What are the common defects of space frame welding
The space frame is widely used in the construction industry nowadays, especially in the construction of the roof of houses and other equipment. It has a good load-bearing effect. Its wide use is inseparable from excellent welding technology, but it is easy to be a little careless in the welding process.
Some defects that occur.
1. Thermal cracks in the space frame. Its basic feature is produced during the cooling process of the weld. The main reason for this is that the sulfur and phosphorus impurities in the steel or welding materials form a variety of brittle and hard low-melting eutectics with steel. During the cooling process of the weld, the solidified low-melting eutectic is in tension, and easy to crack.
2. Cold cracks. Cold cracks produced by welding are also called delayed cracks, and their main characteristic is that they usually occur in the range of 200°C to room temperature. They have delayed characteristics and appear within a few minutes to a few days after welding. The main reason for this is closely related to the selection of steel, the design of the structure, the storage and application of welding materials and the welding process.
3. The space frame is torn in layers. Its main feature is that when the welding temperature is cooled to below 400℃, some plates have a relatively large thickness and a high impurity content, especially a high content of sulfur, and a low-alloy high-strength steel with strong segregation along the parallel direction of the plate rolling , When it is subjected to a force perpendicular to the thickness direction during the welding process, it will produce stepped cracks along the rolling direction.
4. Not fused and not penetrated. The reasons for the two are basically the same, mainly due to improper process parameters, measures and groove size, insufficient cleanliness of the groove and weld bead surface or impurities such as oxide scale and welding slag, and poor welder technology.
5. Space frame air holes. According to its production form, it can be divided into two types, namely precipitation type pores and reaction type pores. Precipitating pores are mainly hydrogen pores and nitrogen pores, while reactive pores are mainly CO pores in the welding of steel, that is, non-ferrous metals. The main feature of precipitated pores is that they are mostly surface pores. The main difference between hydrogen pores and nitrogen pores is that hydrogen pores are mainly single pores, while nitrogen pores are mostly dense pores. The main reason for the generation of pores in the weld is related to the selection, storage and use of welding materials, the selection of welding process parameters, the cleanliness of the base metal of the groove and the degree of protection of the molten pool.
6. Inclusion of slag. The type, shape and distribution of non-metallic inclusions are mainly related to the welding method, welding rod and flux, and the chemical composition of the weld metal. There are many welding defects of the space frame, which will affect the normal use of the product, but the process is a process of gradual optimization from poor to good. Only by finding the cause of the defect can we continue to improve and make better products.