What Is Hot Runner Technology in Injection Mold？
As the plastic manufacturing industry grows, people demand better plastic products. Injection molds play a key role in plastic molding, and improving them speeds up industry progress.
Hot runner technology emerged in the 1940s, significantly changing injection molding. Using heating or insulation keeps the plastic in the runner and gate molten. This prevents solid waste from forming in the system.
Hot runner molds save materials, boost production, improve product quality, and extend mold life compared to cold runner systems.
Many developed countries, including the U.S. and Germany, have adopted hot runner technology. Companies like DME and EWIKON have achieved excellent results using it.
Principles and Structure of Hot Runner Molds
Hot runner technology improves traditional cold runner molds. It eliminates solidified waste in the gating system.
A hot runner mold includes heating rods or coils in the runner system. A temperature controller precisely adjusts the plastic’s temperature. This keeps the plastic molten in the runner and gate, reducing injection pressure loss.
The molten plastic flows from the injection nozzle into the mold cavity. When opening the mold, only the finished product is removed. The system recycles leftover material by reheating it for the next injection.
Hot runner systems have two main types: insulated runner systems and heated runner systems.
Insulated runner systems have flaws and are rarely used. Most manufacturers prefer heated runner systems.
Heated runner systems are classified into internal heating and external heating types.
Hot runner technology is now widely used in mold innovations. Its components include the manifold, nozzle, heater, temperature controller, and auxiliary parts.
(1) Manifold Plate
The manifold plate keeps the melt at a constant temperature before it enters each nozzle. It prevents solid waste formation and reduces injection pressure loss.
There are four common manifold types: straight, H-shaped, Y-shaped, and X-shaped.
(2) Hot Nozzle
The hot nozzle injects molten plastic from the injection machine into the mold cavity.
The nozzle’s design is crucial for the injection process. Nozzles can be open-type, pinpoint-type, or valve-gate-type based on gate structure.
(3) Heating Elements
Heating elements keep plastic molten in the runner and gate during injection.
They include heating rods, thermocouples, heating coils, and heating bands. These components are essential for the hot runner system’s performance.
(4) Temperature Controller
The temperature controller precisely adjusts the plastic temperature during the injection.
It has three types: on-off control, proportional-integral-derivative (PID) control, and advanced intelligent controllers.
A temperature controller includes cables, a central unit, connectors, and plug sockets.
(5) Other Accessories
Successful injection requires additional components.
Key accessories include insulation blocks, junction boxes, and support blocks.
Main Features of Hot Runner Molds
1. Advantages of Hot Runner Technology
Hot runner molds emerged in the 1940s and evolved over 70 years.
With the growth of the mold industry, hot runner technology expanded, offering economic and environmental benefits.
This technology optimizes cold runner molds and brings several advantages.
(1) High Product Quality
Due to uneven temperature and pressure, cold runner molds often cause defects like shrinkage, weld lines, and flash.
Hot runner molds keep plastic molten in the runner and gate, reducing pressure loss.
A temperature controller ensures stable temperature and pressure, preventing solid waste formation.
This reduces shrinkage, deformation, color variation, and cracks. It also improves surface quality, stiffness, and strength.
Additionally, hot runner molds prevent gate material from mixing with new plastic, lowering defect rates.
They are ideal for high-quality products like transparent and thin-walled parts.
(2) Low Energy Consumption
One key feature of the hot runner system is low energy use. Only the final product is removed during molding, reducing solidified waste removal. The system heats the material to the required temperature before injection, reducing sprue waste and cleanup.
The hot runner system prevents sprue waste from traditional runners, saving raw materials and improving energy efficiency. Studies show it can reduce raw material use by 30% to 50%.
It also minimizes defects like warping, shrinkage, color variation, and cracks. This eliminates secondary processes like trimming, painting, and coloring, reducing energy waste and production costs.
For small products with high material waste, energy savings become more significant.
(3) Shorter Molding Cycle
Solidified material can be reused immediately in the next injection, avoiding cooling delays. The cooling cycle matches the product’s cooling time, eliminating sprue removal.
The system also removes the need for secondary processes like trimming and painting. Compared to traditional molds, the hot runner system can reduce cycle times by over 30%.
This makes production faster and more efficient.
(4) High Automation Level
The hot runner system supports automatic gate cutting and continuous molding cycles. The temperature controller precisely manages plastic temperature, ensuring high automation.
Since no manual sprue removal is needed, the system reduces labor waste and boosts efficiency. It is ideal for high-volume plastic part production.
Hot runner gate and runner designs are also more flexible, offering greater design freedom.
(5) Wide Application Range
As mold technology advances, hot runner systems are becoming more versatile. They work with plastics like polyethylene and polypropylene, which have broad melting ranges.
They are also effective for materials with narrow melting ranges, like PVC and POM. The system allows for shorter mold opening distances, making it ideal for long-part molding.
Hot runner technology supports multi-cavity molds and can be combined with other injection methods to expand its applications.
Other benefits include improved working conditions, better environmental protection, and lower electricity use.
2. Disadvantages of Hot Runner Technology
As an advanced mold innovation, the hot runner system has limitations. Understanding these drawbacks helps optimize production and maximize economic benefits.
(1) Complex Mold Structure
The system requires continuous heating in the gating system to keep plastic melted. This demands high design precision, making mold structures more complex.
The high cost of hot runner molds makes them difficult for small or less-experienced manufacturers to adopt.
(2) High-Temperature Control Precision
The system needs zoned heating and multiple temperature controllers to prevent uneven filling. This ensures the molten material remains at a stable temperature.
Poor temperature control can also damage heating components, making repairs more difficult.
(3) High Skill Requirements for Operators
Operating molds with hot runner technology is more complex than cold runner molds. The process requires comprehensive skills and higher maintenance expertise.
Different plastics need specific hot nozzles, so trained operators must handle them.
Hot runner injection technology has drawbacks, such as more startup waste, strict material requirements, heater damage, and high resin cleanliness standards.
However, continuous advancements are reducing these challenges. Hot runner molds have great potential for growth and application.
Development Trends
Hot runner technology is an innovative injection molding method with many benefits. Its use is expanding, shaping the future of injection molds.
Mold industry growth and market demand have driven further improvements in recent years. The main development trends include:
(1) Miniaturization of Components
Miniaturization is a key direction for injection mold development. It enables precision molding and enhances efficiency.
Smaller nozzles allow multi-cavity or multi-gate molds, increasing productivity. Since the 1990s, many companies have developed combined or multi-gate nozzles using miniaturization.
(2) Standardization of Components
Hot runner molds are complex and expensive. Standardizing components extends their lifespan, reduces costs, and simplifies maintenance.
Standardization also helps promote and apply hot runner technology. Computer-aided design (CAD) can further optimize mold designs.
(3) Precision Temperature Control
Injection molding quality largely depends on temperature control. The key to hot runner molding is precise temperature management for runners and gates.
Using advanced technologies like heat pipes can enhance temperature control. This ensures uniform heating, improving product quality.
(4) Expanded Applications
Hot runner technology saves resources, boosts efficiency, and improves product quality. Expanding its applications is a significant development goal.
Combining it with other injection technologies, such as multi-color co-injection and stack hot runner molding, meets various material needs and increases practicality.
Hot runner technology has been used in injection molding for decades. Its unmatched advantages—high product quality, low energy consumption, short cycle times, high automation, and broad applicability—have led to rapid global adoption.
However, key technology gaps and a lack of standardized components limit development in China. The adoption rate remains low, but future growth potential is significant.
Conclusion
Hot runner technology transforms injection molding with efficiency, precision, and resource-saving benefits.
As the industry advances, miniaturization, standardization, and precise temperature control will further improve its capabilities. Expanding its applications, such as multi-color co-injection and stack molding, will enhance its practicality.
Although global adoption is widespread, challenges like high costs, technical complexity, and standardization gaps exist, especially in China.
However, continuous innovation is overcoming these obstacles, making hot runner technology a key driver of future mold manufacturing. Its growing use will lead to higher product quality, faster production, and more sustainable manufacturing practices.