Key points for using hot runner injection molds
As an advanced injection molding machine, the correct use of hot runner injection molds is crucial for ensuring production efficiency and product quality. Before use, the hot runner system must be thoroughly inspected, including the integrity of components such as the hot runner plate, hot nozzle, heating elements, and temperature sensors. The heating elements must be checked for proper operation and the temperature sensors for accuracy and sensitivity to prevent uneven heating that can lead to poor melt flow or decomposition. For example, a factory using a hot runner injection mold to produce PC lenses failed to detect damage to the hot nozzle heating coil. This allowed the melt to cool and solidify at the nozzle, blocking the flow path. This not only impacted production schedule but also damaged the hot nozzle.
The preheating and temperature control of hot runner injection molds are important links during use. Before starting the machine, the hot runner system needs to be slowly preheated to evenly increase the temperature of the hot runner plate and the hot nozzle to avoid thermal stress caused by excessive local temperature differences, which may lead to component damage. During the preheating process, the temperature should be gradually increased according to the set temperature gradient, usually not exceeding 100°C per hour. At the same time, the operating temperature of the hot runner system must be strictly controlled, and appropriate temperature parameters must be set according to the characteristics of different materials to prevent excessively high temperatures from causing material degradation, or excessively low temperatures from affecting melt fluidity. When a plastics factory was producing gears made of PA66, the hot runner system temperature suddenly rose due to insufficient preheating, resulting in cracks in the hot runner plate and causing losses of tens of thousands of yuan.
During the production process, injection process parameters must be properly controlled to adapt to the characteristics of hot runner injection molds. Parameters such as injection pressure, injection speed, holding pressure, and holding time must be adjusted based on the structure and material of the plastic part, as well as the characteristics of the hot runner system. Generally speaking , hot runner systems offer good melt fluidity, and the injection pressure and speed can be appropriately reduced to avoid defects such as flash and overflow. However, for thin-walled parts or parts with complex structures, sufficient injection pressure and speed must be maintained to ensure that the melt fills the mold cavity. A medical device manufacturer, after multiple tests, reduced the injection pressure from 120 MPa to 100 MPa and the injection speed by 15% when producing precision syringes. This not only ensured the molding quality of the plastic part, but also reduced wear on the hot runner system.
Routine maintenance of hot runner injection molds is crucial to extending their service life. After production, residual melt within the hot runner system must be promptly cleaned to prevent it from cooling and solidifying and clogging the runners. This can be done using specialized cleaning tools or by increasing the temperature to allow residual melt to flow out. Regular inspections of the hot runner system’s sealing performance are also necessary to prevent melt leakage. High-temperature grease should be regularly applied to the mating areas between the hot nozzle and the mold to reduce wear. An automotive parts manufacturer has implemented a strict maintenance regime, cleaning the hot runner system after daily production and checking sealing performance and lubrication weekly. This has resulted in the hot runner injection mold’s service life extending by over two years.
Furthermore, the operator’s professional skills and operational standards can also impact the effectiveness of hot runner injection molds. Operators must undergo professional training and be familiar with the working principles and operation of hot runner systems, enabling them to accurately identify and address issues that arise during the production process. During the production process, close attention should be paid to changes in the quality of plastic parts. If surface defects or dimensional deviations are detected, process parameters should be adjusted or the hot runner system should be inspected promptly. An electronics company, through systematic operator training, has enabled them to quickly identify anomalies in the hot runner system and take timely action, reducing downtime caused by improper operation by 50%.
