High-volume concrete plants need to be operating to make producers money. Managers of profitable plants know how to limit any unnecessary downtime. For operators of drum-batched central mix plants, one of these keys to success is long-lived liner wear.
There are many causes of liner wear. Producers know that abrasive, multi-faced coarse aggregate can take a toll on any liner. But just as demanding can be the tough ambient conditions in which these plants must work.
To meet the customer demands of just-in-time process planning, producers have to operate in wide weather extremes. Filling cold drums with almost steam-like water, or hot drums with ice cold batch water, can also push liners to the limit.
Liner manufacturers have taken on this challenge using the best of what modern chemistry can offer. Typically, the liner manufacturer pours a central batch plant mixer liner in a two-step process. The bottom layer is often designed to be stiffer to maintain closer contact with the drum's inner surface following welding. The upper layer, often a different material and color, is designed to be less brittle and more resilient to withstand impact.
Despite the greatest care in the process, the two-pour method may allow moisture and/or other contaminants to deposit on the interface zone. When this happens, the bond between the two layers can be weakened.
This condition is similar to what happens when a piece of plywood is continually positioned in wet and humid weather. Layers first slightly separate and eventually, further exposure causes the problem to progressively worsen. In the case of a dual-poured mixer liner system, the separation is called delamination. When this happens, the condition will eventually require the liner's premature replacement.
Randy Kloos has witnessed liner delamination at a few of his customer's plants. Kloos is president of Kloos & Associates, a Craig, Colo., distributor of material handling equipment and supplies for concrete and aggregate plants. Though rare, when delamination starts, it becomes a problem quickly.
Kloos believes that concerns of peeling layers of urethane and the unnecessary expense of repairing the mess may be a thing of the past. He's been experimenting with a new liner product, Kryptane Evolution. This is a new, single-pour urethane liner specifically developed for concrete plant mixing. The material is a single, multi-plate enforced liner. The product is a dramatic change in application, moving from a dual-durometer style of liner.
When delamination reduces the life-expectancy of the liner, a producer suffers a dramatic budget problem. “The repair process requires a tremendous amount of additional labor to replace the damaged lining area,” Kloos says. “If the entire drum's interior surface has the problem, the repair process often requires six people working around the clock. The process can take three days.”