1、Designation: E 285 08Standard Test Method forOxyacetylene Ablation Testing of Thermal InsulationMaterials1This standard is issued under the fixed designation E 285; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the screening of ablative mate-rials to determine the relative thermal insulation effectivenesswhen
3、tested as a flat panel in an environment of a steady flowof hot gas provided by an oxyacetylene burner.1.2 This test method should be used to measure and describethe properties of materials, products, or assemblies in responseto heat and flame under controlled laboratory conditions andshould not be
4、used to describe or appraise the fire hazard ofmaterials, products, or assemblies under actual fire conditions.However, results of this test method may be used as elementsof a fire risk assessment which takes into account all of thefactors which are pertinent to an assessment of the fire hazardof a
5、particular end use.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to
6、use.1.4 The values stated in SI units are to be regarded as thestandard.2. Referenced Documents2.1 ASTM Standards:2D 792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by Displacement2.2 Federal Standards:3BB-A-106C Acetylene, Technical, DissolvedBB-O-925A Oxygen, Tech
7、nical, Gas and Liquid3. Summary of Test Method3.1 Hot combustion gases are directed along the normal tothe specimen until burn-through is achieved. The erosion rateof the material is determined by dividing the original thicknessby the time to burn-through. The insulating effectiveness isdetermined f
8、rom back-face temperature measurements. Insula-tion index numbers are computed by dividing the times fortemperature changes of 80, 180, and 380C, from the initialambient temperature, by the original thickness. The insulation-to-density performance is computed by dividing the insulationindex by the d
9、ensity of the panel.3.2 The general characteristics of the oxyacetylene heatsource are:3.2.1 Heat Flux835 W/cm2(cold-wall calorimeter).3.2.2 Velocity210 m/s (cold, unreacted gases).3.2.3 Neutral flame conditions.4. Significance and Use4.1 This test method is intended to screen the most obviouspoor m
10、aterials from further consideration. Since the combus-tion gases more closely resemble the environment generated inrocket motors, this test method is more applicable to screeningmaterials for nozzles and motor liners than for aerodynamicheating.4.2 The environment for any specific high-temperature t
11、her-mal protection problem is peculiar to that particular applica-tion. The conditions generated by the oxyacetylene heat sourcein this test method represent only one set of conditions; they donot simulate any specific application. Thus, the test resultscannot be used to predict directly the behavio
12、r of materials forspecific environments, nor can they be used for design pur-poses. However, over a number of years, the test has beenuseful in determining the relative merit of materials, particu-larly in weeding out obviously poor materials from moreadvanced data-generation programs. It has also b
13、een consid-ered for use as a production quality-control test for rocketinsulation materials.4.3 The tester is cautioned to use prudence in extending theusefulness of the test method beyond its original intent,namely, screening. For situations having environments widelydifferent from those of the tes
14、t, the user is urged to modify the1This test method is under the jurisdiction of ASTM Committee E21 on SpaceSimulation and Applications of Space Technology and is the direct responsibility ofSubcommittee E21.08 on Thermal Protection.Current edition approved Nov. 1, 2008. Published December 2008. Ori
15、ginallyapproved in 1965 as E 285 65T. Last previous edition approved in 2002 asE 285 80(2002).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document
16、 Summary page onthe ASTM website.3Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700Robbins Ave., Philadelphia, PA 19111-5098, Attn: NPODS.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.oxyacetylene burner c
17、onditions to suit his requirements orperhaps change to a different heat-generating device thatprovides better simulation.5. Apparatus5.1 GeneralThe apparatus shall consist of an oxyacety-lene burner, a specimen holder, and means for measuring thetime to burn-through and for recording the back-face t
18、empera-ture history of the specimen. Auxiliary apparatus all consist ofa calorimetric device to measure heat-transfer rate as specifiedin 5.5.5.2 Heat SourceThe hot-gas source shall consist of awelding torch with suitable storage for acetylene and oxygen,together with suitable manifolds, flow regula
19、tors, and flow andpressure indicators, as shown schematically in Fig. 1.5.2.1 TorchThe torch shall be a Victor Model 3154andshall be mounted so that the flame can be made to contact thespecimen in less than12 s from the time of actuation.NOTE 1Both a solenoid-powered mechanism and a hand-operatedsys
20、tem of levers and push rods have been found to be adequate for thispurpose.5.2.2 Torch TipThe tip shall be a Victor welding nozzle,Type 4, No. 7, equipped with a water jacket to minimizedamage to the tip (Note 2).4Details of the water jacket areshown in Figs. 2 and 3 and the torch tip is shown in Fi
21、g. 4.NOTE 2Proprietary designation cannot be avoided because of thebroad spectrum of heat flux and flame patterns produced by competitivetorch tips of similar size. The Victor torch tip was selected on the basis ofpopularity, reproducibility of test results, and the relatively high heat fluxit produ
22、ces.5.2.3 Fuel Storage and ManifoldA minimum of threeacetylene cylinders shall be tapped simultaneously through amanifold and suitable pressure regulators. Cylinders shall bestored in an upright position and held at room temperature forat least 1 h, or until at equilibrium with room temperature,befo
23、re using. The complete bank of cylinders shall be changedwhen the gage reads 0.7 MPa (100 psi). Acetylene storagetanks shall be protected by a check valve against accidentalbackflow from the torch. The acetylene shall be maintained at294.2 K (70F) when possible (Note 3). The purity of acetylenegas s
24、hall conform with Federal Specification BB-A-106C. Theminimum acetylene content shall be 98 %.NOTE 3If 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 temperatureshall not be allowed to exceed 299 K (79F) or go below 289 K
25、 (61F).Flow rates are corrected to 294.2 K because most manufacturers use thistemperature as standard for calibration charts.5.2.4 Oxygen StorageA minimum of one oxygen tankshall be tapped through suitable pressure regulators. Theoxygen shall be maintained at 294.2 K when possible (Note 4).The purit
26、y of oxygen gas shall conform with Federal Specifi-cation BB-O-925A. The minimum oxygen content shall be99.5 %.5.2.5 Safety WallThe acetylene and oxygen storage areashall be isolated from the torch and the operating area by asuitable safety wall. For convenience, a two-stage regulatorshall be locate
27、d in the storage space and a single-stage pressureregulator located in the operating area.5.2.6 Pressure RegulatorsThe regulators for the oxygenand the acetylene shall be capable of supplying the flow ofgases specified in 5.2.7.5.2.7 FlowmetersThe flowmeters for the acetylene andthe oxygen shall be
28、capable of supplying an accurate flow ofgases.5A variation of 65 % in gas flow rate due to instrumen-tation inaccuracies shall be permissible. The total flow rate ofunreacted gases shall be 6.37 standard m3/h (294.2 K, 0.1 MPa)(225 standard ft3/h (70.0F, 14.7 psia), and the volume ratio ofoxygen to
29、acetylene shall be 1.20, which corresponds toessentially a neutral (oxygen-free) atmosphere.NOTE 4Flowmeter and pressure-gage settings are not specified be-cause they will vary with the size and brand of flowmeter used. Consultmanufacturers instructions and calibration charts that are furnished with
30、the flowmeters.5.2.8 Flow-Pressure GagesSuitable pressure gages shallbe located at the exit (downstream) side of the flowmeters tomonitor metered gas pressure. These gages shall be capable ofsupplying pressure measurements to maintain an accurate flowof gases in accordance with the specifications st
31、ated in 5.2.7.NOTE 5Pressure gages graduated 0 to 50 psig for oxygen and 0 to 30psig for acetylene, both in 1-psig increments, have been found to besuitable.4Victor Equipment Co., 2800 Airport Rd., Denton, TX 76207.5Fischer-Porter Meter size 4, Fig. 1735, float shape BSVT, equivalent capacity3.35 st
32、andard ft3/min air, has been found satisfactory for this purpose.FIG. 1 Schematic Diagram of Gas SystemE2850825.2.9 Temperature-Measuring DevicesGas temperaturesshall be measured with thermocouples, thermistors, or othersuitable devices located at the exit (downstream) side of theflowmeters. Accurac
33、y shall be within 61.0K(61.8 F).5.2.10 Piping, Hoses, and Needle ValvesAny combina-tion of piping, tubing, hoses, and needle valves may beemployed that have sufficient flow capacity to allow the fueland oxidant to flow and be controlled at the specified flowrates.5.3 Specimen HolderThe specimen and
34、the calorimetershall be supported in a suitable fixture arranged in such afashion that it can be moved to align and set the distance andangle (see 8.4 for specifications) between the specimen, orcalorimeter, and the torch tip (Note 6). The back surface of thespecimen shall be unobstructed by the hol
35、der for a distance of25.4 mm (1.00 in.) out from the center of the specimen. Onlymaterials with a thermal conductivity of 0.2 W/mK (1.4Btuin./hft2F) or less shall contact the back of the specimen.The front surface of the specimen shall be unobstructed for adistance of 48.0 mm (1.89 in.) out from the
36、 center of thespecimen. The total area of contact with front and backsurfaces shall not exceed 52.0 cm2(8.06 in.2).NOTE 6A lathe bed with the specimen holder mounted on the toolcarriage has been found to be adequate for the purpose. Water cooling ofthe holder is recommended to prolong service life.5
37、.4 Back-Face Temperature MeasurementThe back-facetemperature history shall be measured with a No. 28 AWGgage Chromel-Alumel thermocouple.NOTE 7For soft specimens, it shall be permissible to attach a thincopper disk, no larger than 10 mm (0.39 in.) in diameter, to thethermocouple junction.5.4.1 Therm
38、ocouple MountingA spring-loaded, two-holeceramic support rod no larger than 3.2 mm (18 in.) in diametershall be used to maintain good contact between the thermo-couple and the back surface of the specimen.5.4.2 Temperature Data RecordingThe thermocouple emfshall be recorded as back-face temperature,
39、 in degrees Celsius,as a function of time during the test. The data acquisitionsystem (DAS) shall have a sampling rate of1sorless.Provision shall also be provided to record the starting time ofthe test.FIG. 2 Details of Water Jacket for Oxyacetylene TorchFIG. 3 Assembly of Water Jacket for Oxyacetyl
40、ene TorchE2850835.4.3 Starting SwitchAn electric switch shall be installedon the torch mechanism to provide a “test start” event signalfor the DAS for the erosion rate measurement.5.5 CalorimeterThe cold wall heat flux of the hot-gassource shall be measured by using a calorimetric device.5.6 Burn-Th
41、rough DetectorA device such as a mirror,photocell, or direct visual means shall be used to detectburn-through of the specimen for termination of the test. Ifpossible, this should also be included as an event record on theDAS.5.6.1 TimerThe DAS shall provide timing increments of0.1-s, or less, to mea
42、sure the time to burn-through of thespecimen.6. Test Specimen6.1 The test specimen shall be a square, flat panel 6.35 60.41 mm (0.250 6 0.016 in.) thick.6.2 The dimensions of length and width shall both be 101.6+ 0.0, 0.71 mm (4.000 +0.000, 0.028 in.).6.3 Five replicates of each type of specimen sha
43、ll be tested.6.4 The thickness and density of the specimen shall bemeasured before the test.6.4.1 The density shall be measured in accordance with TestMethods D 792. If the immersing fluid is known to haveadverse effects on the specimen, the density shall be deter-mined by a simple weight-to-volume
44、calculation wherein thevolume is determined by scaling the specimen.6.4.2 The thickness at the point of flame impingement shallbe determined with suitable micrometer calipers or equivalent.Reasonable care shall be taken to avoid depressing softspecimens.7. Calibration7.1 The DAS should be calibrated
45、 at frequent intervalsusing known reference voltages. The frequency of calibrationand exact procedure are not given here because of the largevariety of data systems and standard voltage devices on themarket.7.2 The heat flux should be measured at the start of eachtesting day and at any time during t
46、esting when there is asuspicion of faulty torch operation, such as an irregularlyshaped flame or an unusual color or noise in the flame. Thetorch tip should be replaced if the heat flux is outside thespecifications listed below.7.2.1 Mount the calorimeter in the specimen holder andconnect to the DAS
47、. Align the center of the calorimeter withthe center line of the torch (Note 8) and set the correct distancebetween the calorimeter face and the end of the torch tip. Makeheat-flux measurements at on-axis positions of 19.00 and 25.406 0.30 mm (0.748 and 1.000 6 0.012 in.).NOTE 8A metal rod, thin eno
48、ugh to slide into the torch port has beenfound to be suitable for aligning the central axes of the copper cylinder (ofthe calorimeter) and the torch tip. Absolute alignment is difficult becauseof the uncertainty of the exact location of the axis of the hot gas withrespect to the axis of the torch ti
49、p. Moreover, since the torch port has avariable inside diameter, the aligning tool cannot be rigidly held in placeto locate the axis. Best results have been obtained by inserting the tool intothe torch port and slowly rotating the tool so that its free end describes acircle. Alignment adjustments are then made until the circle described isconcentric with the copper cylinder of the calorimeter. Special care shouldbe taken to avoid damaging the internal contour of the torch tip with thealigning tool.7.2.2 Ignite the torch and adjust t
