November 15, 2025

Types of Runner Systems in Injection Moulding

Within injection moulding, efficiency, precision, and product quality rely heavily on one important element: the runner system. The runner system ensures that molten plastic flows smoothly and evenly from the injection unit into the mould cavity.

The understanding of the types of runners in injection molding and their implications for production may result in great improvements in product consistency, reduced waste, and enhanced cycle times.

In this article, we will discuss what runner mould is, the different types of runners a mould can have, and the basic differences that exist between cold and hot runner systems.

We’ll also highlight how industry leaders like Chem Trend are changing the face of molding operations with their innovative mold release agents and process optimization solutions.

What Is a Runner in Mould?

To understand the types of runners in injection molding, it’s important to start with the basics of what is a runner in mould?

A runner within an injection mould refers to the channels that allow the molten plastic, coming from the sprue, into the gate that feeds it into the mould cavity. In essence, it is a kind of passageway by which molten plastic is distributed to different parts of the mould to fill it evenly.

The efficiency in such a process is determined by the design, material, and temperature control of a runner system. If runners are not designed properly, it may lead to uneven filling, longer cooling times, increased wastage of the material, and even product defects like sink marks or warping.

Why Runner Systems Are Crucial in Injection Moulding

Runner systems are more than pathways: they directly affect

Cycle time: The runner design influences how quickly the mould can be filled and cooled.
Material efficiency: Optimized runners lessen waste and, hence, are more cost-effective.
Product quality: Proper flow balance ensures uniform part strength and surface finish.
Ease of automation: Efficient runner systems simplify part ejection and recycling of scrap material.

Companies such as Chem Trend support manufacturers in optimizing these processes with technologically advanced mould release agents and productivity enhancers that improve part release, reduce downtime, and extend tool life.

Different Types of Runner in Injection Molding

Broadly, the types of runner in mold are classified as:

Cold Runner System
Hot Runner System

Each of them has different advantages, limitations, and ideal use cases depending on the scale of production, type of material, and accuracy required. Let’s look at them in detail.

Cold Runner System

A cold runner system is the traditional and most common design found in injection molding. It consists of channels machined into the mould base that are at the same temperature as the mould itself.

How It Works:

When molten plastic is injected, it flows through the sprue into the runner channels. Once the cavity is filled, both the part and the solidified runner are ejected together.

Advantages of Cold Runners:

Cost-effective setup: The design of the mould is simple, thus not costly to make and service.
Material flexibility: Works well with a wide range of thermoplastic materials.
Easy maintenance: fewer components translate to easier cleaning and less downtime.

Simple to operate for low- to medium-volume production.

Disadvantages:

Material wastage: In every cycle, the runner solidifies and has to be removed, which leads to scrap material.
Longer cycle times: Production takes longer because both the runner and the part have to cool.
Less suitable for high-volume runs: Waste and cooling time become costly in a mass production context.

Hot Runner System

A hot runner system keeps the plastic inside the runner channels heated throughout the moulding cycle. The molten plastic remains in a liquid state, eliminating the need to eject or regrind solid runners.

How It Works:

Hot runners use a manifold with internal heating elements and temperature control systems. The molten plastic flows directly into the cavities through heated nozzles, ensuring a consistent temperature and pressure balance.

Advantages of Hot Runners

No material wastage: Since the runner stays molten, there’s no scrap to remove or recycle.
Faster cycle times: No need to cool the runner, reducing total production time.
Improved product quality: Ensures consistent temperature and flow, leading to fewer defects.
Automation-friendly: Ideal for high-volume, continuous production.

Disadvantages

High initial cost: Hot runner systems are complex and require significant investment.
Maintenance challenges: Heating elements and manifolds need precise temperature control and regular maintenance.
Material sensitivity: Not all plastics are suitable due to potential degradation from heat.

Chem Trend supports hot runner moulding processes through advanced purging compounds and release agents.

This maintains the integrity of the hot runner channels, reduces material buildup, and enhances operational efficiency.

Types of Runner Gate in Injection Moulding

In this context, the types of runner gate refer to the various methods in which molten plastic enters the mould cavity from the runner. The method selected for the design of the gate will affect the flow rate, stress distribution, and eventual appearance of the part.

Following are the common types of runner gate used in injection moulding:

Edge Gate

Located along the parting line of the mould.
Normally used for flat parts.
Easy to design and modify.

Submarine Gate

Enters the cavity from below the parting line.
Automatically separates the part from the runner and improves automation.

Pin Gate

Used in hot runner systems.
Provides clean gate marks and is suitable for multi-cavity moulds.

Direct Gate

The molten material flows directly from the sprue into the cavity.
Provides minimum pressure drop and is suited for big parts.

Fan Gate

Wider opening that distributes the material evenly.

Ideal for parts that require uniform filling and low stress marks. The selection of the appropriate types of runner gates depends largely on issues regarding geometry, material properties, and production goals.

To wrap up

Knowledge of the two types of runners in injection molding, namely cold and hot, aids manufacturers in making decisions about efficiency, cost, and quality of the product. While cold runners provide simplicity and low cost, hot runners offer higher precision and faster cycle times.

Both systems, however, require adequate maintenance and process control in order to perform optimally. Supported by valued partners such as Chem Trend, with advancements in release agents and purging solutions, manufacturers can further improve their injection moulding operations: cleaner moulds, smoother production, and more sustainable practices.

Whether you are working with cold-runner or hot-runner systems, the deeper understanding of types of runner in mold is the key for mastering the injection molding process to achieve high-quality, efficient, and repeatable production results.

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