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GB/T 7762-2014: Rubber, vulcanized or thermoplastic -- Resistance to ozone cracking -- Static strain test Delivery: 9 seconds. True-PDF full-copy in English & invoice will be downloaded + auto-delivered via email. See step-by-step procedure Status: Valid GB/T 7762: Historical versions
Similar standardsGB/T 7762-2014: Rubber, vulcanized or thermoplastic -- Resistance to ozone cracking -- Static strain test---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/GBT7762-2014 GB NATIONAL STANDARD OF THE PEOPLE’S REPUBLIC OF CHINA ICS 83.060 G 40 Replacing GB/T 7762-2003 Rubber, vulcanized or thermoplastic – Resistance to ozone cracking – Static Strain Test (ISO 1431-1.2004, Rubber, vulcanized or thermoplastic -Resistance to ozone cracking – Part 1.Static and dynamic strain testing, NEQ) Issued on. DECEMBER 22, 2014 Implemented on. JUNE 1, 2015 Issued by. General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China; Standardization Administration of the People's Republic of China. Table of ContentsForeword... 3 1 Scope... 5 2 Normative references... 5 3 Terms and definitions... 6 4 Principle... 6 5 Apparatus... 6 6 Test pieces... 10 7 Conditioning... 11 8 Test conditions... 12 9 Static strain testing... 13 10 Expression of results... 14 11 Test report... 16 Annex A (Informative) Ozone cracking – Explanatory notes... 18 Annex B (Informative) Method for the determination of ozone concentration – Iodometric titration method... 201 ScopeThis Standard specifies procedures intended for use in estimating the resistance of vulcanized or thermoplastic rubbers to cracking when exposed, under static tensile strain, to air containing a definite concentration of ozone and at a definite temperature in circumstances that exclude the effects of direct light. This Standard applies to rubber, vulcanized or thermoplastic. NOTE Great caution is necessary in attempting to relate standard test results to service performance since the relative ozone resistance of different rubbers can vary markedly depending on the conditions, especially ozone concentration and temperature. In addition, tests are carried out on thin test pieces deformed in tension and the significance of attach for articles in service can be quite different owing to the effects of size and of type and magnitude of the deformation. Explanatory notes on the natural ageing under ozone cracking are given in Annex A.2 Normative referencesThe following referenced documents are indispensable for the application of this document. For dated references, only the edition dated applies to this document. For undated references, the latest edition of the referenced document (including any amendments) applies to this Standard. GB/T 528-2009, Rubber, vulcanized or thermoplastic – Determination of tensile stress-strain properties (ISO 37.2005, IDT) GB/T 2941-2006, Rubber – General procedures for preparing and conditioning test pieces for physical test methods (ISO 23529.2004, IDT) GB/T 11206-2009, Standard test method for rubber deterioration – Surface cracking3 Terms and definitionsFor the purpose of this document, the following terms and definitions apply. 3.1 threshold strain highest tensile strain at which a rubber can be exposed at a given temperature to air containing a given concentration of ozone without ozone cracks developing on it after a given exposure period4 PrincipleTest pieces of rubber vulcanized or thermoplastic are exposed, under static tensile strain, in a closed chamber at a constant temperature, to an atmosphere containing a fixed concentration of ozone. The test pieces are examined periodically for cracking. Three alternative evaluation procedures are described for selected values of ozone concentration and exposure temperature.5 Apparatus5.1 Test chamber This shall be a closed, non-illuminated chamber, thermostatically controlled to within ± 2°C of the test temperature, lined with, or constructed of, a material (for example aluminium) that does not readily decompose ozone. The chamber can be provided with a window through which the surface of the test pieces can be observed. A light to examine test pieces can be installed, but this shall remain switched off at all other times. 5.2 Source of ozonized air The ozonized air shall be largely free of nitrogen oxides in order to avoid errors in the ozone concentration. One of the following items of apparatus shall therefore be used. 5.3 Means of adjusting the ozone concentration When an ultra-violet lamp is used, the ozone concentration can be controlled by adjusting either the voltage applied to the tube or the input-gas flow rate, or by shielding part of the tube from the UV light. 5.4 Means of determining the ozone concentration A means of sampling the ozonized air from the vicinity of the test pieces in the chamber and a means of estimating the ozone content are specified in ISO 1431-3.If required, the methods given in Annex B can also be a reference. 5.5 Means of adjusting the gas flow A mechanism shall be provided that is capable of adjusting the average velocity of the flow of ozonized air in the test chamber to a value of not less than 8 mm/s and preferably to a value between 12 mm/s and 16 mm/s, calculated from the measured gas flow rate in the chamber divided by the effective cross-sectional area of the chamber normal to the gas flow. 5.6 Mounting test pieces for static strain testing Clamps shall be provided to hold the test pieces at the required elongation and with both sides in contact with the ozonized air in such a manner that the longitudinal axis of each test piece is substantially parallel to the direction of gas flow. The clamps shall be made of a material (for example aluminium) which does not readily decompose ozone.6 Test pieces6.1 Standard test pieces shall be as specified in 6.2 or 6.3. Test pieces shall be cut from moulded sheet, or, if required, from a finished product, in accordance with GB/T 2941-2006.Test pieces shall have an undamaged test surface; ozone resistance shall not be assessed on surfaces that have been cut or buffed. 6.2 Wide test piece This test piece shall consist of a strip of not less than 10 mm in width, of thickness 2.0 mm ± 0.2 mm and of length not less than 40 mm between the grips before stretching. The ends of the test piece held in the grips can be protected with an ozone-resistant lacquer. Care shall be taken when selecting the lacquer to ensure the solvent used does not appreciably swell the rubber. 6.3 Narrow test piece This test piece shall consist of a strip of width 2.0 ± 0.2 mm, thickness 2.0 ± 0.2 mm and length 50 mm, between enlarged tab ends 6.5 mm square (see Figure 3). This test piece shall not be used for procedure A.7 Conditioning7.1 Conditioning in the unstrained state For all tests, the minimum time between vulcanization and straining of the test pieces shall be 16 h. 7.2 Conditioning in the strained state After stretching, the test pieces shall be conditioned for a period of between 48 h and 96 h in an essentially ozone-free atmosphere in the dark; the temperature for this conditioning shall normally be a standard laboratory temperature (see GB/T 2941- 2006), but other temperatures can be used if appropriate for particular applications. The test pieces shall not be touched or otherwise disturbed in any way during the conditioning period.8 Test conditions8.1 Ozone concentration The test shall be carried out at one of the following ozone concentrations, expressed in volume fraction. 8.2 Temperature The preferred test temperature is 40°C ± 2°C. Other temperatures, such as 30°C ± 2°C or 23°C ± 2°C, can be used if they are more representative of the anticipated service environment, but the results obtained will differ from those obtained at 40°C ± 2°C. 8.3 Relative humidity The relative humidity of the ozonized air shall normally be not more than 65% at the test temperature. 8.4 Maximum elongation Tests shall normally be carried out using one or more of the following strain levels. (5 ± 1) %, (10 ± 1) %, (15 ± 2) %, (20 ± 2) %, (25 ± 2) %, (30 ± 2) %, (40 ± 2) %, (50 ± 2) %, (60 ± 2) %, (80 ± 2) %9 Static strain testing9.1 General Adjust the rate of flow and temperature of the ozonized gas and its ozone concentration to that required and place the strained test pieces suitably conditioned, in the test chamber. Maintain the test conditions at the required levels. 9.2 Procedure A Unless otherwise specified, strain the test pieces at 20% elongation, condition them in accordance with 7.2, and examine them after 72 h in the test chamber for the development of cracking (an alternative elongation and an alternative exposure period may be given in the appropriate material specification). 9.3 Procedure B Strain the test pieces at one or more of the elongations given in 8.4 and condition them in accordance with 7.2.If only one elongation is used, this shall be 20%, unless otherwise specified. Examine the test pieces after 2 h, 4 h, 8 h, 24 h, 48 h, 72 h and 96 h and, if necessary, at suitable intervals thereafter in the test chamber and note the time until the first appearance of cracks at each elongation. 9.4 Procedure C Strain the test pieces at no fewer than four of the elongations given in 8.4 and condition them in accordance with 7.2.Examine the test pieces after 2 h, 4 h, 8 h, 24 h, 48 h, 72 h and 96 h and, if necessary, at suitable intervals thereafter in the test chamber and note the time until the first appearance of cracks at each elongation so that the threshold strain can be estimated. ......Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al. 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