To browse Academia.edu and the wider internet faster and more securely, please take a few seconds to upgrade your browser.By using our site, you agree to our collection of information through the use of cookies.Roll grinding is economical but limited to materials which are fairly dry and low in fat. 2.4 Cutters.
Feed Manufacturing Technology V Upgrade Your BrowserUnless the fisheries biologist understands and specifies the activities of the feed mill and its laboratory, profitable fish farming will be a matter of chance. By one or more of these processes, a wide variety of ingredients can be prepared into a standardized product. Since most fish have size and texture preferences and often react to colour, odour, and flavour, processing research is an integral part of fish culture. Many feed mills pass all incoming ingredients through a grinder for several reasons. Small fish and fry require plankton-size feeds available in dry form as a meal or granule. Fry have been killed because of their inability to pass through the digestive system large pieces of connective tissue and bone present in dry animal byproducts, or hull fragments found in cottonseed meal and rice bran. On the other hand, dust or fines may become colloidal suspensions in water, so dilute that several mouthfuls carry little nutritive value. Feed Manufacturing Technology V Manual And MechanicalIt is accomplished by many types of manual and mechanical operations involving impact, attrition, and cutting. Hammermills. ![]() The number of hammers on a rotating shaft, their size, arrangement, sharpness, the speed of rotation, wear patterns, and clearance at the tip relative to the screen or striking plate are important variables in grinding capacity and the appearance of the product. Heat imparted to the material, due to the work of grinding, is related to the time it is held within the chamber and the air flow characteristics. Impact grinding is most efficient with dry, low-fat ingredients, although many other materials may be reduced in size by proper screen selection and regulated intake. In this mill, the drive shaft is positioned vertically and screens and hammers are positioned horizontally. Material successfully reduced in size to the diameter of screen holes or smaller, are carried by gravity outside the mill and thence by air or conveyor to storage in make-up bins. Over-size particles, not easily broken, drop through the mill and may be re-cycled or discarded. Thus foreign materials, such as metal and stones, are discharged before they are forced through the screen causing damage. Grinding is done between two discs equipped with replaceable wearing surfaces. One or both of these discs is rotated; if both, they rotate in opposite directions. When one disc is rotated, and the other stationary, the assembly is used for shredding and deferring. Often materials which have been coarsely ground by other mills, are passed through an attrition mill for blending or smoothing out an ingredient or mixture containing liquids which may have clumps. The discs of an attrition mill are generally in a vertical position so that materials not capable of reduction can pass by gravity out of the grinding area. Roller Mills. These are smooth or corrugated rolls rotating at the same speed set at a pre-determined distance apart with material passing between the two. A tearing action may be added by operating the rolls at different speeds and by corrugations which are different for each roll; i.e., the top roll may have off-radial spiral corrugations and the bottom roll lateral corrugations. This last type, called a Le Page cut is used in making granules from hard pellets, as it provides a breaking surface without much impact to cause dust. Roll grinding is economical but limited to materials which are fairly dry and low in fat.
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