Fig. 31 (Pat. 355,050—C.A. Backstrom) shows another very late style of creamer. A pipe delivers the milk into P4. Passing out of the tube separation takes place, and cream falls down the center to P2 and out of O3. When the compartment under the first shelf becomes full of the skim milk, the latter passes up through the slot, S, strikes a radial partition, R, and its course is reversed. Here more cream separates and passes to center and falls directly, and so on through the whole series of annular compartments, until the top one, when the skim milk enters tube T2 and passes out of O2. By this operation there are substantially repeated subjections of specified quantities of milk to the action of centrifugal force, bringing about a thorough separation. By changing the course of the milk in direction, its path is made longer. This machine can run at much lower speed than many other styles, and yet do the same work.
Class III., Solids From Solids.—As for grain machines, which are in this class, it may be said that in centrifugal flour bolters, bran cleaners, and middlings purifiers, though theoretically centrifugal force plays an important part in their action, yet practically the real separation is brought about by other agencies: in some by brushes which rub the finer particles through wire netting as they rotate against it.
The principle exhibited in a separator of grains and seeds is very neat. (Pat. 167,297.) See Fig. 32. That part of the machine with which we have to do consists essentially of a horizontal revolving disk. The mixed grains are cast on this disk, pass to the edge, and are hurled off at a tangent. Suppose at A. Each particle is immediately acted on by three forces. For all particles of the same size and having the same velocity the resistance of the air may be taken the same, that is, proportional to the area presented. The acceleration of gravity is the same; but the inertia of the heavier grain is greater. The resultant of the two conspiring forces R and (Mv2)/2 varies, and is greater for a heavier grain. Therefore, the paths described in the air will vary, especially in length; and how this is utilized the drawing illustrates.
Fig. 32.
Ore.—In ore machines there is one for pulverizing and separating coal (Pat. 306,544), in which there is a breaker provided with helical blades or paddles, partaking of rapid rotary motion within a stationary cylinder of wire netting. The dust, constituting the valuable part of the product, is hurled out as fast as formed. In this style of machine, beaters are necessary not only for pulverizing, but to get up rotary motion for generating centrifugal force. In the classes preceding, the friction of the basket sufficed for this latter purpose; but here there is no rotating basket and no definite charge. As the material falls through the machine, separation takes place. Various kinds of ore may be treated in the same manner.
An "ore concentrator" (Pat. 254,123), as it is called, consists of a pan having rotary and oscillatory motions. Crushed ore is delivered over the edge in water. The heavy particles of the metal are thrown by centrifugal force against the rim of the pan, overcoming the force of the water, which carries the sand and other impurities in toward the center and away.
Amalgamators.—The best ore centrifugal or separator is what is called an "amalgamator." The last invention (Pat. 355,958, White) consists essentially of a pan, a meridian section of which would give a curve whose normal at any point is in the direction of the resultant of the centrifugal force at that point and gravity. There is a cover to this pan whose convexity almost fits the concavity of the pan, leaving a space of about an inch between. Crushed ore with water is admitted at the center between the cover and the pan, and is driven by centrifugal force through a mass of mercury (which occupies part of this space between the two) and out over the edge of the pan. The particles of metal coming in contact with the mercury amalgamate, and as the speed is regulated so that it is never great enough to hurl the mercury out, nothing but sand, water, etc., escape. There have been many different constructions devised, but this general principle runs through all. By having annular flanges running down from the cover with openings placed alternately, the mixture is compelled to follow a tortuous course, thus giving time for all the gold or other metal to become amalgamated. There are ridges in the pan, too, against which the amalgam lodges. It is claimed for this machine that not a particle of the precious metal is lost, and experiments seem to uphold the claim.
A machine for separating fine from coarse clay for porcelain or for separating the finer quality of plumbago from the coarser for lead pencils uses an imperforate basket, against the wall of which the coarser part banks and catches under the rim. The finer part forms an inner cylindrical stratum, but is allowed to spill over the edge of the rim. The mixture is introduced at the bottom of the basket at the center.