Besides material wear, what other factors can shorten the service life of the fixed jaw plate?

As the core working component in direct contact with materials in jaw crushers, the service life of the fixed jaw plate is affected by multiple factors. The compression and friction wear caused by materials on the surface of the jaw plate are the main ways that lead to the failure of the fixed jaw plate. However, in actual production, many non-material wear factors also significantly shorten the replacement cycle of the fixed jaw plate. These factors involve multiple aspects such as equipment installation and assembly, operation and maintenance, and equipment parameter matching. This article will systematically review and analyze the main factors beyond material wear and tear.

1、 Improper installation and assembly

The installation quality of the fixed jaw plate directly affects its stress state and wear rate during operation. Deviation and negligence during installation are often hidden causes of premature damage to the jaw plate.

Poor contact and stress concentration. When installing the fixed jaw plate, if the jaw plate is not tightly attached to the surface of the frame (jaw body) and the gap between the two exceeds the allowable range, it will cause local vibration of the jaw plate under impact load, forming a stress concentration zone and accelerating wear. The data shows that if the installation gap exceeds 0.5mm, the wear rate in this area may be 30% faster than other parts. During installation, it should be ensured that the jaw plate is in smooth contact with the surface of the machine body. If necessary, a layer of plastic material such as lead plate and cement mortar should be placed between the two surfaces to eliminate gaps and ensure uniform force distribution.

Improper fastening leads to looseness. When the jaw crusher is working, the direct force between the material and the jaw plate is relatively large, especially when dealing with materials with high hardness. The installation bolts of the jaw plate are subject to periodic impacts, and the nuts are prone to loosening. After the bolt loosens, the displacement of the jaw plate gradually increases during each crushing cycle, generating greater impact force and forming a vicious cycle. More seriously, if the loose state persists without treatment, the bolts may experience fatigue fracture, the jaw plate may lose effective fixation, violently shake in the crushing chamber, and even directly collide with the body. Simply tightening nuts and bolts before starting up cannot completely solve this loosening problem. Experience has shown that installing springs on fixed bolts can enhance anti loosening and vibration reduction capabilities, effectively extending the service life of the jaw plate.

Parallelism deviation. When assembling the fixed jaw plate and the moving jaw plate, it is necessary to maintain their parallelism to avoid wear or breakage caused by relative sliding between the jaw plate and the moving or fixed jaw during operation. If the parallelism deviation is too large, the contact area between the jaw plate and the material will be uneven, resulting in increased local stress and accelerated wear rate.

2、 Improper setting of equipment operating parameters

If the operating parameters of the equipment itself do not match the working conditions, it will have a significant impact on the service life of the fixed jaw plate.

The eccentric shaft speed is too fast. Eccentric shaft speed is one of the important parameters of jaw crushers, which directly affects production capacity and the wear rate of jaw plates. When the eccentric shaft speed exceeds a certain range of the design value, the already crushed material cannot be discharged from the machine in time, resulting in blockage of the crushing chamber. The material is repeatedly squeezed and rubbed between the jaw plates, exacerbating the wear of the jaw plates. Statistics show that if the speed exceeds 10% of the design value, the lifespan of the jaw plate may be shortened by about 20%. On the other hand, if the speed is too low, the crushing efficiency decreases, and the material stays in the cavity for too long, which also increases wear. The reasonable rotational speed should be determined comprehensively based on the properties of the material and equipment specifications.

Unreasonable adjustment of discharge port. A too small size of the discharge port will increase the residence time of the material in the crushing chamber, causing the fixed jaw plate to be subjected to longer compression and friction, leading to increased wear. In actual production, it is not uncommon for the discharge port to be too small - operators may adjust the discharge port too small in order to pursue finer discharge particle size, but ignore the cost of jaw plate wear. Experimental data shows that adjusting the discharge port from 50mm to 70mm can reduce the wear per unit output of the jaw plate by about 22%. The adjustment of the discharge port should take into account the service life of the jaw plate while meeting the requirements of the discharge particle size.

The meshing angle is too large. If the angle (meshing angle) between the fixed jaw plate and the moving jaw plate exceeds the normal range, the material will generate an upward sliding force during crushing, increasing the friction and wear on the surface of the jaw plate. A reasonable meshing angle is generally controlled between 18 ° and 22 °, during which the material is mainly crushed by extrusion and sliding wear is relatively small.

3、 Improper feeding method and material handling

The operation mode of the feeding process has a direct impact on the stress state and service life of the fixed jaw plate.

Uneven feeding. Excessive or uneven feeding speed can lead to uneven distribution of materials in the crushing chamber, causing excessive local stress on the fixed jaw plate and accelerating wear. Using a vibrating feeder instead of a belt for direct feeding can reduce the impact and uneven load of materials on the jaw plate, resulting in more uniform wear of the jaw plate. If the installation angle of the feeder is too large and the feeding distance is too far, the raw materials will fall from a high place with strong impact force, which will directly increase the impact wear of the jaw plate.

The feeding particles are too large. Mixing large pieces of material exceeding the maximum feeding particle size of the equipment can cause the jaw plate to bear instantaneous impact loads, resulting in cracking or local indentation, seriously affecting the service life of the jaw plate. When the proportion of materials with larger particle size in the feed is high, the service life of the jaw plate may be significantly shortened. Before the material enters the jaw crusher, the particle size of the material should be controlled within the range specified by the equipment through screening or pre crushing.

The fluctuation of material properties has not been adjusted. Many crushers handle different types of materials in actual use, but the equipment parameters are not adjusted in a timely manner. The degree of wear of jaw plates varies greatly among materials of different hardness. When crushing high hardness materials (such as granite and basalt), the wear rate of jaw plates may be 2 to 3 times that of crushing low hardness materials (such as limestone). If the material properties change without adjusting the equipment parameters (such as speed, discharge port size, meshing angle), the wear condition of the jaw plate may deteriorate sharply.

The material contains hard impurities such as iron. Hard impurities such as iron blocks and stones mixed in the material can cause impact and severe wear on the jaw plate, and even lead to jaw plate fracture. Before the material enters the jaw crusher, an iron removal device should be installed to remove iron impurities and protect the jaw plate from abnormal wear.

Blockage and improper cleaning methods. When the crushing ratio is large, the material is easily blocked in the crushing chamber, and the stones cannot be smoothly discharged. Under the pressure of the jaw plate, they will slide back and forth, which will sharply increase the wear of the jaw plate. More seriously, some operators try to save time by using blasting to clear blockages. Although the speed is fast, the excessive impact force will directly change the internal structure of the jaw plate. Although there is no obvious damage on the surface, fine cracks have already formed inside, and the wear rate will double during subsequent use.

4、 Jaw plate material and manufacturing quality

The material selection and manufacturing quality of the jaw plate itself are one of the fundamental factors determining its service life.

The material does not match the working conditions. Different types of jaw plate materials are suitable for different working conditions. High manganese steel (such as ZGMn13) has the characteristic of cold work hardening, and its surface hardness increases from about 180HB to over 500HB under impact load. However, if it is used to crush soft rocks with low to medium hardness, the impact force is not sufficient to fully harden it, and its wear resistance is not as good as other materials. For different crushing conditions, suitable jaw plate materials should be selected based on factors such as material hardness and equipment specifications. Large crushers can withstand high impact loads and can use modified or dispersion strengthened high manganese steel; Small and medium-sized crushers can withstand relatively small impact loads and can be made of medium carbon low-alloy steel or high chromium cast iron/low-alloy steel composite materials.

Casting defects. Defects such as pores and sand holes generated during the casting process can become the starting point of wear and accelerate the failure process of the jaw plate after it is put into use. If there are impurities in the jaw plate, it can also cause stress concentration, and the edges of the impurities are prone to crack formation, reducing the fatigue life of the material. When selecting jaw plates, attention should be paid to the casting quality of the product, and priority should be given to selecting jaw plates that have undergone standardized heat treatment such as water toughening treatment.

Improper heat treatment process. High manganese steel jaw plates require water toughening treatment to obtain a uniform metallographic structure. If the heat treatment temperature is not properly controlled, it can lead to coarsening of the jaw plate grains and a significant decrease in wear resistance. The water toughening treatment temperature should be strictly controlled between 1050 ℃ and 1100 ℃, and the insulation time should be calculated as 1 hour per 25mm thickness of the board. Non standardized processes will significantly reduce the wear resistance of the jaw board.

5、 Defects and structural design of the equipment itself

The structural design and manufacturing accuracy of the equipment itself can also affect the service life of the fixed jaw plate.

The stability of the equipment foundation. The crusher must be installed on a concrete foundation with sufficient bearing capacity. If the foundation rigidity is insufficient or the installation levelness exceeds the standard, it will cause the swing trajectory of the moving jaw to deviate, exacerbating the unilateral wear of the jaw plate. The local settlement of the foundation after long-term operation of the equipment will also affect the uniformity of the force on the jaw plate.

Jaw plate structure design. The tooth profile design, thickness distribution, and other structural parameters of the jaw plate affect its stress distribution during operation. Reasonable structural design helps to disperse stress, reduce local stress concentration, and thus improve the service life of the jaw plate. Medium and small jaw crushers can design the jaw plate as a symmetrical structure from top to bottom. When the lower part is worn, it can be turned around for use, which can extend the service time of a single jaw plate.

6、 Lack of maintenance and management

Lack of systematic inspection and maintenance management can lead to the continuous accumulation and superposition of various adverse factors during equipment operation, ultimately accelerating the failure of the fixed jaw plate.

Lack of daily inspections. If problems such as loose jaw bolts, abnormal discharge ports, and uneven feeding cannot be detected in a timely manner, minor issues will evolve into serious consequences of premature failure of the jaw plate. Establishing a regular equipment inspection system, including measuring the wear of jaw plates, checking the status of fasteners, and monitoring the sound of equipment operation, can help intervene in the early stages of problem development.

Lack of lubrication and maintenance. Although lubrication does not directly affect the jaw plate, good lubrication can reduce wear and vibration of other components of the equipment, indirectly providing stable working conditions for the jaw plate. Regularly checking the lubrication system to ensure sufficient and clean lubricating oil helps to ensure the overall smooth operation of the equipment.