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Product News - Valve Gate Designs Address Heat Expansion Problems, NeedFor Gating Two Materials
December 1, 1999
5 Min Read
Valve Gate Designs Address Heat Expansion Problems, Need For Gating Two Materials
Taking a step away from internally heated, low-voltage hot runner systems it is known for, Ewikon has introduced two new products: the externally heated, 240 v HPS III valve gate nozzle and the HPS III two-component valve gate nozzle.
Because the products are so new, pricing has not yet been set, so please contact the company directly for this information using the Key Contact Directory.
Valve gate has a unique design that is said to address the problem of needle or pin deflection resulting from the difference in growth of the manifold in relation to the other plates of the 'A' side of the mold.
Externally heated manifolds expand in all directions when elevated to process temperature, whereas the surrounding plates, including the 'A' plate and nozzle retainer plate, experience little growth. Nozzles in a hot runner system are held stationary by the 'A' or nozzle retainer plate. Therefore, alignment of the manifold nozzle port to the nozzle bore is affected by the manifold growth.
This does not present a problem in conventional hot runner systems due to the fact that growth can be predicted and molds are designed accordingly. It does, however, create a significant problem in conventional valve gate technology.
The valve pin in most systems passes through the manifold, thus intercepting the melt channel within the manifold. Such systems experience valve pin deflection as the manifold is elevated from ambient to process temperature. The pin deflection creates side loading on the seal and pin, thus shortening the life expectancy of both devices. Leakage of plastic from the melt channel through the seal area to the backside of the manifold is common in such designs.
In contrast, the HPS III valve gate nozzle is designed with the entire nozzle, including the needle drive unit, positioned in front of the manifold.
This self-contained device comprises the nozzle, needle and valve drive unit. A pneumatic or hydraulic drive assembly, located in the front section of the nozzle, drives the valve pin. This entire assembly is located on the parting line side of the manifold.
Unlike other valve gate systems, the drive unit is not sandwiched between the clamp plate and manifold. Therefore, it is not subjected to high temperatures and seal life is extended.
The needle valve is contained within the nozzle housing and does not pass through the externally heated manifold. It is positioned in the center of the nozzle, extending from the tip of the upper head of the nozzle.
Melt enters the nozzle from the manifold and is directed through two melt channels on opposite sides of the valve pin assembly. Because the melt intercepts the needle at the intersection of two flow channels equal and opposite to each other, the needle does not experience side loading or deflection. This extends the life of the needle because side-loading wear is eliminated.
In addition, the needle in the HPS III valve gate nozzle is significantly shorter than that of other valve needles. This translates to less growth and results in improved gate quality. Gate quality is said to be further improved by a conical needle design, which ensures zero position with each closing of the needle.
The HPS III valve gate system incorporates the HPS III 'T' (technical) manifold design. This manifold is characterized by Ewikon's Flow Element technology, which is designed to provide smooth, rounded directional changes through the melt channel. Flow Elements are claimed to minimize shear stress and to eliminate the potential for material hang-ups, which lead to color change and material burning problems. Natural balancing from drop to drop is ensured and manifold stack height is kept to a minimum due to the Flow Element construction.
Two-component valve gate is designed to provide valve gating of two separate materials through one valve gate nozzle, enabling the molding of a two-component part using a common gate point and a one-stage molding process.
The design is said to allow for a wider range of molding solutions in the two-component field. A typical application would be an inner core encased by an outer skin of a second material. This would reduce material costs by being able to use a lower cost material in the inner core.
Other applications include molded parts having a hard surface on one side and a soft surface on the other. For example, a coffee cup molded of hard, food-grade ABS as the inside wall and a TPE outer wall to create a soft touch.
The HPS III Two-Component valve gate nozzle has two moving needles that are independently operated at appropriate stages in the molding cycle. The needle assembly is made up of a solid steel inner needle positioned inside of a hollow outer needle. Both are moved in the open or closed position by way of pneumatic or hydraulic drive units at different times in the molding cycle.
When the inner needle is moved to the closed position and the outer needle to the open position, the first material is injection through the nozzle to the cavity. If the outer needle is closed and the inner needle is opened, the second material can be injected. Closure of both needles seals the gates like a conventional valve gate nozzle.
The new nozzle is built with two independent flow channels entering the nozzle to ensure melt separation until it enters the cavity of the article being molded. Two separate manifolds, each conveying one material, interface with the nozzle.
This two-component valve gate nozzle is heated using 240-volt heaters and can be controlled by conventional hot runner controllers. It is combined with the HPS III manifold technology to provide a complete, engineered system.
Ewikon Hotrunner Systemsof America
East Dundee, IL
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