The wear life of components such as rubber liners is an important part of any wet plant operation. The cost of wear parts and the downtime associated with repair can be a significant drain against site profits.
Natural rubber has become a standard liner material in many applications because of its ability to resist abrasive particles like sand. Abrasive particles strike the resilient rubber surface, which returns most of kinetic energy to the particle. It is this ability of the rubber to deform under load, absorbing an impact and then returning the energy from the impact back to the particle, that make it a popular liner choice for aggregate processing equipment.
In most cases, a rubber liner is the most cost-effective wear material.
Rubber liner inside the inlet of a cyclone.
How To Select Rubber Liners
Reviewing several factors can help you select the most appropriate wear surface for an application, but determining the driving wear factor can be difficult. The factors below are for natural rubber liners, as these are common in the industry.
Size and Weight
The size and specific gravity (weight) of the individual particle is an important consideration when selecting a wear liner
The rubber deforms as the particle hits the surface and absorbs the kinetic energy. The resilient nature of rubber returns most of this energy to the particle, causing it to rebound.
When the rubber thickness and composition is correct, the liner will experience little to no wear and no permanent deformation. However, if the particle momentum is too great relative to the rubber thickness, the impact force cannot be absorbed and the rubber may cut or tear.
Slurries with a majority of coarse or high specific gravity material can overcome the rubber’s ability to rebound the material.
The other part of momentum is the velocity in which the particle is traveling.
Rubber liners have to have enough time to rebound to avoid damage. When above the critical speed, they are unable to recover and absorb energy. In this case, the rubber’s resilience cannot be used to its full extent, and the surface may deteriorate more rapidly. For velocities above 10m/s (30ft/s), consider an alternative wear surface.
Frequency of Impact
The ability of the rubber to rebound from the impact is directly related to its ability to provide a wear surface and not tear.
With slurry applications, the density of the slurry represents this. Low-density slurries have a decreased frequency of impact in addition to the liquid providing a limited buffer. High-density slurries will increase the wear rate though shear number of impacts, which decrease the rubber’s ability to rebound.
Density and velocity can play a major role in the wear life of any material. High-density and high-velocity slurries should be avoided for all wear surfaces.
The shape of a particle will affect the rubber’s ability to absorb the kinetic energy from surface impact.
Material with sharp edges can cut or tear the rubber on impact, especially in high-density applications. Material crushed prior to the wet process part of the system can create rough or jagged profiles. In many cases, handling the material with conveyors and screens prior to the wet plant can reduce the sharpness of the particle.
Throughout the course of this stage, the sand is subject to a level of attrition. As the material goes through these transfer and screening points, the sand rubs against itself, mainly attacking the sharp edges and reducing the surface classification to “rough”. Material that maintains an extremely jagged profile will require an alternative liner material, such as a higher durometer (or harder) rubber, ceramic or hardened metal.
Angle of Impact and Sliding Wear
The angle of impact of the particle relative to the wear surface is of great importance in designing chutes, hoppers and rubber linings in general.
The effect of different angles on wear rate can be significant. At a 90° impact angle, resilience is the major factor in resisting wear, but as the impact angle reduces to around 50°, tear resistance becomes more important.
At very low impact angles, a flat, natural rubber with a high slide wear resistance best handles slurries. This applies to applications where the abrasive force is tangential or in plane to the surface.
Slurry applications have a changing angle of impact, especially within pumps. Piping and other slurry flow areas should avoid sharp changes in direction.
Rubber Hardness and Physical Properties
In broad terms, harder rubbers (higher durometer) are preferred for resisting the high impact/cutting forces that often occur when handling coarse and sharp materials.
A low durometer rubber gives excellent results when used in abrasive slurry service or sliding abrasion where fine to medium particles are being handled. Other physical properties can often play a significant role in optimizing performance.
The key to specifying the correct rubber is exploring the application to determine the major wear factor and selecting the best combination of properties. In a greenfield application, it can be difficult to determine upfront which characteristic it the most predominate. Nearby applications can provide insight to the right choice.
Alternate Wear Material to Natural Rubber
Natural rubber provides the highest, most cost-effective wear life in the majority of sand applications, even when the material is manufactured sand. In applications where the wear life of natural rubber is not acceptable, there are alternative wear materials available.
High Durometer Rubber
When the shape of the material and material size is a high factor in wear, a high durometer rubber can provide greater rip and tear resistance. In some applications, the benefit can be one to three times longer wear life, but high durometer rubber can be limited in effectiveness in some high-density processes.
Hard metal surfaces resist tearing abrasion but are susceptible to high impact-caused wear. The slurry interfacing with a metal surface is much like using sandpaper. A person would get tired and the sand paper would wear out before any serious damage was done, but the constant flow of a slurry will leave a mark. The hardness of the material is a key driver of wear on a metal surface. The life a crusher wear liner faces can indicate if a hard metal liner will provide a good solution for wear life.
Ceramic liners offer good wear resistance and can typically offer two to four times longer life over natural rubber, but these type of liners can be damaged in large particle and high-impact applications. Ceramic liners can be difficult to use around moving parts and complex shapes.
As a default, natural rubber liners will probably be utilized on your wet processing equipment unless there is definitive knowledge of wear issues. Nearby deposits, test pilot plant results, laboratory tests and other indicators can help provide important information up front and determine if an alternative wear material is required. When evaluating a new deposit, keep the above information in mind.