30 Questions and Answers About Ejection of Injection Molding Part 1

The main action in one cycle of the injection molding machine are : clamping, plasticizing, injection, pressure-hold, moving-platen open, ejection.

And the ejection is the last action, which assure the plastic product take out and the next cycle begin successfully. So if there is some problem the cycle will be interruptd and affect the working efficiency of the injection molding machine.

Some problems are repeated always, so that we summary a list for the reference.

For this issue, it is divided into two parts: the other one is on the following link:

30 Questions and Answers About Ejection of Injection Molding Part 2

1. Manual model’s operation is normal. In semi-automatic mode, it’s necessary towait for the end of mold opening. Open the door, only then,the ejector can be ejected. But if before the mold opening, the ejector cannot be ejected.

(1) In some machine, there are option for the Europe and Asia, Change to the Asia model option.

(2) An error occurred in the computer program.


2. When the ejector has [signal] and [pressure] in the controller, it will not ejection action, and the ejector valve has also been changed already.

(1) Check whether the DC24V voltage has passed and whether the ejector signal line is broken.

(2) Check whether there are foreign objects between the ejector plate of the mold, or the mold is damaged already.

(3) Check whether the valve and the hose is blocked.

(4) Check whether the ejector sensor is good.

(5) Check the ejector cylinder, you can confirm the oil pipe with exchange. If the oil pipe is not acted, check the solenoid valve or the liquid valve.


3. There is a new mold withcore-puller. The ejectors should be fully retracted before closing the mold. The mold is OK when it is tested in the mold factory. But after receiving the mold for the production, the ejector pin of the first mold cannot be returned.

(1) Is the ejector back position set badly? Will it be okay to add some lubrication oil to the mold?

(2) It is necessary to understand the structure of the mold more clearly. If all the ejectors are required to be returned back before the core is inserted, there must be a special device on the mold to force the return.

(3) How big is the mold? Is it because the screws on the base plate are not installed properly? Another possibility is that the mold spring is not strong enough and the length is not enough.

(4) Another good way is to add a ejector return device. So the mold ejector will not return and will not lock the mold!

(5) Check the ejector hydraulic cylinder.


4. The ejector cannot stop when it is forwardin. But the forward-stop switch is normal after inspection.

(1) There is a problem with the ejection solenoid valve or the ejection pressure speed is too high or too fast, you can just adjust the pressure and speed.

(2) When this happens, you can turn off the machine and manually open the ejector. At the same time, press the switch to see if the computer has output when the ejection stop switch is OK.


5. There is a lot of pressure when opening the ecjectorand retreating, but the retreating movement is so slow. Why?

(1) Generally, it is caused by blockage of the valve. Clean the valve first.

(2) Check the piston ring of the ejector cylinder. The ejector pin oil seal may be broken.

(3) The process parameters are set correctly, and the proportional output is linear.


6. There is a 1300T injection molding machine. Recently, it was found that the semi-automatic ejector will not retreat after being ejected. It only retreats after closing. The time mode is selected in the computer.

This is the selection of ejector setting mode:

  • eject to the set position without retreating, easy for take out the plastic product manually.
  • Automatically retreat after reaching the position, easy for the plastic product drop automatically.


7. The ejector will automatically move forward during clamping (with a slow speed)in the semi-automatic productionmodel. After high-pressure clamping, press the ejector back. But the ejector is normal before and after in manual mode.

(1) The sealing ring of the ejector cylinder is damaged and the ejector reversing valve is diarrhea.

(2) The valve of the ejector is not reset well.


8. The ejector is set 3 times or 4 times. But it only 1 or 2 action, and sometimes it does not happen once, which results in always product remain staying in the mold cavity.

(1) The electronic linear of the ejector is in poor contact, clean the electronic linear or replace it.

(2) If the program is set to eject 4 times, but the actual eject does not follow the program. It is recommended to reset the computer and try again.

(3) Normally not, first try manually to see if the computer output situation of each ejector action (manual and semi-automatic are not the same).


9. The movement, the pressure and speed of the ejection is related to the opening and locking of the clamping.

(1) Check whether the action is related to other actions besides the action of mold opening and closing.

(2) Check the oil circuit of the ejector valve.

(3) Check the oil seal of the ejector cylinder.


10. The injection molding machine occurred abnormal noise when the ejector pin of the mold was retracted (the hand-touch ejection mechanism has a clear sense of shaking, shaking sound)

(1) First determine where the sound comes from, most of the sound comes from the mold.

(2) There is air in the ejector cylinder.

(3) If there are other actions, the problem is with the oil pump and the oil filter.


11. The machine has no action onopen/close in the clamping unit, the display is indicating that the ejector is not in the right place. And there is no problem with the electronic linear and the sensor. The pressure monitor is also normal. The solenoid valve at the back has also been ok, is there a problem with the set parameters?

(1) If the display is that the ejector is not in right place, the following may be the causes: The sensor switch is broken. Or the sensor cannot be sensed due to a long distance. Or the line is in poor contact. Check!

(2) Increase the ejection position of the ejector slightly. (Greater than zero is fine)

(3) Replace the ejectior back electronic linear wire and the outer metal wire for reliable grounding.


12. The ejector sensor light does not light up. It is still the same after replacing it with a new one. Now the machine does not open and clampthe moldand the machine is in the mold open state.

(1) Check whether the connecting wire of the ejectior-retract induction switch is broken. Whether the DC 24V power supply of the induction switch is normal. Also, check whether the induction switch from the source is PNP or NPN. And whether the replacement is the same as the original one.

(2) There are indicator lights for every action on our machine circuit board. The light that is on during the ejector retreat means the rejector retreat. If the indicator is not on, the ejector retreat has not stopped. Open the output screen of the controller and check for confirmation.


13. The ejector can’t be returned, and there is pressure. But it can be returned after closing the safety door twice. Why?


  • ① Is there a problem with the ejector return setting? If there are induction flashes?
  • ② Is the setting improperly? If the ejector return delay?
  • ③ Is there a problem with the ejector oil seal: aging?

(2) There is a problem with the position setting. Or controller program error.

(3) Check the controller if there is any signal input and output when ejector return back. The ejector back limited switch is in poor contact. Check to see if there is an interface in the middle when the switch was replaced before.


14. The old-fashioned relay injection molding machine, in the semi-automatic production model, after the mold is opened, the ejector rod is not forward. The product can only be ejected manually, Not knowing what went wrong. It is not ejected in the semi-automatic production model. It can only be ejected in manual mode.

(1) It should be that the mold opening position is not set correctly, and the mold opening stop-limited-switch is not pressed.

(2) The mold opening termination relay is not self-locking or there is a contact failure! There are many problems with these old relays.

(3) Check whether the pre-plastic limited-stop-switch or electronic linear is caused by displacement.


15. A machine ejects when the mold is in the opening. After inspection, there is no problem with the circuit IO board, the oil circuit and the directional valve.

(1) There may be a problem with the mold opening linear! The snails are loose.

(2) Is it set to eject during mold opening? Check if the ejector start position is less than the end position of mold opening.

(3) First, see if the ejector pin moves slowly, there is a problem with the seal of the cylinder or the leakage in the solenoid valve.

(4) Try to reduce the effective area of the mold opening position.

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