Cold runner molds are a type of injection molding mold used to produce plastic parts. Unlike hot runner molds that use a heated manifold to keep the plastic material in the runner system molten, cold runner molds have a solid and unheated runner system. Here’s a comprehensive guide to cold runner molds in injection molding:
- Basic Structure: Cold runner molds consist of two main parts: the mold cavity and the runner system. The mold cavity is the space where the final part is formed, while the runner system acts as a pathway to deliver the molten plastic material to the mold cavity.
- Runner System: The runner system in a cold runner mold is solid and not heated. It includes channels, gates, and sprues that guide the molten plastic from the injection machine nozzle to the mold cavity. After the injection process, the plastic in the runner solidifies and is typically ejected as scrap.
- Material Conservation: One of the advantages of cold runner molds is that they help conserve material. Since the runner is solid and not used to form the final part, there is less material waste compared to hot runner molds where the runner material is re-melted.
- Cycle Time: Cold runner molds may have longer cycle times compared to hot runner molds because the cold runners need to be solidified before the part can be ejected. However, advances in mold design and cooling technology have minimized the cycle time difference between the two types of molds.
- Maintenance: Cold runner molds are generally easier to maintain and clean compared to hot runner molds. The lack of heated components in the runner system simplifies maintenance tasks and reduces the risk of material degradation or contamination.
- Cost: Cold runner molds are typically more cost-effective for low to medium volume production runs due to their simpler design and lower initial investment cost. However, for high-volume production, hot runner molds may offer better cost efficiency in the long run due to reduced material waste and shorter cycle times.
- Part Quality: The cold runner system can leave a visible gate mark or scar on the final part. However, with proper design and process optimization, gate marks can be minimized, and the overall part quality can be maintained.
- Applications: Cold runner molds are commonly used for a wide range of applications, including consumer goods, household items, automotive components, and medical devices, among others.
- Design Considerations: When designing parts for cold runner molds, it is essential to optimize the gate locations and consider the material flow to achieve consistent fill and avoid part defects such as weld lines or air traps.
In conclusion, cold runner molds offer a cost-effective and practical solution for a variety of injection molding applications. They are particularly suitable for low to medium volume production runs where material conservation and simplicity in mold maintenance are crucial. Manufacturers should carefully consider the specific requirements of their project and the production volume to determine whether a cold runner mold is the most suitable option for their injection molding needs.
If you’re looking for an affordable and versatile way to produce plastic parts, you may want to consider using a cold runner mold. A cold runner mold is an injection molding tool in which the plastic material is cooled in a separate channel or “runner” before reaching the individual cavities of the mold. This enables you to create multiple parts of varying shapes and sizes from the same mold while reducing waste and increasing quality.
In this article, we will explain what cold runner molds are, how they work, what their advantages and disadvantages are, and how to choose between cold runner and hot runner molds for your injection molding project.
First, let us understand the definition and working principle of cold runner mold. A cold runner mold is an injection molding tool that consists of a main mold part and a separate runner part. When plastic material is injected into the mold, it flows through the runner section and is cooled before reaching the cavity of the mold. This cooling process ensures that the plastic material remains at a lower temperature before entering the mold cavity, thereby reducing the risk of shrinkage and deformation of the material.
Next, let’s take a look at some of the advantages and disadvantages of cold runner molds. First, a major advantage of cold runner molds is that they enable multi-cavity molding. This means you can make multiple parts of different shapes and sizes in the same mold without having to make a separate mold for each part. This saves production costs and time significantly. In addition, cold runner molds can also reduce the generation of waste materials. Because the plastic material is cooled before entering the mold cavity, it does not create excessive waste in the mold. This helps improve production efficiency and product quality.
However, cold runner molds also have some disadvantages. First, because cold runners require additional cooling systems, they are generally more complex and expensive than hot runner molds. In addition, cold runner molds also require longer cooling times, which may lengthen the entire production process. In addition, the design and maintenance of cold runner molds also require more professional knowledge and skills.
Finally, let’s discuss how to choose cold runner and hot runner molds. Before choosing, you need to consider the following factors: shape and size of the part, production quantity, cost budget, and required production speed. For parts with complex shapes, smaller sizes, or parts that require high-volume production, cold runner molds may be a better choice. For parts with simple shapes and larger sizes, or parts that need to be produced quickly, hot runner molds may be more suitable.
In summary, cold runner molds are affordable and versatile injection molding tools that enable multi-cavity molding, reduce scrap, and improve product quality. However, they also have some disadvantages, such as complex cooling systems and long cooling times. When choosing cold runner and hot runner molds, you need to consider factors such as part shape and size, production quantity, cost budget, and required production speed.
What is a cold runner mold?
A cold runner mold is a type of injection molding tool where the plastic material is cooled in a separate channel or “runner” before it reaches the individual cavities of the mold. The plastic resin is injected into the cold runner system, where it solidifies before being directed into the cavities to form the final parts.
There are two main types of cold runner molds: two-plate molds and three-plate molds. In two-plate molds, the mold consists of two halves: one with the sprue, runners, gate, and cavities, and one with the ejection system. The sprue is the channel through which the molten plastic enters the mold from the injection machine nozzle. The runners are the channels that distribute the plastic from the sprue to the gate. The gate is the point where the plastic enters the cavity. In two-plate molds, the sprue and runners remain attached to the part after ejection and have to be manually cut off.
In three-plate molds, the mold consists of three plates: one with the sprue, one with the runners and gate, and one with the cavities and ejection system. The sprue plate contains a hole that aligns with the injection machine nozzle. The runner plate contains channels that connect the sprue plate to the gate plate. The gate plate contains openings that allow the plastic to enter the cavities. In three-plate molds, the sprue and runners are automatically separated from the part as the mold opens.
How does a cold runner mold work?
The working principle of a cold runner mold is as follows:
- The injection machine heats up and melts the plastic resin in a barrel.
- The injection machine pushes the molten plastic through a nozzle into the sprue of the mold.
- The molten plastic flows through the runners and gate into the cavities of the mold.
- The molten plastic fills up and packs the cavities under high pressure.
- The molten plastic cools down and solidifies in both the cavities and the cold runner system.
- The mold opens and ejects or drops out the parts along with the sprue and runners.
- The sprue and runners are either manually or automatically cut off from
the parts. - The sprue and runners are either discarded or reground and recycled for future use.
What are the advantages of cold runner molds?
Cold runner molds have several advantages over hot runner molds, such as:
- Lower initial cost: Cold runner molds are simpler and cheaper to design and manufacture than hot runner molds, which require complex heating systems and controllers.
- Easier maintenance: Cold runner molds do not have any heating elements or electrical components that can malfunction or wear out over time. They also do not require frequent cleaning or purging as hot runner molds do.
- Higher flexibility: Cold runner molds can accommodate different types of plastics, colors, additives, and fillers without affecting their performance or quality. They can also produce parts with different shapes and sizes from
the same mold by using interchangeable inserts or cores. - Better quality: Cold runner molds can reduce or eliminate some common defects in injection molding, such as flow lines, knit lines, sink marks, warping, flash, etc., by optimizing
the gate location, size, shape, and number.
What are the disadvantages of cold runner molds?
Cold runner molds also have some disadvantages compared to hot runner molds,
such as:
- Higher material waste: Cold runner molds generate more scrap material from
the sprue and runners that have to be either discarded or recycled. This can increase the material cost and environmental impact of injection molding. - Longer cycle time: Cold runner molds require more time to cool down the plastic in the cold runner system before opening the mold and ejecting the parts. This can reduce the production efficiency and output of injection molding.
- Larger mold size: Cold runner molds require more space to accommodate the cold runner system, which can increase the mold size and weight. This can limit the number of cavities that can fit in the mold and increase the clamping force required by the injection machine.
How to choose between cold runner and hot runner molds?
The choice between cold runner and hot runner molds depends on several factors, such as:
- Part design: The shape, size, complexity, and quality requirements of the part can influence the type of mold that is best suited for it. For example, parts with thin walls, intricate details, or high cosmetic standards may benefit from hot runner molds, while parts with thick walls, simple geometries, or low aesthetic expectations may be better off with cold runner molds.
- Material type: The type of plastic resin used for injection molding can affect the performance and compatibility of the mold. For example, materials that are sensitive to temperature changes, degradation, or contamination may require hot runner molds, while materials that are stable, durable, or recyclable may work well with cold runner molds.
- Production volume: The number of parts that need to be produced can determine the cost-effectiveness and feasibility of the mold. For example, high-volume production may favor hot runner molds, which can reduce material waste and cycle time, while low-volume production may prefer cold runner molds, which can lower initial cost and maintenance.
- Color change: The frequency and ease of changing colors during injection molding can influence the choice of mold. For example, frequent color changes may be easier with cold runner molds, which can be quickly purged or cleaned, while infrequent color changes may be more efficient with hot runner molds, which can avoid material waste and downtime.
In conclusion, cold runner molds are a type of injection molding tool where the plastic material is cooled in a separate channel or “runner” before it reaches the individual cavities of the mold. Cold runner molds have several advantages and disadvantages over hot runner molds, and the choice between them depends on various factors such as part design, material type, production volume, and color change. By understanding these factors and consulting with an injection molding specialist, you can choose the best mold for your injection molding project.
