A phenomenon in which the sanding pattern is clearly visible after the topcoat has been applied and dried and affects the appearance of the coating (gloss, smoothness, fullness and vividness). The striated scars left by the use of a file on the coated surface are called file lines.

Reason:

(1) The selected sandpaper is too coarse or of poor quality.

(2) Sand the coating before it dries (or cools down).

(3) The surface of the refinished object is in poor condition, with extremely deep file lines or grinding lines.

(4) Insufficient spray thickness.

Prevention:

(1) Grinding sandpaper should be selected according to the process requirements.

(2) The coating is dry and cooled to room temperature before grinding.

(3) For occasions requiring high decorativeness, wet sanding should be used instead of dry sanding.

(4) Improve the surface quality of the coated object before painting or fill it with putty.

(5) Increase the spray thickness.