How to automatically prepare metallographic sample

2022-09-19
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How to automatically prepare metallographic samples

due to the different research materials, there are various methods for preparing metallographic samples, and its procedures can usually be divided into several main processes, such as sampling, inlaying, grinding, polishing and etching

as we all know, it is the most difficult to make metallographic samples with the hardest or softest materials, especially pure copper, which is soft and has good plasticity, and twins are easy to appear if the force is too large. In the era of manual sample making, only old comrades can make good metallographic samples. Nowadays, the emergence of automatic sample preparation equipment makes sample preparation simple and fast, and everyone can make qualified metallographic samples without more skills. Taking pure copper as an example, this paper briefly introduces the process of automatic sample preparation after a buffer transition period of nearly one year. All electrical components can meet the relevant moisture-proof and safety protection level standards. The equipment used is the full-automatic sample preparation equipment of Laizhou Weiyi test equipment manufacturing Co., Ltd., the best metallurgical sample equipment manufacturer in China at present

1. Sampling

the selection of sampling position and inspection surface depends on the characteristics of the analyzed material or part, processing process and heat treatment process, and representative positions should be selected. The metallographic sample is a small part of the whole part. In order to make it convenient and facilitate observation under the microscope, the sample should not be too heavy or too large. Generally, take a cylinder with a diameter of 10 ~ 15mm or a cube with a length of 10 ~ 15mm on each side, and you can put it into the mold of the embedded prototype

the ldq-350a manual automatic metallographic sample cutting machine produced by Laizhou Weiyi Test Instrument Manufacturing Co., Ltd. uses a high-speed rotating thin disc grinding wheel to intercept metallographic samples (see Figure 1). The cutting machine can cut automatically or manually. The cutting speed can be adjusted automatically, especially the fixture design is particularly exquisite, and the sample with any irregular shape can be clamped. It is very suitable for the irregular characteristics of metallographic and electron microscope samples, and it is equipped with an environmental protection cooling device, which is used to take away the heat and lubrication generated during cutting. First of all, we should take the resource-saving development road, so as to avoid the overheating of the sample and the burning of the tissue. The pure copper sample material is soft, and it can be cut with ordinary grinding wheel

Figure 1 ldq-350a manual automatic metallographic sample cutting machine

2 Inlay

because the size, size and shape of the cut samples are irregular and inconsistent, especially the preparation of samples of some belts, wires, sheets, tubes and particles is very difficult, and they can not be used for automatic sample grinding (that is, it is difficult to manually). It is best to inlay the samples so that the shape and size of these samples are consistent. Inlay is divided into cold inlay and hot inlay

the zxq-5 automatic metallographic specimen inlay prototype (see Figure 2) produced by Laizhou Weiyi test equipment manufacturing Co., Ltd. has the function of cooling in and out of water, and is suitable for the thermal inlay of all materials (thermosetting and thermoplastic). After setting the heating temperature, holding time, force and other inlay parameters, put in the specimen and inlay, cover the gland, and press the work button to automatically complete the inlay, No operator is required to be on duty beside the machine. According to the samples with different requirements, you can choose to replace the molds of four specifications, or press two samples at the same time, and the preparation capacity has doubled

Fig. 2 zxq-5 automatic metallographic sample inlay prototype

(1) Polish

after inlaying the sample, first trim the sample into a flat sample, rough grinding only removes the cutting marks, but there are still deep rough grinding marks, which should be further polished by fine grinding; In addition to making the surface smooth and flat, it is more important to reduce the surface damage as much as possible in the polishing of metallographic samples; Each polishing process must remove the deformation layer caused by the previous process (at least the deformation layer produced by the previous process should be reduced to the depth of the deformation layer produced by this process), rather than just removing the grinding marks of the previous process. At the same time, the process itself should reduce the damage as much as possible, so as to facilitate the next process

the purpose of fine grinding is to eliminate the deep grinding marks left during rough grinding and lay a good foundation for the next polishing step; Fine grinding is carried out on sandpaper to show the length of leakage; The water abrasive paper is SiC abrasive, which is insoluble in water. Polishing can be carried out after polishing with 320 #, 500 #, 800 # three kinds of water abrasive paper; For softer metals such as pure copper, finer ones can be used. 1200 #, 2400 #

polishing after fine grinding with sandpaper

(2) polishing

after the sample is polished, it should be carefully washed with water to remove sand particles; The mechanism of polishing and polishing is basically the same, that is, each abrasive particle embedded in the polished fabric fiber can be regarded as a planer. According to its orientation, some can cut metal, while others can only scratch the surface; Because the abrasive particles can only act on the sample with elastic force, The chips it produces (the scratch and deformation layer are much smaller and shallower than that during polishing; in the process of polishing, continuously pour the suspension of polishing powder, and keep the polishing cloth with a certain humidity until the grinding marks are completely eliminated, and the sample reaches a bright surface like a mirror; because these particles are very fine, they can grind away the micro irregularities on the surface of the sample, so that the sample can be polished very bright, until there is no grinding mark; the sample is washed with water after polishing Wash, then blow dry, and do not wipe dry for etching. Laizhou Weiyi test equipment manufacturing Co., Ltd. provides many professional polishing cloths such as flannelette, canvas, velour, wool felt, and polishing consumables such as alumina polishing powder, chromium oxide polishing powder, and high-efficiency diamond polishing agent

the MP-1000 full-automatic grinding and polishing machine (see Figure 3) of Laizhou Weiyi Test Instrument Manufacturing Co., Ltd. directly puts the sandpaper on the grinding and polishing tray, and then uses the buckle to buckle it for direct grinding and polishing. During the grinding and polishing process, the replacement of sandpaper only needs to remove the buckle. This machine is equipped with an automatic grinding and throwing material feeding system, and can grind six samples at the same time, which is convenient and fast

Figure 3 full automatic grinding prototype

4 Etching

is to make the metal sample show its structure. The sample must be etched by some acidic alcohol solution or water solution. The etching time depends on the nature and structure of the alloy, and after the sample is etched. Wash with water immediately. Tilt the sample to let the water flow away as automatically as possible. And drop a few drops of alcohol on the surface. Let alcohol completely cover the surface. Then dry it and observe it under the microscope

the etchant of pure copper is FeCl3 aqueous solution. The organization is shown in Figure 4

Figure 4 microstructure of pure copper sample

5 Conclusion

there are many skills in the preparation of traditional metallographic samples. And more complex. It needs long-term practical experience to master it well. At the same time, it is also time-consuming and monotonous. It is often annoying. Using automatic sample preparation equipment can not only produce samples comparable to manual ones, but also be fast. In particular, 6 ~ 8 samples can be prepared at the same time. The difference between the samples made each time is small. Less unstable factors. Everyone can make samples

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