Cooling Molten Plastic
Plastic products today would not exist without careful temperature control for both process heating and cooling. Injection molding requires that some plastics be heated all the way to 550° F. Because of these high temperatures, proper cooling can be one of the most essential steps in the entire plastic manufacturing process.
Plastic Cooling Timeline
The plastic cooling and recovery stage can take up around 80% of the total manufacturing time for a single plastic component. Optimizing this cooling stage prevents shrinkage and other plastic defects, reduces production time, creates stronger finished parts, reduces costs, and protects valuable injection molding equipment.
Air Cooled vs Water Cooled
There are 2 main methods for removing heat from around a plastic injection mold: air cooled chilling, and water cooled chilling.
Air cooled chilling uses forced air to remove waste heat from injection molding equipment into the surrounding air. Air cooled chilling may be an effective cooling method for low volume plastic manufacturing, however when it comes to high volumes, it is usually insufficient. Air is a less effective heat transfer material than fluid, and will take a long time to cool an injection mold properly before the part is ejected. Air cooling is also a less efficient use of energy because you are paying to cool a larger space instead of directing your cooling power exactly where it is needed.
Water cooled plastic chillers run a chilling fluid (usually a mix of glycol and water) directly around the injection mold. Waste heat transfers into the chilling fluid which then continuously returns to the chiller unit where the cycle begins again. Thermal engineers typically draw up precise heating and cooling specifications for an injection molding machine. These temperature control goals depend upon many factors including type of plastic being used, thickness and dimension of the part, and the design of the mold itself. Using a fluid plastic chiller helps manufacturers hit these temperature goals with more precision than if they were using an air cooled chiller.
Plastic Cooling Strategies
Over the decades, thermal engineers and mold designers have created clever cooling systems to more efficiently remove waste heat from injection molds. The goal is to remove heat quickly and uniformly across the entire mold surface so it can be used again immediately.
It is essential to eliminate hot and cold spots when chilling an injection mold. Mold designers must not only design for complete cooling coverage but also help the chiller maintain the right fluid flow rate. They accomplish this with a variety of cooling channel layouts that can be categorized into 2 main designs: parallel channels and series channels.
These channels are drilled into the top and bottom of the injection mold and chilling fluid flows through continuously during the cooling and recovery stage.
Plastic parts with protrusions, cavities, cores, and more can be difficult to cool evenly. Mold designers have engineered a few different methods for cooling these 3 dimensional features. A baffle is a cooling channel with a blade that runs perpendicular to the main cooling line. Cooling fluid flows into the channel, up and over the blade, and back down to exit the mold. This baffle allows cooling fluid to get in and out of a cavity or core in the plastic part and cool it from the inside.
A bubbler works similarly to a baffle, except its perpendicular channel contains a small tube instead of a blade. Cooling fluid flows up the tube, “bubbles” out the top, and runs down the outside of the tube like a water fountain.
Another method used to cool cores is a thermal pin setup. A thermal pin is contained within a narrow cylinder filled with fluid. This pin extends down into the main cooling fluid line so it can stay cool. As heat from the injection mold transfers into the cylinder, the fluid inside evaporates and turns into vapor. The vapor then condenses on the cool pin and this cycle continues during the whole cooling and recovery stage.
Conformal cooling uses a custom tooled mold with cooling channels that follow the 3 dimensional geometry of the plastic part. Mold designers will make these channels conform to specific shapes around the part’s exterior and interior.
North Slope Chillers Plastic Cooling Solutions
Contact us to find the right injection mold chilling solution for your needs at (866) 826-2993 or [email protected]