GAS SPRINGS
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
summer project pal
Active In SP
**

Posts: 308
Joined: Jan 2011
#1
12-01-2011, 07:53 PM


INTRODUCTION
Gas springs provide controlled motion and speed for elements, such as lids and doors, that open and close. They typically rely on the fluid dampening of a gas such as nitrogen in the cylinder. Important performance specifications for gas springs include absorber stroke, compressed length, extended length, maximum force (P1), and maximum cycles per minute
The absorption or damping action for gas springs can be compression or extension. In a compression gas spring the shock absorption or dampening occurs in the compression direction. In an extension gas spring the shock absorption or dampening occurs in the extension direction. Important physical specifications for gas springs include the cylinder diameter or maximum width, the rod diameter, mounting, and body material. The cylinder diameter or maximum width refers to the desired diameter of housing cylinder. The rod diameter refers to the desired diameter of extending rod. Choices for body materials include aluminum, steel, stainless steel, and thermoplastic.Common features for gas springs include adjustable configuration, reducible, locking, and valve. An adjustable configuration allows the user to fine tune desired damping, either continuously or at discrete settings. A reducible gas spring has an adjustment style for gas shocks in which gas is let out to permanently reduce force capacity. In a locking gas spring the position can be locked at ends or in the middle of stroke. Valves can be included for fluid absorbers, a valve or port, which can be used to increase or decrease fluid volume or pressure.Gas springs are a proven and reliable method of counterbalancing large covers and objects. They offer ideal capabilities for safely lifting, lowering and positioning heavy or cumbersome objects. More versatile than mechanical springs, gas springs offer your product the advantages of speed-controlled dampening, cushioned end motion, simple mounting, compact size, flat force curve, and a wide range of available forces.


.doc   GAS SPRINGS REPORT.doc (Size: 354.5 KB / Downloads: 245)
Product Information




A gas spring is typically comprised of the following parts:
• Cylinder: Heavy gauge steel body; painted and cured to a glossy finish.
• Piston Rod: Chromium-plated, hardened steel, precision-ground and highly polished.
• Piston Assembly: Self-cleaning design automatically opens during each compression stroke to keep the piston area free of contaminants. Not offered by all manufacturers.
• Sealing System: This is the area where most manufacturers differ in their approach. AVM uses a patented Triple-Lobe Rubber Seal, as well as a Rubber O-Ring Piston Seal.
• Seal Backup System: Teflon ring, functions as a backup to the seal system, unique to AVM. Prevents seal wear.
• Temperature Compensation: Optional feature, this module provides for an increase in the force when the temperature drops below approximately 40 F enabling the use of lower forces at room temperatures to provide easier closing efforts.
• Nitrogen Gas Charge: Gas springs are charged with nitrogen most often to 1500 psi, but not more than 2500 psi. It does not react with any of the internal components. The amount of charge varies from 1/3 gram in the smallest springs to about 24 grams in the largest. Nitrogen is inert and is not flammable.
• Glycol Fluid: Lubricant for internal components. Also provides dampening to slow down movement of liftgate just prior to full open. This is a high viscosity index synthetic oil with a pour point of -70 F.



Operating principle of a gas spring
The gas spring is a hydropneumatic adjusting element, consisting of a pressure tube, a piston rod with piston and appropriate connection fittings. It is filled with compressed nitrogen, which acts with equal pressure on differently dimensioned cross-sectional areas of the piston. This produces a force in the extension direction.This extension force can be exactly defined within physical limits through the appropriate selection of the filling pressure.





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).


How the 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.
 The gas pressure on both sides of the piston are equal.
 However, there is the small area of the shaft where the internal gas pressure does not exert any pressure. Therefore, the internal pressure times shaft cross-sectional area equals the output force exerted by the shaft.



CHARACTERISTICS OF GAS SPRINGS
1)LOCKABLE
For gas exchange between the two chambers,separated by the piston ,gas springs are equipped with a bore in the piston.However ,if the piston is equipped with a special valve,inorder to close this bore,the gas spring can be locked in any stroke position desired.In addition ,spring locking as well as rigid locking can be provided.

Spring locking Rigid locking


Spring locking
In the case of spring locking ,the gas spring is filled entirely with gas.Because of the gas compressibility,a spring effect (bounce) is obtained when the valve is closed.this ensures absorbing and damping of sudden impact or pulse-like peak loads(eg. In swivel chairs)
Rigid locking
In case of rigid locking the gas spring is filled with oil.The rigid locking effect is determined by the non-compressibility of oil.This allows rigid locking of the spring and thus the application;even when subjected to greater external forces.

2)DAMPING
To provide the “comfortable” stopping of the application in the end position(eg. For tail gates in vehicles),in most application instances,end-position damping is provided.In addition,either the extension and compression stroke or only the movement in one direction can be damped.Damping can be achieved in either of two ways;either hydraulic or dynamic.
Hydraulic damping Dynamic damping

Hydraulic damping
Inorder to enable gas exchange between both chambers of the pressure tube separated by the piston,the piston is provided with a bore.however if the pressure tube is partially filled with oil and the gas spring is mounted with the piston rod pointing downwards(in this event the oil collect on the seal and guide element of the gas spring),thus at the end of the stroke the oil must flow through the bore in the piston.Due to the viscosity of the oil,the flow resistance is greater than that of gas,and therefore motion is damped.
Dynamic damping
Dynamic damping allows the gas spring to be mounted in almost any orientation.Control of the extension speed of the gas spring is achieved by providing a longitudinal groove inside the pressure tube.In this case the piston does not have a flow conduit so that the gas flows through the groove cross-section.The groove geometry determines the extension speed;the smaller the groove cross-section becomes,the slower the extension or compression speed is.In this way the extension speed is controlled up to the end of the stroke and ensures a gentle stop of the application.By varying the groove geometry,it is possible to pre-define the motion speed of the piston rod over the effective stroke.

3)SPRING CHARACTERISTICS
The spring characteristic is the means of measuring the change in spring force of the gas spring over the entire stroke.Arealistic spring characteristic is illustrated(Force-Stroke diagram).The difference between the force during extension and the force during compression is the product of dynamic friction force.In difference to mechanical springs,the flat and linear spring characteristic is typical for gas springs



When an external force exceeds the force (F3) of the extended gas spring,the piston rod is retracted (compressed)back in to the cylinder.If the extension (F2) is greater than the external force,the piston rod of the gas spring is extended.The increase in the characteristic is determined by the force ratio F2/F1 and is also known as spring characteristic.Standard gas spring have a spring characteristic of between 1.2 and 1.4 (depending on application,various values can also be predefined).

SPECIAL SPRING CHARACTERISTIC
Several application demand specially defined force requirements.For eg. In certain applications the end stroke position may require greater spring force than that of the main stroke run.The standard linear spring characteristic of a gas spring can be adapted to various requirements by adding mechanical coil springs

Progressive spring characteristic Degrssive spring characteristic




Progressive spring characteristic
Inorder to achieve a progressive spring characteristic,a mechanical coil spring is placed between the piston and bottom of the pressure tube.Since the gas spring is supported by the coil during a part of its extension stroke,the gas spring force is increased in its compressed state.
Degressive spring characteristic
By installing a coil spring on the piston rod, the gas spring force is reduced during extension at the end of the stroke by the force of mechanical coil spring.This results in what is known as a degressive spring characteristic.Thus the spring force of the extended gas spring is less than that of a standard gas spring










TERMS ASSOCIATED WITH GAS SPRINGS
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.
Hump
Hump is defined as the difference between the force required to begin closing the liftgate and the maximum force required to close the liftgate at any point in the closing cycle.
Closing and opening efforts
Cold closing and opening efforts
Room temperature closing and opening efforts
Hot closing and opening efforts
Opening and Closing Efforts
For the most part, opening and closing efforts are dictated by one thing: liftgate weight.The lighter the liftgate the easier the opening and closing efforts will be at all temperatures.Currently, opening and closing efforts for an automotive liftgate above 50 pounds total weight should be 12 to 15 pounds to open and close. Acceptable efforts would be in the 15 to 18 pound range.Typically cold hold open effort is set to 3.0 pounds at -30C for an automotive liftgate or hatch.
Relation between self rise angles and efforts
For most systems self rise angles 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.If the designer tries to make the self-rise angle small it will tend to make the closing efforts high. This is because in order for the system to have a small self-rise angle the output force in the compressed position will have to raise. Raising the compressed force tends to raise the extended output force at some proportional rate.
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
Safety
Buckling
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.in
8 mm shaft is .0779 sq.in
10 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.

Side Loading
Side loading is tested as shown in Figure. The gas spring should withstand the loads as shown in the table below for a given shaft diameter.




Shaft Diameter 0 - 10 inches 10 - 20 inches 20 - 30 inches 30 - 40 inches
6 mm 40 lbs 20 lbs n/a n/a
8 mm 79 lbs 40 lbs 27 lbs 20 lbs
10 mm 154 lbs 77 lbs 52 lbs 39 lbs










ADVANTAGES OF A GAS SPRING
Gas springs are used to provide counterbalance and force assistance in applications requiring a convenient and reliable adjustment function.Compared to mechanical springs,for many applications gas springs offers remarkable features which include:
 a flat spring rate flat spring rate (lower change in forces), even for high forces and long strokes
 a compact design,
 straightforward assembly mounting to other equipment
 definable linear, degressive or progressive spring characteristic
 damping of the adjustment motion without additional damping components,
 infinitely-variable locking
 elastic or rigid behavior in locked position.
Gas springs have a number of advantages over coil springs.
1. They can offer a much higher force in a smaller package than coil springs.
2. On compression they do not bounce back, and the extension rate can be controlled, giving a smooth return.
3. Typically gas springs have a low compression rate, but if required this can be increased.
4. With a wider range of end fittings available, gas springs can be easier to fit.
5. A wide range of additional features can also be offered.


Different types of gas springs
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.

Three types of locking gas springs


Tension gas springs
Tension gas springs sometimes referred to as traction springs, these units operate the opposite of compression gas springs.They retract rather than extend.Examples include doors and access panels hinged horizontally at the bottom and any type of cover or lid that must be pulled open or pulled shut.Tension gas springs also find many uses as tensioners on mechanical assemblies and belt drives.

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

ULTRAVIOLET A 10% LOSS OF GLOSS OCCURRED WHEN TESTED TO GM SPECIFICATION

VIBRATION 0-100 HERTZ RANGE ONLY IF NO
BUILDUP OCCURS
HEAT NOSE TEMPERATURE NOT TO EXCEED 25°F

CYCLE FREQUENCY ABOVE AMBIENT DURING RAPID CYCLING



Applications
Automotive
• Trunk lids
• Hatch lids
• Engine hoods
Consumer
• Desks
• Tool boxes
• Sewing machines
• Folding tables
• Seating
• Cabinet doors
Electronic
• Printer covers
• Printers
• Money sorting equipment
• Copy machines
Health & Fitness
• Angle adjustment
• Resistance equipment
• Height adjustment
• Treadmill
Marine
• Engine covers
• Folding beds and tables


Applications


CONCLUSION
The goal is the same with either type of spring; to move or resist the movement of some object.Gas springs in fact can be used in many applications where mechanical springs are applied because of their compact size and accurate adjustment.Gas springs are now achieving greater importance with greater variations being incorporated in it for specialized applications. More versatile than mechanical springs, gas springs offer your product the advantages of speed-controlled dampening, cushioned end motion, simple mounting, compact size, flat force curve, and a wide range of available forces.



************************************************************

REFERENCE
stabilusproduts.htm
mechanicalcomponentsgassprings/learnmore.htm
arvinmeritorgassprings.htm


************************************************

Reply
summer project pal
Active In SP
**

Posts: 308
Joined: Jan 2011
#2
12-01-2011, 08:35 PM

GAS SPRINGS
JOSHY.P.ELIAS
S7 MECHANICAL
ROLL NO . 23
R.I.T

.ppt   GAS SPRINGS1.ppt (Size: 434.5 KB / Downloads: 177)
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
Safety Buckling

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.in 8 mm shaft is .0779 sq.in 10 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






Reply

Important Note..!

If you are not satisfied with above reply ,..Please

ASK HERE

So that we will collect data for you and will made reply to the request....OR try below "QUICK REPLY" box to add a reply to this page

Quick Reply
Message
Type your reply to this message here.


Image Verification
Please enter the text contained within the image into the text box below it. This process is used to prevent automated spam bots.
Image Verification
(case insensitive)

Possibly Related Threads...
Thread Author Replies Views Last Post
  Gas metal arc welding seminar tips 9 4,825 23-10-2013, 09:47 PM
Last Post: sydaimran
Bug Bio-Gas As Alternative Fuel In IC Engines Computer Science Clay 11 12,474 19-07-2013, 05:44 PM
Last Post: Guest
  GAS WELDING ppt study tips 0 618 19-07-2013, 04:33 PM
Last Post: study tips
  Gas Insulated Switchgear (GIS) pdf study tips 0 348 29-06-2013, 03:23 PM
Last Post: study tips
  SEMINAR ON EXHAUST GAS RECIRCULATION study tips 0 461 27-05-2013, 01:06 PM
Last Post: study tips
  REPORT ON GAS KIT FOR TWO WHEELER study tips 0 623 22-05-2013, 04:58 PM
Last Post: study tips
  Development and test of a new catalytic converter for natural gas fuelled engine pdf study tips 0 514 19-02-2013, 09:31 AM
Last Post: study tips
  Study Gas Metal Arc Welding Process and Microstructural Analysis of Mild Steel pdf study tips 0 518 16-02-2013, 09:28 AM
Last Post: study tips
  Exhaust Gas Turbocharger pdf study tips 0 377 14-02-2013, 03:26 PM
Last Post: study tips
  Service Robot for Inspecting Exterior Gas Pipes of High Rise Buildings pdf project girl 0 368 28-01-2013, 02:46 PM
Last Post: project girl