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Joined: Jan 2011
03-02-2011, 10:02 PM
S7M1, Roll No: 27113
Department Of Mechanical Engineering
College of Engineering, Thiruvananthapuram – 16
A gas spring is a type of spring that, unlike a typical metal spring, uses a compressed gas, contained in a cylinder and compressed by a piston, to exert a force. Gas springs are used in automobiles, where they are used to support the weight of doors while they are open. They are also used in furniture, medical, and aerospace applications. Gas springs are also used within the press tooling industry. These units are larger than the normal "strut" type units ranging in force from 2500N to 400,000N (Forty tones).
If a syringe plunger is squeezed with a closed nozzle, the resistance will rapidly rise. In a gas spring the volume is quite large compared to the diameter of the plunger and the gas, which may be dry air or nitrogen is pre-compressed. Hence if a 1 square inch plunger (radius approx 0.56 in) is used with a container with an internal pressure of 30 pounds per square inch (207 kPa), a thirty pound-force (130 N) spring will result. If the volume of gas is large, little increase in strength will result as the rod is pressed in. The gas volume can be altered to change this parameter. The standard gas equation is used to calculate the difference. Pressure x volume / temperature (must be kelvins or degrees Rankine) = pressure x volume / temperature. If the internal plunger has a diaphragm, which extends to the side of the gas tube it will not move. If a fine hole exists it will be a slow-dampened spring, for use on heavy doors and windows. If there is no diaphragm other than the washer to contain it, the result is a quick gas spring, as used on air rifles and recoil buffers. Reducing the gas volume and hence increasing its internal pressure by means of a movable end stop or allowing one tube to slide over another can achieve adjustability. The rod may be hollow by use of clever seals or can be multiple small-diameter rods. A small amount of oil is normally present. The gas may be introduced by Schrader-type valve, using a lip seal around the rod and forcing it to allow gas in by external over pressure or a shuttling O-ring system. Gas springs of high pressure contain a very large amount of energy and could be used as a power pack. In emergency use the gas may be introduced via a gas generator cell as used in air bags. Gas springs are used to operate the main valve on Formula 1 racing cars.
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