Bourne Archive: Muspratt: Bark Mills

http://boar.org.uk/aaiwxw3MusprattL4BarkMill.htm      Latest edit 27 Dec 2010


 

The Bourne Archive

 


Muspratt’s Chemistry, Theoretical, Practical & Analytical (ca. 1859)


Extracts Concerning Leather, 4: Bark Mills.


The web pages linked from this introduction are from an article on tanning, under the heading ‘Leather’. The original article is presented here in several web pages, respectively dealing; 1, with leather; 2, with tanning materials; 3, Sources of tannin; 4, bark crushing mills; 5, varieties of skin; 6, hide preparation; 7, the common tanning process; 8, finishing processes; 9, fancy and speciality leathers.


Vol. 2. pp. 508-9

To render any of the foregoing materials 1 suitable for the present operations of the tanner, it is necessary to bring them into a minute state of division, in order that by the treatment to which they are subjected, they may the more quickly yield up their tannin. With the exception of the inspissated 2 juices, this condition is gained by grinding or cutting machines which reduce the roots, branches, or barks, to a fine powder. Numerous kinds of mechanical adaptations have been introduced into this department, varying in simplicity from old head-stone rollers 3, to very intricate arrangements. It would require too much space to give even a curt description of these; suffice it then that the principles on which they are constructed may be inferred from the machines described here:—

Farcot’s 4 bark-cutting machine, extensively used in France, is shown in elevated section and plan in Figs. 342 and 343, 5 in which A A’ are two fluted cylinders, which supply the bark previously spread upon the table, a, having a raised ledge, h, to the cutting apparatus. This is composed of two parallel circles, fixed upon a common axis, C, having steel plates or knives, B B, screwed upon them, and which are disposed in the form of a helice 6 or spiral. On one end of the axis, C, is the fly-wheel, S, and drum, D, which receives the movement or power by a strap that connects it with the main shaft of the engine; the other end has a pinion, I, which gears into a toothed wheel, J, on the axis of the fluted cylinder, A, and by means of another smaller one acting upon E, on the axis side of A. the motion is likewise transmitted to the latter. By the levers, F F, and a weight, G, the two cylinders, A A’, are regulated to any required proximity. Inside the fluted cylinders is a longitudinal piece of steel, C, which delivers the bark to the revolving knives, and at the same time acts by its sharp edge as a shears towards the cutting knives. The cylinder which carries the cutting knives makes about one hundred and thirty revolutions per minute, as also the feeding cylinders; and the quantity of bark cut averages one thousand six hundred pounds per hour.

The chopped bark is then passed to a mill for reducing it still further, and which is shown in Fig. 344. This machine is on the principle of Weldon’s bark-grinding mill, introduced so far back as 1797. In this figure, A is a conical drum of iron on the end of the shaft, D, which forms its axis, inclosed 7 in the cast-iron hopper, B B, where the coarse bark is deposited. This hopper is firmly secured by screws to a flange, which runs all round the framework, v v, as shown at a a. In the top of the exterior is across beam secured by screws, and having a socket in the middle part through which the axis of the drum passes. The lower part of the shaft rests and turns upon a bed, C, upon the stage, T, and regulated so as to have the cone, A, in position, by the side of the bottom screws, a’ a’ and b. The inner face of the hopper,  B, which is in close contact with the revolving cone, is, like the latter, serrated or grooved, so that the bark passing down is more minutely sundered. Fig. 345 shows the position of the two cutting surfaces with respect to one another. The central drum makes twenty-five revolutions per minute, and in the course of twenty-four hours grinds about eight thousand six hundred pounds of bark. The cutting machine already described is capable of supplying three grinding mills.

Another grinding mill, very much used in America, where it is known as Wiltze’s or Catskill’s, is shown in Fig. 346. This is in principal the same as Weldon’s, only that instead of grooves an arrangement of sharp-edged teeth, both in the inclosed bell and hopper is employed. As the bell turns by the power exercised upon the shaft, the teeth in the former, revolving, also react on the principle of the shears with those of the interior of the case, and the bark is very finely and rapidly reduced. Before the matter is submitted to this machine, it is broken down by passing it into another hopper adjacent to the former, in which there is a sharp-toothed hoop or curb, and which divides the bark into pieces. It is moved at the rate of thirty to forty revolutions per minute, whilst the grinding machine may travel at the rate of one hundred and fifty. With this speed, communicated by a ten horse-power engine, it will grind from one to two chords per hour. The bark is cut short, without being reduced to flour, and thus it is more readily exhausted 8; there is also the additional advantage that, should the bark be moist, it does not become clogged like others.

Next Page: Varieties of Skin.


Commentary

1. ^    These are the barks, roots etc., of various woody species, listed in part 3.

2. ^   This is a Late Latin-based word, meaning thickened or condensed (OED).

3. ^   This would be a cheaply set up answer to the need. A worn-out runner stone from a corn mill, mounted on an axle pivoted at the centre of a circular stone track and propelled by a horse, would roll over the track, crushing the bark. This design mimics those used for crushing woad and cider apples. An elaborate woad mill is shown on Arthur Young’s page 175. A clearer picture of the mechanism appears in Gatty’s Aunt Judy’s Annual Volume (1883), page 551. The same principle is employed by the olive-crushing mill illustrated here.

4. ^   This is probably a product of the mind of Joseph Farcot, or possibly of his father Marie-Joseph.

5. ^   Together, these represent two of the three views of an orthographic projection but as drawn, the plan represents a machine designed the opposite way round from that of the sectioned elevation.

6. ^   This is the French form of the word helix. It was screw-shaped.

7. ^   Inclose is a variant of enclose, derived directly from Latin, while enclose came into English via French. It was once more widely used but now restricted to some legal documents and Acts of Parliament (OED).

8. ^   Drained of its tannin.


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