Evaluation of the quality of plastic products
Quality includes appearance and internal quality.
Appearance quality includes integrity, color and finish.
- Integrity refers to the plastic products obtained by injection molding of the mold, which are completely consistent with the structural shape in the design of the product, and it cannot have defects such as weld-lines, injection defects and shrinkage sinks.
- Color means that the color of the molded plastic product must be consistent with the customer’s demands. For transparent plastic products, the transparency should be good, and there should be no defects such as whiting, black spots, and silver streaks.
- Finish means that the roughness of the surface of the molded plastic product should meet the requirements of the customer. The embossing and blasting should conform to the customer’s specifications.
The internal quality includes whether the tissue is loose or not, and whether there are defects such as bubbles, cracks, and silver spots on the inside.
The dimensions of the molded plastic product must meet the tolerance requirements of the design drawings, and the product must meet the functional requirements of the customer after assembly.
Mechanical properties include tensile and pressure resistance, impact resistance, etc.; chemical properties include acid and corrosion resistance, radiation resistance, and special environment resistance.
18.1.2 Causes of product defects
There are many types of defects in plastic products, and the reasons are also very complicated. There are mold problems, plastic problems and process conditions.
(1) Plastic problems Plastic problems include plastic quality, ingredients and baking materials. If the plastic varieties are not impure, the blending ratio is improper, or the plastics of the baking materials (such as PC, ABS, PA, etc.) are not baked, it will cause problems such as loose internal structure, poor strength, internal bubbles, and silver streaks on the surface. .
(2) Molding process problems The three elements of the molding process include injection pressure, temperature and cycle. Tuning is to find a suitable set of values between the three, so that the mold can form a qualified product in the shortest time. But tuning is a meticulous and complex technology, many of which are caused by improper adjustments.
(3) Mold problems Even if the mold design is handy, plus the mold level master, it is difficult to ensure that the mold has no problems during the test. Mold issues include mold design, manufacturing and wear. One thing to note here is that the structure of the plastic part is unreasonable and can cause defects in the product. However, the problem of product structure directly leads to the problem of mold. As a mold design engineer, it is necessary to have a foresight to the problems that may arise from the unreasonable structure of the product, and to communicate with the customer or product engineer in time to prevent the problem before the mold is manufactured.
Among all the above problems, the mold problem is often the main problem, and it is the most difficult problem to solve.
18.1 – 3 General Approach to Problem Solving
Most of the defects of the product appear during the test. Among these defects, although the problem of the mold is often the main problem, it is much easier and easier to change the plastic and adjust the molding process conditions than to repair the mold. Therefore, the problem is often solved by changing the plastic and adjusting the injection process parameters. Repairing the mold is only considered when changing the plastic and molding conditions does not solve the problem.
Repairing the mold should be very cautious, not very sure not to act rashly. Because once the mold conditions are changed, no major modifications and restitution can be made. Therefore, before the mold is repaired, it should be based on the actual situation of the undesirable phenomenon of plastic products.
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A detailed analysis of the research to find out the real cause of defects in plastic products, and then propose a detailed repair program.