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Washing up: vibrating wash screens
June 1, 2008 By: Leon Luadzers Pit & QuarryIt can be argued that a wet screen is the most important machine in an aggregate washing and classifying system. The wet screen is typically one of the first machines used in the processing of aggregates. Vibrating screens are an effective and economical method of sizing and classifying aggregates. The vibrating action of the screen stratifies feed material, then screens and separates it through the chosen media openings.
 A spray package for wet screens includes spray pipes with nozzles, manifold with control valves, the support structure and connection piping. |
Many specifications require aggregates to be washed and free of deleterious material. A vibrating screen is an efficient tool in washing aggregate. A wash screen can remove dust, dirt or clay off aggregate and size the aggregate at the same time. In many cases, a vibrating wet screen is the only piece of processing equipment needed to create a sized and washed product.
Design types
Wash screens are typically available in an inclined or horizontal screen design, based on the type of aggregate processing system. A majority of stationary plants will use an incline screen that typically use stationary wet systems, while horizontal screens are used in many portable plant applications and utilize live mounted wet systems.
Incline screens, like the IS or TS screen, typically have higher carrying capacities than horizontal screens. The material travel rate is higher for incline screens, resulting in reduced material bed depths. The screening efficiency is improved by the reduced material bed depth and generally improves the screen's ability to wash aggregates.
Horizontal screens, such as the FS screen, can sometimes provide higher screening efficiency rates than incline screens. More of the screen opening is exposed on the horizontal deck, increasing the opportunity for fines to pass through.
Grease-lubricated vibrators are the best choice for wet screen applications. The grease design drastically reduces the opportunity for water to enter the vibrator and contaminate the bearings and other internal parts. The modular vibrator, which relies on grease lubrication, is an excellent choice for wet applications. The modular design essentially eliminates entry points for contamination and has up to 40 percent greater bearing life than traditional oil lubricated vibrators.
 A Metso Minerals wash screen with an MV4 modular vibrator. |
Effective spray package
Both types of wash screens must have a good wet spray package in order for it to be effective. A spray package includes the spray pipes with nozzles, manifold with control valves, the support structure and connection piping. Whether you have an inclined or horizontal screen, the complete wet system should be engineered and assembled in the factory. A factory-built system will provide the optimal aggregate washing and classifying package for the producer.
The operator must provide clean water with adequate pressure in order for the wet system to perform well. The typical wash application requires 3 to 5 gpm per tph of water at 30 to 40 psi. For example, at a feed rate of 500 tph the spray system should be supplied with about 2,500 gpm of water at 40 psi pressure. Keeping in mind, it is easier to adjust back on the gpm and psi if they are too high. But if you don't have enough water or pressure at the beginning, it can result in a dirty aggregate end product.
The combination of a good vibrating screen, factory-installed wash system and adequate water source will create an efficient and effective washing and classifying system for aggregate products.
Metso Minerals
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www.metsominerals.com
Leon Luadzers
is capital equipment manager for Metso Minerals, and part of the company's Vibrating Equipment Team in Columbia, S.C.
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