It feels that the metal content is hard, and the hard noise is certainly much, and some auto repair factories also say so, right?

Wrong.

Many of these statements are those of the auto repair factory and are not scientific. The main semi-metal formula on the original American car contains a lot of metal, have you heard a lot of noise? Noise is not directly related to hardness, grinding disc and noise only indicate that the product formula is immature, and how much metal has nothing to do with it. In fact, metal materials in the formula mainly play the role of connecting fillers and heat conduction, at the same time, their own hardness and disc are not very different, will not cause large wear on the disc, the real disk and increase the braking ability is not you see these metals, but you can not see those hardness is harder than the brake disc grinding agent filler they are actually emery, And your common sandpaper, grinding wheel belongs to the same material.