1、Designation: D7969 15D7969 16Standard Specification forGravity Convection and Forced Ventilation Ovens1This standard is issued under the fixed designation D7969; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This specification covers the performance requirements for general purpose air ovens ordinarily used in testing operations,whic
3、h have a testing chamber up to 0.6 m3 (25 ft3) in volume.1.2 It is applicable to gravity convection ovens designed to operate over all or part of the temperature range from 20C aboveambient room temperature to 200C.1.3 It is applicable to forced ventilation ovens designed to operate over all or part
4、 of the temperature range from 20C aboveambient room temperature to 500C.1.4 This specification does not include safety requirements that are essential for ovens used in the presence of combustiblematerials.1.5 The values stated in SI units are to be regarded as the standard. The values given in par
5、entheses are for reference only andmay be approximate.1.5.1 The SI base unit of the expression of temperature is Kelvin (K), the unit of measure used in this specification is Celsius(C) and has been derived mathematically.1.6 Calibration ovens to this standard are necessary to assure their operative
6、 performance under typical conditions of use andshall be performed periodically, either according to the manufacturers recommendations, the quality requirements of the end user,their customers, or suppliers.1.7 This standard does not purport to address all of the safety concerns, if any, associated
7、with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E145 Specification for Gravity-Convection and Forced-Ventilation Ov
8、ens3. Terminology3.1 Definitions:3.1.1 ambient room temperaturea temperature as recorded, typically but not necessarily, close to room temperature.3.1.2 room temperaturea temperature in the range from 20 to 30C (68 to 86F).3.1.3 standard laboratory atmospherean atmosphere having a temperature of 236
9、2C (73.463.6F) and a relative humidityof 50 6 10 % RH (40 to 60 % RH) shall be the standard laboratory atmosphere.3.1.4 standard laboratory temperaturea temperature of 2362C (73.463.6F) shall be the standard laboratory temperature.4. Oven Types4.1 This specification covers the following four types o
10、f air ovens:4.1.1 Type IAGCAn oven ventilated by gravity convection having a uniformity of temperature within62 % of the differentialbetween oven and ambient temperatures.1 This specification is under the jurisdiction of ASTM Committee D11 on Rubber and is the direct responsibility of Subcommittee D
11、11.15 on Degradation Tests.Current edition approved July 1, 2015Jan. 1, 2016. Published September 2015January 2016. Originally approved in 2015. Last previous edition approved in 2015 asD7969 15. DOI: 10.1520/D7969-15.10.1520/D7969-16.2 For referencedASTM standards, visit theASTM website, www.astm.o
12、rg, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what chang
13、es have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the offici
14、al document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.1.2 Type IBGCAn oven ventilated by gravity convection having a uniformity of temperature within65 % of the differentialbetween oven and ambient temperatures.4.1.3 Type IIAF
15、VAn oven having forced ventilation and a uniformity of temperature within 61 % of the differential betweenoven and ambient temperatures.4.1.4 Type IIBFVAn oven having forced ventilation and a uniformity of temperature within62.5 % of the differential betweenoven and ambient temperatures.5. Performan
16、ce Requirements5.1 The temperature within the testing chamber shall be controllable by an automatic device, and shall be uniform within thetolerances given in Table 1 for the particular type of oven when tested in accordance with Section 6.5.1.1 Conformance to temperature uniformity (Section 6) is a
17、 requirement.5.2 The time constant measurement is nonmandatory and is found in Appendix X1 of this specification.5.3 The rate of ventilation of the testing chamber shall conform to the requirements specified in Table 1 for the particular typeof oven when measured in accordance with the procedure giv
18、en in Section 7.5.3.1 Conformance to the rate of ventilation (Section 7) is a requirement.TEST PROCEDURES6. Temperature Uniformity6.1 Place nine calibrated thermocouples approximately 0.5 mm in diameter (No. 24 gauge) and having a junction size of notmore than 2 mm (0.08 in.), in a clean, properly m
19、aintained, empty testing chamber with any shelves or commonly usedappurtenances in place and all vents fully open.6.1.1 Locate one thermocouple in each of the eight corners of the oven approximately 50 mm (2 in.) from each wall.6.1.2 Place the ninth thermocouple within 25 mm (1 in.) of the geometric
20、 center of the chamber.6.1.3 A minimum length of 300 mm (12 in.) of lead wire for each thermocouple shall be inside the oven to minimize theconduction of heat from the thermocouple.6.2 The ambient room temperature shall not vary during the duration of the test by more than a total of 10C as measured
21、 bya tenth thermocouple placed externally no less than 2 m (78 in.) from the oven and not in contact with materials known to radiateheat or be thermally conductive, preferably suspended at the approximate midpoint height of the oven.6.3 Bring the oven to the specified temperature and allow it to rea
22、ch a steady state.6.3.1 It may require as much as 24 hours to reach a steady state, that is no more than the deviation from the specified temperaturedifferential as indicated in Table 1 for a period of no less than three hours prior to assessment.6.3.2 If a steady state is not achieved, a drift in t
23、he temperature toward the steady-state condition should exist and be within3C of the desired testing temperature (set point) at the time of assessment.6.4 Record the temperatures of the ten thermocouples for a period of no less than three hours at intervals of no greater than 15minutes, and determin
24、e, from the record, the maximum deviation of each point from the desired temperatures.6.5 Report the results of the recorded observations from each of the ten thermocouples including the time period for which theywere obtained.7. Rate of Ventilation7.1 Position a calibrated, digital, vane anemometer
25、, capable of accounting for the diameter of the vane opening diameter andcalculating the volume of air flow, securely to the ovens air exhaust port so that all air exhausted from the oven passes throughthe vane area and does not circumvent it.TABLE 1 Performance Requirements for OvensCharacteristic
26、Type IAGC Type IBGC Type IIAFV Type IIBFVDeviation from specified temperature of test throughout testingchamber during 3 h period for the following differentials betweenambient and test temperatures:#50C | maximum percent of differential 1.0 2.5 0.5 1.2550C | maximum percent of differential 2.0 5.0
27、1.0 2.5Rate of ventilation testing chamber, air changes per hour:Minimum 10 10 50 50Maximum 200 200D7969 1627.1.1 In instances where positioning the anemometer is not possible due to encumbrances of exhaust hoods, permanentlymounted vents, etc., the procedure in E145, Part 5, should be followed and
28、reported accordingly.7.2 Heat the oven to a temperature of 20 6 2C above the ambient room temperature and, while at this temperature, record theairflow through the vane anemometer for a period of at least 30 minutes.min.7.2.1 Calculate the number of changes per hour considering the volume of the cha
29、mber, the air flow recorded by the vaneanemometer, and the time during which the air flow was recorded and report the result as demonstrated in Eq 1.7.2.2 It may be desirable to determine the rate of ventilation at temperatures above the range of a vane anemometer, in whichcase a high temperature (a
30、lso known as a hot-wire or thermal anemometer) may be used following the procedure for a vaneanemometer.7.3 The ambient room temperature shall be measured as described in 6.2 for the duration of the test.7.4 Calculate the number of changes per hour of the air in the test chamber from the following e
31、quation:N5SevD 360 (1)where:N = number of air changes per hours,v = volume of the testing chamber (ft3 or m3), ande = exhaust air flow measured by a vane anemometer per minute (cfm or cmm).NOTE 1It is important, when performing the above calculation, that the units of measure are in agreement, for e
32、xample, ft3 and cubic foot per minute(cfm); m3 and cubic metres per minute (cmm).8. Keywords8.1 forced-ventilation; gravity-convection; ovensAPPENDIXES(Nonmandatory Information)X1. TIME CONSTANTX1.1 The “time constant” is an arbitrary measure of the rate at which a standard specimen is heated follow
33、ing the procedureprescribed below. The value of the time constant should not exceed the maximum value given in Table X1.1 for the particular typeof oven.X1.1.1 Conformance to the time constant is not a requirement, but may be valuable in assessing the ovens performance in routineservice. It should b
34、e studied when other parameters are questioned.TABLE X1.1 Time Constant Performance Requirements for OvensNOTE 1Time constant only, other values for reference only, refer to Table 1 in this specification.Characteristic Type IAGC Type IBGC Type IIAFV Type IIBFVDeviation from specified temperature of
35、test throughout testing chamberduring 3 h period for the following differentials between ambient and testtemperatures:#50C | maximum percent of differential 1.0 2.5 0.5 1.2550C | maximum percent of differential 2.0 5.0 1.0 2.5Time constant, maximum seconds 600 720 480 660Rate of ventilation of testi
36、ng chamber, air changes per hour:Minimum 10 10 50 50Maximum 200 200D7969 163X2. PROCEDUREX2.1 Heat the oven to within 10C of the maximum operating temperature for which it is designed and allow it to stabilize forat least 1 h.X2.2 Alternatively, heat the oven to within 10C of the operating temperatu
37、re for which it is typically used and allow it to stabilizefor at least 1 h.X2.3 Prepare a standard specimen consisting of a smooth brass cylinder 9.5 6 0.1 mm (0.375 6 0.005 in.) in diameter and 576 1 mm (2.25 6 0.05 in.) in length, and solder one junction of a differential thermocouple to it.X2.4
38、Open the door of the oven for 1 min while the standard specimen and differential thermocouple are being suspended in thetesting chamber. Suspend the specimen vertically within 25 mm (1 in.) of the geometric center of the chamber by means of a cordof fine wire (0.3 mm maximum diameter, No. 30 gauge).
39、X2.5 Place the free junction of the differential thermocouple in the air space of the chamber at least 75 mm (3 in.) removed fromthe specimen.X2.6 Close the door and either record or measure the temperature differential every 10 s.X2.7 Determine the time in seconds required for the temeprature diffe
40、rence to decrease to one tenth of the original or maximumvalue (for example, from 120 to 12C) and consider this to be the time constant of the oven and report accordingly.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedi
41、n this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and mu
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