Many who are currently working in an injection mold system actually do not know what an ejector pin does and why it is there, and end up leaving flash on the die casting after it is produced from the mold. That said, it is imperative that the designers and purchasers of die castings have a basic understanding of the ejector pins as to their functions and other related facts.
The ejector pins are basically an integral part of a mold and molding process that forces out the metal casting from the ejector side of the mold after the mold opens when the metal is solidified. The cast basically stays on the ejector side of the die when the mold opens in the machine since the drafts and parts are designed for this purpose.
When the mold opens, a plate inside the ejector half on which all ejector pins are connected will be pushed forward. As the plate moves forward, the ejector pins also move up at the same time in one quick push. And this pushing motion will force the solid casting out of the mold. The casting will then remain on the ends of the ejector pins once out of the mold, and is picked off and removed from the inside of the casting system by a robot, and a new cycle of producing another casting will begin.
As a matter of fact, ejector pins are not always located at the same place in an injection mold system. Instead, it is subjected to the preference of die caster as well as the customer’s agreement. For instance, if the cosmetics is the primary concern for the die casting, the location of ejector pins should primarily be touched base beyond the die designs. The complexity of the die casting will also translate to the size and location of ejector pins used, as well as other considerations.
Following the above, the location and the number of ejector pins can depend on several factors. In addition to the mentioned above, the shape of part, texture and draft of side walls, and the depth of walls are all relevant factors which all translate to how likely the areas of parts will cling to the mold.
Resin choice is another factor for the location and size of ejector pins as well. For stickier resins, more force is required for release from the mold. You may also need wider ejector pins to distribute the removal force if the resins are softer. This is also to keep cooled plastic from being punctured.
The next very important selection factor is the working temperature, as it affects the durability and longevity of your ejector pins. For instance, if an ejector pin that isn’t tolerant to high temperature is used in a high temperature working environment, the ejector will not likely to last very long.
Following the above, there are typically three types of ejector pins that are each designed for a specific working environment temperature: the through hard pins, nitride pins and black ejector pins.
● Through Hard Pins: Through hard pins have the same hardness surrounding the diameter. They are able to withstand working temperatures below 2000C, and are ideal for plastic injection mold.
● Nitride Pins: Nitride pins will last much longer in a working temperature above 2000C as opposed to through hard bins. The reason is that the surface of nitride pins is specially designed with the hardness to ensure optimal life expectancy in a high temperature working environment. This type of ejector pin is most suited for die casting.
● Black Ejector Pins: Black ejector pins are able to withstand working temperature beyond 6000C. Nitride pins and through hard pins are however not designed to sustain such temperature. These pins are coupled with black coatings on the entire body so that they are able to sustain temperature up to 10,000C. Black ejector pins are ideal for automobile injection molding thanks to the additional lubrication. On a general note, they are suitable for any working temperatures, but are typically more expensive.
As you can see, each type of ejector pin is designed to accommodate different working environments, which is why the working temperature will always be one of the most paramount selection factors when buying ejector pins.
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