Prevention of material leakage in the hottest runn

2022-07-25
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Prevention of hot runner leakage

a common concern of mold manufacturers is that the molten material in the hot runner system will flow into the splitter plate groove after leakage. Generally, there are many reasons for material leakage, but there are ways to avoid each reason. As the externally heated hot runner system represents the main application type of hot runner, it is discussed as an example

what causes material leakage in the hot runner

in most cases, the smaller the heat flow under the same conditions, the more difficult it will be to cut and disperse the material leakage in the runner system is not caused by poor design, but because the operation is not carried out according to the design parameters. Generally, the universal testing machine with leakage power generation fluid servo has single space structure and double space structure, which is generated at the seal between the hot nozzle and the splitter plate. According to the design specifications of general hot runner, there is a rigid edge at the hot nozzle, which can ensure that the height of the hot nozzle assembly is less than the actual groove depth on the hot runner plate. This dimension difference (commonly referred to as cold gap) is designed to avoid damage to components due to thermal expansion when the system is at operating temperature. For example, for a 60mm thick splitter plate and a 40mm hot nozzle assembly (with a total height of 100mm), when the temperature rises to the operating temperature of 230 ℃, it usually expands by 0.26mm. If there is no cold gap, thermal expansion will often cause damage to the edge of the hot nozzle. Therefore, the lack of effective sealing under cooling conditions is the main cause of material leakage in hot runner

hot runner leakage is the main cause of mold damage and shutdown

generally, in order to ensure the sealing of the system (hot nozzle and splitter plate), the system must be heated to the operating temperature so that the force generated by it is sufficient to offset the injection pressure, so as to prevent the injection pressure from jacking the two parts. Generally, inexperienced operators will not wait for the system to reach the operating temperature. Worse, they may even forget to turn on the heating system. In this way, the pressure generated on the surface of the hot runner with cold gap can not prevent material leakage before it reaches its operating temperature

in addition, material leakage may also occur in the case of excessive heating. Due to the poor adaptability of the hot nozzle at the edge of the strip steel to thermal expansion, once the system is overheated and reduced to the operating temperature again, the sealing pressure generated by it cannot prevent leakage due to the influence of steel deformation. In this case, in addition to the system damage caused by material leakage, the hot nozzle will be irreparably damaged due to excessive pressure, and the system can be rebuilt so that the hot nozzle needs to be replaced

since the preload of the hot nozzle and splitter plate is very important, the dimension and tolerance requirements provided by the hot runner supplier must be strictly followed in order to effectively prevent material leakage of the system. Therefore, for the mold manufacturer, the height and groove size of all hot nozzle components shall be carefully checked according to the drawing requirements of the hot runner supplier. If there is any problem, it shall also communicate with the hot runner supplier in a timely manner

hot nozzle design options to prevent material leakage

sealing conditions of shunting plate and hot nozzle designed for various hot nozzles. Design with rigid edge and no leak proof function. This design has no active sealing and overheating protection under cooling conditions, and its operating temperature range is 27 ℃. The back of the hot nozzle is fixed on the distributor plate, and the high-temperature bolts that fix the hot nozzle on the distributor plate can prevent leakage under cooling conditions. Because the steel edge needs a certain expansion space at room temperature, the system still needs a cold gap. Although this method can prevent the leakage of molten material from the hot nozzle to the splitter plate, it can not prevent the thermal expansion of components under overheating conditions, and its operating temperature range is 27 ℃. An economical and effective way to prevent material leakage between the hot nozzle and the splitter plate can be applied to the small cavity number system. Since the hot nozzle fixed on the splitter plate with bolts can move together with the splitter plate, this design requires the minimum length of the hot nozzle and limits the mold cavity spacing. The hot nozzle edge is designed to be elastic rather than rigid. The elastic edge can provide preload under cooling conditions and prevent damage to the system. If it is overheated accidentally, it can also absorb thermal expansion, and its operating temperature range can be extended to 110 ℃

how to find material leakage

generally, it is difficult to find whether there is material leakage in the hot runner, because it can not be seen from the outside of the mold. However, if you observe carefully, you can still find material leakage through some signs. Generally, when a new hot runner is set, the operator knows how many times of injection can be contained in the runner. For example, if the runner can contain three times of injection (each injection is the capacity of the runner/mold cavity), there should be molten material in the mold cavity after three injections. If not, it is likely that the molten material leaked into the flow plate groove of benzene free and formaldehyde free materials. When the hot runner is enabled, it must be ensured that the injection volume is set correctly on the machine

during operation, another sign of material leakage is that part of the mold cavity or the product is not fully filled. This is because part of the molten material injected leaked into the splitter plate groove, resulting in insufficient injection molding of the product. On the control interface of the injection molding machine, this situation is displayed as a sudden change in process parameters

if the operator suspects that there is material leakage, the injection molding machine should be shut down immediately and checked after the system cools down. After cleaning the system and detecting the cause of material leakage, all components should also be checked. This is because overheated temperature or cleaning process may cause damage to components. If a component is found to be damaged, it should be replaced immediately

finally, it is worth mentioning that the operation advantage brought by high-quality hot runner mold is far greater than the trouble caused by possible material leakage during operation. Therefore, when purchasing hot runner, customers should fully understand the design and performance of various hot runner to ensure the machining accuracy of important parameters, and provide necessary technical training for relevant personnel

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