Abstract: The development and existing problems of coated abrasive tool industry in our country are introduced. This paper describes how to correctly select coated abrasives in wood processing.
Key words: grinding; Coated abrasives; Abrasive belt
2 Application of coated abrasives in wood processing
The application of coated abrasives in wood processing accounts for about 30% to 40% of its total application fields. Coated abrasives are widely used in wood processing for large surface sanding of wood-based panels. According to the different requirements of the process, the type of broadband sander used is single-sided, and the grinding head can be 1 to 3; There are two-sided types (see Figure 2), and the grinding head is usually 2 to 6, or even up to 8. The front and rear grinding head adopts different grit sand belts, so that the wood-based board can complete the requirements of rough grinding, fine grinding and polishing once it passes through.
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In the sanding of wood-based board, plywood is relatively easy to sanding, it is generally recommended to use paper based sanding tape, although the strength of paper tape is not as good as cloth tape, but the amount of polishing is not large plywood sanding is enough; And the paper tape flatness is good, the error of the joint thickness is small, the sanding surface is fine, the surface quality is good; In addition, there are many sizes to choose from. At present, the quality of domestic wide paper base sanding belt using imported 250 ~ 350 g/m2 paper as baseband has passed the standard, which can fully meet the sanding needs of plywood users. And because of the price, some small and medium-sized plywood factories often choose cheap GXK51 cloth sand belt. The survey shows that although the procurement cost has been reduced, the total cost accounting is often uneconomical due to the low service life and poor surface quality after sanding. As for the production of packaging with low-grade plywood manufacturers is a different matter.
For the sanding of MDF and particleboard, because its sanding load is relatively large, the cloth sanding belt should be generally used. At present, several large factories producing sand belts in China have achieved results in the treatment process of blended cloth and polyester cloth based on wood processing, and the polyester fiber based blended cloth and thick polyester fiber sand belt, that is, the Y-shaped cloth product, the representative specification is 1 350 mm×2 800 mm, has been widely welcomed, and has a tendency to polyester. Nowadays, foreign products of this kind of substrate have basically been squeezed out of our market, and only a few brands such as NORTON's R489 still have some markets. In the choice of abrasive, the sanding of plywood and general wood, because its wood hardness is not high, it is better to grind. It is recommended to use the most common brown corundum, which has better wear resistance. For particleboard, MDF, etc., due to the addition of resin that is difficult to grind in the material, it is recommended to use silicon carbide abrasive with good sharpness, good self-sharpness and suitable for grinding non-metallic materials. Particle board coarse sand can be used brown corundum or silicon carbide, fine sand is suitable for silicon carbide; The coarse and fine sand of MDF should be made of silicon carbide. Hard wood sanding should also use silicon carbide.
At present, there are cases in the market that Y-type cloth sand belt with particle size of 40# and 60# zirconium corundum abrasive is used for fixed thickness coarse sanding. Zirconium corundum crystal is mainly composed of α-Al2O3 and Al2O3-ZrO2 eutectic, with high toughness and wear resistance, is a new type of abrasive developed rapidly in the past 20 years, mainly suitable for high-speed heavy load grinding and difficult to grind metal materials processing. The reason why it is recommended in wood processing is because of the good wear resistance of the zirconium corundum sand belt, and the water resistance of the sand belt, allowing the "washing" method to eliminate the blockage caused by the accumulation of dust on the surface of the sand belt, so that the sand belt can be used repeatedly several times. The author believes that the abrasion resistance of zirconium corundum comes from its "self-sharpening" under certain pressure, but the grinding pressure required for "self-sharpening" may not be achieved during the sanding process of MDF. At the same time, factors such as how to wash, whether there will be deformation of the sand belt in the process of washing, the labor cost of "washing" and the expensive price of the zirconium corundum sand belt need to be considered. Therefore, it is estimated that the application of zirconium corundum sand belt in MDF sanding will not become mainstream.
The sanding requirements of the painted surface of wood products are extremely fine, which not only directly relates to the quality of the final surface paint, but also affects the amount of expensive paint. Some users only consider the cheap price of sand belt, and choose cheap GXK 51 cloth base products, in fact, this approach is wrong. Due to the improper selection of sand belts, the surface of the polished wood products feels very rough, requiring more paint, sometimes up to 3 times as much, and the result is more than the money spent on buying good sand belts. In addition, the back of this cheap cloth base sand belt often has the residual convex defects of the original cloth textile, which will produce scratches on the surface of the workpiece after fine sand, and these defects will be exposed after painting, which requires more repair and processing costs, which is not worth the loss. The selection of flat base band, appropriate particle size, abrasive and other high performance, sharp grinding belt, not only can reduce the number of sanding processes, and the surface of the workpiece after sanding feels smooth and comfortable like water, the amount of paint consumption is significantly reduced. Therefore, it is recommended to use paper based sand belt for wood products. The paper based abrasive belt manufacturing technology of several large factories in our country has become mature, and can fully meet the ideal paint surface polishing requirements.
In recent years, China has developed relatively fast supercoating products, especially 150# ~ 800# paper based sand belt supercoating products, which overcome the problem that the sand belt is easy to block when the paint surface sanding, and have been widely used. The supercoating products are called No-Fil abrasive tools in foreign countries, and the supercoating is the re-coating after the gluing is dried, rather than the secondary gluing. The main principle of the supercoating is the filler with special functions, which will have a certain chemical reaction during the grinding process, which helps to solve the problems of surface blockage, electrostatic adsorption, surface heat dissipation, workpiece burn, etc., so as to improve the grinding conditions and improve the grinding efficiency. It occupies a prominent position in the production technology of modern coated abrasives. Supercoating has two kinds of oily and water-based, water-based or water-based low price, sand sharp, environmental protection; And oily, oily can be applied under relatively large pressure, good durability, suitable for sanding relatively hard paint, in the late use of more advantages.
Furniture, Musical Instruments, wood crafts and other special-shaped surface sanding, coated abrasives are different from other abrasives in the application of an aspect of outstanding, it highlights the flexibility and flexibility of coated abrasives. There are many kinds of coated grinding tools and coated grinding tools used. The sanding wheel and sanding disc shown in Figure 3 are a kind of disk or wheel-shaped coated abrasive tool made of many rectangular emery cloth pieces firmly bonded and fixed on the matrix with a central hole or a central shaft. The shape of the sanding special contact wheel or grinding block shown in Figure 4 is machined according to the surface shape of the part, enabling the sanding belt to sand the workpiece surface in a consistent manner, typically demonstrating the softness of the coated abrasive tool. Figure 5 shows a soft short sand belt placed on an air drum that can be inflated to make it tensioned, and relies on the elasticity and rotation of the air drum to polish the surface of the wood product.
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Non-woven fabric based abrasives (that is, industrial cleaning cloth) in the 2010 Cologne International Hardware Show, almost all coated abrasives booth are displayed, is worthy of attention to the new products. This product (see Figure 6) is a kind of abrasive tool with an open network structure made of non-woven fabric composed of special fibers as the base material and then bonded abrasive, which can be made into sand pages, sand belts, sand rollers, sand wheels and other forms. Due to its unique elastic three-dimensional network structure, it can quickly and effectively improve the surface quality of the machined workpiece without changing the appearance shape and size of the machined workpiece. It can effectively dissipate heat and avoid deformation and discoloration caused by overheating of the workpiece. It also has excellent water, oil and clogging resistance.
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The application of non-woven fabric based abrasive tools is convenient, fast, efficient, the sand grain effect is clear, greatly simplifying the complexity of the surface treatment, and it is not only used in the polishing of the "corner" of the furniture in wood processing; It is also used for final polishing of wood-based panel surfaces (see Figure 7). According to foreign information, the working width from 1 300 ~ 3 200 mm, the particle size of 220# ~ 240# non-woven polishing roller, polishing the wood-based board life can be up to 2 million to 4 million extension meters, the use cost is only equivalent to the same particle size of the sand belt 10% ~ 15%, but also for the next process to save 30% of the amount of paint. Compared with sandpaper, it has a stronger cleaning effect and a weaker grinding effect. At present, non-woven fabric based products are mainly from South Korea and Taiwan, although the domestic progress in recent years is not small, but there is still a gap in abrasive distribution uniformity, product flexibility, elasticity and so on.
