The most used consumable in metallographic sample preparation is metallographic sandpaper. The correct use and proper replacement of metallographic sandpaper are closely related to the quality, efficiency and cost control of sample preparation.
The working principle of metallographic sandpaper grinding the sample surface is to use the sharp abrasive medium particles fixed on the paper base to quickly grind the sample surface, thereby removing the deformed layer on the surface of the metallographic sample. At the same time, the abrasive medium particles involved in the grinding are broken due to the force, the sharp edges are ground away, and the remaining part is in the bonding layer, making its surface blunt.
The picture below is a comparison between new sandpaper and worn sandpaper. It is obvious that the surface of the worn metallographic sandpaper is basically smoothed.
However, the metallographic sandpaper that has been used for a long time will have weaker grinding performance and lower removal rate. The blunt grinding medium particles will cause new damage to the sample surface.
As shown in the figure below, can you guess which grinding effect is better?
Why?
When the sample is ground with worn sandpaper, the surface looks smoother and more reflective than the surface ground with new sandpaper (as shown on the left). In fact, the deformation layer on the surface of this sample is deeper.
The scratches of the new sandpaper on the right overlap more clearly, one scratch is superimposed on another, and an image with a three-dimensional morphology is presented.
How to judge the time to replace metallographic sandpaper?
When the sample is ground with metallographic sandpaper, if a grade of sandpaper needs to be repeated more than three times to grind out a qualified surface, the old metallographic sandpaper used should be replaced.
If it is replaced too early, it will cause waste of sandpaper and directly increase the sample preparation cost; if it is replaced too late, it will affect the grinding effect of the sample, which will not only prolong the sample preparation time, but also increase the difficulty of subsequent polishing.
