1、Designation: E145 94 (Reapproved 2011)Standard Specification forGravity-Convection and Forced-Ventilation Ovens1This standard is issued under the fixed designation E145; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast 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 Department of Defense.1. Scope1.1 This specification covers the performa
3、nce requirementsfor general-purpose air ovens ordinarily used in testing opera-tions, which have a testing chamber up to 0.6 m3(25 ft3)involume. It is applicable to gravity-convection ovens designedto operate over all or part of the temperature range from 20Cabove ambient temperature to 200C and to
4、forced-ventilationovens designed to operate over all or part of the temperaturerange from 20C above ambient temperature to 500C.NOTE 1Ovens are designed for maximum operating temperatures ofabout 200C, 300C, and 500C, the thermal insulation and cost of theoven being dependent on the maximum temperat
5、ure required.1.2 This specification does not include safety requirementsthat are essential for ovens used in the presence of combustiblevapors or gases.1.3 The values stated in inch-pound units are to be regardedas the standard. The metric equivalents of inch-pound unitsmay be approximate.2. Types2.
6、1 This specification covers the following four types of airovens:2.1.1 Type IAAn oven ventilated by gravity convectionhaving a uniformity of temperature within 62 % of thedifferential between oven and ambient temperatures.2.1.2 Type IBAn oven ventilated by gravity convectionhaving a uniformity of te
7、mperature within 65 % of thedifferential between oven and ambient temperatures.2.1.3 Type IIAAn oven having forced ventilation and auniformity of temperature within 61 % of the differentialbetween oven and ambient temperatures.2.1.4 Type IIBAn oven having forced ventilation and auniformity of temper
8、ature within 62.5 % of the differentialbetween oven and ambient temperatures.3. Performance Requirements3.1 The temperature within the testing chamber shall becontrollable by an automatic device, and shall be uniformwithin the tolerances given in Table 1 for the particular type ofoven when tested in
9、 accordance with Section 4.3.2 The “time constant” is an arbitrary measure of the rate atwhich a standard specimen is heated following the procedureprescribed in Section 5. The value of the time constant shall notexceed the maximum value given in Table 1 for the particulartype of oven.3.3 The rate o
10、f ventilation of the testing chamber shallconform to the requirements specified in Table 1 for theparticular type of oven when measured in accordance with theprocedure given in Section 6.TEST METHODS4. Temperature Uniformity4.1 Place nine calibrated thermocouples (Note 2) made fromiron or copper-con
11、stantan wire, approximately 0.5 mm indiameter (No. 24 gauge) and having a junction size of not morethan 2 mm (0.08 in.), in the empty testing chamber withshelves in place and vents open. Locate one thermocouple ineach of the eight corners of the oven approximately 5 cm (2 in.)from each wall and plac
12、e the ninth thermocouple within 2.5 cm(1 in.) of the geometric center of the chamber. A minimumlength of 30 cm (12 in.) of lead wire for each thermocoupleshall be inside the oven to minimize the conduction of heatfrom the thermocouple.NOTE 2If calibrated thermocouples are not available, nine thermo-
13、couples made from the same spool of wire may be used provided they givethe same value for temperature when placed adjacent to one another in thetesting chamber at the temperature of test.4.2 Bring the oven to the specified temperature and allow itto reach a steady state (Note 3). Record the temperat
14、ures of thenine thermocouples for a period of at least 24 h, and determinefrom the record the maximum deviation of each point from thedesired temperatures. The ambient room temperature shall varyby not more than a total of 10C, and the line voltage forelectrically heated ovens shall vary by not more
15、 than a total of5 % during the test.1This specification is under the jurisdiction of ASTM Committee E41 onLaboratory Apparatus and is the direct responsibility of Subcommittee E41.01Apparatus.Current edition approved Dec. 1, 2011. Published December 2011. Originallyapproved in 1959. Last previous ed
16、ition approved in 2006 as E145 94 (2006).DOI: 10.1520/E0145-94R11.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.NOTE 3Some ovens may require as much as 24 h to reach a steadystate. If a steady state does not exist, there is a drift
17、 in the temperaturetoward the steady-state condition.5. Time Constant5.1 Heat the oven to within 10C of the maximum operatingtemperature for which it is designed and allow it to stabilize forat least 1 h. Prepare a standard specimen consisting of a smoothbrass cylinder 9.5 6 0.1 mm (0.375 6 0.005 in
18、.) in diameterand 57 6 1 mm (2.25 6 0.05 in.) in length, and solder onejunction of a differential thermocouple to it.5.2 Open the door of the oven for 1 min while the standardspecimen and differential thermocouple are being suspended inthe testing chamber. Suspend the specimen vertically within 25mm
19、 (1 in.) of the geometric center of the chamber by means ofan asbestos cord of fine wire (0.3 mm maximum diameter, No.30 gauge). Place the free junction of the differential thermo-couple in the air space of the chamber at least 75 mm (3 in.)removed from the specimen. Then close the door and eitherre
20、cord or measure the temperature differential every 10 s.Determine the time in seconds required for the temperaturedifference to decrease to one tenth of the original or maximumvalue (for example, from 120C to 12C) and consider this tobe the time constant of the oven.6. Rate of Ventilation (Note 4)6.
21、1 Seal the ventilation ports, door, and all apertures ofelectrically heated ovens with adhesive tape or by other meansto prevent any air from passing through the oven (Note 5).Connect a watt-hour meter, with the smallest division readingin 0.01 Wh in the electrical supply line to the oven.NOTE 4This
22、 method is only applicable to electrically heated ovens.Methods are being developed by the committee for determining the rate ofventilation of ovens that are not electrically heated and for determining theuniformity of air-flow within the testing chamber.NOTE 5In forced-ventilation ovens, the space
23、around the motor shaftwhere it enters the oven must be closed, but the fan speed must not beaffected by the closure.6.2 Heat the oven to a temperature of 80 6 2C above theambient room temperature, and while at this temperaturemeasure the consumption of electrical energy for a period of atleast 1/2 h
24、. Start and stop the test at corresponding points of the“on-off” heating cycle, that is, at the moment when the heatersare switched on by the thermostat.6.3 Then remove the seals, open the ventilation ports, andmeasure the consumption of electrical energy in the samemanner. The ambient room temperat
25、ure measured at a pointapproximately2m(6ft)from the oven, approximately levelwith its base and at least 0.6 m (2 ft) from any solid object,shall be the same within 0.2C during the two tests.6.4 Calculate the number of changes per hour of the air inthe test chamber from the following equation:N 5 359
26、0 X 2 Y!/VDDT (1)where:N = number of air changes per hour,X = average power consumption during ventilation, W,obtained by dividing the energy consumption deter-mined from the watt-hour meter readings by theduration of the test in hours,Y = average power consumption with no ventilation,computed in th
27、e same manner, W,V = volume of the testing chamber, cm3,D = density of the ambient room air during the test,g/cm3, andDT = difference in temperature between the testing cham-ber and the ambient room air, C.7. Keywords7.1 forced-ventilation; gravity-convection; ovensTABLE 1 Performance Requirements f
28、or OvensCharacteristic Type IA Type IB Type IIA Type IIBDeviation from specified temperature of test throughout testing chamber during24-h period for the following differentials between ambient and test temperatures:50C or less, max, C 1 2.5 0.5 1.25More than 50C, max, percent of differential 2 5 1
29、2.5Time constant, max, s 600 720 480 660Rate of ventilation of testing chamber, air changes per hour:min 10 10 50 50max . . 200 200E145 94 (2011)2ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of
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31、 years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical co
32、mmittee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA
33、19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).E145 94 (2011)3
