ASTM_E_145_-_94_2011.pdf

Designation:E14594(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 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.Scope1.1 This specification covers the performance requirementsfor general-purpose air ovens ordinarily used in testingoperations,which have a testing chamber up to 0.6 m3(25 ft3)in volume.It is applicable to gravity-convection ovens de-signed to operate over all or part of the temperature range from20C above ambient temperature to 200C and to forced-ventilation ovens designed to operate over all or part of thetemperature range from 20C above ambient temperature to500C.NOTE1Ovens are designed for maximum operating temperatures ofabout 200C,300C,and 500C,the thermal insulation and cost of theoven being dependent on the maximum temperature 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.Types2.1 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 temperature 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 temperature 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 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 of 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-constantan 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 place 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.NOTE2If calibrated thermocouples are not available,nine thermo-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 temperatures 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 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 SubcommitteeE41.06Weighing Devices.Current edition approved Dec.1,2011.Published December 2011.Originallyapproved in 1959.Last previous edition approved in 2006 as E145 94(2006).DOI:10.1520/E0145-94R11.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 NOTE3Some ovens may require as much as 24 h to reach a steadystate.If a steady state does not exist,there is a drift 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 c