When we use an automatic metallographic polishing machine for samples, sometimes this situation occurs: the sample is ground unevenly; Alternatively, the sample is thin on one side and thick on the other; Uneven or non parallel at both ends; The straight cylinder has become inclined.

In fact, this situation is very common. Many laboratories are equipped with a flattener and Plasticine to get a flat surface under a microscope. It is a good and effective solution to use the flattener with Plasticine, but it is necessary to analyze its causes.

Uneven grinding is ultimately caused by the unbalanced stress on the sample during the grinding and polishing process. If the stress is balanced, then it should be smoothed out as the grinding progresses, and many inlay blocks need to be leveled during the grinding and polishing process.

Although the size of the inlay block and the fixture cannot be completely consistent due to the existence of tolerances, this factor is not the main factor and has little impact. Otherwise, all automatic metallographic polishing machines cannot achieve leveling, as there are inevitably tolerances in the machinery.

So, what factors led to the problem?

1、 The size of the inlay block is incorrect: the 30mm inlay block is paired with a 1.25 inch (31.75mm) fixture. If there is a significant difference in diameter between the inlay block and the fixture, it is obvious that balance cannot be maintained.

2、 Pressure issue: The pressure should not be too high or too low, usually between 15N and 30N.

3、 Pressure head problem: The pressure head is crooked, resulting in uneven pressure.

4、 The roughness of the side wall of the fixture is inconsistent: the smooth side has low pressure, while the rough side has high pressure. For example, polishing fluid can easily contaminate fixtures, so it is recommended to clean them.

5、 Speed issue: If the speed is too high or too low, it can also cause uneven pressure. Generally, the speed is controlled between 150 to 300 revolutions per minute.

6、 Rotation direction issue: It is possible to rotate the fixture and turntable in the same direction, reduce the grinding rate, and maintain uniform and stable pressure.

7、 Do not use too rough metallographic sandpaper: Coarse sandpaper has a high grinding speed and can easily cause eccentric wear problems.

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