What is a hot runner mold? This might be the first question for someone not fully familiar with the injection molding process. Hot runner molds are a key component of the injection molding process. This article will give you a detailed introduction to all the information about hot runner molds.
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What is a Hot Runner Mold?
A hot runner mold consists of two heated plates with a manifold system (ie, containing heating components, manifolds, and nozzles). The manifold helps maintain a consistent temperature by keeping the molten thermoplastic in the runner at the same temperature as the heating cylinder. Heated runners deliver molten plastic to nozzles that fill mandrels to form the final part.
Hot runner injection molding is suitable for molding plastics that require stable flow and injection pressure. Furthermore, using this method, defects such as sink marks due to fluctuating injection pressure and unfilled molds can be reduced.
Working principle:
In the hot runner mold, the plastic raw material enters directly into the mold chamber rather than passing through a traditional cold runner which allows the runner to cool and solidify between each cycle.
Structure and composition:
Locating Ring – The locating ring aligns the injection mold with the platen of the molding machine. It ensures there is proper alignment of the mold with the machine.
Inlet – When the resin is injected into the mold, this is the entry port where the resin enters from the injection machine nozzle.
Manifold – The manifold enables the flow of resin into different nozzles and injection points (gates).
Nozzles –Nozzles are components where the resin is injected into the cavity through a gate.
What Types of Hot Runner Molds Are There?
Based on the method of maintaining the heat, here are the two types of hot runner molds used in plastic injection molding:
Insulated Hot Runners
Insulated hot runners molds have extremely thick runners in the mold plate, which causes part of the molten plastic to cool down and insulate the system. The insulation reduces heat loss, allowing the mold system to maintain an open plastic flow.
Insulated hot runner molds are less expensive than heated ones because they do not use manifolds and drops. Furthermore, they have flexible gates, reduced defects, and favor easy color change. However, it has a few disadvantages, such as freeze-ups at the gate, non-uniform mold filling, long start-up periods, and the need for a fast cycle to maintain the thermoplastic molten state due to the absence of a manifold system.
Heated hot runners
The heated hot runner is the major type of hot runner system with heating achievable using a heating component in one-half of the mold. However, they come in two designs: externally heated and internally heated.
- Externally heated hot runners: The heating component is outside the mold. As a result, there is no obstruction in the molten thermoplastic flow (better flow control) and no drop in injection pressure. Furthermore, the molten plastic does not freeze and is ideal for color change. Externally heated hot runner molds are suitable for thermosensitive materials.
- Internally heated hot runners: Here, the heating component is in the mold, leading to a drop in injection pressure, incompatibility with color change, and material hanging up and degrading in the mold. However, there is better flow due to the heated runner and gate tip control.
What Are the Advantages and Disadvantages of Hot Runner Molds?
The following is an introduction to the advantages and disadvantages of hot runner molds.
Advantages of hot runner molds:
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Reduced cycle time
The molding cycle of plastic parts is shortened. Many thin-walled parts produced using hot runner molds can be molded in less than 5 seconds. -
Save Plastic
There are no cold runners in the hot runner mold, thus reducing production and material costs. -
Reduce waste
During hot runner mold molding, the plastic melt temperature is precisely controlled in the runner system. Plastic flows into the cavity more evenly, resulting in a consistent part quality. -
Production automation
Subsequent processes are omitted, which is conducive to production automation. The product is finished as soon as it leaves the mold, without trimming the gate and recycling the cold runner. This greatly improves production efficiency.
Disadvantages of hot runner molds:
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Higher initial cost
The cost of hot runner molds and components can be much higher. For low-volume production, the high overhead cost of mold tooling is the main reason why hot runner molds have not gained wider acceptance. -
High equipment requirements
TThe production process of hot runner mold equipment requires precision machining. The integration and cooperation requirements of the hot runner system and the mold are extremely strict. -
Operation and maintenance complex
TCompared with cold runner molds, hot runner molds are more complicated to operate and maintain. Improper use and operation can easily damage the hot runner parts, making production impossible and causing huge economic losses.
What Are the Main Applications of Hot Runner Molds?
Hot runner molds are widely used in various industries, providing numerous advantages and applications in different fields.
Automotive industry: e.g. bumpers, interiors, instrument panels and body panels. The ability of hot runner molds to produce large, complex, and aesthetically pleasing parts with precision and consistency makes them ideal for automotive manufacturers.
Consumer Electronics: Lists complex parts such as laptop casings, cell phone bezels, and buttons. The demand for aesthetically pleasing, lightweight and durable electronics requires high precision and excellent surface finish, which can be achieved by using hot runner molds.
Packaging industry: such as bottles, caps, containers and caps. Hot runner molds enable manufacturers to achieve fast production cycles, ensuring high productivity and meeting the demands of the packaging market.
Healthcare: eg syringes, vials, pipettes and surgical instruments. Hot runner molds reduce the risk of contamination and allow for an efficient production process, meeting the stringent requirements and regulations of the medical industry.
Household appliances: The production of parts such as refrigerator parts, washing machine casings, air-conditioning panels and other parts requires high precision and elegant appearance. The ability to produce large parts with intricate details and excellent surface finish makes hot runner molds the first choice of appliance manufacturers.
Precautions When Choosing a Hot Runner Mold
Choosing the right hot runner mold should be based on price, delivery time, and quantity. However, more important factors rest on the technical aspect of the runner system. Below are a few you should take note
1. Injection Pressure
Due to the consistent temperature of the molten plastic, while passing through the manifold system, the injection pressure drop is low. As a result, it’s important to ensure proper mold flow simulation during injection mold design when working with all materials for injection molding, especially those with poor melt-flow performance.
2. Heating
The heating component can be internal or external. External heating systems are suitable for thermosensitive materials. On the other hand, internally heated systems are suitable for other plastic polymers.
3. Gate Type
Every material and product design requires a unique gate design. Therefore, consider factors such as gate mark, location, and injection of material types when making the gate.
4. Standard or Custom-Made System
Choosing from a standard or custom-made system depends on your requirement. On the one hand, the standard system has standard components and dimensions. Consequently, they are the best choice due to cost, delivery time, and maintenance. On the other hand, custom-made systems are ideal for achieving products with unique designs.
5. Types of Plastics Processing
The plastic polymer you are working with also plays an important role in the choice. For example, glass-reinforced plastic needs molds having gate inserts with good wear resistance or an external heat system runner.
6. Runner Size
The runner size plays a critical role in the system’s performance. Getting it wrong can lead to the degradation of the final components or incomplete filling. Some factors such as the pressure drop, residence time, operation temperature, and shear rate and frequency can determine the size of the runner.
7. Multi-Zone Temperature Control
When working with a large and complex system or a thermosensitive plastic, ensure you use a multi-zone temperature control system to account for heater quality and heat loss.
FAQs About Hot Runner Molds
Q1: Why use hot runner mold for injection molding?
A: The purpose of a hot runner injection system is to maintain a molten flow of plastics or rubber from the injection molding machine nozzle to the gate in a plastic injection mold — keeping the runner above the melting point of the plastic.
Q2: How much does a hot runner injection mold cost?
A: Runner injection molds can cost anywhere from $1,000 to $10,000, depending on order size, part complexity, and other factors.
Q3: Who are the main manufacturers of hot runner molds?
A: The key players in the Hot Runner Mold market are:
- Hillenbrand, Inc.
- Husky Technologies Inc.
- Rex Plastics Inc.
- Hingtung ShenZhen industrial limited
- Shenzhen Rapid Direct Co., Ltd
- The Rodon Group
Q4: What is the difference between a hot runner and a 3 plate mold?
A: Three-plate molds are less expensive than hot runner molds and there is also a runner left over. An advantage to gating with a three-plate mold eliminates the need for cutting the gate off the part. Some multi-cavity molds must have a center gate on each part.
Q5: What is the difference between hot runner mould and cold runner mould?
A: Hot runner mold systems are valued for their ability to produce consistent quality within faster cycle times. Although more expensive than cold runner systems in initial cost and ongoing maintenance, they don't generate waste, thereby offering long-term savings potential.
Conclusion
Only after you understand the runner mold, you will know whether you need it or not. If you are considering buying injection molds but not sure which one is right for you, please contact Hingtung with any questions. If you already know what you're looking for, request a quote and get started today!