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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 2918-1998 Plastics - Standard atmospheres for conditioning and testing. In addition to editorial changes, the following technical changes have been made with respect to GB/T 2918-1998:
——“Clause 2 Normative references" is added (see Clause 2);
——the use conditions of standard atmosphere at all levels, "23/50 is applicable to non-tropical countries and 27/65 is applicable to tropical countries” are added, and the content "when obtaining comparative data on polymers, e.g. for databases, standard atmosphere 23/50 shall be used” is specified (see Clause 5);
——the calibration frequency is added (see Clause 6);
——the method for determining the adjustment time of sample state when the equilibrium cannot be reached for a long time is modified (see Annex A).
This standard has been redrafted and modified in relation to ISO 291:2008 Plastics - Standard atmospheres for conditioning and testing.
The main technical deviations with respect to ISO 291:2008 and their justifications are as follows:
——the adjustments of technical deviations are made for the normative references in this standard so as to adapt to the technical conditions of China. The adjustments are mainly reflected in Clause 2 "Normative reference", which are shown in the following:
ISO 62 is replaced by GB/T 1034, which is identical to the international standard.
——the content of Note 2 in 8.1 is modified to paragraph;
——the content of Note 3 in 8.1 is modified to paragraph.
In addition, the following editorial changes have been made in this standard:
——the informative Annex B "Background information" of ISO 291:2008 is deleted.
——the bibliography is deleted.
This standard was proposed by the China Petroleum and Chemical Industry Association.
This standard is under the jurisdiction of SAC/TC 15 National Technical Committee on Plastic of Standardization Administration of China.
The previous editions of this standard are as follows:
——GB/T 2918-1982 and GB/T 2918-1998.
Plastics - Standard atmospheres for conditioning and testing
1 Scope
This standard specifies the specifications relating to the conditioning and testing of all plastics and all types of specimen at constant atmospheric conditions.
This standard is applicable to all plastics and all types of specimen.
Special atmospheres applicable to a particular test or material or simulating a particular atmosphere are not included in this standard.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 1034 Plastics - Determination of water absorption (GB/T 1034-2008, ISO 62:2008, IDT)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
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.
Note 2: Standard atmospheres correspond to the average atmospheric conditions in laboratories and can be established in conditioning (controlled atmosphere) cabinets, chambers or rooms.
3.2
conditioning atmosphere
constant atmosphere in which a sample or specimen is kept before being subjected to a test
3.3
test atmosphere
constant atmosphere to which a sample or specimen is exposed throughout a test
3.4
conditioning
one or more operations intended to bring a sample or specimen into a state of equilibrium with regard to temperature and humidity
3.5
conditioning procedure
combination of the conditioning atmosphere and the period of conditioning
3.6
ambient temperature
atmosphere conditions corresponding to the usual atmospheric conditions in laboratories with uncontrolled temperature and humidity
Note: The phrase “at ambient temperature” refers to an atmosphere the air temperature of which lies within a specified range, no consideration being given to relative humidity, atmospheric pressure or air-circulation velocity. In general, the air-temperature range extends from 18℃ to 28℃ and is stated as “at an ambient temperature of 18℃ to 28℃”.
4 Principle
If a specimen is exposed to a specific conditioning atmosphere or temperature, then a reproducible state of temperature and/or of moisture equilibrium is reached between the specimen and the conditioning atmosphere or temperature.
It is not the intent of this standard to define procedures specifying how to determine sensitivity to moisture.
Some materials may have special conditioning requirements. Follow the relevant material standards.
5 Standard atmosphere
Unless otherwise specified, use one of the sets of conditions given in Table 1 as the standard atmosphere.
Table 1 Standard atmospheres
Symbol for standard atmosphere Air temperature/℃ Relative humidity (RH)/% Remarks a
23/50 23 50 For non-tropical countries
27/65 27 65 For tropical countries
a When obtaining comparative data on polymers, e.g. for databases, standard atmosphere 23/50 shall be used.
Note: The values in Table 1 apply to normal altitudes with an atmospheric pressure between 86kPa and 106kPa and an air-circulation velocity ≤1m/s.
Foreword I
1 Scope
2 Normative references
3 Terms and definitions
4 Principle
5 Standard atmosphere
6 Classes of standard atmosphere
7 Standard temperature and ambient temperature
8 Procedures
