Valve Gate for Injection Molding

Making high-quality plastic parts in a higher volume used to be challenging with traditional injection molding methods, especially involving cosmetic and medical products. These processes often resulted in quality and strength issues because the molten plastic would run off uncontrollably when injected from the barrel’s nozzle. However, advancements in technology have led to the development of solutions like valve gates, effectively addressing this problem.

Valve gates are a type of hot runner gate equipped with a special valve or pin to control the flow of molten plastic into the mold. They are commonly used in hot runner systems to manage melt flow by controlling the shut-off time. Additionally, they prevent two flow fronts from meeting in the middle, significantly reducing cosmetic issues on injection molded parts.

Hot runner systems offer numerous benefits in injection molding, including faster production cycles. However, without the valve gate, the molten plastic flows freely and can easily escape from the mold. The valve gate serves to block the plastic from flowing out again by closing the exit. This feature adds an extra layer of reliability, especially for projects requiring high repeatability and precision.

With valve gates, it’s easier to reduce cycle time, enhance the part’s aesthetics, minimize waste, and eliminate runner removal operation. These are particularly helpful in automated manufacturing as they allow larger processing windows and speedy mold start-ups.

How it works?

The valve gate nozzle has a valve stem to create a solid seal for the gate. This stem moves forward and applies mechanical force to seal the orifice. During part injection and mold opening, the stem stays closed to prevent stringing and drool.

Valve gates effectively prevent those problems because the seal remains robust, even with high pressure from the hot runner. On the other hand, melt decompression can cause splay and other cosmetic issues on injection molded parts because it requires decompression.

Things to consider

Nozzles used in valve gate molds might leave a mark on the component, often the same size as the gate’s diameter. A slight indentation can be caused by the valve stem extending through the gate. The process of detaching the molded piece from the gate usually doesn’t cause the plastic to break or shear, so any color change or distortion caused by the gate break is rare. Despite variations in process conditions, the quality of the gate remains consistently high. Nevertheless, if the valve stem remains open for too long, allowing the resin in the gate to harden, the solidified plastic might obstruct the valve stem from fitting properly into the gate orifice, thereby causing a post.

Do you need valve gates for your project?

Our team here at HLH Proto will analyze your project requirements. We’ll determine if valve gates are essential to ensure high-quality injection molded parts. Contact us now!


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