The commonly used and widely used metallographic consumables in metallographic laboratories are probably metallographic sandpaper. Due to the large amount used, cost saving is also a major consideration for metallographic sample preparation. Even domestically produced metallographic sandpaper, which costs a few yuan per sheet, will directly reflect the cost. Moreover, imported metallographic sandpaper costs around ten to twenty yuan per sheet, or even more. Every piece of metallographic sandpaper saved is money, which is necessary for users to control costs and save usage. Since that's the case, is it a piece of metallographic sandpaper that needs to be replaced until it's polished? This is making the most of everything, isn't it more economical? Based on my experience, it's not&quo; Sauce purple&# quo;!

    Grinding the surface of the sample with metallographic sandpaper is actually a micro grinding process, using sharp abrasive particles fixed on the paper base to quickly remove the deformation layer on the sample surface. At the same time, the grinding particles involved in the grinding will also be broken, and after the edges and corners are removed, the grinding particles will be in the bonding layer. The removal rate of grinding particles slows down, and the chances of rubbing contact between the sample surface and the paper base increase. Old grinding particles cause more damage to the sample surface, shaping, and rheological properties than sharp grinding particles. See the figure below. Therefore, the surface of the worn sandpaper feels smooth to the touch, and the grinding particles are basically smoothed out.

    So what is the difference between the surface of the sample ground with new and old metallographic sandpaper?


The surface of the sample ground with old sandpaper appears smoother and more reflective than that ground with new sandpaper. But if you look under a microscope, it's really different! As shown in the following figure:

    The surface grinding marks of the sample ground with new sandpaper are clearer, overlapping with each other, presenting an image with a three-dimensional morphology; On the surface ground with old sandpaper, the grinding marks no longer have a clear three-dimensional morphology and appear to be on a flat surface. In this case, the depth of the deformation layer of the sample increases exponentially, only because the grinding marks are flattened, the reflection of the sample is good when observed with the naked eye, indicating the illusion of a more successful sample preparation.


Considering the efficiency and quality of metallographic sample preparation, the overall cost will not be reduced due to excessive savings. It is crucial to grasp the degree of use of sandpaper. My experience is that if a grinding process requires continuous repeated grinding for more than three times to produce a qualified surface, then this metallographic sandpaper should be replaced. Otherwise, it is not saving but increasing the cost of sample preparation in another way. So, don't polish the metallographic sandpaper before replacing it. If you need to replace it, just replace it and don't waste it.