The principle of axial testing is to crash stop the mill, then go inside and take samples at 1m intervals along the axis of the mill. You need to dig down into the media to take the samples as the mill ventilation fan will pull some of the cement off the top of the media while the mill cools sufficiently for you to enter. The size distribution of the samples are then measured in the laboratory. You are looking for progressively finer material along the axis of the mill, reaching the desired fineness at the outlet diaphragm.

Is there a published conversion formula or approximation from Blaine cement fineness values to sieve sizes? (ie 3800 blaine is approximately 325 mesh)

I'm afraid not. The two measures of fineness are quite distinct. Blaine is the total surface area, while sieve residues are the fractions above a certain size. So it would be possible for a 3800 Blaine cement to have a 45micron sieve residue of 10 per cent or 20 per cent. The cement with the coarser 45 micron residue would be compensated by a high proportion of super fine material to yield the same Blaine as the sample with the lower residue. This is why the best way to characterise the fineness of a cement is the Rosin Rammlerslope and characteristic value.

In order to optimise the performance of a ball mill, is there any suggested air velocity through the mill that we should use? Our cement plant has some very old ball mills. One in particular is a 4.572m x 13.9m two compartment mill, closed-circuit, with a Sepax separator 2S-375 separator. The separator and mill are vented by the same dust collector. We are currently running a high mill outlet ventilation on the mill, greater than -4" W.C. What is an acceptable mill ventilation static pressure range for this type mill circuit?