Causes and solutions of defects in the production process of PET tube embryo
In recent years, social and economic development has become more and more rapid, and PET tube embryos have been used more and more in daily life. When we produce tube blank products, we will encounter various defects in the products produced. What should we do? To solve these problems? Jiaoxiang has been engaged in the plastic mold industry for many years, and has its own set of concepts for the manufacture of PET tube embryo molds, and a set of analysis routines and solutions for tube blank product defects.
1. Blistering in the wall of the tube blank is a common problem of tube blank products. It is mainly produced in the middle part of the tube blank. The main reason is that the back pressure is not enough or the exhaust hole is blocked. Solution: If the reason is insufficient back pressure, you can increase the injection pressure. If the vent is clogged, clean the mold vent.
2. Bubble rupture in the preform wall (fork-like, ear-like, fish-bone-like), such phenomena are generally caused by too fast decompression, too long injection molding stroke, too high mold heating temperature and other reasons. Solution: It can be solved by increasing the decompression cycle, reducing the decompression stroke, and reducing the mold heating temperature.
3. The parting line shrinks and voids. This kind of phenomenon occurs on the parting line, which is caused by insufficient injection volume at one time. Solution: The injection volume can be appropriately increased.
4. The preforms are bonded and deformed because the preforms are too hot and the mold is not cooled enough. Solution: At this time, check whether the mold cooling system is faulty. If the cooling system is ok, you can increase the production time or increase the cooling time.
What are the elements of PET tube embryo molding?
1. Plastic processing
Since PET macromolecules contain lipid groups and have a certain degree of hydrophilicity, pellets are sensitive to water at high temperatures. When the moisture content exceeds the limit, the molecular weight of PET decreases during processing, and the product becomes colored and brittle. Generally, the proportion of PET tube embryo
recycled materials should not exceed 25%, and the recycled materials should be thoroughly dried.
2. Selection of injection molding machine
Due to the short stable time of PET after the melting point and the high melting point, it is necessary to use an injection system with more temperature control sections and less self-friction heat generation during plasticization, and the actual weight of the product (water-containing material) should not be less than machine injection. 2/3 of the amount.
3. Residence time
Do not use too long residence time to prevent the decrease of molecular weight, and try to avoid the temperature above 300°C. If the stoppage is less than 15 minutes, it only needs to be treated with air injection; if it is more than 15 minutes, it should be cleaned with viscosity PE, and the temperature of the barrel should be lowered to the PE temperature until it is turned on again.
4. Mold and gate designPET tube embryo
is generally molded with hot runner molds. It is better to have a heat shield between the mold and the template of the injection molding machine. Its thickness is about 12mm, and the heat shield must be able to withstand high pressure. The exhaust must be sufficient to avoid local overheating or fragmentation, but the depth of the exhaust port should generally not exceed 0.03mm, otherwise flashing will easily occur.