classy single screw extruder applications
The extruder can be combined with various plastic forming auxiliary machines, such as pipes, films, support materials, monofilaments, flat wires, winding tapes, extrusion nets, plates, profiles, granulation, cable coating, etc., to form various plastic extrusion and forming lines to produce various plastic products.
PVC is an extremely versatile material and is generally supplied as a dry (powder) mix, as in the case of PVC processing. The PVC compound is sensitive to shear and high temperatures, so it is gently processed with a parallel or conical twin-screw extruder, depending on the required output and pipe size.
PE-Xa (Peroxide crosslinked polyethene) has a very high degree of crosslinking and therefore excellent heat resistance. The manufacture of PE-Xa pipes requires a highly specialised process in which a blend of PE powder, liquid peroxide and stabiliser is melted and homogenised in a twin-screw extruder. To prevent early cross-linking, a low process temperature of 160°C is used for the compounding. Afterwards, the melt is moulded into a pipe blank in a pipe die with optimised flow properties and with a very small amount of special coating.
Polyolefins are generally supplied in the form of pellets. They are particularly suitable for single-screw extrusion because they are only moderately sensitive to shear and thermal stress.
The most common type of extruder used in food processing is the co-rotating with fully meshed parallel twin-screw extruder. Screw extruders are mainly used in the food industry for the production of starch expanded food, protein extruded food, expanded feed and as special chemical or biochemical reactors.
Under the high temperature and pressure of the extruder, the starch in the grain will gelation. For example, when maize flour is puffed, the degree of starch gelation is above 98%, the crude fat is reduced by 60% or even disappears completely and the water solubility increases by more than 40%. This is why extruders can replace drum dryers for the production of dextrinised starch.
Under high temperature and pressure, plant proteins become organised. Under the action of shear between the screw groove and the barrel wall of the extruder, the proteins are strongly unfolded and arranged in a relatively straight line. The unfolded molecular chains become free and can be reoriented and recombined, thus forming a fibrous state. The fibrous structure is similar to that of lean meat, and when rehydrated has a certain elasticity and chewiness. It can be used to reorganise fish proteins such as minced fish and dried fishmeal to produce food products that mimic the flavour of prawns, snappers and chicken.
In feed processing, extruders are mainly used to process whole soybean meal, maize starch, various kinds of cake meal, rice hulls, rice bran, egg shells and fish meal. The feeds produced include floating feeds for fish, high protein shrimp feeds, piglet feeds, chicken feeds feeds for pleasure animals, special aquatic feeds, etc.
The extruder is a new type of biochemical reactor in which a series of biochemical reactions take place during the extrusion process. In addition to denaturing proteins, it also inactivates lipases, lipoxygenases, antitrypsin factors and naturally occurring toxic substances, and blunts the activity of enzymes that can cause food deterioration during storage, largely free of pathogenic bacteria, salmonella, insects and other contaminants.
Screw extruders can also be used for other industrial products, such as the paper industry, the textile industry, metal casting, oil well drilling, etc.
Single screw extruder and twin screw extruder have their own characteristics and applications. In some applications, you can choose either single screw or twin screw.
Extruder can be used in plastics industry, food & Pet food industry, chemicals industry, Pharmaceutical, Minerals and Nonwovens industry. This guide mainly introduces the plastic extruder.
The extrusion system mainly includes feeding system, screw and barrel. It is the core part of the extruder, and the screw is the key core component of the extruder.
The transmission system is usually composed of a motor, a reducer and a bearing. Its function is mainly to drive the screw and supply the torque and torque required by the screw in the extrusion process.
During the extrusion process, the screw speed is required to be stable to ensure uniform product quality. However, under different circumstances, the screw speed needs to be adjustable so that the same equipment can be adapted to extrude different materials or different shapes products.
The heating and cooling system of the extruder consists of a heating device and a cooling device, which is a necessary condition for the smooth operation of the extrusion process. The heating device and cooling device must ensure that the temperature conditions meet the process requirements.
Single screw extruder is mainly used in:Pipe extrusion: suitable for PP-R pipes, PE gas pipes, PEX cross-linked pipes, aluminum-plastic composite pipes, ABS pipes, PVC pipes, HDPE silicon core pipes and various co-extruded composite pipes.
Profile extrusion: Adjusting the speed of the extruder and changing the structure of the extruder screw can be used to produce various plastic profiles such as PVC and polyolefins.
The twin-screw extruder is developed on the basis of the single-screw extruder. Due to its good feeding performance, mixing and plasticizing performance, exhaust performance, extrusion stability, etc., it has been widely used in extruded products. Forming processing.
There are two types of twin-screw extruders: intermeshing and non-intermeshing. And, Intermeshing twin screw extruders have two types: co-rotating and counter-rotating.
The screw system of a parallel twin-screw extruder is generally divided into 4 sections: conveying section, melting section (exhaust port), plasticizing section (vacuum port), and discharging section.Conveying section: The function is to transport materials and prevent backing.
The development trend of twin-screw extruders in the world is toward high torque, high speed, and low energy consumption. The effect of high speed is high productivity. It has unique advantages in processing high-viscosity and heat-sensitive materials. At the same time, higher productivity can be achieved.
For example, the intermeshing counter-rotating twin-screw extruder is excellent in the main application areas of pipe and profile extrusion, especially for PVC materials.
For applications related to compounding and reactive extrusion, the building block self-cleaning co-rotating twin-screw extruder is more excellent and widely used.
In general, the single screw extruder is developing in the direction of high speed, high efficiency and specialization. The twin-screw extruder has good feeding characteristics and is suitable for powder processing. It has better mixing, venting, reaction and self-cleaning functions than the single-screw extruder. When processing plastics and blends with poor thermal stability It also shows its superiority.
Although there are indeed many differences between single and twin screw extruders, they can also be used for some of the same applications, or they can be used in combination. So how should we choose a plastic extruder?
Single-screw extruder is a common extruder equipment. Single-screw extruder is mainly used in plastic processing industry. Single-screw extruder is generally divided into three sections in effective length. The single-screw extruder presses the screw diameter. The size of single-screw extruder pitch and single-screw extruder screw depth determine the effective length of a three-stage single-screw extruder. Single-screw extruders are generally divided by one-third.
High-efficiency single-screw extruder adopts a two-stage overall design to enhance the plasticizing function. The single-screw extruder guarantees high-speed and high-performance stable extrusion. The special barrier is designed for comprehensive mixing. The single-screw extruder guarantees the mixing of materials. The effect of high shear and low melt temperature ensures high performance low temperature and low pressure metering extrusion of materials.
Single-screw extruders are inexpensive to design, so single-screw extruders are widely used. However, the single-screw extruder has its limitations in use. The single-screw extruder mainly performs in the following aspects:
(1) The material transportation of the single-screw extruder mainly depends on friction, so that the feeding performance of the single-screw extruder is limited, and powder, paste material, glass fiber and inorganic filler are difficult to join.
(2) When the head pressure of the single-screw extruder is high, the countercurrent increases and the productivity of the single-screw extruder decreases.
(3) The single-screw extruder exhaust extruder has a small surface regeneration effect in the exhaust zone, and the single screw extruder has a poor exhaust effect.
As common extruder equipment, a single-screw extruder is used in the plastics processing industry. The screw rotates in a heated barrel. Because of its simple structure, easy manufacture, high processing efficiency, and low price, it is widely used. It is the type of extruder with the most mature technology and the most consumption. The single-screw extruder is generally divided into three sections in terms of effective length. The effective length of the three sections is determined according to the diameter of the screw, the pitch, and the depth of the screw, which are generally divided into one-third each.
The single-screw extruder is mainly composed of three parts: extrusion system, transmission system, and heating and cooling system. The single-screw extruder has developed from the initial basic spiral structure
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