Polishing field

Rare earth polishing powder usually consists of ceria, alumina, silicon oxide, iron oxide, zirconia, chromium oxide and other components. Different materials have different hardness and chemical properties in water, so the application occasions are different. The hardness of alumina and chromium oxide is 9, that of ceria and zirconia is 7, and that of iron oxide is lower.

Cerium based rare earth polishing powder is one of the most important rare earth products. Because of its advantages of strong cutting ability, short polishing time, high polishing precision and clean operating environment, it has better application effect than other polishing powders (such as Fe2O3 red powder). At present, the product has a rapid development in China, a wide application, a sharp increase in output, and a promising future.

1.1 the development process of rare earth polishing powder red powder (iron oxide) is an earlier used polishing material in history, but its polishing speed is slow, and the pollution of rust color cannot be eliminated. With the development of rare earth industry, in 1930s, rare earth oxide was first used as polishing powder to polish glass in Europe. In the Second World War, an employee of WF and Barnes J company in Rockford, Illinois, put forward a kind of rare earth oxide polishing powder called barnesite in 1943, which was soon successful in polishing precision optical instruments. Because of the advantages of rare earth polishing powder, such as high polishing efficiency, good quality and small pollution, it has aroused the research of the United States and other countries. In this way, the trend of rare earth polishing powder to replace the traditional polishing powder is developing rapidly.

Foreign countries began to produce rare earth polishing powder 60 years ago. In the 1990s, a variety of standardized and serialized products reached more than 30 specifications.

1.2 composition and classification of rare earth polishing powder

1.2.1 according to the CeO2 content in the rare earth polishing powder, the main component of the rare earth polishing powder is CeO2. According to the CeO2 content, the cerium polishing powder can be divided into two categories: one is the high-quality cerium polishing powder with high CeO2 content, generally CeO2 / Treo ≥ 80%, The other is low-cost polishing powder with low CeO2 content. Its cerium content is about 50%, or less than 50%. The rest is composed of La2O3, Nd2O3 and Pr6O11.

As for ceria polishing powder, the higher the grade of ceria is, the greater the polishing ability is, and the longer the service life is. Especially when the hard glass is circularly polished for a long time (quartz, optical lens, etc.), it is better to use high-grade ceria polishing powder. Low CE polishing powder generally contains about 50% CeO2, the rest 50% La2O3? SO3, Nd2O3? SO3, Pr6O11? SO3 and other alkaline anhydrous sulfates or basic fluorides such as LaOF, ndof, and preof. This kind of polishing powder is characterized by low cost and almost the same initial polishing ability as that of high CE polishing powder. Therefore, it is widely used in glass polishing of flat glass, picture tube glass, glasses, etc., but its service life is inevitably lower than that of high CE polishing powder.

1.2.2 according to the size and particle size distribution of rare earth polishing powder, the size and particle size distribution of

rare earth polishing powder have an important influence on the performance of polishing powder.

For the polishing powder with certain composition and processing technology, the larger the average particle size is, the greater the grinding speed and surface roughness of glass will be. In most cases, the grinding speed of polishing powder with particle size of about 4 μ m is higher. On the contrary, if the average particle size of polishing powder is small, the grinding amount will be reduced, the grinding speed will be reduced, and the flatness of glass surface will be improved. The standard polishing powder generally has a narrow particle size distribution, and there are few too fine and too coarse particles. The polishing powder without large particles can polish a high-quality surface, while the polishing powder with less fine particles can improve the grinding speed. In addition, the rare earth polishing powder can also be classified according to different kinds of additives. The production technology of rare earth polishing powder belongs to micro powder engineering technology, and rare earth polishing powder belongs to ultra-fine powder. Generally, there are three kinds of ultra-fine powder in the world: nano level (1nm ~ 100nm); sub micron level (100nm ~ 1 μ m); micron level (1 μ m ~ 100 μ m). According to the classification method, rare earth polishing powder can be divided into: nano Meter grade rare earth polishing powder, submicron grade rare earth polishing powder and micron grade rare earth polishing powder are three kinds. Generally, the rare earth polishing powder we use is micron grade, and its particle size distribution is between 1 μ m and 10 μ M. according to its physical and chemical properties, the rare earth polishing powder is generally used in the rear process of glass polishing for fine grinding, so its particle size distribution is generally not more than 10 μ M, The polishing powder (including rare earth polishing powder) with particle size larger than 10 μ m is mostly used for rough grinding in the early stage of glass processing. The submicron rare earth polishing powder less than 1 μ m has been paid more and more attention to because of its application in LCD and CD-ROM. Nanometer rare earth polishing powder has also come out. With the development of modern science and technology, its application prospect is unpredictable, but its market share is still very small, which belongs to the research and development stage.

1.3 raw materials for polishing powder: at present, there are several raw materials for the production of cerium rare earth polishing powder in China: (1) cerium oxide (CeO2), which is obtained from the separation of mixed rare earth salts (w (CeO2) = 99%); (2) mixed rare earth hydroxide (re (OH) 3), which is the intermediate raw material after chemical treatment of rare earth concentrate (w (REO) ≥ 50%) (w (REO) = 65%), W (CeO2) ≥ 48%); (3) rare earth chloride (RECl3) with less europium (mainly containing La, CE, PR and Nd, w (REO) ≥ 45%, w (CeO2) ≥ 50%); (4) high grade rare earth concentrate (w (REO) ≥ 60%, W (CeO2) ≥ 48%), there are Inner Mongolia Baotou mixed rare earth concentrate, Shandong Weishan and Sichuan Mianning bastnaesite concentrate.

In addition to the first raw material, the second, third, There are four kinds of light rare earth (w (REO) ≈ 98%), mainly CeO2, w (CeO2) is 48% ~ 50%. China has rich cerium resources, according to estimates, its industrial reserves are about 18 million tons (calculated by CeO2), which lays a solid foundation for the sustainable development of rare earth polishing powder in the future, and is also a unique advantage of China, and can promote the rapid development of rare earth industry in China.

1.4 main production process and equipment

1.4.1 production of rare earth polishing powder of cerium system

using cerium oxide separated from rare earth mixture as raw material, the powder products with large hardness, uniform particle size and fine face centered cubic crystal are processed by physical and chemical methods. The main process is: raw material → high temperature → calcination → water quenching → hydraulic classification → filtration → drying → good cerium rare earth polishing powder products.

Main equipment: calciner, water quenching tank, classifier, filter, drying box.

Main indicators: in the product, w (REO) = 99%, w (CeO2) = 99%; the recovery of rare earth is about 95%; the average particle size is 1 μ m ~ 6 μ m (or the particle size is 200 ~ 300 mesh), and the crystal shape is intact. This product is suitable for high speed polishing. This kind of cerium polishing powder replaced the iron oxide powder (red powder) of classical polishing earlier.

1.4.2 preparation of middle cerium rare earth polishing powder the mixed rare earth hydroxides (w (REO) = 65%, w (CeO2) ≥ 48%) were used as raw materials, the rare earth salt solution was pretreated by chemical method, and the intermediate (precipitant) was added to transform it into middle cerium rare earth polishing powder with w (CeO2) = 80% ~ 85%. The main process is as follows: raw material → oxidation → excellent solution → filtration → acid solution → precipitation → washing filtration → high temperature calcination → fine grinding and screening → intermediate cerium rare earth polishing powder products. Main equipment: oxidation tank, excellent solution tank, acid solution tank, sedimentation tank, filter, calciner, fine grinding screening machine and packaging machine.

Main indicators: in the product, w (REO) = 90%, w (CeO2) = 80% ~ 85%; rare earth recovery rate is about 95%; average particle size is 0.4 μ m ~ 1.3 μ M. the product is suitable for high-speed polishing and has better performance than good cerium rare earth polishing powder.

1.4.3 preparation of low cerium rare earth polishing powder the low-grade cerium rare earth polishing powder can be prepared with rare earth chloride (w (REO) ≥ 45%, w (CeO2) ≥ 48%) as raw material and the synthetic intermediate (precipitant) as double salt precipitation. The main process is as follows: raw material → dissolution → double salt precipitation → filtration and washing → high temperature calcination → grinding → fine grinding and screening → low-grade cerium rare earth polishing powder products.

Main equipment: dissolving tank, settling tank, filter, calciner, crusher, fine grinding and screening machine. Main indicators: in the product, w (REO) = 85% ~ 90%, w (CeO2) = 48% ~ 50%; rare earth recovery rate is about 95%; average particle size is 0.5 μ m ~ 1.5 μ m (or particle size is 320 ~ 400 mesh). This product is suitable for high speed polishing of optical glass. The mixed bastnaesite high-grade rare earth concentrate (w (REO) ≥ 60%, w (CeO2) ≥ 48%) is used as raw material, which can be directly processed by chemical and physical methods, such as grinding, calcination and screening, to produce low-grade cerium rare earth polishing powder.

The main technological process is as follows: raw material → dry fine grinding → batching → powder mixing → roasting → fine grinding and screening → low-grade cerium rare earth polishing powder products. Main equipment: ball mill, mixer, roaster, screening machine, etc. Main indicators: w (REO) ≥ 95%, w (CeO2) ≥ 50%; rare earth recovery ≥ 95%; product granularity is 1.5 μ m ~ 2.5 μ M. the product is suitable for high speed polishing of spectacle and TV picture tube. At present, there are more low-grade cerium rare earth polishing powders produced in China, accounting for more than 90% of the total output.

1.5 application of rare earth polishing powder

due to its excellent chemical and physical properties, cerium rare earth polishing powder has been widely used in the polishing of industrial products. For example, it has been used in a variety of < a href = "http://www.hrbsbh.com/goods/1944.html" target = "_self" ﹤ u href = "http://www.hrbsbh.com/goods/1944.html" > optical glass devices, < a href = "http://www.hrbsbh.com/goods/1945.html" / list-553. HTML "> oscilloscope, < A = "self" _The polishing of metal precision products, etc.

Polishing refers to the machining method of using mechanical, chemical or electrochemical action to reduce the surface roughness of the workpiece, so as to obtain a bright and flat surface. It is to use polishing tools and abrasive particles or other polishing media to modify the surface of the workpiece.

Polishing can not improve the dimensional or geometric accuracy of the workpiece, but for the purpose of obtaining a smooth surface or specular gloss, sometimes to eliminate the gloss (extinction). The polishing wheel is usually used as a polishing tool. Generally, the polishing wheel is made of multi-layer canvas, felt or leather, and its two sides are clamped with metal plates. The rim of the wheel is coated with polishing agent which is uniformly mixed by micro abrasive and grease.

During polishing, the high-speed rotating polishing wheel (the peripheral speed is more than 20 m / s) presses the workpiece, so that the abrasive produces rolling and micro cutting on the workpiece surface, so as to obtain a bright machining surface, the surface roughness can generally reach ra0.63-0.01 μ m; when the non greasy polishing agent is used, the bright surface can be dimmed to improve the appearance. In mass production of bearing steel balls, the method of drum polishing is often used.

A large number of steel balls, lime and abrasives are placed on the inclined