Welding and surfacing technologies can effectively restore metal parts, providing a high degree of reliability and durability of the product. This is also confirmed by the practice of using these methods when performing repair operations in a variety of areas - from car repairs to the production of metal. In the total scope of repair of metal structures, restoration of parts by welding and surfacing takes about 60-70%. The most common repair of steel cylinder blocks, motor shafts, crankcases, chain links, blades, etc.
Welding and surfacing in repair work
Both methods are based on thermal exposure methods with different operating parameters of the connected equipment. Welding is understood as the process of formation of interatomic bonds, which can be used to connect different elements of the part, seal technological gaps and eliminate small defects on the surface. The energy potential for the welding process is ensured by general or local heating of the workpiece.
Typical operations of this kind include fixing additional or broken parts of plates, crowns and bushings. In addition to repairing products with simple geometric shapes, more complex recovery tasks are possible, but in combination with other technological operations. For example, welding thread restoration will be complemented by mechanical dressing and grooving procedures. In addition, in such works, the requirements for overheating of the auxiliary tool, such as dies, which are directly involved in the correction of the thread, should be observed.
As for surfacing, this method involves the application of an additional metal coating on the restored surface. A new technological layer can be useful when repairing worn parts or strengthening the surface in the area of friction.
Applied Equipment
When welding, a current source and equipment are necessarily used to hold the part and the direction of the arc. Most often, a welding converter is used, which includes a motor with a DC generator from 70 to 800 A. Rectifiers with current transformers and ballasts can also be used. If we talk about consumables and auxiliary devices, then the restoration of parts by welding and surfacing is carried out with the connection of holding mouthpieces, electrodes and cooling systems. When surfacing, deforming heads are also used with calipers and elevators that allow mounting on machines (turning or screw-cutting). Special cutters are used to remove excess metal edges and layers.
Part Preparation Requirements
Both during welding and during surfacing, the quality of the operation will be determined to a large extent by the initial state of the workpiece. The surfaces of the part must be cleaned from rust, scale, dirt and grease. Otherwise, the risk of preserving lack of penetration, cracks and slag inclusions increases. Particular attention should be paid to degreasing from factory and preservation oils. This procedure is performed in a hot solution, after which the product is washed and dried. Before restoration of parts by welding, it is recommended to perform sandblasting, which improves the quality of repair. For such tasks, abrasive processing methods are used with the connection of compressor equipment, grinding discs and cutters. Minor traces of corrosion damage can also be removed with manual wire brushes.
What electrodes are used in recovery?
After preparing the main working equipment and the workpiece, you can proceed to the selection of electrodes. The selection depends on the type of metal, the nature of the defect and the requirements for the surfacing layer. As a rule, in common cases of breaks and cracks, conventional welding electrodes with a tensile strength of about 4 MPa are used. To work with carbon steels, it is recommended to use consumables, the rods of which are made of wire grade Sv-08 with a thickness of 1.5-12 mm. Do not ignore the characteristics of the coating. A high stabilizing effect during the restoration of parts by welding and surfacing will provide chalk coating of the E-34 type electrode. It will contribute to a stable process of arc burning, which will allow to form a dense and even seam.
Non-standard electrode consumables such as tape and tubular powder elements are also used today. Usually they are rolled metal tapes up to 0.8 mm thick, the surface of which is filled with various powder alloying mixtures based on ferromanganese, stalinite, etc. These electrodes should be addressed if it is planned to provide the repair area with additional operational properties.
Manual arc welding and surfacing method
When repairing damaged welds, repairing cracks, and sealing sealed enclosures, the manual method with graphite, carbon, or tungsten electrodes can be used. In the course of work, a bundle of rods with a coating is taken and fastened with wire. The ends must be pre-welded and inserted into the prepared holder. In the course of operation, the electrodes will form the so-called wandering arc with a wide field of action. The larger the area of the damaged area, the larger the beam should be. The main difficulty of the welding process in this way is the need to connect a three-phase network, since the same surfacing with a bundle of 5-6 electrodes should be carried out at high current. This method repairs parts of alloyed and low alloy steels of medium and large thickness.
Submerged arc welding method
The automatic surfacing process is characterized in that the electrode feed with the movements of the arc itself along the working surface is fully mechanized. Flux, in turn, provides isolation of the target zone from the harmful effects of oxygen. The method is used to restore the surfaces of flat and cylindrical parts with a wear depth of up to 15 mm. As the size of the defect increases, several layers of surfacing can be used, but in this case, waiting for the polymerization of each previous layer will be required. This technology for the restoration of parts by welding and surfacing requires the connection of current sources in the form of a converter or rectifier with a screw-cutting machine. A flux coating 1-4 mm thick is formed in the working area, after which the electrode wire with an arc is automatically guided. The main advantages of this method with respect to manual welding include minimal metal loss due to spatter. The manual method gives several times more cinder and fumes.
Vibration Arc Surfacing Method
In this case, fusible electrodes are used, which vibrate with short circuits during arc burning. Supplies and transfers of supplies are also automated. Despite the external complexity of the process, the method is quite simple and does not require the use of special equipment. Moreover, ultimately we can expect the exception of the deformation of the part while maintaining hardness without heat treatment. However, there are limitations. So, vibrational methods of repairing parts by welding and surfacing are suitable for workpieces with a diameter of at least 8 mm or a thickness of 0.5 to 3.5 mm. Theoretically, arc welding can be performed in different protective environments with gas or flux, but in practice, liquid insulation is more often used - for example, soda ash solution.
Welding and surfacing in gas protective environments
This method involves the preparation of a special cylinder with a compressed gas mixture. Argon and carbon dioxide gases sent to the high pressure welding zone can be used. The task of the mixture also comes down to the protective function of isolating the workpiece from the negative effects of nitrogen and oxygen in the air. The highest quality welding joints in gaseous media are obtained using tungsten electrodes with a separate input of filler materials into the working area. Surfacing is carried out under direct current with reverse polarity. The process can be mechanized if an electrode wire is used, but operations with gas-electric burners are usually performed manually.
Semi-automatic welding and surfacing methods
The best method for working with aluminum and various alloys of color. Thanks to the flexible adjustment of equipment parameters and the possibility of using different protective environments, the operator can obtain a high-quality weld on a workpiece with a thickness of up to 12 mm with a small current strength. A semi-automatic method of repairing parts by welding is performed using tungsten electrodes with a thickness of 0.8-6 mm. The voltage can vary from 20 to 25 V, and the current strength is within 120 A.
Alternative Pressure Recovery Technology
In addition to thermal methods of welding and surfacing, a wide group of contact or cold methods for changing the structure of metal billets are also used. In particular, the restoration of parts by pressure welding is carried out using mechanical units with punches. In the process of plastic deformation, a welded joint with certain parameters is formed at the contact points. The configuration of the deforming effect will depend on the characteristics of the punch and the compression technique.
Conclusion
To date, there are no more effective ways to correct defects in a metal structure than welding and surfacing. Another thing is that in these segments there is an active development of different methods for implementing technology in practice. The most promising direction can be called the restoration of parts by welding and surfacing on automated equipment. Mechanization of repair operations increases the productivity of the process, its ergonomics and the level of safety for the welder. At the same time, methods of high-precision argon-arc welding with the connection of gas protective media are also being developed. It is still too early to talk about full automation in this direction, but in terms of the quality of the result, this area is advanced.