Welding skills of thick and thin plates

Although there is no so-called technical secret in the welding process, there are many welding technologies, methods and processes in the actual welding process that can make the welding process easier, and these process methods are called technical know-how. Welding know-how can save time, expense and labor, and can even make the difference between success and failure, profit and loss. Most welding processes are mainly based on scientific research, and some welding processes are based on actual welding experience. This is a synthesis of some practical welding experience in practice.


Understanding the common welding problems and solutions in production can help solve some common welding problems. In this part, the key factors to be considered in the design of welds are described. Aiming at the problem of controlling welding deformation, the causes of deformation and the actual correction of welding deformation are introduced. In other design problems, the size of the Angle joint and how to avoid fracture are discussed. The simple design concept mainly introduces some common welding application examples. The elastic matching of welds and the placement of welded joints are discussed in the advanced design concept. Aiming at the welding problems of structural steel, some common welding materials and successful experience in welding practice are introduced. In oxygen-acetylene cutting, techniques for solving welding problems are provided. Cutting applications and the properties of oxygen spears and combustion rods are discussed. For the fasteners often used in welding structure, the common bolts and nuts and how to apply them are mainly introduced.

First, welding process problems and solutions

1.1 Welding of thick plate and thin plate

1. When welding steel workpieces with GMAW and FCAW, if the plate thickness of the workpieces exceeds the maximum welding current that the welder can achieve, how to deal with it? The solution is to preheat the metal before welding. The welding area of the workpiece is preheated with propane, gas or acetylene welding torch specified in the standard, and the preheating temperature is 150 ~ 260℃, and then welding is performed. The purpose of preheating the metal in the welding area is to prevent the weld area from cooling too fast, so that the weld does not crack or fail to fuse.

2, if it is necessary to use molten gas welding or flux-cored wire gas welding to weld a thin metal cover on a thick steel pipe, if the welding current is not properly adjusted during welding, it may lead to two situations: first, to prevent the thin metal from burning through and reduce the welding current, at this time, the thin metal cover can not be welded to the thick steel pipe; Second, too much welding current will burn through the thin metal cover. What should be done in this case? There are two main solutions.

① Adjust the welding current to avoid burning through the thin metal cover, and use the welding torch to preheat the thick steel pipe, and then use the thin plate welding process to weld the two-metal structure.

② Adjust the welding current to be suitable for the welding of thick steel pipes. When welding is performed, the residence time of the welding arc on the thick steel pipe is maintained to be 90%, and the residence time on the thin metal cover is reduced. It should be noted that a good welded joint can be obtained only when you are proficient in this technique.

3, when a thin-walled round tube or rectangular thin-walled tube is welded to a thick plate, the welding rod is easy to burn through the thin-walled tube part, in addition to the above two solutions, there are other solutions?

Yes, a cooling rod is mainly used in the welding process. If a solid round rod is inserted into a thin-walled round pipe, or a solid rectangular rod is inserted into a rectangular pipe fitting, the solid rod will take away the heat of the thin-walled workpiece and prevent burning through. In general, solid round or rectangular rods are tightly installed in most supplied hollow pipe or rectangular pipe materials. When welding, care should be taken to keep the weld away from the end of the pipe, the end of the pipe is the most prone to burn through the weak area.

4, when the galvanized or chrome-containing material must be welded with another part, how should it be operated?

The best process is to file or sand the area around the weld before welding, because galvanized or chromium-containing metal sheets can not only contaminate and weaken the weld, but also release toxic gases during welding.

1.2 Welding of container and frame structure

1, if a welding process method (such as brazing) is used to seal a float or seal the end of a hollow structure, during the final sealing of the weld, in order to prevent hot air from entering the container and causing the container to burst, what will be done?

③ First drill a pressure relief hole with a diameter of 1.5mm on the buoy to facilitate the hot air near the weld and the outside air circulation, and then seal the welding, and finally weld the pressure relief hole.

When welding the structure of the gas storage vessel, pressure relief holes can also be used. It should be noted that welding in a closed container is very dangerous, and should ensure that the inside of the container or pipe is clean before welding, and avoid the presence of flammable and explosive items or gases.

2, when it is necessary to use molten gas welding, flux-cored wire gas welding or tungsten argon arc welding to weld the screen grid, metal mesh or extended metal to the steel structure frame, the metal mesh is prone to burn through and weld seam failure phenomenon, how to deal with it?

① Place non-metallic washers on the wire mesh or extended metal and clamp the washers, wire mesh and frame together, do not allow the use of chromium or galvanized washers, washers should be uncoated.

② Place a larger washer above the washer in the welded position as a heat sink. The upper washer should have a larger hole than the lower washer to avoid the upper washer also being welded together. Plug welding is then performed through the two holes of the washer so that the weld is in the lower washer part. The operator can take some other methods to get enough heat and weld, taking care to prevent the surrounding screen grid or metal mesh from burning through.


③ Another method is to use a metal strip with a hole, align the hole with the part that needs to be welded, and place the cooling washer, and then plug welding.

1.3 Repair of welded components

1. In addition to the common nail lifter, what other methods can be used to remove damaged or rusted screws? Here are two methods.

If the installed screw will not be damaged during heating, the nut and its assembly can be heated with the oxygen-acetylene welding torch until it is red hot, and then quickly water quenched to facilitate the removal of the screw, in this process may require several heating, cold quenching cycle process.

If the screw slot, nut or tooth socket is damaged or missing, a nut may be placed on the upper part of the screw head (or the remaining part), screw the nut tight, and then fill the inside of the nut and screw with metal by any welding method. This will connect the nut to the remaining part of the screw, and then place a wrench or dental pliers on the nut to quickly pull out the screw. This method facilitates the provision of a new grip point and the use of heat to tighten the screw and remove the remaining parts of the set screw by welding.


2. If there is a worn crankshaft, what is the best way to repair and strengthen it with welding? A worn crankshaft can be repaired by using molten gas welding, flux-cored wire gas welding or argon tungsten arc welding. However, in order to obtain a satisfactory surfacing bead shape, the following four requirements must be paid attention to.

① Make the direction of the surfacing pass parallel to the axis of the crankshaft.

② First surfacing a pass at the lower part of the crankshaft, and then rotating the crankshaft 180° surfacing the next pass, so that the welding stress can be balanced and the welding thermal deformation can be significantly eliminated. It should be noted that sequential surfacing on the first weld will cause warping of the crankshaft. The surfacing welding process is suitable for repairing and welding roller crankshaft.

(3) 30% ~ 50% of the deposited metal overlap must be maintained between the two weld paths to ensure that the surface of the weld path is smooth during machining after welding repair.

④ When manual arc welding and flux-cored wire gas shielded welding are used, the residual flux between the weld passes must be cleaned by brush or cutting method. In addition to the above crankshaft repair methods, a surfacing pass can be added every 90° of the crankshaft to further reduce welding deformation. In the repair of bronze or copper parts, the addition of brazed metal is more advantageous than the method of surfacing welding in the removal of stress and deformation. Repair wear by welding.

3, if there is a steel bearing stuck in the equipment, and do not want to scrap the equipment, how should the welding method be used to remove the bearing? First, a bead is welded on the inner surface of the bearing, and the diameter of the bearing is reduced by the tensile force of the bead, and the heat of the welding process can make the bearing move. A pipe with a diameter of 10cm will shrink by 1.2mm if the inner surface is covered with solder channels. The stuck bearing is removed by welding.



4, oil tank or ship plate structure often produce cracks, how to prevent?

First, a small hole is drilled at the end of the crack to facilitate the distribution of the stress at the end in a large range, and then a series of multi-channel welds with different lengths are welded to increase the strength of the steel plate at the front of the crack. Prevent steel plate crack growth.


2.1 Positioning and thickening of the reinforcement plate

1. The welded reinforced plate is often welded to the surface of the steel plate (substrate), and the fillet weld on the outer edge of the reinforced plate is easy to warp the central part of the reinforced plate, leaving the surface of the steel plate and producing angular deformation.


This phenomenon will increase the difficulty of machining and turning processing, how to solve this problem? The solution is to use plug welding or slot welding in the middle part of the reinforcement plate, the surface of the reinforcement plate and the surface of the substrate are tight, and the deformation is eliminated to facilitate mechanical processing. The stiffener is positioned by plug welding or slot welding.

2, sometimes in the small area of the substrate need to thicken the substrate, but the thickening area can not exceed the area of the entire substrate, how to solve? A thick plate metal is inserted into the part of the substrate that needs to be thickened, and then fixed by welding. Embed a thick plate on the substrate.

This can provide sufficient thickness for subsequent machining, boring or drilling, and can replace large thickness parts or cast parts in the equipment.

3. What is the standard method for increasing the rigidity of the plate to carry the load? The standard method of increasing the rigidity of a plate to carry a load is to weld a series of Angle steel vertically on the plate, adding Angle steel stiffeners to enhance the rigidity of the plate.


2.2 Control noise and vibration

1, What technical measures can be used to reduce the noise and vibration of the metal plate? The noise problem, like the vibration problem, can also be solved by reducing the resonance frequency of the metal plate. The main methods used are as follows:

① To increase the rigidity by folding, curling or groove strengthening;

② Cut the plate into a series of small parts to enhance the support;

③ Use surface spraying layer;

④ A layer of damping fiber material is bonded to the surface of the plate.

Vibration caused at relatively low frequencies is usually reduced by increasing the metal stiffness.


2, when you want to weld a plate with another plate in the vertical direction, if there is only a C-shaped fixture, how should you work? During welding, a steel stop or a rectangular object is used as an auxiliary tool, and a C-shaped clamp and a rectangular stop are used to clamp the fillet weld.