A method of manufacturing equal diameter perforated steel pipe

Abstract

The application discloses a manufacturing method of equal-diameter pierced steel pipe and belongs to the technical field of pipe blank piercing. The application improves (1) blank heating and (2) the piercing process in the steel pipe manufacturing process, adjusts the process parameters in the heating process, and improves the piercing mill pass design part and the piercing process, that is, reducing the outlet cone angle of the roller, reducing the diameter of the piercer, increasing the length of the piercer, and adjusting the size of the roller distance, the guide plate distance, the piercer front extension amount and the feeding angle. The application solves the problem that high-alloy steel has poor hot plasticity, and is prone to internal surface tearing, wall deviation and end outer diameter mutation defects in the hot rolling piercing process due to large diameter expansion, improves the material yield, reduces the waste product rate, and improves the contract realization rate.

Description

TECHNICAL FIELD

[0001] The present application relates to a manufacturing method of equal-diameter piercing steel pipe, and belongs to the technical field of pipe blank piercing. BACKGROUND

[0002] The deformation amount borne by the piercer in the whole unit is increasingly large. The parameters representing the piercing deformation include: diameter expansion rate, elongation coefficient, reduction amount at the rolling strip, and reduction amount before the plug.

[0003] The diameter expansion rate of the hot-rolled piercing shell is generally in the range of 5-20%, and the expansion rate of the conical roller piercer is obviously higher than that of the barrel-shaped roller piercer. A large expansion rate is prone to cause internal and external surface defects or aggravate the uneven wall thickness, and thus it is better to adopt equal-diameter or small-expansion piercing.

[0004] When producing high-alloy steel pipes, the piercer roller usually adopted is a conical piercer, and the diameter expansion rate is about 7%. Since the hot plasticity of high-alloy steel is poor, internal surface tearing, wall deviation, and sudden diameter change at the end are prone to occur when producing high-alloy steel. Therefore, a new process satisfying the piercing of high-alloy steel is urgently needed on site, and equal-diameter hot-rolling piercing can effectively solve the problems of internal surface tearing, wall deviation, and sudden diameter change at the end in the process of hot-rolling piercing. SUMMARY

[0005] The present application aims to provide a manufacturing method of equal-diameter piercing steel pipe, and belongs to the manufacturing method of high-alloy steel, which is mainly used to solve the problems of internal surface tearing, wall deviation, and sudden diameter change at the end caused by a large expansion amount in the process of hot-rolling piercing due to the poor hot plasticity of high-alloy steel, improve the yield, reduce the scrap rate, and improve the contract fulfillment rate.

[0006] The technical concept of the present application is that, in the process of expansion piercing, the metal is subjected to a large transverse tensile stress, which is prone to cause internal surface tearing of the metal and unstable rolling to the tail. The transverse tensile stress of equal-diameter piercing is smaller than that of expansion piercing, which can stabilize the rolling process and improve the quality of the internal surface of the steel pipe. The method adopted by the present application is to achieve the purpose of equal-diameter piercing through the design of the tooling and the adjustment of the rolling parameters. The main factors determining the outer diameter of the shell are the piercer pass design and the piercer parameter adjustment: the pass design mainly involves the roller, the plug, the guide plate, and the ejector rod; the piercer parameter involves the roller gap, the guide plate gap, the extension amount before the plug, and the feed angle (after the plug is reduced, the roller gap and the feed angle must be adjusted to make up for the wall thickness increment caused by the reduction of the plug). Through the process, a steel pipe with the same outer diameter of the shell can be produced, the outer diameter size control of the manufactured steel pipe meets the rolling requirements of the rolling mill, the internal hole inspection is free of cracks, scratches, scratches, and defects such as peeling, and the external surface inspection is free of cracks, scratches, and folding defects.

[0007] The application provides a steel pipe manufacturing method, and the production process flow comprises the following steps: blank inspection, blank sawing, centering, blank heating, piercing, straightening and flattening, pickling, grinding, cold rolling, degreasing, heat treatment, straightening and flattening, pickling and finished product.

[0008] The application provides a method for manufacturing equal-diameter piercing steel pipes.

[0009] (1) Blank inspection:

[0010] The blank is inspected, and the ultrasonic nondestructive testing sensitivity standard line of the bottom wave testing is not more than φ3mm, and no large defect cracks are found on the outer surface.

[0011] (2) Blank sawing:

[0012] The blank is sawed according to the weight of the finished product, the length of the blank is 1300mm-3200mm, and the end surface cutting slope is less than or equal to 3mm.

[0013] (3) Centering and punching:

[0014] When the centering hole is punched, the position of the punch is positioned, the diameter of the centering hole is 40mm, the depth is 20mm, the centering hole is smooth and has no burrs.

[0015] (4) Blank heating:

[0016] The blank is heated in an inclined bottom furnace, and the heating system is strictly in accordance with the following process conditions: ① preheating section temperature: 950±30℃, heating time: 4 hours; ② heating section temperature: 1100±20℃, heating time: 2 hours; ③ soaking section temperature: 1180±20℃, heating time: 0.5 hours.

[0017] In the heating section, the blank needs to be turned over by 180°: the blank is turned over every half an hour during the heating process, and the original bottom surface is turned up during the turning over, so that the blank is turned over by 180°, so as to prevent the generation of yin and yang surfaces during heating.

[0018] (5) Piercing deformation

[0019] The application improves the piercing process parameters and the piercing mill pass design part, and specifically comprises the following contents:

[0020] ① The piercing mill pass design part improvement comprises:

[0021] The outlet cone angle of the roller is 2.8°, and reducing the outlet cone angle of the roller can limit the increase of the outer diameter of the steel pipe during the rolling process.

[0022] The diameter of the piercing head of the piercing machine is 180mm, the length of the piercing head is 335mm, the guide plate size is 210-220mm, and the diameter of the ejector rod is 168mm. The diameter of the piercing head is reduced, and the length of the piercing head is increased to ensure deformation stability in the hot rolling piercing process and reduce the diameter expansion amount.

[0023] 2. The piercing head curve is designed as follows:

[0024] The diameter of the piercing head D is 180mm, the length of the piercing head L is 335mm, the length of the reverse cone of the piercing head L4 is 15mm, the length of the sizing section L2 is 5mm, the length of the straightening section L3 is 115mm, and the diameter of the ejector rod is 168mm. The arc R2 of the piercing head tip is 24mm, the arc R1 of the deformation section is 396.96mm, and the arc R3 of the reverse cone is 18mm. The theoretical weight is 45kg.

[0025] 3. The piercing process parameters are adjusted as follows:

[0026] The piercing parameters include roll gap, guide plate gap, piercing head protrusion amount, and feed angle. D1 is the diameter of the billet, and L is the length of the piercing head. The roll gap is designed as D1*0.9, the guide plate gap is designed as D1*0.98, the piercing head protrusion amount is designed as L*0.53, the roll speed is designed as 22r / min, and the feed angle is designed as 8°.

[0027] The beneficial effects of the present application are as follows:

[0028] The present application provides a manufacturing method for equal-diameter piercing, which is innovatively manufactured through a piercing process. The outer diameter size control of the rough pipe manufactured by the method meets the rolling requirements of the rolling mill, ensures the size precision requirements of the finished product, and ensures that the inner hole inspection is free of defects such as cracks, lines, scratches, and peeling, and that the outer surface inspection is free of defects such as cracks, scratches, and folding. The production cost is greatly reduced, and the yield is improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The top head curve designed for the present application is shown in the schematic diagram.

[0030] Figure 2 The schematic diagram of the piercing process is shown.

[0031] Figure 3 The Figure 2 The partial sectional view along line A-A.

[0032] Figure 4 The Figure 2 The top view of the piercing head.

[0033] In the figure: 1-rolling mill, 2-guide plate, 3-piercing head, 4-ejector rod, 5-billet, 6-rough pipe, a is the feed angle, which is the included angle between the rolling mill and the rolling center. DETAILED DESCRIPTION

[0034] The present application is further illustrated by the following examples, but is not limited to the following examples.

[0035] Comparative Example 1: manufacturing process before improvement

[0036] Φ219 blank diameter expansion piercing Φ235*15mm

[0037] (1) blank inspection:

[0038] The size of the blank is Φ219mm, and the ultrasonic nondestructive testing does not exceed the bottom wave detection sensitivity standard line of φ3mm. No large defects such as cracks are found on the outer surface.

[0039] (2) blank sawing

[0040] According to the weight of the finished product, the sawing is marked and cut to size, and the length of the blank is 1500mm, and the end face cutting slope is ≤3mm.

[0041] (3) centering and punching

[0042] The centering hole is positioned by the centering hole, and the centering hole diameter is 40mm, and the depth is 20mm. The centering hole is smooth and has no burr.

[0043] (4) blank heating

[0044] The blank heating is carried out in the inclined bottom furnace, and the heating system is strictly carried out according to the following table. In the heating section, the blank needs to be turned over 180°:

[0045]

[0046] (5) piercing deformation

[0047] The control parameters are as follows: the outlet cone angle of the roller is 3.2°; the diameter of the piercing head is 194mm, the length of the piercing head is 280mm, the guide plate size is 220-230mm, the diameter of the top rod is 180mm; the roller distance is 201mm, the guide plate distance is 224mm, the piercing head protruding amount is 46mm, the roller rotating speed is 25r / min, and the feeding angle is 10°.

[0048] Through the process of the comparative example, the blank of Φ219mm is expanded and pierced to the specification of Φ235*15mm, and the main problems are: inner hole skinning and tail horse's mouth.

[0049] The horse's mouth defect caused by the diameter expansion piercing can only be eliminated by sawing, and the tail length is about 350mm, and the yield loss is about 3.5%.

[0050] Example 1: the manufacturing process of equal diameter piercing steel pipe by using the method of the present application, including the following specific steps:

[0051] Φ219 blank equal diameter piercing Φ219*15mm

[0052] (1) Blank inspection:

[0053] The size of the blank is Φ219mm, and the ultrasonic nondestructive testing does not exceed the bottom wave detection sensitivity standard line of φ3mm. No larger defects such as cracks are found on the outer surface.

[0054] (2) Blank sawing

[0055] According to the weight of the finished product, the length of the blank is 1500mm, and the end face cutting slope is ≤3mm.

[0056] (3) Centering and punching

[0057] The centering hole is positioned by the punch position, the diameter of the centering hole is 40mm, the depth is 20mm, and the centering hole is smooth without burr.

[0058] (4) Blank heating

[0059] The blank heating is carried out in the inclined bottom furnace, and the heating system is strictly carried out according to the following table. In the heating section, the blank needs to be turned over 180° (during the blank heating process, the blank is rolled forward every half hour, and the original bottom surface is turned up, that is, turned over 180°, to prevent the generation of yin and yang surface during heating):

[0060]

[0061] (5) Piercing deformation

[0062] The piercing process parameters and the piercing machine pass design part of the embodiment are improved, which specifically includes the following contents:

[0063] ① The piercing machine pass design part improvement includes:

[0064] The outlet cone angle of the roller is 2.8°, reducing the outlet cone angle of the roller can limit the increase of the outer diameter of the steel pipe during rolling.

[0065] The diameter of the piercer punch is 180mm, the length of the piercer punch is 335mm, the size of the guide plate is 210-220mm, and the diameter of the top rod is 168mm. Reduce the diameter of the piercer punch, increase the length of the piercer punch, and ensure the stability of the deformation during hot rolling piercing, and reduce the expansion amount.

[0066] ② The piercer punch curve is designed as follows:

[0067] Figure 1The design drawing of the pier head curve is as follows: the pier head diameter D is 180 mm, the pier head length L is 335 mm, the pier head reverse cone length L4 is 15 mm, the sizing section length L2 is 5 mm, the straightening section length L3 is 115 mm, the diameter of the pier rod is 168 mm, the pier head tip arc R2 is 24 mm, the deformation section arc R1 is 396.96 mm, and the reverse cone arc R3 is 18 mm. The theoretical weight is 45 kg.

[0068] The technical conditions of the pier head are as follows: chemical composition: Mo matrix, Ti=0.5%, Zr=0.08-0.10%, C=0.02-0.03%; the hardness is uniform, and the transition section connection is smooth; in addition to meeting the size shown in the drawing, the surface of the pier head shell of the piercer is not allowed to have any defects that can scratch, scratch and tear the surface of the steel pipe, and the like; the casting body should not have defects, especially shrinkage holes, cracks or fusion breakpoints; no 1*45° chamfer is added.

[0069] ③The piercing process parameters are adjusted as follows:

[0070] The piercing parameters relate to the roll gap, the guide plate gap, the pier head protruding amount and the feed angle. D1 is the blank diameter (219 mm), and L is the pier head length; the roll gap is designed as D1*0.9, i.e. 197 mm, the guide plate gap is designed as D1*0.98, i.e. 215 mm, the pier head protruding amount is designed as L*0.53, i.e. 177 mm, and the roll rotating speed is designed as 22 r / min, and the feed angle is designed as 8°.

[0071] Through the above pass design and the adjustment of the piercing process parameters, the specification of the finally pierced hollow pipe is Φ219*15 mm, and equal-diameter piercing is realized.

[0072] After equal-diameter piercing by the method of the present application, the horse's mouth defect at the tail is eliminated.

[0073] After the design of the present application, batch production is easy to realize, and the project implementation effect is good. The present application solves the problem that high-alloy steel has poor hot plasticity, and is prone to defects such as inner surface tearing, wall deviation and end diameter mutation during hot rolling piercing due to large diameter expansion, directly improves the material yield by 3.5%, reduces the waste product rate, and improves the contract fulfillment rate.

Claims

1. A method of manufacturing an equal- channel- dimensionally-pierced steel pipe, characterized by The following is included: (1) Billet inspection: The billet is inspected, and the ultrasonic nondestructive testing does not exceed the bottom wave detection sensitivity standard line of φ3mm, and no defects or cracks are found on the outer surface; (2) Billet sawing: According to the weight of the finished product, the length of the billet is 1300mm-3200mm, and the end face cutting slope is ≤3mm; (3) Centering and punching: When the centering hole is punched, the position of the punch is positioned, the diameter of the centering hole is 40mm, the depth is 20mm, and the centering hole is smooth without burrs; (4) Billet heating: Heating is carried out in an inclined bottom furnace, and the heating system strictly follows the following process conditions: ① Preheating temperature: 950±30℃, billet heating time: 4 hours; ② Heating temperature: 1100±20℃, heating time: 2 hours; ③ Soaking temperature: 1180±20℃, heating time: 0.5 hours; (5) Piercing deformation: Including improvement of piercing mill pass design part and adjustment of piercing process: reducing the outlet cone angle of the roller, reducing the diameter of the punch, increasing the length of the punch, adjusting the size of the roller distance, guide plate distance, punch forward amount, and feed angle; The improvement of the piercing mill pass design part includes: the outlet cone angle of the roller is 2.8°, which limits the increase of the outer diameter of the steel pipe during rolling; the diameter of the punch of the piercing mill is 180mm, the length of the punch is 335mm, the size of the guide plate is 210-220mm, and the diameter of the top rod is 168mm; ensure the stability of the deformation during hot rolling piercing, and reduce the expansion amount; The punch is designed as follows: the reverse cone length L4 of the punch is 15mm, the sizing section length L2 is 5mm, the leveling section length L3 is 115mm, the punch tip arc R2 is 24mm, the deformation section arc R1 is 396.96mm, and the reverse cone arc R3 is 18mm; The theoretical weight is 45kg; The technical parameters of the punch are as follows: chemical composition: Mo matrix, Ti=0.5%, Zr=0.08-0.10%, C=0.02-0.03%; the hardness is uniform, and the transition section connection is smooth; The piercing process parameter adjustment is as follows: D1 is the billet diameter, L is the length of the punch; the roller distance is D1*0.9, the guide plate distance is D1*0.98, the punch forward amount is L*0.53, the roller speed is 22r / min, and the feed angle is 8°.

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