Hot runner technology has become an important developing direction of plastic injection molding technology, because of its unique technical advantages such as saving cost and shortening forming period. In Europe and the United States, injection molding production is largely dependent on hot runner technology, but in China, the use of this advanced technology is rare. However, with the further development of the mould industry in China, this technology will be gradually popularized and widely used, so how to select the appropriate hot runner system?
1. Injection pressure
Injection pressure loss in hot runner system can not be ignored. Many hot runner mold users have a misconception that the plastic solution in the hot runner is always hot, so the injection pressure loss of the hot runner is much smaller than that of the cold runner. In fact, in order to meet the needs of the hot runner structure design, the flow distance of the solution in the hot runner system will be greatly increased, so the pressure loss of injection molding in the hot runner system can not be speculated. In practical application, because the pressure loss of injection molding in hot runner system is too large and the injection molding is difficult, the flow distance of solution in hot runner system is large for plastics with poor fluidity (such as PCPOM and so on). The CAE software should be used to analyze and calculate the flow channel in the heavy weight of the parts.
2. Heating mode
One of the main differences between hot runner systems is the way the melt is heated. Internal heating system is the heater is directly installed in the fuse, from the internal heating of raw materials. The external heating system is the external heating of raw materials, so that the raw materials flow through the passage without hindrance. The external heating system solves the dead point problem and makes the shear curve more reasonable. Gate type There are many types of gates to choose from. Factors to be considered include allowed gate marks, gate locations, and type of raw materials for injection molding. Whether it is amorphous, crystalline or thermoplastic elastomer, different gate types are limited to specific raw materials. Knowing the most suitable feedstock for the gate can help select the best gate.
3. Standard or not
In general, hot runner system suppliers provide both standard and non-standard hot runner systems. As far as possible, users should select standard hot runner systems, including standard length and size of nozzles, hot runner plates, gate inserts, etc. This is due not only to the low price of the standard hot runner system, short delivery time, but also to the interchangeability of the parts, which is conducive to future use and maintenance. Once one part is broken, buy another standard part and install it.
4. Types of plastics processed
When selecting a hot runner system, the type of plastics to be processed must be considered. For example, when processing glass-reinforced plastics (such as glass reinforced nylon, etc.), wear resistant gate inserts should be used; if plastics that are easily decomposed easily (such as PVC) are processed, the sprue should be unobstructed, and the hot runner system with no flow dead angle should be used. If the plastics with poor fluidity (such as PCS) are processed, the larger nozzle series should be selected, and the larger section size of the sprue should be used in the hot runner plate.
5. Fuse size
In order to ensure the best system performance, plastic parts and processing conditions need to be analyzed. Therefore, not only the weight of the product should be considered, but also the appropriate melt channel size should be calculated, including melt flow index, injection time, Injection molding cycle and melt temperature, etc. The proper size of the melt channel is very important to the performance of the hot runner. The inappropriate size of the melt channel will lead to the degradation of plastics, or the inhomogeneity or filling of the injection molded parts, as well as the slow change of color, etc. Pressure drop, residence time, temperature rise, shear speed, color exchange frequency and other factors should be taken into account in order to determine the optimum melting channel size.
6. Multi-zone temperature control
If the user needs a large size, complex hot runner system, or plastic which is sensitive to temperature and has a narrow range of processing parameters, the design scheme of hot runner with multi-region temperature control should be selected. In this way, the user can adjust and control the temperature distribution according to the need. An ideal hot runner system should have a uniform temperature distribution, but there are actually a number of reasons for different temperatures around the hot runner: for example, the mass of the hot runner heating module, The excessive loss of heat at the interface between the hot runner system and the die, and the different shearing heat of the plastic solution in the hot runner. The larger and more complex the hot runner system is, the more it should be chosen with multi-zone temperature control.