104 Modern Improvements in Corn-Milling Machinery. 
demand of the mill. In Hungary as many as ten different quali- 
ties of flour are made. It is in this part of the process that 
there are the greatest differences of system and practice in mills. 
It is now necessary to refer more particularly to the " roller- 
mill " as a machine, and to attempt a, general description of the 
points which are common to the many types of this machine 
now in use. One function of the roller-mill in the " breaking" 
process has been described ; the other duty of roller-mills is to 
crush or grind into flour the particles produced by the breaks 
after they have been " purified." For the first duty the rollers 
are grooved or fluted ; for the second they are smooth. For 
the " breaks " chilled iron rollers exclusively are used ; for the 
grinding of the particles, chilled iron and porcelain rollers are 
employed. Cast iron, cast steel, forged steel have been tried, 
but the hardness of the coats of the wheat, and the various odd 
articles of metal or stone that in spite of all precautions find 
their way to the rollers, wear away these materials very rapidly. 
Space cannot be given to a description of the vast variety of 
roller-mills that are in the market, nor to a discussion of the 
principles of their construction, or of the differences between 
the many modes of accomplishing the same object. Such in- 
vestigations are more appropriate to the journals of the milling 
trade. A general sketch of roller-mills may, however, be at- 
tempted. The rollers vary in length from 9 inches up to 40 
inches, and the constructions most generally in use adopt dia- 
meters of from 8 inches to 12 inches. Some engineers prefer 
rollers of very much larger diameters. The grooving of a roller 
when viewed in cross section has a saw-like appearance, varying 
in fineness from 8 or 10 up to 30 or 35 grooves to the inch. The 
saw-teeth also vary somewhat in form, and especially in the 
depth to which the grooves are cut. One maker prefers a tooth 
rounded instead of sharp at the point, but it is a form not much 
used in this country. Oi\ the contrary, the general view is that 
it is needful to keep the teeth of the rollers moderately sharp in 
order that they may cut and not crush the grain, and yet with 
not too keen an edge or they will cut up the bran. The groov- 
ing even of chilled iron wears gradually, and the life of a roller 
in an efficient condition may be reckoned at about two years. 
The roller then requires to be regrooved. The grooves pre- 
ferably are cut in a spiral direction, there being an idea that 
better work is obtained by the scissors-like action of the teetli ; 
but, however tliis may be, there is a real advantage in avoiding 
the danger of the teeth of the two rollers interlocking and de- 
stroying each other, as they would do if the grooves on each 
were parallel with the axis aud the peripheries came into con- 
tact with each other. 
