PC/ABS has a wide range of applications, including automotive interior and exterior parts, LCD TV frames in everyone's homes, smart phone casings, laptop lids, etc. Most of these products contain screw posts and buckles. In addition, like some secondary processing techniques such as painting, electroplating, coating glue, etc., these structures and post-processing processes may induce the phenomenon of internal stress cracking of PC/ABS alloy materials, resulting in a high defective rate.
Why is there stress? This is due to the material's structure that determines the properties of the material. When the PC/ABS is molded, the molecular chains are forced to orient, but due to the benzene ring in the molecular chain, the orientation is more difficult, and after molding, The molecular chains that are oriented have a tendency to return to their natural state, but because the entire molecular chain has been frozen, there is residual stress in the product.
How to analyze the residual stress of PC/ABS? Xiao Bian teach you a few strokes!
Solvent soaking
1. Soak PC/ABS parts with screw grooves or columns in glacial acetic acid for 30s or more. After removal, check the appearance. If there are small and dense cracks, there is internal stress. The more cracks, the greater the internal stress;
2. The ratio of isopropyl alcohol and acetone 3:1 is mixed. Red dye is added. The uniform coloring indicates that the internal stress is small, and the stress at the sites that are not easily colored is large. Attention must be paid.
Moldflow simulation analysis method
Through the mold flow analysis software, the pressure distribution during speed/pressure switching is analyzed. The higher the pressure, the greater the stress involved.
Quarter Ellipse Stress Analysis
Select one-fourth elliptical jig, place the test piece as far as possible, and place the solvent evenly on the test piece. The same kind of raw material test piece is better to be made into 3-5 groups. After the coating is completed, it should be stored at rest (Environmental requirement 23°C, 50 %RH), Observe the test piece cracks, the more cracks, the greater the residual stress.
Screw hole experiment
Use appropriate size screws for tapping experiments. The screws can be coated with some common industrial butters. When necessary, the tapped screws can be placed in a high temperature environment to accelerate the release of stress. Cracking or cracking instructions are involved in the stress.
Stress cracking is the main factor affecting the quality of plastic products. In order to improve product quality, based on the actual situation, it is necessary to take effective measures and measures based on the correct analysis of stress cracking, and to reduce and avoid the influence of product internal stress on products.