Plastic parts in equipment are being used more than ever, from the automotive industry to the medical field, and even in construction. Generally, these parts are made using an injection molding process—one of the fastest and most accurate ways to manufacture plastic parts.
Two different types of molding systems can be used in the injection molding process—cold runner molds and hot runner molds. Each injection molding methods works when a plastic material flows from the spruce into the runner system, and then through a gate into the mold cavity. So, when considering cold vs. hot runner molds, which is better? Both systems have their advantages and disadvantages. Understanding the way each system works will help you decide which process is better for making the plastic parts you need.
Cold Runner Molds
In this system, the runners are kept at the same temperature as the molds. The cold runner system consists of either two or three plates within the mold. The two plate system is the simplest, but requires an ejection system to remove both the runner and the part from the mold. The three plate system enables the part to be ejected separately from the runner, since the runner is on a separate plate from the rest of the part. The three plate molds allow for flexibility in the design. In the cold runner system, it is important that the dimension of the runner be larger than the part. This will ensure that the material fills the part properly and that the mold is not under filled.
- Inexpensive and easy to maintain
- Suitable for more types of polymers, since you don’t have to worry about heat sensitivity
- Color changes can be made quickly
- Longer process than hot runner system
- Need for either robotics or a person to remove runners
- Creates waste if the runners cannot be melted down and recycled
Hot Runner Molds
Hot runner molds are made up of two plates, which are heated using a manifold system. There are two types of hot runners, externally heated and internally heated. Externally heated molds are better for materials that are sensitive to heat, while internally heated molds provide better flow control. There are several methods that can be used to heat the runners, including coils, heating rods, and heating pipes. The hot runner system ensures that the material remains molten throughout the runner process until it enters the mold cavity.
- Faster cycle time
- Eliminates waste because there are no runners
- Can accommodate larger parts and a higher volume of production
- Better consistency and quality of the parts
- Less pressure is needed to push the molten mixture into the mold cavity
- Higher cost to produce molds and maintain equipment
- Color changes cannot easily be made
- May not be suitable for some thermally sensitive material
When considering which injection molding system is better—hot or cold runners—there are many things to consider. A hot runner system eliminates much of the material waste created during cold runner injection molding but is a more expensive system. However, the fact that hot runners create less waste could off-set the cost of maintenance. The cold runner molds, on the other hand, can create waste if the runners are not recycled, but this system is less expensive and easier to maintain.
When choosing between cold runner molds or hot runner molds to make your plastic parts, consult with an experienced professional who can help you determine which method is right for you. You will need to consider cost and the type of material with which you are working, and a knowledgeable injection molder can educate you about your options.