Patent GB-1528875-A (GB)
Title: Air driven centrifuge
IPC: B04B9/08
Filed: 1976-01-29
Abstract: 1528875 Driving and supporting centrifuge rotor BECKMAN INSTRUMENTS INC 29 Jan 1976 [11 April 1975] 03484/76 Heading B2P [Also in Division F2] An air driven centrifuge comprises a housing 12, Fig. 1, in which is formed a chamber 13 in the bottom of which is mounted a seat 17 for supporting a rotor 31 which is located in the chamber and has a lower external surface 32 slanting upwardly and outwardly and incorporating a plurality of flutes 33; means 42 being provided in the seat 17 for directing streams of pressurised air against the surface 32 of the rotor to support the rotor on an air cushion and to spin the rotor as the air streams impinge on the flutes 33, means 78 being selectively movable into frictional contact with a surface on the bottom of the rotor to brake the rotor and to stabilize it as it slows down to a stop. The housing is mounted in a casing 11 having a pivotable cover 14. The seat 17 includes a stator pad 19 which is free floating between annular flanges 22 and 23 on a base member 18 which is sealingly mounted in the housing 12. The rotor may contain sample test tubes arranged in cavities inclined to the rotor axis. The driving air stream is supplied via tube 36, valve 37 and passage 39 into an annular manifold 41 which feeds jet nozzles 42 which direct the pressurised air streams against the driving flutes 33 to drive the rotor: and create a cushion of air between the latter and the seat 17, the air then entering the chamber 13 and exiting through openings 44. In order to support the rotor when it is slowing down, pressurised air is introduced via tube 51, valve 52 and passage 54 into an annular manifold 56 from which the air flows as a sheath through the space formed between a guide bushing 66 and a depending portion 18<SP>a</SP> of the base member 18 and is directed onto a portion of the slanting surface 32 of the rotor where there are no flutes thereby causing the rotor to levitate. Alternatively the levitation air may be directed from the manifold 56 via jet nozzles which are preferably inclined at small angle to the rotor axis of rotation in a direction to oppose rotation of the rotor. The valves 37, 52 may be operated manually or by solenoids 37<SP>a</SP>, 52<SP>a</SP> which are so adjusted that when valve 37 is closed, valve 52 is immediately opened or, preferably, opened just prior to closing of valve 37. Alternatively the levitation air may be continuously fed even while the driving air is being supplied. The brake and stabilizing means 78, as shown in Fig. 1, consists of a frusto-conical brake member mounted on an actuating rod 65 and adapted to frictionally engage the lower inner edge of a P.T.F.E. bushing 61 in a recess 62 in the bottom portion of the rotor 31. The rod 65 is guided through a bushing 66. The rod 65 and hence the brake member 78 are biased towards the rotor by a spring member 71 which passes through a notch 65<SP>a</SP> formed at the lower end of the rod. During normal rotation of the rotor, the brake member 78 is retracted from engagement with the bushing 66 by energizing an electromagnet 76 so that it draws the bottom of the rod 65 against its surface 76<SP>a</SP>. In a modified construction, the rod 65 may be upwardly biased by an electromagnet or by a low pressure air jet when the supply of driving air is discontinued or when the rotor reduces to a predetermined speed. In another construction, Fig. 7, the lower portion of the rotor 31 is conical and the rod 65 is provided with a cylindrical recessed portion in which a P.T.F.E. bushing 82 is mounted so that it engages the rotor when the rod 65 is upwardly biased.