Technical Knowledge Point Of Hot Flow Channel Of Injection Molds

- Oct 10, 2019-

The injection system of heat flow channel can be understood as the extension of injection molding machinery. The function of the hot channel system is to insulate the thermoplastic melt to the vicinity of the mold or directly to the mold.
The hot channel can be heated independently and thermally insulated in the injection mold, which alone can compensate for the heat loss caused by contact with the "cold" mold. Heat channel dies have been successfully used to process various plastic materials. Almost all plastic materials that can be processed with cold channel dies can be processed with heat channel dies.
Its parts are at least 0.1 grams and the largest is at least 30 kilograms. The hot channel mold has a wide range of applications in the fields of electronics, automobiles, medical care, daily necessities, toys, packaging, construction, and office equipment.
A successful hot runner die application project requires multiple links to ensure.
Among them, there are two most important technical factors: One is the control of plastic temperature;
The second is the control of plastic flow.
A typical heat flow system consists of the following parts: 1) MANIFOLD; 2) Nozzles(NOZZLE); 3) Temperature controller; 4) Auxiliary parts.
Advantages of hot runner die:
1) shorten the forming cycle of the parts;
2) Save plastic raw materials;
3) Reduce waste and improve product quality;
4) Elimination of follow-up processes to facilitate production automation;
5) Expand the application of injection molding technology.
At the same time, there are also shortcomings such as increased die costs, high requirements for manufacturing process equipment, and complex operation and maintenance.
In the more developed countries and regions, the production of hot runner dies is extremely active, and the proportion of hot runner dies is constantly increasing. Even some small die factories with less than 10 people are producing hot runner dies. However, the research of hot channel technology in China has just begun, and its application scope is limited to large-scale enterprises. The design capacity is relatively blank, so it is of great significance to the research of the application of this technology.
Type and application of 1 hot runner system
In the application of heat flow channel technology, the correct selection of gate type is very important. The type of gate directly determines the selection of hot channel system components and the manufacture and use of molds. Therefore, according to the different type of gate, the heat flow channel system can be divided into three types: heat tip heat flow channel system, pouring heat flow channel system, Valve heat flow channel system, etc.. Each type of heat flow channel system has its important application characteristics and application range.
Many factors need to be taken into account when selecting the type of gate and hot channel system, the most important of which are the types of plastic matrix and additives, the thickness of the weight and size of the parts, the quality requirements of the parts, the tool life and the output requirements of the parts.
1.1 Hottip Heat Flow System(HOT TIP)
The working principle is to combine the HOT TIP of the veneer at the front of the nozzle with the cooling system to accurately adjust and control the forming temperature of the plastic at the gate. Therefore, the manufacturing materials and shape design of HOT TIP for nozzle inlay are very important.
The HOT TIP hot channel system can be used to process most crystalline and amorphous plastics such as PP, PE, PS, LCP, PA, PET, PBT, PEK, POM, PEI, PMMA, ABSPVC, PC, PSU, TPU, etc.. And ... In general, the hot tip gate is mostly used for the processing of small and medium-sized parts, especially for the processing of small parts.
The gate section diameter is mostly between 0.5 mm and 2.0 mm. The determination of gate section diameter is mainly determined by the weight and wall thickness of the parts. Of course, the quality of materials and parts should also be considered. If a small cross section diameter gate is used, after the injection filling stage, the gate is closed quickly, the pin marks on the part are small, and the surface of the part is beautiful and of good quality.
If the gate diameter is too small, it will cause the plastic to flow through the gate at a high shear rate, which will seriously damage the plastic melt molecular chain structure or the added materials in the plastic, resulting in unqualified products can not meet the requirements for use. In selecting the size of the gate, it is customary to initially determine the size of the gate based on the wall thickness at the gate of the part: the gate diameter =(0.75-1.0) the wall thickness at the gate of the part. The processing of fluidic plastics takes a smaller value, while the processing of refractory plastics or shear sensitive plastics takes a larger value.
Usually the hot tip type gate is directly opened on the part, and it can also be opened on the cold gate and then the cold gate is opened on the part. This is a kind of die system that combines hot channel and cold channel. When making plastic parts with hot tip gate, there will always be more or less traces of gate on the parts. In many cases, the gate trace will affect the surface of the part, affecting the beauty of the part or affecting the assembly with other parts. Therefore, when selecting the location of the gate, the gate should be placed as far as possible on the concave and hidden part of the part.
1.2 SPRUE GATING Poured Heat Stream System
In the pouring hot channel system, the plastic enters the mold cavity through the open channel(OPEN PIPE). Low loss of plastic flow pressure at the gate. The pouring type hot runner system is suitable for injection molding with medium size weight and above parts.
The advantage of using a cast hot channel system is that the plastic has a low shear rate when it is filled through the gate, the residual stress is small, the deformation degree is small, and the mechanical strength of the parts is relatively good. Compared with the hot tip type gate, the pitcher gate size is larger, so the gate Mark may also be relatively large.
Therefore, under normal circumstances, plastic injection molding is often used for moulds with more stringent requirements for the aesthetic degree of the pouring gate; The internal structure parts that require less aesthetic degree can be manufactured by the pouring type hot channel system. People often use the pouring gate and the cold gate together, that is, the pouring nozzle is used as the main gate, and the pouring gate is opened on the cold channel. In this application, the pouring gate can be larger to facilitate the flow of plastics because no one cares about the size of the gate mark on the cold gate.
Similar to the application of the hot tip hot channel system, the control of the plastic temperature and mold temperature at the gate is extremely important. Separate cooling loops need to be set around the gate. Because the size of the pouring gate is relatively large, if the temperature control at the gate is not good, it is more likely that the gate will not be able to seal the flow of the plastic after the mold is opened. The nozzle inlay of the pouring hot channel system also has a variety of dimensions and changes in manufacturing materials. It is necessary to combine the type of plastic to be processed(such as crystalline plastic or amorphous plastic) with the cooling of the gate.