Composite wear of hammer head in hammer crusher: mechanism and systematic control of circular arc wear at the striking end

The wear pattern of the hammer head of a hammer crusher is a direct reflection of its working state. Among them, the gradual wear of the striking end (working end) into a smooth circular arc shape is the most significant and characteristic manifestation of hammer failure process. This phenomenon is not simply a reduction in size, but an inevitable result of the combined effects of various wear mechanisms such as impact, cutting, and erosion. Its evolution directly affects crushing efficiency, energy consumption, and equipment stability.

1、 Phenomenon and Impact: From Geometric Shape Changes to Performance Decline

The striking end of a new hammer head is usually designed as square, angular, or with a certain striking plane. After continuous work, its edges first disappear, and then the overall striking surface presents a consistent circular arc contour. The change in this geometric shape has a chain effect:

Decreased impact efficiency: The arc-shaped surface changes the contact between the hammer and the material from "surface impact" or "edge impact" to "point contact" or "sliding contact", reducing the vertical component of the impact force and preventing sufficient transmission of impact kinetic energy to the material, resulting in an increase in the effective number of impacts required for crushing.

Increased energy consumption and decreased output: In order to achieve the target granularity, the equipment needs to run for a longer time or increase the rotor speed, resulting in an increase in power consumption per unit output and a decrease in processing capacity.

Deterioration of product particle size: The decrease in impact efficiency leads to insufficient crushing of materials, an increase in the proportion of coarse particles in the product, and a wider particle size distribution.

Potential risks of rotor dynamic balancing: The differences in wear patterns and weight loss of each hammer head may lead to uneven distribution of rotor system mass, posing hidden dangers for equipment vibration.

2、 Core mechanism: dynamic process of composite wear

The formation of circular wear is the result of the superposition of three dominant mechanisms in time and space:

High stress impact chiseling wear (dominant mechanism)

When the hammer strikes the material at a high linear velocity, the material (especially sharp mineral particles) acts like a miniature chisel, pressing into the metal surface of the hammer head under the action of impact kinetic energy. If the local stress exceeds the yield strength of the material, it will cause micro cutting and plastic plowing of the metal, directly removing the material. This process is most intense at the edges and corners, as their curvature radius is small and stress is more concentrated, so the edges and corners are first rounded.

Low stress abrasive cutting/erosion wear (continuous action)

The material particles that have not been crushed at once, as well as a large number of already crushed particles, slide relatively on the surface of the hammer head, causing continuous micro cutting and scratching. The high-speed rotating hammer moves in the material bed and also bears the erosion of the material flow. Although this type of wear has a small single removal amount, its frequency of action is extremely high, continuously "polishing" the irregular surface formed by impact, making it tend towards a smooth curved surface.

Impact fatigue wear (sub surface failure mechanism)

Repeated impact loads generate cyclic alternating stresses on the sub surface of the hammer strike end, leading to fatigue microcracks. These cracks often originate at the boundaries or defects of hard phases (such as carbides) and gradually expand and connect, ultimately leading to the peeling of the surface material in a thin sheet shape. This process accelerates the macroscopic shape change and causes the worn surface to exhibit brittle peeling characteristics at the microscopic level.

The formation logic of circular arcs: initially, the edges and corners wear quickly due to stress concentration; Subsequently, the wear rate of each point on the striking surface varies due to different motion trajectories and forces, and the protruding points are preferentially ground flat; Under the continuous synergistic effect of impact, cutting, and fatigue, various points on the surface retreat towards the interior of the material at different rates, ultimately evolving into an equal wear surface with relatively balanced stress distribution - that is, a macroscopic circular arc shape.

3、 Analysis of Key Influencing Factors

The influence of influencing factors on composite wear and arc forming process

Materials with high hardness and strong abrasion properties, such as quartzite and basalt, will rapidly accelerate cutting and impact chiseling. The high viscosity and high moisture content of the material make it easy to adhere, exacerbating erosion and wear.

The equipment and operating parameters, rotor linear velocity, are crucial. The increase in speed will simultaneously increase the impact energy and erosion speed, and the wear will increase exponentially. The particle size and uniformity of the feed directly affect the impact strength and frequency.

The hardness of the hammer head material and the process material determines its ability to resist cutting and chiseling; Resilience determines its ability to absorb impact energy and resist the initiation and propagation of fatigue cracks. Materials with high macroscopic hardness but insufficient toughness are prone to brittle peeling and may have uneven curved surfaces; If the hardness is too low, it is easy to be cut quickly. The casting quality and heat treatment process directly affect the uniformity of the internal structure, which in turn affects the consistency of the wear rate at each point.

The thickness, width, and weight design of the head of the hammer affect its kinetic energy and wear-resistant volume. The initial geometric shape of the striking end (square, ribbed, weld reinforcement, etc.) determines the starting point of wear.

4、 Systematic Control and Optimization Strategy

A systematic approach is needed to slow down the rate of circular wear at the striking end of the hammer.

1. Applicability material selection and manufacturing process control

Material selection: For specific materials, seek a suitable match between hardness and toughness for the working conditions. For example, for medium hard materials with strong impact, high toughness high manganese steel or alloy high manganese steel can utilize work hardening effect; For materials with strong abrasion but moderate impact, high chromium cast iron or multi-element low-alloy steel with certain toughness can be considered.

Composite manufacturing technology: using bimetallic composite casting, high hardness wear-resistant materials (such as high chromium cast iron) are used at the striking end of the hammer head, and high toughness materials (such as alloy steel) are used at the handle and core area, so that different areas of a single component have differentiated performance and targeted resistance to different wear mechanisms.

Process quality control: Ensure that the castings are dense and defect free, and obtain the expected metallographic structure and comprehensive mechanical properties through reasonable heat treatment.

2. Optimization of usage and maintenance strategies

Timely turning and replacement: When the striking end of the hammer is worn to a certain proportion of the initial width (such as 2/3), synchronous turning of the same group can be used to continue working using the unworn part of the other end, which is an effective economic measure to extend the total life. Establish a regular inspection and replacement system based on running time or processing capacity.

Ensure correct installation and balancing: When replacing, the entire set must be carried out, and ensure that the total weight difference and relative weight difference of the hammerheads in the same row strictly meet the technical requirements of the equipment manufacturer to maintain rotor dynamic balance.

Control operating conditions: Maintain uniform and continuous feeding to avoid equipment idling or long-term overload operation. Install and maintain effective iron removal devices to prevent metal foreign objects from entering and causing abnormal impact damage.

3. Application of repair and remanufacturing technology

For large and precious metal hammer heads, wear-resistant welding rod welding repair technology can be used to re weld the edges or restore the size on the worn circular arc surface. This technology requires precise welding process control to avoid hot cracking and stress concentration issues.