12-01-2011, 08:35 PM
GAS SPRINGS
JOSHY.P.ELIAS
S7 MECHANICAL
ROLL NO . 23
R.I.T
JOSHY.P.ELIAS
S7 MECHANICAL
ROLL NO . 23
R.I.T
GAS SPRINGS1.ppt (Size: 434.5 KB / Downloads: 217)
Introduction
A gas spring is an energy storage device similar in function to mechanical springs.
Gas springs store energy by compressing the nitrogen gas within the gas springs.
As a gas spring is compressed, the gas chamber volume is reduced due to the intrusion of the shaft into the gas spring tube; thereby causing the gas spring pressure to rise, storing more energy.
Gas spring
Properties
Gas springs always require some initial force to begin compression.
Gas springs in their “free length” require some initial force before any movement takes place.
This force can range from 20 to 250 pounds.
Gas springs have a controlled rate of extension.
Gas springs can have multiple extension rates within the same gas spring (Typically 2: one through the majority of the extension stroke, another at the end of the extension stroke to provide damping).
Parts of gas spring
Cylinder: Heavy gauge steel body.
Piston Rod: Chromium plated, hardened steel, precision –ground and highly polished.
Sealing system: Triple-Lobe rubber seal, as well as Rubber O-Ring piston seal.
Seal Backup system: Prevents seal wear. Teflon ring is usually used.
Nitrogen gas charge: Nitrogen gas charged up to 2500psi.
Glycol Fluid: Lubricant for internal components. This is a high viscosity index synthetic oil with a pour point of -70F.
Gas spring
How a gas spring works
In its simplest form: the compression of the rod/piston into the tube/cylinder reduces the volume of the tube as it compresses.
When the cylinder is filled with gas, this constitutes the spring like force or action associated with gas springs.
Damping
The most effective damping of gas springs is achieved by using a restrictor type check valve piston, operating initially through the pressurized nitrogen gas and finally into the oil.
Without damping, rapid extension could occur with possible product failure, associated damage, and injury.
How damping is achieved?Compression
Extension
Extension Time
The typical extension time curve for an unloaded gas spring is shown at right. The first portion illustrates the rapid passage through nitrogen gas, followed by a slowdown through the oil.
Crossover - Self-Rise - Self-Close
Crossover is the point in the opening cycle where the gas prop takes over all the lifting action (self-rise).
At this point no further assistance is required by the operator for the door to reach the fully open position.
There is a corresponding crossover position for the closing cycle where the door will fall to the closed position with no operator assistance (self close).
The actual angle at which these two events occur are usually separated by a few degrees.
The separation is due to friction in the gas spring internal components and connectors and with the hinge.
Self rise angle
The self-rise angle is the angle at which the gas spring will lift the door without any assistance from the operator.
For most systems this will take place between 10° and 30° from the full closed position.
This angle will become greater as the temperature falls from ambient and will be smaller as the temperature rises.
Self-close angle
Self-close is the angle at which the door will close without any assistance from the operator.
Self-close is related to self-rise.
The only reason these two angles are not exactly the same is due to friction.
One of the sources of friction is friction internal to the gas spring.
Another source is the friction in the hinge or hinge system.
Life of a Lift Support
All Lift Supports lose output force over time.
When estimating the life of a Lift Support, one must first determine how much force the support can lose before the application becomes unacceptable.
The time it takes to lose this amount of force is considered to be the life of the support.
Factors that affect the rate of force loss are:
Size of the support
Orientation
Amount of cycles
Ambient temperature
Operating Conditions
TEMPERATURE -40°C (-40°F) TO +80°C (176°F)
ALTITUDE VACUUM TO PRESSURIZED CHAMBER
HUMIDITY 0 TO 100%
CORROSION AS PER TESTS
(SALT SPRAY) BODY PASSES 240-480 HOURS PASSIVATED 96 HOURS
DUST & DIRT PASSES FORD ES TEST WITH FINE COAT OF ARIZONA ROAD DUST APPLIED TO CYCLING SHAFT EVERY 1500 CYCLES (4-8 CPM)
ULTRAVIOLET A 10% LOSS OF GLOSS OCCURRED WHEN TESTED TO GM SPECIFICATION
VIBRATION 0-100 HERTZ RANGE ONLY IF NO HEAT BUILDUP OCCURS
CYCLE FREQUENCY NOSE TEMPERATURE NOT TO EXCEED 25°F ABOVE AMBIENT DURING RAPID CYCLING
SafetyBuckling
Buckling of a gas spring will not occur if the stroke meets the recommended length requirements of the chart shown.
It is based on the EULER equation for long slender rods, and the design limitations of overall spring length, for smaller shaft diameters.
The pressure in a gas spring is determined by: pressure = output force/shaft area. The shaft areas are as follows:
6 mm shaft is .0491 sq.in8 mm shaft is .0779 sq.in10 mm shaft is .1217 sq.in
Burst Pressures
Burst pressures of gas springs are recommended to be a minimum of 5 times the charge pressure to meet design requirements.
Different types of gas springs
1)Micro Gas Springs
Micro compression gas springs offer users many advantages due their small size and low force.
The table below shows standard sizes.
Micro springs are also available in 316 stainless steel and in custom strokes and lengths.
Locking Gas Springs
A locking gas spring incorporates a mechanism to enable the rod to be locked at any point in its travel.
This locking mechanism operates when the plunger rod is depressed by opening a valve in the piston.
When the plunger rod is released the valve closes and the passage of oil or gas is prevented, locking the piston in that position.
Applications
Applications
CONCLUSION