Hot Runner Injection Molding

Hot Runner Injection Molding

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Hot Runner Injection Molding Overview

The term “hot runner” in hot runner injection molding refers to a series of heated components. These components play a part in melting the plastic and injecting it into mold cavities.

Components of Hot Runners System in Injection Molding

The hot runner system in injection molding comprises multiple components. The key components for your reference include the following:


Manifold plays its part in directing the resin to multiple channels/ nozzles/ injection points. The manifolds are suitable where you need multiple gates/nozzles per component.


Its component that injects resin through the gate into the cavity. You can install the nozzles on mold plates with or without using a manifold.

Temperature Control Box
Temperature Control Box

The temperature control box assists in controlling the temperature of the resin and keeping it beyond the recrystallization point.

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Working Mechanism

The hot runner system in injection molding works by following these steps:

Injection Initiation – The first step is injection initiation which involves the closing of the mold and the injection of plastic material through the nozzle.

Hot Runners Activation – The plastic material or resin passes through the manifold, which is a heated channel. It plays a key role in melting and forwarding the plastic through the gate into the mold.

Temperature Regulation – The thermocouples and heaters maintain the specific temperature within nozzles and runners. This plays a great role in keeping the plastic or resin molten throughout the process.

Working Mechanism

Hot Runner Vs. Cold Runner Injection Molding

The term “hot runner” in hot runner injection molding refers to a series of heated components. These components play a part in melting the plastic and injecting it into mold cavities.

The cold runner injection molding utilizes non-heated channels. In this type, the molten resin flows through the channel and solidifies before ejection from the mold. The cost you face in a cold runner system is far less than what you face in a hot runner system.

Types of Hot Runner Injection Molding Systems

Some of the key types of hot runner systems are:

Insulated Type

The insulated type hot runners have a greater thickness. Higher thickness cools down some sections of melted resin, which further plays its role in insulation. The insulation cut off heat loss, thus keeping the mold system operating optimally.

These runners are cheaper because they do not use drops or manifolds. Apart from this, these runners feature flexible gates, minimize defects, and contribute to convenient color change.

Heated Type

There are two types when it comes to heated type runners. They both use the heating element. The following section will throw light on these types:

Externally Heated

In this type, the heating element is present on the exterior of the mold. This keeps the material in the molten state and maintains the injection pressure. These runners are highly desirable for thermosensitive materials.

Internally Heated

In this type, the heating element is present inside the mold. These runners contribute to better resin flow because of the heated runner and gate tip control. The undesirables of this type include lower injection pressure, no color change, mold degradation, and hanging of material.

Gate Types in Hot Runner Injection Molding

Consider the key types of gates in hot runner injection molding as follows:

Open Type

The open-type gate in hot runner injection molding offer no barrier to the flowing resin. It is the simplest one, and you can easily implement it in your design. With this type, you can face drooling issues and cosmetic defects. The other drawback of this type is that the resin keeps flowing whether the mold is closed or not.

Valve Gate

The valve gate refers to the gate which uses a mechanical valve to control the resin flow. The valve features a pin that seals off the orifice after injection. Hence allowing the resin to solidify and cool off. This gate type eliminates drooling and gate marks.

Hot Sprue Brushing Type

This gate features a brush at the orifice, which plays a key role in interrupting the resin flow. You can reduce stringing and post-processing with a hot sprue brush gate.

Sequential Valve Gate

The sequential valve gate features multiple gates, each with a valve pin. This gives you complete control over resin filling and flow within the specific mold. A sequential valve gate is perfect for the creation of complex components.

Consideration in Hot Runner Injection Molding

Multiple things need your attention while dealing with the hot runner injection molding. Considering these things will help you achieve efficiency and effectiveness.

Runner Size

The size of the runner greatly impacts the molding operation. The wrong size cannot only result in incomplete filling but also leads to component degradation. The number of things such as operation temperature, pressure drop, shear rate, and residence time affect the size of the runner.

Gate Type

The gate type determines which material you can use for injection molding. Therefore select the gate type, location, and mark considering this factor.

Production Volume

The volume of production you want to achieve with hot runner injection molding greatly matters. Pay attention to the selection of components while choosing the hot runner injection molding, as this is going to affect the volume of production.

Maintenance Requirement

Considering the maintenance measures needed for the hot runner system is essential. You can assess yourself if you can cope with these measures or not. This is critical and has effects on performance efficiency and productivity.

Injection Pressure

The injection pressure for hot runner systems is lower than that in cold runner systems. For effective injection pressure design, perform simulations for different materials. This is truly effective for materials having poor melt flow and where you need to manufacture larger components.

Advantages of Hot Runner Injection Molding

The key advantages of hot runner injection molding include the following:

Reduce Material Wastage

With hot runner injection molding, you can cut off material waste. It allows you to feed the material as per mold requirements, hence limiting excess material utilization. This ultimately leads you to cost-effective and eco-friendly production.

Improves Production Efficiency

The hot runner injection molding boosts your productivity by keeping the temperature constant. You don’t need to raise or lower the temperature to facilitate the melting process. This reduces the cycle times and contributes to faster manufacturing.

Seamless Surface Finish

The hot runner system plays its part in catering good control in molted material flow. This ensures consistent and smoother surface finishing with greater dimension stability.

Flexible and Reliable

With the hot runner system, you can select any resin material you want. You have complete freedom to design shapes featuring any level of complexity. This way, you can offer reliable and consistent results.

Factors to Consider in Hot Runner Injection Mold Design

Mold design influences the operation of the hot runner injection molding. While choosing a specific mold design, consider these aspects:

Material Selection

The material choice for hot runner injection molding greatly influences the strength, durability, production cost and heat resistance. This, in turn, affects the product consistency and quality.

Temperature Control

Uniform temperature and temperature control greatly matter within the mold. This is because they decide on flow characteristics and uniform product dimensions.

Thermal Expansion

To eliminate or minimize deformation or wrapping, take into account thermal expansion. This will also result in accurate and precise mold components.

Flow Analysis/Balancing

Performing the flow analysis ensures effective material distribution within the mold. This way, you can minimize defects and improve product quality.

Hot Runner Injection Molding Tips

Keep Temperature Uniform
Keep Temperature Uniform

Temperature variations can affect the final product quality. This also reduces productivity and increases the associated costs. Make sure to keep the temperature uniform throughout the molding operation.

Reduce Resin Leakage

While carrying out the injection molding, ensure proper sealing. This not only prevents temperature, material, and energy loss. But ensure high-end mechanical properties.

Eliminate Bubbling
Eliminate Bubbling

Temperature control and the right material are key to eliminating bubbling. Make sure to avoid bubbling as it weakens the end product structure.

Maintain Uniform Pressure

The constant level of pressure is crucial for superior quality and balanced fill. Examine and regularly assess the injection pressure to ensure high-quality output.

Ensure Effective Cooling
Ensure Effective Cooling

Optimum cooling time and precise cooling channels assist in this regard. This can help you achieve shorter cycle times and eliminate product wrapping.

Employ Hardened Pins
Employ Hardened Pins

Hardened pins are the key to longer part consistency and reliability. You can get defects-free products by employing hardened pins in the hot runner injection molding.

Properly Start Your System

Before beginning the injection molding operation, calibrate settings and verify the set parameters. This way, you can eliminate costly errors and harness stable production.

Hot Runner Injection Molding Applications

Some key applications where you can use hot runner injection molded components are as follows:

Automotive Industry

In the automotive industry, you can use hot runner injection molding to manufacture dashboards, grilles, bumpers, door panels, and interior trim.


The electronics industry uses many hot runner injection molded parts such as electric device casings, mobile casings, and laptop components.

Packaging Industry

In the packaging industry, using a hot runner system, you can manufacture containers, caps, bottles, etc.

Medical Accessories

The Plethora of medical equipment and accessories comes from using a hot runner system. The key items include IV parts, syringes, disposable components, etc.

Household Appliances

You can manufacture various household accessories such as refrigerator parts, washing machine accessories, chairs, tables, vacuum cleaner components, etc. All this is possible through hot runner injection molding.

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