1、Designation: D5470 12D5470 17Standard 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 ca
2、se of revision, 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 Thi
3、s standard covers a test method for measurement of thermal impedance and calculation of an apparent thermalconductivity for thermally conductive electrical insulation materials ranging from liquid compounds to hard solid materials.1.2 The term “thermal conductivity” applies only to homogeneous mater
4、ials. Thermally conductive electrical insulatingmaterials are usually heterogeneous and to avoid confusion this test method uses “apparent thermal conductivity” for determiningthermal transmission properties of both homogeneous and heterogeneous materials.1.3 The values stated in SI units are to be
5、regarded as standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of reg
6、ulatory limitations prior to use.1.5 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Orga
7、nization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D374 Test Methods for Thickness of Solid Electrical Insulation (Metric) D0374_D0374ME691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodE1225 Test Method for T
8、hermal Conductivity of Solids Using the Guarded-Comparative-Longitudinal Heat Flow Technique3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 apparent thermal conductivity (), nthe time rate of heat flow, under steady conditions, through unit area of aheterogeneous material, per
9、 unit temperature gradient in the direction perpendicular 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 parts which contribute, either proportionally or synergistically, to theproperties of the combination.3
10、.1.4 homogeneous material, na material in which relevant properties are not a function of the position within the material.3.1.5 thermal impedance (), nthe total opposition that an assembly (material, material interfaces) presents to the flow of heat.3.1.6 thermal interfacial resistance (contact res
11、istance), nthe temperature difference required to produce a unit of heat fluxat the contact planes between the specimen surfaces and the hot and cold surfaces in contact with the specimen under test. Thesymbol for contact resistance is RI.1 This test method is under the jurisdiction of ASTM Committe
12、e D09 on Electrical and Electronic Insulating Materials and is the direct responsibility of SubcommitteeD09.01 on Electrical Insulating Products.Current edition approved Jan. 1, 2012Nov. 1, 2017. Published February 2012November 2017. Originally approved in 1993. Last previous edition approved in 201
13、12012as D5470 11.D5470 12. DOI: 10.1520/D5470-12.10.1520/D5470-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM web
14、site.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prio
15、r editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 1942
16、8-2959. United States13.1.7 thermal resistivity, nthe reciprocal of thermal conductivity. Under steady-state conditions, the temperature gradient, inthe direction perpendicular to the isothermal surface per unit of heat flux.3.2 Symbols Used in This Standard:3.2.1 = apparent thermal conductivity, W/
17、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 heat flow per unit area, W/m2.3.2.6 = thermal impedance, temperature difference per unit of heat flux, (Km2)/W.4. Summary of Test Method4.1 This stan
18、dard is based on idealized heat conduction between two parallel, isothermal surfaces separated by a test specimenof uniform thickness. The thermal gradient imposed on the specimen by the temperature difference between the two contactingsurfaces causes the heat flow through the specimen. This heat fl
19、ow is perpendicular to the test surfaces and is uniform across thesurfaces with no lateral heat spreading.4.2 The measurements required by this standard when using two meter bars are:T1 = hotter temperature of the hot meter bar, K,T2 = colder temperature of the hot meter bar, K,T3 = hotter temperatu
20、re 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, measurements are taken to compute the following parameters:TH = the temperature of the hotter isothermal surface
21、, 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 the two isothermal surfaces divided by the heat flux through them,Km2/W, andapparent thermal conductivity = calculated fro
22、m a plot of specimen thermal impedance versus thickness, W/mK.4.4 Interfacial thermal resistance exists between the specimen and the test surfaces. These contact resistances are included inthe specimen thermal impedance computation. Contact resistance varies widely depending on the nature of the spe
23、cimen surfaceand the mechanical pressure applied to the specimen by the test surfaces. The Measure and record the clamping pressure appliedto the specimen should therefore be measured and recorded as a secondary measurement required for the method except in the caseof fluidic samples (Type I, see se
24、ction 5.3.1) where the applied pressure is insignificant. The computation for thermal impedanceis comprised of the sum of the specimen thermal resistance plus the interfacial thermal resistance.4.5 Calculation of apparent thermal conductivity requires an accurate determination of the specimen thickn
25、ess under test.Different means can are able to be used to control, monitor, and measure the test specimen thickness depending on the materialtype.4.5.1 The test specimen thickness under test can is able to be controlled with shims or mechanical stops if the dimension of thespecimen can change during
26、 the test.4.5.2 The test specimen thickness can is able to be monitored under test with an in situ thickness measurement if the dimensionof the specimen can change during the test.4.5.3 The test specimen thickness can is able to be measured as manufactured at room temperature in accordance with Test
27、Methods D374 Test Method C if it exhibits negligible compression deflection.5. Significance and Use5.1 This standard measures the steady state thermal impedance of electrical insulating materials used to enhance heat transferin electrical and electronic applications. This standard is especially usef
28、ul for measuring thermal transmission properties ofspecimens that are either too thin or have insufficient mechanical stability to allow placement of temperature sensors in thespecimen as in Test Method E1225.5.2 This standard imposes an idealized heat flow pattern and specifies an average specimen
29、test temperature. The thermalimpedances thus measured cannot be directly applied to most practical applications where these required uniform, parallel heatconduction conditions do not exist.5.3 This standard is useful for measuring the thermal impedance of the following material types.D5470 1725.3.1
30、 Type IViscous liquids that exhibit unlimited deformation when a stress is applied. These include liquid compounds suchas greases, pastes, and phase change materials. These materials exhibit no evidence of elastic behavior or the tendency to returnto initial shape after deflection stresses are remov
31、ed.5.3.2 Type IIViscoelastic solids where stresses of deformation are ultimately balanced by internal material stresses thuslimiting further deformation. Examples include gels, soft, and hard rubbers. These materials exhibit linear elastic properties withsignificant deflection relative to material t
32、hickness.5.3.3 Type IIIElastic solids which exhibit negligible deflection. Examples include ceramics, metals, and some types ofplastics.5.4 The apparent thermal conductivity of a specimen can is able to be calculated from the measured thermal impedance andmeasured specimen thickness if the interfaci
33、al thermal resistance is insignificantly small (nominally less than 1 %) compared tothe thermal resistance of the specimen.5.4.1 The apparent thermal conductivity of a sample material can is able to be accurately determined by excluding the interfacialthermal resistance. This is accomplished by meas
34、uring the thermal impedance of different thicknesses of the material under testand plotting thermal impedance versus thickness. The inverse of the slope of the resulting straight line is the apparent thermalconductivity. The intercept at zero thickness is the sum of the contact resistances at the tw
35、o surfaces.5.4.2 The contact resistance can is able to be reduced by applying thermal grease or oil to the test surfaces of rigid testspecimens (Type III).TEST METHOD6. Apparatus6.1 The general features of an apparatus that meets the requirements of this method are shown in Figs. 1 and 2. This appar
36、atusFIG. 1 Test Stack Using the Meter Bars as CalorimetersD5470 173imposes the required test conditions and accomplishes the required measurements. It should be considered to be is one possibleengineering solution, not a uniquely exclusive implementation.6.2 The test surfaces are to be smooth within
37、 0.4 microns and parallel to within 5 microns.6.3 The heat sources are either electrical heaters or temperature controlled fluid circulators. Typical electrical heaters are madeby embedding wire wound cartridge heaters in a highly conductive metal block. Circulated fluid heaters consist of a metal b
38、lockheat exchanger through which a controlled temperature fluid is circulated to provide the required heat flow as well as temperaturecontrol.6.4 Heat flow through the specimen can is able to be measured with meter bars regardless of the type of heater used.6.4.1 Electrical heaters offer convenient
39、measurement of the heating power generated but must be combined with a guard heaterand high quality insulation to limit heat leakage away from the primary flow through the specimen.6.4.2 Heat flow meter bars can are able to be constructed from high conductivity materials with well documented thermal
40、conductivity within the temperature range of interest. The temperature sensitivity of thermal conductivity must be considered foraccurate heat flow measurement. The thermal conductivity of the bar material is recommended to be greater than 50 W/mK.6.4.3 Guard heaters are comprised of heated shields
41、around the primary heat source to eliminate heat leakage to theenvironment. Guard heaters are insulated from the heat source and maintained at a temperature within 60.2 K of the heater. Thiseffectively reduces the heat leakage from the primary heater by nullifying the temperature difference across t
42、he insulation.Insulation between the guard heater and the heat source shouldwill be at least the equivalent of one 5 mm layer of FR-4 epoxymaterial.6.4.4 If the heat flow meter bars are used on both the hot and cold surfaces, guard heaters and thermal insulation is not requiredand the heat flow thro
43、ugh the test specimen is computed as the average heat flow through both meter bars.6.5 Meter bars can are able to also be used to determine the temperature of the test surfaces by extrapolating the linear arrayof meter bar temperatures to the test surfaces. This can is able to be done for both the h
44、ot side and cold side meter bars. SurfaceFIG. 2 Guarded Heater Test StackD5470 174temperatures can also are able to be measured with thermocouples that are located in extreme proximity to the surfaces althoughthis can be mechanically difficult to achieve. Meter bars can are able to be used for both
45、heat flow and surface temperaturemeasurement or for exclusively one of these functions.6.6 The cooling unit is commonly implemented with a metal block cooled by temperature controlled circulating fluid with atemperature stability of 60.2 K.6.7 The contact pressure on the specimen can is able to be c
46、ontrolled and maintained in a variety of ways, including linearactuators, lead screws, pneumatics, and hydraulics. The desired range of forces must be applied to the test fixture in a directionthat is perpendicular to the test surfaces and maintains the parallelism and alignment of the surfaces.7. P
47、reparation of Test Specimens7.1 The material type will dictate the method for controlling specimen thickness. In all cases, prepare specimens of the samearea as the contacting test surfaces. If the test surfaces are not of equal size, prepare the specimen equal to the dimension of thesmaller test su
48、rface.7.1.1 Type IUse shims or mechanical stops to control the thickness of the specimen between the test surfaces. Spacer beadsof the desired diameter can is able to also be used in approximately 2 % volumetric ratio and thoroughly mixed into the sampleprior to being applied to the test surfaces.7.
49、1.2 Type IIUse an adjustable clamping pressure to deflect the test specimen by 5 % of its uncompressed thickness. Thisrepresents a trade-off between lower surface contact resistance and excessive sample deflection.7.1.3 Type IIIMeasure the sample thickness in accordance with 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 anycontamination and dirt particles. Do not use solvent that will react with or contaminate the specimens.8. Procedure8.1 Determinati
