Guide reading: The Edge Treatment Technology of high precision transformer copper strip is an advanced technology in the field of copper processing. This paper introduces the characteristics of the edge treatment technology by rolling and scraping, and expounds the triune rolling technology and its characteristics, which is independently innovated by CHALCO, some suggestions on the development of high precision copper strip edge treatment technology in China are put forward. In recent years, more and more attention has been paid to the edge quality of Strip, and the shearing precision of Strip is higher and higher, but there are always burrs in the edge of strip after shearing. If there is burr on the edge of the Strip used in dry-type transformer, it may pierce the insulation layer of the transformer and cause breakdown. For high precision transformer copper strip, the edge should be rounded corner or rounded edge. At present, the edge treatment technology of transformer belts in our country is still at the research stage. Most transformer belts are not specially treated, the edge burr is large, and the edge quality depends entirely on the precision of the shearing equipment and the level of the cutting edge adjustment technology, as a result, 80% of China's transformer belt is dependent on imports. Therefore, it is of great significance to study the edge treatment technology of transformer copper strip. Moreover, this technology can also be applied to the edge treatment of aluminum transformer belt, cable belt, bimetal clad copper belt, etc. . This paper mainly introduces two methods of edge processing, namely rolling and scraping, and emphasizes on the self-developed Trinity Rolling Technology.

1.Technical requirements for copper strip of transformer

1.1 The grade, status and specification of transformer copper tape are Tu1, T2, status M, thickness 0110 ~ 215 mm, width 50 ~ 1050 mm. Transformer with high-voltage band, low-voltage Band of the division. For high-voltage winding, the width is generally & Lt; 300mm; for low-voltage winding, the width is ≥300mm. 

1.2 mechanical and electrical properties: B ≥195MPA, 10≥35% , HV = 46 ~ 65; TU1 conductivity ≥100% IACS, T2 conductivity ≥98% iacs.

 1.3 The appearance quality and special requirements of the Strip should be straight, the side bending should not be more than 2 MM/M, the side without Burr (or less than 0102 mm) ; the side shape has three kinds of cutting edge (no sharp corner, Burr) , round corner and round edge, round edges are best (figure 1) .

2.High precision processing technology of transformer with edge

The technology of strip edge treatment emerged in the 1990s, which is mainly applied to the edge treatment of stainless steel strip and the opening groove of stainless steel pipe before welding. With the application of copper strip in dry-type transmission transformer, the technology is gradually applied to the edge treatment of transformer strip and improved. Such as Germany's KME , MKM, Wallander and Taiwan first stretch copper and other enterprises to produce the transformer strip, the edge has been specially processed, thickness & Lt; 018 mm thin strip edge for the right angle without burr edge, the thick strip edge with thickness ≥018mm is smooth round corner edge or round edge, which can meet the quality requirement of high precision transformer copper strip.

The edge treatment of the Strip is mainly to remove the excess metal in the edge by mechanical method or other means, so that there is no sharp angle, Burr, and no corrosion, pollution of the Strip surface. The technical principle seems to be very simple, and the application in the field of edge treatment of steel strip has been more mature, but for copper strip there are some difficulties. Compared with steel strip, copper strip is softer, thinner (generally 015 ~ 210mm) and wider (generally 500 ~ 1020mm, stainless steel strip is 50 ~ 500mm) , which brings difficulty to control and precision of the whole processing line. In addition, it is required that the shape of the treated copper strip is good, and the defects such as non-edge arching, wave and tearing can not be treated intermittently and leakage, because one over-standard burr and several over-standard burrs have basically the same effect on the transformer. There are many methods to deal with the edge of metal strip, such as rolling, scraping, milling, arc (laser) and so on. This paper focuses on the application of more rolling method and scraping method. Arc method is mainly used in the detection and removal of edge burrs.

2.1 rolling method is an earlier 

method to treat the edge of transformer strip by crushing burrs or pressing them into the Strip Matrix to cause slight plastic deformation at the edge. The traditional rolling device consists of a pair of flat rollers or steel rollers with slight taper, which are usually installed at the back of the disc shears or at the front of the winding device of the transformer. The roller is a follow-up roller (driven by the Strip) , the pressure can be adjusted by hydraulic cylinder according to the thickness and state of the Strip. The utility model has the advantages of simple structure, low investment, easy installation, long service life of the tool, low maintenance cost, and low requirements for the Strip shape, at the same time, it can also be used in air-cushion furnace, cleaning machine, acid-alkali washing machine, etc. . Its disadvantages are: can not completely eliminate the edge Burr, sharp angle, can not achieve the ideal round corner, round edge, rolling the edge will appear slightly hardened; control accuracy is low, easy to cause the edge broken wave, and because rolling will produce a certain plastic deformation, this may result in a variation in width, resulting in over-tolerance; as the burr is pressed or pressed into the strip substrate, the vibration and hot burr will re-tilt during the transformer operation, piercing the insulation layer and causing partial discharge. Therefore, basically, the traditional rolling method can not produce high-precision transformer belt. Fig. 2 is a non-roller rolling method adopted by a foreign company. The upper and lower rolling cutter head rotates with the movement of the Strip, and the pressure of the upper and lower cutter head on the edge of the Strip is adjustable. The treatment effect of this method is basically the same as that of the traditional cone roller rolling method.

2.2 scraping method is to use a group or more components of the edge of the formation of the tool belt mechanical cutting, cutting off excess metal, edge without Burr, and achieve the need for the edge shape (round corner, round edge) . At present, this method is widely used in the treatment of transformer strips over 018mm abroad. The speed of the treatment line can reach 80 ~ 150m/min or even higher. Scraping method is usually realized by a separate production line, called trimming unit. Its main equipment consists of: uncoiler, clamping device, welding machine, leveling machine, scraping processor, chip collection device, hydraulic shear, tension system, coiler; AUXILIARY EQUIPMENT: Automatic Control System, tool cooling and lubricating system, hydraulic system, etc. . Its main equipment is described below. 

2.2.1 in order to produce continuously, reduce geometry loss and improve processing efficiency, general trimming machine is equipped with Argon arc welding machine. 

2.2.2 leveller for scraping method, strip shape is very important, otherwise it may cause processing discontinuity or edge tear and other defects. Therefore, half of the trimming line has a 7-roll or 9-roll strip leveler.

 2.2.3 scraping processors most of the scraping processors use multiple sets of tools, through a number of small scraping to achieve edge dressing. On the one hand, it can prevent the edge from being torn and damaged by large feed, and on the other hand, it can prevent the edge from being oxidized and discolored by excessive mechanical heat. Generally 2 groups, 3 groups, 5 groups, 7 groups, up to 9 groups of tools. During the processing, the feed amount of the front tool is relatively large, and the amount of the back tool is gradually reduced. After scraping, it is necessary to polish the edge. This is because the second burr is very easy to appear in the process of scraping. Each group of cutting tool feed control precision requirements are very high (01001mm) , so the equipment adjustment mechanism and control system requirements are very high. 

2.2.4 in order to prevent sticking and cutting edge from breaking, and to improve the service life of the cutting tools, the scraping tools are mostly made of cemented carbide, and the cutting edges are treated with special coating to increase the wear resistance of the cutting edge. For Easy installation, the cutter head is mounted on a special cutter holder. Because the trimming speed of the edge is 80 ~ 150m/min and the tool consumption is large, the quick tool change mechanism is necessary. At present, most of the blades used abroad are square, and each side has a number of cutting edges. On the one hand, the efficiency of cutting tools can be improved. On the other hand, considering the quick change of cutting tools, a special device can rotate the direction of the blades, the new blade can be put into use quickly and the whole process takes only a few seconds. Fig. 3 shows a kind of blade designed by a foreign manufacturer.

2.2.5 Blade Cooling and lubrication device if the blade in the work process heating, will affect the effectiveness of the tool, so also the blade cooling. Blade cooling generally adopts air cooling. There is also the use of lubricating oil cooling, but also play the role of lubrication, reduce tool wear. However, the lubricant can not pollute the plate surface, requiring volatile, no residue, it is best not to use oil cooling. 

2.2.6 the production line of scrap-collecting device should be equipped with special copper scrap-collecting device. In general, vacuum suction is used to prevent copper scrap from affecting the surface quality of the Strip. 

2.2.7 scraping control mode there are two control modes for scraping depth. In the first model, the cutting depth is pre-set by the tool pressure load, that is, the scraping depth remains constant even if the width changes or the plate forms an arch, the width and size are precise. Fig. 4 is a sketch map of a scraping edge trimming unit; Fig. 5 is a field photo of a scraping edge trimming unit.

Scraping method is the most advanced edge treatment method of Metal Strip at present, which can not only remove all burrs, but also modify the shape of edge according to the user's requirements and meet the requirements of high precision transformer strip. At present, this method is widely used in the edge treatment of transformer strip abroad, but the equipment is complex, the mechanism is precise, the control precision is high, the investment is high (230 ~ 260 million euros) , the blade is expensive, the wear is quick, the use cost is high. In addition, the Strip with shape of 10 ~ 20I is suitable for processing. At present, most domestic copper strip rolling mills are not equipped with flatness meter, and the flatness can not reach such a high level.

3.Three-in-one rolling method

Three-in-one rolling method is a new edge treatment technology developed on the basis of traditional rolling method. By rolling the edge of the Strip, a slight plastic deformation occurs on the edge to form a chamfered edge, and then the chamfered edge is extruded to eliminate the chamfered corner, and the width of the Strip is controlled to complete the deburring and trimming of the edge, to achieve a good edge shape.

 3.1 the feature of the device is that the three-in-one rolling method is greatly improved compared with the traditional rolling method. By changing from one-in-one treatment to three-in-one treatment, that is, from simple treatment to refined treatment, not only the burr on the edge can be eliminated, but also the fillet can be basically realized, it can meet the quality requirement of high precision transformer belt. In particular, the edge extrusion station is added, so that the overturning burr is not easy to tilt, to achieve a smooth transition of the edge, while solving the problem of a small amount of spreading in the rolling process, the width of the Strip is accurate. The equipment is simple, reasonable structure, simple operation and easy maintenance, the processing speed is fast, it can reach 100 ~ 120 M/min, the shape requirement is not high, it is very suitable for copper strip production enterprises in our country, the volume is small, the utility model can be directly installed in the coiling tension zone of the production line such as slitting, air cushion furnace, cleaning, etc. (having the stable tension necessary for the edge treatment) . Compared with scraping method, the secondary coiling and coiling are reduced, and the production efficiency and the finished product rate are improved. 

3.2 The treatment effect table 1 and Table 2 are respectively the examination results of the shape and Burr of the strip edge after the treatment by the Trinity Rolling Device developed by ourselves and the German scraping equipment. It can be seen that the triune rolling method burr can reach below 01006mm, the edge is rounded edge, while the scraping method can reach below 010001mm, the edge shape is right-angled edge, rounded edge, and even can reach round edge.

4.Development of strip edge treatment technology in China

At present, the domestic dry-type transformer belt manufacturers have more than 100. With the increase of national investment in power construction, dry-type transformer is faced with great development opportunity, which drives the fast growth of consumption of transformer strip. According to the statistics of relevant departments, the demand in 2004 was about 3.12 million tons, and the annual growth rate was 20% . The burr and shape of the edge is the key to restrict the domestic copper strip production enterprises to seize the market, which should be paid enough attention to. Edge deburring and shape processing technology is a cutting-edge technology, which is held every year in the world. Due to the tight blockade of the technology abroad, most of the domestic transformer belts are still on the simple rolling edge treatment at present, although some enterprises have made some explorations on the way and technology of the edge treatment of the Strip, but it didn't work.

As the largest manufacturer of transformer belts in China, Chalco has developed a triune edge treatment technology through long-term research, which has treated more than 20,000 tons of transformer belts. The edge of the treated strip is chamfered, smooth and without Burr, and the effect is good, and it is praised by users. This technology is in the international advanced, domestic leading level, filled the domestic blank, and has applied for a patent. At present, Chalco is improving its automation, the improved device control accuracy is higher, the operation is more simple and intuitive. With the development of transformer belt from dry-type transformer to oil-immersed transformer, transformer brings a wider development space. Edge processing technology and equipment will become an important magic weapon for transformer belt manufacturers to seize this market.

Source: Tongxinbao

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