Wear Liners — What’s Right?
This has been a frequent question asked of us. I answered it a few years ago in our "snail mail" newsletter but, now that you are bringing it up again, I think it deserves to be discussed once more.
Liners can provide abrasion resistance, corrosion resistance, improved sanitation and clean-out, and improved flowability. Although my answer here will focus on abrasion resistance enhancement in chutes, transitions, spouts, and hoppers, it is important to keep in mind that liner selection will offer inherent differences with regard to the other above parameters.
We all have struggled at times with liner selection, comparing useful life with or without liners to upfront capital cost. The applications for liners are diverse in bulk material handling. Many of the materials handled impose potential severe wear in areas of impact and sliding.
As it applies to these applications, abrasion is the gradual removal of a surface as a result of contact with another material. In the case of liners, this can be imposed by the impact or the sliding of materials such as aggregates or whole grain or by the impact of high-velocity dust particles on the exposed surface. More specifically, this wear can be classified into the following categories:
- Impact abrasion. Removal of a wear surface by the spalling, gouging, or cutting action of impacting abrasive particles.
- High-stress abrasion. Removal of a wear surface in small quantities by the sliding, cutting, and plowing action of smaller abrasive particles under high loads.
- Low-stress abrasion. Removal of a wear surface in small quantities by the sliding, cutting, and plowing actions of smaller free-flowing abrasive particles under lighter loads.
Design of the chute, spout, or hopper providing lower-velocity, minimal directional changes, or a dead box to allow material to impact material can often minimize wear, but space limitations, required clean-out, or the physical properties of the material being handled will make proper liner selection and proper installation a must.
Although there are variances within these categories, the more commonly used liners in bulk material handling fall into these categories:
- Abrasion-resistant steel (AR)
- Ultra-high molecular weight polyethylene plastics (UHMW)
- Ceramic combination composite.
I’ll try to break down the advantages and disadvantages of each as I see them.
- Abrasion-resistant steel (AR). The advantages are medium cost, wide availability of variance in hardness and alloy composition to custom fit the application, workability and ease of installation, and relatively low coefficient of thermal expansion. The disadvantages are high weight per square foot, noise during impact, and corrosion.
- Ultra-high molecular weight polyethylene plastics (UHMW). The advantages are low cost, workability and ease of installation, low coefficient of friction, low water absorption minimizing potential freezing of material to the liner, low weight per square foot, noise reduction, and resistance to corrosion. The disadvantages are relatively low resistance to abrasion, and relatively high coefficient of thermal expansion.
- Urethane. The advantages are medium cost, wide availability of variance in hardness and abrasion resistance characteristics, workability and ease of installation, low weight per square foot, noise reduction, resistance to corrosion, and relatively low coefficient of thermal expansion. The disadvantages are toxic fumes from burning, and low abrasion resistance in higher velocity pneumatic applications.
- Ceramic. The advantages are excellent resistance to abrasion and extended useful life, low coefficient of thermal expansion, resistance to corrosion, and high temperature applications. The disadvantages are relatively high material and installation cost, and subject to breakage.
- Ceramic combination composite. The advantages are enhanced resistance to abrasion with energy absorption of the urethane, resistance to corrosion, noise reduction, and relatively low coefficient of thermal expansion. the disadvantage is relatively high material cost.
These bullet points are not meant to be an exhaustive list but should provide enough information for you to compare liners for your application.
Answered by Tim Lease, P.E., President of WL Port-Land Systems Inc.