Salem

mined ore 9 quality, smelted, smelter was in just this ore, but the output was 7 quality
how it happened and why?
next time - melted ore 5.45 quality remained one place to complete the download, but it was the ore only 4.93 quality - after smelting got a bar of 4.7 and a bar at 2.21
morning laid the different ore, the ore was from 0.54 to 3.87 at the outlet was 2 bar at 6.64 !!! and 2.26
how it happened and why?

The leftover iron in the smelter is affecting the % of the iron bars that are being produced. So, unless its a brand new smelter you will have different % output each time.
My advice is not to worry unless you get 50% or more iron.
But, if you are into things like that you can pretty much make new smelters for every 1%. Maybe you are into that self mazochistic crap.

thanks for the answer. Now everything is clear