Figure 6-3.-Apron feeder.4. The gradation of raw material.5. The extent of wear to the corrugated surfaces ofthe jaw plates.6. The rate of feeding.Feeding problems may develop due to irregularshapes and unwieldy nature of quarry run rock. Feedingproblems can drastically reduce production. Somecommon problems are blocking, bridging, choking, andpacking.Blocking occurs when an oversize rock settles overthe jaw opening and stops the flow of incoming material.The jaw continues to operate but no crushing takesplace. To prevent blocking, you should let the maximumsize of material processed be 2 inches less than the jawcrusher size. Blocking can be controlled or eliminatedby using a scalping grizzly to prescreen material. Foroptimum production, the ideal feed size is 75 percent ofthe jaw size.Bridgingoccurs when two rocks, within themaximum size, arrive at the same time. The two rocksinterlock and bridge the jaws open. When this occurs,all production stops. When large rocks approach theopening, they should be fed individually to preventbridging.Chokingcontinuallyoccurs when the jaw chamber isoverfilled. This creates an overloadcondition and causes the engine to lug down and maydamage the equipment. For optimum production, theoperator should try to keep the jaw chamber 75 percentfull.Packing occurs when feed material cakes and packsin the crusher chamber. Plastic material, such as clay,may become sticky and cause this problem. Packing canbecome so severe that it completely stops production.Packing can be reduced or eliminated by prescreeningor prewashing the material. In most cases, the mostpractical solution is to wet down the materialthoroughly. Then process the material even though it isalmost in the form of a slurry.The jaw crusher can produce at a rate of 55 to 185tph, depending upon the product setting and thetoughness of the material being crushed. The maximumproduct setting is 5 inches, and the minimum setting is1 1/2 inches.WARNINGKeep all parts of your body out of the jawcavity when you are operating or adjusting thejaws.6-3
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