Welding process of large diameter flange
Large-diameter flange is usually used in some large-scale furnace and tank equipment to connect or strengthen. This kind of equipment is generally made by non-standard, which belongs to single piece or small batch production. The conventional processing is to cut out the circular plate according to the size on the whole steel plate, and then cut off the inner circle on the circular plate. This processing method is simple, but requires large blank size and operation space, so it can be used for adding Large diameter flange will cause low material utilization and low economic benefit.
Structural analysis of large diameter flanges
Table of Contents
There is a large-diameter flange on the annealing furnace of a certain factory. The material is 45# steel. The dimensions and technical requirements are shown in Figure 1. The inner hole of the flange and the cylinder wall of the annealing furnace are connected by welding; the flange should be drilled with Φ25 that there are 24 fastening bolt holes, which are matched with another flange, and a rubber sealing ring is added in the middle. In order to ensure the sealing effect, the flatness of the flange is required to be higher; the width of the flange plays a supporting role, and the shape of the inner circle And size error can be eliminated during welding. As long as the outer circle is smooth, the appearance will not be affected. Therefore, the roundness and dimensional tolerance of the inner and outer holes of the flange are not high.
Fig.1 Dimensions and technical requirements for large diameter flanges
Welding process of large diameter flange
Due to the low utilization rate of materials processed by conventional methods, the flange is processed by the combined method: that is, the entire flange is equally divided into 8 equal parts, and the shape of each part is 1/8 ring, and 8 is down when the material is blanked. 1/8 ring is assembled on the plane to form a complete flange, and then connected by welding method, and the finished product is obtained after drilling. The following figure:
The welding process of the flange is now introduced in detail:
Draw the stakeout diagram on the blank according to the size of Figure 3. In order to improve the efficiency of stakeout, you can use template stakeout, that is, first put the picture on the cardboard according to 1:1, and then cut the cardboard into a template for stakeout operation.
Use an oxyacetylene cutter to cut the material, first draw a line on the material as shown below, and then use an oxyacetylene cutter to cut it along the contour line. In order to effectively use the material, some suitable size scrap can be used as the blank.
Cutting and welding groove
Due to the high mechanical performance requirements of the flange, in order to ensure sufficient strength after welding, the joint adopts a bilateral V-shaped groove, so the weldment after the blanking is cut with an oxyacetylene cutter to cut both ends into a shape like Figure 4 shows the structure.
Welding is the most important step in the entire process. The selection of welding methods, the setting of welding parameters and the technical level of the welder will all affect the quality of the product.
In order to accurately connect the 8-segment ring into a circle, first draw a circle with a diameter of 2300 on a flat workbench, and then match the inner diameter of the 8-segment ring with the circle drawn on the workbench, and The gap between each segment of the ring is adjusted evenly. Then the 8 segments of the ring are preliminarily fixed by spot welding.
Manual arc welding and CO2 gas shielded welding are commonly used welding equipment in some machinery manufacturing plants. The cost of CO2 gas shielded welding is low, which is 40-50% of manual arc welding. It has high production efficiency, simple operation and weld seam crack resistance. High, small deformation after welding, so CO2 gas shielded welding can be used to complete the welding work.
The welding wire is selected according to the steel type of the welded structure. For carbon steel and low-alloy high-strength steel, the welding wire that meets the mechanical performance requirements is mainly selected according to the principle of “equal strength matching”. At the same time, the selection must be made under the premise of ensuring the performance of the welded joint Welding material to achieve maximum welding efficiency and reduce welding cost. The flange material is 45# steel, and its application is an annealing furnace. Welding wires such as H08MnSiA, H08MnSi and H10MnSi with a diameter of 1.2mm can be used.
The specification parameters of carbon dioxide gas shielded welding include power source polarity, arc voltage, welding current, gas flow, welding speed, wire extension length, DC loop inductance, etc. Here is the welding of common materials, using short-circuit transfer welding technology, the current is DC reverse connection, and use a lower arc voltage, a smaller welding current welding, the gas flow is generally 8 ~ 25L/min.
In order to ensure the welding quality, pay attention to the arrangement of the welding sequence when welding. The 8 weldments cannot be welded in sequence. Instead, they must first be welded into 4 components, and then the four components should be welded in pairs, and finally welded into a whole. Welding ensures uniform welding process, reduces welding deformation and reduces the difficulty of correction.
After the welding is completed, first use a grinder to polish the weld. At the same time, during the welding process of the flange, due to the local high temperature heating, the temperature distribution in different areas is unbalanced, and a certain degree of welding deformation will occur, including the flange Plane deformation and circumferential deformation, the flange after welding must be corrected. According to the use of the flange, the plane deformation of the flange should be leveled. According to the equipment and technical conditions of the workshop, mechanical correction method or The flange is leveled by flame heating correction method. If the conditions are limited, manual hammering can also be used for leveling, that is, the welded flange is placed on a large surface, and the flanges are flattened with a hammer, and the flange is turned over, Repeat the leveling.
The flange has 24 bolt holes evenly distributed, and the drilling workload is very large. From the technical requirements, the hole edge distance of each hole is not high, and the relative position of the hole and the hole is relatively high. In order to ensure the accuracy, the method The flange hole should be processed with a matching drilling method. In addition, this flange requires a lot of space for drilling, but it cannot be drilled and then welded, because the uneven shrinkage after welding will lead to a large deviation in the hole position and cannot be correct. assembly.
It has been proved that the large-diameter flange made by the welding process meets the requirements of use. Compared with conventional processing, this process can improve the utilization rate of materials, and is especially beneficial to the application of leftover materials, and is not limited by the existing profile specifications. It has certain economic benefits in practical applications.
Source: China Large Diameter Flange Manufacturer – Yaang Pipe Industry (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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