How does the flow mark phenomenon occur in injection molding

Plastic
1. Poor liquidity.
Improper use of molding lubricant.
Mold
The mold temperature is too low.
"The vertical runner, runner, or gate is too small.".
"If the vertical runner, runner, or gate is too small, the flow resistance increases. If the injection pressure is insufficient, the advance of the melt adhesive wave front will become slower and slower, and the plastic will become colder and colder. The injection pressure and pressure retention are not sufficient to tightly press the condensed skin onto the mold surface, leaving a shrinkage mark in the vertical flow direction of the melt adhesive, which is like a growth ring.".
3. Insufficient exhaust.

Injection Molding machine

1. Insufficient injection pressure and pressure holding
The injection pressure and pressure holding are not sufficient to tightly press the condensed skin onto the mold surface, leaving a shrinkage mark in the vertical flow direction of the melt, which is like a growth ring.
By increasing the injection pressure and holding pressure, the condensed layer can be tightly pressed onto the mold surface until the product is shaped, and no flow marks are generated.
2. Improper detention time
"The retention time of plastic in the material tube is too short, and the temperature of the melt adhesive is low. Even if the mold cavity is reluctantly filled, it is still unable to compact the plastic during pressure maintaining, leaving shrinkage marks in the vertical flow direction of the melt adhesive, which are like annual rings.".

3. Improper Cycle Time

When the cycle time is too short, the heating of the plastic in the material tube is not enough, and the temperature of the melt adhesive is low. Even if the mold cavity is reluctantly filled, it is still unable to compact the plastic during pressure maintaining, leaving a shrinkage mark in the vertical flow direction of the melt adhesive, which is like a growth ring. The cycle time must be extended until the plastic is fully melted and the melt temperature is high enough to cause shrinkage marks in the flow direction to occur without cause.
4. The temperature of the feed pipe/nozzle is too low.