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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Hydraulic Press. History of invention and production
Directory / The history of technology, technology, objects around us A hydraulic press is the simplest hydraulic machine designed to generate large compressive forces. Formerly called the "Brahma press" as it was invented and patented by Joseph Brahmah in 1795.
The action of a hydraulic press is based on one of the most important properties of water - its low ability to compress. Due to this, the pressure exerted on the water enclosed in a closed vessel is transmitted in all directions with the same force, so that each unit of the surface has the same pressure as the pressure produced from the outside. The force with which the surface is affected is determined by the formula F=P•S, where P is the pressure and S is the area to which the force is applied. Imagine a closed vessel filled with water (or any other incompressible liquid) into which two pistons are inserted. By acting on the smaller piston with a force F, we will make the larger piston rise. The force with which water will press on this piston (as follows from the above formula) will be as many times greater as its area is larger than the area of the smaller piston. This is the essence of the effect of hydraulic amplification. For example, if the smaller piston is pressed with a force of 10 kg, then the effect on the piston in the other knee, the diameter of which is twice as large, will be four times greater (since the area of \u40b\u1bthis piston is four times larger), that is, it will be equal to 4 kg. By appropriate selection of the diameters of both pistons, it is possible to achieve an extremely large increase in the pressure force exerted by water on the second piston, but to the same extent to decrease the speed with which it will rise upwards. (In our example, in order for the large piston to rise XNUMX cm, the small piston must move XNUMX cm.)
This remarkable property of an incompressible fluid, which has received the widest use in modern technology, was discovered by Pascal. In his treatise on the equilibrium of liquids, published posthumously in 1663, he wrote: “If a vessel full of water, closed on all sides, has two holes, and one has an area a hundred times larger than the other, with pistons tightly inserted, then one person pushing a small piston will counterbalance the strength of a hundred people pushing a hundred times larger and overpower 99 of them." After the publication of Pascal's treatise, the idea of a hydraulic press was in the air, but it could not be put into practice for more than a hundred years, because they could not achieve the necessary tightness of the vessel: at high pressures, water seeped between the walls of the cylinder and the piston and no reinforcement was obtained. In the 90s of the XNUMXth century, the well-known English inventor Brama took up the creation of a hydraulic press. He also had to face the problem of sealing, but Brahma helped solve this problem with his employee and future great inventor Henry Maudsley, who came up with a special self-sealing collar (cuff).
Maudsley's invention was in fact equal to the invention of the press itself, since without it it could never work. Contemporaries were well aware of this. Maudsley's student J. Nesmith wrote later that if Maudsley had not invented anything other than this self-sealing collar, even then his name would have entered the history of technology forever. The collar was a ring that had the shape of an inverted V in the section, it was pulled out of a piece of thick yuft, well soaked in warm water, using a cast-iron mold, which consisted of an annular recess and a solid ring corresponding to its inner surface. Before complete drying, the skin had to be saturated with fat so that it retained its softness. When the cylinder was filled with water under high pressure, the edges of the leather collar moved apart, tightly pressing against the surface of the cylinder and closing the gap. With large piston diameters, such a collar turned out to be too flexible and therefore easily lagged behind. In this case, a ring was placed inside it, similar to the one used for stretching. In 1797, Brahma built the first ever hydraulic press. Here EE represent the posts, D the cover, and C the platform of the press integral with its piston, while the outer cylinder was cast together with the base for the posts. In the section of the cylinder presented next to it, Maudsley's collar is visible, also shown separately in an enlarged form under the letter Q. The press cylinder was connected by a flexible tube to a free-standing pressure pump. Its solid piston was set in initial motion by means of a lever GH, a connecting rod H' and a guide rod K. The pump was usually mounted on a cast-iron box that served as a reservoir for liquid (water, glycerin or oil), liquid flowed back into the same reservoir when the pressure reached set value and the safety valve V lifted its load P or when the screw plug was opened to release the liquid and allow the piston to drop down again. Brahma's press served as a model for many other hydraulic devices invented later. Soon a jack was created - a device for lifting weights. In the 20s of the XNUMXth century, the press began to be widely used for stamping soft metal products. However, several more decades passed before powerful forging presses suitable for stamping steel and iron parts were created. The urgent need for such presses appeared in the second half of the 120th century, when the size of the processed workpieces increased markedly. Their forging required more and more powerful steam hammers. Meanwhile, in order to increase the impact force of the steam hammer, it was necessary either to increase the weight of the falling part, or the height of its fall. But both had their limits. The rapid process of mechanical engineering, the need to forge more and more large objects finally brought the weight of the woman (the striking part of the hammer) to a colossal size - about XNUMX tons. With the fall of such huge masses, of course, it was impossible to achieve the necessary accuracy. In addition, the impact force, which causes a sharp deformation of the object, acted due to inertia only on the surface layer of the forging. From a technological point of view, slow but strong pressure was much more appropriate, since the metal got time to expand, and this contributed to a more correct deformation. Finally, strong hammer blows shook the soil so much that it became dangerous for the surrounding buildings and structures. For the first time, a forging press was developed in 1860 by the director of the workshops of the state railways in Vienna, J. Gaswell. The workshops were located within the city near residential buildings, so it was not possible to place a powerful steam hammer in them. Then Gaswell decided to replace the hammer with a press. The press he created was served by a double-acting steam engine with a horizontal cylinder, which drove two pumps. The power of the press was 700 tons, and it was successfully used in stamping locomotive parts: pistons, clamps, cranks, and the like. Exhibited in 1862 at the world exhibition in London, he attracted the liveliest interest. Since that time, more and more powerful presses began to be created in all countries. The English engineer Whitworth (one of the students of Henry Maudsley and himself an outstanding inventor), carried away by the example of Gaswell, set himself the difficult task of creating such a press that could be used to produce products directly from iron and steel ingots. In 1875 he received a patent for his first forging press. The Whitworth press consisted of four columns fixed in a foundation slab. On the upper part of the columns there was a fixed transverse beam (traverse) with two hydraulic lifting cylinders - with their help, a movable traverse moved up and down, on which a stamp was installed below. The device of the press was based on the combined use of power pumps and hydraulic accumulators. (A hydraulic accumulator is a device that allows you to accumulate hydraulic energy; it consists of a cylinder and a piston to which the load is attached; first, the water entering the cylinder lifts the load, then, at the right moment, the load is released, and the water, leaving the cylinder under it pressure, does the necessary work.)
In the Whitworth press, an array P was placed between four columns at a certain height above the anvil K; a large cylinder C was inserted inside it, the piston of which E was the forging part of the press. This piston was connected to the pistons of two small cylinders a and a1, also inserted into the array, so that in operation all three pistons rose and fell simultaneously. The space C above the piston of the large cylinder was connected to the box D, where water was driven by pumps. For small cylinders, the space above the piston was connected to the tube of the cargo accumulator AB, the load of which was balanced with the weight of all three pistons E, a and a1. The forging work itself was carried out as follows: the valve d in the pressure box was opened, the water of the pumps was directed into the space above the piston of the large cylinder, which caused all three pistons to fall. At the same time, a large piston compresses the metal, and small pistons press on the water below them and with this pressure raise the balancing weight of the accumulator. When the pressure pump valve was closed, the pressure on the large piston ceased, and then the raised weight of the accumulator began to fall, transferring pressure to the water, which raised all three pistons. Thus, the load and three pistons balanced with it represented, as it were, two scales. The pumps were powered by a steam engine. To monitor the compression force, an arrow F was connected to the forging piston, which made it possible to carry out forging with exceptional accuracy. Whitworth's hydraulic press was first used to forge castings in 1884. Until that time, the forging of gun barrels at the Whitworth plant, like many other blacksmithing operations, was carried out on steam hammers. However, the advantage of hydraulic presses over steam hammers was undeniable. So, for example, forging a gun barrel from an ingot weighing 36 tons required 5 weeks and 3 intermediate heatings; with the use of a hydraulic press, which gave a force of 33 tons, forging an ingot weighing 4000 tons took only 37 days and required 5 intermediate heatings. Replacing the hammer with a press reduced the cost of forging large parts by about seven times. Therefore, in a short time, Whitworth's presses became widespread. Soon, the use of hydraulic forging presses led to major technical transformations at large metallurgical and machine-building plants. Heavy steam hammers were dismantled everywhere and replaced with presses. By the beginning of the 90s of the XIX century, there were already presses with a capacity of 1000 tons. Author: Ryzhov K.V.
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