The ultimate goal of metallographic sample preparation is to prepare a flat mirror surface for observation after corrosion or direct observation. The importance of grinding and polishing is obvious. Polishing is the last step in the sample preparation stage, and it is also the most important and critical step.

Grinding and polishing should be graded for plane grinding. The disk surface provides abrasive grains, and the sample is loaded on the disk surface and grinded with the abrasive grains.

In the early days, sample preparation was manually loaded, and the pressure size and pressure angle had great individual differences. In addition, we always rotate the sample when holding the sample to ensure consistent surface grinding and polishing. It can be seen that manual grinding and polishing has a high experience threshold.

With the advancement of technology, automatic grinding and polishing machines can replace manual grinding and polishing of samples, and one or more samples can be clamped on the sample holder. By quantitatively setting the rotation speed and direction of the disc and the clamp, the grinding power parameters are clarified; by quantitatively setting the eccentricity of the polishing clamp and the disc, the isotropic grinding of the sample is ensured; by quantitatively setting the pressure value, the positive loading pressure on the sample surface is clarified; by quantitatively setting the suspension type and the dripping speed, the abrasive addition parameters are clarified; by setting the disc type and the polishing liquid type in different steps, the consumables configuration is clarified.

In this way, it seems that all the open variables of grinding and polishing are well controlled. In fact, it is not. Due to the friction in the circumferential direction, the sample has the power to rotate. Whether the sample rotates during the grinding and polishing process is an important open point. The constraint relationship between the sample and the holder is divided into two categories. The sample is directly placed in the holder with a circular hole, which drives the sample to rotate. The sample can rotate by itself and loads pressure through the top pressure cylinder, which is the so-called single-point loading; the other is to lock the sample in the holder, drive the sample to rotate, and the sample does not rotate by itself. The sample is driven to load through the middle connecting handle, which is the so-called center loading. High-end grinding and polishing machines support two clamping methods.

Single-point loading and center loading have their own advantages and disadvantages.

The advantage of single-point loading is that the number of samples is free and flexible, as long as it is within the maximum number of holes, and the sample is easy to take and put, especially suitable for regular observation of the effect in the later stage of grinding and polishing. The disadvantage is that the sample rotates and moves in a small range in the holder. The rotation strictly controls the grinding trajectory of the sample, and the small range of movement is easy to cause rounded corners.

The advantage of center loading is that the sample is locked on the clamp, so the grinding trajectory of the sample can be accurately controlled, and the reproducibility of sample preparation can be improved. Especially for the rough grinding and fine grinding stages, the grinding rate is very large, and the grinding effect of the sample is controlled. In addition, due to the center loading, the grinding effect of samples of different materials is the same. Of course, the disadvantage is also the limitation of the number of samples. Because it is center loading, the number of samples must be centrally symmetrical to ensure the balance in the hand. For example, the number of clamps for a six-station clamp can be 2, 3, 4, or 6 samples. If it is insufficient, it must be supplemented with replacement samples. In addition, center loading does not support the observation of samples taken out in the middle, and it cannot be guaranteed that each sample is on the same grinding reference surface after reinstalling it.

In summary, single-point loading and center loading have their own advantages and disadvantages. The general optimization method is that for rough grinding, fine grinding, and even rough polishing stages, it is best to use center loading mode, and switch to single-point loading mode in the polishing stage, so that the polishing effect can be checked at any time. Therefore, it is best for the grinder and polisher to have the function of supporting both single-point loading and center loading. This increases the technical difficulty of equipment manufacturing. Currently, only a few companies can develop equivalent equipment, such as Denmark's Struers and Shanghai Truer Company.

There is no simple distinction between center loading and single-point loading, only suitability and inappropriateness. The choice should be made according to the specific sample preparation conditions. At the same time, it is also very important to learn from the methods of professionals. Obtaining relevant experience from professional metallographic solution suppliers can achieve twice the result with half the effort. Domestic professional companies such as Shanghai Truer have more than ten years of experience in commissioned sample preparation, accumulated a large amount of sample preparation information, and established a special database, which can quickly obtain the best sample preparation solution.

All microscopic analyses are the accumulation and crystallization of countless details, and the same is true for metallographic analysis. Even the most insignificant errors may create obstacles for subsequent observations. Industry practitioners must be in awe and pursue perfection.

Shanghai Truer Company has been deeply involved in the metallographic testing industry for decades and has long practiced the concept of exquisite metallography. It is a leading metallographic solution provider in China. Truer takes international giants as benchmarks, faces difficulties, concentrates on research, overcomes key equipment and consumables that restrict the development of the industry, and creates a complete metallographic industry chain integrating equipment, consumables and sample preparation training; the company is equipped with a cutting-edge metallographic laboratory and has a team of highly qualified experts. For more than ten years, it has provided metallographic analysis and sample preparation training services to thousands of customers, and provides customized metallographic laboratory solutions.

If you have any metallographic questions, you can get in touch with them to get the information you want.