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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Rolling mill. History of invention and production
Directory / The history of technology, technology, objects around us A rolling mill is a machine for forming metals between rotating rolls. After the steelworkers have cast the ingot, this huge bar of steel must be turned into products - into the body of a car, a railway rail or a construction beam. But for this it is necessary that the ingot takes a form convenient for the manufacture of parts - either a long beam with a cross section in the form of a square, circle, beam, or a steel sheet or wire, etc. The ingot takes these various forms at rolling mills.
Hot rolling began to be used only at the beginning of the 1769th century, and at first more or less thin iron sheets were prepared in this way, but already from XNUMX they began to roll wire in this way. The first rolling mill for iron ingots was proposed by the English inventor Kort when he was developing the puddling method. Kort was the first to guess that in the manufacture of some products it is more rational to charge the hammer only with the extraction of slag, and give the final shape by rolling.
In 1783, Kort received a patent for a method he invented for rolling shaped iron using special rollers. From the puddling kiln, the cracker came under the hammer, here it was forged and received its original shape, and then passed through the rollers. This method then became very common. However, it was only in the XNUMXth century that rolling technology was brought to its proper height, which was largely due to the intensive construction of railways. Then rolling mills were invented for the production of rails and wagon wheels, and then for many other operations. The construction of a rolling mill in the XNUMXth century was simple. Rolls rotating in opposite directions captured a white-hot metal strip and, compressing with more or less force, carried it between their surfaces. Thus, the metal of the product was subjected to strong compression at high temperature and the workpiece acquired the required shape. In this case, for example, iron received properties that it did not have by nature. Separate grains of metal, which before rolling were located in its mass in disorder, were stretched during strong compression and formed long fibers. Soft and brittle iron became elastic and durable after that.
By the end of the century, the rolling technique had improved so much that not only solid, but also hollow products were obtained by this method. In 1885, the Mennesmann brothers invented a process for rolling seamless iron pipes. Prior to this, pipes had to be made from iron sheet - they were bent and welded. It was both long and expensive. At the Mennesmann mill, a round blank was passed between two rolls set obliquely to each other, which acted on it in two ways. First, due to frictional forces between the rolls and the billet, the latter began to rotate. Secondly, due to the shape of the rolls, the points of their middle surface rotated faster than the outer ones. Therefore, due to the oblique arrangement of the rolls, the workpiece seemed to be screwed into the space between them. If the blank were solid, it would not be able to pass. But since it was preliminarily strongly heated to a white heat, the metal of the workpiece began to twist and stretch, and loosening took place in the axial zone - a cavity appeared, which gradually spread along the entire length of the workpiece. After passing through the rolls, the billet was mounted on a special rod (mandrel), due to which the correct circular section was given to the inner cavity. The result was a thick-walled pipe.
To reduce the wall thickness, the pipe was passed through a second so-called pilgrim rolling mill. It had two rolls of variable profile. When rolling the pipe, the distance between the rolls first gradually decreased, and then became larger than the pipe diameter. What is the structure of modern rolling mills? The ingot usually passes through several rolling mills. The first of them is blooming or slabing. These are the most powerful rolling mills. They are called crimping because their purpose is to compress the ingot, turn it into a long beam (bloom) or a plate (slab), from which certain products will then be made on other mills. Bloomings and slabs are gigantic machines. The productivity of modern bloomings and slabs is about 6 million tons of ingots per year, and the mass of ingots is from 1 to 18 tons. Before crimping, the ingots must be well heated. They are kept from four to six hours in heating wells at 1100-1300 degrees Celsius. Then the ingots are taken out with a crane and placed on an electric trolley - an electric car, which delivers them to the blooming or slabing. Blooming has two huge swaths. The upper one can rise and fall, reducing or increasing the clearance between itself and the lower roll. The red-hot ingot, having passed through the rolls, falls on a roller table - a conveyor of rotating rollers. The operator continuously changes the direction of rotation of the blooming rolls and rollers of the roller table. Therefore, the ingot moves through the rolls either forward or backward, and each time the operator reduces the gap between the rolls more and more, compressing the ingot more and more. Every 5-6 passes, a special mechanism - the tilter turns the ingot 90 degrees to process it from all sides. In the end, a long beam is obtained, which is directed to the shears along the roller table. Here the timber is divided into pieces - blooms.
Rolling also takes place on a slab, with the only difference being that the slab has 4 rolls - 2 horizontal and 2 vertical, which process the ingot from all sides at once. Then the resulting long plate is cut into flat billets - slabs. Bloomings and slabs are used only at those plants where steel is poured in the old way - into molds. Where continuous casting plants (CURs) operate, ready-made blooms or slabs are obtained. Finished blooms and slabs go to other rolling shops, where special rolling mills make them, as metallurgists say, profiles, or profile metal, that is, blanks of a certain thickness, shape, profile. Sheet mills that roll slabs into sheets have smooth rolls. On such rolls it is impossible to roll a rail or other product of a complex profile. In rolls, for example, rail and beam mills, cuts are made of the shape that is necessary to obtain the product. In each roll, as if half of the profile of the future product is cut out. When the rolls approach each other, it turns out, as metallurgists say, a stream, or a caliber. There are several such calibers on each pair of rolls. The first has a shape that is only remotely similar to the shape of the product, the next ones are getting closer and closer to it, and finally, the last caliber exactly corresponds to the dimensions and shape of the product that you need to get. Steel is unyielding, and it has to be deformed gradually, passing through all the calibers in turn. That is why most mills have not one pair of rolls, but several. Beds with rolls (they are called stands) are installed in parallel either in a row or in a checkerboard pattern. The hot workpiece rushes along the roller tables from stand to stand, and even in each stand it moves forward and backward, passing through all calibers.
Today, high-performance continuous rolling mills are becoming more and more widespread. Here the stands are in series one after the other. Having passed one stand, the workpiece enters the second, third, fourth, etc. After each compression, the workpiece is stretched, and each subsequent stand must pass a workpiece of increasing length through itself in the same period of time. Some continuous mills roll metal at a speed of 80 meters per second (290 kilometers per hour), and they process several million tons per year. For example, the productivity of the 2000 sheet-type continuous strip mill operating at the Novolipetsk Metallurgical Plant reaches 6 million tons. In the USSR, fundamentally new casting and rolling mills were created at the All-Union Research Institute of Metallurgical Engineering. Their processes of continuous casting are combined into a single stream with continuous rolling. Today, dozens of such mills operate in our country for rolling steel, aluminum and copper wire. The need for pipes for transporting oil and natural gas over long distances necessitated the creation of pipe mills. The diameter of oil and gas pipes has increased. The first pipelines were 0,2 meters in diameter, then they began to produce pipes of large diameters - up to 1,4 meters. Two fundamentally different pipe production technologies are used. The first way: the workpiece is heated to 1200-1300 degrees Celsius, and then a hole is made in it on a special mill (it is stitched) - a short pipe (sleeve) with thick walls is obtained. Then the sleeve is rolled into a long tube. This is how seamless pipes are obtained. The second way: the steel sheet or strip is rolled into a tube and welded in a straight line or in a spiral. Continuous units for seam-butt welding of pipes have high productivity. This is a complex of dozens of machines and mechanisms operating in one production line. Everything is automated here: the operator who manages the complex has only to press the buttons on the control panel. The process begins with the heating of a continuous steel strip. Then the machines roll it into a pipe, weld it at the seam, stretch it in length, reduce it in diameter, calibrate it, cut it into pieces, cut the thread. 500 meters of pipes every minute - this is the productivity of the complex. In recent years, a new direction has appeared: rolling mills do not produce blanks, but immediately finished machine parts. On such mills, automobile and tractor axle shafts, textile spindles, parts of tractors, electric motors, and drilling machines are rolled. Here, rolling replaced labor-intensive operations: forging, stamping, pressing and machining on various metal-cutting machines - turning, milling, planing, drilling, etc.
This direction also includes roll-forming mills that have become widespread, producing bent profiles, and mills that roll high-precision shaped profiles. The first mills bend products of complex shape from a steel sheet, the second mills roll complex products with very precise dimensions. In both cases, the products do not need further processing on machines. They are cut into pieces of the desired length and used in machines, mechanisms and building structures. Author: Musskiy S.A.
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