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Common defects and prevention of cold drawn seamless steel pipes
1. Folding After drawing, the inner and outer surfaces of the steel pipe show linear or spiral folds, which appear partially or throughout the length of the steel pipe.
Causes: There are folds or inclusions on the surface of the pipe material, serious scratches and cracks, there are edges and corners at the grinding part of the pipe material or the aspect ratio (H/b) is insufficient.
Prevention and elimination methods: Strictly control the quality of piercing and hot rolling.
2. The size is out of tolerance(Including wall thickness out of tolerance, uneven wall thickness, diameter out of tolerance, elliptical eccentricity) The diameter exceeds the standard deviation. On the same cross-section, the pipe wall is thin on one side and thick on the other side, with unequal diameters. The difference between the long and short axes exceeds the standard requirements.
Cause:
1. The drawing mold is improperly selected, or the mandrel (inner mold) is improperly adjusted.
2. The design and manufacture of the inner and outer molds are unreasonable or severely worn, or the hardness is insufficient, causing deformation and wear.
3. The heat treatment time is long, the temperature is high, or the heat treatment performance is uneven.
4. The law of increasing and decreasing walls is not properly controlled.
Causes: There are folds or inclusions on the surface of the pipe material, serious scratches and cracks, there are edges and corners at the grinding part of the pipe material or the aspect ratio (H/b) is insufficient.
Prevention and elimination methods: Strictly control the quality of piercing and hot rolling.
2. The size is out of tolerance(Including wall thickness out of tolerance, uneven wall thickness, diameter out of tolerance, elliptical eccentricity) The diameter exceeds the standard deviation. On the same cross-section, the pipe wall is thin on one side and thick on the other side, with unequal diameters. The difference between the long and short axes exceeds the standard requirements.
Cause:
1. The drawing mold is improperly selected, or the mandrel (inner mold) is improperly adjusted.
2. The design and manufacture of the inner and outer molds are unreasonable or severely worn, or the hardness is insufficient, causing deformation and wear.
3. The heat treatment time is long, the temperature is high, or the heat treatment performance is uneven.
4. The law of increasing and decreasing walls is not properly controlled.
5. The tabulation preparation is unqualified.
6. The steel pipe is flattened during straightening, causing large errors.
Prevention and elimination methods:
1. Correctly design and select the extubation mold.
2. Correctly implement the heat treatment system and heat evenly.
3. Adjust the straightening machine correctly and calibrate all components and measuring tools of the extubation machine frequently.
4. Master the rules of increasing and decreasing walls of different steel types and different specifications of steel pipes.
5. Prepare the drawing table correctly and reasonably.
6. The ovality can be re-straightened, and part of the ovality can be removed.
6. The steel pipe is flattened during straightening, causing large errors.
Prevention and elimination methods:
1. Correctly design and select the extubation mold.
2. Correctly implement the heat treatment system and heat evenly.
3. Adjust the straightening machine correctly and calibrate all components and measuring tools of the extubation machine frequently.
4. Master the rules of increasing and decreasing walls of different steel types and different specifications of steel pipes.
5. Prepare the drawing table correctly and reasonably.
6. The ovality can be re-straightened, and part of the ovality can be removed.
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3. Demarcation Longitudinal straight scratches on the surface of the steel pipe are called scratches. The scratches vary in length and width, and are mostly groove-shaped, with the bottom of the groove visible.
Cause:
1. The draft surface is not smooth, has cracks or bonded metal.
2. The excessive part of the hammer head has edges and corners, and the tool is worn.
3. There is insufficient pickling or iron oxide scale remains on the capillary tube.
4. Improper operation of phosphating and saponification processes.
5. The inner and outer molds are damaged or severely worn.
6. The intermediate annealing is uneven and the deformation is insufficient.
Prevention and elimination methods:
1. Improve the surface quality of the extubation mold.
2. After pickling the steel pipe, rinse the oxidized iron scale.
3. The transition part of the hammer head should be smooth and without edges.
4. Check the surface of the mold and steel pipe frequently, and deal with any problems in time.
1. The draft surface is not smooth, has cracks or bonded metal.
2. The excessive part of the hammer head has edges and corners, and the tool is worn.
3. There is insufficient pickling or iron oxide scale remains on the capillary tube.
4. Improper operation of phosphating and saponification processes.
5. The inner and outer molds are damaged or severely worn.
6. The intermediate annealing is uneven and the deformation is insufficient.
Prevention and elimination methods:
1. Improve the surface quality of the extubation mold.
2. After pickling the steel pipe, rinse the oxidized iron scale.
3. The transition part of the hammer head should be smooth and without edges.
4. Check the surface of the mold and steel pipe frequently, and deal with any problems in time.
4. Dou pattern The surface of the steel pipe presents uneven annular waves or waves arranged uniformly one by one along the length direction, appearing partially or throughout the entire length on the inner and outer surfaces of the steel pipe.
Cause:
1. Uneven performance after heat treatment. Low-temperature steel causes uneven performance during hot rolling.
2. Improper rinsing after pickling and poor phosphating lead to uneven saponification.
3. The core rod is thin and elastic deformation occurs during drawing, causing jitter.
2. The draft shape is unreasonable and the entrance cone angle is too large, which makes the contact area between the steel pipe and the die hole too small, making the drawing deformation unstable and shaking.
Prevention and elimination methods:
1. Carry out heat treatment according to operating procedures to achieve uniform softening performance.
2. The quality of pickling, phosphating and saponification must be controlled.
3. Draw according to the specified deformation amount.
4. Select the core rod size correctly.
Cause:
1. Uneven performance after heat treatment. Low-temperature steel causes uneven performance during hot rolling.
2. Improper rinsing after pickling and poor phosphating lead to uneven saponification.
3. The core rod is thin and elastic deformation occurs during drawing, causing jitter.
2. The draft shape is unreasonable and the entrance cone angle is too large, which makes the contact area between the steel pipe and the die hole too small, making the drawing deformation unstable and shaking.
Prevention and elimination methods:
1. Carry out heat treatment according to operating procedures to achieve uniform softening performance.
2. The quality of pickling, phosphating and saponification must be controlled.
3. Draw according to the specified deformation amount.
4. Select the core rod size correctly.
5. Pull out the concave In the longitudinal direction of the steel pipe, the pipe wall is inwardly concave in a strip shape, and its length is irregular.
Cause:
1. When drawing (air drawing) thin-walled steel pipes without mandrels, the diameter reduction is too large.
2. The end of the steel pipe hammer head has edges and corners or the excessive part has wrinkles and excessive deformation.
3. The pipe material is partially thin (such as grinding points).
Prevention and elimination methods:
1. When empty-drawing thin-walled pipes, the diameter reduction amount must be reasonably allocated.
2. The end of the hammer head should have no edges, corners or wrinkles.
3. Clean up local defects on the surface of the pipe material.
Cause:
1. When drawing (air drawing) thin-walled steel pipes without mandrels, the diameter reduction is too large.
2. The end of the steel pipe hammer head has edges and corners or the excessive part has wrinkles and excessive deformation.
3. The pipe material is partially thin (such as grinding points).
Prevention and elimination methods:
1. When empty-drawing thin-walled pipes, the diameter reduction amount must be reasonably allocated.
2. The end of the hammer head should have no edges, corners or wrinkles.
3. Clean up local defects on the surface of the pipe material.