What is Air Bubbles or Blisters defects
Air Bubbles are molding defects that appear when gas is trapped in the melt material and injected into the cavity leaving a cosmetic defects in the plastic molding part, we also call this as gas traps issues or blisters defects.
There some some reason to cause this Bubbles or Blisters defects.
Air Bubbles issues caused by Injection molding machine setting
Back pressure too low. As the plastics material is melted and augured through the heating cylinder, air becomes trapped within the melt. One of the uses of back pressure is to force this air out before it gets injected into the mold cavity image. Back pressure should be set at 50 psi (345 kPa) and increased in increments of 10 psi (69 kPa) until the ideal setting is reached.
High melt temperature will cause this air bubbles issues as well. When plastic is overheated often a gas will be given off from degradation plastic material. Much like moisture in the plastics material can form bubbles that can be carried in the melt stream and injected into the mold cavity. If the melt temperature is above the recommended molding temperature will cause this bubbles. When troubleshooting such bubbles defects it will be beneficial to reduce the melt temperature.
Air Bubbles defects caused by plastic mold
As a plastics material is injected into a mold cavity, it starts to cool immediately and a skin begins to form on the surface of the plastic part. If this skin forms too quickly, any air that is mixed into the plastics material and are is not allowed to escape through the surface as intended, causing a blister defects. A mold temperature is too cool that will cause the skin to form too soon. Increasing the mold temperature will help allow trapped air to escape by delaying the hardening of that skin.
Venting issue will cause lots of molding defects but the bubbles issues as well. The most common mold related problem that can lead to bubble issues is a lack of venting. If gas is trapped in the melt stream and not allowed to vent properly the gas can very easily lead to a blister defects, make proper venting on the mold cavity, or the end of fill area, and the deep ribs that could avoid lots of molding issues.
Air Bubbles or blisters defects caused by raw material.
This practice increases the amount of air that gets trapped in the melt because the regrind material, uneven particles of regrind material create pockets of air between them and the smaller, when you use the regrind material make sure that there is no other type of raw material mixed together, two material mix together will have different melt temperature so that blisters defects will present. Another solution, make sure the material is drying properly, some of material that needs to dry as long as 4 hours such as PC or PA66 material.