Cold runner system is used when molding LSR. The advantages of this compound can be maximized and the production efficiency can be raised to the highest limit. By processing the product in such a way, it is not necessary to remove the injection channel, thereby avoiding increasing the labor intensity of the operation and sometimes avoiding a large waste of material. In many cases, the channel-less construction also reduces operating time.
The plastic injection nozzle is controlled by a needle valve for positive flow. At present, many manufacturers can provide injection nozzles with air-controlled switches as standard equipment, and they can be installed in various parts of the mold.
Some mold manufacturers have specially developed an open cold runner system, which is so small that multiple injection points need to be set in an extremely limited mold space (and thus fill the entire cavity). This technology makes it possible to mass-produce high-quality silicone rubber products without the need to separate the nozzle.
If a cold runner system is used, it is important to create an effective temperature gap between the hot cavity and the cold runner. If the runner is too hot, the compound may start to vulcanize before injection. But if cooled too quickly, it will absorb too much heat from the gate area of the mold, resulting in incomplete vulcanization.
For products injected with conventional sprues (such as submerged sprues and tapered sprues), it is suitable to use small-diameter injection ports for feeding (the diameter of the feed port is usually 0.2mm-0.5mm) for casting. For low-viscosity LSR compounds, like thermoplastic compounds, it is very important to balance the runner system. Only in this way can all mold cavities be filled evenly with the compound. Using the simulation software for designing the runner system can greatly simplify the development process of the mold, and prove its effectiveness through the mold filling test.
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