Twin-screw extruders have barrels with an extension range of 4 and 6D, allowing for precise process design to meet specific customer requirements. All barrels allow for precise temperature control. Cooling is achieved by cooling water injection and high-performance electric heating rods for direct and fast heating. The auxiliary equipment of the twin-screw extruder consists of a straightening device, a preheating device, and a cooling and heating device. The following is a detailed description of the auxiliary equipment.
Here is the content list:
l Straightening device
l Preheating device
l Cooling device
One of the most common types of plastic extrusion rejects is eccentricity, and bending of the wire core in various patterns is one of the most important causes of insulation eccentricity. In sheath extrusion, scratches on the sheath surface are also often caused by the bending of the cable core. Therefore, a variety of extrusion units in the straightening device is essential. The main types of straightening devices are roller type (divided into horizontal and vertical type); pulley type (divided into single pulley and pulley group); stranded pulley type, which plays a variety of roles such as dragging, straightening, and stabilizing tension; pressure pulley type (divided into horizontal and vertical type), etc.
Cable core preheating is necessary for both insulation extrusion and sheath extrusion. For the insulation layer, especially the thin layer of insulation, the existence of pores should not be allowed, the core can be completely removed from the surface of the water, oil, and dirt through high temperature preheating before extrusion. For the sheath extrusion, the main role is to dry the cable core, to prevent the role of moisture (or moisture around the bedding layer) to make the sheath in the possibility of porosity. Preheating can also prevent the plastic from being extruded due to sudden cooling and residual internal pressure. In the process of extruding plastic, preheating can eliminate the cold line into the high-temperature heat, in contact with the plastic at the mouth of the die to form a disparity in temperature, to avoid fluctuations in plastic temperature and lead to fluctuations in extrusion pressure, to stabilize the amount of extrusion and ensure the quality of extrusion. Extrusion unit is used in the electric heating core preheating device, requires sufficient capacity, and ensures rapid temperature rise, so that the core preheating and cable core drying efficiency. The preheating temperature is restricted by the speed of wire release, generally similar to the temperature of the head.
The formed plastic extrusion layer after leaving the head should be immediately cooled and shaped, otherwise, deformation will occur under the action of gravity. The way of cooling usually uses water cooling, and according to the water temperature is different, divided into rapid cooling and slow cooling. Rapid cooling is the direct cooling of cold water, rapid cooling of plastic extrusion layer sizing is beneficial, but for crystalline polymers, due to sudden heat cooling, easy to internal residual stress in the extrusion layer organization, resulting in the use of the process of cracking, general PVC plastic layer using rapid cooling. Slow cooling is to reduce the internal stress of the product, in the cooling water tank placed in sections of different temperatures of water, so that the product gradually cool down and set, PE, PP extrusion on the use of slow cooling, that is, after hot water, warm water, cold water three cooling.
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The single screw extruder is mainly composed of 3 parts: extrusion system, transmission system, and heating and cooling system. The following is a detailed introduction to the basic structure of the single screw extruder.
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Heating and cooling system
The main role of the extrusion system of the single-screw extruder is to melt and plasticize the polymer material to form a uniform melt, to realize the transformation from the glassy state to the viscous flow state. And in this process to establish a certain pressure, by the screw continuous extrusion delivery to the head die. Thus, the extrusion system plays an important role in the molding quality and output of the extrusion process.
The extrusion system mainly includes the feeding device, screw, and barrel, which is the most critical part of the extruder, of which the screw is the heart of the extruder, the material through the rotation of the screw in order to move in the barrel and get pressurized and part of the heat.
The drive system of a single screw extruder is usually composed of a motor, reducer, and bearing, whose role is 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 and does not change with the change of screw load to ensure the uniform quality of the product. However, in different situations, the screw is required to be able to achieve variable speed in order to achieve a machine that can adapt to the requirements of extruding different materials or products of different shapes. In most extruders, the change of screw speed is achieved by adjusting the motor speed. The drive system of the single-screw extruder is also equipped with a good lubrication system and a device for rapid braking.
The heating and cooling system of a single screw extruder consist of a heating device and cooling device, which are necessary for the extrusion process to be carried out smoothly. The heating and cooling devices must ensure that the polymer materials are melted and plasticized and the temperature conditions during the molding process meet the process requirements.
The cooling device is generally set up in the extruder barrel, screw and hopper bottom, and other parts. Barrel cooling can be water-cooled or air-cooled, air-cooled is generally used for small and medium-sized single-screw extruders; large single-screw extruders are mostly water-cooled or a combination of the two forms. The cooling device at the bottom of the hopper is mainly to strengthen the solid material conveying effect, to prevent the material particles from becoming sticky due to the heating, blocking the material mouth and thus affecting the feeding. Generally, for extruders with a screw diameter of 90mm or more and high-speed extruders, a cooling device must be installed at the bottom of the hopper.
Our company focuses on twin-screw extruders, micro twin-screw extruders, plastic extruders, parallel twin-screw extruders, and other kinds of research and development and manufacturing as the core of the isotropic rotary twin-screw compounding extruder. If you still want to know more, you can consult our company.
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The twin screw extruder's standard equipment includes a sturdy base frame dedicated to housing the temperature control unit and oil lubrication system. The equipment features advanced control software for seamless integration into digital factories, ready for Industry 4.0, greatly improving ease of use. The following is a detailed description of the operating procedures of the twin screw extruder.
Here is the content list:
l Start up operation
l Stop the machine
Start up operation
1.Close the power main gate of the twin screw extruder.
2. Turn on the power at the operation panel: Press and hold the power button clockwise to turn and then release.
3. Set the temperature of each temperature zone: for example, a zone temperature according to the process requirements set the corresponding temperature, press the set button, and then adjust the up and down arrows to the desired temperature, press the set button.
4. Set the feeding rate: according to the process, requirements can be fed rate between 0 ~ 10 to set.
5. Set the host speed of the twin screw extruder: set the host speed between 0~30 according to the process requirements.
6. Add cooling water to the cooling tank.
7. In turn on the fan: press the operation button on the operation panel.
8. When you need to start the operation of the vacuum pump, you can start the vacuum pump.
9. Turn on the cutter switch.
1. Twin screw extruder normal stopping sequence: stop the feeder: close the vacuum line valve, open the vacuum chamber on the cover; gradually reduce the main screw speed; shut down the pelletizer and other auxiliary equipment: off the motor, each external water inlet valve.
2. Twin screw extruder emergency stop: (1) in case of an emergency need to stop the host, you can quickly press the electrical control cabinet red emergency stop button, and the host and the feed speed knob back to zero, and then the total power switch off. After eliminating the fault, you can restart the machine again in normal driving order. (2) encounter equipment automatic protection trip stop: need to set the various parameters knob to zero, and then reset the parameters, press the reset button and start the machine again.
1. The normal production of the first shift machine, be sure to first check whether the barrel, hopper seal is the original closed kind, such as changes or damage, should check the hopper, the machine inside the Jane there are no foreign objects.
2. Pay attention to the screw to start at a low speed, the air time can not exceed 3min.
3. Must pay attention to check the purity of each batch of material, do not allow any impurities mixed into the material.
4. The beginning of the material to pay attention to the first small amount, evenly added material, while paying attention to observe the current meter (torque meter) pointer changes.
For granular material, use metering to add material. When you first start to feed production, be sure to pay attention to the extruder production work overload phenomenon. After the forming die lip out of the material, and then gradually increase the screw speed as appropriate.
5. Often check the working condition of the motor carbon brush, abnormalities should be replaced or adjusted promptly.
6. The screw cleaning work is not allowed to use steel tools scraping material, the application of copper brush, shovel cleaning.
7. When the process temperature is suspected of displaying problems on the instrument, use mercury temperature, meter actual measurement of the machine Jane, and molding mold degree. Refer to the mercury temperature measured temperature, adjust the calibration instrument to show the temperature.
If you still have questions, you can consult our company. Our company's website is https://www.njjyextrusion.com/
Material delivery method
In a single-screw extruder, there is friction drag in the solids conveying section and viscous drag in the melt conveying section. The friction properties of the solid material and the viscosity of the molten material determine the conveying behavior. If some materials have poor friction properties, if the feeding problem is not solved, it will be difficult to feed the materials into the single-screw extruder. In twin-screw extruders, especially intermeshing twin-screw extruders, the conveying of materials is to some extent forward displacement transmission, and the degree of forward displacement depends on the relationship between the flight of one screw and that of the other screw. the proximity of the relative screw grooves. The screw geometry of the closely intermeshing counter-rotating extruder results in a high degree of positive displacement delivery characteristics.
Material flow velocity field
At present, the flow velocity distribution of the material in the single-screw extruder has been described quite clearly, while the flow velocity distribution of the material in the twin-screw extruder is quite complicated and difficult to describe. Many researchers just do not consider the material flow in the meshing area to analyze the flow velocity field of the material, but these analysis results are very different from the actual situation. Because the mixing characteristics and overall behavior of a twin-screw extruder are primarily determined by the leakage flow that occurs in the intermeshing zone, the flow situation in the intermeshing zone is quite complex. The complex flow spectrum of the material in the twin-screw extruder shows macroscopic advantages that the single-screw extruder cannot match, such as sufficient mixing, good heat transfer, large melting capacity, strong exhaust capacity and good temperature control of the material, etc.
A plastic extruder performs all of the following processes through a barrel with a screw and auger channel. The plastic pellets enter the barrel through a hopper at one finish of the barrel and are then transferred through the screw to the opposite finish of the barrel. What are the working principle and molding principles of a plastic extruder? The following is a detailed description.
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Pressure and shearing, etc., convert the solid plastic into a uniform and consistent melt and send the melt to the next process. The production of the melt involves processes such as mixing additives such as masterbatches, blending resins, and re-crushing. The finished melt must be homogeneous in consistency and temperature. The pressurization must be high enough to extrude the viscous polymer.
To have sufficient pressure, the depth of the threads on the screw decreases as the distance to the hopper increases. The external heating and the internal heat generated in the plastic and the screw due to friction softens and melts the plastic. The design requirements for plastic extruders often vary from polymer to polymer and from application to application. Many options involve discharge ports, multiple loading ports, special mixing devices along the screw, cooling and heating of the melt with or without an external heat source (adiabatic plastic extruders), the relative size of the gap variation between the screw and the barrel, and the number of screws. For example, twin-screw plastic extruders allow for more thorough mixing of the melt than single-screw plastic extruders. Tandem extrusion uses the melt-extruded from the first plastic extruder as feedstock for the second plastic extruder, which is typically used to produce extruded polyethylene foam.
D L the characteristic dimensions of plastic extruders are the diameter of the screw (D) and the ratio of the length of the screw (L) to the diameter D L/D (D) (L/D. Plastic extruders usually consist of at least three segments. The first section, near the L/D) filling hopper, is the filling section. Its function is to allow the material to enter the plastic extruder at a relatively smooth rate. In general, this section will be kept at a relatively low temperature to avoid clogging the charging channels. The second section is the compression section, where the melt is formed and the pressure is increased. The transition from the charging section to the compression section can be abrupt or gradual (gentle). The last half, the metering section, is adjacent to the plastic extruder outlet and its main operate is that the uniformity of the fabric flowing out of the plastic extruder. In this section, the material should have sufficient residence time to ensure uniformity of composition and temperature.
At the end of the barrel, the plastic melt leaves the plastic extruder through a head that is designed in an ideal shape for the extruded melt stream to pass through.
Another important part is the drive mechanism of the plastic extruder. It controls the rotational speed of the screw, which determines the output of the plastic extruder. The power required is determined by the viscosity (flow resistance) of the polymer. The viscosity of the polymer depends on the temperature and flow rate and decreases with increasing temperature and shear. Plastic extruders are equipped with screens that keep impurities out of the screen. To avoid downtime, the screens should be able to be changed automatically. This is especially important when processing resin with impurities, such as recycled material. The extruder's screw is divided into feeding section, plasticizing, melting section, temperature according to the process parameters of the plastic particles, the model according to the diameter of the screw 20, 36, 52, 65, 75, 95, 120, 135. Plastic particles heated by the movement of the screw to change the original state, there are many types, depending on the specific application. The capacity of the frequency conversion is proportional to the diameter of the screw and then adjusted according to the different raw materials.
The extrusion method of plastic extruders generally refers to the melting of plastic at a high temperature of about 200°C. The melted plastic is then passed through a die to form the desired shape. Extrusion molding requires a deep understanding of the characteristics of plastics and extensive experience in mold design and is a technically demanding molding method.
Extrusion molding is a method of a continuous flow of material through a die by heating and pressurizing in an extruder, also known as "extrusion molding". Compared with other molding methods, it has the advantages of high efficiency and low unit cost.
Extrusion is mainly used for molding thermoplastics, but it can also be used for some thermosets. Extruded products are continuous profiles, such as tubes, rods, wires, sheets, films, wire, and cable cladding, etc. In addition, it can also be used for mixing, plasticizing and granulating, coloring, blending, etc. plastics.
The extruded products can be called "profiles", which are also called "profiles" because of their irregular cross-sectional shape.
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Time: May 27-30, 2021
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