What is the injection mold ejection system?

Product ejection is the last step in the injection molding process. After the product solidifies in the mold, an effective method is needed to eject it from the mold. The quality of the ejection will ultimately determine the quality of the product. Therefore, the ejection of the product cannot be ignored. And the product must not be deformed, whitened, cracked, or damaged during the ejection. This device is the ejection system, and there are several types of ejection systems:

1. Round ejector pin
2. Flat ejector pin
3. Sleeve
4. Ejector block
5. Stripper plate
6. Slant pin
7. Air ejector

The following principles should be observed when designing the ejection system:

1. In order to prevent the product from being deformed, cracked, or perforated due to ejection, the thrust point should act on the part of the product that can withstand the greatest force, that is, the part with good rigidity, such as the ribs, flanges, and the wall edges of shell-shaped products.
2. In order to avoid the ejection marks affecting the appearance of the product, the ejection device should be installed on the hidden surface or non-decorative surface of the product. For transparent products, special attention should be paid to the selection of the ejection position and ejection form.
3. The ejection stroke is generally 5~10mm after the product leaves the mold. For simple and large products, the ejection stroke is 2/3 of the product depth.
4. Return rod (RP): After the ejector ejects the product, its top will be much higher than the mold cavity. To avoid damaging the mold core before the next mold closing, a protective mechanism must be provided, so a return rod (RP) is provided, and a pull-back mechanism and a spring can also be provided to help it reset.
5. The end face of the ejector is generally 0.05~0.1mm lower or higher than the mold cavity surface. Whether it is high or low depends on consultation with production and development personnel.

Introduction of Injection Mold Ejector Device

1. Dome ejector pin
   Dome ejector pin: It is the most common and simplest ejector device. Both the dome ejector pin and the ejector pin hole are easy to process, so it has been widely used as a standard part. When processing a longer ejector pin hole, the contact surface between the ejector pin and the mold can be reduced by expanding the hole after a certain distance from the surface of the male mold insert. Avoid erosion to simplify mold manufacturing. The ejector pin needs to be quenched to have sufficient strength and wear resistance. When the surface of the finished product is a curved surface, attention should be paid to the anti-rotation of the dome ejector pin.
2. Flat ejector pin
   Flat ejector pin: When the finished product has a small space and a deep rib, it is not easy to place a dome ejector pin. Generally, the placement is at the bottom of the finished product rib. The flat ejector pin hole is generally processed by wire cutting. The flat ejector pin needs to be quenched to have sufficient strength and wear resistance. The shape of the flat ejector pin (as shown in the figure) increases the ejector pin strength at the R angle.
3. Sleeve
   Sleeve (ejector tube): It is used when the finished product has a boss. Generally, the placement is at the bottom of the finished product boss.
4. Ejector block
   In some molds, the side wall of the finished product is too deep, which can easily wrap the mold core and generate a large demolding force. In order to make the finished product easy to demold, an ejector block is used in combination with an ejector pin.
5. Stripper plate
   The ejector plate is suitable for the demolding of cylindrical plastic parts, thin-walled containers and various shell-shaped plastic parts. The main features of this ejector mechanism are uniform and stable ejection force, large ejection force, and the plastic parts are not easy to deform. There is no ejection mark on the surface. The structure is also simpler than the ejector mechanism, and there is no need to set a reset device. When the mold is closed, the ejector mechanism can be reset by the thrust of the fractal surface of the female template. The disadvantage of this structure is that the cavity and core need to be set on the male mold and the female mold respectively, and the concentricity between the outer shape and the inner hole of the molded plastic part is low.
6. Oblique pin
   When there are more oblique pins in the finished product and it is not easy to arrange the ejector pins in other places, the oblique pin can be used directly to eject the finished product.
7. Air ejection
   Whether it is in the male or female mold, the air ejection method is very convenient, and there is no need to install a push plate. During the ejection process, all parts of the entire product are subjected to the same pressure, so even soft plastic can be removed from the mold without deformation. Usually, air ejection requires a minimum demoulding slope greater than 2∘. For products with complex shapes that require a large demoulding force, it cannot meet their requirements.