In the 1930s, the processing of grain for the first single-screw extruder come out, it began to be used to produce extruded corn. During World War II, Japanese used it in the production of compressed rations. In the 1960s, continued single-screw extruder began after a twin-screw extruder, and used in the field of food processing. 50 era, the United States extrusion technology to feed industry, mainly for processing of pet food, animal feed pretreatment to improve digestion and palatability, and the production of ruminant protein feed supplement the feed of urea (Loscicki, 1982) . In the 1980s, extrusion technology abroad has become the fastest growing new feed processing technology, its special processing of animal feed, aquaculture feed, early post-weaning feed materials and resources development with the traditional method of processing unparalleled advantages . International representative Extruder manufacturer in addition to Denmark's SPROUT-MATADOR, the United States Insta-pro, Wenger and Anderson, Germany, KARL, Buhler of Switzerland, among others.
From 70s to start study of food extrusion technology and extrusion machines. In 1980, Beijing Institute of Food imitation of the first self-heating-PJ-1-puffing cereal extruder. Wuxi University of Light Industry in 1982 from France's Clextral the introduction of a BC-45-type twin-screw extruder, the beginning of the extrusion processing techniques (such as the Hui-wen. 1999). At the same time, many manufacturers have been from the world's major companies have introduced advanced extrusion equipment. In the introduction of foreign equipment at the same time, some of the equipment, feed production plant has also produced different types of extrusion equipment, representative of the domestic manufacturers have a Extruder shepherd Group, Zhengchang Group, Yang Beijing Hyundai Engineering Machinery Technology Development Co., Ltd. .
With the Expander increasingly used in actual production, must raise the level of design Expander at the same time, raise the level of use. This article only twin-screw extruder, and other characteristics of the structure of the principle to make a brief description. Expanded want to be helpful to the user's machine.
1. Twin-screw Extruder working principle and advantages
1.1 pairs of Screw Extruder structure
With materials by conveyor to the quenching and tempering equipment, materials in the conditioner in high temperature steam quenched by diarrhea trough Expanded access to institutions, in a pair of parallel engagement of the screw pump sent from the shape of a certain mode of the hole Cut into tablets out in an instant.
1.2 Pairs of Screw Extruder principle Expanded
Figure 2 shows a typical twin-screw extrusion machine extruded body by a pair of parallel engagement of the screw push forward material, the screw is divided into three sections: expected to lose, Compression melting, Uniform section. Lost in the material, material from the hopper into the suspected plane, with the turning of the screw, along the forward direction of the spiral groove transportation, and gradually compacted. Compressed into the melting, due to structural changes in the spiral, increasing the pressure, due to come from outside the barrel, as well as heating materials in two between the screw and screw and barrel to the strong mixing, blending, shearing , The temperature of material to begin melting, until all the melting. As the spiral groove further room for smaller, the materials to further boost heating, cooking has been so full of raw materials starch paste, fat, protein degeneration and a series of complex biochemical reactions, both organizations, arrived in uniform, by diverting the board "" Puffing out of the cavity material evenly assigned to a template, the pressure at this time is usually 3 ~ 6Mpa (in accordance with the requirements of the Expanded), the temperature can reach 150 ~ 200 ℃, because of the closed sleeve in this high pressure over the squeeze Under the pressure of saturated steam temperature, so water will not evaporate quickly when the material from the shape of a certain mode of the hole in an instant out of time, the rapid release of pressure, rapid evaporation of free water, materials resulting expansion of the water from the rapid loss of material, So that the product quickly cooled to around 80 ℃, which was cured stereotypes, and to maintain its shape after expansion.
1.3 Pairs of Screw Extruder features
Twin Screw Extruder relatively late development in China, because of its Expanded the scope of the larger changes in the characteristics of raw materials, the need to screw speed in a larger range of adjustment than the principle of single screw confidential Expanded much more complex, in particular There are larger structural differences, in particular the barrel, screw, thrust bearings gear box layout of the complex, resulting in an increase in the cost of equipment, such as single screw used a belt drive, and the use of twin-screw extruder gear box drive , Both in manufacturing efficiency and drive quite different. (Twin-screw and single screw-expanding
Machinery distinction see table 1).
2. Twin-screw extruder in aquatic feed
Extrusion is the process of raw materials at high temperatures, high pressure, the moment of the aging process, and set transport, crushing, squeezing, mixing, shearing, forming and milk in one, and the process can be thick, high-fat, high water Copies of the raw materials, production processes are generally beyond compare, it was increasingly used for aquaculture feed, pet food, culture, and other high-end specialty food and feed production.
2.1 Processing process
Micro-crushing raw materials → ingredients, mixed-puffing → → → pelletizing spray drying → → → cooling measures package.
Expanded material advantages of aquatic products 2.2
2.2.1 good water resistance
Expanded in the process of forming a network structure of expanded aquaculture feed particles in the water very good stability, whether floating or sinking feed, feed soaked in water for 12 hours can not keep collapsing, can maintain the water quality of culture, not only significantly reduce feed The waste, but also good for the health of aquatic animal growth provides a good environment.
2.2.2 higher peptic
Expanded materials in the process of high temperature and high pressure, strong shearing of starch, protein, and other material generated by the change to improve the digestibility of such substances, puffing aquatic feed starch gelatinization degree in general more than 85%, while the ordinary Hard particles aquatic feed only about 40%, only the starch digestibility on the hard particles is much higher than ordinary materials and Fisheries; strong role could squeeze some of the compact of cellulose, keratin, such as degradation of the parcel so that it can not digest The nutrients can be released so that the substantial increase in digestibility.
2.2.3 excellent palatability
Expanded appropriate course of the temperature and pressure so that the role of the feed particles and finished with a porous texture characteristics of the uniform, and some have a fragrance material, an increase of feed attractant, to stimulate the appetite of the fish, increased feed intake.
2.2.4 broadens the scope of the use of raw materials
The food industry, brewing industry, agriculture and other industries due to the waste contains excessive moisture, grease or cellulose instead of easily processed into other forms of aquatic feed, and the twin-screw mechanism of expanded them to do to make the best use, enriched Feed resources.
2.2.5 facilitate the management culture
Feed not only able to adapt to the fish used to feed, while farmers make an accurate understanding of aquatic animal feed, in a timely manner to adjust the amount. Expanded use of feed to reduce the breeding of the harm the water quality of nutrition, can reduce the frequency of changing the water, for water, and reduce the amount of oxygen-increasing.
2.2.6 improved the safety of animal feed
Extrusion process to be effective in addition to the pathogenic bacteria in raw materials and raw materials in the passive part of the anti-nutritional factors, diet can reduce the amount of drugs. Expanded aquatic products than it expected other forms of aquatic feed more secure, this security is the result obtained through physical methods, without adverse side effects. Greatly reducing the drug residues in aquatic products for human food safety is of great significance.
2.3 aquaculture feed twin-screw Extruder choice
In new and retrofitted aquatic feed production line, the first thing to consider twin-screw Extruder selection, based on production capacity and investment choices to match the size of the Expander; in the transformation of production lines should also be considered when the original mill, cooler, dryer The effect of production and production capacity can meet the requirements of the selected Expander, it is necessary to fully consider the possibility of using existing equipment in order to reduce investment.
2.3.1 Expander the effects of expanded
Extruder selected aquatic feed production to meet the effects of expanded several of the following:
A. particles forming rate of ≥ 99%;
B. particles floating rate = 100%, the rate of sinking ≥ 99%;
C. uniform particle size, color, with very good water resistance;
D. floating in the water and is expected to maintain 10h, sinking in water is expected to maintain 3h not bad, leave.
2.3.2 Extrusion machine of life
Different manufacturers of twin-screw Extruder due to transmission, structural characteristics, the use of materials, processing technology, and so different, very different life. Extruder in the selection, first of all should pay attention to the overall design of the structure is reasonable, the parts manufacturing process, the selection is excellent, the wearing parts, such as how to wear; followed by the power transmission sector should be noted that the design is reasonable, is effective in reducing transmission process The energy consumption.
2.3.3 Operability
Extrusion is the process in general semi-automatic or manual operation, the operation to consider the twin-screw Extruder labor intensity of the operation, convenience, contingency measures are completed properly. If large-scale twin-screw extruder is equipped with a lifting spiral and demolition tools in order to replace easily spiral or barrel; whether the spilled material in the blocking device in order to rule out the plane when the conditioner of material from its extruded into the body; puffing outside Heating measures are completely safe and reliable; Jacket whether test pressure testing, and so on.
Several special injection molding machine screw brief (c)
(A) PC material (PC) features:
1. Non-crystalline plastic, no melting point, glass transition temperature of 140 ℃ -160 ℃, melting temperature of 215 ℃ -225 ℃, forming temperature 230 ℃ -320 ℃;
2. Viscosity, high-temperature processing, and narrow the scope and easy to break down and use screw to avoid overheating;
3. Sensitive to water, high temperature resin easy hydrolysis, drying temperature 120 ℃ -130 ℃, 4 hours.
Selected parameters:
1. L / D for its thermal stability, viscosity of the great features to enhance the effect of plastics as much as possible to select a large aspect ratio;
2. Because of its wide scope of the melting temperature, feeding a long paragraph, all of paragraph short, medium compression ratio, in order to increase the effectiveness of plastics may choose to use plastic barrier over-head;
3. Such as flame retardants, or to join the PC glass fiber reinforced materials, may choose to wear the use of corrosion-resistant high-quality stainless steel screw material, as well as three small pieces.
(B) PMMA (plexiglass) features:
1. Tg 105 ℃, melting temperature is greater than 160 ℃, decomposition temperature of 270 ℃, forming a wide temperature range of 180-250 ℃;
2. Viscosity, liquidity is poor, which is more sensitive to shear rate, processing, strictly control the temperature;
3. Bowl temperature of 240 ℃ -250 ℃, than 260 ℃ stranded when the time is not more than 8 minutes;
4. More absorbent, drying temperature 80 ℃ -90 ℃, 3 hours.
Selected parameters:
1.L / D select the aspect ratio 20-22, gradually taking the general screw-L1 = 35-45%, L2 = 35-40%;
2. Compression ratio ε general admission 2.3-2.6;
3. For some of its hydrophilic, the screw in the use of front-end structure of the mixing head.
(C) PA (polyamide), the common PA6 (nylon 6), PA66 (nylon 66) features:
1. Crystalline plastic more and different types, nor its melting point, melting point on the narrow scope of the general PA66 its melting point 260 ℃ -270 ℃;
2. A low viscosity, good liquidity, the more obvious point, poor thermal stability;
3. The higher water absorption, the dryer temperature 80 ℃, no more than 120 ℃, time to 16 hours. If raw materials exposed to air 8 hours, use a vacuum oven at about 105 ℃, 12-hour period.
Selected parameters:
1.L / D longer than the 18-20 select the type of mutation screw;
2. 2.5-3.5 select the compression ratio general, to prevent overheating decomposition h3 :0.067-0 .089 D;
3. Because of their low viscosity, the apron off and barrel should be a small gap of about 0.05-0.08, screw and barrel space 0.08-0.12;
4. Nozzle can be equipped with self-locking spring-mouth radio.
(D) PET (polyester) Chemical Name: PET characteristics:
1. Melting point of 250 ℃ -260 ℃, blow molding PET wider temperature, about 255 ℃ -290 ℃, enhance the level GF-PET up to 290 ℃ -315 ℃, and so on;
2. A high melting point and low viscosity, adhesion and metal, easy hydrolysis;
3. Hydrophilic, viscous material at a high temperature of the water sensitive, dry temperature 150 ℃ -160 ℃, 4 hours or more.
Preferences:
1.L / D generally take 20-22, three distribution L1 = 50-60%, L2 = 20-30%;
2. Use of low shear and low compression ratio of the screw compression ratio ε = 1.8-2.2, because the cut lead to overheating or opaque color h3 = 0.09-0.10D;
3. The use of recycling material (film material), increase the transmission capacity of the feed section, the mandatory use of plastic feed system.
(E) PVC (polyvinyl chloride)
The heat-sensitive materials are generally divided into hard and soft, the difference between the raw materials added to Plasticizers of the number, less than 10% of the rigid, more than 30% for soft.
Characteristics:
1.'s No point, 60 ℃ soften, 100 ℃ -150 ℃ viscoelastic state, 140 ℃ melt forming a narrow temperature range, poor thermal stability, easy to break down, 170 ℃ rapid decomposition, softening point close to the break point, the release of decomposition HC1 gas.
2. UPVC due to the high melt viscosity, thermal stability worse time temperature will lead to decomposition, the general corrosion of steel have effect;
3. Strict temperature control, screw design as much as possible to cut low to prevent overheating, the flow must be smooth and should not be dead, the plot is expected to prevent decomposition;
4. Screw barrel to prevent corrosion;
5. Injection process to be strictly controlled.
Preferences:
1.L / D = 18-21, h3 = 0.067-0.08D, ε = 1.6-2, L1 = 40-45%, L2 = 35-45%, to prevent the possession of material non-apron over his head 20 ℃ -30 ℃, using chrome-plated hardware of the screw;
2. The choice of temperature;
① molten plastic tube multi-unit air-cooled;
② low high-shear mixing bowl UPVC special screw device. |