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This Standard is identical to international standard ISO 291:1997 "Plastics — Standard Atmospheres for Conditioning and Testing". Technical contents and redaction method of this Standard are equivalent to ISO 291:1997, except some editorial changes base on China's national conditions.
Previous edition of this Standard is GB/T 2918-1982 "Plastics-Standard Atmospheres for Conditioning and Testing" Compared with the preceding edition, main technical content changes are as follows:
1. Standard atmosphere was changed from (23/50) into (23/50 and 27/65).
2. Tolerance of temperature and relative humidity was changed form "only consider about time deviation" into "consider about either time deviation or deviation of sample position in the test atmosphere".
3. Grade 1 tolerance of relative humidity was changed form "± 2 %" into "± 5 %", and Grade 2 tolerance of relative humidity was changed form "± 5 %" into "± 10 %".
4. Humidity requirements in relation to two types of atmosphere "standard temperature" and "room temperature", which was changed form "normal humidity (i.e. 45 % ~ 75 %)" into "do not have to control relative humidity".
5. "Normal temperature" was changed into "room temperature", and the temperature range was changed from "10 ℃ ~ 35 ℃" into "18 ℃ ~ 28 ℃".
6. For the period of conditioning, supplement the requirements of "a minimum of 4 h for ambient temperatures of 18 ℃ to 28 ℃" in this Standard.
7. Supplement the three terms and definitions of "standard atmosphere", Chapter 3 "Principle", Appendix A and Appendix B in this Standard.
This Standard replaces GB/T 2918-1982 from the implementation date hereof.
Appendix A of this Standard is normative, and Appendix B is informative.
This Standard was proposed by the Ministry of Chemical Industry of the People's Republic of China.
This Standard is under the jurisdiction of National Technical Committee on Plastic of Standardization Administration of China - Subcommittee on product (SC 4).
Drafting organizations of this Standard: Chenguang Chemical Research Institute of the Ministry of Chemical Industry.
Participating drafting organizations of this Standard: Sichuan University, Beijing Institute of Aeronautical Materials, Beijing Plastics Research Institute and Shanghai Plastics Research Institute.
Chief drafting staff of this Standard: Wang Yongming.
First issue time of this Standard: March 2, 1982.
ISO Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
ISO 291 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 6, Ageing, Chemical and Environmental Resistance.
This second edition of ISO 291 cancels and replaces the first edition (ISO 291:1977), which has been technically revised.
Annex A of this International Standard is an indispensable part of this document, and Annex B is for information only.
NATIONAL STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
中华人民共和国国家标准
Plastics — Standard Atmospheres for Conditioning and Testing
塑料试样状态调节和试验的标准环境
GB/T 2918-1998
idt ISO 291:1997
Replace GB/T 2918-1982
1 Scope
This Standard sets out specifications relating to the conditioning and testing of all plastics and all types of test specimens at constant atmospheric conditions which correspond to the average atmospheric conditions in laboratories.
Special atmospheres applicable to a particular test or material or simulating a particular climatic environment are not included in this Standard.
2 Definitions
For the purposes of this International Standard, the following definitions apply:
2.1 Standard atmosphere
Preferred constant atmosphere for which specific air temperature and humidity values, as well as limit ranges for atmospheric pressure and air-circulation velocity, are specified, the air not having any significant additional constituents and the atmosphere not being subject to any significant additional radiation influences.
Note:
1 Standard atmospheres permit a defined state to be attained and maintained for samples or specimens.
2 Standard atmospheres correspond to the average atmospheric conditions in laboratories and can be established in conditioning (controlled atmosphere) cabinets, chambers or rooms.
2.2 Conditioning atmosphere
Constant atmosphere in which a sample or test specimen is kept before being subjected to test.
2.3 Test atmosphere
Constant atmosphere to which a sample or test specimen is exposed throughout the test.
2.4 Conditioning
One or more operations intended to bring a sample or test specimen into a state of equilibrium with regard to temperature and humidity.
2.5 Conditioning procedure
Combination of the conditioning atmosphere and the period of conditioning.
Note 3: In this Standard the conditioning atmosphere and the test atmosphere are usually selected as the standard atmosphere.
2.6 Ambient temperature
Environmental conditions corresponding to the usual atmospheric conditions in laboratories with uncontrolled temperature and humidity.
3 Principle
If a test specimen is exposed to a specific conditioning atmosphere or temperature, then a reproducible state of temperature and/or moisture equilibrium is reached between the test specimen and the conditioning atmosphere or temperature.
4 Standard Atmospheres
Unless otherwise specified, use the conditions given in Table 1 as the standard atmosphere.
Table 1 Standard Atmospheres
Symbol for standard atmosphere Air temperature t
℃ Relative humidity U
% Remarks
23/50 23 50 Shall be used unless otherwise specified
27/65 27 65 May be used for tropical countries if agreed on by all parties
Note 4: The values in Table 1 apply to normal altitudes with an atmospheric pressure between 86 kPa and 106 kPa and an air-circulation velocity ≤ 1 m/s.
5 Classes of Standard Atmosphere
Table 2 gives two different classes of standard atmosphere corresponding to different tolerance levels for the temperature and relative humidity. The tolerances given in Table 2 apply to the specimen-stowage space in a test enclosure or conditioning enclosure and include deviations both with respect to time and with respect to the position of the test specimen in the enclosure.
