1、Designation: D5470 12Standard Test Method forThermal Transmission Properties of Thermally ConductiveElectrical Insulation Materials1This standard is issued under the fixed designation D5470; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re
2、vision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope*1.1 This standa
3、rd 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 homo-geneous materials. Th
4、ermally 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 SI units are to be regarded
5、 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 limitations prior to use.2.
6、Referenced Documents2.1 ASTM Standards:2D374 Test Methods for Thickness of Solid Electrical Insu-lation (Withdrawn 2013)3E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE1225 Test Method for Thermal Conductivity of SolidsUsing the Guarded-Comparative-L
7、ongitudinal Heat FlowTechnique3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 apparent thermal conductivity (), nthe time rate ofheat flow, under steady conditions, through unit area of aheterogeneous material, per unit temperature gradient in thedirection perpendicular to the
8、 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 which rel-evant propert
9、ies are not a function of the position within thematerial.3.1.5 thermal impedance (), 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 to produce a unit of
10、heatflux at the contact planes between the specimen surfaces andthe hot and cold surfaces in contact with the specimen undertest. The symbol for contact resistance is RI.3.1.7 thermal resistivity, nthe reciprocal of thermal con-ductivity. Under steady-state conditions, the temperaturegradient, in th
11、e direction perpendicular to the isothermalsurface per unit of heat flux.3.2 Symbols Used in This Standard:3.2.1 = 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 flux, or time rate of h
12、eat flow per unit area,W/m2.3.2.6 = 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 test1This test method is under the jurisdiction of ASTM
13、 Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.01 on Electrical Insulating Products.Current edition approved Jan. 1, 2012. Published February 2012. Originallyapproved in 1993. Last previous edition approved in 2011 as D5470 11. DOI
14、:10.1520/D5470-12.2For 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 Summary page onthe ASTM website.3The last approved version of this historic
15、al standard is referenced onwww.astm.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1specimen of uniform thickness. The thermal gradient imposedon the specimen by th
16、e temperature difference between the twocontacting surfaces causes the heat flow through the specimen.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=
17、hotter temperature of the hot meter bar, K,T2= colder temperature of the hot 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, mea
18、surementsare taken to compute the following parameters:TH= the temperature 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
19、 surfaces divided by the heat flux through them,Km2/W, andapparent thermal 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 spe
20、cimen thermal impedance computation.Contact resistance varies widely depending 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 measuremen
21、t required for the method except in thecase of fluidic samples (Type I, see 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 th
22、ermal conductivity requires anaccurate determination of the specimen thickness 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 st
23、ops if the dimension of thespecimen can change during the test.4.5.2 The test 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 temper
24、ature in accordance with TestMethods D374 Test Method C if it exhibits negligible 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. T
25、his standardis especially useful for measuring thermal transmission prop-erties of specimens that are either too thin or have insufficientmechanical stability to allow placement of temperature sensorsin the specimen as in Test Method E1225.5.2 This standard imposes an idealized heat flow pattern and
26、specifies an average specimen test temperature. The thermalimpedances thus 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 m
27、aterial types.5.3.1 Type IViscous liquids that exhibit unlimited defor-mation 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 deflecti
28、on stresses areremoved.5.3.2 Type IIViscoelastic solids where stresses of 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
29、relative to material thickness.5.3.3 Type IIIElastic solids which exhibit 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
30、the interfacial thermal resistance isinsignificantly small (nominally less 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 me
31、asuring thethermal impedance of different thicknesses of the materialunder 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
32、 surfaces.5.4.2 The contact resistance can be reduced by applyingthermal 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 th
33、e required test conditions and accom-plishes the required measurements. It 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 ele
34、ctrical heaters or tempera-ture controlled fluid circulators. Typical electrical 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
35、 provide the required heat flow aswell as temperature control.D5470 1226.4 Heat flow 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 a
36、nd high quality insulation to limit heat leakage awayfrom the primary flow through the specimen.6.4.2 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 con
37、ductivity must be considered foraccurate heat flow measurement. The thermal 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 insul
38、ated from the heat sourceand maintained at a temperature within 60.2 K of 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 equivalen
39、t of one 5 mm layer ofFR-4 epoxy material.6.4.4 If the heat flow meter bars 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 b
40、e used to determine the tempera-ture of the test surfaces by extrapolating 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
41、to the surfaces although this canbe mechanically difficult to achieve. Meter 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 flu
42、id with atemperature stability of 60.2 K.6.7 The contact pressure on the 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 isperpendicul
43、ar to the test surfaces and maintains the parallelismand alignment of the surfaces.7. Preparation of Test Specimens7.1 The material type will dictate the method for controllingspecimen thickness. In all cases, prepare specimens of the sameFIG. 1 Test Stack Using the Meter Bars as CalorimetersFIG. 2
44、Guarded Heater Test StackD5470 123area as the contacting test surfaces. If the test surfaces are notof equal size, prepare the specimen equal to the dimension ofthe smaller test surface.7.1.1 Type IUse shims or mechanical stops to control thethickness of the specimen between the test surfaces. Space
45、rbeads of the desired diameter can also be used in approxi-mately 2 % volumetric 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 t
46、rade-off between lower surface contactresistance and excessive sample deflection.7.1.3 Type IIIMeasure the sample thickness in accordancewith Test Method C of Test Methods D374.7.2 Prepare specimens from material that is in original,as-manufactured condition or as noted otherwise. Remove anycontamin
47、ation and dirt particles. Do not use solvent that willreact with or contaminate 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
48、 be tested.8.1.1.2 Turn on the heating and cooling units and letstabilize at the specified set points to give an average sampletemperature of 50C (average of T2and T3), unless otherwisespecified.8.1.1.3 Zero the thickness measuring device (micrometer,LVDT, laser detector, encoder, etc.).8.1.2 Machin
49、es without an in situ thickness measuringapparatus.8.1.2.1 At room temperature, measure the specimen thick-ness in accordance with Test Method C of Test Methods D374.8.2 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 p
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