If you can design the mold in this fashion, off-the-shelf ejector blades can be used with somewhat less concern about steel types and hardnesses causing adhesive wear and galling.įIG 8 Cross-section of a well-supported thin ejector blade. Ideally, this split bushing can be flush with the parting line or flush with the bottom of a deep rib. 5, can often help minimize the unsupported length for various mold designs, as well as being a simple component to repair in the event of wear, erosion, or galling. The unsupported length is the distance between two locations where the blade is held or supported.Ī split bushing, as shown in Fig. Therefore, it is crucial to keep the unsupported length to a minimum. That value is, at best, an estimated guess, because it is dependent on so many factors, such as the amount of pack and hold pressure. There are mathematical formulas for calculating whether a blade might buckle, but one of the primary variables is how much force is required to eject the part. Since ejector blades are typically very thin, they are prone to buckling under pressure while trying to eject a part. An alternate relief method is to machine the hole or slot in the mold on a slight taper-½° per side or less-after the first ¼ to ½ in.įIG 4 A wire-EDMed ejector blade. However, chamfering the edges is a relatively simple method for relieving the corners-starting about ¼ to ½ in. I don’t recommend doing this because it usually results in slight down-flash in the corners when molding medium- to low-viscosity resins at high injection pressures. Some moldmakers prefer to chamfer the corners instead of adding a radius. Unless the slot or hole is relieved, the length of the radius on the ejector blade must be slightly longer than the stroke of the ejector plate, plus the length of the bearing surface. Therefore, a small radius must be added to some or all four corners of the ejector blade, depending on how it was installed. If this is not taken into consideration, the ejector blade will most likely gall and seize within the first few minutes of sampling a new mold. Most standard ejector blades have dead-sharp corners. When machining a slot or hole by milling, grinding or EDM, you will always have a very small inside corner radius.
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