Flash point determination method

Wednesday - 19/12/2018 03:29
1. Definition of flash temperature and flash point. 
Flash point, the lowest temperature at which a liquid (usually a petroleum product) will form a vapour in the air near its surface that will “flash,” or briefly ignite, on exposure to an open flame.
 -So : Flash temperature   at which a mount of vapor from lubricant will be burnt when there is fire. 
-And:
- The minimum
“the lowest temperature at which a substance generates a sufficient amount of vapor to form a  mixture that can be ignited.”
- The flash point and the ignition point depend on the viscosity: 
+ The lower viscosity lubricant has, the lower ignitition point is.  
+ Opposite, The higher viscosity lubricants has, the higher ignitition point is.
- The flash point and ignitition point also depend on oil base. 
+ Napthenic base oil has slower flash point and ignitition point than Paraffinic base oil at the same viscosity. 
Conclusion: 
For similar compounds, flash point and ignition point increase as molecular weight increases.

For example: Viscosity lubricant, FO, DO oil ...
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2. Why should test and try the flash point? 
 Because: 
-
Preventing fire and explosion when lubricants work at high temperatures.
-Avoid the loss means the lubricants have to work in environment in which the miximum temperature is lower than the flash temprature in order to avoid the lubricant loss due to exploition, evaporation. 
-Normally, the flash temperature do not change a lot compared to new oil. If it is lower, it will be mixed . If it's higher, it is contaminated or mixed with the highr viscosity lubricant.  
3. There are two ways to determine the flash temperature:
-Open-cup method Cleveland (COC + Cleveland Open Cup) 
-Closed- cup method Pensky – Marsten (PMCC – Pensky Martens Closed Cup)
As:

+ The mixture of OD diesel oil with lubricating oil reduces the flash point and viscosity.
+ For synthetic lubricants used for 02 engines, it is not possible to use Cleveland flash point, as well as brake oil (HBF3 / 4), we have to use the PMCC method. Because PMCC has a flash point lower than COC so it's higher safety.
- Method of experiment to determine flash point:
+ Test-fire: D = 5/32 "(4mm)
+ Stir the sample
+ Temperature increases from 50C - 60C / min (90F - 110F)
+ And every 10 C (20F) increases, we put the flame until it reaches 1040C (2200F). When above 1040C, we put the fire on test when the temperature increased 2.70C (50F). If the fire burns on the evaporation surface of the sample, that is called flash point and if the fire lasts for 5 seconds,it is called the ignition point.

 
The flash point of lubricant, Flash point determination method, Method of determination  flash temperature.

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