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Ejector Pins
Original: Original | Author: dgmfmoldclamps | Publish Time: 2020-03-19 | 16394 Views | Share:
What are ejector pins?
What are ejector pins made of?
What is the function of the ejector pin?
How to use the ejector pins?


What are ejector pins?

Ejector pins are the "bouncers" of the injection molding world. They apply a force to eject a part from the mold, and in some cases can leave marks. Once the mold is opened, the pins extend into the mold cavity, push the part out, and then retract, allowing the mold to close and be refilled.

What are ejector pins made of?

While many molders use core pins made of copper alloys, there are many benefits of using them for ejector pins as well. They have terrific heat-transfer properties and are very resistant to galling.

What is the function of the ejector pin?

Ejector pins help safely remove parts from molds after they have been made. Here are some tips on how to properly locate and use those pins. Ejector pins are the “bouncers” of the injection molding world. They let technicians apply a force to eject a part from the mold, and, in some cases, can leave marks.

How to use the ejector pins?

(1) The ejector pins should be arranged so that the ejection force is as balanced as possible. The demolding force required for complex structures is large, and the number of ejectors should be increased accordingly.

(2) The ejector pins should be set ineffective parts, such as bone, column, steps, metal inserts, and some thick structural parts. The ejector pins on both sides of the bone and column should be arranged as symmetrically as possible. The distance between the sides of the ejector pins and the bone and column is generally D = 1.5mm. In addition, the centerline of the ejector pins on both sides of the column should be as far as possible to pass through the center of the column.

(3) Avoid setting up ejector pins across steps or on inclined surfaces. The top surface of the ejector pins should be as smooth as possible, and the ejector pins should be arranged at the structural part where the rubber parts are better stressed.

(4) A flat ejector pin should be used when the plastic part is deeper (depth 20mm) or it is difficult to arrange a dome needle. When a flat ejector pin is required, the flat ejector pin should be inserted as much as possible to facilitate processing.

(5) Avoid sharp steel and thin steel, especially the top surface of the ejector pin should not touch the front mold surface.

(6) The arrangement of ejector pins should consider the side distance between the ejector pins and the water conveyance channel to avoid affecting the processing and water leakage of the water conveyance channel.

(7) The ejector function of the ejector is taken into consideration. In order to exhaust the ejector, the ejector should be arranged at the place where the vacuum is easy to form. For example, at the larger plane of the cavity, although the rubber packing force is small, it is easy to form a vacuum, which results in an increased demolding force.

(8) For plastic parts with appearance requirements, the ejector pin cannot be arranged on the appearance surface, and other ejection methods shall be used.

(9) For transparent plastic parts, the thimble cannot be placed on the part that needs to transmit light.

How to select ejector pins?

B. Selection principle of ejector pins

(1) Use a large diameter ejector pin. That is if there is enough ejection position, larger diameter, and size-first ejector should be selected.

(2) The size of the ejector pins should be as small as possible. When selecting an ejector pin, the size of the ejector pin should be adjusted to minimize the size specifications, and the preferred size series should be selected as far as possible.

(3) The ejector used should meet the ejection strength requirements. During ejection, the ejector pin must withstand large pressure. To avoid bending and deformation of the small ejector pin, when the ejector pin diameter is less than 2.5mm, an ejector pin should be used.

After the product completes a forming cycle, the mold is opened, and the product will be wrapped on one side of the mold, which must be removed from the mold. This work must be completed by the ejection system, which is an important part of the entire mold structure. It generally consists of an ejection, reset and ejection guidance.

1.Design principles of the ejection system

There are various ejection systems, which are related to the shape, structure and plastic properties of the product. Generally there are ejectors, ejector pins, push pins, ejection blocks, and pneumatic compound ejection.

The structure diagram of the ejection system is shown in the figure.

 DGMF Mold Clamps Co., Ltd what are ejector pins, how ejector pins work, what are ejector pins made of, what are ejector pins used for,

How to design ejector pins?

The ejector pins design principles are as follows:

When selecting the parting surface, try to keep the product on the side with the parting mechanism.

Ejection force and position balance ensure that the product will not deform or burst.

The ejector pin must be set at a place that does not affect the appearance and function of the product.

Try to use standard parts as safe and reliable as possible to facilitate manufacturing and replacement.

The ejection position should be set at a place with high resistance and not too close to the insert or core. For box-like deep cavity molds, the side resistance is the largest, and the top and side ejection methods should be used at the same time to avoid product deformation and bursting.

When there are thin and deep stiffeners, pushers are usually set at the bottom.

Avoid setting thimbles at the product inlet to avoid cracking.

For thin meat products, set an ejector pin on the manifold to take the product out.

The fit between the ejector pin and the ejector pinhole is usually a clearance fit. If it is too loose, it will easily cause burrs, and if it is too tight, it will cause a seizure. In order to facilitate processing and assembly and reduce the friction surface, generally, a mating length of 10 to 15 mm is reserved on the movable mold, and the remaining part is enlarged to 0.5 to 1.0 mm to form an escape hole.

In order to prevent the ejector pin from rotating during production, it must be fixed on the ejector plate. There are various forms, and it must be determined according to the ejector size, shape and position.

What are the ejection types?

In the structure of the injection mold, the quality of the ejection mechanism directly affects the quality of the finished plastic product. If the design is not good, the plastic part will produce a series of defects, such as warping deformation, cracks, and whitening of the plastic part. The determination of the ejection type is the most important link in the ejection design. The ejection force and the ejection resistance are used to optimize the ejection type, number, and ejection position.

(1) Ejector pin

The ejector pin is the simplest and most common form of the ejector. Because of its convenient manufacturing, processing and repair, and good ejection effect, it is most widely used in production. However, the circular ejection area is relatively small, which is prone to stress concentration, product penetration, and product deformation. Avoid using in tubular box products with small demolding gradient and high resistance. When the ejector pin is relatively slender, generally a stepped ejector pin is provided to enhance rigidity and avoid bending and breaking.

(2) Sleeve Pin

The sleeve pin is also called the ejector sleeve pin or sleeve pins, and it is suitable for products with ring, tube or center hole. It is ejected with uniform contact force throughout the week, which will not deform the product and will not leave obvious ejection marks, which can improve the concentricity of the product. However, avoid using the products with thick and thin surrounding meat to avoid damage due to processing difficulties and weakened strength.

(3) Push Pin

The push pin is suitable for a variety of containers, boxes, cylinders and thin products with a central hole. The ejection is smooth and uniform, and the ejection force is large, leaving no ejection marks. Generally, there is a fixed connection to prevent the pushpin from being pushed down during production or demoulding, but as long as the guidepost is long enough and the ejection stroke is strictly controlled, the pushpin may not be fixed.

How to select plastic mold ejector pins?

The ejection system is one of the important functional structures of the injection mold. It consists of a series of ejection parts and auxiliary parts, which can have different ejection actions. The ejector pin is the most common ejection method. Ejector-type ejection elements, including ejector pins, shoulder ejector pins, flat ejector pins, and push pins. The precautions for the selection of the ejector pins are as follows:

1. Prevent deformation or damage of plastic parts, correctly analyze the size and location of the plastic part's adhesion to the mold cavity, and select a suitable demoulding device so that the ejection force is applied to the plastic part with the greatest rigidity and strength. The part, that is, as far as possible against the wall, bone, and column, the area of action is as large as possible (that is, as large as possible, a thimble with a large diameter) to prevent deformation or damage to the plastic parts.

2. The structure is reasonable and reliable. The ejection mechanism should work reliably, be flexible in movement, easy to manufacture, easy to replace, and have sufficient strength and rigidity.

3. If the diameter of the ejector pin is less than φ2.5 and the position is sufficient, a shoulder ejector should be used; if the pusher wall is below 1mm or the pusher wall diameter ratio is 0.1, the pusher with a shoulder should be used. The effective mating length of the ejector pin = (2.5 ~ 3) D, the minimum must not be less than 8mm, we generally take 20-25mm during the production process.

4. Try not to place the ejector pin on the insert splicing place

5. It is recommended to use a flat ejector pin for the long-arc glue position above 10mm. The shorter the flat body part, the better the strength and the easier the processing. The length of the cylindrical part should be indicated in the design specifications; for pipe positions above 10mm, it is recommended to use a push tube to eject.

6. For the occasion with an oblique ejector pin, in order to prevent the product from sliding with the oblique ejector pin, the surface of the ejector pin near the oblique ejector pin should be ground with a "+" slot.

Row position, inclined top

When the sidewall of the rubber part has a concave-convex shape, a side hole, and a buckle, the side core must be pulled out before the mold is ejected from the mold. This mechanism is called the row position. Holes on the outer side of the plastic parts require core pulling off the rear mold. If the groove on the inner side of the rubber part is ejected obliquely, the top opening distance is not enough.

In addition, the use of oblique ejection, ejection mechanism completed at the same time ejection and core pulling are called oblique ejection. For the parts that need to be cored on the rubber parts, when the space for the position is not enough, the inclined top mechanism can be used to complete it. In the oblique ejection mechanism, the oblique ejection distance should be greater than the core pulling distance (B> H) to prevent ejection interference.

Both the inner and outer sidewalls of the plastic parts are concave. The inner side has bone barriers and insufficient height. The front side of the outer side must be lined up, and the inner side must be ejected obliquely. There must not be any clamps around the side holes of the rubber parts. The side holes must be pulled out of the front mold row, and the buckle should be ejected obliquely.

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