Hot Runner vs Cold Runner Injection Mold: Key Differences You Need to Know

Hot Runner vs Cold Runner Injection Mold: Key Differences You Need to Know


An injection mold is a component designed according to the intended product using processes such as CNC machining and is where the molten plastic is injected and cooled. There are several injection molds types. However, based on the temperature held by the runner and the mold, there are two mold systems: hot runner and cold runner.Get more news about Hot Runner Mold Design,you can vist our website!

Each mold system uses a different mechanism which affects plastic fabrication differently. As a result, there is a need for a proper understanding of the hot runner mold vs cold runner mold comparison before selection. This article does the hot runner vs cold runner injection molding comparison by introducing both systems, how they work, and their differences. Furthermore, it shows how to choose the right mold for your project.
A hot runner mold 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.

Types of Hot Runner Mold
Based on the method of maintaining the heat, here are the two types of hot runner molds used in plastic injection molding:

Insulated Hot Runners
Insulated hot runners molds have extremely thick runners in the mold plate, which causes part of the molten plastic to cool down and insulate the system. The insulation reduces heat loss, allowing the mold system to maintain an open plastic flow.

Insulated hot runner molds are less expensive than heated ones because they do not use manifolds and drops. Furthermore, they have flexible gates, reduced defects, and favor easy color change. However, it has a few disadvantages, such as freeze-ups at the gate, non-uniform mold filling, long start-up periods, and the need for a fast cycle to maintain the thermoplastic molten state due to the absence of a manifold system.

Heated hot runners
The heated hot runner is the major type of hot runner system with heating achievable using a heating component in one-half of the mold. However, they come in two designs: externally heated and internally heated.

Externally heated hot runners: The heating component is outside the mold. As a result, there is no obstruction in the molten thermoplastic flow (better flow control) and no drop in injection pressure. Furthermore, the molten plastic does not freeze and is ideal for color change. Externally heated hot runner molds are suitable for thermosensitive materials.
Internally heated hot runners: Here, the heating component is in the mold, leading to a drop in injection pressure, incompatibility with color change, and material hanging up and degrading in the mold. However, there is better flow due to the heated runner and gate tip control.
What is a Cold Runner Mold?

A cold runner mold is the basic injection mold with runners at the same temperature as the mold cavity. The system involves injecting the molten plastic into locating ring. Afterward, the molten plastic passes through a sprue and runner, which are cold, before entering the mold cavity. As a result, when the plastic cools, it takes the shape of the mold cavity with the solidified plastic in the runner attached.

The cold-runner mold features a large runner (larger than the part), removing the tendency of underfilling the mold. Aside from that, it is suitable for working with any plastic polymer irrespective of heat sensitivity, is less expensive than hot runners, and is easily maintained. However, they generate waste.