6 points about ejector pins help your injection molding work increase 50%!

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6 Points about ejector pins help your injection molding work
increase 50%!
Written By Jasmine of DGMF
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.

How to design ejector pins?
The ejector pins design principles are as follows:
① When selecting the parting surface, try to keep the product on the side with the parting
mechanism.
② Ejection force and position balance ensure that the product will not deform or burst.
③ The ejector pin must be set at a place that does not affect the appearance and function of the
product.
④ Try to use standard parts as safe and reliable as possible to facilitate manufacturing and
replacement.
⑤ 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.
⑥ When there are thin and deep stiffeners, pushers are usually set at the bottom.
Avoid setting thimbles at the product inlet to avoid cracking.
⑧ 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.
⑩ 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 φ 2.5 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.
DGMF Mold Clamps Co., Ltd is the plastic injection mold components supplier, please contact us
for the ejector pin size and other information you need, thank you.

6 points about ejector pins help your injection molding work increase 50%!

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