1、Designation: D 5470 06An American National StandardStandard Test Method forThermal Transmission Properties of Thermally ConductiveElectrical Insulation Materials1This standard is issued under the fixed designation D 5470; the number immediately following the designation indicates the year oforiginal
2、 adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defen
3、se.1. Scope*1.1 This standard covers a test method for measurement ofthermal impedance and calculation of an apparent thermalconductivity for thermally conductive electrical insulationmaterials ranging from liquid compounds to hard solid mate-rials.1.2 The term “thermal conductivity” applies only to
4、 homo-geneous materials. Thermally conductive electrical insulatingmaterials are usually heterogeneous and to avoid confusion thistest method uses “apparent thermal conductivity” for determin-ing thermal transmission properties of both homogeneous andheterogeneous materials.1.3 The values stated in
5、SI units are to be regarded asstandard.1.4 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 l
6、imitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 374 Test Methods for Thickness of Solid Electrical Insu-lationE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE 1225 Test Method for Thermal Conductivity of Solids byMeans of the Gua
7、rded-Comparative-Longitudinal HeatFlow Technique3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 apparent thermal conductivity (l), nthe time rate ofheat flow, under steady conditions, through unit area of aheterogeneous material, per unit temperature gradient in thedirection p
8、erpendicular to the area.3.1.2 average temperature (of a surface), nthe area-weighted mean temperature.3.1.3 composite, na material made up of distinct partswhich contribute, either proportionally or synergistically, to theproperties of the combination.3.1.4 homogeneous material, na material in whic
9、h rel-evant properties are not a function of the position within thematerial.3.1.5 thermal impedance (u), nthe total opposition that anassembly (material, material interfaces) presents to the flow ofheat.3.1.6 thermal interfacial resistance (contact resistance),nthe temperature difference required t
10、o produce a unit ofheat flux at the contact planes between the specimen surfacesand the hot and cold surfaces in contact with the specimenunder test. The symbol for contact resistance is RI.3.1.7 thermal resistivity, nthe reciprocal of thermal con-ductivity. Under steady-state conditions, the temper
11、ature gra-dient, in the direction perpendicular to the isothermal surfaceper unit of heat flux.3.2 Symbols Used in This Standard:3.2.1 l = apparent thermal conductivity, W/mK.3.2.2 A = area of a specimen, m2.3.2.3 d = thickness of specimen, m.3.2.4 Q = time rate of heat flow, W or J/s.3.2.5 q = heat
12、 flux, or time rate of heat flow per unit area,W/m2.3.2.6 u = thermal impedance, temperature difference perunit of heat flux, (Km2)/W.4. Summary of Test Method4.1 This standard is based on idealized heat conductionbetween two parallel, isothermal surfaces separated by a testspecimen of uniform thick
13、ness. The thermal gradient imposedon the specimen by the temperature difference between the twocontacting surfaces causes the heat flow through the specimen.1This test method is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibi
14、lity ofSubcommittee D09.19 on Dielectric Sheet and Roll Products.Current edition approved April 1, 2006. Published April 2006. Originallyapproved in 1993. Last previous edition approved in 2001 as D 5470 01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer
15、 Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA
16、 19428-2959, United States.This heat flow is perpendicular to the test surfaces and isuniform across the surfaces with no lateral heat spreading.4.2 The measurements required by this standard when usingtwo meter bars are:T1= hotter temperature of the hot meter bar, K,T2= colder temperature of the ho
17、t meter bar, K,T3= hotter temperature of the cold meter bar, K,T4= colder temperature of the cold meter bar, K,A = area of the test surfaces, m2, andd = specimen thickness, m.4.3 Based on the idealized test configuration, measurementsare taken to compute the following parameters:TH= the temperature
18、of the hotter isothermal surface, K,TC= the temperature of the colder isothermal surface, K,Q = the heat flow rate between the two isothermal surfaces,W,thermal impedance = the temperature difference between thetwo isothermal surfaces divided by the heat flux through them,Km2/W, andapparent thermal
19、conductivity = calculated from a plot ofspecimen thermal impedance versus thickness, W/mK.4.4 Interfacial thermal resistance exists between the speci-men and the test surfaces. These contact resistances areincluded in the specimen thermal impedance computation.Contact resistance varies widely depend
20、ing on the nature of thespecimen surface and the mechanical pressure applied to thespecimen by the test surfaces. The clamping pressure applied tothe specimen should therefore be measured and recorded as asecondary measurement required for the method except in thecase of fluidic samples (Type I, see
21、 section 5.3.1) where theapplied pressure is insignificant. The computation for thermalimpedance is comprised of the sum of the specimen thermalresistance plus the interfacial thermal resistance.4.5 Calculation of apparent thermal conductivity requires anaccurate determination of the specimen thickn
22、ess under test.Different means can be used to control, monitor, and measurethe test specimen thickness depending on the material type.4.5.1 The test specimen thickness under test can be con-trolled with shims or mechanical stops if the dimension of thespecimen can change during the test.4.5.2 The te
23、st specimen thickness can be monitored undertest with an in situ thickness measurement if the dimension ofthe specimen can change during the test.4.5.3 The test specimen thickness can be measured asmanufactured at room temperature in accordance with TestMethods D 374 Test Method C if it exhibits neg
24、ligible com-pression deflection.5. Significance and Use5.1 This standard measures the steady state thermal imped-ance of electrical insulating materials used to enhance heattransfer in electrical and electronic applications. This standardis especially useful for measuring thermal transmission prop-e
25、rties of specimens that are either too thin or have insufficientmechanical stability to allow placement of temperature sensorsin the specimen as in Test Method E 1225.5.2 This standard imposes an idealized heat flow pattern andspecifies an average specimen test temperature. The thermalimpedances thu
26、s measured cannot be directly applied to mostpractical applications where these required uniform, parallelheat conduction conditions do not exist.5.3 This standard is useful for measuring the thermalimpedance of the following material types.5.3.1 Type IViscous liquids that exhibit unlimited defor-ma
27、tion when a stress is applied. These include liquid com-pounds such as greases, pastes, and phase change materials.These materials exhibit no evidence of elastic behavior or thetendency to return to initial shape after deflection stresses areremoved.5.3.2 Type IIViscoelastic solids where stresses of
28、 defor-mation are ultimately balanced by internal material stressesthus limiting further deformation. Examples include gels, soft,and hard rubbers. These materials exhibit linear elastic prop-erties with significant deflection relative to material thickness.5.3.3 Type IIIElastic solids which exhibit
29、 negligible de-flection. Examples include ceramics, metals, and some types ofplastics.5.4 The apparent thermal conductivity of a specimen can becalculated from the measured thermal impedance and mea-sured specimen thickness if the interfacial thermal resistance isinsignificantly small (nominally les
30、s than 1 %) compared to thethermal resistance of the specimen.5.4.1 The apparent thermal conductivity of a sample mate-rial can be accurately determined by excluding the interfacialthermal resistance. This is accomplished by measuring thethermal impedance of different thicknesses of the materialunde
31、r test and plotting thermal impedance versus thickness.The inverse of the slope of the resulting straight line is theapparent thermal conductivity. The intercept at zero thicknessis the sum of the contact resistances at the two surfaces.5.4.2 The contact resistance can be reduced by applyingthermal
32、grease or oil to the test surfaces of rigid test specimens(Type III).TEST METHOD6. Apparatus6.1 The general features of an apparatus that meets therequirements of this method are shown in Figs. 1 and 2. Thisapparatus imposes the required test conditions and accom-plishes the required measurements. I
33、t should be considered tobe one possible engineering solution, not a uniquely exclusiveimplementation.6.2 The test surfaces are to be smooth within 0.4 micronsand parallel to within 5 microns.6.3 The heat sources are either electrical heaters or tempera-ture controlled fluid circulators. Typical ele
34、ctrical heaters aremade by embedding wire wound cartridge heaters in a highlyconductive metal block. Circulated fluid heaters consist of ametal block heat exchanger through which a controlled tem-perature fluid is circulated to provide the required heat flow aswell as temperature control.6.4 Heat fl
35、ow through the specimen can be measured withmeter bars regardless of the type of heater used.6.4.1 Electrical heaters offer convenient measurement of theheating power generated but must be combined with a guardheater and high quality insulation to limit heat leakage awayfrom the primary flow through
36、 the specimen.D54700626.4.2 Heat flow meter bars can be constructed from highconductivity materials with well documented thermal conduc-tivity within the temperature range of interest. The temperaturesensitivity of thermal conductivity must be considered foraccurate heat flow measurement. The therma
37、l conductivity ofthe bar material is recommended to be greater than 50 W/mK.6.4.3 Guard heaters are comprised of heated shields aroundthe primary heat source to eliminate heat leakage to theenvironment. Guard heaters are insulated from the heat sourceand maintained at a temperature within 6 0.2 K of
38、 the heater.This effectively reduces the heat leakage from the primaryheater by nullifying the temperature difference across theinsulation. Insulation between the guard heater and the heatsource should be at least the equivalent of one 5 mm layer ofFR-4 epoxy material.6.4.4 If the heat flow meter ba
39、rs are used on both the hot andcold surfaces, guard heaters and thermal insulation is notrequired and the heat flow through the test specimen iscomputed as the average heat flow through both meter bars.6.5 Meter bars can also be used to determine the tempera-ture of the test surfaces by extrapolatin
40、g the linear array ofmeter bar temperatures to the test surfaces. This can be donefor both the hot side and cold side meter bars. Surfacetemperatures can also be measured with thermocouples that arelocated in extreme proximity to the surfaces although this canbe mechanically difficult to achieve. Me
41、ter bars can be used forboth heat flow and surface temperature measurement or forexclusively one of these functions.6.6 The cooling unit is commonly implemented with a metalblock cooled by temperature controlled circulating fluid with atemperature stability of 6 0.2 K.6.7 The contact pressure on the
42、 specimen can be controlledand maintained in a variety of ways, including linear actuators,lead screws, pneumatics, and hydraulics. The desired range offorces must be applied to the test fixture in a direction that isperpendicular to the test surfaces and maintains the parallelismand alignment of th
43、e surfaces.7. Preparation of Test Specimens7.1 The material type will dictate the method for controllingspecimen thickness. In all cases, prepare specimens of the samearea as the contacting test surfaces. If the test surfaces are notof equal size, prepare the specimen equal to the dimension ofthe sm
44、aller test surface.FIG. 1 Test Stack Using the Meter Bars as CalorimetersFIG. 2 Guarded Heater Test StackD54700637.1.1 Type IUse shims or mechanical stops to control thethickness of the specimen between the test surfaces. Spacerbeads of the desired diameter can also be used in approxi-mately 2 % vol
45、umetric ratio and thoroughly mixed into thesample prior to being applied to the test surfaces.7.1.2 Type IIUse an adjustable clamping pressure todeflect the test specimen by 5 % of its uncompressed thickness.This represents a trade-off between lower surface contactresistance and excessive sample def
46、lection.7.1.3 Type IIIMeasure the sample thickness in accordancewith Test Method C of Test Methods D 374.7.2 Prepare specimens from material that is in original,as-manufactured condition or as noted otherwise. Remove anycontamination and dirt particles. Do not use solvent that willreact with or cont
47、aminate the specimens.8. Procedure8.1 Determination of test specimen thickness.8.1.1 Machines with in situ thickness measurement appara-tus.8.1.1.1 Close the test stack and apply the clamping pressurerequired for the specimen to be tested.8.1.1.2 Turn on the heating and cooling units and letstabiliz
48、e at the specified set points to give an average sampletemperature of 50 C (average of T2and T3), unless otherwisespecified.8.1.1.3 Zero the thickness measuring device (micrometer,LVDT, laser detector, encoder, etc.).8.1.2 Machines without an in situ thickness measuringapparatus.8.1.2.1 At room temp
49、erature, measure the specimen thick-ness in accordance with Test Method C of Test Methods D 374.8.2 Load the specimen on the lower test stack.8.2.1 Dispense Type I grease and paste materials onto thelower test stack surface. Melt phase change compounds todispense onto the stack.8.2.2 Place Type II and III specimens onto the lower teststack.8.3 Close the test stack and apply clamping pressure.8.3.1 Type I materials being tested with shims to control thetest thickness require only enough pressure to squeeze outexcess material and contact the shim but not too much pre
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