Laboratory twin-screw extruder is mainly used for research on polymer plastics. It is mainly used in universities, enterprises and research institutes. Research and development, the main feature is the smaller screw diameter, which greatly reduces the amount of materials used during application development.
Structural features
The distinguishing feature of the split co-rotating parallel twin-screw extruder is that the barrel can be split and the screw and barrel lining can be combined at will.
1. Split barrel
In the past, the barrel of laboratory twin-screw extruder experimental machines was integral and could not be opened. The split laboratory twin-screw extruder is a split type. It consists of an upper and lower barrel. The lower barrel is fixed on the frame. The upper barrel is connected to the lower barrel through a worm gear reducer. Normally, the upper half of the barrel and the lower half of the barrel are fastened with two rows of bolts. When it is necessary to open the barrel, just loosen the bolts and turn the worm gear box handle to open the barrel.
2. Building block screw and barrel
The screw and barrel of the main machine of the split laboratory twin-screw extruder adopt advanced “building block” design. The screw is composed of various types of screw blocks set on the mandrel. The inner lining of the barrel is The sleeve can be adjusted according to the different screw blocks, so that it can be flexibly assembled according to the material variety and other process requirements. The ideal thread element structure is combined to realize various processes such as material conveying, plasticizing, refining, shearing, exhausting, pressure building and extrusion, thus better solving the so-called universal screw problem that is generally difficult to balance. The contradiction between sex and specificity is achieved to achieve the goal of one machine with multiple uses and one machine with multiple functions. Another advantage of the “building block” design is that worn screw and cylinder components can be partially replaced, avoiding the scrapping of the entire screw or cylinder and greatly reducing maintenance costs.
The twin screws of the main machine are high-speed co-rotating meshing types, which can produce very strong and complex material transfer and exchange, split blending, shearing and kneading in various threads and mixing elements. These functions can be fully adjusted and controlled by changing the screw configuration and operating process conditions to meet the requirements of various processes.
Accurate measurement and reasonable feeding methods are the key to strictly implementing the formula, and are also the first step to ensure product quality. We are equipped with a variety of feeding methods based on the performance of the material and the needs of users, such as volume measurement and dynamic weight loss. Measurement, etc. to meet the needs of different products.
Advanced control system. The extruder is equipped with an advanced and beautiful control system. Most of its control components are imported components with good quality and high sensitivity. The operating parameters of the host such as current, voltage, temperature, torque, etc. are very intuitive, so it is very convenient to operate and the requirements for operators are not high.
The system is equipped with several cutting methods such as drawing water-cooled pelletizing, hot-cut water-cooling, hot-cut air-cooling, etc. It can be configured according to different materials and user requirements.
Advantages
1. Intuitively understand the wear and tear of wearing parts
Because it is easy to open, the wear degree of the threaded components and the inner bushing of the barrel can be found at any time, so that effective repair or replacement can be carried out. This prevents unnecessary waste from being discovered only when problems occur with the extruded product.
2. Reduce production costs
When manufacturing masterbatch, it is often necessary to change the color. If it is necessary to change the product, open the open processing area within a few minutes. In addition, the mixing process can be analyzed by observing the melt profile on the entire screw. At present, when changing the color of ordinary laboratory twin-screw extruders, a large amount of cleaning materials are needed to clean the machine, which is time-consuming, energy-consuming, and wastes raw materials. The split laboratory twin-screw extruder can solve this problem. When changing colors, it only takes a few minutes to quickly open the barrel and perform manual cleaning. This way, no or less cleaning materials can be used, saving costs.
3. Improve labor efficiency
During equipment maintenance, ordinary laboratory twin-screw extruders often need to remove the heating and cooling systems first, and then pull out the screw as a whole. The split twin-screw is not needed. Just loosen a few bolts, turn the worm gear box handle device and lift the upper part of the barrel to open the entire barrel for maintenance. This not only shortens the maintenance time, but also reduces the labor intensity.
4. High torque and high speed
At present, the development trend of laboratory twin-screw extruders in the world is towards high torque, high speed, and low energy consumption. The effect of high speed is high productivity. The split laboratory twin-screw extruder belongs to this category, and its speed can reach up to 500 rpm. Therefore, it has unique advantages in processing high-viscosity and heat-sensitive materials.
5. Wide range of applications
Wide range of applications, suitable for processing a variety of materials
6. High output, high quality and high efficiency
It has other advantages of ordinary laboratory twin-screw extruders and can achieve high output, high quality and high efficiency.
Application examples
1. Glass fiber reinforcement and fuel retardant granulation (such as: PA6, PA66, PET, PBT, PP. PC reinforced flame retardant, etc.)
2. High filler granulation (such as: PE, PP filled with 75% CaCO.)
3. Granulation of heat-sensitive materials (such as PVC, XLPE cable materials)
4. Concentrated color masterbatch (such as: filled with 50% color powder)
5. Anti-static masterbatch, alloy, coloring, low-fill blending and granulation
6. Cable material granulation (such as sheathing material, insulation material)
7. XLPE pipe material granulation (such as: masterbatch for hot water cross-linking)
8. Thermosetting plastic mixing and extrusion (such as: phenolic resin, epoxy resin, powder coating)
9. Hot melt adhesive, PU reaction extrusion granulation (such as: EVA hot melt adhesive, polyurethane)
10. K resin and SBS devolatilization and granulation
Laboratory twin-screw extrusion experimental machine auxiliary equipment
Straightening device
The most common type of plastic extrusion waste is eccentricity, and various types of bending of the wire core are one of the important reasons for insulation eccentricity. In sheath extrusion, scratches on the sheath surface are often caused by bending of the cable core. Therefore, alignment devices in various extrusion units are essential. The main types of straightening devices are: roller type (divided into horizontal type and vertical type); pulley type (divided into single pulley and pulley group); winch type, which has multiple functions such as dragging, straightening, and stabilizing tension; Press wheel type (divided into horizontal type and vertical type), etc.
Preheating device
Cable core preheating is necessary for both insulation extrusion and sheath extrusion. For the insulation layer, especially the thin layer insulation, the existence of pores cannot be allowed. The wire core can be completely removed from the surface moisture and oil by high-temperature preheating before extrusion. For sheath extrusion, its main function is to dry the cable core to prevent the possibility of pores in the sheath due to moisture (or moisture around the cushion layer). Preheating can also prevent the residual internal pressure caused by the sudden cooling of the plastic during extrusion. During the plastic extrusion process, preheating can eliminate the large temperature difference formed when the cold wire enters the high-temperature machine head and contacts the plastic at the die mouth, avoiding fluctuations in the extrusion pressure caused by fluctuations in plastic temperature, thus stabilizing the extrusion volume and ensuring Extrusion quality. Electric heating wire core preheating devices are used in the extrusion unit, which requires sufficient capacity and rapid temperature rise, so that the wire core preheating and cable core drying efficiency are high. The preheating temperature is restricted by the pay-off speed and is generally similar to the temperature of the machine head.
Cooling device
The formed plastic extrusion cladding should be cooled and shaped immediately after leaving the machine head, otherwise it will be deformed under the action of gravity. The cooling method usually uses water cooling, and is divided into rapid cooling and slow cooling according to different water temperatures. Rapid cooling is direct cooling with cold water. Rapid cooling is beneficial to the shaping of plastic extruded cladding. However, for crystalline polymers, due to the sudden cooling, internal stress is likely to remain inside the extruded cladding structure, resulting in cracks during use. Generally, PVC The plastic layer is rapidly cooled. Slow cooling is to reduce the internal stress of the product. Water of different temperatures is placed in the cooling water tank in sections to gradually cool down the product and shape it. For the extrusion of PE and PP, slow cooling is used, that is, through hot water, warm water, and cold water. Three stages of cooling.
The difference between laboratory twin-screw extrusion experimental machine and single-screw extruder
Single-screw machines and twin-screw machines: one has one screw and the other has two screws. They are both driven by a motor. The power varies with different screws. The power of a 50-cone double screw is about 20KW, and the power of a 65-cone machine is about 20KW. It is 37KW. The output is related to the material and screw. The output of 50 cone double is about 100-150KG/H, and the 65 cone double is about 200-280KG/H. The output of single screw is only half. Extruders can be divided into single-screw, twin-screw and multi-screw extruders according to the number of screws. Currently, single-screw extruders are the most widely used and are suitable for the extrusion processing of general materials. The laboratory twin-screw extruder has the characteristics of less heat generated by friction, relatively uniform shearing of the material, large screw conveying capacity, relatively stable extrusion volume, long residence time of the material in the barrel, and even mixing.
The laboratory twin-screw extruder has the characteristics of forced extrusion, high quality, wide adaptability, long life, low shear rate, not easy to decompose materials, good mixing and plasticizing performance, and direct molding of powders. Automatic temperature control, vacuum exhaust and other devices. Suitable for the production of tubes, plates, special-shaped materials and other products.
Single-screw extruders occupy an important position both as plasticizing and granulating machinery and as molding and processing machinery. In recent years, single-screw extruders have developed greatly in the industry. At present, the large-scale single-screw extruder for granulation produced in Germany has a screw diameter of 700mm and an output of 36t/h.
The main sign of the development of single-screw extruders is the development of its key component – the screw. In recent years, people have conducted a lot of theoretical and experimental research on screws. So far, there are nearly a hundred types of screws. Common ones include separation type, shear type, barrier type, split type and corrugated type.
From the perspective of single-screw development, although single-screw extruders have been relatively perfect in recent years, with the continuous development of polymer materials and plastic products, new screws and special single-screw extruders with more characteristics will emerge. Generally speaking, single-screw extruders are developing in the direction of high speed, high efficiency and specialization.
The laboratory twin-screw extruder has good feeding characteristics and is suitable for powder processing. It has better mixing, exhaust, reaction and self-cleaning functions than a single-screw extruder. It is characterized by processing plastics with poor thermal stability. It shows its superiority even more when used with blends. In recent years, foreign laboratory twin-screw extruders have developed greatly. Various forms of laboratory twin-screw extruders have been serialized and commercialized. There are also many manufacturers producing them. They are roughly classified as follows:
(1) According to the relative position of the two axes, it can be divided into parallel and conical;
(2) According to the meshing procedure of the two screws, there are meshing type and non-meshing type;
(3) According to the rotation direction of the two screws, they can be divided into the same direction and the opposite direction, and the different directions can be divided into inward and outward;
(4) According to the screw rotation speed, there are high speed and low speed;
(5) According to the structure of the screw and barrel, there are two types: integral and combined.
On the basis of the laboratory twin-screw extrusion experimental machine, in order to make it easier to process blends with poor thermal stability, some manufacturers have developed multi-screw extruders such as planetary extruders.
Routine maintenance of laboratory twin-screw extruder
1. After 500 hours of use, there will be iron filings or other impurities ground from the gears in the reduction box. Therefore, the gears should be cleaned and the lubricating oil of the reduction box should be replaced.
2. After using it for a period of time, conduct a comprehensive inspection of the extruder to check the tightness of all screws.
3. If there is a sudden power outage during production and the main drive and heating stop, when the power is restored, each section of the barrel must be reheated to the specified temperature and kept warm for a period of time before the extruder can be started.
4. If the steering of the instrument and pointer is found to be full, check whether the contact of the thermocouple and other lines is good.
