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Hydraulic press


Hydraulic press
At the heart of the hydraulic press is one of the most important properties of water - its low compressibility. Due to this pressure, the water produced, enclosed in a closed vessel, is transmitted in all directions with the same force, so that each unit area has to the same pressure as the pressure from the outside.

The force with which the impact is on the surface, determined by the formula F = P • S, where P - pressure, S - area to which the force is applied. Imagine a closed vessel with water (or any other incompressible fluid) in which two pistons inserted. Acting on a smaller piston with a force F, we can get to climb the larger piston. The force with which the water will be to put pressure on the piston (as shown in the above formula) is as many times greater in number with an area greater than the area of ​​the smaller piston. This is the essence of the effect of hydraulic amplification. For example, if the smaller piston to press with a force of 10 kg, the influence exerted on the piston in the other knee diameter twice to four times larger (as the area of ​​the piston in a four-fold increase), that is, it will be equal to 40 kg. Appropriate selection of the diameters of the two piston can achieve extremely large increase in the pressure force exerted by the water on the second piston, but to the same extent decrease the rate at which it will rise upwards. (In our example, to a large piston rose to 1 cm, small should fall by 4 cm.)

This remarkable property of incompressible fluid that has received the widest use of modern technology, was opened by Pascal. In his treatise on fluid balance, published posthumously in 1663, he wrote: "If a vessel full of water, enclosed on all sides, has two openings, and one has an area of ​​a hundred times more than the other, with a tight-inserted piston, the a man pushing a small piston will balance the force of a hundred people who will push a hundred times more, and 99 of them will overcome. "

Following the publication of the treatise Pascal's idea of ​​a hydraulic press in the air, but to implement it in practice could not be more than a hundred years, because they could not achieve the necessary tightness of the vessel: at higher pressures the water seeped between the piston and the cylinder walls, and no amplification was impossible. In the 90 years of XVIII century for the creation of a hydraulic press took up the famous English inventor Brahm. He also had to face the problem of sealing, but this task Brahma helped resolve his future collaborator and a great inventor Henry Maudsley, who came up with a special self-sealing collar (collar). The invention Mawdsley was virtually equal to the invention of the press, because without it, he could never work. Contemporaries were well aware of it. Pupil J Maudsley. Nesmith wrote later that if Maudsley did not invent anything, except that the self-sealing collar, even then his name would be forever entered the history of art. The collar is a ring, which had a cross-sectional view of the V facing the letter, he pulled out a thick piece of Russian leather, well soaked in warm water, using a cast-iron mold, consisting of a ring-shaped recess and a continuous ring, match its inner surface. Before complete drying of the skin had to infiltrate the fat that it has maintained its softness. When filling the cylinder with water under high pressure the edges of the leather collar parted, tightly clinging to the surface of the cylinder and closing a gap. For large diameter piston a collar is too flexible and therefore easy to keep up. In this case, it was placed inside the ring, similar to what was used for drawing. In 1797, Brahma built the first hydraulic press in history.

Here EE depict racks, D - cover, and C - the press platform, integral with its piston, while the outer cylinder was cast together with a base for struts. In the present section can be seen next to the cylinder collar Maudsley, also shown separately enlarged by the letter Q. The cylinder press was connected to a flexible tube with separate pressure pump. Its solid piston movement was set in the initial GH via a lever rod H 'and the guide rod K. The pump is normally strengthened at the cast iron box serves as a reservoir for liquids (water, oil or glycerin) in the same reservoir fluid flowed back when the pressure reached set value and safety valve V lifted his load P or when the shutter opens the screw to release the liquid and allow the piston to move down again.

Press Brahma became a model for many other hydraulic devices, invented later. device for lifting - jack Soon was created. In the 20 years of XIX century, the press has become widely used for stamping products from soft metal. But it took several decades before were created powerful forging presses, suitable for stamping of steel and iron parts.

The urgent need for such presses appeared in the second half of the XIX century, when significantly increase the size of workpieces. They require the forging of ever more powerful steam hammers. Meanwhile, to increase the impact force of a steam hammer had to either increase the weight of falling parts, or the height of its fall. But both had their limits. Rapid Engineering process, the need for ferrules increasingly large pieces finally brought women weight (beating of the hammer) to colossal size - about 120 tons. In the fall of huge masses, of course, it was to achieve the required accuracy is impossible. In addition, the impact force, causing a sharp distortion, thanks to inertia acting only on the surface layer otkovki. From a technological point of view, slow but strong pressure was much more appropriate, since the metal was getting time Hrazdan, and this contributed to a more regular strain. Finally, the strong blows of the hammer so shook the ground that it had become dangerous to the surrounding buildings and structures.

The first forging press was developed in 1860 by the director of the state railway workshops in Vienna John. Gazvellom. Workshops were located in the city close to residential buildings, so place them in a powerful steam hammer was not possible. Then Gazvell and decided to replace the hammer press. He created the press served by a steam engine of double action with horizontal cylinder actuates the two pumps. Power of the press was 700 tons, and it has been successfully used at stamping locomotive parts: pistons, clips, cranks, and the like. Exposed in 1862 at the World Exhibition in London, he has attracted great interest. Since that time, more and more powerful presses were established in all countries. English engineer Whitworth (one of the disciples of Henry Maudsley and himself an outstanding inventor), delighting Gazvella example, has set a difficult task - to create a press that we could use to get products directly from the iron and steel ingots. In 1875 he received a patent for his first forging press.

Press Whitworth consisted of four towers, fortified in the base plate. On top of the column was fixed located crossbeam (traverse) two hydraulic lifting cylinders - with them is moved up and down movable cross member on which the die was set at the bottom. Device media based on the combined use of force pumps and hydraulic accumulators. (Hydraulic accumulator - a device that allows you to accumulate hydraulic energy; it consists of a cylinder and a piston, which is attached to the goods; first water entering the cylinder lifts the load, and then, at the right time, the load is released and the water coming out of the cylinder under its pressure, performs work necessary) in the press Whitworth between the four columns at a certain height above the anvil K placed array P.; It was inserted into the large cylinder C, E and the piston which was part of the forging press. This piston was connected with two pistons and a small cylinder a1, also inserted in the array so that in all the three pistons go up and down simultaneously. C The space above the piston of a large cylinder was connected with the box D, which was accelerated water pumps. In the small space above the piston cylinder was connected to the truck battery tube AB, the load which was balanced with the weight of all three pistons E, a and a1.

The real work of forging as follows: open the valve in the discharge box d, the water pumps were sent to the space above the piston of a large cylinder, making all three piston fell. This large piston compresses the metal, and small pistons pressured water under them and this pressure lifted load balancing battery. When the pump discharge valve is closed, the pressure on the large piston was stopped, and then raised load the battery begins to descend, passing the pressure on the water, which has raised all three of the piston. Thus, the load-balanced, and with him three pistons were like two scales. The pump is driven by a steam engine. To monitor the compression force with forging piston was connected to the arrow F, which made it possible to keep forging with exceptional accuracy.

Whitworth first hydraulic press was used for forging of castings in 1884. Until that time, forging gun barrels in the factory Whitworth, like many other forging operations, conducted on a steam hammer. However, the advantage of hydraulic presses to steam hammers appeared certain. For example, a forging ingot gun barrel weighing 36 t 5 required 33 3 weeks and the intermediate heating; using the hydraulic press, let's force of 4,000 tons, forging ingot weighing 37, 5 t took only 4 days and required 15 intermediate heating. Replacement hammer forging press reduces the cost of operation of large parts about seven times. Therefore, in a short time, press Whitworth widespread. Soon the use of hydraulic forging presses has led to serious technical transformation of large metallurgical and machine-building plants. Heavy steam hammers were everywhere dismantled and replaced by presses. By the early 90-ies of the XIX century already had the press with a capacity of 1000 tonnes.

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