Ejector System Design Principles
Aviation
February 10, 2021
Edward Nelson
In the plastic injection molding process, ejection of the plastic product is the final step. In this context, ejection refers to the process of removing the final product from a mold. The quality of the ejection and the quality of the plastic product are directly linked, making ejection a critical facet of production. There are seven design principles every ejector system should adhere to. In this blog, we will cover each of them.
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First, to prevent the plastic product from being deformed during ejection, the ejection force must be distributed evenly and as close as possible to the core or the part that is being ejected.
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The ejection force should be applied to the part with the highest rigidity and strength of plastic. Avoid putting a force on thin parts and ensure that the active surface is as large as possible. Ideal areas to place the force include the outstanding flange, the rib, or the wall edge of the shell. The majority of cylinder-shaped plastic produces are released by using ejector plates.
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In order to avoid ejector marks leaving imperfections on the plastic product, the ejection position should be set on a concealed or internal surface of the product. If the product is made from transparent plastic, the ejection position must be carefully chosen.
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To avoid marks and deformations caused by vacuum adsorption, a combined ejection approach (an ejector pin/plate or pin/block combination) or ventilation with porous steel may be necessary. The ejector pin’s clearance should be enlarged for ventilation, and an intake valve should be used whenever necessary.
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The ejector mechanism should be reliable, flexible, strong, and resistant to wear. For instance, regarding ejections with swing rods and wedges, the strength and wear of the sliding surfaces should be sufficient, and the surfaces should have lubricating grooves to improve their sliding capabilities.
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The length of the ejector mold return pin should have close contact with the cavity. There should be a distance between the two of no greater than 0.1 mm while the mold is closed.
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Finally, because a return spring is used for the return of the ejector plate, and return springs are not always reliable, they cannot be used as an early return mechanism.
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