
As shown in FIG. 7, the first appropriate molding condition range (I) in which edge waves and warpage do not occur is determined by the down-build coefficient η
is within the range of 0.3 to 1.25, and the fin path total reduction R is within the range of 0.55 to 1.25%, and depending on the value of η, approximately η = 1.05. The lower limit rises almost linearly with η = 0.5 as the lowest point and η = 0.5 as the intermediate inflection point, and the upper limit decreases almost linearly with η = 0.6 as the highest point and η = 1.2 as the intermediate inflection point. It was something to do.

This first appropriate molding condition range H) can be roughly expressed in a mathematical formula as shown in the following formula. Here, equation (1) is the Tth
(Equation 2 also corresponds to solid line B, Equation (3) also corresponds to solid line C, Equation (4) also corresponds to solid line D, and Equation (5) also corresponds to solid line D. E, and equation (6) also corresponds to the solid line F.As is clear from Fig. 7, the downbuild amount (downbuil coefficient η) It can be seen that when is large or small, the range of the appropriate fin path total reduction R becomes small.

If the first appropriate molding condition range (I) is exceeded, edge waves or warpage will occur significantly, and
Buckling in the circumferential direction of the edge portion of the raw tube or a defective tube shape may occur. On the other hand, regarding the relationship between the downbuilding amount DH (downbuilding coefficient η) and the fin pass reduction distribution, research has shown that the occurrence of edge waves and warpage is mainly influenced by the first fin pass reduction distribution; It has been found that the influence of the reduction distribution of the second and third fin passes is relatively small.

Based on this knowledge, we conducted an experiment and found that the edge wave determined by the downbuild amount DH expressed by the downbuil coefficient η and the first fin pass reduction distribution ratio δ (= ., As shown in FIG. 8, the appropriate molding condition range (2) is that the downbuil coefficient η is also within the range of 0.3 to 1.25, and the first fin pass reduction distribution ratio δ is 75% or more. Moreover, the lower limit increased almost linearly depending on the value of η, with the lowest line being approximately η=0.45×1.2. This second appropriate molding condition range () can be roughly expressed as a mathematical formula as shown in the following formula. Here, equation (7) corresponds to solid line G in FIG. 8, equation (8) also corresponds to solid line H, and (9)
The formula also corresponds to the solid line I.

If the downbuil coefficient η and the first fin pass reduction distribution ratio δ deviate from the second appropriate molding condition range (), the occurrence of edge waves or warpage becomes noticeable.

As described above, the range of appropriate molding conditions in which neither edge waves nor warpage occur is the first and second range.
It satisfies both the ranges (I) and () of the appropriate molding conditions at the same time, and the down build amount and total fin pass do not deviate from both the first and second appropriate molding condition ranges (I) and (). By selecting the reduction and the first fin pass reduction distribution, it is possible to stably manufacture an electric resistance welded steel pipe that is free from edge waves and warpage and has excellent welded part shape quality and shape and dimensional accuracy.

Next, a specific example of selecting appropriate molding conditions using the present invention will be described.

For example, when down-build molding with a down-build coefficient η-0.6 is adopted, the fin path total reduction R is approximately 0.8 to 1.25%, as is clear from Figure T.
As is clear from FIG. 8, the first fine pass reduction distribution ratio δ is within the range of 75% to 100%, while considering the improvement of material yield and the prevention of roll flaws. The total reduction R and the first fin pass reduction distribution ratio δ are selected. As a result, it is possible to form an excellent raw pipe without causing edge waves or warpage. Regarding the selection of the amount of downbuild, due to the problem of the time required to change the downbuild setting in actual operation, the Finpass Total Reduction R according to the present invention is used.
Also, the appropriateness of the first fin pass reduction distribution ratio δ.
The downbuild amount D is adjusted so that the range of molding conditions is relatively wide.
Selection of H is also extremely beneficial in terms of productivity in actual operation. An embodiment according to the invention is shown in FIGS. T and 8.

The experimental material is a high-strength electric resistance welded steel pipe that corresponds to API standard API5LX-X-60 and has a ratio t/D of the pipe wall thickness t to the pipe outer diameter D of approximately 1.0%. In the figure, ◯ marks indicate cases in which no edge waves or warpage occur, and × marks indicate cases in which edge waves or warpage occur. Here, to determine the presence or absence of an edge wave, the depth d of the edge wave is determined by the span 1 of the edge wave, as shown in FIG.
This was done by the edge wave steepness divided by s (d/11s). In other words, a detailed investigation into the effect of edge wave steepness on weld quality revealed that there is no problem as long as edge wave steepness (d/1s) is 20 x 10-4 or less. Regarding the presence or absence of wave generation, it is evaluated that if d/1s≦20×10−4, there is no edge wave generation, and if d/1s>20×10−4, it is evaluated that edge waves are generated. In addition, to evaluate the warpage in the longitudinal direction of the raw pipe, as shown in FIG. ) is used as an index for warpage evaluation. That is, based on the product specification standard, if the warp curvature 1/ρ is 6.6 × 10-7 (n-1) or less,
It is evaluated that no warpage occurs. It should be noted that the first fin pass reduction distribution ratio δ shown in FIG. There is. In the above embodiments, the present invention was applied to a cage roll type electric resistance welded steel pipe forming mill, but the scope of the present invention is not limited to this, and is applicable to a step roll forming process as shown in Fig. 5. It is clear that the present invention is similarly applicable to semi-cage roll forming, which is a combination of step roll forming and cage roll forming, when downbuild forming is employed. As explained above,
According to the present invention, the amount of downbuild of the strip does not deviate from the range of relatively simple appropriate forming conditions, which makes it easy to select the appropriate forming conditions, the total reduction of the fin pass of the tandem type fin pass roll, and the reduction of the first fin pass. By selecting the weld distribution ratio, it is possible to simultaneously and reliably prevent the occurrence of edge waves at the joint edges of the raw pipe and warpage in the longitudinal direction of the raw pipe, and therefore improve the quality and size of the welded part. It is possible to stably manufacture electric resistance welded steel pipes with excellent accuracy.

In addition, it is possible to omit warpage straightening work using sizing rolls in the post-process, which was conventionally performed, and has the excellent effect of improving work efficiency and productivity.

[Brief explanation of drawings]

Fig. 1 is a plan view showing the process of forming an ERW steel pipe in a cage roll type ERW steel pipe forming mill, Fig. 2 is a front view, and Fig. 3 is taken along line I-I in Fig. 2. 4A and 4B are plan views and front views schematically showing the forming state of the strip plate and the down building forming state, and FIG. 5 is an enlarged sectional view along the line, and FIG. Plan view showing the state where edge waves are generated, Figures 6A and B
7 is a perspective view showing a raw pipe in which warping or reverse warpage has occurred, and FIG. A diagram showing the appropriate molding condition range (I), FIG. 8 is a diagram showing the appropriate molding condition range () of the downbuil coefficient η and the first fin pass reduction distribution ratio δ, and FIG. Schematic diagram showing the evaluation method of Edge Wave, Part 1
FIG. 0 is a perspective view showing a method for measuring warpage of a blank pipe. 10...band plate, 10a...edge part,
10b... Central part, 12... Breakdown roll, 14... Edge forming roll, 16... Outside cage roll, 1
8...Inside cage roll, 20, 22,
24...Finpas roll, 26...
Raw pipe, 26a...Edge part, 28...
Squeeze roll, 29...Erw steel pipe.

Claims (1)

[Claims] 1. A method for forming an electric resistance welded steel pipe, in which the strip is formed into a cylindrical shape while the center portion of the strip is lowered as the forming progresses, and then rolled down in the tube circumferential direction by tandem fin pass rolls to finish form the tube. , the downhill coefficient η is 0.3 to
The value is within the range of 1.25, the fin pass total reduction R is within the range of 0.55 to 1.25%, and
Depending on the value of η, approximately η=1.05 is the lowest point, η=0.
The lower limit rises almost linearly with 5 as the intermediate inflection point, the highest point is approximately η = 0.6, and the upper limit falls almost linearly with η = 1.2 as the intermediate inflection point. Furthermore,
The first fin pass reduction distribution ratio δ is 75% or more, and is within an allowable range in which the lower limit increases almost linearly with the lowest line being approximately η = 0.45 to 1.2, depending on the value of η. 1. A method for forming an electric resistance welded steel pipe, characterized in that by forming the material pipe as a value, the generation of edge waves at the joint edges of the material pipe and the occurrence of warpage in the longitudinal direction of the material pipe are simultaneously prevented.