Production process control of cold drawn precision seamless Steel Pipes
Cold drawn (or cold-rolled) precision seamless steel pipes have no oxide layer on the inner and outer walls, can withstand high pressure without leakage, high precision, and high smoothness
Cold bending without deformation, expansion and flattening without cracks, and surface treated with rust prevention.
Mainly used for mechanical structures, hydraulic equipment, and pneumatic or hydraulic components of automobiles and motorcycles, such as cylinders or cylinders.
In general, ordinary cold drawn steel pipes are used as billets and then precision drawn seamless steel pipes are produced through precision drawing processes. To ensure precision
The quality of steel pipes needs to be adjusted according to existing production conditions during the production process. The basic process flow is as follows:
Hot rolled capillary ¡ú Inspection and grinding of capillary ¡ú Acid washing of capillary ¡ú Re inspection after pickling of capillary ¡ú Cold drawing (intermediate annealing and acid washing) ¡ú Fine drawing
Straightening before passing ¡ú Pickling and lubrication ¡ú Fine drawing ¡ú Pre processing of finished products ¡ú Warehousing
Compared with ordinary cold drawn steel pipes, the production of cold drawn precision seamless pipes has added a hot-rolled capillary acid pickling and re inspection process, mainly to ensure the quality of the capillary
The outer surface of the tube has no defects such as folding or cracks, and the inner surface of the tube with defects such as folding, severe marking, and pitting is selected.
The surface smoothness of the tools used in the production of precision seamless steel pipes for general cold drawing is required to be Ra0.4 or above, and the dimensional accuracy should reach
H3 or above, with a hardness requirement of HRC70 or above. At the same time, it is required that there should be no phenomenon of top or mold sticking steel during the drawing process,
When drawing high-strength steel grades above 45 # steel or small-sized steel pipes, there should be no head burst, and the head and outer mold should have good resistance
Wear resistance, etc.
Annealing and pickling are very important processes in all cold drawn pipe production, as they largely determine the properties of the finished pipe
Can be related to surface quality. During annealing, the steel pipe is heated to form an oxide scale on the surface composed of three types of iron oxides (from the outside)
From inside, they are Fe2O3, Fe3O4, FeO).Annealed steel pipes must undergo surface oxide scale removal treatment (i.e. acid pickling) before entering the next process, ensuring the quality of the annealed steel pipes
The quality not only affects the performance of the steel pipe but also affects the removal of the oxide scale. Low temperature annealing causes difficulty in drawing, and the lifespan of cold drawing molds
Shortened lifespan, prone to phenomena such as bursting of the plug and breakage of the plug core rod connection.
The pickling temperature, pickling time, etc. must be strictly controlled. Steel pipes are prone to form Fe2O3 on the surface during sulfuric acid pickling
The "black slag" mainly composed of Fe3O4 forms surface black spots in subsequent production. Fe2O3 and Fe3O4 are easily soluble in hydrochloric acid to prevent
The formation of black spots is achieved by adding 5-10g/l of NaCl to the acid pool.
The lubrication of steel pipes is often achieved through phosphating and lubrication (saponification), which generates hydrochloric acid with strong adhesion ability on the surface of the steel pipe in the phosphating solution
Salt layer, followed by the steel pipe in the lubricant, adsorbs lubricant through the phosphating layer attached to the surface, thereby achieving the purpose of steel pipe lubrication of Phosphating agents provided by professional manufacturers are generally used for steel pipe phosphating. Properly controlling the composition, concentration, and temperature of the phosphating solution can Achieve good phosphating effect.
