Designation:E 285–80(Reapproved 2002)
Standard Test Method for
Oxyacetylene Ablation Testing of Thermal Insulation Materials 1
This standard is issued under the fixed designation E 285;the number immediately following the designation indicates the year of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon (e )indicates an editorial change since the last revision or reapproval.
1.Scope
1.1This test method covers the screening of ablative mate-rials to determine the relative thermal insulation effectiveness when tested as a flat panel in an environment of a steady flow of hot gas provided by an oxyacetylene burner.
1.2This test method should be used to measure and describe the properties of materials,products,or assemblies in response to heat and flame under controlled laboratory conditions and should not be used to describe or appraise the fire hazard of materials,products,or assemblies under actual fire conditions.However,results of this test method may be used as elements of a fire risk assessment which takes into account all of the factors which are pertinent to an assessment of the fire hazard of a particular end use.
1.3This standard does not purport to address all of the safety concerns,if any,associated with its use.It is the responsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.
1.4The values stated in SI units are to be regarded as the standard.
2.Referenced Documents 2.1ASTM Standards:
D 792Test Methods for Density and Specific Gravity (Rela-tive Density)of Plastics by Displacement 22.2Federal Standards:3
BB-A-106a Acetylene,Technical,Dissolved BB-O-925a Oxygen,Technical,Gas and Liquid
3.Summary of Test Method
3.1Hot combustion gases are directed along the normal to the specimen until burn-through is achieved.The erosion rate of the material is determined by dividing the original thickness by the time to burn-through.The insulating effectiveness is
determined from back-face temperature measurements.Insula-tion index numbers are computed by dividing the times for temperature changes of 80,180,and 380°C,from the initial ambient temperature,by the original thickness.The insulation-to-density performance is computed by dividing the insulation index by the density of the panel.
3.2The general characteristics of the oxyacetylene heat source are:
3.2.1Heat Flux —835W/cm 2(cold-wall calorimeter).3.2.2Velocity —210m/s (cold,unreacted gases).3.2.3Neutral flame conditions.
4.Significance and Use
4.1This test method is intended to screen the most obvious poor materials from further consideration.Since the combus-tion gases more closely resemble the environment generated in rocket motors,this test method is more applicable to screening materials for nozzles and motor liners than for aerodynamic heating.
4.2The environment for any specific high-temperature ther-mal protection problem is peculiar to that particular applica-tion.The conditions generated by the oxyacetylene heat source in this test method represent only one set of conditions;they do not simulate any specific application.Thus,the test results cannot be used to predict directly the behavior of materials for specific environments,nor can they be used for design pur-poses.However,over a number of years,the test has been useful in determining the relative merit of materials,particu-larly in weeding out obviously poor materials from more advanced data-generation programs.It has also been consid-ered for use as a production quality-control test for rocket insulation materials.
4.3The tester is cautioned to use prudence in extending the usefulness of the test method beyond its original intent,namely,screening.For situations having environments widely different from those of the t
est,the user is urged to modify the oxyacetylene burner conditions to suit his requirements or perhaps change to a different heat-generating device that provides better simulation.
5.Apparatus
5.1General —The apparatus shall consist of an oxyacety-lene burner,a specimen holder,and means for measuring the
1
This test method is under the jurisdiction of ASTM Committee E21on Space Simulation and Applications of Space Technology and is the direct responsibility of Subcommittee E21.08on Thermal Protection.
Current edition approved Dec.8,1980.Published February 1981.Originally published as E 285–65T.Last previous edition E 285–70.2
Annual Book of ASTM Standards ,V ol 08.01.3
Available from Standardization Documents Order Desk,Bldg.4Section D,700Robbins Ave.,Philadelphia,PA 19111-5098,Attn:NPODS.
1
Copyright ©ASTM International,100Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.
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time to burn-through and for recording the back-face tempera-ture history of the specimen.Auxiliary apparatus all consist of a calorimetric device to measure heat-transfer rate as specified in 5.5.
5.2Heat Source —The hot-gas source shall consist of a welding torch with suitable storage for acetylene and oxygen,together with suitable manifolds,flow regulators,and flow and pressure indicators,as shown schematically in Fig.1.
5.2.1Torch —The torch shall be a Victor Model 3154and shall be mounted so that the flame can be made to contact the specimen in less than 1⁄2s from the time of actuation.
N OTE 1—Both a solenoid-powered mechanism and a hand-operated system of levers and push rods have been found to be adequate for this purpose.
5.2.2Torch Tip —The tip shall be a Victor welding nozzle,Type 4,No.7,equipped with a water jacket to minimize damage to the tip (Note 2).4Details of the water jacket are shown in Figs.2and 3and the torch tip is shown in Fig.4.
N OTE 2—Proprietary designation cannot be avoided because of the broad spectrum of heat flux and flame patterns produced by competitive torch tips of similar size.The Victor torch tip was selected on the basis of popularity,reproducibility of test results,and the relatively high heat flux it produces.
5.2.3Fuel Storage and Manifold —A minimum of three acetylene cylinders shall be tapped simultaneously through a manifold and suitable pressure regulators.Cylinders shall be stored in an upright position and held at room temperature for at least 1h,or until at equilibrium with room temperature,
before using.The complete bank of cylinders shall be changed when the gage reads 0.7MPa (100psi).Acetylene storage tanks shall be protected by a check valve against accidental backflow from the torch.The acetylene shall be maintained at 294.2K (70°F)when possible (Note 3).The purity of acetylene gas shall conform with Federal Specification BB-A-106a.The minimum acetylene content shall be 98%.
N OTE 3—If this is not possible,the flow rate shall be corrected to 294.2K in accordance with the flow rate specified in 5.2.7.The gas temperature shall not be allowed to exceed 299K (79°F)or go below 289K (61°F).Flow rates are corrected to 294.2K because most manufacturers use this temperature as standard for calibration charts.
5.2.4Oxygen Storage —A minimum of one oxygen tank shall be tapped through suitable pressure regulators.The oxygen shall be maintained at 294.2K when possible (Note 4).The purity of oxygen gas shall conform with Federal Specifi-cation BB-O-925a.The minimum oxygen content shall be 99.5%.
5.2.5Safety Wall —The acetylene and oxygen storage area shall be isolated from the torch and the operating area by a suitable safety wall.For convenience,a two-stage regulator shall be located in the storage space and a single-stage pressure regulator located in the operating area.
5.2.6Pressure Regulators —The regulators for the oxygen and the acetylene shall be capable of supplying the flow of gases specified in 5.2.7.
5.2.7Flowmeters —The flowmeters for the acetylene and the oxygen shall be capable of supplying an accurate flow of gases.5A variation of 65%in gas flow rate due to instrumen-tation inaccuracies shall be permissible.The total flow rate of unreacted gases shall be
6.37standard m 3/h (294.2K,0.1MPa)(225standard ft 3/h (70.0°F,14.7psia)),and the volume ratio of oxygen to acetylene shall be 1.20,which corresponds to essentially a neutral (oxygen-free)atmosphere.
N OTE 4—Flowmeter and pressure-gage settings are not specified be-cause they will vary with the size and brand of flowmeter used.Consult manufacturers’instructions and calibration charts that are furnished with the flowmeters.
5.2.8Flow-Pressure Gages —Suitable pressure gages shall be located at the exit (downstream)side of the flowmeters to monitor metered gas pressure.These gages shall be capable of supplying pressure measurements to maintain an accurate flow of gases in accordance with the specifications stated in 5.2.7.
N OTE 5—Pressure gages graduated 0to 50psig for oxygen and 0to 30psig for acetylene,both in 1-psig increments,have been found to be suitable.
5.2.9Temperature-Measuring Devices —Gas temperatures shall be measured with thermocouples,thermistors,or other suitable devices located at the exit (downstream)side of the flowmeters.Accuracy shall be within 61.0K (61.8F).
5.2.10Piping,Hoses,and Needle Valves —Any combina-tion of piping,tubing,hoses,and needle valves may be employed that have sufficient flow capacity to allow the fuel and oxidant to flow and be controlled at the specified flow rates.
4
Victor Equipment Co.,2800Airport Rd.,Denton,TX 76207.
5
Fischer-Porter Meter size 4,Fig.1735,float shape BSVT,equivalent capacity 3.35standard ft 3/min air,has been found satisfactory for this
purpose.
FIG.1Schematic Diagram of Gas
System
5.3Specimen Holder —The specimen and the calorimeter shall be supported in a suitable fixture arranged in such a fashion that it can be moved to align and set the distance and angle (see 8.4for specifications)between the specimen,or calorimeter,and the torch tip (Note 7).The back surface of the specimen shall be unobstructed by the holder for a distance of 25.4mm (1.00in.)out from the center of the specimen.Only materials with a thermal conductivity of 0.2W/m·K (1.4Btu·in./h·ft 2·°F)or less shall contact the back of the specimen.The front surface of the specimen shall be unobstructed for a distance of 48.0mm (1.89in.)out from the center of the specimen.The total area of contact with front and back surfaces shall not exceed 52.0cm 2(8.06in.2).
N OTE 6—A lathe bed with the specimen holder mounted on the tool carriage has been found to be adequate for the purpose.Water cooling of
the holder is recommended to prolong service life.
5.4Back-Face Temperature Measurement —The back-face temperature history shall be measured with a No.28AWG gage Chromel-Alumel thermocouple.
N OTE 7—For soft specimens,it shall be permissible to attach a thin copper disk,no larger than 10mm (0.39in.)in diameter,to the thermocouple junction.
5.4.1Thermocouple Mounting —A spring-loaded,two-hole ceramic support rod no larger than 3.2mm (1⁄8in.)in diameter shall be used to maintain good contact between the thermo-couple and the back surface of the specimen.
5.4.2Temperature Recorder —The thermocouple emf shall be recorded as back-face temperature,in degrees Celsius,as a function of time during the test.The response time of the recorder shall be 1s or less for full-scale deflection and the chart speed shall be at least 12m/s (approximately 8in./min).The recorder shall be equipped with a suitable auxiliary timing pen to indicate the starting time of the test.
5.4.3Starting Switch —An electric switch shall be installed on the torch mechanism to actuate the timing pen on the temperature recorder and the electric clock for the erosion rate measurement.
5.5Calorimeter —The cold wall heat flux of the hot-gas source shall be measured by using a calorimetric device.5.6Burn-Through Detector —A device such as a mirror,photocell,or direct visual means shall be used to detect burn-through of the specimen for termination of the test.5.
6.1Timer —An electric time clock,0to 1000s graduated in 0.1-s increments,shall be used to measure the time
to
FIG.2Details of Water Jacket for Oxyacetylene
Torch
FIG.3Assembly of Water Jacket for Oxyacetylene
Torch
burn-through of the specimen.
6.Test Specimen
6.1The test specimen shall be a square,flat panel 6.3560.41mm (0.25060.016in.)thick.
6.2The dimensions of length and width shall both be 101.6°+0.0°,−0.71mm (4.000+0.000,−0.028in.).
6.3Five replicates of each type of specimen shall be tested.6.4The thickness and density of the specimen shall be measured before the test.
6.4.1The density shall be measured in accordance with Test Methods D 792.If the immersing fluid is known to have adverse effects on the specimen,the density shall be deter-mined by a simple weight-to-volume calculation wherein the volume is determined by scaling the specimen.
6.4.2The thickness at the point of flame impingement shall be determined with suitable micrometer calipers or equivalent.Reasonable care shall be taken to avoid depressing soft specimens.
7.Calibration
7.1Temperature recorders should be calibrated at frequent intervals using known reference voltages.The frequency of calibration and exact procedure are not given here because of the large variety of recorders and standard voltage devices on the market.A general procedure found to be satisfactory,however,consists of connecting a potentiometer to the input side of the recorder.Various input voltages are set on the potentiometer and the recorder is adjusted to read these voltages.
7.2The heat flux should be measured at the start of each testing day and at any time during testing when there is a suspicion of faulty torch operation,such as an irregularly shaped flame or an unusual color or noise in the flame.The torch tip should be replaced if the heat flux is outside the specifications listed below.
7.2.1Mount the calorimeter in the specimen holder and connect the thermocouple leads to the temperature recorder.Align the center of the calorimeter with the center line of the torch (Note 8)and set the correct distance between the calorimeter face and the end of the torch tip.Make heat-flux measurements at on-axis positions of 19.00and 25.4060.30mm (0.748and 1.00060.012in.).
N OTE 8—A metal rod,thin enough to slide into the torch port has been found to be suitable for aligning the central axes of the copper cylinder (of the calorimeter)and the torch tip.Absolute alignment is difficult because of the uncertainty of the exact location of the axis of the hot gas with respect to the axis of the torch tip.Moreover,since the torch port has a variable inside diameter,the aligning tool cannot be rigidly held in place to locate the axis.Best results have been obtained by inserting the tool into the torch port and slowly rotating the tool so that its free end describes a circle.Alignment adjustments are then made until the circle described is concentric with the copper cylinder of the calorimeter.Special care should be taken to avoid damaging the internal contour of the torch tip with the aligning tool.
7.2.2Ignite the torch and adjust the gas flow rates to the conditions set forth in 5.2.7.After flow conditions are stabi-lized,record data according to applicable calorimeter standard.7.2.3Make three trials at each position.The average heat flux at the two distances of 19.0and 25.4mm should be 83564
0and 520660W/cm 2,respectively.Replace the torch tip if the heat flux is outside these specifications.
8.Procedure
8.1Check the alignment of the thermocouple with the center of the torch tip and adjust if needed.
8.2Place the specimen in the holder and secure it firmly.8.3Mount the thermocouple against the backside of the specimen and connect the leads to the recorder.
8.4Set the distance between the specimen face and torch tip to 19.060.30mm (0.74860.012in.)and the angle between torch and specimen to 906
3°.
FIG.4Victor Type 4,No.7Torch
Tip
8.5Ignite the torch and adjust the gasflow rates to the conditions set forth in5.2.7.Afterflow conditions are stabi-lized,start the temperature-recorder chart drive and allow the torchflame to contact the specimen.Terminate the test at the instance that burn-through is detected.
8.6Record the burn-through time in seconds from the electric timer,which is actuated when theflame contacts the specimen and is stopped when the test is terminated.Record the time for back-face temperature changes of80,180,and 380°C from ambient temperature.
8.7Testfive replicates of each type of specimen.
9.Calculation
9.1Insulation Index—Calculate the insulation indexes for each replicate by dividing the time for back-face temperature changes of80,180,and380°C(from ambient)by the original thickness of the specimen,as follows:
I T5t T/d(1) where:
I T=insulation index at temperature T,s/m,
t T=time for back-face temperature changes of80,180, and380°C,s,and
d=thickness of specimen,m.
9.1.1Average Insulation Index—Calculate the average in-sulation index as follows:
~I T!avg5(I T/N(2) where:
(I T)avg=average insulation index at temperature T,s/m, (I T=sum of individual values of insulation indexes at
temperature T,and
N=number of replicates.
9.1.2Standard Deviation—Calculate the standard deviation as follows:
S T5=(@I T2~I T!avg#2/~N21!(3) where:
S T=standard deviation at temperature T,
(I T)avg=average index at temperature T,
I T=individual values of indexes at temperature T,
and
N=number of replicates.
9.1.3Insulation-to-Density Performance—Divide the aver-age insulation index at each temperature by the average density of the replicates as follows:
~P avg!T5~I T!avg/D avg(4) where:
(P avg)T=average insulation-to-density ratio at tempera-ture T,s·m2/kg,and
D avg=average density of the replicates,kg/m3.
9.2Erosion Rate—Calculate the erosion rate for each rep-licate by dividing the original thickness of the specimen by the time to burn-through as follows:
E5d/b(5) where:
E=erosion rate,m/s,
d=thickness of panel,m,and
b=burn-through time,s.
9.2.1Average Erosion Rate—Calculate the average erosion rate as follows:
E avg5(E/N(6) where:
E avg=average erosion rate,m/s,
(E=sum of individual values or erosion rates,and
N=number of replicates.
9.2.2Standard Deviation—Calculate the standard deviation as follows:
S E5=@(~E2E avg!#/~N21!(7) where:
S E=standard deviation of erosion rates,
E avg=average erosion rate,
E=individual values of erosion rates,and
N=number of replicates.
9.3Average Heat Flux—Calculate the average heatflux as follows:
F avg5(F/N(8) where:
F avg=average heatflux,W/m2,
editorial hand(F=sum of individual values of heatflux at each test position,and
N=number of trials at each test position.
10.Report
10.1Report the following information:
10.1.1Identity or composition of the sample.Whenever possible,identify components by their chemical names;state the amount of each component present;and,in the case of fibrous reinforcements,give the direction and orientation of the fibers,
10.1.2Thickness of the specimen,m,
10.1.3Density of the specimen,kg/m3,
10.1.4Average insulation indexes at the specified tempera-ture rises,s/m,
10.1.5Standard deviations of insulation indexes at the specified temperature rises,
10.1.6Average insulation-to-density ratios at the specified temperature rises,s·m2/kg,
10.1.7Average erosion rate,m/s,
10.1.8Standard deviation of the erosion rate,and
10.1.9Average heatflux at the test conditions,W/m2.
11.Precision
11.1When the test method is used by a single operator in repetitive tests on a homogeneous material,the mean deviation from the arithmetic average is approximately65%.
11.2When the test method is used by competent operators in different laboratories,the mean deviation from the average is approximately65%.
12.Keywords
12.1ablation;convection;oxyacetylene;thermal
insulation
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