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.

Ejector pin

1)Ejector position:Ejected 10 – 15mm away from the edge of molding product (controlled by the retainer plate)

2)Ejection Types

1.Pin Ejector   2.Blade Ejector  3. Ejector Sleeve  4. Stripper Bar Ejector 5. Stripper Plate Ejector 6. Lifter  7. Air Ejector

3)Basic Ejection Requirements

  • Product evenly ejected without ejection marks, unbroken and in shape;
  • Main ejection parts: walls, ribs, holes and bars;
  • Set a standstill locking where the gradient or slope is slight;
  • Add skid-proof stripes where the gradient is steep;
  • The pin is level with or 0.2mm higher than the parting surface;
  • The interval between ejector pins needs to be an integer;
  • Ejector pin is at least 1mm away from the parting surface; if the parting surface is higher than 30mm, it should be at least 2mm away from the edge; if the parting surface is higher than 60mm, it should be at least 3mm away from the edge;
  • Set a 0.5mm clearance between ejector pin and ejector plate & B plate;
  • Set a 20mm, 30mm and 35mm clearance between ejector pin and parting surface for small, medium and large size molds;
  • Better more than less, better large than small.



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