Firstly , during the polishing process, the operator may have applied inappropriate polishing method / technique or ununiform force, or the polisher rotates too fast during the process, causing the mold surface to heat up, which gives the mold an even surface after polishing, i.e., the appearance of flow lines.
2．Issues with Mold Steel
Another issue lies in the mold itself. That is, the mold steel is not well selected, e.g., may contain some impurities, causing wave lines or other related issues after polishing.
3．Issues with Polishing Materials
The last issue lies in the selection of polishing materials, e.g., the sand paper used for mold polishing is not flat enough. At the same time, during mold polishing process, over polishing also causes steel lines on the mold surface. So, there are many reasons for the occurrence of steel lines during mold polishing. However, you can avoid these issues by cooperating with a legitimate polishing service provider.
In conclusion, a high quality mold should be free of any lines or streaks, but is rather flat and glossy, which should be ensured from the multi-faceted aspects from mold steel selection to polishing operation!