Four aspects to understand hot runner of injection mold

Hot runner meaning

Hot runner technology is an advanced technology applied to the feed runner system of plastic injection molds. It is a hot direction in the development of plastic injection molding technology.

The hot runner molding means that the plastic, sent from the injection machine nozzle to the gate, is always kept in a molten state. When unloading mould, it does not need to be solidified and taken out as waste. And then, the molten material retained in the feed system can be injected into the cavity during the next injection.

The ideal injection molding system should form parts with consistent density, which are not affected by all runners, flash and gates. Compared with cold runners, hot runners must maintain the molten state of the material, and will not be sent out with the molded parts. The hot runner process is sometimes called a hot manifold system, or runless molding.

Basically, the hot manifold can be regarded as an extension of the barrel and the nozzle of the injection molding machine. The function of the hot runner system is to deliver the material to each gate in the mold.

Advantages and disadvantages of hot runner technology

---Conventionally, the cold runner injection molding often has the following unfavorable factors:
1. Difficulty in filling the mold.
2. Deformation of thin-walled large parts.
3. Waste of raw materials in runner.
4. Different quality of injection molded parts in multi-cavity molds.

---For these problems, hot runner technology provides a relatively complete solution. In general, to adopt hot runners has the following benefits:
1. Save raw materials and reduce costs.
2. Shorten the molding cycle and improve machine efficiency.
3. Improve the surface quality and mechanical properties of products.
4. Pinpoint gate can be used without three plate mold.
5. Single product can be molded with side gates economically.
6. Improve automation degree.
7. Use needle valve gates to control gate freezing.
8. The quality of injection parts in multi-cavity molds is consistent.
9. Improve the surface aesthetics of injection molded products.

---However, each technology has its own shortcomings. Hot runner technology is no exception. Below is its some shortages:
1. Complex mold structure, its high cost and high maintenance cost.
2. The process is to keep stable after turning on the machine for a while, resulting in a large number of waste products.
3. When melt leakage and heating element failure occur, it has a great impact on product quality and production progress.

The third disadvantage above needs special attention. It is able to reduced by purchasing high-quality heating elements, hot manifold and nozzles, as well as carefully maintaining them during using.

Composition of hot runner system

The hot runner is composed of four parts: hot manifold, nozzle, heating element and temperature controller.

What kinds of molds are suitable for hot runners ?

Hot runner has many benefits as mentioned above. Do you know if every mold can use hot runners? The answer is no. Generally speaking, hot runner technology is only used for plastic molds, on the contrary, not every plastic mold is suitable for it.