1902 Encyclopedia > Agriculture > Machines for Preparing the Crops for Market: (b)Thrashing Machines. (c) Winnowing Machines.

(Part 27)


Machines for Preparing the Crops for Market: (b)Thrashing Machines. (c) Winnowing Machines.

Thrashing Machines

It is now sixty-five years since an ingenious Scotch mechanist, Andrew Meikle, produced a thrashing-machine so perfect that its essential features are retained unaltered to the present day. Indeed, it is frequently asserted that, after all the modifications and supposed improvements of the thrashing-machine which have been introduced by various parties, the mills made by Meikle himself have not yet been surpassed, so far as through and rapid separation of the grain from the straw is concerned. The unthrashed corn is fed evenly into a pair of slowly revolving fluted rollers of cast-iron, by which it is presented to the action of a rapid revolving cylinder or drum armed with four beaters, which are square spars of wood faced with iron, fixed parallel to its axis, and projecting about four inches from its circumference. The drum is provided with a dome or cover, and the corn being partly held by the fluted rollers as it passes betwixt the drum and its cover, the rapid strokes of the beaters detach the grain from the ears, and throw the straw forward upon slowly revolving rakes, in passing over which the loose grain is shaken out of the straw, and falls through a granting into the hopper of a winnowing and riddling machine, which rids it of dust and chaff, and separates the grain from the unthrashed ears and broken straw, called roughs or shorts. The grain and roughs are discharged by separated spouts into the apartment below the thrashing-loft, whence the corn is fed into the rollers, and the thrashed straw falls from the rakes into the straw barn beyond. Since Meikle’s time further additions have been made to the machinery. In the most improved machines driven by steam or a sufficient water power, the grain is raised by a series of buckets fixed on an endless web into the hopper of a double winnowing-machine, by which it is separated into clean corn, light, whites or capes, and small seeds and sand. The discharging spouts are sufficiently elevated to admit of sacks being hooked on to receive the different products as they fall. When barley is thrashed, it is first carried by a separate set of elevators, which can be detached at pleasure, into a "hummeller," in which it is freed from the awns, and then raised into the second fanners in the same manner as the other grain. The hummeller is a hollow cylinder, in which a spindle fitted with transverse blunt knives revolves rapidly. The rough grain is poured in at the top, and, after being acted upon by the knives, is emitted at the bottom through an opening which is enlarged or diminished by a sliding shutter, according to the degree of trimming that is required. A large set of elevators is usually employed to carry up the roughs to the feeding-board, that they may again be subjected to the action of the drum. The roughs are emptied, not directly on the feeding-board, but into a riddle, from which the loose grin passes by a canvass funnel direct to the winnower in the apartment below, and only the unthrashed ears and short straw are allowed to fall upon the board.

The alterations that have been made upon the thrashing-machine since Meikle’s time chiefly affect the drum. Meikle himself tried to improved upon his beaters by fixing a projecting ledge of iron on their outer edges, so as to give them a scotching action similar to that of flax-mills. This strips off the grain from oats or barley very well when thinly fed in; but its tendency is to rub off the entire ears, especially of wheat, and also to miss a portion of the ears, whenever there is rapid feeding in. More recent trials of drums on the scotching principle show them to be on the whole inferior to the plain beater.

We have already referred to the general use of portable thrashing-machines in the eastern counties of England. These, for the most part, have drums with six beaters upon a skeleton frame, which revolve with great rapidity (about 800 times per minute, hence often called high-speed drum), within a concave or screen, which encloses the drum for about one-third its circumference. These screens consists alternately of iron ribs and open wire-work, and is so placed that its inner surface can be brought into near contact with the edges of the revolving beaters, and admits of this space being increased or diminished by means of screws. No feeding-rollers are used with this drum, the unthrashed corn being introduced directly to it.

Another form of drum, acting on the same principle as that just referred to, but cased with plate-iron, and having for beaters eight strips of iron projecting about one-fourth of an inch from its surface, and which works within a concave which embraces it for three-fifths of its circumference, is in use when it is desired to preserve the straw as straight and unbroken as possible. These are made of sufficient width to admit of the corn being fed in sideways, and are called bolting machines, from the straw being delivered in a fit state for being at once made up into bolts or bundles for market. Although the term beaters is retained in describing these drums, it is evident that the process by which the grain is separated from the ears is rubbing rather than beating. This necessarily requires that only a narrow space intervene between drum and concave, and that the corn be fed in somewhat thinly. Such machines thrash clean, whether the ears are all at one end of the sheaf or not, and deliver the straw straight and uninjured; but it is objected to these by some that they are slower in their operation than those with the beating drum, are liable to choke if the straw is at all damp, that the grain is sometimes broken by them, and that they require greater power to drive them.

A further and more recent modification is the peg-drum. In this case the drum is fitted with parallel rows of iron pegs, projecting about 2_ inches from its surface, which in its revolutions pass within one-fourth of an inch of similar pegs fixed in the concave in rows running at right angles to the drum. Great things were at first anticipated this invention, which, however, it has failed to realize. But iron pegs have more recently been added to the common beater-drum with apparent success. The beaters in this case are made one-half narrower than usual, and have stout iron pegs, formed of square rods, driven into their faces, angle foremost and slightly reflected at the points. These act by a combination of beating and rippling, and are said to thrash clean and to be easily driven.

There is thus a great variety of thrashing-machines to be found in different parts of the country, the comparative merits of which are frequently and keenly discussed by agriculturists. The extraordinary discrepancies in the amount and quality of the work performed by different machines, and in the power required to effect it, are due quite as much to the varying degrees of skill with which their parts are proportioned and put together, as to varying merit in the respective plans of construction.

In the best examples of 6-horse power stationary steam engines and thrashing-machinery, as found in the Lothians, fifty quarters of grain, taking the average of wheat, barley, and oats, are thrashed, dressed, and sacked up ready for market, in a day of ten hours, with a consumption of 7 1/2 cwt. of good coals, and a gross expenditure for wages, value of horse labour, fuel, an wear and tear of machinery of 9d. per quarter.

The exigencies of the labour market are giving a powerful stimulus of the use of labour-saving contrivances of all kinds; and hence the recent introduction of straw elevators, to be worked either by horse-power or by the same steam-engine that is driving the thrashing-machinery. The later plan finds most favour in England, where it has already been adopted to a considerable extent.

The Royal Agricultural Society of England has done much towards ascertaining the real merits of the various thrashing-machines now in use, by the carefully conducted comparative trials to which it has subjected those which have been presented in competition for its liberal prizes. The accuracy of these trials, and the value of the recorded results, have been much enhanced by the use of an ingenious apparatus invented by Mr. C. E. Amos, consulting engineer to the Society , which is figured and described at p. 479 of vol. xi. of the Society’s Journal. A pencil connected with this apparatus traces a diagram upon a sheet of paper, recording every variation of the power employed during the experiment to work the machine under trial. For reasons already stated, we regard it as unfortunate that the patronage of this great Society has hitherto been so exclusively bestowed upon portable machines.

Winnowing Machines

We have already referred to the farmers, which, except in portable machines, are almost invariably found in combination with thrashing-machinery, so as to deliver the grain into the corn-chamber in a comparatively clean state; and we have also noticed the further contrivances by which, when there is a sufficient motive power at command, the complete dressing of the grain goes on simultaneously with the thrashing. The winnowers used in such cases do not differ in construction from those worked by hand. Indeed, it is usual to have one at least than can be used in either way at pleasure. In these machines the separation of the clean from the light grain, and of both from dust, sand, and seeds of weeds, or other rubbish, is effected by directing an artificial blast of wind upon a steam of grain as it falls upon a riddle. There is thus a combination of fanning and sifting, which is used in different degrees according to the views of the mechanist, In some forms of this machine the benefit of the artificial last is in a great measure lost through an injudicious application of it.

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