ASTM D4470-2018 Standard Test Method for Static Electrification《静电的标准试验方法》.pdf

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1、Designation: D4470 18Standard Test Method forStatic Electrification1This standard is issued under the fixed designation D4470; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indic

2、ates 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 generation of electrostaticcharge, the measurement of this charge and its associatedelectric field, and the test conditions which must

3、 be controlledin order to obtain reproducible results. This test method isapplicable to both solids and liquids. This test method is notapplicable to gases, since a transfer of a gas with no solidimpurities in it does not generate an electrostatic charge. Thistest method also does not cover the bene

4、ficial uses of staticelectrification, its associated problems or hazards, or theelimination or reduction of unwanted electrostatic charge.21.2 The values stated in SI units are to be regarded as thestandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated w

5、ith its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized

6、 principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3D618 Practice for Conditio

7、ning Plastics for TestingD1711 Terminology Relating to Electrical InsulationD5032 Practice for Maintaining Constant Relative Humidityby Means of Aqueous Glycerin SolutionsE104 Practice for Maintaining Constant Relative Humidityby Means of Aqueous Solutions3. Terminology3.1 Definitions:3.1.1 For defi

8、nitions of terms used in this specification, referto Terminology D1711.3.1.2 conducting material (conductor), na material withinwhich an electric current is produced by application of avoltage between points on or within the material.3.1.2.1 DiscussionThe term “conducting material” is usu-ally appli

9、ed only to those materials in which a relatively smallpotential difference results in a relatively large current since allmaterials appear to permit some conduction current. Metalsand strong electrolytes are examples of conducting materials.3.1.3 electric field strength, nthe magnitude of the vector

10、force on a point charge of unit value and positive polarity.3.1.4 excess electrostatic charge, nthe algebraic sum ofall positive and negative electric charges on the surface of, orin, a specific volume.3.1.5 insulating material (insulator), na material in whicha voltage applied between two points on

11、 or within the materialproduces a small and sometimes negligible current.3.1.6 resistivity, surface, nthe surface resistance multi-plied by that ratio of specimen surface dimensions (width ofelectrodes defining the current path divided by the distancebetween electrodes) which transforms the measured

12、 resistanceto that obtained if the electrodes formed the opposite sides ofa square.3.1.6.1 DiscussionSurface resistivity is expressed inohms. It is popularly expressed also as ohms/square (the size ofthe square is immaterial). Surface resistivity is the reciprocal ofsurface conductivity.3.2 Definiti

13、ons of Terms Specific to This Standard:3.2.1 apparent contact area, nthe area of contact betweentwo flat bodies.3.2.1.1 DiscussionIt is the area one would calculate bymeasuring the length and width of the rectangular macroscopiccontact region.3.2.2 dissipative material, na material with a volumeresi

14、stivity greater than 104ohm-cm and less than 1012ohm-cm,1This test method is under the jurisdiction of ASTM Committee D09 onElectrical and Electronic Insulating Materials and is the direct responsibility ofSubcommittee D09.12 on Electrical Tests.Current edition approved April 1, 2018. Published Apri

15、l 2018. Originallyapproved in 1985. Last previous edition approved in 2010 as D4470 97 (2010).DOI: 10.1520/D4470-18.2Vosteen, R. E., and Bartnikas, R., Chapter 5, “Electrostatic ChargeMeasurements,” Engineering Dielectrics, Vol. IIB, Electrical Properties of SolidInsulating Materials, Measurement Te

16、chniques, R. Bartnikas, Editor, ASTM STP926, ASTM, Philadelphia, 1987.3For 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

17、 website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment

18、 of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1a resistivity range between conductive and insulating materialas defined in this test method.3.2.3 real contact area, nthe regions of contact betweentwo bodies

19、through which mechanical actions or reactions aretransferred.3.2.3.1 DiscussionSince real bodies are never perfectlysmooth, at least on a microscopic scale, the real contact area ofapparently flat materials is always less than the apparentcontact area.3.2.4 triboelectric charge generationthe formati

20、on, withor without rubbing, of electrostatic charges by separation ofcontacting materials.44. Significance and Use4.1 Whenever two dissimilar materials are contacted andseparated, excess electrostatic charge (triboelectric charge) willbe found on these materials if at least one of the materials is a

21、good insulator. This excess charge gives rise to electric fieldswhich can exert forces on other objects. If these fields exceedthe breakdown strength of the surrounding gas, a disruptivedischarge (spark) can occur. The heat from this discharge canignite explosive atmospheres, the light can fog photo

22、sensitizedmaterials, and the current flowing in a static discharge cancause catastrophic failure of solid state devices. Electric forcescan be used beneficially, as in electrostatic copying, spraypainting and beneficiation of ores. They can be detrimental aswhen they attract dirt to a surface or whe

23、n they cause sheets tostick together. Since most plastic materials in use today havevery good insulating qualities, it is difficult to avoid generationof static electricity. Since it depends on many parameters, it isdifficult to generate static electricity reliably and reproducibly.5. Apparatus5.1 C

24、harging MechanismsThe charging mechanisms canbe constructed in a variety of ways; preferably it will be madeas analogous to the particular application as possible. Someexamples of charging mechanisms are described in 5.1.1, 5.1.2,and 5.1.3.5.1.1 Powder or Liquids Transported Through Tubes orDown Tro

25、ughsContact between the specimen and wall of thetube will charge the specimen or the tube, or both. Either thespecimen or the tube must be insulating, or partially insulating.When the specimen is separated from the tube, electrostaticcharge will be generated. This charge can be measured bycatching a

26、 known amount of the specimen in a Faraday cage,or measuring the charge remaining on the tube. It is permissiblefor trough to be substituted for the tube and gravity used toaffect the movement of the specimen along the trough.5.1.2 Webs Transported Over RollersContact between theweb and the roller s

27、urface will charge the web if it is aninsulator or partial insulator. If the rollers are insulators orpartial insulators they will become charged thus lowering, oreliminating, the charge transfer to the web after a period oftime. The electric field on the web can be measured with afieldmeter, or the

28、 charge on the web can be measured with acylindrical Faraday cage if the width of the web is not toolarge.5.1.3 Transport of Insulating or Partially Insulating SheetMaterialSheet materials are able to be transported on airlayers, by sliding down chutes, by vacuum platens, and bypinch rollers. Of the

29、se types of transport, pinch rollers andsliding down chutes generate the largest amount of charge.Generally, the better the contact (larger real contact area), thegreater will be the charge generated. Pinch rollers are usuallya high pressure, small apparent area of contact, leading to arelatively la

30、rge real area of contact between the sheet androllers. Sliding serves to multiply the real area of contact overthat which would be obtained with a contact without sliding.5.2 Electrostatic Charge MeasurementsFig. 1 shows ablock diagram of the typical components necessary for thismeasurement while Fi

31、g. 2 shows a schematic diagram.5.2.1 Faraday CageThe Faraday cage consists of twoconducting enclosures, one enclosed and insulated from theother. The inner enclosure is electrically connected to the shuntcapacitors and the electrometer input. It is insulated from theouter enclosure by rigid, very hi

32、gh resistance, insulators whichhave resistance practically independent of relative humidity (anexample is polytetrafluoroethylene (PFTE). The inner enclo-sure shall be of such construction that the test specimen can besubstantially surrounded by it. The outer enclosure is con-nected to ground and se

33、rves to shield the inner enclosure fromexternal fields which could affect the measurement.5.2.2 Shunt CapacitorsIt is possible shunt capacitors willbe be necessary to reduce the measured voltage to a rangewhere it can be read by the electrometer. Such shunt capacitorsmust have very low leakage insul

34、ation relatively unaffected byrelative humidity changes (for example, polystyrene). Keepthem short-circuited when not in use and protected from highrelative humidity.5.2.3 ElectrometerThe electrometer voltmeter measuresthe voltage developed on the Faraday cage and shunt capaci-tors. The electrometer

35、 must have a high impedance (such as100 T or higher) and a low drift rate concordant with the timeof measurement. Electrometers are available with built-inshunt capacitors selected by a range switch. Electrometers arealso available with negative feedback circuits which minimizethe effect of input ca

36、pacity. These circuits reduce the inputvoltage drop to nearly zero minimizing the effects of leakage ofcharge to ground and polarization of insulators.5.2.4 Display UnitThe display unit indicates the voltagedeveloped on the electrometer. If the input capacitance isknown and does not vary, or if nega

37、tive feedback is used, the4Shashoua, V. E., “Static Electricity in Polymers: Theory and Measurement,”Journal of Polymer Science, Vol XXXIII, 1958, pp 6585.FIG. 1 Block Diagram of Apparatus for Measurement of Electro-static ChargeD4470 182display unit can be calibrated to measure the charge on theFar

38、aday cage directly. The unit can be a meter showing theinstantaneous value or be a more complicated equipment, suchas a strip chart recorder giving a reading as a function of time.The electrometer and display unit can be combined in oneinstrument.5.2.5 Electrical Connnections:5.2.5.1 Connections to

39、Faraday CageConnections fromthe inner enclosure of the Faraday cage to the shunt capacitorsand the electrometer must be highly insulated and well shieldedfrom external electric fields. They will preferably be stable intime and in the different ambient conditions in which measure-ments are made. Pref

40、erably, they will be rigid, although it ispermissible for shielded cable to be used if it is low noise cablewhere flexing will not lead to the generation of static chargebetween the shield and the insulation of the cable. When usingcable or rigid connections, the capacitance of these must beconsider

41、ed when calculating or measuring the capacitance ofthe input system, unless using an electrometer with negativefeedback.5.2.5.2 Connections to Display UnitNo special connect-ing wires are normally necessary between the electrometeroutput and the display unit. Manufacturers recommendationsshall be fo

42、llowed when connecting an external display unit tothe electrometer output.5.3 Electric Field Strength MeasurementsThe diagram ofFig. 3 illustrates the major parts of a commercially availablerotating vane fieldmeter. A commercially available vibratingplate fieldmeter is illustrated in Fig. 4. The set

43、up required forcalibration of a fieldmeter is shown in Fig. 5.5.3.1 Rotating Vane FieldmeterIn Fig. 1 an electrostati-cally charged material placed at a known distance from thesensing unit will induce electrostatic charge in the face of thesensing unit, the rotating vane, and the fixed sensor plate.

44、When the rotating vane covers the sensor plate, the inducedcharge in the sensor is small. When the opening in the rotatingvane is opposite the sensor, the induced charge in the sensor isa maximum. Thus the rotating vane produces a periodicallyvarying electrical signal on the sensor plate. This signa

45、l isamplified, processed, and read on a suitable display unit. Thesefieldmeters can be made polarity-sensitive by inducing acharge of known polarity on the sensor with an internal sourceor by phase detection circuitry. Efforts must be made toadequately shield the sensor and associated circuits from

46、noisegenerated by the motor driving the rotating vane.5.3.2 Vibrating Plate FieldmeterIn Fig. 2 a vibratingsensor plate is enclosed in a sensing unit. A charged materialplaced in front of the sensing unit induces a charge in the faceplate and in the sensor. As the sensor moves away from thecharged m

47、aterial, less charge is induced on the sensor. As itmoves toward the charged material, more charge is induced onthe sensor. This produces a periodically varying electricalsignal on the sensor plate. This signal is amplified, processed,and read on a suitable display unit. Charge polarity is deter-min

48、ed by phase detection circuits. Again, the sensor andassociated circuits must be adequately shielded from noisegenerated by the driving mechanism.5.3.3 Display UnitThe display unit can contain the powerswitch, circuits to process the signal (amplifiers, rectifiers,phase detectors, and the like), and

49、 a meter showing theinstantaneous value of the electric field. Alternatively, a stripchart recorder giving a reading as a function of time ispermissible.6. Test Conditions6.1 Static electrification depends upon many parameters. Toobtain reproducible results apparatus must be constructed tocontrol all the measurable parameters and to keep all theunmeasurable parameters constant. The known parameters areas follows:6.1.1 Cleanliness of Material SurfacesStatic electrifica-tion of contacting materials is a surface phenomenon. Thus, thesurfaces must be kept