Mold exhaust is so important, you don't even know?

Time:2019-05-10 11:30:57 / Popularity: / Source:

Exhaust of polycarbonate injection molding is very important in plastic injection molding technology, but it is often overlooked or ignored by many people. During polycarbonate injection molding process, there is a large amount of air in cavity, and injection molding machine can shoot at a speed of bullet. In such a rapid filling process, air in cavity must be quickly discharged. Otherwise it will cause various problems on the product. Main issues are as follows:
  1. Filling speed of product is slow, which affects filling speed and causes material to cool, especially thin-walled parts, which is not conducive to rapid filling of product;
  2. Pressure inside mold is large, and internal stress is formed on the product, which is a factor causing deformation of product and poor surface brightness;
  3. Temperature at the end of product flow rises sharply under high pressure, causing problems such as burning of product and fragility of welded joint;
  4. Causes temperature of material to rise, carbonization, formation of rubber powder on the surface of product, and defective products;
  5. Continuous high temperature of mold forming surface has a great influence on service life of polycarbonate injection molding.
Above problems are caused by poor exhaust gas, do you still pay attention to it?
To prevent and solve above problems, only mold exhaust is solved. However mold exhaust is also technically work. It must not be taken lightly and must be taken seriously. So how should we design and process venting groove?
1. Many plastic molding plant exhausts are processed by fitter himself according to experience. In fact, it is not correct. Mold exhaust should be designed by mold design according to results of mold flow analysis, material overflow value and experience, and processed by processing department. Then it is the correct approach;
2. Choice of venting position and depth is also important:
A. Do not design venting groove according to product size and wall thickness at a certain distance near gate. Because pressure near gate is large and pressure holding time is long, it is easy to form a cloak;
B. Depth of venting groove should not be same. Gate should be centered until material flow end and it should be gradually deepened. If material overflow value is 0.05MM, it can be designed as near gate area to flow end and gradually be 0.01, 0.015, 0.025, 0.03. Product flow end can even be designed to 0.05MM or deeper, and venting groove can be designed according to product wall thickness and injection pressure. Many plastic molding plant often afraid of trouble to design and process into same depth, which it is also wrong.
3. Spacing of venting groove should also be gradually encrypted with gate as center. Some even have to be designed as a full-circle parting surface venting groove, which uses parting surface to vent, but it should be noted that depth of full venting is also different. Otherwise it will cause a cloak near gate, but end of flow is poorly exhausted;
4. Venting groove must be designed at the end of runner and deep enough.
5. Mold inserts should be made into exhaust groove as much as possible, inserts should be designed as far as possible under deep ribs and deep grooves, and exhaust groove should be designed. Otherwise, filling defects and product gas trapping will be caused.
6. Structure of slider is also designed to be exhausted like a mold core, and design rules are same as those of mold core;
7. Exhaust groove must be designed at the location of product weld line, and depth of exhaust groove should be large;
8. For some thin-walled parts, because filling speed is very fast, it is necessary to make a complete exhaust sheet on the surface, and exhaust depth should be well grasped;
9. Some polycarbonate injection molding obviously made exhaust system but poorly exhausted. What happened? Please check if exhaust gas you have made is not open to atmosphere. If exhaust groove cannot be connected to atmosphere, it will become ear of scorpion. Especially insert venting is ignored by many people. This is very noteworthy;
10. Exhaust section in front section of exhaust sump is preferably 0.8~1.5 from product. It must not be too far away. Back end is deepened to above 0.5 and is open to atmosphere.
9. Do exhaust vents have to be properly polished, isn't it done by many people? Why does venting groove need to be polished? Because hot air is often discharged with some plastic dust, venting groove is too rough to hinder dust discharge. Glue powder sticking to venting groove will hinder venting and is difficult to clean;
10. Venting tank must be cleaned regularly. It is not to clean product after product has gone wrong. Mold maintenance should be cleaned up and even cleaned every shift.

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