Preparation process of ABS sheet
(1) The raw material is dried. ABS pellets are extremely hygroscopic and must be used before use.
Dry. Drying can use hot air circulation oven or hot air hopper type reclaimed material
Dryer. The drying process undergoes three stages of preheating, constant temperature drying and temperature drying. The drying process parameters usually used are: the drying temperature of the new pellet is (85 +/- 5) ° C, and the recycled material is (90 +/- 5) ° C; the drying time is not less than 3.5 h, but it is not suitable. Too long.
The factors affecting the drying effect are as follows:
1 The nature of the raw materials, including the raw material composition and the shape of the particles. Generally, the stronger the hygroscopicity of the raw materials, the slower the drying speed; the addition of additives increases the hygroscopicity; the larger the raw material particles, the longer the diffusion process and the slower the drying speed.
2 The lower the humidity of the drying medium (air), the higher the moisture absorption capacity, the faster the drying speed, and the easier it is to dry.
3 The higher the drying temperature, the greater the energy of the water molecules, and the higher the diffusion rate, the faster the drying speed. For this reason, the drying temperature should be high and should not be low, so as not to cause discoloration, agglomeration and decomposition of the pellets.
4 The faster the flow rate of the drying medium, the stronger the heat transfer between the medium and the material, and the faster the drying speed.
(2) Extrusion molding
The key to extrusion molding ABS sheet is the plasticizing effect, and the main factors affecting the plasticizing effect are set temperature, screw speed and screw design parameters. In addition, the factors affecting the feeding effect and exhaust effect cannot be ignored.
(3) Cooling and shaping
During the cooling and setting process, constant temperature water is used to control the temperature of the three rolls, and the temperature of the constant temperature water can be controlled by cooling water and heating. The cooling setting process parameters are: three rolls and traction line speed: 0.9m/min~4.1m/min; upper roll temperature in three rolls: 80°C～118°C, medium roll temperature: 95°C～120°C, lower roll temperature : 75 ° C -90 ° C; the temperature of the cooling water of the three-roll constant temperature system is not higher than 35 ° C.
It is worth noting that if the temperature of the three rolls is too high, the sheet will be too soft and leave the roll to form fine horizontal stripes; if the temperature is too low, the sheet will be separated, causing hem or roll marks; if the temperature of the three rolls is improperly matched It also causes the sheet to bend. The roller spacing will affect the thickness of the sheet, and the spacing between the middle and upper rolls will be improperly adjusted, which will result in pinholes or hem. When the three-roll line speeds are inconsistent, the sheet will be wavy.
If the traction is too tight, the sheet shrinkage will be high.
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