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Section summary |
---|

1. Definition |

2. Calculation of
ATEX speed |

What is referred here as "ATEX" speed for a mixer of bulk solids is the rotation speed of the shaft for which the tip speed of the mixer agitator reaches 1 m/s.

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 u_{tip} = 1 m/s allows to calculate the
"ATEX speed"

**Equation 1 : Tip Speed calculation**

With :

- 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

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**Table
1 : "ATEX speed" for different mixer agitating tool radius**

Radius (m) | ATEX speed rpm |
---|---|

0.2 | 47.7 |

0.3 | 31.8 |

0.5 | 19.1 |