The Complete guide To Hot-runner System

Table of Contents

I. Introduction

As far back as the sixties when the hot runner system was launched, it was clear that the journey to a revolutionary injection molding system had already begun.

These systems were designed to solve issues with molding small, intricate parts. But they have since evolved to become a standard in manufacturing various plastic parts, including automotive components, medical devices, and consumer goods. But if you’re still confused about all of this injection molding thing, just think of it as a process that keeps plastic fluid while it moves to the molding stage. However, the following sections of this article will make things clearer. So, Let’s go.

II. Hot Runner System Merits

There are several merits of a hot runner system for manufacturers especially in the mold manufacturing industry which often includes things like cost savings, improved quality, and production effectiveness. The following highlights other benefits that you can get from hot runner systems. 

  • Flexibility in designs – Hot runner systems provide greater flexibility in designs as the system allows for the injection of multiple materials at once, allowing for complex shapes and designs to be created without the need for various molds. This, in turn, helps you make more intricate designs with fewer parts, saving you both time and money.
  • Improve the efficiency of the molding system – A molding process’ efficiency goes up a notch with a hot runner system. The system uses a heated manifold to maintain the molten plastic’s temperature, allowing for a more consistent and even flow of material. This leads to less waste, fewer defects, and a better final product.
  • Melt flow balance – the melt flow balance is another advantage the hot runner system provides. The plastic is evenly distributed throughout the mold, which ensures uniform wall thickness and reduces the risk of warpage or other defects.
  • Molding automation – With full molding automation using methods like CNC machining, there’s less need for manual labor. Therefore, manpower is reduced, and consistency in quality is achieved through the production line. 
  • Optimal part quality – The system’s temperature control and balanced melt flow accuracy ensures that each part produced is of high quality, with consistent properties and dimensions.
  • Processing cost deduction – A hot runner system will help reduce processing costs because production is done with minimal defects and waste. And this increases production efficiency and reduces costs.
  • Reduction in cycle time – Hot runner systems lead to a decrease in cycle time because the consistent flow of material and little need for manual labor means that parts can be produced faster, saving you time and increasing your production capacity.
  • Runner elimination – The elimination of runners reduces the overall cost of production and results in a more environmentally friendly process.
Hot-runner System

III. Hot Runner System Demerits

Most systems have their drawbacks despite their overwhelming benefits and the hot runner system is not an exception. Some of its demerits are highlighted below. 

  • The complexity of operation & maintenance – The setup and maintenance of these systems require a high level of expertise. Therefore, if any error is made during design, this could be costly and may lead to many repairs. It can also affect smaller operations. Especially those with fewer resources to train employees in their functionalities.
  • High requirement for equipment – Hot runner systems require specialized machinery, monitoring systems, and controllers. And this equipment is typically expensive. Its availability and acquisition must also be from a trusted supplier.
  • Increased cost – A drawback that must be considered is the cost. Yes, effective production process and speed are some advantages of a hot runner system. Nevertheless, they are expensive and difficult to maintain. And, of course, not all manufacturers can afford it.
  • Thermal contraction and expansion – This limitation is due to the different design options available. Some hot runner system designs don’t have proper elimination of heat generated during production, which can likely lead to the expansion and contraction of the mold. This can sometimes lead to deformities in the final product.
  • Degradation of heat-sensitive resin – Some materials, such as resins manufacturers work with, are heat sensitive, leading to reduced product quality or complete failure. This can be a significant disadvantage for manufacturers.

IV. Hot Runner System Types

Considering the types of hot runner systems helps manufacturers identify the most suitable one for their manufacturing process right from the mold design stage. Thankfully, there are two major options that manufacturers have, and they are highlighted below. 

  • Fully hot runner (Open type hot runner) – The fully hot runner system maintains a consistent temperature throughout the entire hot runner system. This type is mainly deployed for molds with many cavities and complex shapes. The heat generated is maintained all round the system making it possible to keep the plastic fluid from nozzle to mold. It’s an excellent option for large-scale production runs where speed and efficiency are crucial.
  • Semi-Hot Runner (Valve Needle Type, Valve Gate Type) – There are two options available for this type of hot runner system. Valve needle-type systems are ideal for more complex parts requiring precise plastic flow control. However, the valve gate type systems are best suited for components with tight tolerances or complex geometries, as they allow for greater control over the filling of the mold. Furthermore, the application of which hot runner system determines which to select.
Hot-runner System

V. Hot Runner System Components

The components  that make up the hot runner system are crucial to the effectiveness of the entire system while each plays their role well. So, let’s look at each piece and their indispensable roles critically.

  • Hot Runner Nozzle – The entry point of the fluid plastic into the mold is the nozzle. The nozzle ensures consistent flow, and the even distribution of the plastic around the mold.
  • The Manifolds – The manifold is another essential component of the hot runner system. The manifolds are the channels that distribute molten plastic from the nozzle to the different mold cavities. In addition, it comes in different shapes and sizes depending on the number of nozzles needed for the specific mold design.
  • Temperature Controllers – The temperature controllers monitor and adjust the temperature of the nozzle, manifolds, and mold cavities, ensuring that the plastic is injected at the optimal temperature for the specific material being used.
  • Flow Control – This regulates the flow and amount of melted plastic that flows through the molds. Hence the name, flow control.
  • Connections – This component transfers molten plastic between the nozzle, manifolds, and mold cavities. They must be strong, reliable, and able to withstand high temperatures and pressures.

VI. How Hot Runner System Works

The hot runner system is basically a controlled arrangement of fluid plastic movement from the melting point to the final molding stage. The main parameters controlled include the temperature of the fluid plastic and its flow through the system. Essentially, there is a central controller responsible for the regulation of heat and flow of the molten plastic and a nozzle that directs the pliable plastic to the molds. The nozzle has a specified pressure and temperature at which to effectively push the plastic to the mold as it also ensures quality and consistency of the finished product. However, everything begins with the melting of the raw plastic material at the manifold where it is heated to a molten state. Also, the manifold ensures the plastic remains fluid as it travels through the system. 

VII. Important Things to Consider When Choosing a Hot Runner System

If you’re looking to invest in a hot runner system, there are several factors you need to take into account. Never fail to consider these factors highlighted below in your choice of a suitable system.

First is material compatibility. Dissimilar materials require different nozzle designs and heating elements. Therefore, the hot runner system you choose should be compatible with the material you plan to use. This includes the temperature range and viscosity of the material. 

Secondly, you need to consider the part design. This is important because the hot runner system you choose should be able to evenly distribute the molten plastic to avoid any filling issues or warping. And this can only be guaranteed if it is well-designed. It also increases the speed of production especially during rapid prototyping

Thirdly, the cost. The hot runner system can be capital-intensive but can save you money in the long run by reducing waste and improving efficiency. Consequently, you need to weigh its advantages against cost implications that include repair and maintenance costs.

Finally, maintenance. This event is a huge part that must be considered because maintenance is critical to keeping your hot runner system running smoothly. More so, looking for a system that is easy to maintain and has readily available spare parts is paramount. Regular maintenance can extend the life of your system and prevent downtime.

Hot-runner System

VIII. Hot Runner VS. Cold Runner: The Difference

While the main difference between the hot and cold runner systems may be obvious from their names, exploring the fundamental differences in their approach to injection molding is still important. 

The first is that while the former keeps the plastic material in the runner hot and molten, the latter allows the plastic to cool and solidify in the runner. 

Also, in a hot runner system, the molten plastic flows directly into the mold cavity, which makes room for a faster and more efficient production process with less waste. For the cold runner system, cycle times are longer considering the time it takes to cool and discharge the final plastic product before setting up for another cycle.

And thirdly, while a hot runner system may cost more upfront, it can offer more significant cost savings in the long run due to increased productivity and reduced material waste. However, a cold runner system may be more suitable for simpler or smaller production runs.

IX. Conclusion

In conclusion, using a hot runner system offers numerous benefits, including reduced cycle time, better part quality, and lower production costs. However, proper system design, installation, and maintenance are crucial to achieving these benefits. Again, to lessen the downtime experienced during the whole production process, a clear functional understanding of the individual parts that make up the system like the nozzle, manifold, and controller is essential. With this complete guide, you’ll be equipped with the knowledge to make informed decisions about hot runner systems and their implementation in your injection molding process.


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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