What are ejector sleeves and how they work?

ejector sleeves for plastic injection mold

Ejector sleeves

1) The application of ejectors sleeves is required when a product features a hollow pillar structure and a great height. The matching relationship between pillars and sleeves is shown in the diagram below:

Ejector sleeves application

When a product features a pillar that is equipped with shockproof rubber, the ø3/16” + ø1.7 sleeve should be selected. If number 5 sleeve option is selected, there will come the stepped sleeve pin, of which the dimensions are shown in the diagram. For mold base below 30 x 40, category A sleeve pins should be applied; for mold base over 30 x 40, category B sleeve pins should be applied. See the diagram:

sleeve pins types in plastic injection mold

The order should be placed in the following format:

ø1/4” x sleeve length x ø3.5 x 30 x ø2.6 x L

ø1/4”x sleeve length x ø3.5 x 50 x ø2.6 x L

If a CD slider needs a sleeve, the sleeve dimensions will be unified as:
ø 6.35 x sleeve length x ø1/8” x sleeve pin length, in consideration of convenient pin replacement.


2) Sleeve pins are often fixed in plastic injection mold by headless screws. However, when several sleeve pins are very close to each other, briquettes and hex socket head cap screws will be used to fix them.

ejector sleeves fixation in plastic injection mold

3) Usually, the fixing holes of a button employ the sleeve ejector, with the standard ø3.57 x ø1.59 sleeve selected without exception. When it is not possible to use the standard size sleeve, it has to be guaranteed that the hole size is kept unchanged while the outer circle is appropriately enlarged, to make it possible for the application of a standard sleeve. The matching relationship between the sleeve pin and the cavity is shown in the diagram below:

sleeve pins design

4) Prevent sleeve from contacting with the knock-out hole.

What is the stop pin?

stop pins for plastic injection mold

The function of the stop pin

1.Reduce the contact surface betwwen ejector plates and clamping plates,it is easy to control the flatness of ejector plates by adjusting the thickness of stop pins.

2.Buffer against ejector plates

The material of stop pin

S45C,hardness HRC40°~45°

Position of stop pin

1.An STP must be installed under the RP to prevent deformation caused by large stress,see pic 1#

2. Avoid to interfere with other mold components,such as support,EGP,KO .etc. see pic 2#

The quantity of stop pins

The quantity of stop pin designing

Note:For a large size plastic injection mold, Stop pin is needed to increase the supporting points of the ejector backing plate, so as to prevent ejector plates from deformation


Important Considerations for the Ejecting System(ejectors)

ejecting system ejector pins for plastic injection mold

What should we pay attention to the ejecting system?

2.1 Keep at least a distance of 3/32” between ejector hole edge and other holes;
2.2 A clearance of 1/64’’ should be kept for ejector holes on the ejector plate;
2.3 A clearance of 1/32’’ should be kept for ejector holes on the  plate of injection mold;
2.4 All ejector pins should adopt the standard dimensions; the ejector base cannot be ground lower;
2.5 For materials like LDPE and PP, the diameter of each ejector pin must be measured, because flash will be likely caused when the clearance between pin and hole is larger than 0.02mm;
2.6 The verticality and glossiness (Ra ~ 0.25μm) of pin holes have to be guaranteed in ejecting system;
2.7 For materials like PP, PE and Nylon, hole diameter = pin diameter + 0.01mm; for materials like HIPS, PC and ABS etc., hole diameter = pin diameter + 0.02mm;
2.8 Ejector pin should pass through the mold base, ejector plate and mold components in a straightforward way;
2.9 Upon installation of all ejector pins, the ejector plate should be able to slide downwards freely;
2.10 Labels in the same direction should be provided near the location of all ejector pins and screw heads, so as to prevent wrong installation;
2.11 All pins need to come with dowels, to prevent wrong installation;
2.12 Upon installation of ejector pins, everything needs to be checked before covering the back panel;
2.13 After installation of the supporter, use a flashlight to examine each rib and hole from the direction of the mold core, to see if there is any problem with pins or sleeve ejectors. Cover the back panel when everything’s OK.
2.14 When designing the location of ejector pins, in addition to guaranteeing sufficient ejection force, it has to be ensured that the product can be ejected in a straightforward way;
2.15 There are two types of ejector pins, i.e. though-hardened and nitrided;
2.15.1 Though-hardened – surface hardness is 65~74HRC, and steel core hardness is 50~55HRC;
2.15.2 Nitrided – the nitrided surface hardness is 65~74HRC.