Hot runner is to ensure that the plastic of the runner and gate is kept molten by heating. Since there is a heating rod and heating ring near or in the center of the runner, the entire runner from the nozzle of the injection molding machine to the gate is in a high temperature state, so that the plastic in the runner remains molten, generally do not need to open the runner to take out the condensate after shutdown, and only need to heat the runner to the required temperature when starting up. Therefore, the hot runner process is sometimes referred to as a hot collector system, or as channelless molding.

What is a hot runner?

Hot runner is to ensure that the plastic of the runner and the gate is kept molten by heating, because the heating rod and heating ring are arranged near the runner or in the center of the runner, the entire runner from the injection molding machine barrel exit to the gate is in a high temperature state, so that the plastic in the runner remains molten, generally do not need to open the runner to take out the condensate after shutdown. When turning on, just heat the runner to the desired temperature. In short, the hot runner is an extension of the barrel of the injection molding machine.

Second, the structure of the hot runner system

Hot runner system generally includes two kinds: open hot runner and needle valve hot runner.

Open hot runner is generally composed of several parts, such as injection nozzle, diverter plate, hot nozzle, temperature control box and accessories.

Needle valve type hot runner is generally composed of injection nozzle, diverter plate, hot nozzle, temperature control box, cylinder or cylinder, valve needle, and accessories.

The mouth of the hot runner is divided into large water mouth and pointed mouth.

The shunt plate is used in a mode of multi-cavity or multi-point feeding, single point eccentric feeding. The size of the diverter plate is mainly determined by the distribution of the cavity on the mold, the arrangement of the nozzle and the position of the gate.

The temperature control box includes a host, cables, connectors and wiring male and female sockets. Hot runner accessories usually include: heater and thermocouple, runner seal ring, connector and junction box. It is mainly used to control the temperature of the diverter plate and the hot nozzle.

Advantages and disadvantages of hot runner technology

Benefits

1, save raw materials, reduce costs. (Although the cold head is still recyclable, but based on manpower factors, the mixture ratio of recycled materials... In order to maintain normal operation, some cold material heads must be accumulated, resulting in the retention of funds.)

2, shorten the molding cycle, improve machine efficiency. (Since there is no limitation on the cooling time of the runner system, the parts can be ejected in time after forming and curing. Many thin-wall parts produced with hot runner molds can be formed in less than 5 seconds.)

3, improve the quality of the product (in the hot runner mold molding process, the plastic melt temperature is accurately controlled in the runner system. The plastic can flow into each mold cavity in a more uniform state, resulting in a consistent quality part.)

4, improve the degree of automation. (The plastic is finished after the hot runner mold is formed, and there is no need to trim the gate and recycle the cold runner. Many foreign product manufacturers combine hot runner with automation to greatly improve production efficiency.

However, every technology will have its own shortcomings, and hot runner technology is no exception:

1, the mold structure is complex, the cost is high, the maintenance cost is high.

2, it takes a period of time to start the process will be stable, resulting in more waste at the beginning.

3, melt leakage, heating element failure, great impact on product quality and production schedule.

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

Four, design program

First, according to the structure of the plastic parts and use requirements, determine the position of the feed port. As long as the structure of the plastic part allows, the nozzle and nozzle head in the fixed die insert do not interfere with the molding structure, the feed port of the hot runner system can be placed in any position of the plastic part. The feed port position of conventional plastic injection molding is usually selected according to experience, and the cooling effect of each part of the mold is analyzed to determine the ideal feed port position.

Second, determine the nozzle head form of the hot runner system. The use characteristics of plastic materials and products are key factors in the selection of nozzle head form, and the production volume of plastic parts and the manufacturing cost of molds are also important factors in the selection of nozzle head form.

Third, according to the production batch of plastic parts and the tonnage size of the injection equipment, determine the number of cavities per mold.

Fourth, determine the mold structure size according to the structure of the plastic parts, and then select the nozzle standard length series size according to the thickness size of the fixed mold insert and the fixed template, and finally trim the thickness size of the fixed template and other sizes related to the hot runner system.

Fifth, determine the shape of the hot runner fixing plate according to the shape of the hot runner plate, arrange the power cord lead groove on the plate, and design sufficient cooling water loop near the hot runner plate, nozzle and nozzle head.