Pipeline automatic welding technology and processing technology control

All-position automatic welding of the pipeline means that when the pipeline is relatively fixed, the welding trolley drives the welding to move around the pipe wall along the track to realize automatic welding. Generally speaking, the all-position automatic welding device is composed of welding trolley, walking track, automatic control system and other parts. The purpose of developing the all-position automatic welding device is to improve welding quality and labor productivity, and reduce labor intensity of workers.
    Welding trolley The
    welding trolley is a driving mechanism that realizes the automatic welding process. It is installed on the welding track and moves circularly along the pipe wall with the welding. It is one of the important links to realize the automatic welding of the nozzle. The welding trolley should have the characteristics of beautiful appearance, small size, light weight and convenient operation. Its core parts are walking mechanism, wire feeding mechanism and welding swing adjustment mechanism. The walking mechanism is composed of a motor and a gear transmission mechanism. In order to make the walking motor execute the position and speed commands issued by the computer control unit, the motor should have a speed measurement feedback mechanism to ensure that the motor is accurately aligned at each position of the pipe ring seam, and has a relatively high Good speed tracking function. The wire feeding mechanism must ensure that the wire feeding speed is accurate and stable, has a small moment of inertia, good dynamic performance, and should have sufficient driving torque. The welding swing adjustment mechanism should have the functions of welding relative to the weld seam swinging left and right, staying at the left and right ends, controllable up and down, left and right postures, and adjustable welding angles. The above-mentioned parts of the welding trolley are all programmable and automatically controlled by a computer. After the program is started, the various parts of the welding trolley coordinate their actions in accordance with the logical sequence of the program. When needed, the welding process can also be manually intervened. At this time, the program can automatically adjust the welding parameters and execute according to the amount of intervention.
    Welding track
    The track is a special mechanism for the welding trolley to move and locate, which is mounted on the pipe. Its structure directly affects the smoothness and position of the welding trolley, and also affects the welding quality. The track should meet the following conditions: convenient assembly and disassembly, easy positioning; reasonable structure, light weight; certain strength and hardness, wear and corrosion resistance. The track is divided into two types: flexible track and rigid track. The so-called rigid track means that the body of the track is relatively rigid and not easily deformed, while the flexible track is relatively rigid. The two types of tracks each have their own characteristics. The rigid track has accurate positioning and small deformation after installation, which can ensure that the welding trolley runs smoothly. The welding radial adjustment during welding is small, but the weight is large and the assembly and disassembly are inconvenient. However, the flexible track is easy to assemble and disassemble, has a lighter weight, and has less precision than a rigid track.     The smoothness of
    wire
feeding directly affects the welding quality. Wire feeding methods can be simply divided into two ways: wire drawing and wire pushing. When the wire is drawn, the welding is close to the installation position of the wire feeder. During the welding process, the resistance of the welding wire after leaving the wire feeder is small, so the wire feeding process can be ensured smoothly, but the wire feeder and the welding wire reel must be installed in the welding trolley. The upper part increases the weight of the welding trolley, which makes manual assembly and disassembly difficult, and the increase in weight can easily cause the welding trolley to walk unevenly. The use of a small welding wire with a diameter of 0.8mm or 1.0mm (weight is about 5kg) reduces the weight and load of the welding trolley, and makes the welding process easy to control, but it has a certain impact on the welding efficiency. When using the wire push method, the wire feeding mechanism is installed outside the welding trolley, which reduces the size and weight of the welding trolley. You can use a high-power wire feeder and a large welding wire with a diameter of 1.2mm (weight about 20kg). Thereby improving welding efficiency. However, because the wire feeder is far away from the welding when pushing the wire, there must be a wire feeding hose connected between the two. When the welding wire is continuously pushed to the welding nozzle, the friction resistance of the welding wire is relatively large, and the welding process The curvature of the wire feeding hose has a certain effect on the smoothness of the wire feeding. In severe cases, the wire feeding will not be smooth. Therefore, the above factors must be fully considered when using the wire pushing.
    Selection of welding process
    At present, in addition to manual welding, automatic submerged arc welding and gas shielded welding are more commonly used for pipeline welding.
   Automatic submerged arc welding has the characteristics of good weld formation, high welding efficiency and low welding cost. For pipeline construction, automatic submerged arc welding can be used for double pipe joint welding, referred to as “two to one”, that is, the welding is fixed in a certain Position, the tube rotates. Obviously, it is impossible to rotate the pipe when welding long-distance pipes, so “two-by-one” can only be used for pipe prefabrication. If the submerged arc welding process is used for all-position automatic welding of the pipeline, the welding device must be equipped with a flux injection, support and recovery mechanism, which makes the structure of the welding device more complicated, which brings inconvenience to operation, assembly and disassembly, and increases The load of the trolley is affected, and the stability of the trolley is affected. Submerged arc welding generally uses thick wire and high current welding methods. For all-position automatic welding, welding defects such as droplet and flow may occur due to the high deposition rate, which affects the formation and quality of the weld. Therefore, the submerged arc It is more difficult to realize automatic welding in all positions of pipelines.
    The welding process of flux-cored wire and gas shielding is adopted. If it is formed in multiple passes, it will be time-consuming and time-consuming to remove the slag on the surface of the weld; Circulating cooling water can greatly improve the welding efficiency, so that not only the structure of the welding device is complicated, but also the weight is increased. Because the price of the flux-cored welding wire is higher, and the gas source of the shielding gas must be solved at the same time, the welding cost is higher. The single use of self-shielded welding wire saves shielding gas, but it is difficult to remove slag. The welding process with solid core wire and gas shielding is adopted. If it is formed in multiple passes, the welding process can be simply divided into three stages: bottoming, filling, and covering. It is not necessary to clean the surface of the weld and proceed directly to the next process, but the welding The speed is slower than that of forced forming. The shielding gas is generally pure carbon dioxide gas, carbon dioxide and argon or a mixed gas of carbon dioxide and oxygen. The mixed gas of carbon dioxide and argon can make the arc combustion stable and have less spatter during welding. However, the source of argon gas is difficult to find and the price is higher during field construction. From the economic point of view, it is best to try to weld oil pipelines as much as possible. Use pure carbon dioxide as a protective gas. For construction in areas where conditions permit, it is ideal to use carbon dioxide and argon as the protective gas.
    way to control
    In the welding process, the walking speed of the welding trolley, the wire feeding speed and the left and right vibration frequency of the welding are the three main parameters, and the up and down adjustment of welding can be ignored. Divide the circumference of the pipe into two semicircles on the left and right with a vertical line, and then divide the two semicircles in the clockwise and counterclockwise directions to determine the welding nodes. Through a large number of experiments, ideal welding parameters can be obtained at each node of the weld. However, the actual welding data will not be exactly the same as the test data. During the welding process, the welding parameters can be adjusted according to the actual situation, such as wire feeding speed, vibration frequency and other parameters. However, the adjustment of these parameters are interrelated. When the wire feeding speed is adjusted properly, the vibration frequency and the welding car speed may not be appropriate. Only through a certain period of exploration can several parameters be adjusted and matched. If another control method is adopted, the situation is different. Taking wire feeding speed, welding vehicle walking speed, and welding vibration frequency as three dependent variables, they are placed in a spatial coordinate system, time is used as the independent variable, welding current and voltage are used as boundary conditions, and finally the wire feeding speed and welding The relationship between the traveling speed of the trolley and the vibration frequency of the welding is the spatial coordinate equation. In actual welding, the above three parameters are adjusted at the same time for each adjustment, so as to ensure the accuracy of the adjustment process.
    Facing the increasingly fierce international market competition, in order to occupy a place in the pipeline welding market, it is necessary to improve the level of construction equipment and technology. Therefore, research on pipeline all-position automatic welding devices has very important practical significance to improve the level of pipeline construction in China.  

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