One plan (Pat. 346,030), designed to combine the advantages of a direct acting motor and an oscillating shaft, mounts the whole machine, motor and all, on a rocking frame. The spindle is of course in fixed bearings in the frame. However, the plan is not practical.
In driers the direct acting engine has many advantages over the belt. The atmosphere is always very moist about a whizzer, and there are frequently injurious fumes. The belt will be alternately dry and wet, stretched and limp, and wears out rapidly and is liable to sever. In all machines in which the shaft oscillates, if the center of oscillation does not lie in the central plane of the belt, the tension of the latter is not uniform. This affects badly both the belt and the running. A reference to the various figures will show the best position for the pulley.
The greatest difficulty experienced with belting is in getting up speed and stopping. The basket must not be started with a sudden impulse. Its inertia will resist and something must give way. A gradual starting can be obtained by the slipping of the belt at first, but this is expensive. The best plan is to conduct the power through a species of friction clutch - an iron disk between two wooden ones. This has been found to work admirably.
The first centrifugals had no brakes. They ran until the friction of the bearings was sufficient to stop them. This occasioned, however, rapid wearing and too great a loss of time. The best material for a brake consists of soft wood into which shoe pegs have been driven, and which is thoroughly saturated with oil. The wooden disks referred to just above are of the same construction. The center of oscillation ought to be in the central plane of the brake as well as that of the pulley, but the preference is given to the pulley.
Figs. 15 and 16 (I) give sectional views of a brake for hanging machines. Figs. 19, 20, and 21 give two sections and a view of a brake which can be used on both hanging and standing machines. A very simple form of brake is shown in Figs. 24, 26, and 27 (A), a mere block pressing on the rim of the basket.
A machine in most respects like a whizzer is used for the "extraction of oil and fat and oily and fatty matters from woolen yarns and fabrics, and such other fibrous material or mixtures of materials as are from their nature affected in color or quality when hydrocarbons are used for the purpose of extracting such oily or fatty matters, and are subsequently removed from the material under treatment by the slow process of admitting steam, or using other means of raising the temperature to the respective boiling points of such hydrocarbons, and so driving them off by evaporation." In the centrifugal method carbon-bisulphide, or some other volatile agent, is admitted and is driven through the material by centrifugal force, when the necessary reactions take place, and is allowed to escape in the form of hydrocarbons. A machine differing only in slight particulars from the above is used for cleansing wool.
Another application is the drying of loose fiber. Two distinctive points deserve to be noticed in the centrifugal used for this purpose. An endless chain or belt provided with blades moves the material vertically in the basket, and discharges it over the edge. During its upward course the material is subjected to a shower of water to wash it.
Very material savings are made in many factories by collecting the metal chips and turnings, coated and mixed with oil, which fall from the various machines, and extracting the oil centrifugally. The separator consists of a chip holder, having an imperforate shell flaring upward and outward from the spindle (in fixed bearings) to which it is attached. When filled, a cover is placed upon it and keyed to the spindle. Between the cover and holder there is a small annular opening through which oil, but not chips, can escape. Fig. 29 (Pat. 225,949 - C.F. Roper) is designed (like the greater part of the drawings inserted) to show relative position of parts merely, and not relative size. This style of machine can be used for sugar separating (Pat. 345,994 - F.P. Sherman) and many other purposes, to which, however, there are other styles more especially adapted.
There are two distinct kinds of centrifugal filterers, working on different principles. Petroleum separators (Pat. 217,063) are of the first kind. They are in form in all respects like a sugar machine. The flakes of paraffine, stearine, etc., which are to be extracted, when chilled are very brittle and would be disintegrated upon being hurled against a plain wire gauze and would escape. Even a woven fabric presents too harsh a surface. It is necessary to have a very elastic basket lining of wool, cotton, or other fibrous material. The basket itself may be either wire or perforated, but must have a perfectly smooth bottom.
As the pressure of the liquor upon the filtering medium per unit of surface depends entirely upon its radial depth, mere tubes, connecting a central inlet with an annular compartment, will serve the purpose quite as well as a whole basket. In this style of machine (Pat. 10,457) the filtering material constitutes a wall between two annular compartments. The outer one is connected with a vacuum apparatus.
Filterers of the second kind work on the following principle: If a cylinder be rapidly revolved in a liquid in which solid particles are suspended, the liquid will be drawn into a like rotation and the heavy particles will be thrown to the outer part of the receptacle. If a perforated cylinder is used as stirrer, the purified liquid will escape into it through the perforations and may be conducted away. The impurities, likewise, after falling down the sides of the receptacle, are carried off. The advantages of this method are that no filtering material is needed and the filtering surface is never in contact with anything but pure liquor.