Welding deformation control of large opening of stainless steel scraper condenser Li Xiangming A series of effective deformation control measures were formulated for the welding deformation that occurred. By taking measures, the design requirements were met, and the successful experience of manufacturing such products was explored.

Manufacturing task of 6 scraper condensers. The scraper condenser is one of the key equipment for the localization of polyester equipment. The main material is 0Cr18Ni9. The structure is as shown. Its main manufacturing difficulty is the control of welding deformation of large openings.

As shown, the device is equipped with a scraper in the horizontal cylinder, the design requires that the gap between the scraper and the cylinder is (105) mm, and the straightness of the cylinder does not exceed 4 22, the tolerance of the ellipticity of the cylinder does not exceed 4mm. Such manufacturing accuracy is inherently difficult to achieve, and its vertical cylinder (! = 1500mm) and horizontal cylinder (! = 1600mm) perpendicularly intersect, and the intersection line almost intersects the horizontal cylinder diameter. With such a large nozzle joint, collapse and deflection during the welding process are inevitable.

1 The stainless steel scraper condenser has large openings and welding deformation. Stainless steel has the characteristics of small thermal conductivity and large thermal expansion coefficient. This determines that the welding deformation of stainless steel is more obvious than that of carbon steel under the same conditions.

The opening of the cylinder body not only destroys the continuity of the cylinder body, but also weakens the strength of the cylinder body, so it is easy to deform during the welding process: First, the lateral shrinkage of the ring seam is unevenly distributed in the thickness direction of the plate. Angular deformation caused by bending stress; second is the radial shrinkage deformation caused by the circumferential shrinkage of the ring seam. The superposition of these two deformations will produce collapse and deflection deformation. The larger the opening diameter, the more severe the weakening of the cylinder strength, the longer the weld, the more filler metal, resulting in greater welding heat input, the more serious the deformation.

The open joint welding seam is a closed welding seam, its restraint is greater than that of a free joint, the residual stress after welding is also large, and the welding deformation is relatively complicated. We borrow the welding stress caused by the disc insert block to seal the weld seam, and make a qualitative analysis of the deformation trend of the welded pipe.

= 12mm disc center open! = 300mm hole, welding!

= The stress distribution of 300mm inserts is shown as below. It can be seen from the figure that the radial residual stress "+ is tensile stress and the tangential residual stress" 6 is tensile stress on the inner panel, and it is the largest near the weld, which gradually decreases from the weld to the compressive stress.

Develop a process to prevent welding deformation In order to prevent the cylinder from deforming during the process of opening and welding, a series of anti-deformation measures were adopted through research and testing to develop a reasonable process.

The size of the welding line energy has a great influence on the cooling rate after welding, the size of the welding molten pool and the size of the welding heat affected zone. Therefore, in the entire process from opening, spot welding to welding, heat input and line energy are controlled at any time, which is used as the main means of preventing deformation.

First of all, the margin of the scribe line should not be too large when opening the hole, and the hole should be accurately opened according to the scribe line 5 (do not exceed the line. Opening 1 hole is too large when welding gold rights reserved, http: // level electrode diameter / mm Welding current / A arc voltage / V welding speed / (mmmin1) spot welding 3.290 -200 !: a radial residual stress; the stress distribution law shown by the welding stress caused by the welding stress caused by the encapsulation of the welding seam by all-directional residual stress disc inserts The reason can be explained.

Due to the symmetry of the test plate, only half of the test piece needs to be discussed. Total shear stress by 71 and! 72 is superimposed, 71 is the tangential stress caused by the shrinkage of the weld in the tangential direction, 72 is the tangential stress caused by the longitudinal direction of the inner panel (flat axis direction); radial residual stress! : Mainly caused by the shrinkage of the board in the radial direction (! Axis direction).

The residual stress caused by the circumferential shrinkage and radial shrinkage of the circular weld seam. The stress and deformation law caused by the disk insert closing the weld seam are consistent with the welding law of the open-hole nozzle. According to the above stress and deformation analysis, it can be qualitatively predicted that the deformation shown in the figure will occur when taking over the welding. The filling amount is large, and the welding heat affected zone is also enlarged. Ensure that the size of the opening can reduce the deformation. In order to control the heat input, the cutting torch cannot be used to cut the hole, and the cold cutting method of the grinder should be used. The bevel adopts inside chamfer 6mmx45. The bottom welding pass must be 3.2mm welding rod to ensure penetration. Use double-sided welding to avoid collapse and deformation of the weld.

Welding methods as small as possible, short arc welding, and fast non-swing welding are used as much as possible. Welding line energy is strictly controlled, and large-scale welding methods are prohibited. Welding specifications are shown in Table 1. Table 1 Welding specifications After each section of weld is welded, hit the weld bead with a planer to release stress to reduce deformation. After each welding layer is welded, the water cooling method is used to reduce the temperature to dissipate the heat of the weld and reduce the heated area, so as to reduce the deformation. (The water-cooled heat dissipation method is not suitable for welding materials with high hardenability!) The interlayer temperature is controlled below 100A to ensure that the weld is golden yellow, and there should be no blueness of the weld.

Welding feet and weld seam height should also be paid attention to when welding, the purpose is to reduce welding deformation by reducing the amount of metal deposited.

Forming control starts from cutting and strictly controls to ensure the size of the cylinder. Strictly check the spheronization so that the ovality tolerance does not exceed 4mm. During the whole process from spheronization, point pairing to welding, pay attention to the isolation and protection of the cylinder to avoid the increase of ovality due to external collision.

Manufacturing tooling, prefabricated anti-deformation In order to effectively prevent the welding deformation as shown, in addition to controlling the line energy, a tooling consisting of arc plates, ribs and bottom plates was manufactured according to previous experience, as shown.

The tooling is divided into upper and lower parts, using a welded structure. Through the support of the jack, the arc plate can restrain the roundness of the barrel to prevent radial deformation of the barrel during the welding process; and the rib plate can connect the entire tooling into two organic wholes, which increases stability , And can effectively restrain the deflection of the cylinder during welding.

At the same time, in order to better control the deflection, use two ", 20mm ring support rings on both ends of the cylinder. Fix the support ring on the cylinder, and then connect it with four sections of equal length channel steel and arc plate tooling. As a result, the tensile and supporting forces of these four support channel steels can effectively control the welding diagram of the flexible metal structure during welding! Schematic diagram of the tooling structure Through the tooling, the cylinder body is first supported to a certain pre-deformation, as shown by the dotted line in the middle. Use 5 jacks to open the distance between the tooling (see the position of the jack), the middle 50, and the other 4 20, screw jacks. (The hydraulic jack cannot be used because it is easy to produce pressure relief after being stressed. ) In this way, when opening and welding, due to the constraints of tooling, the amount of deformation is very small, and this small amount of deformation just cancels out with the pre-deformation, and the deformation is controlled to a minimum. The reverse deformation method closes the welded joint in a circle Not only can reduce the deformation after welding, but also can greatly reduce the residual stress of welding. The barrel and tooling to be welded are as shown.

The amount of deformation is determined based on past experience. The maximum diameter of the pre-deformation of the cylinder is 1612mm, the tooling is removed after welding, and the final roundness of the lumber is 3.5mm, which fully meets the design requirements.

Before the large opening, the reinforcement ring is first manufactured according to the intersecting line of the short section. Use tooling to restrain the cylinder and make the cylinder a certain pre-deformation. Then add a welding reinforcement ring at a predetermined position to increase the rigidity of the cylinder and restrict the deformation of the opening. The hole can only be opened and the groove be polished after the weld bead of the reinforcement ring cools.

Before welding, one should be added near the weld of the short section! > 20mm annular support ring to increase the rigidity of the short section and prevent collapse; place a support on the bottom of the cylinder corresponding to the opening to prevent the cylinder from flexing and deforming.

When welding, first use a multi-layer multi-pass welding method to weld the outer bevel and fill the bevel. After cooling, use a wooden hammer to strike around the weld bead on the reinforcement ring, especially the highest and lowest positions of the intersecting lines that are prone to large deformation, release the stress, and then remove the tooling, weld the inner groove welding equipment, weld the outer fillet welding Seam to ensure that the welding feet are 6mm. After welding, the stress is released by hammering and the tooling is removed. If there is a small amount of deformation or the ellipticity does not meet the process requirements, it can be adjusted using mechanical correction methods.

3 Conclusion The welding deformation problem of large openings is a common problem in the production of pressure vessels. Due to the thermal physical properties of stainless steel, the welding deformation of stainless steel is more serious than that of low-carbon steel. Only through technological means, as much as possible to control the amount of deformation, so that it can meet the requirements of product quality.

In the entire production process of the scraper condenser, a set of corresponding anti-deformation measures were adopted to effectively control the welding deformation: the ellipticity of the barrel was controlled at about 3.5mm; the maximum distance from the inner wall of the barrel to the scraper was 13mm. Minimum distance 8mm, deviation

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