Liner material can be the same in conical mills. The only advantage of conical mills is to achieve "classification" of the ball charge along the mill axis; with the large balls at the mill feed (for the coarse feed) and the small balls at the mill discharge. Today, these mills are obsolete since...
I would agree with canuckminer: typical reduction ratio you can achieve with conventional crushers (gyratory and cone crushers) is 4 to 6. Check with crushers manufacturers suchs as Metso or Sandvik.
I would not recommend using hammer mills at all since feldspar is very abrasive and the hammers...
