Patent GB-1087070-A (GB)
Title: Method and apparatus for fractionating particulate materials
IPC: G01N15/04
Filed: 1965-11-26
Abstract: 1,087,070. Wet separation of granular materials. BAHCO A.B. Nov. 26, 1965 [Nov. 26, 1964], No. 50409/65. Heading B2H. The distribution of particle size in a particulate material is determined by introducing the particulate material, from a liquid suspension of the material, into a stream of liquid which flows through a substantially horizontal passage with a substantially laminar flow and at a constant velocity, the material being introduced so that all particles enter the stream at substantially the same height and at the same position along the length of the passage. The particulate material is fractionated in the stream of liquid as a result of the particles of different sizes accompanying the liquid over different distances in the direction of of which the first and the last are shown at 8 and 9, and on which the particles settle. The glass sheets are removed by lifting the upper of the two separable parts constituting the apparatus. The suspension of particulate material is introduced into a chamber 6 which is open to atmosphere and communicates with the passage 3 by way of a narrow slot 7. Agglomeration of the particles passing through the slot is prevented by an ultrasonic transmitter 16. The liquid level in the chamber 6 corresponds to the level of the lower orifice of the capillary tube 11 since both are at atmospheric pressure. If the capillary tube 11 is closed, the liquid level in the chamber 6 will be determined by the lower orifice of the capillary tube 12. i.e. the liquid level in the chamber 6 drops. In operation, with pure liquid having been introduced in the container 1 and the valve 5 having been opened so that the liquid level in the chamber 6 becomes adjusted to the level of the lower orifice of the capillary tube 11, the latter is then closed flow so that particles of different sizes settle out from the liquid on to the bottom of the passage at different distances from the particle inlet. As shown, liquid 13 is supplied to a passage 3 from a container 1 which is closed to the atmosphere except by way of two capillary tubes 11, 12 which extend to different levels within the liquid. The passage 3 is connected to an outlet tube 4 provided with a tap 5 and an outlet capillary tube 4a. Guiding members 15 are positioned in the inlet 2 of the passage to ensure laminar flow. On the bottom of the passage 3 are arranged a number of detachable glass sheets, so that the liquid level in chamber 6 drops to the level of the lower orifice of the capillary tube 12. A suspension of the particulate material of a volume equal to the volume of chamber 6 between the level of the lower orifices of the capillary tubes 11, 12 is then introduced into the chamber 6 and at the same time capillary tube 11 is opened. Thus the level in the chamber 6 will be brought up to that of the lower orifice of capillary tube 11 without any flow of liquid taking place through the slot 7. The flow is allowed to continue from the container 1 through the passage 3 by maintaining valve 5 opened. While the liquid level in container 1 drops from the level of the lower orifice of capillary tube 11 to the level of the lower orifice of capillary tube 12, no liquid will flow from chamber 6 into passage 3 and thus the particles which separate from the suspension in the chamber 6 by sedimentation drop through the slot 7 and pass into a substantially laminar flow of constant velocity in the passage 3.