Figure 6-1.-Primary unit.Most crusher and screening units plants areequipped with some type of feeder to regulate the flowof material into the crusher unit. A heavy-duty aprontype of feeder (fig. 6-3) is usually used to feed theprimary crusher. Raw materials from the pit or quarryare deposited into the hopper of the heavy-duty apronfeeder that moves the material onto the deck of thevibrating grizzly. The rate of flow of the feeder belt iscontrolled by the operator using the START and STOPbuttons located on the control panel.Figure 6-2.-Jaw crusher.As material is moved out of the apron feeder, it isprocessed across the vibrating grizzly. The deck isnormally a bar type of screen with a 1 1/2-inch fixedopening. It screens out material smaller than 1 1/2 inchesand routes the oversized material through the jawchamber to be crushed. The undersized material isrouted through a chute to the undercrusher conveyer.From this point the material can join the jaw crusherproduct by closing a flop gate. This material can bedirected through another chute (by closing a flop gate)and routed to a by-product stockpile.The vibrating grizzly prescreens material that isalready down to size, allowing the material to bypass thejaw crusher. The grizzly also dry-cleans the material byvibrating it vigorously. The flop gates on the grizzlyenable the operator to select and decide what to do withsmaller particles.Oversized material is routed through the jawcrusher where it is gradually reduced in size by a seriesof elliptical- downward crushing strokes and is thendischarged onto the undercrusher delivery conveyerbelt. The product size is determined by the productsetting adjustment made at the discharge end of the jawplates.The hourly rate of production to be obtained from agiven size jaw crusher depends upon a number ofvariable factors:1. The toughness of the raw material.2. The product setting.3. The reduction ratio. (The size of the material fedto the crusher compared to the product size.)6-2
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