Fault Evolution of Fixed Jaw Plates Caused by Internal Porosity and Shrinkage Cavities

Fixed jaw plates are the core wear-resistant and load-bearing components of jaw crushers. Internal porosity and shrinkage cavities in castings are recessive defects formed during the casting process, mostly distributed in thick-wall hot spot areas and difficult to identify through routine visual inspection. Under the continuous extrusion, impact and friction loads during ore crushing operations, these internal defects will gradually expand and evolve over service time, leading to various obvious faults, directly shortening the service life of components and increasing production operation and maintenance costs.

Fatigue crack propagation and matrix cracking are the most common evolution forms. Porosity and shrinkage cavities are essentially discontinuous pores inside the casting, acting as natural stress concentration sources. During crushing operations, the jaw plate bears alternating extrusion loads and impact loads, and stress will continuously concentrate at the edges of the pores, gradually initiating microcracks. As the operation time increases, cracks propagate along grain boundaries into the interior of the matrix, and multiple cracks interconnect to form macroscopic cracking. In the early stage, it only manifests as fine lines on the surface of the jaw plate, and in the later stage, it gradually extends and deepens. In severe cases, it causes overall fracture of the jaw plate, leading to sudden equipment shutdown. When processing high-hardness materials such as granite, the impact load is stronger, and the crack propagation speed will be significantly accelerated.

Local surface spalling and tooth chipping are typical results of near-surface defects. When porosity and shrinkage cavity defects are close to the tooth surface, the repeated extrusion and friction of materials during the crushing process will gradually wear away the base metal above the defects, making the internal pores gradually exposed. The stress state at the edges of the exposed pores is unbalanced, and under continuous impact of materials, surface metal spalling is prone to occur, forming pits and spalling on the tooth surface. If the defects are located in stress concentration areas such as tooth crests and tooth roots, it will further cause tooth fracture and chipping, damage the tooth profile structure of the jaw plate, lead to coarser crushing particle size and reduced crushing efficiency, and at the same time aggravate the abnormal wear of the matrix by materials.

Uneven eccentric wear is the main manifestation of diffuse porosity. The matrix in the internal porous area has poor compactness, and its hardness and wear resistance are lower than those of normal metallographic structures. Under the continuous friction of crushing operations, the wear rate of the area corresponding to the defect will be significantly higher than that of the surrounding normal area, forming local concave eccentric wear. This uneven wear will destroy the flatness of the jaw plate tooth surface and tooth profile parameters, change the stress state of materials, and further accelerate the wear rate. At the same time, eccentric wear will lead to unbalanced overall stress on the jaw plate, increasing the probability of secondary problems such as loosening of fixing bolts and intensified frame vibration.

Instant fracture under extreme working conditions is the fault form with the highest risk. When there are concentrated large shrinkage cavities or dense porous areas inside the casting, the effective load-bearing cross-sectional area of the matrix will be greatly reduced. If extreme working conditions such as large material jamming and impact of uncrushable debris occur during production, the jaw plate bears instantaneous peak load, and the defective part will become a fracture breakthrough, causing instantaneous overall fracture of the jaw plate. Such faults are highly sudden, which can easily cause collateral accidents such as crusher cavity damage and surrounding component damage, increasing maintenance costs and downtime.

Internal porosity and shrinkage cavity defects are highly concealed, so it is necessary to control the process quality from the casting source. Hunan Xiangjian Machinery Technology Co., Ltd. focuses on the field of mine wear-resistant parts. In the production of fixed jaw plates, it strictly controls the casting and heat treatment processes, and supports batch-by-batch quality inspection to ensure the compactness and structural reliability of castings. For customized high-reliability fixed jaw plates, please visit the official website https://www.xjgmg.com for consultation.