Hot Runner Injection Mold Making

How Many Types of Hot Runner System Are There?

Selecting the appropriate hot runner configuration is of vital importance for balancing production speed, part quality and mold cost. The hot runner system is mainly classified based on its gating method and manifold configuration:

1. Valve Gate Hot Runner Systems

After the injection molding process is completed, the gate is physically sealed by a mechanical valve needle (driven by pneumatic or hydraulic power). Because it can eliminate “dripping” and “adhesion”, it leaves almost no obvious gate marks and can achieve continuous injection molding of large parts, thus is suitable for high-gloss surfaces, automotive interior components, medical equipment or other industries requiring aesthetic or smooth surfaces. We adopt advanced technology to control the manufacturing accuracy of the valve-type gate system within ≤ 0.05mm, achieving a surface smoothness of Class-A.

2. Thermal Gate (Open Gate) Systems

Often referred to as Nozzle Gates, these systems rely on precise temperature control at the tip to create a “frozen plug” between cycles.

• Best For: Small to medium parts where a small circular gate mark is acceptable on the non-aesthetic side.
• Advantages: Lower capital investment, simpler maintenance, and a compact design ideal for tight cavity spacing.

3. Single-Drop vs. Multi-Drop Systems

These configurations define the scale of your production:

• Single-Point (Single-Drop): Directs the melt into a single cavity. It is the most cost-effective solution for large, single-cavity molds.
• Multi-Point (Multi-Drop): Features a complex manifold that feeds multiple cavities or multiple points on a single large part. This is essential for high-volume efficiency and achieving balanced flow in multi-cavity molds.

4. Specialized Hot Runner Configurations

• Co-injection (multi-material) system: Specifically designed for injection molding of parts with multiple components or different colors. These systems control two different polymer melt streams through a single nozzle, enabling “soft touch” composite injection or functional material layering, thus achieving the superimposition of multiple materials (or colors).
• Hybrid (semi-hot) gate system: This is a clever combination of hot and cold runner systems, where a small cold runner sub-gate is supplied by a hot runner manifold. Compared to the traditional cold runner, it has significant advantages in significantly shortening the production cycle and reducing material waste, while the initial mold cost is lower than that of the full hot runner system.
• Insulated runner systems: An alternative to heated systems, these employ large channels that enable the plastic’s outer layer to function as an insulator while maintaining the core’s molten state. They are still a specialized solution for certain low-conductivity thermoplastics, but they are less prevalent in high-precision molding today.

What’s the Difference Between Hot Runner vs. Cold Runner Molds

The fundamental difference lies in thermal management. While both systems transport molten plastic to the mold cavity, the cold runner permits the delivery channel to solidify along with the part, while the hot runner keeps the material’s temperature constant.

A heated manifold connects directly to the injection machine’s nozzle in this setup. It keeps internal temperatures steady – usually ranging from 150 to 200℃ – so the resin stays in a fluid state and never solidifies inside the runner. This design maximizes material efficiency to the fullest. With no solidified runner waste left behind, there is zero sprue scrap to discard. On average, this cuts down material costs by 10 to 15 percent. It also delivers consistently high-quality finished parts.

The stable pressure and temperature levels minimize internal stress within each component, resulting in exceptional dimensional stability that meets strict precision standards.

Of course, there is an upfront consideration. The initial capital expenditure is higher, and the system calls for specialized technical upkeep. Even so, the 30 percent shorter cycle times it enables often lead to a full return on investment within the first year of high-volume production runs.

Cold runner systems rely on unheated channels that cool down and solidify completely with every production cycle. After each run, the solidified plastic structure, often referred to as a “plastic tree”, has to be ejected from the mold. It can then either be ground down for recycling or disposed of as waste.

This option stands out for its cost-effective entry point. Lower tooling costs and simpler mold designs make it an excellent fit for low-to-medium production volumes and prototyping projects where budget and flexibility are key priorities.

Maintenance is another major advantage. Without the need for complex electrical heaters or sensors, these molds are easier to maintain. They also carry a lower risk of unplanned downtime caused by electrical malfunctions.

That said, there are trade-offs to consider. Slower cycle times, a result of waiting for the thick runner structure to cool fully, and increased material waste make this system less practical for long-term, high-capacity manufacturing operations.

Why Choose Hot Runner System?

Traditional injection molding creates a “runner” of solidified plastic that must be reground or discarded. Hot runner systems achieve near-100% material efficiency. By eliminating the runner, you save on raw material costs, a critical factor when using expensive engineering resins like PEEK, PSU, or medical-grade polycarbonates.

Consistent thermal regulation is the cornerstone of crafting flawlessly finished components. Every gate on our hot runner systems comes with precise PID temperature control capabilities.

A balanced material flow curbs uneven internal stress, effectively warding off warping and sink marks in the final product. What’s more, gate vestiges (the faint traces left where plastic enters the mold) are nearly undetectable. This makes the technology a top pick for manufacturing parts with strict aesthetic demands, like consumer electronics and automotive interior components.

Standard molds usually require manual or mechanical “demolding/degating” (cutting off the runners that have also cooled to a solid state with and attached to the parts) and secondary classification operations. However, the parts produced by hot runner systems can be directly and “ready for shipment” ejected. This eliminates the need for manual post-processing, thereby significantly reducing labor costs and the risk of human errors.

In a cold runner mold, the cooling time is dictated by the thickest part – often the runner itself. Since the hot runner manifold keeps the resin molten, you only wait for the part to solidify. This results in a 30% reduction in cycle time, allowing you to produce thousands more units per shift.

While the manifold requires power to stay heated, the overall energy footprint is often lower in high-speed production, becuase molten plastic flows easier than cooling plastic, requiring less hydraulic or electric pressure from the injection machine, which reduces wear and tear on the equipment.

1. Hot Runner Design

The success of a hot runner system is determined during the design phase. We focus on four pillars: thermal stability, pressure management, material compatibility, and serviceability.

Precision Pressure Management

It is a common misconception that hot runners always have lower pressure loss. In reality, the longer flow paths in complex manifolds can result in significant pressure drops.

• Our Approach: For resins with poor flow characteristics (e.g., PC or POM), we conduct Moldflow® Analysis to calculate the optimal runner diameter, minimizing shear heat while ensuring the cavity fills completely without stressing the machine.

Heating Methodology: Internal vs. External

• Internal Heating: Best for high-volume production of stable resins; offers excellent energy efficiency.
• External Heating: The industry preference for heat-sensitive polymers. It ensures a smooth, unobstructed melt channel, preventing “dead spots” where material could stagnate and degrade.

Balanced Runner Sizing

We calculate runner cross-sections based on the Melt Flow Index (MFI) and the required injection speed.

• Too Large: Increases residence time, leading to thermal degradation.
• Too Small: Causes excessive shear stress and pressure loss.
• The Goal: A “Balanced Manifold” where the plastic reaches every cavity at the exact same temperature and pressure.

Cooling Circuit Integration

Ironically, a hot runner system requires an exceptional cooling design.

• Thermal Isolation: We design specialized cooling channels around the gate and manifold contact points to prevent heat transfer to the mold base, ensuring fast cycle times and preventing part warping.