Patent GB-166238-A (GB)
Title: Improvements in means adapted to impart vibratory motion to screens
IPC: B07B1/28
Filed: 1919-07-28
Abstract: 166,238. Mitchell, B. A. July 28, 1919. Fixed sieves; sieves with compound or variable motion.-A screen is provided with a vibrator for producing minute circular vibrations of high frequency in a plane at right-angles to the surface of the screen. In the form shown in Figs 2, 3, and 5, the material to be sifted passes from a hopper 20 to the sieve through an opening 23 controlled by a gate 24. The screen frame is pivoted at its upper end with adjusting-bars 33 having a number of holes 34 adapted to be engaged by removable bolts 35 in order that the inclination of the screen may be varied. The ends of the screen cloth 40 are wrapped round rods 41 mounted in slotted tubes 42 which are engaged by the arms 43<a> of bolts 43 by means of which the tension of the screen cloth can be adjusted. The vibration 46 is mounted above the screen and comprises a central housing 47 mounted on a beam 50 secured to the lower wall of the screen frame and end casings 48 bolted to the central housing. A shaft 51 driven by a belt passing over a pulley 52 extends through the central housing into the end casing and carries rotary unbalanced members 58. Ball bearings 56, 62 are provided as shown, and the space within each end casing is filled with oil or other lubricant. The vibrations set up by the rotation of the shaft 51 are transmitted to the screen 40 by plates 68 mounted on collars 69 secured to the end casings. The lower ends of the plates 68 carry strips 72 of wood or other material which bear directly on the upper surface of the screen cloth. In a modification, the vibrator is mounted below the screen, and the central housing of the vibrator forms the casing of an electric motor, the armature of which is mounted on the shaft 51. In another modification, Fig. 10, the vibrator comprises a single unbalanced rotary member 140 connected by flexible shafting to an electric motor 136. In this form, the vibrator is mounted directly on the screen cloth by means of members 141. In the form shown in Fig. 11, the vibrator comprises two complementary casings 145 secured together by bolts 146 and provided with parts forming a spherical projection 147 seated in a recess in a plate 149 mounted on the supporting-member 150, to which the vibrator is secured by a strap 151. The stator frame 152 of an electric motor is mounted within the casing, the rotor being mounted on a shaft 157 which extends through cylindrical bearings 154. On the ends of the shaft 157 are mounted roller casings 158 provided with slots or grooves 159, in one of which are mounted balls 161 which produce the unbalanced effect. The balls in the roller casings at opposite ends of the shaft are preferably placed on opposite sides of the shaft, so that the vibrations produced at one end of the casing are 180‹ out of phase with those produced at the other end. The vibrations are transmitted to the screen in the same manner as in the form shown in Figs. 2 and 3. Fan wheels 165 are mounted on the shaft 157 on each side of the rotor in order to cause air to circulate through a passage 167 and around the windings for cooling purposes, the air being- finally discharged through ports 169.