Very fine concentric grooves on the surface, like a record. A sign of a high cooling rate; solved by increasing temperature and speed.
The record groove effect is seen on the part surface as regular rings resembling the surface of a record. It comes from the melt front pausing and speeding up again as it advances instead of flowing smoothly. It usually appears in parts with a long flow path and a thin wall, in areas far from the gate.
A wrong diagnosis leads to turning the right parameter in the wrong direction. This defect can be confused with the ones below; the right-hand column gives the practical way to tell them apart.
| Confused with | How to tell them apart |
|---|---|
| Tiger Stripes | Tiger stripes appear as alternating glossy-matte bands and are irregularly spaced. The record groove effect forms regular, evenly spaced rings. |
| Flow Lines | Flow and color streaks are lines running in the flow direction. The record groove effect takes the form of rings perpendicular to the flow direction. |
As the melt advances it cools and its viscosity increases. Beyond a certain point the front cannot advance smoothly; it pauses and speeds up again. That is why the defect becomes pronounced toward the end of the flow path.
Raising the melt and mold temperatures and increasing the injection speed are applied together; the aim is for the front to advance without pausing. The permanent solution, however, is to enlarge the gate cross-section or to change the gate position so as to shorten the flow path.
Yes. Moving to a grade with higher flowability makes it easier for the front to advance without pausing. If the defect disappears with a different grade in the same process, the mold design is at its limit.