ROLIYR-MILLS.
//in'OriCai. —According to Rhvs Jenkins, the earliest record of the use of rolls for crushing corn, etc., is that made by Samuel Hartlib in 165r.
In T721, John Mortimer invented a roller-mill which consisted of a pair of iron rolls, about 4 inches in diameter and from 18 to 20 inches in length, enclosed in a and run at different speeds; this mill was used for crushing malt and for the manufacture of flour, and many machines which were employed for the same purposes were constructed from Mortimer's model. Before the close of the eighteenth century roller-mills were exten sively used for crushing oats, beans, and malt. 1,Vorthy of especial men tion is the one devised in 1774 by Samuel Watson; this was designed for grinding wheat between a central roll and a " breast " (see pi. 3), and, with the addition of a small roll to the central roll, for crushing oats and malt. In 1775, Rawlinson combined a pair of metal rolls with a pair of stones or metal discs, thus effecting both roller-crushing and stone In iSlo, Williams first employed the weighted-lever pressure arrange ment. The patent of Parsons and Lambrook embraced circumferentially grooved rolls geared to give differential speed. The first three-high roller mill was that of Plummer (1853), who also applied springs to the bearings. In 1854, Spiller combined a roller-and-breast will with the ordinary stones. In 1856, Alexanler White highly recommended preliminary rolling before grinding, especially for hard wheat, as "greatly facilitating the grinding process and improving the quality of the flour." In 1862, Buchholz, whose dccorticator is described on page 42, invented a series of grain-cleaning-, crushing-, sifting-, and purifying-machines, but, being "a man before his time," his inventions were not then appreciated.
In England up to this period (1862) the rough-and-ready bruising-mill, by numerous ingenious _and necessary details, had been perfected and developed into an apparatus which possessed not only niceties of design and workmanship, but also a precision of movement which produced most satisfactory results. Meanwhile, however, according to Henry Simon, the roller-mill had been constructed in Switzerland as early as 1825, the rolls being of iron and haying a smooth surface. It was first practically used on a large scale, about 1839, at Budapest, Hungary, and embodied the important principle of differential speed.
In T873, Frederick Wegmann, a Naples miller, suggested the freeing of the rollers from rigid pressure by fixing the journals of one of the rolls in levers on which a weight would exert a continuous pressure, while it would admit of independent adjustment. Later, in place of weights, adjustable springs were applied, and these are now almost universally used in roller-mills. Wegmann suggested the use of porcelain instead of iron for facing the rolls. Porcelain, however, being a material much finer in texture than burr-stone, cuts the bran too fine for easy separation from the flour. Smooth chilled-iron rolls, on the contrary, do not reduce the bran-particles, but flatten them, thus rendering separation easy. Porcelain rolls, moreover, wear rapidly and are liable to crack, whereas chilled-iron rolls will run for years even in severe work, and when worn can be easily recut at a moderate cost, and will again serve for another series of years. In Budapest, the cradle of roller-milling, the use of porcelain rolls, after a long trial, has been abandoned, and cast-iron rolls have been almost universally substituted.
In the early roller-mills one roll was belt-driven, while the other was driven by contact only; but, as this was found to impart au uncertain motion, cog-wheels of different diameters were substituted. Finally, skew spur-wheels of correct figure and even pitch were found to produce the best results. The driving of the rolls by belts has, therefore, been discontinued in Europe.
American millers and machinists, always ready to adopt improvements and to introduce new machines, were not slow in discerning the superior ity of roller-mills and in substituting them for stone mills. The mill stone merchant-mill was perfected in every necessary automatic device and had passed into history before the present century began, Oliver Evans having taken this first successful step. (See p. 43.) Roller-milling began early in the United States. Before 184o there was issued a patent which embodied the use of rolls for reducing grain. Since the issue of this patent many improvements have been made, and it may be said that the Amer ican roller-mills surpass all others in adaptability and ingenuity of con struction. Vast merchant-mills have been erected in different parts of the United States, and the manufacture of flour is now receiving the attention which its importance demands.