Injection molding is a way of making plastic parts. Molten plastic is injected into a mold, then cooled and solidified to make the part. This process, which can also involve CNC machining and other precision methods, is used to make components and prototypes for product design and small batch production.
So when choosing the right mold for your project, it's important to understand the different mold designs. Injection molding uses two main types of molds: hot runner and cold runner.
Hot runner molds use heated runner channels to inject molten plastic into the mold. This makes sure the plastic flows smoothly as it cools. On the other hand, cold runner injection molding use channels that are not heated to move molten material from the nozzle into the mold. This makes the molding process simpler and cheaper.
Each system has its own features, and choosing between hot runner and cold runner injection molding affects both the manufacturing process and the final product.This article will look at the parts of cold runner system injection molding and how it works.
A cold runner injection system is made up of two or three plates inside a mould, and the system injects plastic into the mould through a gate and feeds a runner that directs the part into the mould cavity.But the simplest cold runner injection molding is just a two-plate mould with a parting line between the plates. This system has runners and parts that are all joined up, and you can only gate it from the side. There is also an ejector system that separates the runners and parts from the mould when you are producing the product.
The three-plate cold runner system has three plates, with two parting surfaces that allow the mould to be split into three parts when the part is ejected.
Runners are connected to separate plates, so only the part needs to be ejected.Three-plate moulds allow for greater design flexibility and the flexibility to install gates as required by the application. But remember, you'll need to recycle and regrind (or treat) the runners to minimise waste, which can sometimes increase cycle times.
Nozzle: If any dirt or particles find their way into the water jacket, you’ll need to dispose of the entire weld assembly. Some nozzles come with removable water jackets, which simplify the cleaning process significantly. The design of these nozzles can differ depending on the supplier, especially in cold runner injection molding systems.
Nozzle Tips: When comparing nozzle tips in hot runner versus cold runner systems, there are noticeable differences. Some systems feature nozzles with a fixed tip, while others use spring-loaded tips that expand slightly when heated. This expansion ensures the nozzle maintains constant contact with the mold, which is crucial in cold runner system injection molding to prevent leaks and ensure precision.
Runner Manifolds: The design of the runner manifold also varies between hot and cold runner molds. In cold runner systems, gun-drilled manifolds are commonly used, but these can create challenging-to-clean spots at the end of the runner channels where material might cure. However, manifolds with a split-plate runner design in cold runner injection molding allow for easy removal of the plate, making cleaning and material changes quicker and more efficient.
Piston Assembly: The piston assembly is vital for controlling the material flow in both hot and cold runner molds. While cold runner systems may use external air lines with barbed fittings, some modern designs eliminate these components entirely. By incorporating gun-drilled air passages, these systems avoid the risk of air line damage and connection errors, leading to a more reliable and streamlined operation.
Pneumatic Connections: In cold runner systems, pneumatic connections typically involve either external air lines or an air terminal box with a quick-disconnect coupler. This setup allows for easy integration with the molding machine, ensuring seamless communication between the valve gate controller and the cold runner system, enhancing the overall efficiency of the molding process.
The cold runner molding system is always getting better, giving designers and users more options and flexibility. These improvements are making cold runner injection molding more efficient, precise, and effective, and allowing for more innovative and cost-effective solutions in production.
According to different product structure and customer demand situation, will choose different mould runner structure. The common liquid silicone cold runner mould, the sprue is designed with needle valve structure, which can reduce the material waste of the runner and save the liquid silicone material.
Liquid silicone cold runner mould, its structure in addition to the panel, bottom plate, upper and lower templates, heating plate, heat insulation plate, mould core, and cold runner plate, cylinder plate. Needle valve sprue is a key technical component of cold runner mould.
Its features contain:
1、It can directly feed the glue from the surface of the product, which will not produce injection traces and will not waste the material;
2、It can be injected quantitatively or in small quantities, which is suitable for the production process of very micro-volume products;
3, can be adjusted through the control cold runner injection molding for the opening and closing time of the nozzle, the balance of the feed port can be adjusted to a uniform discharge state.
Of course, liquid silicone needle valve type cold runner injection molding also has some disadvantages, which is why not all the moulds choose this structure:
Therefore, before processing liquid silicone mould, you need to choose the appropriate runner and structure according to the actual situation.
