Advantages of hot runner technology
1. Saving plastic raw materials
Due to the lack of condensation in the hot runner. Or a very small cold material handle, basically no cold runner gate material needs to be recycled, especially for expensive plastic products that cannot be processed with recycled materials, which can greatly save costs. If the hot runner is used for normal production, it usually takes 2-3 months to recover the cost of the hot runner.
2. Improve product quality
Compared with the three plate mold with double parting surfaces, the plastic solution temperature in the hot runner system is not easy to decrease, maintaining constant humidity, and there is no need for a cold runner mold to increase the injection temperature to compensate for the decrease in plastic solution temperature. Therefore, the plastic solution in the hot runner system is easier to flow, and for large, thin-walled, and difficult to process plastic products, it is easier to form. After demolding, the residual stress of the product is low, and the product deformation is small. The hot runner system makes the gate smaller, When choosing a needle valve type hot runner for pouring, only the valve needle marks can be seen.
3. Improve productivity and achieve automated production
After the plastic product is formed by a hot runner mold, there is no need to build a gate. The process of taking the condensate handle is conducive to the automatic separation of the gate and the product, facilitating the automation of the production process, and shortening the plastic product forming cycle.
4. Strengthen the function of the injection machine
The plastic solution in the hot runner system is conducive to pressure transfer, and the pressure loss in the runner is relatively small, which can significantly reduce injection pressure and locking force, reduce injection and holding time, and make it easier to form large-sized plasticity with long processes on smaller injection machines. Choosing smaller injection machines and reducing the cost of injection machines strengthen the functions of injection machines and improve injection molding processes.
5. Improve product consistency and balance
6. The hot runner system can be manually balanced according to the rheology principle. The mold filling balance is achieved through temperature control and controllable nozzle. The effect of natural balance is also very good. The precise control of the gate ensures the consistency of multi cavity molding and improves the precision of plastic parts.
Limitations of hot runner technology
1. Increase in mold costs
The components of the hot runner system are relatively expensive, with a relatively complex structure and high machining costs, resulting in a significant increase in mold costs. Sometimes, the cost of the hot runner system can exceed the cost of the cold runner mold itself. If the production volume of the product is small, choosing a hot runner system may not be compensated. Therefore, the high price of the hot runner system is the main obstacle to promoting hot runner technology.
2. Improvement of mold production process requirements
Due to the involvement of multiple disciplines in hot runner technology, such as mold materials, heating materials, electronics, etc., precision machining machinery is required to ensure the hot runner mold. The fit between the hot runner system and the mold is extremely strict, and a series of issues such as mold material expansion also need to be considered. If the fit is not good, overflow will occur. Phenomena such as gate freezing have led to a decrease in the quality of plastic products, resulting in severe inability to produce.
3. Has certain selectivity in the number and distribution of plastic raw materials and small cavities
The hot runner system cannot be applicable to all plastics. Thermosensitive plastics have a greater risk of burning, and after plasticizing in the injection material, it is necessary to prevent overheating and decomposition in the hot runner system. Due to the diameter of the hot runner nozzle, the number and distribution of some small cavities are limited.
4. Increased maintenance costs
Compared to cold runner molds, hot runner molds are relatively complex. Improper use or operation can easily damage hot runner parts. If the runner is blocked, it is necessary to stop the machine for cleaning and maintenance.
(1) Leakage of hot runner system
The sealing components of the hot runner system fail, the system pressure exceeds the clamping force of the components, and the system temperature is too high, which often leads to solution leakage and easily damages the heating components. The main reasons for leakage in the hot runner system are as follows:
1. The central support pad is too high
2. The support pad is too low
Insufficient clamping force on the fastening screws of the 3-channel plate
4 channel plate nozzle overheating
The blockage of the 5 channel plate channel is too loose or the design is unreasonable
(2) Gate blockage
Gate blockage is generally caused by low temperature or blockage of impurities at the gate.
1. Unreasonable nozzle design, insufficient heat at the tip
2. The nozzle has too much contact with the mold, resulting in too fast heat transfer
3. The straight body of the discharge hole is too long, generally not exceeding 0.3mm
4. The nozzle and mold are not well matched, and the discharge gap is too small
The tip of the nozzle is too far from the discharge gate
(3) Gate casting and wire drawing
Casting and wire drawing are generally caused by overheating in the gate area, especially for heat sensitive plastics. Pay attention to adjusting the temperature of the heat flow plate and nozzle, pay attention to the type and structure of the nozzle during design, and design a cooling system around the gate to accelerate the cooling speed.
(4) Common faults of temperature controller
The temperature controller displays abnormally, displaying ", HHH", the aviation plug is not properly plugged in, the thermocouple wire is in poor contact, or the thermoelectric coupling is open circuit. Display "LLL" thermocouple wire reversed.
The temperature controller trips, usually due to leakage or internal short circuit of the heating element.
The temperature display of the 3 temperature controller has reached the upper limit, but the temperature continues to rise. The heater continues to operate, and the fault is usually caused by damage to the thyristor or solid-state relay.