In order to meet the needs of different plastic processing, there are many types of screw, the following are common: gradual (equidistance unequal depth), gradient (equal depth is not equal distance), mutant, torpedo head type.
The selection of the screw type is mainly determined by the physical properties of the plastic and the technical specifications of the extruder.
(1) The softening of non-crystalline polymers is accomplished within a relatively wide temperature range. Generally, equidistant gradient screws are used. The crystalline polymer melts at a relatively narrow temperature range, and generally isometric screws are used.
(2) On small plastic extruders, such as the φ45 extruder screw, a full thread type with unequal equidistant depths is used. The length and diameter of the screw are relatively small, and it is mainly used for extruding small-section insulating layers and jacket layers. Extrusion speed is faster.
(3) The medium-sized screw adopts the full-thread type with equal distance and thread depth gradient. Its length-to-diameter ratio is larger than that of the small-sized screw, and the pitch of the thread is equal, from shallow to deep from the root. The thread at the end of the thread is deeper, the thread at the root is shallower, so that the plastic has more extrusion volume without affecting the screw strength, the extrusion speed is fast, the plastic is plasticized well, and the insulating layer and the protection are generally produced for the middle and small-sized extruders. The ideal screw for the jacket.
(4) Large screw diameter is generally more than 150mm, such as φ150, φ200, φ250 extruder. There are two types of large screws: one is equidistantly unequal depths, such as φ150 and φ200 extruders; the other is that the screw is divided into three sections, ie equal depth, equal depth, and unequal depth. Φ250 extruder, compression ratio between 2 and 3, length to diameter ratio of about 15:1, mainly used to produce large-section wire and cable insulation and jacket layer.
Silicone oil generally refers to silicone oil, and silicone oil is generally dimethyl silicone oil. It is a polyorganosiloxane with a chain structure of different degrees of polymerization. It is made by dimethyldichlorosilane hydrolysis to obtain the initial polycondensation ring, the ring body is cracked, refined to obtain a low ring body, and then the ring body, head capping agent, catalyst together can be mixed to obtain a variety of different degrees of polymerization, after reduced pressure distillation to remove the low boiling substance can be prepared to obtain silicone oil.
The most commonly used silicone oil, the organic group is all methyl, called methyl silicone oil. Organic groups can also be used with other organic groups instead of partial methyl groups to improve a certain performance of silicone oil and suitable for a variety of different uses. Common other groups are hydrogen, ethyl, phenyl, chlorophenyl, trifluoropropyl and the like. In recent years, organic modified silicone oil has been rapidly developed, and many organic modified silicone oils with special properties have emerged.
Silicone oil has many special properties, such as small temperature and viscosity coefficient, high and low temperature resistance, oxidation resistance, high flash point, small volatility, good insulation, small surface tension, non-corrosive to metals, non-toxic and so on. Because of these properties, silicone fluids have excellent results in many ways. Among the various silicone oils, methyl silicone oil is the most widely used and is the most important variety of silicone oil, followed by methylphenyl silicone oil. A variety of functional silicone fluids and modified silicone fluids are mainly used for special purposes.
Properties: colorless, tasteless, non-toxic and not easy to volatilize liquid.
Uses: There are a variety of different viscosities. It has high heat resistance, water resistance, electrical insulation and low surface tension. Commonly used as advanced lubricating oil, shock oil, insulating oil, defoamer, mold release agent, polishing agent, isolating agent and vacuum diffusion pump oil, etc.; Emulsion can be used for car tire glazing, instrument panel glazing, etc. Methyl silicone oil is the most commonly used. After emulsification or modification, it is used to smooth and soft finish on the textile finish, and emulsified silicone oil is also added to the shampoo of daily care products to improve the lubrication of hair. In addition, there are ethyl silicone oil, methyl phenyl silicone oil, nitrile-containing silicone oil, polyether modified silicone oil (water-soluble silicone oil) and so on.
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