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The technological process of stainless steel welded pipe

Views: 0     Author: Site Editor     Publish Time: 2022-02-17      Origin: Site

Stainless steel welded steel pipe is referred to as stainless steel welded pipe,is made of stainless steel strip after crimping machine and mold. The strength of the welded pipe is generally lower than that of the seamless pipe, but the production process is simple, the production efficiency is high, the varieties and specifications are many, and the equipment capital investment is small. Since the 1930, with the rapid development of high-quality steel strip continuous rolling production and welding as well as inspection technology. The quality of welded pipes has developed by leaps and bounds and has replaced seamless steel pipes in more and more fields, such as pipes for heat exchange equipment, decorative pipes, and medium & low pressure fluid pipes.

This article takes the manufacturing process of Sumwin stainless steel pipe as an example to introduce the specific manufacturing process of stainless steel welded pipe

1. The simple flow chart of pipe making is as follows:

ss pipe processing

2. Rolling and annealing process:

Calendering(re-rolling): Under normal temperature conditions, the hot-rolled raw material is formed under a certain pressure by a rolling mill, and the cold-rolled steel strip with a certain thickness tolerance and good shape is formed. The purpose is to reduce the thickness specification, control the thickness accuracy of the product, improve the surface finish, improve the structure of the steel, and improve the performance of the product.

Annealing: refers to the heat treatment process in which the steel strip is rapidly cooled under high temperature conditions to obtain solid solution and saturated solid solution. The purpose is to eliminate and improve the structural defects and internal stress left over from the previous process, improve the plasticity and toughness of the steel, and improve the corrosion resistance of the stainless steel.

3. Production process features for re-rolling and annealing:

3.1. Steel strips undergo varying degrees of work hardening during rolling. After the work hardening exceeds a certain level, the steel strip is too hard and brittle to continue rolling. Therefore, after a certain number of passes of cold rolling, the steel strip is often subjected to softening heat treatment to restore the plasticity of the steel strip, reducing the deformation pressure and then continuing to roll thin. In the rolling production process, the cold rolling work completed before each softening and annealing is called a "Rolling process", under certain rolling conditions, the harder the steel and the thinner the finished product, the more rolling process is required.

3.2. The calendering process must use process cooling and lubrication. Practice has proved that about 84%-88% of the deformation work of cold-rolled strip is converted into heat energy. The rise of roll temperature and the uneven distribution of roll temperature will destroy the normal roll line and directly affect the shape and dimensional accuracy of the strip. At the same time, the high temperature of the roll will also make the cold rolling process lubricant ineffective, so that the cold rolling cannot be carried out smoothly. Therefore, in order to ensure the normal production of cold rolling, effective measures to cool and adjust the roll temperature should be taken for the rolls and strips. Generally, water is used for cooling, and process lubrication is used to reduce the temperature of the rolls, reduce the deformation resistance of the metal, and prevent the metal Sticky roll. Commonly used process lubrication is emulsion, mineral oil, vegetable oil, etc.

3.3. Eliminate work hardening by annealing to obtain a satisfactory metallographic structure. When the performance requirements are different, the requirements for the metallographic structure after annealing are different, and the process of bright heat treatment is also different. The bright annealing of the surface without oxidation is obtained by heat-treating the strip under the H2 protective gas. To meet the requirements of the BA board, the protective atmosphere in the furnace must be very strictly controlled to avoid oxidation as much as possible. Another key problem is that the entire strip is required to be uniform in width and length. The commonly used annealing equipment is a muffle-type bright annealing furnace, which adopts a large-sized muffle tube, and evenly organizes the heating air flow from the outside of the muffle tube to spiral around, so that the strip is heated evenly. In addition, how to maintain the purity of the shielding gas in the furnace is also a key issue. The muffle cover has good sealing performance and will not pollute the protective atmosphere such as the material of the electric heating furnace body, providing a relatively pure environment space. In addition, the strip steel inlet and outlet of the vertical furnace are located at the bottom of the furnace, and the furnace pressure is stable, so compared with the horizontal furnace, the risk of air entering is much smaller. However, the inlet and outlet sealing boxes of the bright annealing furnace, the strip conveying section, the tension adjustment rollers and the furnace top guide roller boxes should all meet the sealing requirements, so that oxygen and water vapor cannot enter, and protective gas cannot escape.

4. Slitting process:

4.1. Definition: Slitting is to cut the coiled steel strip into strips through the slitting equipment, and then rewind it into coils to facilitate the stamping, shearing and forming of the next process. When slitting, it is necessary to ensure that the operator of the metal slitting machine test machine has the qualification certificate, and is familiar with the operation process, and operates in strict accordance with the operation process.

5. Pipe making process

The following are the most commonly used 26 groups of simple pipe making process

Shelf - Stamping - Forming - Welding - Cooling - Weld Surface Treatment - (straightening) - Length - Cutting

5.1.Molding

The forming part of the unit is composed of 26 forming rollers, including 11 groups of horizontal forming rollers (active rollers) and 15 groups of vertical rollers (passive rollers). The forming rollers are arranged as follows: feeding frame—steel die—1 group (active roller)—2 group (passive roller vertical mold)—3 group (active roller)—4 group (passive roller vertical mold)—5 group (active roller) - 6 groups (passive roller vertical mold) - 7 groups (passive roller vertical mold) - 8 groups (passive roller vertical mold) - 9 groups (active roller) - 10 groups (passive roller vertical mold) - 11 groups (active roller vertical mold) )—12 groups (passive roller vertical mold)—13 groups (active mold)—14 groups (passive welding mold)—15 groups (active roller)—16 groups (passive roller flat mold)—above the welding mold is the main engine electric Box welding machine - 16 groups used to be grinders 1, 2, 3 groups - there are 17 18 groups of passive roller vertical molds in the middle of the grinding machine - 19 groups (active molds) - 20 groups (passive roller vertical molds) - 21 groups (active roller vertical molds) Die)—22 groups (passive roller vertical mold)—23 groups (active roller mold)—24 groups (passive roller vertical mold)—25 groups (active roller vertical mold)—26 groups (passive roller vertical mold)—cutting table—unloading rack . Forming adopts double radius comprehensive bending forming method.

This forming method takes the radius of the finished tube as the edge bending radius, bends the edge of the strip to a certain deformation angle, and basically remains unchanged in the subsequent forming passes, while the bending of the middle part of the strip is formed according to the circular bending method. Make deformation assignments. The above forming method has the advantages of edge variation and circumference variation at the same time, the deformation is uniform, the forming process is stable, the relative elongation of the edge is small, and the forming quality is good.

There are a series of difficulties in the production of stainless steel welded pipes, such as the unstable forming of the quality of the explosion and the quality of the weld, which is easy to cause "wave" and "bulging" problems and leakage welding, etc. The most important thing is the relative extension of the edges. "Bulge" caused by overgrown. There are many factors that affect the elongation of the strip edge. In addition to the factors of raw materials and finished product specifications, there are also the formation of the bottom line of the forming, the number of forming frames, the diameter of the forming rollers, the distance between the frames, the design of the hole pattern, the arrangement of the forming rollers and the speed. poor and other factors.

5.2.welding

The stainless steel tube is welded by argon tungsten are welding, which is TIG welding with argon as the protective gas. The arc between the tungsten electrode and the strip heats and melts the strip, forming a molten pool for welding. The tungsten electrode, arc area and molten strip are all protected by argon gas without oxidation, the protection effect is good, the alloy transition coefficient is relatively high, and the welding seam composition is easy to control, which ensures the stability and high quality of the welding process. of welds. Because TIG welding has no electrode metal transition problem, the arc phenomenon is relatively simple, the reproducibility of the welding process is strong, and the welding quality is stable. It is the main welding method for stainless steel pipes.

The use of the welding machine is controlled by the flow of argon and nitrogen. Generally, the flow of argon is controlled at 3-6L/min, and the flow of nitrogen is controlled at 3-7L/min. When using the welding machine, the maximum current used should not exceed 60% of the standard number of the machine. The pipe maker should reasonably control the welding speed and current according to the thickness of the welded steel pipe. During production, the current control and the taper of the tungsten needle and the speed of the vehicle determine the quality of the welding, so the current size and the speed of the vehicle should be adjusted according to the actual welding conditions.

5.3. Cooling and surface treatment

After welding, the pipe is cooled by the water spray cooling method. After the welding is completed, the water pipe is directly sprayed with water to the welding port to achieve the cooling effect and at the same time clean the impurities. Immediately after cleaning, three thousand-page wheel units are used to perform surface treatment on the welded joints to make the welded joints smoother. If it is a round tube, it can be cut to length directly. If it is a square tube, it needs to be straightened by a character straightening die and then cut to a fixed length.

5.4. Straightening and cutting (fixed length)

The square tube is cut to length on the basis of the round tube after the straightening die. The square tube is to adjust the hard circular tube into a straight tube. When straightening, the stainless steel tube passes through the center of the straightening body and the centrifugal block, and the centrifugal block rotates with the straightening body area while doing radial movement in the straightening body, so that the stainless steel tube produces elastic-plastic bending deformation when walking. After the pipe reaches the ideal straightness

6. external polishing:

6.1.Outer Polish Definition:

The polishing process of stainless steel is the process of cutting chips on the surface of the tube. The friction between the optical material, the optical instrument and the surface of the tube is used to achieve the cutting of the surface of the tube and obtain the corresponding smooth surface. The polishing of stainless steel can be divided into internal and external polishing. The existing external polishing is to use a combination of different coarse-grained hemp wheels, grinding wheels, cloth wheels and wool wheels for polishing to obtain a corresponding smooth surface.

In the polishing process, the polishing wax should be used together with the hemp wheel and cloth wheel.

6.2. The difference between the square polishing machine and the circular polishing machine:

The installation of the hemp wheel group of the square polishing machine is arranged in the way of "vertical group-flat group-vertical group-flat group", which is convenient for all four surfaces of the square tube to be fully polished; the circular polishing machine is just a two-way grinding wheel In addition, the three-way power rotation of the lower roller is used to polish the round tube.

6.3. Standard installation method of grinding wheel of polishing

Round polishing machine: the first assembly of 600# or 800# grinding wheel, the middle of the oil hemp wheel, the seventh, eighth and ninth assembly of the cloth hemp wheel, the tenth assembly of the wind wheel.

Square polishing machine: Assemble 400# or 600# grinding wheels in the first and second, with oil hemp wheels in the middle, and cloth and hemp wheels in the last three groups at the end to ensure clean wax collection

6.4. Factors affecting the polishing quality of abrasive tools

Since mechanical polishing is mainly done manually, polishing technology is still the main reason for affecting polishing quality. In addition, it is also related to abrasive materials (hemp wheel, cloth wheel, polishing wax), surface condition before polishing, heat treatment process, etc. High-quality steel is a prerequisite for obtaining good polishing quality. If the surface hardness of the steel is uneven or the characteristics are different, polishing difficulties often occur. Various inclusions and pores in the steel are not conducive to polishing

The effect of different hardness on polishing process The increase of hardness increases the difficulty of grinding, but the roughness after polishing decreases. As the hardness increases, the polishing time required to achieve lower roughness increases accordingly. At the same time, the hardness increases, and the possibility of over-polishing is correspondingly reduced.

The influence of the surface condition of the workpiece on the polishing process During the mechanical polishing process of the pipe, the surface layer will be damaged by heat, internal stress or other factors, and improper polishing parameters will affect the polishing effect

7. Package:

The polished steel pipe will directly enter the packaging process. The packaging process is relatively simple. It is only necessary to inspect the surface of the steel pipe to prevent defective products from being mixed into the packaging.


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