2 Crushing—Grinding—Sifting—MixingOutside the plant
is a smaller out-building that holds the guts of two enormous “crushers”—large rotating spools with teeth that pulverize the chunky materials to softball size or smaller. The trucks drop their loads into one of two side-by-side pits (one for shale, one for clay) that feed into the crushers below. Once the materials are crushed in a storm of noise and vibration (imagine several anvils in a clothes dryer), they travel up a pair of inclined conveyor belts (a)
to the grinding and sifting operation next to the main plant building.
Grinding and sifting are carried out behind closed doors, simply to contain the epic amounts of dust they create. The conveyor belts outside bring the materials to belts running along the roof ridge, which dump into one of nine bins the size of small cabins. These bins deliver the shale and clay to the grinders, where three wheels rotating in different directions reduce the material to a consistency “like talcum powder,” Belden says. The ground material moves by conveyor to a separate area for sifting. Overhead bins (b) steadily release it onto a series of canted sifting screens (c) that work by vibration— even the catwalks shake jarringly while the system runs. Various gauges of interchangeable screens achieve specific levels of fineness, set to the type of brick being made at a given time.
After sifting, the clay and shale are mixed together. Barium carbonate is added to the mix in measured amounts to prevent unsightly white “scumming” on the brick and to reduce efflorescence during the firing. Belden Brick also adds a mined powder called garnet as a coloring agent for dark red bricks. Once the mixture reaches the first of two large tubs, water is added. In the first tub and then in the second, large augers churn the material vigorously before a belt takes it to what is known as a batch feeder.