Extrusion Equipment Extrusion processing technology has been used in food industry for more than 100 years, but it was used in feed processing industry in 1950s. At the beginning, it is mainly used for processing pet feed, pretreatment of animal feed and raw materials to improve the digestibility and palatability, and production of urea for ruminant protein supplement. In the 1980s, extrusion technology became the fastest developing new feed processing technology in foreign countries. It has incomparable advantages over traditional processing methods in special feed, aquatic feed, early weaning piglet feed and feed resource development. In recent years, due to the development of extrusion processing technology and the improvement of processing technology, the price of extruder has decreased, and the further research on the physicochemical properties and nutritional value of feed by extrusion technology, the application of extruder in feed industry has been further promoted.
Basic knowledge of extrusion processing First. Characteristics of extrusion processing Extrusion processing mainly has the following advantages: 1.It can work out different density products, meet the needs of different breeding objects. According to the density requirement of the product, the structure, parameters and operation of the extruder can be changed. 2.It can be manufactured in different shapes and sizes. The shape and size of the product are controlled according to the structure, shape and size of the die hole. 3.It can be used as the pretreatment of feed material to make starch gelatinize, destroy or reduce the activity of anti-nutritive factors (soybean). 4.It can be used for sterilization. High temperature and high pressure during extrusion can kill all kinds of microorganisms and bacteria. If properly stored, the product can be stored for a long time. 5.It can be used as feed material to develop. Feathers and animal slaughtering waste can be utilized as feed protein resources by extrusion processing. 6.It can improve the digestibility and palatability of feed products. 7.It can improve the stability and durability of aquatic feed, reduce waste and pollution of water quality. 8.Extruding process will not discharge waste water and gas, so it will not cause environmental pollution. Although extrusion processing has the advantages mentioned above, it also has obvious disadvantages. Extrusion processing consumes high electricity. The high temperature and high pressure produced in the extrusion process will seriously damage the heat-sensitive nutrients in the feed, and the content of vitamins and other nutrients in the extrusion products is much lower than the growth needs of feeding animals. In addition, the high cost and low bulk density of expanded products may reduce the actual feed intake of feeding animals, thus reducing the rate of weight gain and increasing the cost of breeding. Therefore, expanded feed is not suitable for all the breeding objects, but mainly suitable for high value-added breeding products. Second. Principles of extrusion processing Extrusion processing is a process in which the shape, internal structure and properties of materials are changed by placing them under high temperature and pressure in the extrusion chamber and then releasing them to normal pressure. Processing method is by means of extrusion machine screw rotation forward thrust will be produced by the material, material by mixing in the process, the action of friction, shear and extrusion, makes the temperature and pressure of the extrusion cavity material greatly increased (temperature can reach 120°C to 200°C, pressure in 1 MPa above, due to the high pressure effect to avoid the water boiling). Materials at high temperature and pressure, starch gelatinization, protein denaturation, some of the naturally formed toxicity, for example, soybean trypsin inhibitor was destroyed, a large number of microorganisms in the product was killed, and the storage period can lead to the deterioration of all kinds of enzyme activity passivation. In this process, in order to avoid great damage to the nutrient composition in the material, the retention time of the material in the high-pressure section of the extrusion chamber should not be too long, generally only 5~10 seconds. Then from a certain shape of the die hole extrusion, from high temperature and pressure suddenly reduced to atmospheric pressure, so that the material rapidly expand, free water in this pressure difference under the sudden evaporation. Water can expand by about 200 times, and grain by several to a dozen times. Some products do not need a large expansion rate (such as submerged fish feed), can be used in the extrusion chamber at the end of the outlet to reduce the pressure and temperature (the temperature can be reduced to no more than 100 degrees), in order to achieve the extrusion products less expansion or not expansion.