Notes of cold drawn seamless tubes

Production of cold drawn seamless tubes needs attention to control:

1, Capillary tube
The wall thickness of the capillary tube should be uniform, and the surface defects on the inner and outer surfaces should be small; the outer surface polishing and inner hole defect cleaning equipment should be arranged.

2, Reexamination
Compared with ordinary cold drawn steel pipe, cold drawn seamless tubes production increases the hot-rolled capillary pickling re-examination process, mainly to ensure that there are no defects such as folding and crack on the outer surface of the capillary tube, and the inner surface is excluded from folding and severely scribed. Tubes with defects such as pockmarks.

3, Tools
Generally, the surface roughness of tools used in the production of cold drawn seamless tubes is 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 the tip or mold sticking phenomenon cannot occur during the drawing process.

4, Annealing
Annealing is a very important process in the production of all cold drawn tubes. The quality of the annealing affects both the performance of the steel tube and the removal of the scale. Cold drawn steel tubes require a non-oxidizing bright annealing furnace equipment.

5, Pickling
Seamless tube is easy to form "black slag" mainly composed of Fe2O3 and Fe3O4 in the acid pickling process, and surface dark spots are formed in subsequent production. Fe2O3 and Fe3O4 are easily soluble in hydrochloric acid, and 5-10 g/l of NaCl is added to the acid bath to prevent the formation of dark spots.

6, Lubrication
Resin should be used as a lubricant. This kind of lubrication has obvious difference compared with phosphating and lubrication (saponification). The drawn steel tube exhibits the true color of the iron matrix, and has a high finish and a beautiful appearance like a cold rolled tube.