To learn how hot runners and manifolds are used in injection molding, it helps to understand what these are. Hot runners are associated with heated components, which facilitate the injection of plastic resin into mold cavities. Molds can be made with either ‘Hot Runner’ or ‘Cold Runner’ mold construction philosophies. Wise use of a ‘Hot Runner’ mold strategy for appropriate part geometries can prove highly valuable for effective tooling and cost efficient molding.
Manifolds, similar to hot runners, are also used to control temperature in injection molds and in the runner system. When used separately from hot runners, these manifolds are commonly referred to as water manifolds. These systems attach to the main injection mold as an auxiliary system designed to route cooling water from a chiller or tower into passages in the mold itself. By controlling the water flow rates for ideal thermodynamic exchange, manifolds control the mold temperature and thus the cooling environment for molding.
Because these two components work in tandem, they are often referred to as hot runner manifolds when connected with injection molding equipment. In addition, individual ‘hot runners’ can be managed and controlled on a tree like system of controlled distributed plastic feeding into the mold at discrete points. This can allow optimization relative to plastic melt reducing wasted material, as well as improving the cycle time for injection molding. When deployed correctly, hot runner manifolds are highly beneficial.
Using Hot Runner Manifolds
Plastic, regardless of application, begins in a mold that is classified as a cold or hot runner. Although there are advantages and disadvantages of each, many injection molding manufacturers prefer the hot runner system. For hot runner molds, the manifold system heats plates that melt plastic. From there, the plastic is sent to nozzles that fill the cavities in the mold. Sometimes there are “heater bands” which keep the material warm inside the runner system prior to entering the mold itself.
Although there are various types of hot runner systems, the two primary ones are internally heated and externally heated. The biggest advantage of internally heated systems is that the flow of plastic is better controlled. However, when dealing with polymers that are sensitive to variations in heat, externally heated systems are the preferred choice.
By using the hot runner manifold process for injection molding, cold runner slugs are completely eliminated. Because of this, regrind and recycling performed with virgin plastics have no impact on cycle times. In addition to faster cycle times, the hot runner system does not require any robotics for removing the runners, larger parts can be accommodated, and there is less risk for potential waste. Additionally, electronic control is possible through sequential valve gate technology that allows plastic to be deployed in a controlled sequential fashion into the part that may further improve cycle time, minimize warpage on cooling, and allow maximum processor control.
Injection molding that involves hot runner manifolds is beneficial in many ways. However, there is some risk for downtime as manifold systems require preventative maintenance. In addition, the up front cost on the molds can be more expensive. Even there however, there are options available. At GTV, we have developed options that allow cost effective, simplified hot runners to be used even in some prototype tooling applications as part of our plastic prototyping services. Because of this and its many other benefits in high volume production, a well thought out hot runner mold strategy is an excellent option for an injection-molding manufacturer.
If you need plastic and metal products designed, prototyped, or manufactured, Vowin is a reputable and trusted source. Please ask how our comprehensive prototyping services, tooling activities and engineering services can be of assistance in your product development.