Cold-drawn seamless steel tubes are manufactured using the cold-drawing process, which offer excellent mechanical properties and surface quality. Here are some key factors in the production of cold-drawn seamless steel tubes:
1.Raw Material Selection:
- The cold-drawn cylinder is drawn from the hot-rolled pipe, and the selection of the hot-rolled pipe, specifications, and quality directly affects the wire drawing process and finished product quality.
- When selecting materials, it is advisable to choose materials with low hardness and good plasticity, ensuring strength requirements are met.
- Pipe specifications should be chosen based on the specifications of the finished product, ensuring elongation is between twenty and forty percent; too low elongation affects surface strength, while too high makes drawing difficult.
- Material surfaces should be free from severe defects such as pits, cracks, folds, scars, and ovality.
2.Pipe Pre-treatment:
- Untreated steel pipes may face difficulties in drawing due to high friction coefficients between the pipe surface and the mold.
- Pre-treatment processes include rust removal, phosphating, saponification, forming a dense metallic soap film to reduce friction between the steel pipe and the mold, ensuring smooth drawing.
- Pre-treatment helps reduce mold wear, improve yield, efficiency, and results in a smooth and uniform surface with effective rust prevention.
3.Mold Design:
- Mold size accuracy and surface quality directly affect the dimensional precision and quality of the finished product.
- Determination of inner and outer mold diameters should consider the rebound of the finished product after cold drawing.
- Mold surfaces should have low roughness requirements, usually one to two grades lower than the finished product.
- High-strength wear-resistant materials should be selected for mold construction.
4.Prevention of Transverse Cracking:
- Improve the heating quality of billets by strictly following heating requirements and avoiding low-temperature heating.
- Regularly shift materials in inclined furnaces to ensure uniform heating, preventing the appearance of positive and negative faces.
- Strictly control rolling rhythm to ensure thorough heating of billets and avoid black heart phenomena.
- Use high-quality heavy oil to ensure the quality of billet heating.
5.Improving Wall Thickness Precision of Raw Pipes:
- Adjust the perforation and rolling process parameters to improve the accuracy of rolling tools such as rolls.
- Accurately adjust the centering position, install roller devices to align the billet’s center during perforation, avoiding eccentricity.
- Install and adjust pinch rolls properly, ensuring the top rod is tight to prevent sinking.
- Regularly maintain equipment to ensure wall thickness precision.
6.Avoiding Rapid Water Cooling and Cold Rolling of Steel:
- Coordinate production pace to minimize the time the rough pipe stays on the platform.
- Ensure the final rolling temperature of the steel pipe is not below 850°C, preventing rapid water cooling.
7.Preventing Straightness and Rolling Breakage of Raw Pipes:
- Improve the quality of working molds, regularly inspect and replace worn molds.
- Periodically inspect the surface quality of rough pipes and address issues promptly.
8.Improving Grinding Quality of Raw Pipes:
- Grind away surface defects thoroughly to ensure quality grinding.
9.Annealing After Grinding of Raw Pipes:
- Annealing after grinding eliminates residual stress, improves internal structure, enhances plasticity, and facilitates deformation during cold drawing.
The comprehensive consideration of these factors ensures the production quality and performance of cold-drawn seamless steel pipes.
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