Operating Principle of the wheat is led from the feeding-hopper to a pair of spirally-grooved rolls, which rim toward each other at different speeds and are set apart slightly less than the diameter of the wheat-berries, whereby every berry is broken in its passage between the rolls. The process of bolting follows this first break ing of the wheat, which is then led to another pair of rolls, having finer and sharper grooves and working closer together than the first pair. These second rolls break the grain still finer, the resulting product of the second breaking being sifted and led to a third pair of rolls (having finer and sharper grooves and being closer set than the second pair), by which it is further ground and sifted until all the interior portion of the grain is sepa rated from the bran. The roller-mills are therefore so arranged as to increase the pressure on the wheat at each successive cracking, and by reducing the size of grooves of the rollers all the flour-bearing particles are gradually scraped from the bran. The chief object is to avoid the production of any flour during the successive breakings, and to preserve as much as possible the interior of the wheat in the form of gritty frag ments known as "semolina" or "middlings," from which the flour is pro duced.
The Noiseless (pl. 5, fig. 3) is so clearly illus trated that an extended description in detail is unnecessary, although the principal features that distinguish this machine may be given, to enable the reader better to understand its construction and operation. The mill is self-contained upon and within one solid iron frame, thus securing and permanent adjustment to all the working parts. Eccentric swing-boxes arc provided for levelling the rolls and for maintaining than in accurate position. The rolls may be thrown apart at will, or, should an ungrindable substance accidentally be introduced with the grain, they will automatically move apart and return to their original position with out changing their adjustment. End play of the rolls is prevented by collars on the journals. The adjustable countershaft through the lower part of the frame secures the important feature of differential motion without the use of gears and renders it possible to drive both pairs of rolls from one driving-pulley with one driving-belt. The use of belts instead of gears causes the machine to run without noise. The feeding devices maintain a uniform flow of grain over the entire working-faces of the rolls, which arc constantly cleaned by the automatic scrapers.
Rol three-high roller-mill with smooth rollers is shown in transverse vertical section in Figures 4 and 5 (p1. 5). The centre roll in fixed bearings; the upper and lower rolls are carried in adjustable levers, for throwing the rolls apart or for independently adjust ing each end, and for effecting these adjustments without interfering with the grinding-pressure. Two distinct materials can be treated at the same time; the feed of one material, passing between the upper and central rolls, falls through the spaces between the vertical tubes (A) into the under hopper, while the second material is ground between the centre and lower rolls and falls through the inside of the tubes. This arrangement of cross
channels has the appearance, in front elevation, of a gridiron. The prin cipal advantage of three-high roller-mills is that the downward pressure on the central roll is counteracted by an equal upward pressure, so that the friction due to this pressure is eliminated in the bearings of the central roll. There arc thus only four bearings under pressure, whereas in the four roll mill, above described, there are eight bearings.
Modern sectional elevation in Figure 2 shows the arrangement of a modern 20o-barrel mill equipped with the latest improved machinery. It is a five-break mill—that is, it has five pairs of fluted rolls for breaking the grain, including the bran-rolls, and uses eleven pairs of smooth rolls on the middlings. The break-separations are made on double scalping-reels (a), and the subsequent separations on round reels (b) and on the centrifugals? The outfit of this mill consists of eight noiseless double-roller mills, four double scalping-machines, ten round reels, five purifiers, one purifier for coarse middlings, three flour packers, one too-bushel hopper-scale, six cyclone dust-collectors, one receiving and one milling separator, and two scourers. Mills of larger capacity—five thousand barrels per day and upward—are equipped on the same general plan, but with an increased duplication of machines.
the preceding pages there have been noted the various forms of mealing-apparatus employed from the earliest times, including the more recent automatic and improved methods of manipulating the grain-products, as well as the machines constructed on higher scientific principles and requiring for their impulsion the employment of great force. The foundation of a philosophical system of milling rests on the structural peculiarities of the grain, from the study of which has resulted the invention of the roller-mill. The greatest advance in modern meth ods is, however, not only in the substitution of cylindrical rollers for flat stones, but also in the invention and perfection of every mechanical and manipulating detail embodied in the various auxiliary machines, devices, and processes for the intermediate treatment of the product.
The central idea of modern milling is the production of the greatest quantity of pure flour from a given quantity of wheat, or, in the language of the miller, to make " branless flour and flourless bran." Perfect bread can be made only of pure flour, and was first produced by the Hungarian method, as exhibited in the Vienna bread, "which is a smooth, irregularly rounded, small loaf or roll. It presents a rich reddish-brown crust and a delicately-shaded, yellowish, almost white interior. It is always light, evenly porous, free from acidity in taste or aroma, faintly sweet without the addition of saccharine matter to the flour or dough, slightly and pleas antly fragrant, palatable even without butter, and never cloying on the appetite." There is, however, no secret about its production. The prin cipal constituents are Hungarian flour—that is, pure flour—and press yeast, manipulated with cleanliness, care, and intelligence.