Tangshan Fengnan Shunjie cold-formed steel strip Rectangular Pipe Production process

Fang Torque tube A series of processes are required from raw materials to finished products. The production process mainly depends on the product variety. To complete these processes, various mechanical equipment and welding, electrical control, and detection devices are required. These equipment and devices are arranged in a variety of reasonable ways according to different process requirements.

The rectangular tube mainly uses the skin effect and proximity effect of high-frequency current to make the current highly concentrated on the edge to be welded, so that it can be heated to the welding temperature within one hundredth of a second, and then pressure welding is carried out under the action of the extrusion roller.

According to the nature of slag, electrodes can be divided into two categories: acid electrode and alkaline electrode. The electrode whose slag is mainly acid oxide is called acid electrode. The electrode whose slag is mainly alkaline oxide and calcium fluoride is called alkaline electrode. Among carbon steel electrode and low alloy steel electrode, low hydrogen electrode (including low sodium hydrogen electrode, low potassium hydrogen electrode and low hydrogen iron powder electrode) is alkaline electrode; Electrodes of other coating types are acid electrodes.

Alkaline electrode has higher ductility and toughness, lower diffusible hydrogen content, and better crack resistance than acid electrode with the same strength level. Therefore, when alkaline electrode is specified in product design or welding procedure specification, acid electrode cannot be used instead. However, the welding process performance of alkaline electrode (including arc stability, slag removal, spatter, etc.) is poor, easy to vent, and there are many toxic gases, smoke and dust.

① Main production process (main inspection process) of rectangular tube: preparation and inspection of tube blank → heating of tube blank → piercing → rolling of tube → reheating of raw tube → sizing (reducing) → heat treatment → straightening of finished tube → finishing → inspection (non-destructive, physical and chemical, bench inspection) → warehousing

② The main production processes of cold-rolled (drawn) seamless rectangular tubes: blank preparation → pickling lubrication → cold-rolled (drawn) → heat treatment → straightening → finishing → inspection. Production process of square and rectangular tubes: seamless square tubes are produced by hot rolling (about 80~90%) or cold rolling and cold drawing (about 10~20%). The billets used for hot rolling pipes include round, square or polygonal ingots, rolled billets or continuous casting billets, and the quality of the billets has a direct impact on the quality of the pipes. There are three basic processes for hot rolling pipes: ① threading ingots or blanks into hollow thick wall tubes on the piercer; ② The capillary is thinned on the extension machine and extended into a waste pipe with a wall thickness close to that of the wall;

③ Rolled into the required finished pipe on the finishing mill. The production process of roll piercing forming seamless rectangular tube is represented by the large outer diameter of the square tube produced by the pipe rolling unit series. The commonly used two roll cross rolling piercing process of the piercer is shown in Figure 2. The round tube blank is pierced and rolled into a hollow thick wall tube (capillary), and the axes of the two rollers form an inclined angle with the rolling line. In recent years, the inclination angle has increased from 6 °~12 ° to 13 °~17 °, which accelerates the perforation speed. For square pipes with a diameter of more than 250mm, secondary perforation is adopted to reduce the wall thickness of the capillary. New processes such as perforation with active rotating guide plate, perforation with rear thrust, axial discharge and circular top welded square tube have also made some progress, thus strengthening the perforation process and improving the capillary quality.

Continuous square and rectangular tube production. The continuous square and rectangular tube production equipment consists of a piercer, a continuous pipe mill, and a tension reducing mill. See Figure 1 for the process flow. The round billet is threaded into a blank and inserted into a mandrel. It is continuously rolled by a two high mill with 7~9 rolls whose axes are 90 ° to each other. After rolling, the mandrel is pulled out, and after reheating, the tension reducing can be carried out to roll a 165m square tube. The annual output of 140mm continuous pipe rolling mill is 400000-600000 tons, which is 2-4 times of that of automatic pipe rolling mill. The characteristics of this unit are that it is suitable for producing square tubes with an outer diameter of less than 168mm, large equipment investment, large installed capacity, mandrel length of 30m, and complex processing and manufacturing. The limited mandrel continuous rolling mill (MPM), which appeared in the late 1970s, forced the mandrel to move at a speed less than that of the square tube by external force during rolling, which can change the metal flow conditions. The short mandrel is used to roll long tubes and large diameter square tubes.