Material leakage problem in the hot runner system
Publisher: Administrator Date: 2023-11-02
Hot runnerThe invention and application of has brought more development opportunities for mold manufacturers; From general-purpose plastics such as polypropylene and polyethylene, to engineering plastics such as polycarbonate and glass fiber reinforced nylon, many different materials can be processed through hot runner systems. However, this technology and equipment often bring some troubles to mold manufacturers, with material leakage being one of the problems
The different size of the melt channel directly affects the performance of the hot runner. Improper melt size can lead to plastic degradation, uneven or incomplete filling of injection molded parts, and slow color change. When determining the size of the melt channel, mold manufacturers should consider factors such as pressure drop, residence time, temperature rise, shear rate, and color change frequency.
After determining the system type, it is then necessary to choose the appropriate gate type and its filling speed. There are various types of gates, and factors to consider include: allowable gate marks, gate position, and type of injection material. Whether it is amorphous or crystalline plastics, different gate types have limitations on specific raw materials. Most hot runner systems can be matched with different sizes of hot nozzles, each of which can provide a specific filling speed. A gate that is too small will limit plastic filling and may cause excessive shear, leading to material degradation.
Analysis and Countermeasures of Material Leakage Causes
One of the most frustrating issues for mold manufacturers is that the molten material in the hot runner system leaks and flows into the splitter slot. This is also one of the main reasons for mold damage and stoppage.
Most of the leakage situations are not due to poor system design, but rather to failure to operate according to design parameters. Leakage usually occurs at the sealing area between the hot nozzle and the splitter plate. According to the design specifications of general hot runner, there is a steel edge at the hot nozzle to ensure that the height of the hot nozzle component is less than the actual groove depth on the hot runner plate. The purpose of designing this size difference (commonly referred to as cold gap) is to avoid thermal expansion causing component damage when the system is at operating temperature.
Leakage may also occur under excessive heating. Due to the poor adaptability of the hot nozzle with steel edges to thermal expansion, the sealing pressure generated by the system cannot prevent leakage due to the influence of steel deformation when the system is heated to operating temperature. In this case, in addition to material leakage causing damage, excessive pressure can also cause irreparable damage to the hot nozzle, requiring replacement.
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