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Why hot runner system is better than the cold runner system?

March 08, 2021
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2 main categories of molds in injection molding

hot runner

Although plastic injection molding started its journey in the late 19th century, today the injection molding process has blossomed into one of the most versatile techniques. But molds still fall into two major categories such as hot runner and cold runner systems.

Basically, both systems either they are hot or cold have their own specific advantages. Further, they have ideal design flexibility as well as can reduce cycle times and costs. But in several conditions, hot runner systems will probably be your wiser choice.

Today we are going to explore what are runner and gate in a mold? You will actually learn about hot runner mold with some of its incredible advantages. Moreover, how do hot runner systems work? As well as what is the difference between a hot runner and a cold runner?

What are runner and gate in a mold?

A runner in the mold is essentially a channel cut into the mold. Moreover, it allows the molten material in order to flow from the nozzle to the cavity.

On the other hand, a gate is an opening tool in a mold. Further, through a gate, molders inject the molten plastic inside the final part. It is actually a boundary between part and scrap.

What is the difference between sprue and runner?

Actually, the sprue is a channel with a large-diameter. It helps to enter the material into the mold. And the runner is generally a channel with a smaller diameter and it helps to direct the molten metal towards the individual part.

The importance of runner’s size for better pay-offs for all molding projects

The perfect size of the runner in the hot runner and cold runner systems is essential for the best pay-offs for all your projects. Moreover, proper sizing of runners is extremely important for a given component and mold design.

In fact, selecting the smallest runner system is better in comparison to large runners. Actually, large runners need a longer cooling time as well as consume more material and scrap. Further, they also need additional clamping force.

While the smallest runners can maximize efficient use of raw material and better energy consumption during the injection molding process. But the size of the runner totally depends on the molding machine’s injection pressure ability.

Additional features of using the perfect size of a runner system are:

Basically, the perfect size of a runner in the hot runner and cold runner systems provide several benefits, for example:

  1. It can achieve the optimal number of cavities
  2. Also, can minimize the waste
  3. Ideal runners also can provide efficient energy consumption
  4. They allow for easy injection
  5. Best sizing runners can ideally control the filling, packing as well as cycle time.

What is a hot runner mold?

Usually, a hot runner mold has two plates that can be heated by using a manifold system. there are actually two types of hot runner molds available such as internally heated as well as externally heated hot runners.

Moreover, in that condition when molders need to control more flow, they actually prefer internally heated molds.

What is the advantage of hot runner mold?

In fact, there are numerous advantages of hot runner molds over cold runner mold. But hot runner molds should always be designed perfectly. They are very easy to use as well as they can help any injection molding company to save extra costs.

Moreover, they can also increase the productivity of injection molding companies.

Hot runner molds also have 6 ideal advantages:

  • They are ideal to use with most plastic materials and part designs
  • These runners are very easy to maintain
  • Hot runner molds are available for single cavity as well as for multi-cavity molds
  • Molders even can use hot runner mold with close pitch mold designs
  • They also can reduce the extra number of moving plates in a mold
  • Further, they can give good gate vestige.

What is a hot runner system?

As we have already explained that hot runner mold has two plates that have been heated with a multiplex system. These multiplex systems are useful to maintain a consistent temperature that helps to keep the melted thermoplastic in the runners according to the temperature of the heating cylinder.


In the next step, the heated runners help to deliver the melted plastic to nozzles that fill the core mold in order to create the final part. This heated runner system has contained inside a separate plate.

Actually, this separate plate always remains stable during the whole cycle of molding. After this, the core plate of molding opens in order to expose the final product without attaching any runners.

Two main types of runner systems

In fact, a hot runner system has several types but actually, they fall into two major versions. These are:

  • Hot tip hot runner system
  • Valve gate runner system.
Hot tip hot runner system:

Generally, it is the standard as well as the general-purpose version of the hot runner system. it is the same as we have mentioned above.

Moreover, it is highly cost-efficient in comparison to the valve gate system. It is one of the most common runner systems that are in use.

Basically, the hot tip hot runner system is a perfect solution for producing simple products in mass production.

Valve gate hot runner system:

it is a special style of the injection point. Further, it features a mechanical valve that helps to automatically close as the machine injects plastic into the mold. As a result, molders get smooth and flattened products. This product has no visible abrasions on its surface.

This system is a perfect hot runner system for creating attractive and good-looking products. The products that have high aesthetic looks attract customers.

Consequently, the valve gate hot runner system is highly efficient in comparison to the general-purpose hot runner system. But it is an expensive hot runner system.

It is a fact that the cold runner system has its own value but hot runner systems are actually the technology of the future. Further, these runner systems are also extremely important in the present.

How do hot runner systems work?

Actually, it is very simple and beneficial. This system delivers molten material to several mold cavities to produce a plastic product.

Furthermore, this heated material travels from the molding machine nozzle through internal channels. These internal channels are also known as runners and hence can be delivered directly into multiple cavities at the same time.

What is cold runner mold?

The main difference is that a cold runner system maintains the molds and runners at the same temperature. Cold runner molds generally have two or three plates. these plates are held inside the mold base.

Basically, molders inject the melted thermoplastic into the mold from a nozzle through the sprue. Next, it fills the whole network of runners that lead to the mold cavities.

What is the difference between a hot runner and a cold runner?

In fact, a hot runner system holds material in a molten state during the whole runner process till it flows inside the mold cavity. While in a cold runner system, the molds and runners are maintained at a similar temperature.

hot runner 2021

A three-plate cold runner mold has the ability to allow for flexibility in design.


Hence, the hot runner system is an extremely efficient process for creating ideal plastic products. It is also greatly advantageous in comparison to the cold runner system as it ensures to save more plastic materials.

Basically, saving material is one of the biggest concerns in the present industry. The hot runners also enable manufacturers to reduce waste and reuse more plastic.

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