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|2. Calculation of
1 m/s is commonly accepted, for stainless steel equipment, as the limit below which a metal metal contact will not create a spark susceptible to inflame a cloud of dust.
It is very important to run the mixer below the "ATEX speed" when loading and discharging the mixer, which are the process steps where a dust cloud can be formed at concentration that can lead to explosion. During mixing, the concentration of dust is normally too high to create an explosion - some exceptions, operators to review each case - thus allowing to run a mixing speed.
The "ATEX speed" can be calculated by expressing the tip speed of the agitator as a function of the agitator radius and its rotation speed. Equalling utip = 1 m/s allows to calculate the "ATEX speed"
Equation 1 : Tip Speed calculation
- R is the radius of the mixing tool (center of shaft to tip of paddle) in m
- n is the mixing speed in rpm
Equation 2 : "ATEX speed"
Examples for different radius
1 : "ATEX speed" for different mixer agitating tool radius
|Radius (m)||ATEX speed rpm|