Cold drawn seamless pipe has the advantages of no oxide layer on the inner and outer walls, no leakage under high pressure, high precision, high finish, no deformation after cold bending, no cracks in flaring and flattening, and anti-rust treatment on the surface. It is mainly used for mechanical structure, Hydraulic equipment and pneumatic or hydraulic components of automobiles and motorcycles, such as cylinders or oil cylinders.
Process flow of seamless pipe cold drawing:
Hot-rolled capillary → capillary inspection, grinding → capillary pickling → re-inspection after capillary pickling → cold drawing → straightening before fine drawing pass → pickling, lubrication → fine drawing → finished product pretreatment → storage
What should be noticed when cold drawing seamless pipes?
1. Capillary
The capillary wall thickness should be uniform, and the inner and outer surface defects should be less; the outer surface polishing and inner hole filling shortage cleaning equipment should be equipped.
2. Recheck
Compared with ordinary cold drawn steel pipes, the production of cold drawn seamless pipes adds a pickling re-inspection process for hot-rolled capillary pipes, mainly to ensure that the outer surface of the capillary pipe is free from defects such as folds and cracks, and to eliminate folds and serious scribing on the inner surface. , pitted surface and other defects of the capillary.
3. Tools
Generally, the surface finish of the tools used in the production of seamless pipes is required to be above Ra0.4, the dimensional accuracy is above H3, and the hardness is required to be above HRC70. At the same time, it is required that no plug or die sticking to steel occurs during the drawing process.
4. Annealing
Annealing is a very important process in the production of all seamless pipes. The quality of annealing affects both the performance of the steel pipe and the removal of scale. No oxidation bright annealing furnace equipment is required for cold drawing of seamless pipes.
5. Pickling
In the process of sulfuric acid pickling, the seamless pipe is prone to form "black slag" mainly composed of Fe2O3 and Fe3O4, and form black spots on the surface in the subsequent production. Fe2O3 and Fe3O4 are easily soluble in hydrochloric acid. In order to prevent the formation of black spots, 5-10g/l NaCl can be added to the acid pool.
6. Lubrication
Resin should be used as a lubricant when seamless pipes cold drawing. This kind of lubrication is obviously different from phosphating and lubricating (saponification). The drawn steel pipes show the true color of iron matrix, which has both high smoothness and coldness. Beautiful appearance and color like rolled pipe.
The production process of cold drawn seamless pipes is generally more complicated than that of hot-rolled pipes. The wall thickness of seamless pipes after cold drawing is generally smaller than that of hot-rolled seamless pipes, but the surface looks brighter than hot-rolled seamless pipes. Much rough, and the caliber doesn't have too many burrs. The seamless pipe specification after cold drawing is higher than that of hot rolling.
