What is hot runner mold

Hot runner mold is a type of injection molding system that uses heated material feed channels, or “hot runners,” to maintain the temperature of the plastics as it flows through the injection mold. This allows for a more consistent and efficient molding process, as the plastic does not have to be reheated between shots so the cycle time will be reduced and will save the waste runner materials ( sometimes has no any runner with hot runner systems). Hot runner systems are commonly used in the production of large quantities of plastic parts, such as in the automotive and consumer goods industries, or used in the stack mold.

DONGGUAN SINCERE TECH CO.LTD(SINCERE TECH) provides plastic injection mould solutions to industries of all types and sizes. For almost 20 years DST has designed, built, and worked on almost every type of mold existing in the plastic industry.

We are experienced in building custom plastic molds for a variety of hot runner mold systems, from hot runner manufacturers like:

Our state-of-the-art mold building facilities include High precision CNC machines, automatic CMM measurement machine, and Two heads of EDM Machines to create many types of custom molds, including complex specialty injection molds, insert molds, unscrewing molds, overmolding, hot runner mold, cold runner mold, stack mold, gas-assisted injection molds, double injection molds (2k molding), etc. We can build molds for both cold runner systems and hot runner systems.

Hot Runner Molding: Efficient High Production

Here are some key characteristics and advantages of hot runner molds:

1. Runner System: In a hot runner mold, the runner channels are heated, allowing the molten plastic to flow freely from the injection unit to the mold cavities without solidifying. This eliminates the need for a separate runner system, which is typically discarded or recycled in cold runner systems.
2. Material Efficiency: Hot runner molds are more material-efficient because there is no waste generated from runners. This can result in cost savings for materials, especially for high-volume production.
3. Reduced Cycle Time: Hot runner molds often have shorter cycle times compared to cold runner molds because there is no need for the plastic to cool and solidify in the runner channels.
4. Improved Part Quality: Hot runner systems can help produce high-quality plastic parts with minimal defects, such as weld lines, since the plastic enters the cavities in a fully molten state.
5. Complex Geometries: Hot runner molds are well-suited for parts with complex and intricate geometries, as they allow precise control over the flow of molten plastic to different areas of the mold.
6. Material Compatibility: Hot runner systems are compatible with a wide range of plastic materials, including heat-sensitive polymers that may not be suitable for cold runner molds.
7. Temperature Control: Hot runner systems require more sophisticated temperature control systems to maintain the desired temperature in the runner channels and nozzles, which can add complexity and cost to the mold design.
8. Maintenance: Maintenance of hot runner systems can be more complex than that of cold runners due to the presence of heated components.

Hot runner molds are commonly used in industries where high precision, minimal material waste, and fast production are critical, such as automotive, medical, and consumer goods manufacturing. The choice between hot runner and cold runner molds depends on the specific requirements of the molding project, production volume, part complexity, and material selection.

Choosing the system to employ depends on the requirements of the part to be produced. A few of the considerations include:

Hot runner mold structure

• Type of material to use – virgin or “regrind”
• Colour changes during the production run
• Single or multiple design production
• Part complexity
• Colour requirements
• Physical characteristics of the material

The primary difference between the two systems is that the hot runner eliminates the excess material retained in the feed channels of a cold runner mold. This feature reduces the number of production steps required and saves in material and energy costs.

Furthermore, mostly hot runners use 100% virgin resins; no reprocessed or “re-grind” material is added. This is an important feature for specific applications where regrinding can cause the material to yellow, or detracts from the material properties, such as clarity in light pipe or lens production, where long-lasting transparency is a specific requirement.

Hot runner molding systems normally inject melted material directly into the individual mold cavity. Hot runner is almost always used for large volume production of thermoplastic injection molded parts, or multiple part production using multi-cavity molds and stack-molding technology.

Hot runner molds are two plate molds with a heated runner system inside one half of the mold. A hot runner system is divided into two parts:

• The manifold has channels that convey the plastic on a single plane, parallel to the parting line, to a point above the cavity
• The drops, situated perpendicular to the manifold, convey the plastic from the manifold to the part

Hot-Runner Systems: The advantages and disadvantages

Primary advantages of hot runner systems include:

• Shorter, faster cycle times – most of them have no runners to cool
• Smaller machines – reduced shot volume into runners
• Automated processing – runners do not need to be separated from the parts
• Gates at the best position for economical design
• Elimination of runners means
• Materials cost savings – no runner to regrind or reprocess
• Least expensive cost/piece
• Reduction of energy costs
• No runners to remove or regrind
• Reduces the possibility of contamination
• Lower injection pressures
• Lower clamping pressure
• Consistent heat within the cavity
• Shorter cooling time
• Shot size reduced
• Cleaner molding process
• Eliminates nozzle freeze

Disadvantages to hot runner mold systems that need to be considered:

• Hot runner molds are more complex and expensive to build than cold runner molds
• Higher initial start-up costs than for cold runner systems
• Complex initial setup prior to running the mold
• Higher maintenance costs – more susceptible to:
  • Breakdowns
  • Leakage
  • Heating element failure
  • Wear caused by filled materials
• Risk of thermal damage to sensitive materials
• Elaborate temperature control required
• The colors change is more complex than the cold runner, sometime you will spend lots of time and cost to clean up the hot runner systems, especially for transparency and white color parts.

Hot Runner Molds: Applications & Possibilities

Hot-runner systems are almost always used when large runs have to be manufactured in highly automated production. Additionally, technological advances enable us to build molds with gates positioned to yield the best quality molded parts.

Hot runner molds are sometimes connected to needle valve nozzles, which are activated with precise computer-controlled timing. This allows for a number of advanced processes, including:

• In-Mold Decoration – lamination with a colored film coating
• Multi-Cavity Molds – cavities with different geometries and/or volumes
  • Parts that belong together produced in one mold
  • Injection valve opening and closing can be adjusted to the conditions of each individual cavity
  • Injection pressure and holding pressure may be adjusted  independently of each other
• Controlled Volume Balancing – a weld line can be shifted into a non-critical area of the molded part
• Stack Molding – two or more mold bases in production simultaneously creating multiple parting lines

Partner with Sincere Tech Mould suppliers for your custom injection molding needs, and benefit from our comprehensive capabilities, unwavering commitment to quality and sustainability, and our drive to exceed your expectations at every step of the process. Together, let’s bring your innovative ideas to life.