Flash point

Closed-mouth flash point, wide-mouth flash point; you can understand it once you know what the flash point means

The open flash point is the value obtained using a specified open flash point tester, and it is expressed in °C. It is commonly used to determine lubricating oils. When determining the open-cup flash point according to the standard method of GB/T 267-88, the sample is placed in the inner crucible up to the specified mark. First, the temperature of the sample is raised rapidly, then increased slowly; as it approaches the flash point, the temperature is raised at a constant rate. At specified temperature intervals, a small flame from an igniter is passed over the surface of the sample at a defined speed. The lowest temperature at which the vapor on the surface of the sample ignites due to the flame from the igniter is considered the open-cup flash point. Continue the tests until the lowest temperature at which the sample ignites due to the flame of the igniter and burns for at least 5 seconds is determined, which is then taken as the open-cup flash point. To accurately measure the flash point, it is necessary to strictly control the operating conditions, especially the rate of temperature increase. The repeatability of this method (repeated tests performed by the same operator using the same instrument) must have a difference in results not exceeding 8℃ ； The difference in reproducibility results (when two laboratories test the same sample) must not be greater than 16°C. The precision of the closed-cup method is higher; the difference between repeated measurements must not exceed 2°C/5.5°C (for flash points > 104°C) ； The difference in reproducible results shall not be greater than 3.5°C/8.5°C (flash point > 104°C). The closed-cup flash point is the value obtained using a specified closed-cup flash point apparatus, and it is expressed in °C. It is commonly used to determine kerosene, diesel oil, transformer oil, etc. When determining the closed-cup flash point according to the standard method of GB/T 261-2008, the sample is poured into the test cup, stirred continuously at a specified rate, and heated at a constant rate. At specified temperature intervals, with stirring interrupted, a heat source is introduced at the opening of the test cup to cause the sample vapor to ignite instantaneously and spread to the lowest temperature on the liquid surface; this temperature represents the flash point under ambient atmospheric pressure, which is then corrected using a formula to obtain the flash point under standard atmospheric pressure. The difference in the reproducibility results of this method shall not be greater than 0.029X (where X is the average of the two tests) ； The difference in reproducibility results must not be greater than 0.071X. 1 Experimental purpose: To study the variation patterns of the flash point of mixed liquids through numerous experimental tests. 2 Experimental principle: Depending on the type of flash point tester used, flash points can be divided into closed-cup flash point and open-cup flash point. It should be determined according to the product quality specifications whether to measure the closed-cup flash point or the open-cup flash point for each type of oil. Generally, petroleum products with high volatility are tested for their closed-cup flash point, as when the open-cup flash point is determined, the vapor formed by heating the oil disperses into the surrounding air, resulting in a higher measured flash point. For most lubricants and heavy oils, due to their low volatility, the open flash point is commonly measured. The principle of determining the closed-cup flash point is to place the sample in the oil cup up to the ring mark, then heat the sample at a slow, constant rate while stirring continuously. At specified temperature intervals, with stirring stopped temporarily, a small flame is introduced into the cup; the lowest temperature at which the flame causes the vapors on the sample to ignite is considered the closed-cup flash point. The principle of open-cup flash point determination is to fill the test sample into the test cup up to the specified mark. First, raise the temperature of the sample, then increase it slowly; when approaching the flash point, raise the temperature at a constant rate. At specified temperature intervals, a small test flame is passed across the test cup; the lowest temperature at which the vapor on the surface of the liquid is ignited by this test flame is taken as the result for determining the open flash point.

The result obtained by using a specified open-flame flash point tester is called the open-flame flash point

A closed-flash point and an open-flash point