1、 What is a hot runner?

Hot runner is a method of heating to ensure that the plastic in the runner and gate remains in a molten state. Due to the presence of heating rods and heating rings near or in the center of the runner, the entire runner from the outlet of the injection molding machine barrel to the gate is in a high temperature state, allowing the plastic in the runner to remain molten. After stopping the machine, it is generally not necessary to open the runner to remove the condensate. When restarting the machine, only the runner needs to be heated to the desired temperature. In short, a hot runner is an extension of the barrel of an injection molding machine.

2、 Structure of hot runner system

Hot runner systems generally include two types: open hot runner and needle valve hot runner.

An open hot runner is generally composed of several parts, including an injection nozzle, a splitter plate, a hot nozzle, a temperature control box, and accessories.

The needle valve type hot runner is generally composed of several parts, including injection nozzle, splitter plate, hot nozzle, temperature control box, cylinder or oil cylinder, valve needle, and accessories.

The mouth forms of hot runner are divided into large water mouth and pointed mouth.

The splitter plate is used for multi cavity or multi-point feeding of the first mock examination and single point eccentric feeding. The size of the splitter plate is mainly determined by the distribution of the mold cavity, nozzle arrangement, and gate position.

The temperature control box includes the host, cables, connectors, and wiring male and female sockets. Hot runner accessories typically include heaters and thermocouples, runner sealing rings, connectors, and junction boxes. Mainly controlling the temperature of the splitter plate and hot nozzle.

3、 Advantages and disadvantages of hot runner technology

benefit

1. Save raw materials and reduce costs. (Although the cold material head can still be recycled, due to factors such as manpower, the mixing ratio of recycled materials, etc., in order to maintain normal operation, it is necessary to accumulate some cold material heads, which leads to the retention of funds.)

2. Shorten the molding cycle and improve machine efficiency. (Due to the lack of cooling time limitations in the runner system, the workpiece can be ejected in a timely manner after solidification. Many thin-walled parts produced using hot runner molds can have a molding cycle of less than 5 seconds.)

3. Improve product quality (During the hot runner mold forming process, the temperature of plastic melt is accurately controlled in the runner system. Plastic can flow into each mold cavity in a more uniform and consistent state, resulting in parts with consistent quality.)

4. Improve the level of automation. After plastic is formed by a hot runner mold, it becomes a finished product without the need for trimming or recycling cold runners. Many foreign product manufacturers combine hot runners with automation to greatly improve production efficiency

However, each technology has its own shortcomings, and hot runner technology is no exception:

1. The mold structure is complex, with high cost and maintenance costs.

2. It takes some time for the process to stabilize after startup, resulting in a high amount of waste at the beginning.

3. When melt leakage or heating element failure occurs, it has a significant impact on product quality and production progress.

The third disadvantage mentioned above can be reduced by purchasing high-quality heating elements, hot runner plates, and nozzles and carefully maintaining them during use.

4、 Design Program

Firstly, determine the position of the feeding port based on the structure and usage requirements of the plastic parts. As long as the structure of the plastic part allows, the nozzle and nozzle head inside the fixed mold insert do not interfere with the forming structure, and the feeding port of the hot runner system can be placed at any position of the plastic part. The feeding port position for conventional plastic injection molding is usually selected based on experience, analyzing the cooling effect of various parts of the mold, and determining the ideal feeding port position.

Secondly, determine the nozzle head form of the hot runner system. The material and product usage characteristics of plastic parts are key factors in selecting the nozzle head form, and the production batch of plastic parts and the manufacturing cost of molds are also important factors in selecting the nozzle head form.

Thirdly, determine the number of cavities per mold based on the production batch of plastic parts and the tonnage of injection equipment.

Fourthly, determine the size of the mold structure based on the plastic part structure, and then select the standard length series size of the nozzle based on the thickness size of the fixed mold insert and the fixed template. Finally, adjust the thickness size of the fixed template and other dimensions related to the hot runner system.

Fifthly, determine the shape of the hot runner fixed plate based on the shape of the hot runner plate, arrange power line lead slots on the plate, and design sufficient cooling water loops near the hot runner plate, nozzle, and nozzle head.

Sixth, complete the design drawing of the plastic mold for the hot runner system.