How to extend the service life of movable jaw plates

I. Overview

The movable jaw plate (referred to as the moving jaw plate) of the jaw crusher is a key working component that comes into direct contact with the material. Under long-term compression and sliding friction, the tooth profile on the surface of the jaw plate will gradually wear out, resulting in a decrease in crushing efficiency and a coarsening of product particle size. The service life of jaw plates is affected by various factors, including installation quality, feeding method, material characteristics, equipment operating parameters, matching of jaw plate materials, and daily maintenance level. By systematically and targetedly controlling these factors, the service life of the movable jaw plate can be effectively extended without replacing equipment, reducing accessory consumption and downtime maintenance costs.

2、 Material pretreatment - reducing wear and tear from the source

The properties of materials are one of the important factors affecting the wear rate of jaw plates. In production practice, pre-treatment of materials entering the crusher can reduce the wear burden on the jaw plate from the source.

Setting up a screening device is a simple and cost-effective pre-treatment measure. A heavy-duty grid screen or pre screening vibrating screen can be installed between the feeder and the jaw crusher to pre separate materials with a size exceeding the upper limit of the rated feed inlet of the jaw plate and qualified fine materials that do not need to be crushed, so that the jaw crusher only processes materials that need to be crushed. For raw materials with high soil content, high-pressure water spray or desliming screen can be added on the grid screen to reduce material viscosity in advance, prevent material adhesion in the crushing chamber and subsequent blockage of the conveying system.

The control of material moisture content is also important. Generally, it is required that the moisture content of the material does not exceed 10%. When the moisture content of the material exceeds 15%, the material is prone to adhere to the lining plate of the crushing chamber and the inner wall of the discharge port, gradually accumulating to form a blocking layer, blocking the discharge channel, prolonging the residence time of the material in the crushing chamber, and thus exacerbating the wear of the jaw plate. For materials that are difficult to reduce humidity, a drying process can be added before feeding, or a small amount of anti sticking agent can be sprayed in the crushing chamber (matching the characteristics of the material to avoid contamination).

The installation of iron removal devices is also a necessary preventive measure. Installing iron removal devices or screening pre-treatment equipment at the feed inlet to separate metal impurities such as iron blocks mixed into the material in advance can effectively prevent serious chiseling damage to the jaw plate caused by hard impurities, and avoid scratches, cracks, and even fractures of the jaw plate due to local high stress impact.

3、 Standardized installation - ensuring smooth contact and reliable fastening

The installation quality of the jaw plate directly determines its stress state and operational stability during the crushing process. In actual production, unstable contact between newly installed jaw plates is one of the common reasons for increased wear. To solve this problem, we need to start from the following aspects.

During installation, the jaw plate should be level with the body. It is advisable to use soft metals (such as lead plates, zinc plates) as gaskets and install them between the jaw plate and the moving cone or fixed cone. After the bolt is tightened, the soft metal layer undergoes plastic deformation due to compression, which can fill the small gap between the two contact surfaces, evenly distribute the pressure, and avoid local stress concentration. The thickness of the gasket should be determined based on the actual gap, generally controlled within the range of 3-5mm.

The process of bolt tightening also deserves attention. The "diagonal step-by-step tightening method" should be adopted, which means gradually applying force in 2-3 stages according to the diagonal order, and finally using a torque wrench for verification. For M20 bolts, the torque is generally controlled within the range of 300~500N · m. During long-term operation of the equipment, continuous impact and vibration can cause the fixing bolts to loosen. Simply tightening the bolts before starting up is often difficult to completely solve the problem. A spring anti loosening device can be installed on the fixed bolt - consisting of an inner spring cover, a spring, and an outer spring cover. After threading the device on the bolt and tightening the nut, the spring is compressed to generate tension, which can automatically compensate for the loosening trend of the bolt caused by the crushing force, thereby extending the service life of the jaw plate.

When the gap between the jaw plate and the body is too large (such as a gap greater than 1mm) and no plastic gasket is used, it can cause excessive local stress on the jaw plate, and long-term use may result in corner warping or even detachment. During installation, a feeler gauge should be used to check the fitting area, ensuring that the contact area between the jaw plate and the jaw body is not less than 95%.

The fit of teeth is also an important point that cannot be ignored in the installation process. The movable jaw plate and the fixed jaw plate should be in a basic meshing state, that is, the tooth peak of the movable jaw plate should align with the tooth groove of the fixed jaw plate. This coordination method not only subjects the material to compression but also bending during the crushing process, which is beneficial for improving crushing efficiency and reducing abnormal wear of the jaw plate.

For the requirement of parallelism, thin gaskets such as copper, lead, or zinc should be used for fine adjustment after installation to ensure that the parallelism deviation between the moving jaw plate and the fixed jaw plate is less than 1mm/m, avoiding unnecessary relative sliding between the jaw plate and the machine body during operation, and preventing additional wear or breakage caused by this.

4、 Scientific feeding - uniform distribution and center alignment

The feeding method has a significant impact on the wear distribution and wear rate of the jaw plate. The goal of scientific feeding is to ensure that materials enter the crushing chamber in the correct way, appropriate amount, and uniform distribution.

Center alignment is a prerequisite for scientific feeding. The centerline of the discharge port of the feeder (such as a vibrating feeder) should be strictly aligned with the centerline of the inlet of the crushing chamber of the jaw crusher, and the vertical drop of the material should be minimized as much as possible. By installing a guide groove or buffer plate, the material can be prevented from falling into one side or causing impact splashing. This measure can avoid excessive wear on one side of the jaw plate caused by material overload.

Uniform feeding of the full material layer is the key to stable operation. Adjust the frequency and amplitude of the feeder to ensure that the inlet of the crushing chamber is always filled with material without overflowing. Operators can use the reading of the motor ammeter as a basis for judging whether the feeding amount is appropriate, rather than relying solely on visual observation. Modern production lines can use level gauges or automatic control systems based on current feedback to achieve automatic adjustment of feeding speed, which is an important technical means to achieve stable production.

The feeding amount should be strictly controlled within the rated processing capacity of the equipment - insufficient feeding will reduce processing efficiency, but excessive feeding can easily cause blockage of the crushing chamber, which in turn exacerbates jaw plate wear. It is recommended to record the wear morphology of the jaw plate every time it is replaced. If asymmetric wear occurs, it should be checked and the center of the feeding point should be adjusted in a timely manner.

5、 Material adaptation - timely adjustment of equipment parameters

Sampling inspection of each batch of materials entering the crusher is an important means of controlling jaw plate wear. When the properties of the material (hardness, particle size, moisture content, mud content, etc.) change, the main parameters of the crusher should be adjusted in a timely manner to match the material, thereby reducing abnormal wear of the jaw plate. Specifically, operators need to master the adjustment of the following key parameters:

Claw angle adjustment: The angle between the movable jaw plate and the fixed jaw plate has a direct impact on the biting conditions of the material and the stress state of the jaw plate. The clamp angle should generally be controlled within the range of 18 °~22 ° and should not exceed 25 °. When the clamp angle is too large, the material is prone to slip in the crushing chamber, and the sliding stroke of the material relative to the surface of the jaw plate increases, accelerating cutting wear; At the same time, the lateral force borne by the jaw plate increases, leading to an increase in local stress. If the clamp angle is too small, the effective volume of the crushing chamber will decrease, and the material will be excessively squeezed in the chamber, which will also accelerate wear.

Eccentric shaft speed adjustment: The speed determines the swing frequency of the movable jaw plate. Within a reasonable speed range, increasing the speed can increase the number of crushing cycles per unit time, thereby increasing production. But when the speed is too high, the crushed material cannot be completely discharged from the discharge port in time, resulting in blockage of the crushing chamber, prolonged compression and sliding time between the material and the jaw plate, and accelerated wear rate of the jaw plate. The speed adjustment should be carried out gradually, with each increase of 5% to 10% followed by observation of the discharge situation to find the appropriate speed that matches the current material properties.

Adjustment of discharge port size: The discharge port size should be set according to the requirements of product particle size. On the premise of meeting the product particle size index, the discharge port should not be too small, otherwise the material discharge will be obstructed, and the material will be repeatedly squeezed in the lower part of the crushing chamber. The wear of the lower area of the jaw plate will be significantly accelerated, and the pressure inside the crushing chamber will increase, increasing the risk of fatigue peeling of the jaw plate.

6、 Reasonable material selection - matching materials with working conditions

The reasonable selection of jaw plate material is the basis for extending its service life. There are differences in the requirements for jaw plate material under different working conditions.

For large jaw crushers, the crushed material has a large block size, and the impact load borne by the jaw plate is also large. In such strong impact conditions, modified or dispersion strengthened high manganese steel (such as ZGMn13Cr2, Mn18Cr2, etc.) can be selected as the jaw plate material. The initial hardness and yield strength of modified high manganese steel have been improved, which can better adapt to high impact conditions.

For small and medium-sized crushers, the impact load they bear is relatively small, and it is difficult to fully work harden them using high manganese steel. Under such working conditions, medium carbon low-alloy steel or high chromium cast iron and low-alloy steel composite materials can be selected to achieve technical and economic benefits that are closer to actual needs.

There are differences in the force distribution between the movable jaw plate and the fixed jaw plate: the movable jaw plate bears a greater impact force, and first of all, it should be ensured that it has sufficient toughness to resist the impact; And the fixed jaw plate is supported by the frame, which can consider the hardness requirements more. This differentiated material selection strategy helps to improve the efficiency of the entire jaw plate.

The selection of jaw plate material should also consider technical and economic effects. On the same device, through reasonable material matching, the wear resistance of the jaw plate can be significantly improved, the service life of the jaw plate can be extended, and the spare parts cost per unit product can be reduced.

7、 Inverted use and weld repair - extending service life

When the jaw plate shows a certain degree of wear, methods such as inverted use and welding repair can be adopted to further extend its service life.

Inverted use: Due to the fact that jaw plates are usually made in a symmetrical shape, the wear on the lower part is often more severe than that on the upper part. Therefore, when the lower part of the jaw plate is worn to a certain extent but there is still a lot of surplus in the upper part, the jaw plate can be inverted for use during minor repairs, so that the underutilized part of the upper part can continue to function and improve the utilization rate of the entire jaw plate material. Inverted operation requires checking the crack condition of the jaw plate, and jaw plates with cracks are not suitable for inverted use.

Welding repair: For severely worn jaw plates, welding can be used to restore the tooth profile. When repairing, it is advisable to use high manganese steel type overlay welding electrodes (D256, D266, etc.), and the power supply can be DC reverse connection or AC power supply. The specific operations include the following key points:

Before welding, the surface of the welded area should be polished off by 2-3mm with a grinding wheel to remove the hardened layer formed after wear and avoid the occurrence of welding cracks.

When welding, the process of "low current, small weld bead, discontinuous" should be adopted. First, a layer should be welded on each tooth, and then the second layer should be welded to avoid welding one tooth at a time and then welding another tooth to make the base material heated as evenly as possible.

After welding, the weld bead should be hammered appropriately to eliminate welding stress, and the cooling rate of the weld deposit area should be appropriately accelerated. If conditions permit, the jaw plate can be placed in water and only the weld deposit area should be exposed for welding.

The D256 high manganese steel welding rod has outstanding work hardening properties, with an initial hardness of HB ≥ 170 after surfacing. After work hardening, it can reach HB450~500, which is suitable for wear repair under severe impact loads.

8、 Daily maintenance and regular inspections

Establishing a daily maintenance system for the system is an important guarantee for extending the service life of the jaw plate.

Regularly check the wear of the jaw plate and use a caliper to measure the remaining tooth height at different positions on the jaw plate. When the tooth height wear exceeds 2/3 of the original height, inverted use or weld repair should be considered; When the remaining height is less than one-third of the original height, it should be replaced in a timely manner.

Regularly check the tightening status of bolts, it is recommended to use a torque wrench for inspection every shift, and the deviation should be controlled within ± 10%; Measure the wear of the jaw plate weekly (at least 3 points) and establish a wear record.

Regularly check the operation status of the equipment, pay attention to whether the current of the motor is stable, and whether there are any abnormal vibrations or noises in the equipment. If any abnormalities are found, stop the machine for troubleshooting in a timely manner and do not operate it with any problems. The operating temperature of the bearing should be controlled within the specified range - in general, the temperature rise of the bearing should be less than 35 ℃, and the maximum temperature should not exceed 70 ℃.

Pay attention to the lubrication of the equipment, especially for moving parts such as eccentric shafts, connecting rods, and bearings. Add sufficient lubricating grease on time and do not use inferior oil products