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Different Types and Applications of Hot Runners

Over the years, plastic injection molding has been useful in the quality of mass production of various parts. Plastic injection molding machines use hot runners to maintain a consistent temperature and keep the plastic in the molten state. This ensures quick delivery of the melted plastic to the molding cavities. 

The additional heating system has resulted in reducing the manufacturing time and cost. Today, we’ll discuss hot runners and their types. A deeper understanding of how these hot runners work will help you choose the best system for your plastic injection molding. Keep reading to learn!

Understanding Hot Runners

Hot runners are a high-tech delivery system for molten plastic. It has a network of heated channels equipped with a series of nozzles that inject precise amounts of molten plastic into different parts of the mold. 

Unlike simple systems with just one entry point, hot runners can have anywhere from 1 to nearly 200 nozzles, depending on the mold’s complexity. And the best part? They keep the plastic flowing continuously, boosting production efficiency. 

Hot runner molds are two-part systems.

They have two heated plates and a network of channels called a manifold. This manifold acts like a thermal highway, keeping the molten plastic flowing smoothly by matching the temperature of the heating chamber. The hot plastic then travels through this network, directed by precisely positioned nozzles that fill the core mold cavities and shape the final product.

Hot runner molds are two-part systems

This heated runner system is a part of the separate plate that stays stationary during the molding or plastic. At the end, the detached core molding plate opens, delivering the final molded products. In general, hot runner systems are either externally heated or internally heated. 

The externally heated systems are ideal for thermal variation-sensitive polymers. Internally heated systems have a better flow and tip control. The only limitation is the color change which is possible in externally heated systems. Overall, hot runners can be used when precision and high-quality parts are needed. For instance, they may be used for automobiles and remote controls. 

Different Parts of Hot Runners

Hot runners consist of the following components: 

Different Parts of Hot Runners
  • Inlet: Plastic enters the injection nozzle via the inlet.
  • Manifold: The manifold regulates the molten plastic temperature and delivers the plastic to the mold cavity via heated nozzles. It is placed on the stationary plate.
  • Locating Ring: An adjustable ring for the correct placement and alignment of nozzles and injection mold. 
  • Heater Technology: A hot running system with various temperature control systems and flow controls. 

What are the Different Types of Hot Runners?

Here are the different types of hot runner systems: 

Valve Gate Hot Runners

This is one of the most popular and efficient hot runner systems. It stores the plastic in a molten state and releases it precisely from the valve gate. The valve gates allow accurate flow of plastic and lead to better quality end products. 

This is due to the placement of the nozzle and how it remains in control with the needle valve. Hence, it reduces wasteful production with defects, gate marks,  or excessive plastic. 

Besides, these parts are more aesthetically pleasing to look at. Valve gate hot runners are mostly used in the medical and eyewear industries. It has a fast output, fewer shear tears, and a better appearance. 

Hot Sprue Runners

This system uses a hot sprue where plastic is added for heating and melting when production is ongoing. The Hot Sprue runners work with single-cavity molds, making production convenient and easy to control. 

Hot sprue runners have two feeding methods – direct and indirect. They have the ability to produce multiple items at the same time. They do not store the molten plastic but heat it as it passes through the machine nozzle to the molding cavity. The hot tip gate in the hot sprue system has a continuous flow. It is efficient but may leave a gate mark on the mold. 

Insulated Hot Runners

Insulated hot runner molds offer an alternative approach. Instead of relying on heated manifolds and drops, they utilize thicker runners in the mold plate. These thicker runners partially cool down, creating a natural insulation layer. This insulation minimizes heat loss, letting the plastic flow within the system.

Compared to heated hot runners, they have several advantages, such as:

  • Lower cost due to the absence of complex manifold
  • Simple system 
  • Fewer drops

They have more gate flexibility and reduced defect rates. Additionally, changing colors is easy when using insulated runners. Despite the freezing limitation at gates and long start-up periods, insulated hot runners are efficient. 

Heated hot runners

Heated hot runners are of two types–externally and internally heated. These are great for materials sensitive to heat. They work using a heating component present in one part of the mold. The heating component is present on the outside in externally heated runners. 

These runners are able to maintain injection pressure as there is better thermoplastic flow and control. Moreover, the plastic does not freeze at the gate, thus, allowing easy color change. 

Internally heated hot runners have a heating component in the mold. This may lead to a drop in injection pressure due to freezing around the gate. Their one major advantage is better flow and tip control.

How Does a Hot Runner Operate?

Hot runners streamline the molten plastic flow to the molds. They ensure smooth injection molding and facilitate color or material changes during the process. The temperature can be regulated to ensure the plastic flows in a liquid state to fill perfectly into the molds. 

With the right temperature as per the material, the resin in the hot runner machine barrel quickly reaches the liquid state. The gates open, and the liquid flows to generate specific shapes.

Advised Temperature Settings 

Material and Type Melting Point (°C)Recommended temperature
Zytel® HTN (Polyphthalamide/PPA)295 – 310310 – 325
Delrin® (Polyoxymethylene/POM) 178 190-215
Rynite® (Thermoplastic polyester resins/PET) 250 285
Crastin® (Polybutylene Terephthalate/PBT) 223 250 – 260

Applications of Hot Runners

Here are some of the applications of hot runners: 

  • Medical equipment like syringes and sterile containers
  • Furniture– chairs, tables, cabinets
  • Toys, trays, and hangers
  • Remote controls
  • Automobile parts
  • Kitchen containers, bottles, utensils, trash bins
  • Laptop and phone cases
  • Electrical parts like switch covers, insulation, and wire covering

Top 5 Hot Runner Brands

Here are the top hot-runner brands: 

  • Synventive Molding Solutions: Custom hot runner systems for automotive bumpers and medical instruments. A global brand that can make hot runner system solutions as per exact specifications.
  • EWIKON: With over four decades of experience, a German brand serving industries like packaging, medical technology, and automotive. 
  • Hotset America Corporation: The brand has special thermocouple technology to ensure temperature regulation in hot runners producing precise amounts of voltage.
  • HRSflow: The brand has advanced hot runners with prewired assembly stack molds, eliminating the need for separate control units. 

What to Consider When Choosing Hot Runners 

Here are some prerequisites to consider when choosing hot runners: 

What to Consider When Choosing Hot Runners

Heating 

Consider the heating component requirements. If you’re using thermosensitive materials, go for the external heating system. Plastics like polymers will work best with internal heating systems. 

Injection Pressure

Maintaining injection pressure as needed is crucial for molding without defects. However, the injection pressure tends to decrease when the molten resin/plastic flows through the manifold. This makes it important to have an adjustable injection pressure to suit different kinds of materials in a liquid state. 

Runner Size

An appropriate-sized runner will endure the system and offer a good performance. Consider factors like temperature, pressure changes, and shearing when choosing the size of the runner. This will prevent defects and filling issues in the mold. 

Temperature Regulation 

Pick a system with a reliable multi-zone temperature controller. This will make the operation easy and prevent energy loss. 

Plastic-type

The type of plastic in use is important for the working of the runner system and deciding how much heat will be needed. If you’re using a strong material, the system must suffice the high-temperature needs and force. 

Gate

Choose the right design gate, mark, and location based on the product requirement and materials.

Design 

You may pick a hot runner system based on your needs. The custom-designed system will go hand in hand with the required volume, cost and intricate mold designs. 

Advantages of Hot Runners

Hot runners have several advantages when it comes to quality, cost, and production time. Here’s a compilation of significant advantages of hot runners. 

Improve Part Quality

Hot runners have precise delivery of the molten plastic to the molds. This enhances the product quality. There are minimal gatemarks on the end products; hence, better aesthetic appeal. This also leads to a reduction in defective products and redoing the molding work for correct parts. 

Decrease in Cycle Time

Hot runners are ideal for faster cycle time, which is possible as the plastic remains in a desired liquid state and temperature. This ensures better flow at all times, preventing delays in repeatedly heating the plastic. 

Cost 

Hot runners have an efficient process that does not generate material waste after the molding. This allows the saving of more plastic materials and reusing the discarded plastic after each cycle. 

Reduce Waste

Another big benefit of using hot runners is a reduction in solid resin/plastic wastage. The molten plastic flow can easily be controlled, and only the appropriate amount reaches the molding plates. 

Design Flexibility

Hot runners in injection molding offer flexibility in designing due to the positioning of gates. The system has edge gates, hot tip gates, and valve gates for adjusting the plastic flow. 

Minimal Defects

The products made using hot runners have minimal defects such as bubbles, sink marks, discoloration, and no flow lines. This is due to the constant application of heat and keeping the plastic in a consistent state before molding. 

Automation

Post-production is not required when the parts are perfectly fabricated in the hot runners. The end products do not have gate lines or require trimming and filing after production. 

Easier color change and material change

With consistent injection pressure and no freezing at the gate, hot runners make it possible to make color changes. The increased flow helps to push out the old color material more effectively, reducing the chance of residual color contamination in the final product.

Moreover, hot runners have a smaller volume of molten plastic residing within the system compared to cold runners. This means less material needs to be replaced when switching colors, leading to a faster and more efficient color change process.

Limitations of Hot Runner

Before delivering into hot runners and CNC machining, be aware of some of its limitations. 

  • High Investment: The initial investment will be considerable as the molds and runners are complex machines. There will be a periodic maintenance cost to ensure the system runs smoothly. 
  • Precision in machines: The hot runner system will only work well with advanced equipment. Not doing so may result in system failure and defects in the end products.

Wrapping Up

Hot runners are ideal for fabricating high-quality items in plastic molding. They are efficient and precise in making intricate parts. Moreover, the hot runner systems allow quick production with minimal waste and defective products. Also, in comparison to cold runners, hot runners prove to be better as they ensure better flow. 

Moreover, they enable high production in bulk while also eliminating plastic waste. To get the most out of these systems, make sure you invest in high-tech equipment and choose the right model as per the needed volume. Connect with professionals like HiTop Industrial mold designing for expert advice and premium services. 

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