ContentsContents1)1) IntroductionIntroduction2)2) Importance of testImportance of test3)3) ObjectiveObjective4)4) Construction of machine & working PrincipleConstruction of machine & working Principle Machine modelMachine model5.5. InstructionsInstructions 1.Standards 1.Standards 2.Prepration of sample 2.Prepration of sample 3.Operation3.Operation 4.Calculation4.Calculation

6.6. Factors affects on permeabilityFactors affects on permeability7.7. ReferencesReferences

Introduction Introduction Air permeability of a fabric Air permeability of a fabric is a measure of how well it is a measure of how well it allows the passage of air allows the passage of air

through it.through it.

OROR

The volume of air in mm The volume of air in mm which is passed in one which is passed in one

second through 100mm^2 second through 100mm^2 of the fabric at a pressure of the fabric at a pressure difference of 10 mm head difference of 10 mm head

of water .of water .

Permeability is a measure of the ability of a porous material to transmit fluids.It is an important property of technical textiles particularly in protective applications,such as auto and wearable airbags where even the low permeability of the fabric can extend the interactive time in impact. Limited permeability of parachute fabric can stabilise its descent.

Fabric permeability relates to its geometric structure strongly as well as to the path ofstreamlines for flow through the structure. Therefore, development of an analytical fabricpermeability model requires a background of fluid mechanics and knowledge of mechanics of textile fabrics.

Permeability is dependent upon the porosity of the fabric. The porosity is largelydetermined by the tightness of the fabric weave. Therefore any fabric that has reasonably tight weave is suitable for this perspective

Importance of testImportance of testWear comfortWear comfort

Maintenance of wear comfort is directly relate to air permeabil i ty as,Maintenance of wear comfort is directly relate to air permeabil i ty as,

Perspirat ion Perspirat ion : perspirat ion helps to lose heat through the body when : perspirat ion helps to lose heat through the body when i ts enrapture r ise heat is taken from the body by i ts enrapture r ise heat is taken from the body by

waterwater vapours in order to supply the heat needed to vapours in order to supply the heat needed to evaporat the moisture from the skin .evaporat the moisture from the skin .

HypothermiaHypothermia : In cold weather high loss of heat as during working can : In cold weather high loss of heat as during working can cause frostbite or hypothermia which can cause cause frostbite or hypothermia which can cause irreparable body damage or even death. irreparable body damage or even death.

DehydrationDehydration : in hot weather perspirat ion is the only problem and : in hot weather perspirat ion is the only problem and the sensation of wetness, it can cause dehydration the sensation of wetness, it can cause dehydration

or or heat stroke by large heat lose.heat stroke by large heat lose.

ObjectiveObjective

Finding different values of air flow from fabric Finding different values of air flow from fabric samples at different pressures , for testing samples at different pressures , for testing required quality of fabric for require use . required quality of fabric for require use .

Air permeabil i ty of fabrics with various densit ies

Machine model : MO21SMachine model : MO21SMachine measure permeability by Machine measure permeability by

drawing air through the specimen with a drawing air through the specimen with a vacuum pump.vacuum pump.

air flow measured by a selected flow meter .air flow measured by a selected flow meter .

instrument has 4 flow meter.instrument has 4 flow meter.

ranges of air flow 0.05 ml/sec to 416 ml/secranges of air flow 0.05 ml/sec to 416 ml/sec . .

This is the schematic diagram or internal structure of machine you can get a clear idea that how

internal parts are connected or assembled with each other.

Schematic Diagram

Air pump

Flow meter tubesManometer

Clamping device

Pressure valve

Pressure valve

Construction of machineConstruction of machine• clamping device for securing the test clamping device for securing the test

specimen in a flat tensionless state.specimen in a flat tensionless state.

• device to prevent air leaking from the device to prevent air leaking from the edges called guard ringedges called guard ring

• a pressure gauge or manometer to a pressure gauge or manometer to measure the pressure drop from side measure the pressure drop from side of the specimen to the other.of the specimen to the other.

• an air pump to draw a steady flow of an air pump to draw a steady flow of air through the clamped specimen air through the clamped specimen

• a means of adjusting the airflow rate to a means of adjusting the airflow rate to achieve specific pressure drop from achieve specific pressure drop from one side of the specimen to the other.one side of the specimen to the other.

• a flow meter to measure the actual a flow meter to measure the actual rate of air flow through the specimen rate of air flow through the specimen

InstructionsInstructions

• StandardsStandards• Preparation of samplePreparation of sample• Operation Operation • calculationcalculation

For testing sample and operating machine we need to know following in formations

standardsstandards

Air f low range = 0.05 to 416.0 ml/secAir f low range = 0.05 to 416.0 ml/sec

4 * flow meters = flow meter no.1 = 0.1 to 1.0 ml/sec4 * flow meters = flow meter no.1 = 0.1 to 1.0 ml/sec flow meter no.2 = 0.4 to 5.8 ml/secflow meter no.2 = 0.4 to 5.8 ml/sec flow meter no.3 = 4 to 40 ml/secflow meter no.3 = 4 to 40 ml/sec flow meter no.4 = 4 to 400 ml/secflow meter no.4 = 4 to 400 ml/sec

0402 0301

Standard Measuring Chamber = BS5636:1990Standard Measuring Chamber = BS5636:1990

Test Area = 508 mm^2+- 1mm^2Test Area = 508 mm^2+- 1mm^2Orifice diameter= 25.432 mm +-0.25mmOrifice diameter= 25.432 mm +-0.25mmTest specimen = subject to sample sizeTest specimen = subject to sample size

Recommended Measuring Chamber = Recommended Measuring Chamber = ENIso9237:1995ENIso9237:1995

Test area = 20 cm^2 +- 0.5 %Test area = 20 cm^2 +- 0.5 %Orifice Dia = 50.46mm Orifice Dia = 50.46mm

Test specimen = subject to sample sizeTest specimen = subject to sample size

Pressure measurementPressure measurement

Direct reading = Maximum range 2kPa (204 mm water )Direct reading = Maximum range 2kPa (204 mm water )Manometer = NB (1Pa = 0.102 mm water)Manometer = NB (1Pa = 0.102 mm water)

Instrument weight and DimensionsInstrument weight and Dimensions

weight of instrument =15kgsweight of instrument =15kgsweight of pump unit = 11 kgsweight of pump unit = 11 kgsoverall size of instrument = 370D * 660W *600ltoverall size of instrument = 370D * 660W *600ltoverall size of pump unit = 200 * 270 * 350overall size of pump unit = 200 * 270 * 350

Preparation of samplePreparation of sample

Preparation of samplePreparation of sample

Condition the fabric to be tested for 24 hour by the standard B51051 : Condition the fabric to be tested for 24 hour by the standard B51051 : relative humidity 65+_ 5 rh temperature 20+_2 c .relative humidity 65+_ 5 rh temperature 20+_2 c .

Condit ioning room with above mentioned condit ions

Analysis of sample for selecting flow meter tube, e.g porous or what ……

The preparation of stack sample (a shipment or a party taken from the track number)

To prepare mass sample, random samples are taken at least as much as the numbershown in Schedule from a party. In mass sample, there should not be the moistureexposed or damaged, the follow-up gives the pieces during transportation.

The Number of parts in a partyThe Number of parts in a party Minimum number of parts in Stack Minimum number of parts in Stack SamplesSamples

≤≤334-104-1011-3011-3031-7531-75≥≥7676

1122334455

Schedule - Mass Sample

Mass, from each piece that makes up the sample, a laboratory sample, the single mostand at least 1m in length is cut ( It should be provided randomly from one place from the most recent tip of the part at least 3 m distance). It is necessary to ensure that thereare no wrinkle regions and a visible mistake in a laboratory sample. Before the experi-ment,the samples should be conditioned and the experiment should be done in standard atmospheric conditions

The suggested conditions for the experiment:

Experimental surface area = 20 cm2 Pressure drop = 100 Pa for clothing fabrics Pressure drop = 200 Pa for industrial fabrics

Operation of machine contains following 14 steps follow these steps and operate the machine easily.

Precautions

Close all valve of machine carefully before operating the machine operate machine if you know the method look any damaged part if any like open wire etc.

Insert the plug and On the main electric switch

Step 1

slide fabric between the measuring chamber and the top clamp and firmly screen downslide fabric between the measuring chamber and the top clamp and firmly screen down

the knurled cap avoiding air leakage at the edges of the fabricthe knurled cap avoiding air leakage at the edges of the fabric

Step 2

set manometer to zero (0) adjust by using black knob if require.set manometer to zero (0) adjust by using black knob if require.

Step 3

Completely close control valve A and C valve B should never be fullyCompletely close control valve A and C valve B should never be fully closed because it is for fine adjustments .closed because it is for fine adjustments .

Step 4

Valve “A”

Valve “C”Valve “B”

select flow meter by switches on the front of machineselect flow meter by switches on the front of machine

Step 5

Flow meterIs selectedOn the basisOf fabric e.g ifFabric is lookingPorous so for thisWe should onTube 3 or 4 Because these Tubes measure PressureFrom 4 to 40 & 400 mlAnd we know porous fabric can pass flow in b/w These range.

select flow tube no4 using flow tube select tube according to fabricselect flow tube no4 using flow tube select tube according to fabricStep 6

Turn on vacuum pump using foot switch for passing air through specimenTurn on vacuum pump using foot switch for passing air through specimenStep 7

Regulate flow of air through specimen by the help of valves and the selected Regulate flow of air through specimen by the help of valves and the selected

flow meter.flow meter.

For information

Gradually open valve “C” until the required pressure is shown on the manometer tubeGradually open valve “C” until the required pressure is shown on the manometer tubeStandard is 100Pascal.Standard is 100Pascal.

Step 8

Note reading when manometer indicate selected pressureNote reading when manometer indicate selected pressure

Step 9

A particular pressure will be selectedon manometer by regulating valve “c”

Note reading at flow tube after selecting pressure at manometer

If the flow tube float has not moved close valve cIf the flow tube float has not moved close valve c

Step 10

select flow tube no3 and repeat above again no valve movement close valve cselect flow tube no3 and repeat above again no valve movement close valve c

Step 11

3

If again no movement of float select flow tube no2If again no movement of float select flow tube no2

Step 12

2

Gradually open " valve A " until required pressure drop is shown on the manometerGradually open " valve A " until required pressure drop is shown on the manometer

Valve “A” is used for Flowing tube 1 and 2

Step 13

if float tube does not rise as in case of flow tube no3 and above closeif float tube does not rise as in case of flow tube no3 and above closevalve “A” switch to flow tube 1 and gradually open " valve A " until requiredvalve “A” switch to flow tube 1 and gradually open " valve A " until requiredpressure drop is shown on the manometer.pressure drop is shown on the manometer.

Step 14

01

Record reading across the top of the float if it rise upRecord reading across the top of the float if it rise up

Step 14

1.Preparing appropriate samples in accordance with standard for the air permeability 2.Conditioning the samples 3.Setting the pressure and time of the air permeability test device in accordance with the sample. 4.Placing the sample to the device 5.Running the device 6.Reading the value of air permeability of the sample from the indicator of the device at the end of the test. 7.After taking the arithmetic mean of the test results, to calculate the value of air permeability. 8.Repeating the test for the appropriate number of samples in accordance with standard.

Conclusion

calculationcalculation

Air permeability (R) is calculated as mm / s by using the following equation .

The pressure drop caused by the resistance of the The pressure drop caused by the resistance of the specimen is measured by a different pressure gauge specimen is measured by a different pressure gauge the out put is the air resistance R measured in the out put is the air resistance R measured in kilopascals time’s seconds/meter (k Pa.s/m ) found kilopascals time’s seconds/meter (k Pa.s/m ) found from this equation :R=P1-P2/v=^p/v where P1 is from this equation :R=P1-P2/v=^p/v where P1 is pressure 1 and P2 is pressure after passing from pressure 1 and P2 is pressure after passing from volume v volume v

Follow below stepsFollow below steps

volume flow of air per unit water pressure per unit area volume flow of air per unit water pressure per unit area of fabric . calculate the mean air flow from the 5 or 10 of fabric . calculate the mean air flow from the 5 or 10 flow meter reading in litres/minutes or flow meter reading in litres/minutes or millimeters/minute (depended upon flow meter read) millimeters/minute (depended upon flow meter read) then convert to ml/second.then convert to ml/second.

Solution Method

this is then divided by the test area of thethis is then divided by the test area of thespecimen (508^2) / 100 .specimen (508^2) / 100 .record the result to an accuracy of 5 % i.e 2 or 3record the result to an accuracy of 5 % i.e 2 or 3significant figures quoting the air permeability insignificant figures quoting the air permeability inml/(cm^2/s) quoting the air permeability inml/(cm^2/s) quoting the air permeability inml/cm^2/s at 100 Pa or whatever pressure to ml/cm^2/s at 100 Pa or whatever pressure to meat other specifications.meat other specifications.e.g mean flow meter readied = 0.5 e.g mean flow meter readied = 0.5 liters/minuteliters/minute =0.01 =0.01 liters/secondliters/second =10 =10 ml /secondml /second therefore 10*100 = air permeability 2.0 ml cm^2/s at therefore 10*100 = air permeability 2.0 ml cm^2/s at

(100 Pa ).(100 Pa ).

Figures 4 and 5 show a p vs. t graph as obtained and the air permeability calculated as volume of free air (i.e. reduced to 100 kPa).

I t can be shown that:Air permeability of the fabric = (V. dp/dt) / (Patm .A ) in appropriate units,

Where, V = effective tank volume dp/dt = rate of pressure decay A = test area Patm = atmospheric pressure= 0.987 bar

Figure 4: Pressure vs. time graph for a nylon 66 fabric

Figure 5: Calculated fabricair permeability vs. pressure

1.Type of material 2.Linear density of yarns "warp-weft" 3.Warp and weft density per cm 5.Twist factors 5.Type of spinning 6.Difference of denting system 7.Type of stitches 8.Form and relative porosity 9.Type of woven construction 10.Thickness & weight

Factors AffectingFactors Affecting

• Construction factor and finishing techniques can have an Construction factor and finishing techniques can have an appreciable effect upon air permeabilityappreciable effect upon air permeability

• By causing a change in the length of airflow paths By causing a change in the length of airflow paths through a fabric .hot calendaring thus can be used to through a fabric .hot calendaring thus can be used to flatten fabric componentsflatten fabric components

• Fabrics with different surface textures on either side can Fabrics with different surface textures on either side can have a different air permeability depending upon the have a different air permeability depending upon the direction of air flow (ASTM-D737-04)direction of air flow (ASTM-D737-04)

• For woven fabrics yarn twist is also important as For woven fabrics yarn twist is also important as twist increases the circularity and density of the yarn twist increases the circularity and density of the yarn increase thus reducing the yarn diameter and cover increase thus reducing the yarn diameter and cover factor and increasing the air permeabilityfactor and increasing the air permeability

• Yarn crimp and weave influence the shape and Yarn crimp and weave influence the shape and area of the interstices between yarn and may permit area of the interstices between yarn and may permit yarns to extend easily such yarn extension would yarns to extend easily such yarn extension would open up the fabric ,increase the air permeability open up the fabric ,increase the air permeability (ASTM-D737-04)(ASTM-D737-04)

Manual of machine

Fabric Testing book

Textile Testing

Physical Testing of Textiles

Textile learner

Teachers help

Source How to reach to source

Go to TTQC lab Textile MUET or contact company

Central library MUET reference hall, textile books section

Central Library MUET reference hall, textile books section

Textile Department MUET department library

www.textilelearner.blogspot.com

Madam Sidhra