![]() It cannot be welded, but it can be ground or wire EDM-ed to a larger size.įIG 3 Four common methods of installing an ejector blade.Ī very common method of installing ejector blades is in a wire-EDM hole. While this is an acceptable method, it is difficult to repair. Another method is to install the entire width of the blade in one component. This will cause accelerated wear and down-flash. The odds of perfectly aligning the machined slots are slim to none. The worst method is when a portion of the blade rides in more than one mold component. There are four common methods of installing an ejector blade in a mold, as shown in Fig. Ra is equal to a metric rating of 0.10 μm. ![]() Offshore component parts are made to various different standards, such as DIN (German Institute for Standardization), JAP (Japanese Standards Association), JIS (Japanese Industrial Standards), or Euro Metric, which all have metric dimensions and tolerances. When you evaluate the surface-finish rating of any component, keep in mind that there is a huge difference between Ra in microinches and in micrometers. If the specifications of the component are in inches, the surface finish is correspondingly in microinches. Conversely, for DIN, JIS and other metric specifications, the Ra surface finish is in micrometers 1 microinch (μin.) = 0.0254 micrometers (μm). For example, an English rating of 4.0 μin. When the surface finish of both components is very smooth, any applied lubricant creates a fine film between the components, which helps prevent them from touching one another-like when the tires on your car hydroplane in the rain. This is called elastohydrodynamic lubrication, or EHL. Rougher surfaces also have higher coefficients of friction, which cause them to get hot, wear faster and potentially gall. Objects with high Ra values have irregularities on the surface, which can create nucleation sites for cracks and corrosion to form. Ra is the arithmetic average of the surface heights measured across the peaks and valleys of a surface with a profilometer. The surface finish plays a couple of important rolls in determining the performance of an object. One important aspect when selecting a blade ejector is the surface finish-actually surface roughness-which is usually specified in Ra units. undersized blade-knowing that it will be cost-effective in the future. Effectively, this moldmaker starts off with a 0.005-in. I know a tool shop that intentional grinds a few thousandths off all four sides of brand-new ejector blades. Their reasoning is when the slot or hole wears out, they don’t have to order a custom blade after repairing the mold. This could be important when molding very low-viscosity materials, such as nylon. But keep in mind that people make mistakes. You would be wise to apply the old Russian proverb of “trust but verify” (No, former President Ronald Reagan did not invent this saying.) All component parts should be measured before blindly installing them into a mold. A few of the offshore mold-supply companies offer tolerances as low as +0.0000 to -0.0001 in. According to the domestic websites I reviewed, those tolerances have gotten much better and are typically +0.0000 in. Years ago, the width and thickness of OTS (off-the-shelf) ejector blades were not very accurate and had to be re-ground to size. But if an ejector blade wears out its slot, the slot needs to be increased and a custom blade needs to be installed, or you need to weld the worn-out slot and machine it to its original size. Depending on how the blade was installed, it may not even be possible to repair by welding. It is relatively easy and inexpensive to increase the diameter of a worn hole for an ejector pin and install a pin that is a standard 0.005 in. If an ejector pin or an ejector blade wears, you simply replace it. But if either a pin or blade wears the hole or slot it rides in … that’s a different story.
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