Each passage through the rolls changes the condition of bran, and the oftener it goes through them the lighter and cleaner it becomes, until all the floury portion is removed.
The Austrians use corrugated rolls for the purpose of cleaning bran, the finest being on the last, as in the break rolls. It is more scientific and philosophical to clean the bran in this way than to rub off the flour between burrs in this way than to rub off some of the branny portion as well as the glutinous part.
Rollers for the first cleaning are from eight to ten inches in diameter and from three to five hundred corrugations are used, and this increases up to one thousand for the last rolls used; but fine corrugations wear out soon, and the rolls have to be frequently corrugated or the bran has to be finished on burrs.
The use of rollers is preferable to that of stones for bran, and their use is considered an important advance in milling by most German experts.
As the advantage of the use of rolls instead of burrs consists in the production of a greater amount of middlings, this advantage should be experienced in the cleaning of bran. As the small starchy particles adhering to the bran are separated in the shape of middlings instead of flour, a better quantity of flour is produced from these middlings both in color and strength than that which is made from the stones' product.
Differential speed in rolls is not only better in making middlings, but in grinding bran as well. This has been proved by several experiments.
There is no doubt but that there is less care bestowed on the hanging and care of shafting than upon any other means used in applying power to manufacturing purposes. If the steam engine or the water wheel is in good order, and performing their work properly, and the machines driven by them are also in good order, there is seldom a thought bestowed upon the media between the actuating power and its ultimate development, except the necessary attention which must be paid to the belting, and oiling of the machinery.
Often, when the result of the power is not satisfactory, it is not the driving power that is at fault, but the result may be found in the shafting, or other intermediate transferers of the power. Generally, in such a case, the belts are examined and their condition assumed for the imperfect transmission of the power from the prime mover.
The condition of the belts is a very important point in all manufacturing, but more particularly in mills where a steadiness of motion is a desideratum, and attention to them will save many dollars in the course of a year; but there are other as important elements which are not always taken into consideration, and the principal one is the condition of the shafting. A line of shafting running perfectly true, without jumping or jerking, turning smoothly and noiselessly, is a delight to the mechanical eye; and the first thing always examined by a thorough millwright when he enters a mill, is the shafting.
Perhaps there is nothing will strike a person who has been out of the milling business for some time so much as the change in the system of bolting. This is caused by the numerous separations, and it is in this the whole secret of gradual reduction lies.