TABLE OF CONTENTS There are probably more machines equipped with the under-tub vibrator than any other design. The introduction of tub-type vibrators in the 1950s featured this method and it continues to be used today. The vibrator is attached beneath the tub itself, having pie-shaped flyweights fitted to the shaft ends. Vibration input is upward producing a rise and fall motion to the tub, the eccentricity develops the orbital path of the mass motion opposite of the vibrator rotation. Variable speed is a desirable feature that aids in controlling any variables in mass density.
Machines equipped with magnetic vibrators are usually limited to less than 10 cu ft (0.28 m 3) in capacity. The vibration input is from the underside of the tub and operates at a constant 3600 cycles per minute. Voltage is controlled via a rectifier console. Increasing the voltage strengthens the magnetic field resulting in a longer pull to the armature, thus increasing the stroke. The theory is that variable strokes simulate the variable speed and amplitude of a mechanical vibrator without changing weights.
Round bowl vibrators are available in a number of "diameter ratios" the ratio of the center section diameter to the channel cross-sectional diameter (Fig. 10-16). A 1:1 ratio means the processing channel has the same diameter as the center section diameter. A 4:1 ratio means the center section diameter is four times that of the channel diameter. Generally, the closer this ratio is to unity (1:1), the lower the cost of the machine.
