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How to Avoid Flashing and Bubbles in your Plastic Production

Jul 13, 2018 8:00:00 PM

After analyzing the short shot the sink marks issues, we've decided to come back to some other issues you can encounter during your injection molding plastic production: Flashing and Bubbles.

If you are interested in Plastic Molding, you might want to have a look to our post about Adding Plastic Molding to your Project!

The Flashing

What is Flashing?

During the injection, sometimes a little bit of plastic can seep out of the die joint make a small rib. This is called flashing. Some examples are pictured below : 

PCB Flashing example 

How can Flashing be Avoided?

As you probably have guessed, flashing is not a good phenomenon in injection molding production, and it can cause die joint damage if the flashing cannot be immediately cleaned from the die joint and direct clamp.  The damage will be evident as it will create flashing in next product. For this reason, it's very important to look out for flashing marks in injection molding production.

There are many reasons that the flashing exist in injection molding production. Some examples include that the injection pressure is too high, the terminal injection speed is too fast, or that mould clamping force isn’t enough. Below is the some analysis and how to improve.

Reason analyze Improving method
1.The melt tempereture or mold tempereture is too high. Make adjustments to the temperature appropriately for the materials and mold

2.The injection pressure is too high or the injection

speed is too fast.

Adjust the speed of the injection nozzle so as to inject the plastic at the correct rate for the materials
3. Holding pressure is too high. Adjust the pressure of the clamps to loosen the grip
4.the joint face isn’t fit or the accuracy is poor. Repair and check the mold or make the joint face more precise

5. Mould clamping force isn’t enough(the plastic product has flashing around edge).

Increase the mould clamping force
6.the projected area of product is too large. Change the machine with larger mould clamping force
7.partial flashing due to gate imbalance Rebalance the gate
8. mold deformation. Use a harder material for the mould 

9.that pressure maintaining change time or location is

too late

Make it early from injection to pressure maintaining

10. The material of mould is bad or easy to wear and tear.  

 Choose the better mould material and suitable heat treatment

11. The viscosity of the plastic is too low(like PA or PP).

 Change the plastic material with high viscosity or doping

The situation above can be help you to solve the flashing.
 

Bubbles

How do bubbles happen in plastic?

When the mold cavity fills up, it is possible that the flow of the plastic is too quick and air cannot escape quickly enough from the mold. When this happens, bubbles can form in the materials. Some examples are pictured below:

 

 PCB bubbles examplePCB bubbles example

The bubbles in the first picture are ones from the vacuum vesicle and the other is small bubbles in the plastic. The reasons and improving method of the plastic with bubbles in the below table:

Reason analyze Improving method
1. Backpressure is low or the melt tempereture is too high.         Increase backpressure or make the melt tempereture low.      
2. Raw materials are not fully dried. Increase the intensity of the drying process 
3. The screw rotate speed or the injection speed is too fast. Decrease the speed of the screw or the injection pressure
4. The gas cannot expel quickly enough. Make the air vent larger to improve the exhaust effect
5. The size of gate is incorrect Decrease the size of gate or change the shape of gate

 

If all of this is a bit complicated to you, don't worry! We'll keep talking more about these topics. We're also able to help you through any of this problems as well. Contact us if you need any help with your plastics or electronic casing projects!