Hot runner mold heating, which method is better?

Which method is better for heating the hot runner of the mold?

Mold heating ensures that the plastic melt has good fluidity in the mold cavity. Therefore, the temperature of the mold directly affects the molding, quality, and performance of the product to be processed.

Hot runner is a heating component used in injection molds to inject melted plastic particles into the mold cavity. The runner is also called a runnerless runner. Through the heating of the runner and the runner, the plastic in this section of the runner from the injection machine nozzle to the cavity entrance is kept in a molten state, so that when opening the mold, only the plastic part needs to be taken out, without taking out the runner and runner condensate. This not only shortens the molding cycle, saves raw materials, greatly improves production efficiency, and reduces costs, but also ensures the transmission of injection pressure in the runner. To a certain extent, it overcomes the defects of dents and shrinkage caused by insufficient shrinkage compensation of plastic parts.

Hot runner molds are a brand-new structure compared to traditional molds or three-plate molds. Hot runners are generally composed of hot nozzles, main manifolds, temperature control boxes, and accessories. However, there are many ways to heat the mold, including direct heating with electric heating tubes, steam heating, electromagnetic heating, and thermal oil heating. Which heating method is more suitable depends on the specific application environment.

There are two commonly used heating methods, one is electric heating, and the other is to pass heat medium into the mold, often using hot water or hot oil for heating. This heating method is more convenient and cheaper. If the injection machine is equipped with a mold temperature controller, it is also more convenient to adjust the temperature of the heat medium.

In the electric heating of the mold, there are two types of electric heating devices used, one is resistance heating, and the other is induction heating. The induction heating device has a complex structure and a large volume. GSM molding molds almost all use resistance heating. Electric heating components are set around or inside the mold to heat the mold.

Generally, electric heating is used for molds that need to provide sufficient heat energy and have high temperature requirements, such as thermosetting plastic molds and hot runner plates of hot runner molds. In order to achieve uniform heating of the mold, ensure the molding temperature requirements, and reduce the loss of electric heating power, when designing the electric heating system, electric heating has the advantages of a large temperature adjustment range, easy installation, easy maintenance, clean, pollution-free, and high efficiency and energy saving. Therefore, it is widely used.

Types of mold electric heating tubes

Single-head electric heating tubes, double-head electric heating tubes, spring heating coils, flexible and deformable electric heating tubes.

For general injection molds, single-head electric heating tubes are commonly used.

Electric heating tube lead-out method

The internal lead-out is led out from the inside of the electric heating tube, and the lead is not easy to break, but the cost is high.

The external lead-out terminal pin extending from the electric heating tube is welded with a high-temperature lead, which is relatively low in cost and widely used.

How to use the mold electric heating tube

Insert type

Wrap type

Sleeve type

Hot runner mold

The manifold is the central component of the hot runner system. The manifold is a mold with multiple cavities or multiple feeding points. It distributes the plastic melt transmitted from the main channel nozzle to each injection point nozzle through the manifold. The manifold can make the mold cavity evenly filled, the plastic flow balanced, and the system heat balanced. The manifold series includes X-type, H-type, I-type, Y-type, and K-type.

There are two ways to heat the hot runner manifold

One is internal heating, that is, setting a heating rod in the flow channel to heat the plastic from the inside of the flow channel. The other is external heating, which generally opens a heating hole in the direction parallel to the flow channel, inserts a heating rod or installs a heating ring, and heats the flow channel from the outside of the flow channel. Compared with these two methods, the internal heating method has higher thermal efficiency, but it is easy to cause local overheating in the hot runner system and increase the flow resistance of the melt; although the external heating method will not cause local overheating and the flow resistance in the runner is small, the runner is easy to process, the heating device is easy to purchase, and the maintenance is convenient, but the heating efficiency is low.

Hot nozzles are divided into

open hot nozzles and needle valve hot nozzles. Since the form of the hot nozzle directly determines the selection of the hot runner system and the manufacture of the mold,

therefore, the hot runner system is often divided into open hot runner system and needle valve hot runner system accordingly. Generally, spring heating coils and flexible deformation tubes are used.

Advantages of hot runner molds

Save raw materials, reduce costs, shorten molding cycles, improve machine efficiency, improve product surface quality and mechanical properties, improve the surface aesthetics of injection molded products, and can economically mold single products with side gates. The quality of injection molded parts of multi-cavity molds is consistent, and the degree of automation is improved.

However, every innovative technology brings advantages, but also has shortcomings, and hot runner mold technology is no exception

Hot runner molds have complex structures, high costs, high maintenance costs, and require a certain amount of time to start up before the product process can be stable