How to deal with hot runner leaks
Some of these leaks are not due to poor system design, but rather to failure to follow design parameters. Leakage usually occurs at the seal between the hot nozzle and manifold. According to general hot runner design specifications, there is a steel edge at the hot nozzle that ensures that the height of the hot nozzle assembly is less than the actual slot depth on the hot runner plate. The purpose of designing this dimensional difference (often referred to as the cold gap) is to avoid damage to the component due to thermal expansion when the system is at operating temperature.
1. The back of the hot nozzle is fixed to the manifold; the high temperature bolts that hold the hot nozzle to the manifold prevent leakage under cooling conditions. This system still requires a cold gap because the steel edge requires some room for expansion at room temperature. Although this method actively prevents leakage from the hot nozzle to the manifold, it does not prevent the thermal expansion of the part under superheated conditions.
2. The hot nozzle bolted to the manifold moves together with the manifold. This design has a minimum length requirement for the hot nozzle and a limit on the cavity spacing. It is an economical and effective way to prevent leakage between the hot nozzle and manifold, and is suitable for systems with a small number of cavities.
3. The nozzle edge is designed to be flexible rather than steel. The flexible edge provides preload under cooling conditions and prevents damage to the system. It also absorbs thermal expansion if accidental overheating occurs, allowing for an extended operating range of ±110°C.
