Impact fatigue of impact crusher plate hammer: mechanism and systematic response to end blunting and dynamic balance failure

The failure of the plate hammer in a counterattack crusher is a typical dynamic fatigue process, characterized by "blunt end wear" and the resulting "dynamic balance failure of the rotor system". These two phenomena are mutually causal and together constitute a key challenge that restricts the service life of the plate hammer and affects the stable operation of the equipment.

1、 Failure manifestation: from material loss to system vibration

1. End dullness - a direct consequence of impact fatigue

The plate hammer is the core component that rotates at high speed and directly impacts materials. Its working end (striking end) is subjected to hundreds of high-energy impacts per minute during operation. Under cyclic impact loads, irreversible damage accumulates on the surface and subsurface of the material, causing the metal material at the cutting edge or striking surface to gradually lose its shape, changing from sharp or square to circular arc. This process is not only simple wear, but also the result of impact fatigue leading to the initiation and propagation of microcracks in the surface hardening layer of the material, ultimately resulting in the detachment of small fragments.

2. Dynamic balance failure - a systemic problem caused by uneven mass distribution

At the beginning, the total mass and center of mass distribution of a group of hammers are strictly balanced. When the wear degree of each plate hammer is inconsistent (which is a common phenomenon), the amount of mass reduction varies, causing the center of mass of the entire rotor system to deviate from the geometric rotation center, resulting in unbalanced mass. This imbalance will generate periodic centrifugal inertia force under high-speed rotation, manifested as intensified equipment vibration, abnormal increase in bearing load, and accompanied by abnormal noise.

2、 Core mechanism: Fatigue accumulation and crack propagation under impact load

Impact fatigue failure follows a clear physical process:

Phase 1: Microplastic deformation and work hardening. With each impact, the surface material of the plate hammer undergoes microplastic deformation under high pressure stress, while the dislocation density increases, resulting in work hardening effect, which increases the surface hardness but brittleness.

Phase 2: Microscopic crack initiation. Under continuous cyclic impact, microcracks are initiated at the interface between the hardened surface or hard phases (such as carbides) and the matrix due to stress concentration.

The third stage: crack propagation and material peeling. Microscopic cracks continue to propagate and connect during subsequent impacts. When the crack size reaches a critical value, the surface material peels off in a thin or granular form, which is macroscopically manifested as wear. This process is particularly intense at the end of the plate hammer where the impact energy is most concentrated and the stress is highest.

3、 Analysis of influencing factors

Multiple factors interact to determine the development rate of impact fatigue.

The influence mechanism of influencing factors on end wear and fatigue, and the potential impact on dynamic balance

When crushing high hardness and highly abrasive materials (such as basalt and quartzite), the peak impact stress is high, the abrasive cutting effect is strong, and fatigue and wear are accelerated. Intensify the random differences in wear of each plate hammer.

The higher the linear velocity of the rotor, the greater the kinetic energy of a single impact, and the faster the impact fatigue process. At the same time, the wear rate also increases accordingly. Rotational speed is the square multiple factor of centrifugal force, and slight mass differences can cause severe vibrations at high speeds.

Materials with insufficient toughness of the hammer material are difficult to absorb impact energy through plastic deformation and are prone to crack initiation; Insufficient hardness results in poor wear resistance. Materials suitable for counterattack breaking conditions need to achieve a reasonable balance between high toughness and high hardness. Uneven material properties can lead to different wear rates of the same group of plate hammers.

Improper design and installation of the plate hammer fastening method may result in slight movement during operation, generating additional friction and impact. Unreasonable geometric shapes of the striking surface can cause stress concentration. Inconsistent installation torque and significant initial weight difference are the direct causes of disrupting the initial dynamic balance.

Continuous uneven feeding conditions and mixed material particle sizes can cause differentiated impacts on different hammers or different parts of the same hammer, resulting in uneven wear. It is the main working condition factor that causes inconsistent wear and tear.

4、 Systematic management strategy

To address this challenge, a systematic technical management approach is required, covering the entire process from material selection to maintenance.

1. Material selection and quality control

Applicable materials: Materials with good impact toughness matrix, such as multi-element alloy steel or specially treated high toughness high chromium cast iron, can be considered. The hard phase (carbide) in its organization should be fine and dispersed to delay crack propagation.

Symmetrical casting and balancing: It is required that the mass distribution of a single plate hammer is symmetrical, and the weight difference of the same batch of plate hammers is controlled within the range specified by the equipment manufacturer (usually within ± 0.5kg).

2. Usage and maintenance operation specifications

Group replacement and periodic replacement: All plate hammers must be replaced in groups, and mixing old and new is strictly prohibited. For plate hammers with adjustable heads, overall turning can be performed during operation to balance wear at both ends and extend the overall service life.

Accurate installation and fastening: Use a torque wrench to cross tighten bolts strictly according to the specified torque and sequence, ensuring consistent installation firmness of all plate hammers. After installation, manually rotate and check for any interference.

Monitoring wear and establishing replacement standards: Regularly measure the remaining weight or end wear length of the plate hammer. It is recommended that when the mass loss of a single hammer reaches a certain proportion of its original mass (such as 15% -25%, refer to the equipment manual), or when the mass difference between hammers in the same group exceeds the allowable value, replacement should be planned instead of complete wear and tear.

Control feeding and operating conditions: Ensure continuous and uniform feeding, and prevent metal foreign objects from entering the crushing chamber to avoid abnormal impact.

3. Condition monitoring and predictive maintenance

Vibration monitoring: Install vibration sensors at the rotor bearing seat to monitor the trend of changes in vibration velocity or displacement values. The continuous increase in vibration value is the most direct and sensitive indicator of the deterioration of dynamic balance.

Data based decision-making: Combining running time, processing capacity, wear measurement data, and vibration trends, establish a predictive replacement model for plate hammers to achieve planned shutdowns and avoid sudden failures.