Briefly describe cold drawn tube related knowledge

- Sep 05, 2019-

Cold drawn steel pipes are one type of steel pipes, that is, one classified according to different production processes, which is different from hot rolled (expanded) pipes. It is formed by multi-pass cold drawing in the process of expanding the diameter of the capillary tube or the raw material tube, and is usually carried out on a single-chain or double-chain cold drawing machine of 0.5 to 100T. Cold-rolled (dial) steel pipe in addition to general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, petroleum cracking pipe, mechanical processing pipe, thick-walled pipe, small diameter plus internal die cold drawn pipe other steel pipe It also includes carbon thin-walled steel pipes, alloy thin-walled steel pipes, stainless thin-walled steel pipes, and special-shaped steel pipes. Cold drawn steel pipe can have an outer diameter of 6mm and a wall thickness of 0.25mm. The outer diameter of the thin-walled pipe can be up to 5mm and the wall thickness is less than 0.25mm. The precision and surface quality are obviously better than the hot-rolled (expanded) pipe, but the process is affected. Restricted, its caliber and length are subject to certain restrictions.


It is the work hardening of the cold drawn steel pipe. The metal is plastically deformed during cold drawing, and multiple slip systems are started inside the crystal. The dislocation motion intercepts each other, many dislocations are pinned, causing dislocation accumulation, and the dislocation source stops. The above series of processes leads to a decrease in the mobility of dislocations and a significant increase in dislocation density in the crystal. When the plastic deformation occurs further, the stress increases enough to cause the dislocation of the pinning to start moving, the screw bit is misaligned and slipped, and the blade dislocation cannot be slipped, so that the dislocation is intercepted, and the degree of immobility is increased.


Therefore, by increasing the internal dislocation density of the metal by cold drawing, the dislocation mobility is lowered, and it is difficult to generate dislocations and it is difficult to move dislocations, so that the hardness and strength of the metal material are improved. This is the metallurgical principle of cold drawing.


When cold drawing, the steel pipe is plastically deformed by a mold of a certain shape and size under the action of force. At present, the extraction method in production can be roughly divided into three types: reduced diameter extubation, reduced outer wall extubation and reduced inner wall extubation. When cold drawn, the steel tube occurs under the action of drawing force, positive pressure and friction. The corresponding deformations are mostly through three stages of diameter reduction, wall reduction and sizing, and corresponding stresses are generated inside the deformation zone, wherein the axial direction is tensile stress, the radial direction and the circumferential direction are compressive stress, and the metal is always in the process of extubation. Pulling and two-direction compressive stress state, which is the basic mechanical feature of the cold drawn tube deformation process.


Cold drawn steel pipe, cold rolled steel pipe unit is a complete set of equipment for producing pipes by cold rolling, cold drawing or cold rolling combined with cold drawing. It is a unit for deep processing of hot rolled pipe or welded pipe.


Different processing methods and corresponding auxiliary processes are selected according to the processing properties of the metal, the pipe size, the quality requirements, and the investment and benefits. The basic processes of cold-rolled cold drawn tubes are: (1) pipe material supply, the pipe material used is hot-rolled finished pipe or semi-finished pipe, extruded pipe and welded pipe; (2) pipe material preparation, including inspection, bundling, acid Washing, cleaning, rinsing, neutralizing, drying, applying lubricants, etc.; (3) cold working (cold rolling or cold drawing); (4) finishing of finished products including heat treatment of finished products, straightening, sampling, cutting head and tail, inspection ( Manual inspection and various flaw detection), hydraulic test, oiling, packaging, storage, etc. Different product finishing content is different.


The production characteristics of the cold-worked pipe unit are that the pipe material is usually subjected to multiple cold deformations and work hardening from the input to the finished product. Therefore, the whole production process is composed of a plurality of preparation processes and deformation processes, and has the characteristics of reciprocating cycle, and thus the number of processes The production cycle is long, the metal consumption is large, the production efficiency is low, and the general production scale is not large.


The simultaneous deployment of cold drawing and cold rolling mills in the unit is beneficial to their respective advantages, especially for the production of high-alloy steel pipes such as stainless steel and non-deformable non-ferrous metal pipes. The cold drawing machine has a single and multiple straight stripper and a reel extubator (see reel extubation). The length of the pipe when the single cold drawing is 50m, and the length of the coil is several hundred meters. The tonnage of the cold drawing machine is as small as 30kN and is as large as 7000kN. Conventional cold-rolled pipe mills are available in two-roll cold-rolled pipe mills and multi-roll cold-rolled mills.