What is a Hot Runner Mould

A hot runner mould is an injection mold with a manifold system (i.e., containing a heating component, manifold, and nozzle) that ensures that molten plastic injected into the mold maintains its temperature.

Hot runner injection molding is suitable for   molding plastics that require steady flow and injection pressure for part fabrication. Furthermore, with the method, there is a reduction in defects such as sink marks that occur due to fluctuating injection pressure and underfilled molds.

A hot runner system is an assembly of heated components used in plastic injection molds .that inject molten plastic into the cavities of the mold. (The cavities are the part of the mold shaped like the parts to be produced.)

By contrast, a cold runner is simply a channel formed between the two halves of the mold, for the purpose of carrying plastic from the injection molding machine nozzle to the cavities. Each time the mold opens to eject the newly formed plastic parts, the material in the runner is ejected as well, resulting in waste. A hot runner system usually includes a heated manifold and a number of heated nozzles. The main task of the manifold is to distribute the plastic entering the mold to the various nozzles which then meter it precisely to the injection points in the cavities.

Unlike cold runner systems, hot runner systems do not require sprue and runner systems. They are feed systems that convey molten plastic from the machine nozzle into the cavity. It uses a heated manifold to keep that plastic in a molten state. The heated plastic travels from the molding machine nozzle through internal channels called “hot runners” and can be delivered into multiple cavities at the same time. The only component that needs to be removed each cycle is the part itself, ensuring the mold can be cycled again very quickly. The increased cycle time and reduced plastic waste is ideal for high-volume production.

A hot runner mold system is an assembly of many different parts:

-Manifold, generally heated by electricity

-A number of controllers, determined by the number of injection points

-Thermostat to control the heat of the manifold

-Plate, where the runners sit. This component is also heated

The hot runner system is widely applicable in plastic product fabrication due to the following advantages:

• Reduced cycle time: One main difference between a hot runner and cold runner injection molding is the cycle time. Hot runner injection molds have a faster cycle time due to the plastic being kept at optimum temperature, increasing flowability.

• Reduced material wastage: It’s more cost-effective as the mold system generates little to no material waste.   

• Optimal Part Quality: Parts made using hot runner molds have better final quality due to the excellent filling profile and injection pressure.  

• Molding Automation: Automation is possible because there is no need for post-processing processes such as trimming, waste recycling, and removal of runners.  

• Design Flexibility: There is flexibility in injection mold design in the placement of the gate using the hot tip gate, valve gate, or edge gate. As a result, there is an increase in part aesthetics and optimum filling of mold cavities during the injection.