Add waste materials to ABS sheet
1. Material selection and performance
ABS is an amorphous polymer. Under the action of heat and external force, it enters the viscous flow state from the glass state at room temperature through a high elastic state to form a uniform viscous liquid, and then is cooled and shaped by an extrusion die and a three-roller, and returns from a viscous flow state through a high elastic state. To the glass state. ABS can only be shaped by entering the viscous flow state, and it must have the same effect of heat and force to enter the viscous flow state.
The advantages of ABS are:
1 Because ACN is contained in the acrylonitrile unit, ABS has good surface hardness, chemical resistance, heat resistance and high strength, and the heat resistance temperature can reach 90 °C:
2 Butadiene unit makes ABS have good toughness and elasticity, and the impact strength will not drop rapidly even at low temperature, and the low temperature resistance reaches -40 °C.
The 3 styrene unit keeps the molecular chain rigid, making the material stiff, shiny, and has good electrical properties and thermal flow. Therefore, the comprehensive performance of ABS is better.
The disadvantages of ABS are:
1 The weather resistance is poor, and the long-term storm is easy to turn yellow in the air. This is because the butadiene unit contains double bonds and will degrade under the action of ultraviolet rays. For this reason, black PP film must be used for packaging ABS sheets.
2 easy to absorb moisture, packaging ABS sheet should pay attention to sealing and storage period (usually 28d);
3 It is not resistant to organic solvents such as acetone. Therefore, when selecting foaming agents, defoamers, and refrigerants, consider whether stress cracking occurs due to dissolution, swelling, or erosion when exposed to ABS for a long period of time.
According to different types of refrigerators, the thickness of ABS box plates is 3.0mm-3.2mm; the thickness of door panels
It is 1.6mm-1.8mm. In order to reduce the cost, 20%~30% recycled material can be added to ABS new pellets.
(1) Dryer. It is preferable to use a countercurrent dehumidifying and drier for drying the ABS for extruded sheets. Generally dry hopper capacity should reach 2t
(2) Extruder. The equipment used for ABS sheet is generally a single-screw extruder. The screw form is a single-lead, full-spiral, equal-pitch two-stage feed with a length to diameter ratio of 25-35. The first feed section of the screw has a higher compression ratio. For a 2.5:1, the second feed section has a compression ratio of 2:1 and a threaded angle of 17.7 degrees.
The main advantage of the two-stage screw is that it can use the exhaust equipment to help the drying system. The volatile components emitted from the discharged compound material show obvious advantages under the same conditions than the single-stage extruder. Very important. The screw should be driven by a stepless speed-regulating motor. The material must have a more sensitive cooling device to facilitate temperature control. The error range of the single-zone temperature should be between ±3 °C.
The filter in the extruder is a device that ensures that the material can filter impurities as it advances, and promotes uniform melting of the material and reduces speed fluctuations. ABS extruded sheet should be hydraulically changed quickly to ensure that the net is not stopped.
There are only three types of plate extruder die, namely straight channel type, fish tail type and hanger type. ABS sheet processing should use a hanger-type die, and the flow line of the hanger-type die can better control the uniform flow of the hot melt from the lip and reduce the phenomenon of "local overheating" in the die.
(3) Polishing (or modifying) the roll. The polishing roll consists of three independently driven high-gloss rolls. The introduction roll is a method in which a molten slab formed by a handpiece is drawn by a pressure applied between two rolls and pressed to a desired thickness. The middle roll also plays the role of polishing (or modifying) and cooling the surface of the plate, and the three rolls are all heated by steam. In addition, the speed fluctuation of each roller should be within 1% during normal production.
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