Low smoke halogen-free cable material granulator

& Low-smoke halogen-free cable material granulator:
The formula of low-smoke halogen-free cable material is relatively unique. A large amount of inorganic fillers or organic compounds are added to the base material [such as ethylene vinyl acetate resin] to It meets the performance of low combustion smoke, halogen-free, environmentally friendly, non-toxic, and flame retardant. However, due to the large filling volume of low-smoke halogen-free cable materials and the relatively large viscosity of the melt, the screw rotation shear during production, as well as between low-molecular materials, between low-molecular materials and screws, barrels, and between low-molecular materials and high-molecular materials The friction between polymers is more serious than other cable materials, which will generate a lot of heat, causing the temperature of the extruder to rise rapidly, which can easily cause the flame retardant to decompose in advance and produce pores.
Generally, low-smoke halogen-free cable materials will soften at ℃ and can be extruded at ~℃. However, the products of some manufacturers have a higher usage ratio, high melt viscosity, and require higher temperatures for extrusion. Cable factories that are not familiar with the situation will extrude cables at low temperature and low speed, which will cause the production speed to decrease and the efficiency to decrease. At the same time, the various properties of the material cannot be fully displayed. Extrusion equipment The most basic and versatile equipment for wire and cable extrusion molding is the single-screw extruder. The screw is the most important component of the extruder, which is related to the application range and production efficiency of the extruder. In view of the high filling of low-smoke halogen-free cable materials, a lot of heat is generated due to shearing during production, which requires a better cooling system to cool down. At the same time, the extrusion die corresponding to the cable is also the key to the success of cable extrusion. The main component of screw wire and cable extrusion equipment is the screw, which is related to the application range and production efficiency of the extruder. In order to meet the needs of different plastic processing, there are many types of screws. Low-smoke halogen-free cable materials are filled with a large amount of magnesium hydroxide and aluminum hydroxide. When the compression ratio of the extrusion screw is large, it is easy to cause the chemical bonds of the polymer to break, and the mechanical properties such as the tensile strength and elongation at break of the product will deteriorate. decline. At the same time, the screw compression ratio is large and the extruder speed cannot reach the normal level, causing the material to stay between the barrel and the screw for a long time. In addition, the friction of the molten material during the extrusion process is large, which generates a large amount of friction heat. The molten material is in an uncontrollable high temperature state in the barrel, which causes premature decomposition of the flame retardant and generates bubbles inside the material, ultimately leading to material failure. Therefore, for low-smoke halogen-free cable materials, a special screw for halogen-free materials is generally used. The compression ratio at the front end (extrusion end, metering section) of this screw is:, and the compression ratio at the rear end is:. The picture shows a special screw made of low-smoke and halogen-free materials. If there is no special screw, an ordinary screw can be used, but its compression ratio cannot be too large. It is generally suitable between ∶::.
& Low-smoke halogen-free cable material granulator
Extrusion Cooling device of the machine During the extrusion process, due to the particularity of low-smoke halogen-free cable materials, the molten material generates a large amount of heat due to friction, which requires the extrusion equipment to have a good cooling device to control the process temperature. This is a problem that cannot be ignored. If the temperature is too high, large pores will be formed on the surface of the cable. If the temperature is too low, the overall current of the device will increase, which can easily damage the device. I once saw a cable factory in Shanghai change the air cooling of the extruder cooling system to a water cooling system. After the change, the temperature rise was a bit slow, but the temperature rise was steady, the cooling speed was fast, and the system temperature was stable. There are many filling materials in the extrusion die for low-smoke halogen-free cable materials, which results in large differences in the strength, draw ratio and viscosity of the melt in the molten state from other cable materials, so the selection of molds is also different. The mechanical properties of low-smoke and halogen-free cable materials are not as superior as ordinary cable materials and low-smoke and low-halogen materials. Its stretch ratio is small, only about . , which requires that the die set should not be too large, otherwise the surface of the cable may not be dense and the extrusion package will be loose. When the extrusion temperature is set, the low-smoke halogen-free cable material will soften at ℃ and can be melted and extruded at ℃. If the extrusion temperature (actual temperature inside the equipment) reaches ~℃, there is a risk of decomposition of the flame retardant. If it exceeds ℃, it will no longer be usable. Too low an extrusion temperature will increase the overall current of the equipment, affecting equipment life and production efficiency. At the same time, due to different formula systems, the extrusion process temperatures of various low-smoke halogen-free flame-retardant polyolefin cable materials are also different. And the extrusion process temperature of the same material on different extrusion equipment is also slightly different, mainly depending on the different screw structures of the extruder. Generally speaking, on extruders with large shear forces, the extrusion process temperature is lower than on extruders with small shear forces. In addition, the temperature in different temperature zones has different effects on the surface quality of cable extrusion. Among them, the die head has the greatest impact, followed by the metering section. If the temperature in these two zones is too high, it will easily cause material decomposition, thus affecting the extrusion surface quality. With the continuous advancement of technology, the process temperature range of the relatively mature low-smoke halogen-free flame-retardant polyolefin cable materials currently on the market is still relatively wide. Generally, the temperature in each zone is controlled within the range of ~℃, and a smooth and delicate cable surface can be obtained. The temperature setting of the low-smoke halogen-free cable material in the extruder is recommended: zone ～ ℃ zone ～ ℃ zone ～ ℃ zone ～ ℃ flange ～ ℃ head ～ ℃ die opening ～ ℃. Generally speaking, the process temperature range of low-smoke halogen-free flame-retardant polyolefin cable materials is narrower than that of polyvinyl chloride, non-flame-retardant and halogen-containing flame-retardant polyolefin cable materials. Correspondingly, the extrusion temperature setting should have a temperature gradient, so that the low-smoke halogen-free cable material can be better plasticized and extruded. The extrusion temperature setting is related to the extrusion equipment. The temperature setting of small extruders is higher and that of large extruders is lower. Taking the extruder as an example, the temperature in the first zone should not be too high. High temperature will plasticize the cable material in the first zone, resulting in uneven thrust, uneven discharge from the die, and even the screw and barrel being non-concentric. The first area is the metering section of the screw. The cable material must be completely plasticized here. The temperature should not be too high. Otherwise, the flame retardant will decompose prematurely and produce bubbles. The temperature of the flange section should not be lower than the first area. Otherwise, the performance of the cable material after extrusion will be adversely affected. The temperature of the die opening should not be too high, otherwise the die opening phenomenon will occur, commonly known as "salivation" or "casting". The cooling method of the low-smoke and halogen-free sheath shrinks more sharply during extrusion, causing the outer layer of the sheath to have been cooled and set, while the inner cable material is still in a high-temperature, unset state, thus burying the risk of stress concentration and even eventually causing the cable to Stress cracking of outer sheath. In order to reduce stress concentration during the production process, it is recommended to use segmented cooling during the sheath extrusion process. Such as hot water cooling (circulating water) & warm water cooling & air cooling & cold water cooling. During the cable cooling process, special attention should be paid to the fact that the cable entering the water tank after coming out of the die mouth must be completely immersed in the cooling water. Otherwise, in addition to stress concentration problems, a series of small dots may appear on the surface of the cable. The surface of the outer sheath of the cable will be pitted, affecting the appearance of the cable.
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