The above table is a reference table for surface roughness and smoothness in fields such as mechanical processing. The description of Surface states in the lower column of the above table is the state seen by the naked eye. In the field of metallography, it can also serve as a reference. We only need to connect visual and experimental observations in the field of metallography with the above table. Note that the unit used in the above table is micrometers, which is the same as the unit of consumable particle size used in metallographic preparation.

Firstly, the metallographic preparation is divided into two stages. The first stage involves polishing, smoothing, and polishing before proceeding to the next stage. The second stage is after polishing. Although the polishing stage can also be divided into three small stages: coarse polishing, medium polishing, and fine polishing (final polishing), these three small stages have relatively small grinding amount and fine machining surface. Putting them together as the second stage is appropriate. Let's talk about the similarities and differences between these two stages, as well as their corresponding relationships with the table above.

The polishing process and machining process are quite similar, both of which use mechanical means to physically remove the surface layer of the workpiece (sample), while cooling with substances such as water and oil. Due to the similar processing processes, this stage is relatively easy to compare. Basically, the particle size of metallographic sandpaper should correspond to the size of the machining marks in the table above.

Surface of P180 metallographic sandpaper, magnified by 50X

Generally speaking, metallographic sandpaper is used sequentially from coarse to fine. The thickness of the first layer of sandpaper is determined by the surface of the sample, and the span of each layer of sandpaper should not be too large, controlled within one-third of the particle size. The latter layer of sandpaper is generally recommended to be above P800, including P800. It can be said that the finer the better. However, metallographic sandpaper is generally only available for P4000, and the practical significance of finer sandpaper in the future is not significant because the particle size of P4000 sandpaper is only 5µ m. This is approaching the middle polishing in the next stage of polishing.

During the polishing stage, we usually differentiate by the particle size of the polishing agent. The commonly used particle size range for polishing agents is 9µ M-0.02µ Between m. Compared to machining, the polishing process is very gentle and pursues surface quality, with little need for dimensional accuracy. At this stage, the pursuit is to remove scratches and obtain high-quality surfaces. Generally speaking, the polished surface appears in a mirror like state. This is the same as surfaces with high machining requirements.

In summary, we can compare the grinding state (fine sandpaper, fine grinding) with the&quo; in the table above; Slightly visible knife marks” Correspondingly. Generally speaking, in the final state of polishing, the surface of the sample has a mirror like appearance when observed with the naked eye, but is covered with scratches.

For the surface of the final polished (precision polished) sample, no scratches can be observed with the naked eye, and it can basically match the&quo; in the table above; Shiny Gloss&# quo; Correspondingly. And a 1-micron polished surface can still see a few scratches, which can be compared to" Distinguishable machining trace direction” Correspondingly. By analogy, the appearance of a 3-micron polished surface to the naked eye is roughly similar to" Visible machining marks; This statement.

I hope that with the advancement of industry technology in the future, qualitative and quantitative analysis of these things will definitely bring people a sense of clarity.

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