ASTM D572-04(R2019) pdf free download

ASTM D572-04(R2019) pdf free download.Standard Test Method for Rubber—Deterioration by Heat and Oxygen
5. Oxygen-Pressure Vessel
NOTE 2—Caution: Adequate safety provisions are important when heating oxidizable organic materials in oxygen since the rate of reaction may become very rapid in some cases, particularly if large surface area is exposed, and very high pressures may be developed. If the same equipment is used for the oxygen-pressure test and the air-pressure heat test, Test Method D454, care must be exercised to see that the thermostatic controls are properly set, since the specimens may react very rapidly with oxygen at the temperature of the air-pressure heat test. Liquids acceptable as heating media for one test may be hazardous when used for the other test. 5.1 The oxygen-pressure chamber shall consist of a metal vessel designed to retain an internal atmosphere of oxygen gas under pressure, with provisions for placing rubber specimens within it and subjecting the whole to controlled uniform temperature. Because of the superior temperature control and heat transfer, metal vessels completely immersed in a liquid medium are recommended for purposes of referee tests. The apparatus shall conform to the following requirements: 5.1.1 The size of the chamber shall be optional but shall be such that the specimens may be suspended therein vertically without undue crowding and without touching each other or the sides of the chamber. 5.1.2 The source of heat is optional but shall be located outside of the aging chamber proper. 5.1.3 The heating medium is optional. Water, air, or other fluids known to be safe in the presence ofoxygen may be used. Water has an advantage because of its rapid heat transfer and noncombustible nature. If air is used, the heated air shall be thoroughly circulated by means of mechanical agitation, and baffles shall be used as required to prevent local overheating and dead spots. Oils or other combustible fluids are extremely hazardous in the presence of oxygen and should not be used as heating media for this test.5.1.4 Automatic temperature control of the heating medium by means of thermostatic regulation shall be used. The regu- lation system shall be provided with power failure protection and over-shoot protection to prevent accidental runaway tem- perature increase. 5.1.5 The temperature should be automatically recorded over the entire test period using a temperature-measuring device capable of measuring at the specific temperature to within 61°C. For apparatus not equipped with automatic recording capabilities, temperature shall be measured with sufficient frequency to ascertain that the temperature limits specified in 10.2 are adhered to. If the pressure chamber is completely immersed, the temperature may be taken as that of the heating medium. The sensitive element of the temperature- measuring device shall be close to the pressure chamber but not touching it. If the pressure chamber is not completely im- mersed in the heating medium, the sensing element may be placed in a thermometer well extending into the pressure chamber. The thermometer well should be filled with water, or oil, to a depth sufficient to cover the element, in order to facilitate heat transfer. If it is confirmed by actual check that the temperature of the oxygen within the chamber is the same as that of the heating medium, the temperature may be taken in the heating medium instead of in the thermometer well. If air is used as the heating medium, a check ofthe oven temperature shall be made by means of temperature-indicating devices placed in various parts of the oven to verify the uniformity of heating. In any case, it is desirable to verify the recorded temperature by checking with a temperature-indicating device having its sensitive element directly exposed to the oxygen within the pressure chamber. 5.1.6 Positive, rapid, and complete circulation ofthe heating medium shall be maintained so as to assure accurate, uniform heating.