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Injection Mould Ejection System Design

The design principle of eject system
The ejector system has a variety of forms. It relates to the shape, structure and plastic properties of the product. Generally, there are ejector pins, jacking tubes, push plates, ejector blocks, pneumatic composite ejectors, etc.

injection mould ejection system

The design principles of the ejector system are as follows:
  1. When selecting the parting surface, try to keep the product on the side of the mould release mechanism.
  2. Top output and position balance to ensure that the product is not deformed, not broken.
  3. The thimble should be located where it does not affect the appearance and function of the product.
  4. The use of standard parts as far as possible is safe and reliable for manufacturing and replacement.
  5. The ejection position should be set at a large resistance, not too close to the insert or core. For box type and other deep cavity moulds, the side resistance is the largest and the top surface and side surface should be ejected at the same time so as to avoid deformation of the product.
  6. When there are thin and deep ribs, the top rod is generally set at the bottom.
  7. At the product inlet, avoid setting the thimble to avoid cracking.
  8. For thin meat products, the thimble is placed on the runner and the product can be carried out.
  9. The thimble needle and the thimble hole usually have a clearance fit. If it is too loose and easy to produce burrs, it is too tight and easy to cause jams. In order to facilitate processing and assembly, and reduce the friction surface, generally 10 to 15 mm of mating length is reserved on the movable mould, and the remaining part is expanded by 0.5 to 1.0 mm to form an escape hole.
  10. In order to prevent the thimble from turning during production, it must be fixed on the thimble plate. The form of the thimble is various and must be determined according to the size, shape and position of the thimble.
The selection principle of the type of ejection
In the injection mould structure, the design of the ejection mechanism directly affects the quality of the plastic products. If the design is not good, the plastic parts will produce a series of defects, such as: warpage, deformation, cracks, and top white phenomena of the plastic parts. The determination of the ejector type is the most important part of the ejector design. The ejector type and quantity and the ejector position are optimized based on the ejector force and ejection resistance.
  • The ejector rob is the simplest and most common form of ejector mechanism. Because of its convenient manufacturing and processing, it has a good top-out effect and is widely used in production. However, the circular ejection area is relatively small, which tends to result in stress concentration, wear through the product, and product distortion. In tubular box products with small draft angle and high resistance, try to avoid using them. When the mandrel is relatively slender, it is generally provided with a stepped thimble to strengthen the rigidity and avoid bending and breaking.
  • Top pipe, also known as the tube or department pin, is suitable for ring, tube or center hole products. It pushes out evenly throughout the entire week, does not deform the product, and does not easily leave a clear top mark, which can increase product concentricity. However, the use of thick, thin products around the product should be avoided to use, avoiding damage due to processing difficulties and reduced strength.
  • The push plate is suitable for thin products with a variety of containers, boxes, tubes and elongate strips with central holes. It has a smooth and even ejection, and it has a large ejection force without leaving any traces. Generally, there will be a fixed connection so as to prevent the push plate from being pushed down during production or mould releasing, but as long as the guide column is long enough to strictly control the ejection stroke, the push plate may not be fixed.



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