How to Prevent Plastic Leakage in the Injection Molding Process?

In the injection molding production process, the injection molding machine leakage of plastic is a highly undesirable situation.

This not only leads to equipment damage but also has adverse effects on the timely delivery of products and increases the complexity of repair work.

However, it is important to note that machine leakage is typically the result of individual negligence, which can result in financial losses for the company. The correct approach is to promptly rectify the issue, identify the root causes of the leakage problem, and take measures to prevent a recurrence during subsequent injection molding processes.

This article will introduce methods to prevent plastic leakage in the injection molding process, aiming to assist technicians who may encounter such issues in their work.

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Ways to Prevent Plastic Leakage in the Injection Molding Process

1. Injection molding technicians and mold setters should inspect the machines every 2 hours. During the inspection, use a flashlight to check the nozzle area for any signs of plastic leakage.

Inspection Checklist 1:

① Is the material hopper full?

② Are the temperatures within the normal range?

③ Is the air blower functioning correctly?

④ Are there any signs of plastic leakage from the nozzle?

Inspection Checklist 2:

① Are the temperatures at five points on the front and rear mold within the normal range?

② Are the water pipes clear, or are there any bends or blockages?


Inspection Checklist 3:

① Are the guide pillars and clean blocks of the mold properly lubricated?

② Are the ejector pins and lifters moving smoothly and resetting properly?

③ Is the parting line being cleaned on schedule?

Inspection Checklist 4:

① Are the melt temperatures in each section of the injection molding machine within the set range?

② Has there been any loosening or change in back pressure?

③ Have there been any changes in the injection parameters?


Inspection Checklist 5:

① Is the safety top rod properly set and not loose?

② Is the safety gate functioning properly and falling smoothly when released?

③ Is the mold template secure?

Inspection Checklist 6:

① Has the fallen material been promptly cleaned up from the machine?

② Are the nozzles and tools on the machine collected in a timely manner?

③ Is the 5S status of the workbench and machine station satisfactory?


Inspection Checklist 7:

① Are machine documents such as work instructions, production orders, and checklists complete?

② Has the first piece been inspected and approved?


Inspection Checklist 8:

① Are employees following correct operational procedures?

② Is the product meeting quality standards?

③Is the work attitude of the employees normal?


① Technicians should inspect the machine every 2 hours. Check the box if everything is normal. If there are any exceptions, make improvements immediately and record them. Submit the report to the supervisor before the end of each workday.

② Supervisors should perform inspections every 6 hours.

③ After daily confirmation, the supervisor should hand over the documentation to the clerk for archiving.


This inspection procedure should be part of a performance reward and penalty system, mandatory for technicians and mold setters to follow. In the industry, there are auxiliary devices available for leak detection, which, when installed where conditions permit, can make the work of technicians easier.

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2. Before every mold change, check if the mold nozzle matches the machine nozzle’s radius (R). Ensure there are no dents or fractures on the nozzle. If any issues are found, they should be fixed using a lathe before setting up the mold. Many technicians in small factories tend to use grinders to address such problems, which is not a reasonable practice.


3. After completing each production order, perform final part inspection and confirm the integrity of the locating ring. Ensure it matches the machine properly. Injection molding originally did not involve nozzle actions, but due to many non-compliant operations, there is an added focus on nozzle actions.


4. Regularly check if the forward pressure on the injection table is sufficient and inspect the oil seals of the moving cylinder for any leaks or damage. Periodically verify if the injection table nozzle and flange hole, as well as the center point of the ejector pin, align on the same axis. Unauthorized adjustments to the injection table balancing screws are not allowed.

5. Setting the nozzle temperature and hot runner temperature too high can cause leaks. Setting the forward pressure of the injection table too low, improper adjustment of forward movement time, and improper forward movement shot card positioning can all lead to leakage.


6. If the nozzle and flange are not tightened to the barrel or do not seal properly, it can result in molten plastic leaking through gaps.


7. During mold setup, confirm that the mold nozzle is aligned with the centerline of the machine. Ensure an adequate number of locating rings are securely in place (use 8 for machines below 400 tons, 12 for 450-650 tons, 16 for 800-1200 tons, and 16 for 1200-1600 tons) to prevent mold shifting and potential leakage during the production process.

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