Plastic injection molding is a widely used manufacturing process, but it comes with its own set of challenges. One common and never-ending issue faced by manufacturers is the forming of bubbles in molded products.
These bubbles can lead to defects and compromise the quality of the final output and nobody wants that. So, In this guide, we’ll see what causes the forming of bubbles in plastic injection molding and how you should prevent the same.
But before do, it is important to understand what causes this problem in the first place. So, let’s see to it quickly now.
And hey, If you’re looking for Quality Used Plastic Injection Molding Machines, you can always reach out to us.
Causes of Bubbles in Molded Parts
Simply put, the bubbles are formed mainly based on two reasons:
- Trapped Gas and
- Vacuum Void
Trapped gas encompasses various elements, including air, moisture vapor, resin volatiles, or decomposition gasses from polymers or additives. On the other hand, vacuum voids emerge during the cooling phase, particularly in thicker sections of the part.
Now we found out what’s causing the bubble, let’s address the problem at hand.
How to Determine If the Bubble is Caused by Trapped Gas or Vacuum Void?
How to Rule Out the Possibility of Trapped Gas?
Before we dive into the details, do note that molded parts should be tested within four hours of production, for the most accurate result. There is not a given solution for this but surely the steps would definitely help you out.
There is no one-stop solution to determine the type of bubble you have gotten. Gas bubbles can arise from various sources, such as flow-front issues, mold or machine problems, poor venting, excessive decompression, or resin degradation due to overheating or prolonged residence times.
A systematic approach to this issue is to find out what type of bubble we have gotten. To rule out the possibility of gas bubbles, We can start by lowering the pressure of the hold of your machine to see if the problem gets resolved in your next end product.
If the problem still persists, we have to check the filling parts of your machine for any potential problems. For this, we have to do a short-shot study. Don’t get taken aback by hearing the word “study”. It is nothing but a process of reducing the full load of your filling gradually by 10% from the desired filling for a precise end product. To identify when and where bubbles appear, it’s recommended to examine the flow pattern of each part.
These steps are enough to identify and rectify your problem, If you still see those bugging bubbles, we are dealing with the vacuum voids. How to resolve this? let’s talk further.
Addressing the Vacuum Voids
When there’s not enough plastic in the mold, it can cause gaps or depressions in the finished product (voids or sinks). To fix this, adding more plastic material into the mold is necessary. This ensures that every part of the mold is properly filled. So, making sure the amount of plastic is consistent and not over-compressed helps to get the right shape without deformities.
If this doesn’t work, increasing the pressure or the time the mold stays closed (hold time) can help pack the plastic into all the corners of the mold. However, if the entry point for the mold closes too quickly, the plastic might not reach all areas of the mold, leading to voids. So, Slowing down how fast the plastic fills the mold, using gas or extra pressure, and adjusting the back pressure helps control the flow of plastic. Following these will ensure the plastic is filled throughout the mold.
Not working? Don’t worry. Adjustments in injection mold temperature can rectify this issue. Lowering barrel temperatures and increasing injection and holding pressures create good conditions for mold filling. This will reduce the likelihood of vacuum bubbles in your molten plastic.
By following these steps, you can improve the quality of your plastic parts by minimizing gaps, depressions, or any other possible defects in the molding process.
Conclusion
We hope you have now got a clear picture of addressing the bubble issues on the molten plastic. Make sure you ensure what type of bubble you got and take the necessary steps we have mentioned and you are good to go!
You can reach out to us if you have any questions and as we said before, we Sell Quality Used Machines if you’re ever up for that!
