Hydraulic press

A hydraulic press is a non -bonded molding machine operating according to the hydrostatic principle.

Principle of operation

According to the law of the hydrostatic pressure in a fluid is constant, and thus a force acting on a wall of the vessel are multiplied.

The vessel had two flat surfaces with the contents and. The pressure was without power. Now acts on the first surface, a force so increases the pressure on. After the hydrostatic Basic Law this is the same. The force on the second surface is proportional to the surface area.

The hydraulic press, which is named after its inventor, Joseph Bramah also Bramahsche press, is an application of this Act in order to multiply the force acting on a piston of a pump power.

It consists of a suction and pressure pump, which exerts the pressure, and a piston which receives the pressure to transmit it to the body to be pressed. By a lever, the pump piston is raised, the water enters the container through the screen, raises the valve and thus reaches under the piston.

When one depresses the lever, so the piston goes down, the back -driven water closes the valve, lifts the valve and passes through the other tube in the cavity of the press; There now presses against the piston, it lifts the disc, and thus the body to be pressed is compressed.

When the piston is depressed by any force, each has the surface of the vessel walls, which is the cross-section of the piston equivalent to withstand an identical pressure. Now one can consider, but the lower surface of the piston as a part of the vessel wall; so many times that is the cross section of the piston is greater than the cross section of the piston so many times also the force with which the piston is lifted be greater than the force with which the small piston is depressed.

If the cross section of the piston is one-hundredth of the cross section, as a mass of 50 kg is lifted when a 0.5 kg mass is depressed. When the lever is pressed down with a mass of 50 kg, however, such as when the lever arms of strength and resistance behave as 6:1, the effect is the same as if one had directly mass of 300 kg on the piston. The piston could therefore lift a mass of 30,000 kg.

Of the force which is applied to the lever, a portion of friction resistance is lost before it is propagated to the piston; therefore, the effect will always be less than it should be according to the above calculation.

Development

A fair improvement underwent the first hydraulic press by applying a special seal ( obturator ) of the large piston, which is attributed by some to scorn Mathias in London, of the other Benjamin Hick in Bolton.

This consists of an upturned Sohllederring which has the shape of an inverted U and is sharpened at both ends. This ring is in a recess of the cylinder and is forced through the water against the piston and cylinder. To maintain the shape of the leather ring is a composite of two parts metal ring.

In Germany and France, the hydraulic press seems to have found only after the second Paris Peace attention. So are Gilbert ( Annals of Physics, vol 60, 1819) that at the beginning of the year 1818 the mechanic Neubauer have designed a hydraulic press in the machine factory of Nathusius in Hundisburg at Magdeburg, which is set by two people on the move, a pressure of 150,000 kg produced and particularly to press out the beet juice, oil from the seeds has been used etc..

In France, the Montgolfier mechanic to be have been one of the first who has used the hydraulic press with success to the oil presses, and such a press was at the Paris Industrial Exhibition of 1819.

Application

Since then, Joseph Bramah in London by him (1795 ) invented press as packing press for hay, flax and cotton, at all to replace the screw presses in factories and factories, as well as for lifting loads instead of the cranes, as producers large print at the gunpowder factory and strange enough related as metal planing and drilling machine, this machine has gained such a wide field of use, that it may be called now almost obvious.

In general, to use them wherever you need it to have a relatively larger part of the way of about 30-90 cm a very strong pressure sustained and applied uniformly to a substance to its compression.

In addition to their use for testing the strength of construction materials ( bars, chains, ropes, stones) has the hydraulic press used in the beet sugar, stearine, oil and rubber production met with considerable success, as for pressing of tubes of lead and tin, also when lifting heavy loads ( as an elevator ) to the movement of the rudder of large ships, etc.; also it is used to set-up and removal of the railroad car wheels and the axles and pressing of the jaws in preparation for the coin production.

Very important these machines are also known as Appreturmaschinen in different tissues, and finally they currently serve more than earlier than packing presses to huddle substances that would occupy a large space and difficult to transport (eg hay), in a small room.

Through the application of the principle of the hydraulic press in and no connection with the 1843 invented by Armstrong accumulator a whole new category of tools and machine tools has emerged ( hydraulic tools ).

Haswell used the hydraulic press first in the forging of metals and opened (eg extensive use of molds or dies for forging) a wide range of new work operations.

The main difficulty was to overcome this, was in the slow movement of the plunger, while the had to cool down every piece of work so far that occurs then the pressure could only have a very insufficient effect.

Haswells machine, which is free from this inconvenience, granted other forging equipment compared with the advantage that you can regulate the pressure as desired, which now acts uniformly on the inner parts of the iron is gradually increased and brings about the complete filling of the molds without vibration.

At Tangyes scissors is the cylinder, the fixed and movable with the piston at the same time scissor blade is the pressure pump the lever to the piston movement and f the vessel, from which the pressure pump sucks the fluid pressure (water, glycerol, etc. ). Iron bars of 75 mm side length of the square should, where the lever working hours, a man who can cut through in a 2 ¼ minutes. People uses scissors everywhere with success where few workers are up for grabs.

Similarly, the hole machine is constructed by the pusher or punch is attached to the movable piston of the press. With such a machine, a man, a hole of 25 mm diameter in a 21.5 mm thick iron plate is able, in about ½ minute squeeze. Also hydraulic riveting machines and winches are built according to this system and are characterized, like the hole machines with large capacity with sufficient ease and portability of. This is certainly not to deny that the machines ( the nature of the action of water after ) work very slowly.

Hydraulic presses today

In modern hydraulic presses, the pressure in the medium is applied by means of electric motors and high capacity pumps. Common are pressures up to 300 bar pressure in the medium, thus depending on the piston diameter pressing forces of several thousand tons (up to 800 MN or about 80,000 t) can be realized. Depending on the pressing force, the presses are running with C- or O- frame, also are single-, double - and (rarely ) triple-action types available. One common, universally applicable design is single-acting with active die cushion in the press force range 100-2500 t.

Use of modern hydraulic presses

Hydraulic presses come across the spectrum of metal forming used. They are particularly suitable for drawing operations, since they can afford the maximum power regardless of the ram position over the entire stroke length. Also they are used for cutting. Likewise, the repeater is used as a test and Spotting and try-out presses.

In general, hydraulic presses are more flexible and easier to prepare than mechanical presses, but do not reach their cycle times. Therefore, they are particularly very common in smaller companies.

Benefits

• Speed ​​and power easy to control
• Drive can be installed anywhere
• Overload protection
• High forces generated

Disadvantages

• Leaks
• Limited life of hydraulic fluid
• Low stroke rate