The flash point is defined as the lowest temperature at which the oil can flash in contact with the flame under test conditions. That is, the temperature at which the oil meets the flame and starts to flash when the temperature is rising.
What are the factors that affect the flash point determination of lubricating oil.
First, the instruments used
Generally, the results measured by the open flash point tester are higher than those measured by the closed flash point tester, which is due to the structure of the open flash point tester.
Second, the water content of the sample
When the sample contains water, it must be dehydrated before the flash point can be determined. The closed cup flash point determination method specifies that the water content of the sample is not more than 0.05%, and the open cup flash point determination method specifies that the water content of the sample is not more than 0.1%. Otherwise, it must be dehydrated. This is because the water dispersed in the oil will vaporize to form water vapor during the heating test, and sometimes form bubbles to cover the liquid surface, affecting the normal gasification of the oil and delaying the flash time. The result is higher. When the flash point of heavy oil with more water is measured by the open-cup method, the sample is easy to overflow from the oil cup when heated to a certain temperature due to the vaporization of water, which makes the experiment impossible.
Third, sample size
The loading amount of the oil test must meet the requirements. The sample in the cup should be loaded to the circular scribed line according to the requirements. Too much or too little loading will change the space volume above the liquid level, thus affecting the concentration of the oil vapor and air mixture, making the measured flash point low or high.
Fourth, heating speed
If the heating speed is too fast and the sample evaporates rapidly, the local concentration of the mixer will reach the lower explosive limit and flash ahead of time, resulting in low measurement results. If the heating speed is too slow, the measurement time will be extended, and the number of ignition times will increase, which will consume some oil vapor, delay the time for the mixture of oil vapor and air to reach the flash point concentration, and increase the temperature to reach the lower explosive limit. Therefore, the heating rate must be strictly controlled according to the standard.
Fifth, atmospheric pressure
The flash point of oil is related to external pressure. The oil is volatile at low pressure, so the lower the measured flash point is, the higher the flash point is. The standard stipulates that the flash point measured at 101.3kpa atmospheric pressure is the flash point under standard pressure. If the atmospheric pressure deviates, the measured flash point needs to be corrected at atmospheric pressure.
Sixth, ignition control
The diameter of the spherical flame used for ignition, the distance from the sample liquid level and the residence time shall be strictly in accordance with the national standards. If the diameter of the spherical flame is too large, the distance from the liquid level is too close, and the residence time is too long, the measurement result will be lower, and on the contrary, it will be higher than normal.