Plan and Power of a Flour Mill of Many Years Ago, by Prof. B. W. Dedrick, 1931
The development of milling and the changes in the methods of grinding and bolting are in a large measure, responsible for improvement in the types of machines used and the power transmission appliances involved in the operation of the flour mill and, in turn, manufacturing plants other than flour mills. The lever, shafts, gear wheels, pulley and belt, water wheels and wind mills were first used in connection with the grinding of grain long before their use in other pursuits. When man first applied a lever or handle to turn his crude millstone, he found it gave him more power. As long as he pounded the grain or rubber it on a flat stone, he apparently required no assistance, merely using such a stone as he could lift or more. But when he discovered by turning the stone in a rotary manner a better and finer meal was made by this method, that is, a true grinding or attritive action - it required more exertion to turn the stone than the simple pounding action, hence he sought some means by which he could more easily turn the stone and in due course of time he used a stick which he attached to the movable ton stone to secure leverage in turning, this being the first application of the lever as a mechanical means in developing rotary motion. It would be interesting and enlightening as well to trace the development of milling from its earliest stage through the centuries of the human race to a higher state, and in time to develop a high order of civilization, even thousands of years ago.
It will suffice to say that as man progressed he sought to produce flour as white and pure as his crude mills would permit and as this involved a separation of the husky part of bran from the flour part, the sieve was early invented and used. So it seems the great desire for white bread was the incentive to invent machines and means to operate them, and thus led to the various stages of development and improvement in milling throughout the ages. A change or improvement in the grinding method and making flour, in nearly every case, meant a new or more complex mechanical problem, either in the production of the special machine or type used in the process or in the method of driving or application of mechanical power. Man probably ground his grain for some thousand of years by mere hand, or more correctly man power until the fashioning of the lever as a sweep made possible the use of animal power. Then later he used crude water wheels and wind mills. Then in out age came the steam engine first, and later the gas and oil engines and electric power. Few are aware that the first successful use of the steam engine outside of pumping for mines was to furnish power to operate a flour mill.
While it is true that something like a hundred and forty years ago, the millstones were driven as were also the bolting apparatus, by mechanical power, yet, the mill was not a connected whole or an automatic affair, but had remained a broken or disconnected process. Oliver Evans, called the "Father of American Milling," invented the elevator, the endless band or belt with attached buckets to receive and lift the meal from the millstones on the first floor, to discharge into the bolting reels on the second, third or perhaps fourth floor where as before it had to be carried up on the backs of men, or lifted up in bags or tubs hauled to the upper floor by rope and tackle on by a friction drum. The elevator took the wheat as received and dumped the grain into bins or hoppers, cleaners, etc., situated on the upper floors. He also invented or brought into use the worm or screw conveyor that took or conveyed meal, flour, etc., from one place to another on the level as on one floor and as conveyors under the flouring reels, that gathered the flour from the bolts. The cooler was another machine that he invented. This spread and cooled the warm meal before its entry into the bolts. These aids made it possible to make milling a continuous operation, automatic in action and functioning as one machine, the process continuous from the receiving of the wheat, until its issue in the form of flour, bran and shorts.
Evans' plan of a flour mill, drawn by him over a century ago, shows the marine elevator leg, taking wheat from a vessel in the river to the rear of the mill. This elevator was so arranged that it could be swung out over the vessel and lowered into, or lifted there from by an attachment at the head, the head itself supported by a segmental casing that permitted the afore said movement, a universal joint allowing flexibility. The users of power and the transmitting mediums, as shafts, gears, pulleys, etc., that converts that power into actual motion and work of the machines of the various lines of manufacture are not aware or give thought to the fact that in the first instance these were used in the conversion of grain into meal. Now when we speak about power in its relation to machines or machinery, we mean that driving force or energy which sets in motion and keeps in motion, engines or motors of all kinds and from these as the initial converters of the latent forces residing in coal, wood, gas, or other fuel, water, etc., we derive power. Thus the engine, water wheel, wind mill and electric motor are means which convert this force or energy into mechanical power, transmitted to machines by the pulley wheel, shafts, gears, belts and chains.
The early power transmission appliances or means were that of shafts and gears, representing the old pin or peg gear wheels. Practically no belts were used. this particular design was drawn from an old print of the 16th century, and gears of this kind were used until a little over a century ago, and may still be found in some of the oldest mills in the eastern section of the United States. The old mill, erected nearly a hundred years ago at Houserville, Pennsylvania, near State College, is or was until lately in operation, still had retaining gears of this type, mounted on wooden shafts. A hundred years ago, the immense water wheels, generally of the overshot type, were constructed of wood, and mounted on great wooden shafts, the journals being of cast iron and often a foot or more in diameter. Most of the shafts throughout the mill were also wooden, anywhere from 6 inches to 12 inches in diameter or thickness. Some shafts were square, but mostly octagonal in form, and where sometime later iron cog wheels were used, the hub was also octagonal, and wedges used to fasten and position the wheel. The cog wheel is mounted to the shaft connected to the water wheel, and transmits motion to pinion wheel by means of the peg wheel mounted on the shaft. On the same shaft is a lesser face wheel, that meshes into a pinion mounted on an upright shaft or spindle. The shaft is assumed to be the "upright" which transmitted power and motion to the shafts and machinery on the upper floors, it would be connected up or its length would reach the uppermost story, sections being coupled together. However, the shaft would also more aptly represent the spindle of the millstone , because of it speed in this instance of "gear up" would be more suitable for the millstone, since the speed will be, if we do a little figuring, about 216 revolutions per minute, whereas about 50 at the most was the highest speed of the "upright" in the old mills. The driving wheel has, let say 36 pins inserted in the outer rim of the wheel. The pinion or driven wheel has 10 bars. If the water wheel makes 10 revolutions per minute, then we have 36 X10 divided by 10 equals 36 revolutions of the pinion wheel. Now let us say the lesser face wheel has 48 pins inserted in the side of the rim to transmit motion from a horizontal shaft to a vertical shaft. If pinion on the vertical shaft has 8 bars we get 48X36 divided by 8 equals 216 revolutions for the spindle. The amount of power required by the millstones alone would be about 15 horse power. If the cut is turned quarter way around to the left, and assume like the first pinion, as an "upright" we get an idea as to how horizontal shafts were driven at right angles to the "upright" shaft. It is obvious that in such an arrangement, three or four shafts could be driven from the lesser face wheel. Again if we assume the first pinion wheel to be the spindle of a millstone, and the wheel driving it the bull or driving wheel, three of four fairs or sets of millstones could be so disposed as to be driven by this one wheel, and in some mills were so arranged and driven.
In some of the oldest mills the millstones were driven direct from the old type of flutter or scroll water wheels, the stone being suspended on the end of the upright water wheel shaft. The plan of a flour mill of sixty years ago (the Oliver Evans type with simplified metal gearing), the source of power, the transmitting shafts and gears, and distribution of power to the various machines. It also gives an idea of the simple process of milling some sixty or seventy years ago. This hook up makes the process automatic and continuous. Wheat for instance is dumped (from outside of the mill) into the receiving hopper or dump into the receiving hopper or dump bin, and from there conveyed to the elevator, when it is discharged into the boot (from a conveyor from the bottom of the grain dump) , and carried or elevated up to the top floor, and cleaned on a rolling screen that takes out the dirt and seed on the first section, lets through the wheat on the second section, and passes over the roughage as sticks, straws, oats, etc., over the end, the wheat going to the smutter, now called scourer - where the wheat is cleaned by a scouring action and then goes to the "wheat garner" over the millstone (on the second floor). The wheat being ground (by the millstones on the first floor), the meal is now elevated to the cooler (the hopper boy in the attic), where the hot meal spread out and cooled (by the rake), thence going to the long hexagonal reel (on the second floor), sometimes twenty feet long. The bolt or reel, hopper boy or cooler conveyors are part of the Oliver Evans system. The bolter is of the old type with a long narrow hopper divided into sections with values, so that the various separates are received in their proper compartment ( the grades being: flour, seconds, middlings, shorts and bran); then drawn off. Note that the end view of the reel. Instead of wooden wheels and shafts, we now have iron core wheels with wooden teeth or cogs. The mill plan offers some problems in power transmission, also presents a few belt drives. The millstones must run something like 175 to 200 revolutions per minute. The overshoot water wheel, 20 feet in diameter, turns 10 revolutions per minute, hence it is evident some gearing up must be done to run the shaft taking power off the water wheel to make say 50 revolutions. This would necessitate having a spur gear on wheel axle five times the diameter or with five times the number of teeth than that of the wheel on the transmitting shaft. Since the upright shaft also turns 50 revolutions, the gear wheels are bevel or rather miter wheels, each of the same diameter and number of teeth. If the shaft transmitting power and motion to the millstone spindle also turned 50 revolutions, a pair of miter wheels would give the speed required. The millstone spindle had a pinion with 18 teeth, and is driven by a core wheel having 72 teeth or cogs, these being of maple wood. Now we have as in the former example 72X50 divided by 18 equals 200 revolutions per minute. It will be noted that all power and motion to the various machines, like the hopper boy, elevators and reel are taken off the upright shaft. The different speeds are attained by iron bevel gears, so adapted as to size and teeth ratio as to give the proper speeds required. The reel turns 28 revolutions, the cooler (hopper boy) 20 and the elevator head pulleys, 40 revolutions. the machinery in the old mill, except the grain cleaning machine and millstone were slow moving, most of them well under 50 revolutions. The rolling screen is driven by a belt from the elevator cross shaft and turns 40 revolutions. The smutter (grain cleaner), it will be observed is driven by a belt. A pulley 36 inches in diameter on the upright drives by belt an intermediate upright, having on it a 12 inch pulley, which gives this shaft 150 revolutions. A 36 inch pulley on this shaft drives the smutter having a 10 inch pulley on its spindle, the speed of which is 540 revolutions per minute. Thus in a two drive we have raised the speed from 50 to 500 revolutions and over, or a ration of new process milling came into vogue, there were most fast, running machines, like the middlings purifier whose sieves and fan ran from 500 to 600 or more revolutions; suction or ventilating fans from 700 to 1,500 revolutions and scouring machines running as high as 750 to 800 revolutions and separators also requiring high speeds, so that shafting and machines were being driven more and more by belt instead of gear wheels (cog wheels). Machines could be set in line and a shaft overhead or any reasonable distance away, and the power transmitted by belt more easily and economically, besides doing away with the rattle of gear wheels and dangers incidental to unguarded cogged wheels. The upright shaft still held its own during the period allotted to the "new process," but intermediate line shafts belt driven enabled high speed of the later system of roller milling the old, heavy and cumbersome upright shaft was banished, and taking its place a vertical belt drove a counter shaft on say the second or third floor, from the main or jack shaft in the basement of the mill. Other shafts and machines were in turn driven from this main counter shaft. Such a mill as the American or Flat Grinding System would require 27 to 30 horse power and the distribution of power would be about as follows: one pair of millstones - 48 inches in diameter - 17 to 19 horse power; cooler (hopper boy) 1.5 horse power; reel (bolter) 2.5 horse power; elevator, conveyor and screen 2.0 horse power; and the smutter 4 to 5 horse power. Such a mill was capable of turning out 100 barrels of flour in a day of twenty four hours. The power required would vary with the load, that is the amount of grain in bushels per hour, as wheat ground on the millstone for flour, grinding at the rate of 20 bushels per hour, when the stone or burr was in good trim or sharp. However when a stone became worn or dull its grinding capacity was impaired, and it would require one to three more horse power. With the progress in milling and the adoption of what was called the "new process" milling, whereby patent flour was made the machinery was more than doubled. Two pairs of stones somewhat smaller than used in the first example and a still smaller stone to grind the purified middlings would take about 20.0 horse power; 3 grin cleaners, 7.0 horse power; 4 reels and bran duster 4.5 horse power; 2 middlings purifiers, 3.0 horse power; and 5 elevators, shafting, etc., 6.5 horse power or a total of 41.0 horse power. Note this article by Prof. B. W. Dedrick was reprinted in Old Mill News, Winter 1995, pages 18-20.
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