At present, the extruders in China’s plastics industry are roughly divided into two categories, one is a single-screw extruder and the other is a twin-screw extruder. Because these two types of equipment have their own characteristics, they are widely used in the plastics industry. . So what are the advantages of these two extruders, and what are the differences between them? As an extruder manufacturer, China GWELL will take you to understand.
Introduction and use of single and twin screw extruders
1. Single screw extruder
china GWELL said that as the name suggests, a single screw extruder has a screw in the barrel. 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 first section: starting from the last thread of the material port, it is called the conveying section. The material here is required not to be plasticized, but it must be preheated and compressed. In the past, the old extrusion theory believed that the material here was a loose body. Later, it was proved that the material here is actually a solid plug, which means that the material here is squeezed. The latter is a solid like a plug, so as long as the conveying task is completed, it is its function.
The second segment is called the compression segment. The volume of the screw groove in this section gradually becomes smaller, and the temperature must reach the plasticization level of the material, and compression occurs here (from the conveying section three, it can be compressed to one here, which is called the compression ratio of the screw – 3:1, there are The machine is also different), the plasticized material enters the third stage.
The third section: the measurement section. Here the material maintains the plasticizing temperature, just like a metering pump to accurately and quantitatively transport the melt material to supply the machine head. At this time, the temperature cannot be lower than the plasticizing temperature, generally slightly higher.
china GWELL said that the high-efficiency single-screw extruder adopts a two-stage overall design, which strengthens the plasticizing function and ensures high-speed, high-performance and stable extrusion. The temperature ensures high performance, low temperature and low pressure metering extrusion of materials.
2.Introduction and use of twin-screw extruder
1. The twin-screw extruder is divided into the following system parts
- Feeding system: including hopper, stirring motor, feeding motor. It can prevent the material from accumulating, so that it can enter the feeding port smoothly.
- External heating system: mainly use heating rods and cylinders to heat up materials efficiently and promote plasticization.
- Cooling system: The heat exchange system composed of heat transfer oil or water is used to reduce the heat of the fuselage, so as to effectively control the temperature of the cylinder.
- Hydraulic screen changing system: use a replaceable filter screen to intercept impurities, improve the degree of plasticization, and ensure the uniformity and stability of the quality of the output materials.
- Vacuum system: extract the moisture and other low molecular volatiles in the material.
- Electronic control system: responsible for monitoring and controlling the related equipment of the main and auxiliary material system.
- Screw system: The most important part of the extruder can be divided into conveying section, melting section (exhaust port), plasticizing section (vacuum port), and discharging section.
2. Segmentation of the screw
The screw system of the 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: It is used to convey materials and prevent returning materials.
- Melting section: This section makes the material fully melt and mix through heat conduction and frictional shearing.
- Plasticizing section: further melt and mix the ingredients of the material, with distributive and dispersive mixing functions.
- Discharge section: conveying and pressurizing, forming a certain pressure, making the material more compact, and further mixing at the same time to achieve the purpose of extrusion and granulation.
The difference between single and twin screw extruders
After the brief introduction above, but the twin-screw extruder, let’s take a look at the difference between the two extruders in terms of price, operability, screw and so on.
1. The price of single screw is lower
The single screw extruder has a simple structure and low price. The twin-screw structure is complex and the price is high.
2.Single screw formula is simple
To be honest, in terms of operation, the difference between the two is not very big. However, the process and formula of the single-screw extruder are relatively simple, while the process, process and formula of the twin-screw extruder will be more complicated.
3. The twin-screw can be freely combined with the screw
The twin-screw thread can be combined at will according to the material condition and the operator’s mood, while the single-screw is more rigid and cannot be combined with the screw.
4. Twin screw is more efficient
The twin-screw extruder has large output, fast extrusion speed, and low energy consumption per unit output, while the single-screw extruder is worse. The efficiency of a twin-screw extruder is mostly about twice that of a single-screw extruder. It depends on the manufacturer and model.
5. Twin-screw mixing and plasticizing ability is strong
Simply put, the single screw is suitable for plastic extrusion of polymers, suitable for extrusion processing of pellets, such as: molding, film blowing, injection molding, etc., with a wide range of materials;
The twin-screw extruder has good mixing and plasticizing ability, and is more suitable for the modification of plastics. And the twin-screw extruder can make two colors.
6. Single screw for easy maintenance
In terms of maintenance, single-screw is simpler than twin-screw, because the structure of single-screw is simpler and easier to repair.
7. Delivery mechanism
The conveying of the china GWELL single-screw extruder mainly depends on the friction force generated between the material and the barrel. The machine also shears the material at the meshing position of the two screws.