Types and applications of hot runner system
In the application of hot runner technology, the correct choice of gate type is very important. Gate type directly determines the selection of hot runner system components and the manufacture and use of mold. Therefore, according to the different gate types, hot runner systems can be divided into three types: hot tip hot runner system, pouring sleeve hot runner system and valve hot runner system. Each type of hot runner system has its important application characteristics and application scope.For example,the cloth washing machine injection mold .
Many factors need to be considered when selecting the type of gate and hot runner system, among which the most important ones are the type of plastic matrix and additives, the weight, size and wall thickness of parts, the quality requirements of parts, the service life of tools and the output requirements of parts，such as the industrial part injection mold.
1. Hot tip hot runner system
Its working principle is that the HOTTIP of the insert located at the front end of the nozzle is combined with the cooling system to accurately adjust and control the plastic molding temperature at the gate. Therefore, the manufacturing material and shape design of nozzle insert HOTTIP are very important.
HOT TIP hot runner system can be used to process most crystalline and amorphous plastics such as PP, PE, PS, LCP, PA, PET, PBT, PEEK, POM, PEI, PMMA, ABSPVC, PC, PSU, TPU, etc. Generally speaking, hot tip gate is mostly used for machining small and medium-sized parts, especially for machining tiny parts.
The gate section diameter is mostly between 0.5mm and 2.0mm.. The diameter of the gate section is mainly determined by the weight and wall thickness of the parts, and of course, the quality requirements of materials and parts should also be considered. If the gate with smaller cross-section diameter is used, the gate will be closed quickly after the injection filling stage, the trace of the gate on the part will be small, and the surface of the part will be beautiful and the quality will be good.
If the diameter of the gate is too small, the shear rate of the plastic flowing through the gate will be too high, which will seriously damage the molecular chain structure of the plastic melt or the added materials in the plastic, resulting in the unqualified product quality that cannot meet the use requirements. The usual way to choose the gate size is to preliminarily determine the gate size according to the wall thickness at the gate of the part: gate diameter =(0.75-1.0) the wall thickness at the gate of the part. The value of plastic that is easy to flow is smaller, while that of plastic that is difficult to flow or sensitive to shear is larger.
Usually, the hot tip gate is directly opened on the part, or it can be opened on the cold runner and then the cold gate is opened on the part. This is a mold system that combines hot runner with cold runner. When using hot tip gate to make plastic parts, there will always be gate marks on the parts more or less. In many cases, the gate mark will be higher than the surface of the part, which will affect the beauty of the part or the assembly with other parts. Therefore, when selecting the gate position, the gate should be placed in the concave shelter of the part as far as possible.
2. pouring sleeve type hot runner system
In the pouring sleeve hot runner system, plastic enters the mold cavity through an OPENPIPE. The plastic flow pressure loss at the gate is small. The jacketed hot runner system is more suitable for injection molding of parts with medium size and weight.
The advantages of using the pouring sleeve hot runner system are that the shear rate experienced by the plastic when flowing through the gate to fill the mold is low, the residual stress of the parts after molding is small, the degree of deformation is small, and the mechanical strength of the parts is better. Compared with hot tip gate, the size of sprue bushing gate is larger, so the gate trace may be larger.
Therefore, in general, the plastic injection molding method is often used for molds with strict requirements on the aesthetics of gates; However, the internal structural parts with low requirements on the aesthetics of the gate can be manufactured by the pouring sleeve hot runner system. People also often use the pouring sleeve gate in combination with the cold runner, that is, the pouring sleeve nozzle is used as the main runner and the pouring sleeve gate is opened on the cold runner. In this application, the pouring sleeve gate can be opened larger to facilitate the plastic flow, because no one cares about the size of the gate trace on the cold runner.
Similar to the application of hot-tip hot runner system, it is very important to control the plastic temperature at the gate and the mold temperature. It is necessary to set up an independent cooling circuit around the gate. Because the size of the pouring sleeve gate is relatively large, if the temperature at the gate is not well controlled, it is more likely that the gate will not seal the plastic flowing after the mold is opened. The nozzle insert of the sprue hot runner system also has a variety of sizes, shapes and manufacturing materials, which should be comprehensively considered in combination with the type of plastic to be processed (such as crystalline plastic or amorphous plastic) and the cooling of the gate.、
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