Cause analysis of the crack of jaw crusher frame

The jaw crusher frame is the most important jaw crusher spare parts of the whole equipment, and the service life of the frame directly determines the service life of the equipment. The frame structure of the jaw crusher the frame of the jaw crusher is divided into integral frame and combined frame according to the structure. The integral frame is not suitable for large crushers due to the difficulties in manufacturing, installation, and transportation, but mostly used by small and medium-sized crushers. It is more rigid than the combined frame, but its manufacture is more complex. The combined frame is used for the large crusher. It has two forms: one is through the combination of embedded pins and bolts between the frame walls. For example, the 1200×1500 jaw crusher frame is divided into two parts, the upper frame and the lower frame are connected by bolts, and the joint faces are subject to strong shear by keys and pins. The key and pin also function as assembly positioning. The other is a welded combination, ~ h9oox 1200 jaw crusher frame. The rigidity of the utility model is better than the combined frame connected by the embedded pin, and the processing, assembly, and disassembly are more convenient. 1500×2100 crusher adopts a welded combined frame. In terms of the manufacturing process, the whole frame is divided into integral casting frames and integral welding frames. The former is difficult to manufacture, especially the single piece small batch production, while the latter is easy to process and manufacture, with lighter machine weight. However, the requirements of the welding process and welding quality are relatively high, and the internal stress is required to be eliminated after welding.

The porosity and cracks on the welding frame of the jaw crusher are the main causes of frame cracking. The causes of the porosity and cracks are as follows:

1. Low ambient temperature:Since the welding was in winter, the tightening temperature was lower than 0 ~ C. When welding at low temperature, the crack tendency increases because of the fast cooling rate of weld metal. Especially for Q345, because its alloy element content is more than that of low-carbon steel, the hardening tendency is larger than that of low-carbon steel, and the tendency of cracks is larger when welding at low temperature
2. Welding rod drying of crusher:In the process of welding the frame of jaw crusher, manual arc welding is adopted, and the welding rod is E5016 of low hydrogen type. It is required to dry the electrode for 350-400% for 2 days before welding, and take it when it is used after heat preservation. However, through tracking the welding process, it is found that the drying temperature of the electrode is only about 200 ℃, which makes the absorbed moisture in the electrode coating and the crystal water in the composition of the coating not be removed completely, so as to increase the air relic L and crack tendency caused by moisture.
3. Weldment cleaning:Because the electrode E5016 is sensitive to water, oxide skin, rust and oil on the surface of the weldment, it is required to clean the surface of weldment strictly to prevent air hole. However, in the actual welding process, the process is not strictly carried out, which makes the tendency of porosity and crack increase.
4. Restraint stress:The main weld structure of the frame is a closed weld. In addition, straight-through welding is adopted in the welding sequence, resulting in large welding stress and restraint stress.
5. No post-heating and hydrogen elimination measures:Hydrogen in the weld is the main cause of the cold crack in the low alloy high strength steel. Preheating before welding and heating after welding can reduce the cooling rate of weldment after welding, prolong the cooling time, and hydrogen can be released more fully, so as to reduce the hydrogen content in the weld and reduce the phenomenon of cold cracking and material hardening. After welding, timely post-heating can not only make hydrogen escape fully, but also reduce residual stress and hardenability to a certain extent. Choosing appropriate post-heating temperature can make up for preheating temperature.

The main reason of the frame cracking is the casting defect of the whole casting frame:

1. Stomata:The reasons are as follows: ① the gas involved in liquid metal casting exists in the casting in the form of pores after solidification of alloy liquid. ② The subcutaneous air hole formed under the skin of the casting after the metal reacts with the mold. ③ The gas adhered to the slag or oxide skin in the alloy liquid is mixed into the alloy liquid to form pores.
2. Loose:Formation reasons: ① alloy liquid degassing is not clean and loose. ② Finally, there is no shrinkage in the solidified part. ③ Local overheating, excessive moisture and poor exhaust.
3. Inclusions:Causes of formation: ① foreign matter mixed with liquid alloy and poured into human mold. ② The refining effect is not good. ③ The surface of the inner cavity of the mold is peeled off by foreign matters or modeling materials.
4. Slag inclusion:Cause of formation: ① slag removal is not clean after refining and modification. ② There is not enough standing time after refining and metamorphism. ③ The pouring system is unreasonable and the secondary oxide skin is rolled into the alloy liquid. ④ After refining, the alloy liquid is agitated or polluted.
5. Crackle:Causes: ① uneven cooling of each part of the casting. ② During the solidification and cooling process, the casting can not be shrunk freely due to the external resistance, and the internal stress exceeds the strength of the alloy to produce cracks.
6. Segregation:Formation reason: the concentration of solute in precipitated phase and liquid phase is different during alloy solidification. In most cases, the concentration of solute in liquid phase is rich but it is too late to diffuse, which makes the chemical composition of successively solidified part uneven.
7. Composition out of tolerance:Causes: ① the composition of the intermediate alloy or the pre cast alloy is uneven or the error of composition analysis is too large. ② Charge calculation or batching weighing error. ③ The smelting operation is improper, and the easily oxidized elements are burnt too much. ④ The melting and stirring are uneven, and the distribution of easily segregated elements is uneven.
8. Pinhole:Formation reason: the gas (mainly hydrogen) dissolved in the liquid state of the alloy precipitates from the alloy during the solidification process and forms evenly distributed holes. When using unqualified elbow plate and elbow plate pad, when the crusher is under strong impact, the elbow plate does not have self breaking protection, resulting in frame cracking.

Mr. Nick Sun     NICK@XZHUAGANG.COM