The Consequences of Improper Installation: Early Fracture Mechanism And Systematic Prevention Caused by Improper Fit of Lining Plate

The replacement of wear-resistant lining plates is a routine operation in the maintenance of mining crushing equipment such as cone crushers, jaw crushers, and ball mills. However, a often underestimated but extremely harmful problem is that the lining plate cannot achieve a comprehensive and tight fit with the equipment body (such as the crushing frame and grinding cylinder) after installation. This "non fitting" state is one of the core causes of early fracture of lining plates, bolt shearing, and even damage to equipment bodies, and its destructive nature often far exceeds uniform wear.

1、 Definition and causes of the state of "non conformity"

'Non fitting of lining plate' does not refer to complete detachment of the lining plate, but rather to the presence of local gaps or poor contact areas between the back of the lining plate and the supporting surface of the machine body after tightening the bolts. The main causes include:

Improper installation surface treatment: Before replacing the new lining plate, the residual old filling material (such as zinc alloy, epoxy resin), oxide scale, oil stains or uneven damage on the supporting surface of the machine body were not thoroughly cleaned. These residues become the 'cushion layer', preventing the lining board from falling into the design position.

Failure of filling process: For designs that require grouting (using zinc alloy, resin composite materials, or cement slurry) to fill the gaps on the back of the lining plate, if the grouting is not full, there are voids, or the grouting ratio and curing process are improper, it will result in insufficient strength of the filling layer and inability to form effective support.

Deformation of lining plate or machine body: The lining plate itself undergoes deformation due to the release of casting stress or improper transportation and storage, or the equipment body undergoes slight deformation due to long-term stress or thermal stress, resulting in mismatched contour of the mating surface.

Incorrect tightening sequence and torque: Failure to tighten the bolts in the specified diagonal cross sequence in multiple steps, or failure to use a torque wrench resulting in insufficient or uneven pre tightening force. A single point that is too tight may cause the lining plate to warp, forming a "three-point contact" suspension.

2、 Core Failure Mechanism: From Local Suspension to Fatigue Fracture

The fundamental mechanism of early fracture caused by the misalignment of the lining plate is to change the stress boundary conditions during the design of the lining plate, resulting in a sharp concentration of local stress.

1. Mechanical model under ideal fitting state

In the design state, the back of the lining plate is subjected to a continuous and uniformly distributed reaction force from the support surface of the machine body. During work, the crushing force transmitted by the material is converted into compressive stress, which is evenly borne by the entire support surface. The lining plate mainly bears pressure and is in a relatively favorable stress state.

2. Mechanical mutations in non compliant states

When there is a local non fitting area (i.e., a "suspended area"), the back of the lining plate in that area loses support. Under the same crushing force:

The lining plate in the suspended area is like a "simply supported beam" or "cantilever plate", undergoing bending deformation.

Bending deformation causes tensile stress on the working surface of the lining plate and compressive stress on the back surface. However, the tensile strength of most brittle wear-resistant materials, such as high chromium cast iron and certain alloy steels, is much lower than their compressive strength.

At the edge of the suspended area, which is the transition zone from non fitting to fitting, the stress state undergoes a drastic change, resulting in extremely high stress concentration.

3. Crack initiation and rapid propagation

Under cyclic working loads, the tensile stress and stress concentration points mentioned above will become the source of fatigue cracks. Cracks first initiate on the back (tensile side) or stress concentration zone of the lining plate, and propagate inward under each impact load. Due to the limited toughness and fast crack propagation rate of wear-resistant materials, brittle fracture occurs far before reaching the wear life. The fracture surface often exhibits typical fatigue shell pattern characteristics.

3、 Specific consequences and chain reactions

Early fracture of lining plate: This is the most direct consequence. Fracture usually starts from bolt holes, lining plate edges, or internal defects, causing the lining plate to fracture and fail as a whole or in part, resulting in unplanned downtime and loss of spare parts.

Failure of fastening system: Micro movement and bending of the lining plate will generate additional shear and bending stresses on the fixed bolts, leading to bolt shearing or fatigue fracture. The bolt head or broken part may fall into the crushing chamber, causing secondary damage to the equipment.

Equipment body damage: The body without lining protection (such as ball mill cylinder, crushing frame) will be directly exposed to material impact, causing it to be worn through or hit into pits, and the maintenance cost and difficulty far exceed replacing the lining.

Deterioration of production indicators: Broken lining fragments may block the discharge port or mix into the product, causing damage to the crushing cavity line, resulting in a decrease in production capacity, loss of control over product particle size, and an increase in energy consumption.

4、 Systematic preventive and corrective measures

To prevent early breakage caused by improper installation, it is necessary to establish standardized installation procedures and quality control points.

1. Preparation and inspection before installation

Thoroughly treat the contact surface: Use tools such as air picks and grinders to completely remove all old fillers, rust, and burrs on the support surface of the machine body and the back of the lining plate until the metal color is exposed. Check the flatness with a ruler.

Trial assembly of lining plate: Without adding filling material, lift the lining plate into place, preliminarily tighten the bolts, and use a feeler gauge to check the gap between the lining plate and the machine body. Any area where a plug gauge of 0.5mm or more can be inserted must be recorded and processed.

2. Standardized installation process flow

Proper use of filling materials:

Zinc injection: Preheat the lining plate and the machine body, use dry zinc ingots to ensure good fluidity of the molten zinc liquid, and overflow from the injection hole indicates that it is filled.

Resin injection: strictly mix resin and curing agent according to the manufacturer's ratio, use low-pressure injection method, inject from the lowest point, exhaust from the highest point, ensure no bubbles.

Scientific fastening program:

A calibrated torque wrench must be used.

Perform final tightening according to the torque values and sequence specified in the equipment manual (usually diagonally crossing and tightening in increments of three to four times).

After one shift of equipment operation, thermal tightening must be performed to compensate for the relaxation of pre tightening force caused by temperature rise and vibration.

3. Verification and monitoring after installation

Acoustic inspection: Use a small hammer to lightly tap on various parts of the lining plate, and judge whether it fits properly through sound. Clear and consistent metallic sounds usually indicate good adhesion; A dull and hollow sound indicates the presence of gaps.

Establish installation records: Record the installation date, operator, torque value, grouting batch number, and other information of each lining plate to achieve traceability.

Initial operation monitoring: In the initial stage after installation, strengthen the inspection of equipment vibration, noise, and bolt status to promptly detect abnormalities.