JP5625744B2 - Detection method of steel strip weld seam in forged steel pipe manufacturing - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method for detecting a steel strip weld seam in forged steel pipe production, and more specifically, a weld seam that is a defective product portion (welding by a steel strip weld seam, that is, welding by joint welding of longitudinal ends of steel strips). The same is true for the seam, the same applies to the following), especially after pipe making and before coating the resin, the weld seam is reliably detected and removed, and the weld seam passes the edge roll. The present invention relates to a method for detecting a welded seam portion of a steel strip in forged welded pipe production, which reduces wear of an edge roll due to impact pressure generated when the steel strip is welded.

  A forged steel pipe is manufactured by heating a steel strip in a heating furnace, cutting it into a steel pipe of a predetermined length through steps of forging and processing with a forming roll and adjusting the outer diameter and pipe thickness with a drawing mill. If this manufacturing process is carried out independently for each coil, the productivity is remarkably reduced. Therefore, the longitudinal ends of the steel strip to be charged in the heating furnace are successively welded (joint welded) to continuously pass through and manufacture. . Therefore, a steel strip welded seam portion (hereinafter also simply referred to as a seam portion) in which adjacent steel strips are welded to each other is generated in the manufactured steel pipe. The steel pipe including the seam is inferior in mechanical strength compared to the product steel pipe not including the seam. Therefore, for quality control of the product, the seam is reliably detected, and a predetermined length in the middle of the production line after pipe making is obtained. It is necessary to remove at an early stage after cutting. In particular, when a resin coating is applied to a manufactured steel pipe, the seam is completely invisible from the appearance when the resin is coated, making detection extremely difficult. Therefore, the seam is reliably detected and removed before the resin coating process. There is a need.

Conventionally, as a method for detecting a seam portion, in Patent Document 1, immediately after welding the steel strip, the welded portion is painted by spray marking, and a seam portion is detected by using a laser sensor or the like in the seam portion detecting step to identify the seam portion. A method for detecting a part is disclosed.
Patent Document 2 discloses a method for detecting a joint portion with a plate thickness meter. Compared to the parts other than the welded part, the seam part is generally thicker due to the added height of the welded part. Therefore, using the thickness gauge, the thickness greater than the specified threshold value was detected and used as the joint part. .

JP 2006-102777 A JP-A-6-304636

  However, in the method disclosed in Patent Document 1, the steel strip surface is pressed with an auxiliary roll or the like during the conveyance from the marking step to the joint detection step, so that the paint at the marking portion is easy to peel off. There was a problem that the joint could not be detected reliably. In addition, there are problems that the spray nozzle is likely to be clogged, and that the marking of the seam portion fails, and there is a problem that a permanent cost is required for the replacement cost of the spray liquid, and these problems are unsolved problems.

Further, in the method disclosed in Patent Document 2, when the plate thickness in the vicinity of the welded portion is thick and the weld bead height is low, if the threshold value for detecting the joint portion is lowered, the joint portion is not detected (undetected) However, there is a problem of misdetection (false detection) as a joint other than the welded portion, which hinders operation, and this point is also an unsolved problem.
In order to solve the above-mentioned problems, the present invention accurately detects a seam portion that is a defective product portion to achieve accurate quality control, and the amount of wear of the edge roll that occurs when the seam portion passes the edge roll. An object of the present invention is to provide a method for detecting a steel strip weld seam in forged steel pipe production.

The present invention made to solve the above-mentioned problems
(1) When the steel pipe is manufactured by welding the longitudinal ends of a plurality of steel strips sequentially, continuously heating and forming, and forging the steel strip widthwise ends, before the heating furnace for heating An edge roll for rolling in the width direction of the steel strip installed on the steel strip is used to detect the occurrence of an impact load when the steel strip passes through the edge roll, and the detected position of the impact load is detected by the steel strip. Identified as the weld seam of
And the pressing load of the edge roll is set to 6.0 to 8.8 kN,
Further, forging contact characterized in that a load value 1.3 times the average load of the edge roll is used as a threshold value, and the impact load is generated only when a measured load on the edge roll is equal to or greater than the threshold value. It is a method of detecting a steel strip weld seam in steel pipe production ,
Also, the detection method of the steel strip welded seam portion in forge welding steel pipe production according to (2), characterized in that additionally provided an accumulator to absorb the impact by the generated impact load (1).

  According to the present invention, in producing a forged steel pipe, in the step of detecting the joint portion of the longitudinal end portion of the steel strip, the occurrence position of the impact load when the steel strip passes through the edge roll is detected, and this generation By identifying the position as a seam part, it is possible to accurately detect the seam part. Further, by absorbing the impact load with an accumulator, the impact on the edge roll can be reduced, and wear of the edge roll can be reduced.

Schematic which shows the example of the impact load which generate | occur | produced when the joint part passed the edge roll in this invention. Schematic which shows the example of the impact relaxation method of the edge roll by an accumulator in this invention.

In the manufacturing process of forged steel pipes, the present inventors are not a method that detects falsely when detection conditions fluctuate, such as conventional spray marking or plate thickness measurement, as a method for detecting a seam portion. Then, the method that can be surely detected was studied earnestly.
As a result, as shown in FIG. 1, when the seam portion 20 of the steel strip 4 passes the edge roll installation position (the roll gap position between the edge upper roll 1 and the edge lower roll 3), We paid attention to the impact load generated on the edge roll due to the step. In FIG. 1, (a) is a perspective view showing the state of the passing plate, (b) is a transition diagram of the detected load, and in FIG. 1 (b), 5 is a pressing load (in the case of 8.8 kN), 6 is the holding load (in the case of 6.0 kN), 7 is the impact load of the steel strip passage part identified as the seam (maximum of about 23 kN when the detected load is 8.8 kN), 8 is the seam as in 7. It is an impact load of the steel strip passage part identified as (maximum of about 12 kN when the detected load is 6.0 kN). The seam part is the part where the steel strip longitudinal end is welded, and compared to the normal steel strip part without the seam part, the thickness of the seam part becomes thicker as the welded part rises in the plate thickness direction In many cases, the impact load is surely generated when the seam passes the edge roll. Further, even if there is a possibility of undetected or false detection in the method of Patent Document 2 (when the plate thickness near the welded portion is thick and the welded portion is thin), a step is generated in the welded portion, so that the edge roll An impact load is generated. Furthermore, there is a slight difference in plate thickness between the steel strips that are welded at the ends in the longitudinal direction, and an impact load is also generated by the difference in level.

Therefore, when the seam portion passes the edge roll, an impact load is surely generated. Therefore, if this impact load is detected, the seam portion can be reliably identified.
In addition, since the pressing load of the edge roll varies somewhat even in the normal steel strip part, it is better to identify the steel strip longitudinal direction part where the load exceeding the change is detected as a seam part. The load of the edge roll was measured and the average value was always calculated, and the load became 1.3 times or more than the average load (that is, the load value 1.3 times the average load) It was grasped that it was good to identify the longitudinal direction site | part of a steel strip used as a threshold value and used as the load more than this threshold value as a seam part.

  Further, when the pressing load of the edge roll is increased, the impact load due to the passage of the joint portion is increased and it is easy to detect. However, the load on the edge roll increases due to the impact load, and wear tends to proceed. Therefore, as shown in FIG. 2, the edge roll 1 or / and 3 is vertically movable (in the example of FIG. 2, only the edge-up roll 1 is movable in the edge-up roll movable direction 12), and the accumulator 11 is By attaching, the impact load is absorbed, and even if the pressing load of the edge roll is increased, it is possible to reliably detect the joint portion while reducing the load on the edge roll. In FIG. 2, reference numeral 10 denotes a hydraulic pipe that transmits the oil pressure of the accumulator 11 to the upper edge roll 1.

In both the inventive example and the conventional example, for steel strips having a thickness of 3.8 mm to 4.2 mm, the end portions in the longitudinal direction of the steel strip are sequentially welded, and a total of 101 pieces (the number of joint portions is 100 pieces) are joined. The welded steel pipe was manufactured by letting the steel plate through, and the joint detection rate, undetected rate, and false detection rate (all are the number rate (%)) were examined.
In Example 1 of the present invention, when the pressing load of the edge roll is set to 6. OkN, the load is constantly measured, and an impact load exceeding 1.3 times the average load (this is set as the load threshold) is detected. Was identified as the seam. In this case, the detected impact load was about 12 kN (about twice the average load), and it was found that it could be detected reliably.

As Example 2 of the present invention, when the pressing load of the edge roll is set to 8.8 kN, the load is constantly measured, and a case where an impact load exceeding 1.3 times the average load is detected is identified as a joint portion; did. In this case, the detected impact load was about 23 kN (about 2.6 times the average load), and it was found that it could be detected reliably.
As a conventional example 1, the spray marking device was attached and the spray was sprayed to the joint to weld the steel strip, but the spray nozzle was clogged in the middle, and after the nozzle was replaced, spray spraying was continued again. However, the seam portion cannot be detected during the nozzle replacement, and the joint detection rate is greatly reduced.

As Conventional Example 2, a thickness gauge was installed to constantly measure the thickness of the steel strip. In this case, when the measurement plate thickness exceeded this threshold value with 1.2 times the average plate thickness as a threshold value, the excess steel strip longitudinal direction portion was determined as the seam portion.
Table 1 shows these results. From Table 1, it was found that the example of the present invention can detect the seam portion more reliably than the conventional example.

  In addition, as Example 3 of the present invention, forged welded steel pipes were manufactured by passing 101 steel strips similar to those described above in the same manner. At that time, the above production is performed under the two conditions of the case where the accumulator 11 is attached to the edge rolls 1 and 3 (Invention Example 3 (1)) and the case where the accumulator 11 is not attached (Invention Example 3 (2)). The wear amount of the edge roll was examined for each. The results are shown in Table 2. The pressing load of the edge roll was set to 7.3 kN. As shown in Table 2, Example 3 (1) of the present invention with an accumulator installed can reduce the impact load when the seam passes through the edge roll, compared to Example 3 (2) of the present invention without installation. It was found that the amount of wear of the roll (difference in roll diameter from the initial stage) can be reduced.

1 Edge roll (on-edge roll)
2 Edge roll load 3 Edge roll (roll under edge)
4 Steel strip 5, 6 Holding load
7, 8 Impact load of steel strip passage identified as seam portion 9 Load indicator 10 Hydraulic piping 11 Accumulator 12 Roll movement direction on edge 20 Seam portion (steel weld zone)

Claims (2)

When the steel pipe was manufactured by welding the longitudinal ends of a plurality of steel strips sequentially, continuously heating and forming, and forging the steel strip widthwise ends, it was installed in front of the heating furnace for heating. , Using an edge roll for rolling the end portion in the width direction of the steel strip, detecting the occurrence of an impact load when the steel strip passes through the edge roll, and detecting the location of the detected impact load at the weld seam of the steel strip Identified as
And the pressing load of the edge roll is set to 6.0 to 8.8 kN,
Further, forging contact characterized in that a load value 1.3 times the average load of the edge roll is used as a threshold value, and the impact load is generated only when a measured load on the edge roll is equal to or greater than the threshold value. A method for detecting a weld zone of a steel strip in steel pipe production. Detection method of the steel strip welded seam portion in forge welding steel pipe production according to claim 1, characterized in that annexed the accumulator to absorb the impact by the generated shock load.

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