Car plastic PC / ABS common problems and solutions

PC/ABS Overview
PC / ABS, polycarbonate and acrylonitrile-butadiene-styrene copolymer and mixture, is a thermoplastic plastic made of polycarbonate (PC) and polyacrylonitrile (ABS) alloy, combining two materials Excellent properties, moldability of ABS material and mechanical properties of PC, impact strength and temperature resistance, UV resistance and other properties.
Material injection molding
Drying treatment
Drying before processing is a must. The humidity should be less than 0.04%, and the recommended drying condition is 90~110 °C, 2~4 hours;
Barrel temperature
Feeding area: 50 ~ 70 ° C (70 ° C), melt temperature: 230 ~ 300 ° C, barrel constant temperature: 200 ° C, mold temperature: 70 ~ 90 ° C;
Injection pressure
80 to 150 MPa (800 to 1500 bar);
Holding pressure
40% to 50% of the injection pressure to avoid shrinkage of the product, in order to minimize the internal stress of the product, the pressure should be set as low as possible;
Back pressure
As long as 5 ~ 10MPa (50 ~ 100bar), to avoid the generation of frictional heat;
Injection speed
Medium injection speed to minimize frictional heat; multi-stage injection; recommended for some products from slow to fast;
Screw speed
The maximum screw speed is 0.5m/s, and the metering stroke is (1.0~3.0)D, because the melt is sensitive to overheating and excessive residual time in the barrel; the residual time should not exceed 6min, and the retention in the hot runner The time should also be as small as possible. The amount of residual material is 2 to 5 mm depending on the metering stroke.
Material performance characteristics
PC/ABS plastic properties
1. Good comprehensive performance, high impact strength, chemical stability and good electrical performance;
2, good fusion with plexiglass, made of two-color plastic parts, and can be chrome-plated, painted;
3, with high impact, high heat, flame retardant, enhanced, transparent and other levels;
4, the fluidity is a little worse than HIPS, better than PMMA, PC, etc., and good flexibility.
Material application field
1. Interior and exterior decoration of the car: instrument panel, decorative column, instrument front cover, grille, interior and exterior trim parts;
2, business equipment chassis and built-in components: notebook / desktop computer, copier, printer, plotter, display;
3. Telecom, mobile phone casing, accessories and smart card (SIM card);
4, electrical products, electronic product housing, meter cover and housing, household switches, plugs and sockets, cable and wire pipelines;
5, household appliances, such as washing machines, hair dryers, microwave ovens inside and outside parts.
Common grades of materials
PC/ABS production companies and common brands
Basic innovative plastics (C2800, C6200, C6600, 1200, C1110, CX7240, CM6140, C1100HF, etc.)
Bayer (T65XF, T85XF, T45PG, T65PG, FR2000, FR3010, FR3002, FR3008, etc.)
Taiwan Chi Mei (PC540, PC345, PC365, etc.)
Japanese Teijin (TN-7000, TN-3713B, TN-3715B, etc.)
Taiwan Taihua (AC2300, AC3100)
Common problems and solutions
1, the silver wire problem
Silver wire defect is the most common problem of PC/ABS material. Silver wire, also known as silver grain, water flower, flower flower, etc., is a silvery white filamentous stripe phenomenon appearing along the flow direction on the surface of the product, gas interference, among which The gas produced is mainly divided into three components:
(1) Air: the glue and the air entrapped during the injection phase;
(2) Moisture: the moisture contained in the material itself;
(3) Pyrolysis gas: a gas produced by high temperature hydrolysis/thermal decomposition.
Solution: First check if the material is dry enough. After confirming that the material is dry enough, adjust the injection molding process to improve the silver wire defect. At the same time, poor injection molding silver wire is also related to mold exhaust.
2, the problem of flow marks
Flow marks are produced when the material is injected. The reason is that the material has poor fluidity. The flow marks are different from the silver lines. It is not caused by moisture or material decomposition, and the appearance is different.
Solution: It can be avoided by increasing the temperature of the material to improve the fluidity. Appropriately improving the mold problem to increase the fluidity of the material in the mold and reduce the injection speed can also be solved.
3, shrinkage holes and dent problems
The shrinkage cavity is caused by insufficient filling of the material in the cavity.
Solution: Appropriately increase mold temperature and material temperature to improve material flow, prolong injection pressure, increase injection pressure, increase injection speed to improve filling, and increase gate size and heating gate flow To reduce and eliminate shrinkage of the product;
The dent is caused by improper temperature of the material and improper design of the product. When the temperature of the material is too low, not only shrinkage holes but also dent problems will occur. The temperature of the material is too high and the mold temperature is too high, which will cause the melt to cool. The time is excessively contracted, resulting in dents.
Solution: Use appropriate processing problems to increase injection speed and measures.
4, warpage deformation problem
The warping deformation of the injection molded parts is due to the unreasonable design of the parts, improper gate position and unreasonable injection molding conditions, resulting in internal internal stress, uneven shrinkage or excessive, excessive mold temperature or uneven mold temperature. It causes difficulty in demolding the film of the workpiece, or uneven cooling, and warp deformation also occurs;
Solution:
(1) Processing technology: lengthen the injection molding cycle, reduce the injection temperature, adjust the injection pressure and injection speed, and slow down the ejection speed, increase the ejection area, and maintain the balance of the ejection force;
(2) Product design: increase the wall thickness, add reinforcement and fillet reinforcement to reduce warpage;
5, the problem of marking
Usually due to the "melt fracture" caused by the expansion of the melt into the cavity during high-speed injection;
Solution:
(1) Forming process: reduce the occurrence of speckle by increasing the temperature of the material, increasing the nozzle temperature, slowing down the injection speed, etc.;
(2) Mold: Improve the mold temperature, add overflow tank, increase gate size, and modify gate shape.
6, pitting problem
Solution:
(1) Poor dispersion, adding dispersant or oil, raising temperature, adding back pressure.
(2) Pay attention to the mold problem. Try it with something else.
(3) Whether the temperature of the baking material is sufficient.
(4) Mold temperature adjustment.
7, the product "skinning" problem
The peeling problem of plastic products is closely related to the cracking of fluid caused by high shear force. Under low shear stress or rate, small disturbance caused by various factors is suppressed by melt; while in high shearing At stress or rate, disturbances in the fluid are difficult to suppress and develop into unstable flow; when a critical shear force is reached, the fluid will be broken.
Solution:
(1) Materials: The PC and ABS components are partially compatible, so it is necessary to add a suitable compatibilizer during the modification to improve the compatibility. Of course, because of the poor skinning caused by the mixing, we need the first step to eliminate;
(2) Mold: The principle of mold design is to follow the direction of cutting as much as possible. In general, products with dense dermatoglyphics are more prone to skinning (diffuse shearing of the melt in the cavity and the inner wall of the cavity during high-speed filling); at the same time, the gate size is too small. Will cause excessive shearing when the melt passes through the gate, which in turn causes the product surface to peel;
(3) Injection molding process: The main direction is to avoid excessive shearing. When the product is difficult to fill, it can be improved by high-speed and high-pressure method. Therefore, in the actual injection molding process, the injection temperature/die temperature and the fluidity of the material can be considered to reduce the flow resistance during the actual filling process, thereby Avoid excessive shear caused by high speed and high pressure.

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