Hoyt Man Wisdom

The Impact of “Impact” Wear

Wear-sideTransporting, crushing, conveying and the screening aspects of all aggregate processing facilities deal with localized and, in many cases, severe wear areas. Areas of aggregate impact upon processing components can create unusually rapid wear where aggregate is transferred from one point to another in the processing flow. Depending upon the “transfer mode” and the impact media in use, the “impact of impact” can be minimized. Other than aggregate conveying, two specific “modes” of aggregate transfer are involved in almost all aggregate processing plants. This is either an “impact” transfer or a “sliding” transfer mode. Both of these “modes” of material transfer can result in an unusually high rate of wear to the transfer media’s surface, although, believe it or not, correct impact applications can be beneficial — both in transferring and in efficient aggregate screening. The following information addresses the effects of aggregate impact upon screening and material transfer surfaces.

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Throughput & Screening Efficiency

ScreeningEfficiencyThese two terms cannot be considered without regard to the screen media’s wear-life. Depending on the particular screening media in use, there is sometimes a fine line between efficiency and wear-life. The Vibrating Screen Manufacturers Association (VSMA) or the manufacturer of your vibrating screen can accurately determine the screening capacity needed on each deck for your aggregate separation requirements. These screening efficiency calculations involve aspects such as tons per hour, top size feed, open area of the screen media, and the inclination of the vibrating screen. Based on this information, the required square footage of screening surface can be determined. There are, however, several additional options to consider when examining the screening efficiency of your aggregate screen and screening situation.

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Blinding

Deck blinding is a real challenge for many aggregate operations. Soft, powdery limestone is notorious for bad blinding, but this problem can occur in almost any type of aggregate. Dust-sized particles often deposit themselves on flat surfaces inside a shaker, including the tops of the screening wires. Add a little moisture and the deposits become like hard cement. Please refer to the diagram at right.

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Plugging/Pegging

pluggingThis is the occurrence of near-sized material trapped in the openings, or apertures, of the screen media’s openings. This “near-sized” material attempts to pass through the openings, but because of its particular shape, this aggregate cannot freely travel over, or freely pass through, the apertures. Therefore, these aggregate particles become “wedged” in the openings and cannot be dislodged, creating the plugging or pegging conditions.

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Wear of Screening Surfaces

Wear-sideWear is a naturally occurring process in all aggregate producing plants. Wear begins the moment that aggregate comes into contact with any and all processes in aggregate producing facilities. Abrasion or friction of the aggregate coming into contact with steel or other synthetic surfaces manifests the wearing situation, and this wear occurs on all surfaces “where the steel meets stone.” Loader buckets, crushers, bins, chutes, conveyor belts, transfer points and screen media are most subject to rapid wear caused by the aggregate. These are the primary high-wear areas involved in aggregate production. Specifically, however, we would like to address screen wear.

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