Advantages
- Shortened Cycle Time:Since the runner does not need to be demolded,cooling time is reduced,thereby shortening the cycle time.
- Cost Reduction:Savings are made on the demolding ,transportation ,recycling ,storage , and pre-drying costs of the runner.
- Reduced Injection Volume:The elimination of the runner reduces the injection volume,allowing the use of smaller injection molding machines.
- Decreased Clamping Force and Plasticizing Capacity:The reduction in runner area decreases the projected area,thereby reducing the clamping force and plasticizing capacity.
- High Gate Design Flexibility:The hot runner system provides greater flexibility in the geometric design of the gate.
- Cooling and Pressure Advantages:Cooling is no longer an issue in the hot runner system,and lower pressures can be used.
- Reduced Melt Shear Stress:Increasing the cross-sectional area of the runner can reduce melt shear stress.
- Support for Advanced Technologies:Hot runner technology is the foundation for advanced techniques such as stack molding,sandwich molding,hot plastic resin foaming injection,and multi-color injection molding.
- Improved Molding Quality:Effective design of the thermal insulation area in contact with the surface,selection of appropriate materials,and individual cooling of gates can increase holding pressure time,improve the quality of molded parts ,and reduce part shrinkage.
Limitations
- High Mold Cost:Hot runner molds are more expensive,especially those with needle valve shut-off systems.
- High Energy Costs:The energy cost of hot runner molds is higher than that of traditional molds.However,considering the energy required for the main and sub-runners in a cycle,the hot runner system may be more advantageous.
- High Operation and Maintenance Costs:The operation and maintenance costs of hot runner systems are higher and require specially trained personnel.
- Increased Complexity:Hot runner molds are more complex than traditional molds and require careful operation and high precision.
- High Thermal Equilibrium Requirements:To minimize thermal and mechanical damage to the melt,a high degree of thermal equilibrium must be maintained,and the equipment temperature must be strictly controlled.
- Material Thermal Degradation Risk:The residence time of the material in the hot runner may exceed the allowable value,leading to thermal degradation.The type of heating(internal or external)may also cause material thermal degradation.
- Part Wear and Corrosion:Parts that are highly susceptible to wear and other hot runner components,such as nozzle tips and thermocouples,should be easily inspectable and replaceable.Metal surfaces are prone to chemical corrosion and require a protective layer.
- Difficulty in Color Change:Stagnant areas in the hot runner make color changes more difficult and may cause material degradation.
- Thermal Insulation at Gate Area:Thermal insulation should be achieved in the gate area to prevent thermal degradation or unwanted material cooling.
- Mechanical Stress on Miniaturized Parts:Miniaturized hot runner parts(such as micro-molding)can lead to high mechanical stress,especially for hot runner nozzles with high processing temperatures and high internal pressures.The lack of effective data makes the design of reliable parts complex.