Scientific American Supplement, No. 303, October 22, 1881

by Various

The germ middlings, after being slightly crushed as before stated, are sent to a reel covered with five feet of No. 13 cloth, five feet of No. 14, and the balance with cloth varying in coarseness from No. 7 to No. 00. The flour from this reel goes into the patent, the tailings to the red dog rolls, the middlings from next the tail of the reel which still contain some germ to the second germ rolls, while the middlings which are free from germ go to the middlings stones.

The tailings from purifiers 3, 4, 5, and 6, the material from the reel following the second germ rolls, which is too good for shorts, but not good enough to be returned into middlings again, and the tailings from the reel following the first germ rolls are sent to the red dog rolls, which, as I have stated, are finely corrugated. Following these rolls is the red dog reel. The flour goes to the red dog bin, the tailings to the shorts bin, while some stuff intermediate between the two, not fine enough for the flour but too good for shorts, is returned to the red dog rolls.

This finishes the programme. I have not given it as one which is exactly suited to winter wheat milling. However, as I said before, the general principles are the same in either winter or wheat gradual reduction mills, and the various systems of gradual reduction, although they differ in many points, and although there are probably no two engineers who would agree as to all the details of a programme, the main ideas are essentially the same. The system has been well described as one of gradual and continued purification. In the programme above given the idea was to fit up a mill which should do a maximum amount of work of good quality with a minimum amount of expenditure and machinery. In a larger mill or even in a mill of the same capacity where money was not an object, the various separations would probably be handled a little differently, the flour and middlings from the first and fifth breaks being handled together, and those from the second, third, and fourth breaks being also handled together. The reason for this separation being that the flour from the first and fifth breaks contain, the first a great deal of crease dirt, and the fifth more bran dust than that from the other breaks, the result being a lower grade of flour. The object all along being to keep the amount of flour with which dirt can get mixed as small as possible, and not to lower the grade of any part of the product by mixing it with that which is inferior, always bearing in mind that the aim is to make as many middlings as possible, for they can be purified while the flour can not, and that whenever any dirt is once eliminated it should be kept out afterwards. This leads me to say that if a miller thinks the adoption of rolls or reduction machines is all there is of the system, he is very much mistaken. If anything, more of the success of the mill depends upon the careful handling of the stuff after the breaks are made, and here the miller who is in earnest to master the gradual reduction system will find his greatest opportunities for study and improvement. A few years back it was an axiom of the trade that the condition of the millstone was the key to successful milling. This was true because the subsequent process of bolting was comparatively simple. Now the mere making of the breaks is a small matter compared with the complex separations which come after. In the foregoing programme we had five breaks or successive reductions. Although this is better than a smaller number, I will here say that it is not absolutely essential, for very good work is done with four breaks. The mill for which this programme was made, including the building, cost about $15,000, and is designed to make about sixty per cent. of patent, thirty-five per cent. of baker's, and five per cent. of low grade, results which are in advance of many larger and more pretentious mills.

One difficulty in the way of adapting the gradual reduction system to mills of very small capacity is that the various machines require to be loaded to a certain degree in order to work at their best. It is only a matter of short time when our milling inventors will design machinery especially for small mills; in fact they are now doing it, and every day brings it more within the power of the small miller to improve his manner of milling. To show what can be done in this direction I will briefly describe a mill of about ninety barrels maximum capacity per twenty-four hours, which is as small as can be profitably worked. I will premise this description by saying it is designed with a view to the greatest economy of cost, the best trade of work, and to reduce the amount of machinery and the handling of the stuff as much as possible. This latter point is of much importance in any mill, either large or small, no matter upon what system it is operated, for it takes power to run elevators and conveyors, and especially in elevating and conveying middlings, especially those made from winter wheat, their quality is inured and a loss incurred, by the unavoidable amount of flour made by the friction of the particles against each other. So much is this the case that in one of our largest mills it is deemed preferable to move the middlings from one end of the mill to the other by means of a hopper bin on a car which runs on a track spiked to the floor, rather than to employ a conveyor. A mill built as I am going to describe would require from fifty to sixty horse-power to run it, and including steam power and building would cost from $10,000 to $12,000, according to location. I give it as of interest to those among your number who own small mills and may contemplate improving them.

The building is four stories high, including basement, and thirty-two feet square. It would be some better to have it larger, but it is made this small to show how small a space a mill of this size can be made to occupy. No story is less than twelve feet high. The machinery Is very conveniently arranged, and there is plenty of room all around. The system is a modification of the gradual reduction system, the middlings being worked upon millstones. The first break is on one pair of 9 x 18 inch corrugated iron rolls, eight corrugations to the inch, the corrugations running parallel with the axis of the rolls. The second break on rolls having twelve corrugations to the inch, the third sixteen, and the fourth twenty to the inch, while the fifth break, where the bran is finally cleaned, has twenty-four corrugations to the inch. The basement contains the line shaft and pulleys for driving rolls, stones, cockle machine, and separator. The only other machinery in the basement is the cockle machine. The line shaft runs directly through the center of the basement, the power being from engine or water wheel outside the building. The first floor has the roller mills in a line nearly over the line shaft below, the middlings stones, two in number, at one side opposite the entrance to the mill, the receiving bin at one side of the entrance in the corner of the mill, and the two flour packers for the baker's and patent flour in the other corner. This arrangement leaves over half of the floor area for receiving and packing purposes. The bolting chests, one with six reel and the other with three reel begin on the second floor and reach up into the attic. An upright shaft from the line shaft in the basement geared to a horizontal shaft running through the attic parallel with the line shaft below, comprise about all the shafting there is in the mill. There is a short shaft on the second floor from which the two purifiers on this floor and the two in the attic are driven, and another short shaft on the first floor to drive the packers. There are four purifiers, two on the second floor, and two more directly over them in the attic. The elevator heads are all directly upon the attic line shaft, and the bolting chests are driven by uprights dropped from this shaft. The combined smutter and brush machine is on the third floor at one end of the bolting chests and directly over the stock hoppers. This comprises all the machinery in the mill. The programme is about as follows:

The break reels are clothed as follows: First break No. 20, wire cloth, second break No. 22, third break No. 24, and fourth break No. 24. The material passing through these scalping reels, now called chop, goes to a series of reels, the first clothed with Nos. 6, 4, and 0. The material passing over the tail is sent to the germ purifier, that passing through Nos. 4 and 0, to the coarse middlings purifier, and that through the No. 6 goes to the reel below clothed with Nos. 12 and 13. Some nice granular flour is taken off from this reel; the remainder, which passes over the tail and through the cutoffs, goes to the next reel below clothed with Nos. 14, 15, and 9. Some good flour comes from the 14 and 15; that which passes through the 9 goes at once to the stones without purifying, while that which passes over the tail is sent to the fine middlings purifiers.

After the purification, the middlings are ground on stones and bolted on Nos. 13 and 14 cloth, after having been scalped on No 8. The germ middlings are crushed on smooth rolls and bolted on Nos. 12 and 13. What is not crushed fine enough goes with poor tailings to the second germ rolls, and from these to a reel by themselves or to the fifth reduction or bran reel. A mill of this kind could be made much more perfect by an expenditure of two or three thousands dollars more. I have instanced it to show what can be done with gradual reduction in a very small way.

In mills of from three hundred to five hundred barrels capacity and still larger, the programme differs considerably from that I have sketched, the middlings being graded and handled with little, if any, returning, and are sized down on the smooth rolls, a much larger percentage of the work of flouring being done on millstones. For a three hundred barrel roller mill, the following plant is requisite: five double corrugated roller mills, five double smooth roller mills, three pairs of four foot burrs sixteen purifiers, four wire scalping reels, six feet long, one reel for the fifth break, one reel for low grade flour, eight chop reels, seven reels for flour from smooth rolls, three reels for the stone flour, two grading reels, three flour packers, and necessary cleaning machinery. The reels are eighteen feet thirty-two inches. The programme is necessarily more complicated.

When it comes to the machinery to be employed in making the reductions or breaks, the miller has several styles from which to choose. Which is best comes under the head of what I don't know, and moreover, of that which I have found no one else who does know. Each machine has its good points, and the mill owner must make his own decision as to which is best suited to his purpose. The main principles involved are to abrade the bran as little as possible while cleaning it thoroughly, and to make as little break flour, and as many middlings as possible, the latter to be made in such shape as to be the most easily purified. Regarding the difference between spring and winter wheat for gradual reduction milling, it may be stated something after this manner: Spring wheat has a thinner and more tender bran, makes more middlings because it is harder, and for the same reason the flour is more inclined to be coarse and granular. In milling with winter wheat, especially the better varieties, there will be more break flour made, the middlings will be finer with fewer bran specks, and the bran more easily cleaned, because it will stand harsher treatment. Winter wheat, moreover, requires more careful handling in making the breaks, not because of the bran, but to avoid breaking down the middlings, and making too much and too fine and soft break flour. In order to keep the flour sharp and granular, coarser cloths are used in bolting, and because the middlings are finer the bolting is not so free and a larger bolting surface is required. In milling either spring or winter wheat there should be ample purifying capacity, it being very unwise to limit the number of machines, so that any of them will be overtaxed. The day has gone by when one purifier will take care of all the middlings in the mill.

There is one point which is of much interest to mill owners who wish to change their mills over to the gradual reduction process, that is, how far they can utilize their present plan of milling machinery in making the change. Of course the cleaning machinery is the same In both cases, so are the elevators, conveyors, bolting chests, etc. But to use the millstone is a debatable question. After carefully considering the matter I have come to the conclusion that it has its place, and an important one at that, under the new regime, viz., that of reducing the finer purified middlings to flour. The reason for this lies in the peculiar construction of the wheat berry. If the interior of the berry were one solid mass of flour, needing only to be broken up to the requisite fineness, it could be done as well on the rolls. But instead of this, as is well known, the flour part of the berry is made up of a large number of granules or cells, the walls of which are cellular tissue, different from the bran in that it is soft and white instead of hard and dark colored. It is also fibrous to a certain extent, and when the fine middlings are passed between the rolls instead of breaking down and becoming finer, it has a tendency to cake up and flatten out, rendering the flour soft and flaky. It does not hurt the color, but it does hurt the strength. When the millstone is used in place of the roll the flour is of equally good color, and more round and granular. I know that in this the advocates of smooth rolls will differ from my conclusions, but I believe that the final outcome will be the use of millstones on the finer middlings, and in fact on all the middlings that are thoroughly freed from the germ.