For previous article reading, please refer to "Talking about mold optimization from perspective of injection molding process 1, 2, 3, 4, 5, 6.
Selection and optimization of hot runner molds
Hot runner mold refers to a mold that uses a heating device to keep melt in runner from solidifying. Because it has a shorter forming cycle than traditional molds and saves more raw materials, hot runner molds are widely used today.

 

Hot runner system generally consists of several parts such as hot nozzles, manifolds, temperature control boxes and accessories. Hot nozzles generally include two types: open hot nozzles and needle valve hot nozzles. Since form of hot nozzle directly determines selection of hot runner system and manufacture of mold, hot runner system is often divided into an open hot runner system and a needle valve hot runner system. Manifold is used when there are multiple cavities in one mold or when there are multiple feeding points or when there is a single feeding point but material level is offset. Material is usually P20 or H13. Manifolds are generally divided into two categories: standard and non-standard. Their structural form is mainly determined by distribution of cavities on mold, arrangement of nozzles and position of gate. Temperature control box includes main machine, cables, connectors, male and female wiring sockets. Hot runner accessories usually include: heaters and thermocouples, runner sealing rings, connectors and junction boxes.

 

Although there are many hot runner manufacturers and a variety of hot runner product series in the world, a typical hot runner system consists of following parts:

 

1. Hot runner plate (MANIFOLD)

 

2. Nozzle (NOZZLE)

 

3. Temperature controller

 

4. Auxiliary parts

Hot runner molds have many advantages. With improvement of injection molding product quality and development of injection molding automation production, hot runner molds are becoming more and more popular. Their advantages are mainly reflected in:
1. Molding cycle
Because there is no cooling time limit for runner system, parts can be ejected in time after cooling. Many thin-walled products produced with hot runner molds can be completed within 5 seconds.
2. Save raw materials
In pure hot runner molds, there is no cold runner, so no waste is generated. This is more valuable for product projects with expensive plastic prices. At the same time, when plastic prices rise, hot runner mold technology is an effective way to reduce waste and reduce material costs.
3. Improve product quality
During hot runner mold molding process, plastic melt temperature is accurately controlled in runner system, and plastic can flow into each mold cavity in a more uniform state to produce parts of consistent quality. Gate quality of hot runner molded products is good, residual stress is low after demolding, and part deformation is small. Therefore, many high-quality products are produced using hot runner molds.
4. It is conducive to automated production.
After hot runner mold is formed, product is finished product. There is no need to trim gate and process cold runner, which is conducive to automated production. Many manufacturers combine hot runners with automation to greatly improve production efficiency.

1. It is best not to use hot runner molds for plastics with poor thermal stability (easy to decompose and discolor);
2. Choose a hot runner with a needle valve hot nozzle to prevent hot nozzle from producing "drooling" or wire drawing problems;
3. Choose a hot nozzle with suitable materials and designs (to prevent generation of cold materials);
4. Choose a hot runner with a more stable temperature control system (this is key point);
5. For plastics with poor temperature resistance, a hot runner mold with a cooling ring hot nozzle should be selected;
6. Glass fiber reinforced plastics should be selected with good wear resistance. Hot runner made of steel;
7. Choose hot runner mold with external heating type and heat insulation board (even heat transfer);
8. Choose hot runner mold with terminal cover (to prevent terminal damage and short circuit caused by foreign matter such as oil, water, dust, etc.);
9. Hot runner should be smooth and have no "dead corners" to prevent sticking and heat from producing decomposition products (yellowing, black spots, black stripes, etc.);
10. For multi-cavity plastic parts, hot runner mold with balanced glue feeding in runner should be selected;
11. Choose hot runner mold with high cost performance, good reputation, big brand and good service;
For later reading, please refer to "Talking about mold optimization from perspective of injection molding process 8".