Fig. 54.
The movable slab a, fitted with an upright rim at its edges, has underneath two projecting pieces d, working against deeply toothed wheels e, which fastened on the shaft b, are driven round by the pulleys c. The teeth of the wheels catch on the projecting pieces at every revolution of the shaft and push them rather gently on one side, and when the tooth-points slide from under the slab, it drops down as much as it has been previously raised. Each tooth of the wheel coming into contact with the projections, the same motion is repeated several times, causing the slab to oscillate up and down.
This oscillation of the slab is controlled by means of a hand lever f, occurring on the shaft g, and fixed crosswise thereon, so that we can only show it in cross section on the diagram. The lever f attaches itself to the under part of the slab, raises it, and so throws the wheels out of contact with the projecting pieces, but without stopping the rotation of the shaft b.
Shaking tables have also witnessed considerable improvements with the lapse of time, and we shall now proceed to treat these in more detail, especially as several recent constructions offer and illustrate many interesting mechanical points.
Fig. 55.
Fig. 56.
An old type of machine, that is nevertheless still much employed, is illustrated in fig. 55. Here the slab is caused to osculate by shaking wheels introduced underneath, each possessing six, eight, or more teeth. The slab is raised and lowered by contact with wedge-shaped parts, the effect produced being greater or less according as the moulds are large or small, heavy or light, and in proportion to the consistency of the chocolate mass which they contain, e. g. whether it is solid or semi-liquid.
Quite an improved construction is shown in fig. 56. Here the table is attached to a vertical axle, which is moved up and down by means of a toothed wheel fixed on its bottom end. There is also a cylinder arrangement under the whole machine to assist in controlling the vertical motion of the shaft, and as it is provided with automatic lubrication, there is no danger of any wearing out of the apparatus and consequent irregularity of functioning.