Before you consider running your plastic products on metal or plastic runners, you should first understand what running on a runner entails. A runner is a molded piece of plastic that serves as a support for your product as it moves through the injection molding process. The primary objective of using runners is to reduce the cost of production and to prevent melt-back. Melt-back happens when the same part is loaded back into the injection molding machine and it creates an inconsistency in the final product. To help you decide if running your next project on runners will be beneficial, we have outlined some pros and cons of this manufacturing technique.
What Are the Benefits of Using Plastic Runners?
There are many advantages to running your products on runners. First, runners reduce the cost of part production because you will be purchasing fewer tools, and maintenance will be less frequent. Additionally, you will have an easier time controlling the temperature of the melt and minimizing defects like undulations or sink holes in the product. You will also eliminate some of the inherent issues of injection molding, such as feed rate inconsistency, as well as reduce the risk of contamination. Runners are typically made of strong, durable materials, such as steel or injection-molded plastic, so they can withstand the extreme pressures of being loaded, melted, and unloaded again. When compared to other materials, runners are also more predictable, which will allow you to more accurately calculate how much material you will need in your raw stock.
Which Products Should Be Run on Runners?
Almost all injection-molded products that require support can be run on runners. Some common items that are typically run on runners include automotive parts, medical devices, and consumer goods. The only exception is if the design of your product requires a hemispherical cavity for holding a vacuum. This is called a vacuum assist and is used when the amount of pressure required to push your product through the mold will be too great for the runner to withstand. When deciding which products should be run on runners, it is important to consider the type of product you will be manufacturing. Products that need support, have a low volume, or are made of hard-to-inject materials will all benefit from the use of runners. Additionally, if you are trying to avoid a long lead time on your project, the use of runners may speed up the manufacturing process.
Which Products Should Not Be Run on Runners?
If your product requires a hemispherical cavity for holding a vacuum, it should not be run on runners. This is because the vacuum must be directly below the product, not above it. Runners are also not ideal for high-volume orders. If you are injection molding a massive number of parts, the runners will get too hot and distort, which will cause the product to be deformed or misshapen. In this scenario, it would be better to use a stationary mold. When considering which products should not be run on runners, it is important to remember that runners are intended to support the product only. If your product requires a large core, you may not be able to fit it on the runners.
Why Is It Challenging to Inject Mold Plastic On Runners?
Even if you decide to run your products on runners, there are some challenges to overcome. First, you may need to adjust your injection pressure to account for the fact that the runners will be hotter than the barrel. In fact, the runners may be up to 10°F hotter than the barrel when the product is first loaded, which can be challenging to adjust for. Additionally, you will need to make sure you are running the appropriate cycle time to allow the product to cool before ejection. If you don’t allow enough time for the plastic to cool, the runners will get too hot, and the product may be deformed. Runners are typically made of steel or a strong, durable plastic, so they can withstand the extreme pressures of being loaded, melted, and unloaded again. However, the runners will still be susceptible to defects, such as sink holes. In order to prevent sink holes and other defects, it is important to make sure the runners are clean and free of any debris that could damage the mold.
The Downsides of Using Plastic Runners
While runners reduce many of the challenges that come with injection molding and make it easier to produce consistent parts, they do have some downsides. First, they are more expensive than stationary molds and require more raw stock. As mentioned above, you will need to clean the runners after each use to prevent sink holes and other defects. Additionally, because the runners are in direct contact with the product and the mold, the runners will likely need to be replaced more frequently than stationary molds. Running your products on runners does have its challenges, but the benefits of this manufacturing technique will likely outweigh the negatives.
Conclusion
When you are deciding which manufacturing technique will work best for your project, be sure to consider the type of product you are making and how it will be used. If you are looking to reduce your production costs, then running your products on runners may be the best option for you.
