Injection molding is a well-known production process and is used by top firms around the world to make plastic products in large numbers. This process is technical and makes use of machines. Thus, it reduces human efforts, increasing efficiency and reducing cost. What you may not know though is that there’s more. The injection molding process has an extension or rather still can be diversified.

One extension of injection molding is the heat runner system. It is more known as a hot runner system. People think of it as an extension of injection molding. However, it has its own features. It has its own usage. It has its own type but occurs after injection molding. Some even say that it improves the injection molding system. Whether this is true or not, we will find out.

So, this article aims to give you information. Inform you of the hot runner system. All it entails into a short intro. Thus, we begin with a definition of the hot runner system.

What is Hot Runner System

Many writings define it differently. But one regular theme is its relation to injection molding. The hot runner system is an extension of injection molding tech also known as hot sprues. It is a system of parts, physically heated so that they can better move melted material from machine nozzles to the mold cavities for molding.

The design of hot runners is that they improve efficiency. They reduce cycle time by improving production efficiency. It’s a group of heated parts used in injection molding. And this helps inject melted plastic into mold cavities. It is simply the opposite of the cold runner system. So, instead of no heat, its parts are heated.

It was first developed in the early 60s but gained importance in the 80s and 90s. It became more vital with the craze for plastic materials.

Features/ Uses of a Hot Runner System

A hot runner system comprises many parts. These include a heated manifold and heated nozzles. The nozzles are often many.

The main aim is to distribute plastics properly and to send melted plastics to the nozzles which then ensure precise injection into the mold cavities. This ensures efficiency in the distribution of plastics. Thus, improves the injection molding process. It saves cycle time and reduces plastic waste.

Hot runners tend to be complex. For they have to maintain molten at a uniform temperature. Even while the injection machine cools, it tends to be hard. So, there is a hot runner controller to control the heat levels of the hot runner. This helps retain a uniform molten in nozzles. These are the basic uses of the hot runner system.

Advantages of a Hot Runner System

Like everything in life, the hot runner has pros and cons. Hot runner offers some pros such as flexible design, reduced cycle time, improved efficiency, and much more. These pros benefit the final result of molding. So, these benefits include;

Improved Efficiency

In general, hot runners improve the efficiency of injection molding. It has no solid runners that need removal. It is always to run. That is, runs when the system gets to operating temperature. Starting it is easy. And it can use low injection pressure to operate which reduces deflection in the mold.

Reduced Cycle Time

The hot runner also reduces cycle time. For it is thinner than cold runners and weighs less. Thus, allowing the thickest part to control cooling. This helps to save cycle time in molding.

Flexible Design

Also, the hot runner makes the gate location flexible. With other runners locating the gate may be an issue. But with the hot runner, the gate location is no issue. The nozzle can locate the gate at many points.

This allows gate placement at the best filling point without fear that the runner won’t locate it. So, it gives freedom to gate design and location.


Unlike the cold runner, the hot runner is reusable. More modern materials call for new processes. And the cold runner doesn’t meet up. Often it makes you cannot reuse it. Or if you can, it is costly to store. It is noisy and dusty to clean.

Molding Automation

Top firms are automating their processes that are looking for ways to produce more with less human effort. And the hot runner system fits this bill. When paired with automation, the link is hassle-free. It has no runners that get tangled. So, hot runner aids automation.

Difference Between Hot Runner and Cold Runner Injection Mold System

There exist two runner systems – the hot runner and the cold runner systems. They are both runner systems. But differ in some ways. Some of these are clear, while others are not.

Hot runner directly injects into the cavity while cold runner first injects into a sprue. Hot runner injects directly into the cavity. This helps to keep the sprue and runner hot. In each cycle, only the part is removed. This reduces the duffle time and improves the product’s look.

But cold runner injects into a sprue – a central channel which now flows plastic to the runner. This process slows down cycle time. Also, the plastics cool on the cold runner. In each cycle, you’ve to cool and remove extra plastics. The cold runner is also heavy and causes spots on products.

The hot runner is more expensive than the cold runner. Cell phone cases come from hot runners while keyboards come from cold runners. Bottle caps come from the hot runner system. While electronic housing come from a cold runner system

These are some differences between hot and cold runner systems.

Types of Hot Runner System

There are two primary types of hot runners. They differ based on the type of injection point. Each type has its use and traits. The types of hot runner systems include;

·       Hot Tip Hot Runner System

The first is the hot tip runner system. As the name denotes, it has a hot tip point. It is the standard hot runner. For it is a multi-purpose runner. That is, you can use it for many purposes.

It is ideal for the production of simple items in numbers. Firms see it as the most economical option. It is also the most used type of hot runner.

It has a hot tip at the front of the nozzle. It is mostly used for small parts. And also to produce medium-sized parts. When using a hot tip runner, it leaves gate marks. Though, these can be a few or more. It’s better to position the sprue in a concealed part.

·       Sprue Gating Hot Runner System

In this hot runner system, there is an open pipe. Through which the plastic moves to the mold’s cavity. Unlike hot tip which is ideal for medium-sized parts. It is ideal for parts higher than medium size.

It gives less deformation and improves mechanical strength. However, it is bigger than the hot tip. Thus, gate marks would appear and are often larger than those in the hot tips. But you can combine it with a cold gate to have better aesthetic results.

In this runner, temperature control is vital. You have to manage the mold heat level as well as the plastic heat level. The wrong temperature can stop the functions of the sprue. Such as closing the plastic flow after mold opens.

·       Valve Gate Hot Runner System

Valve gate on the other hand is unlike hot tip. It is another type of hot runner system. It has a mechanical valve which is automated. That is after the machine injects plastics into the mold. It closes automatically.

This allows for a seamless closure which leaves no marks on the product. It is ideal for aesthetics. Valve gate takes into detail, style, and design. So, for an item where beauty is very vital, use a valve gate hot runner for a better design.

Valve gate tends to be more efficient than the hot tip. But higher efficiency comes with higher cost. The valve gate hot runner system costs more.

It is way more expensive than the hot tip runner. But if you need that stylish aesthetics and extra efficiency, don’t relent to spend that extra cash on the valve gate.


In summary, gate types are vital to hot runners. Beyond the type of hot runner, you have to choose the ideal gate. Also, as we have seen, hot runners differ. They have different uses and traits. So, the selection is the key. You need to make the right choice.

One way to choose is to assess the plastic feature. A hot tip is ideal for small-sized parts and medium. Sprue gating is ideal for larger parts. So, if your part is small. You can use the hot tip runner system. Also, the valve gate focuses on design and automation. So, if you want a very good design. Then go for valve gate hot runner.

Hot runner is the tech for now and the future. Its compatibility with automation makes it stand out. But still, an ideal system depends on its usage. So, assess the hot runner your product needs. And go for it. If you’re searching for an injection molding system, check RJC.