Patent GB-1467493-A (GB)
Title: Preparative ultracentrifuge
IPC: B04B9/12
Filed: 1974-10-10
Abstract: 1467493 Bearings G I VOLKOV V M DENISOV A E ERMISHIN J P ZAOZERSKY V V ZOZIN V P KAPITONOV I K KIKOIN V A LEBEDEV N M LYSTSOV L I MATVEEV T V POPOV V A RYABOV A G SUKHOV V M SYSOEV A A SHISHIN N M SHATALIN S A SHESTERIKOV N F MARTYNOVA O S MARTYNOVA and A S MARTYNOVA 10 Oct 1974 43860/74 Heading F2A [Also in Division B2] An ultracentrifuge for separating substances of different densities in a liquid phase comprises an evacuable housing 1, Fig. 1, which contains a vertically mounted rotor 2 surrounded by a rotor-temperature-regulating shell 8 and adapted for accommodation of vessels for the substances to be centrifuged, the rotor being disposed coaxially with and below a magnetic suspension 3 and above a drive 4 and a support 6, the drive being an electric motor whose armature 11 is in the form of a sleeve 50, 51, Fig. 3, fixedly secured to the rotor and the magnetic suspension being disposed within the housing and comprising an annular permanent magnet 26 with a magnetic conductor 27. The shell 8, Fig. 1, is surrounded by a coil 10 of a cooling unit evaporator (not shown). A cylindrical member 7 is mounted within the housing to protect the latter against breakage of the rotor during rotation. A cover 21 closes an opening in the upper plate 16 of the housing and is held by guides 20; the cover is mounted on ball bearings (not shown) and is rolled aside to uncover the opening. A sleeve 22 is attached to the plate 16 and is provided with grooves for split support rings 23 for mounting a triangular flange 24 for attachment of the magnetic suspension 3. Microswitches (not shown) are mounted on the bearing surface of each ring for closing the rotor rotation control circuit included in the centrifuge control system. The magnetic suspension 3, Fig. 2, comprises an armature 36 of ferromagnetic material which is fixedly secured to the centrifuge rotor and an annular permanent magnet 26 mounted in a cup 25 which is secured to the flange 24 by means of screws 42 after centering by means of screws 41. The upper side of the magnet 26 adjoins a flange portion of the conductor 27 which is in the form of a bush made of soft magnetic material and secured by screws 28 to the cup 25 to provide a gap between its lower portion and the armature 36 so that a lifting pull is produced on the rotor so as to limit the pressure exerted by a flexible support spindle 5, Fig. 1, or 56, Fig. 5, of the rotor on a step bearing 75 of the support 6. The rotor temperature is sensed by a thermistor 30 mounted by means of a holder 31 in member 29 screwed in the conductor 27 and forming part of a rotor temperature control system which includes the sleeve 8. The magnetic suspension 3 is provided with a protective cover 43 and handles 44 attached to the flange 24 facilitate handling of the suspension.  The support 6 comprises a sleeve 62 which is secured to the lower plate 15 of the centrifuge housing 1 and which has mounted on it the disc 61 and an inductive tacho-generator 63 for measuring the rotor speed. A sleeve 64 is vertically movable within the sleeve 62 and is connected thereto by means of an elastic strip 66 which is in contact with a limiting disc 71 clamped to the sleeve 62 and serving to prevent the strip 66 from being drawn inside the sleeve 62 when the centrifuge housing is being evacuated. A sleeve 72 mounted in the upper part of the sleeve 64 is integrally formed with a bush 73 into which is press-fitted a mandrel 74 carrying the step bearing 75 which receives the enlarged end of the rotor flexible support spindle 56. The spindle extends through the cylindrical projection 60 and through an annular insert 78. The latter serves to centre the bearing 75 and is mounted in the bush 73 and is connected by springs 79 to the sleeve 64. A post 76 has one end inserted in the bush 73 and the other end secured to a needle 77. A pressure pick up 82 is provided in the lower part of the sleeve 64 and consists of coils 85 disposed in a casing 83 retained in the sleeve 64 by a ring 84, each coil having a core 87 of soft magnetic material. A bar 88 passes through bushings 94 extending through the cores. The upper end of the bar terminates in a toe 89 which the needle 77 of the post 76 rests. A diaphragm 90 is connected at each end of the bar 88. A ferromagnetic disc 93 is mounted on the bar between the bushings 94 so that a gap 8 is provided between the disc and the end of each core 87. The space inside the sleeve 64 above the upper diaphragm 90 contains oil for lubricating the rubbing surface of the spindle 56 and the step-bearing 75 and to damp oscillations of the rotor 2 during operation of the centrifuge.  Prior to use, the rotor 2 with the sample containing vessels is mounted in the housing 1. The rotor weight is transmitted via its spindle 56 to the step bearing 75, bush 73, post 76, needle 77, toe 89, bar 88, diaphragms 90 and then through the cores 87 to the casing 83 of the pressure pickup 82 and thence to the movable sleeve 64. As a result, the sleeve 64 moves down until the rotor touches the disc 61. Movement of the sleeve causes bending of the elastic strip 66 which is of such rigidity that when it is bent the pressure exerted on the step-bearing 75 does not exceed a predetermined value. The magnetic suspension 3 is then mounted in the housing and the cover 21 is closed. The air evacuation and temperature control systems are operated to maintain the interior of the housing at the required pressure and temperature. As the pressure within the housing drops, the atmospheric pressure acting on the strip 66 and on the lower end of the sleeve 64 causes the latter to move upwards until its flange 65 abuts a shoulder on the sleeve 62. Simultaneously the rotor 2 also moves upwards and is supported only by the spindle 56 resting on the step bearing 75. When the upward movement of the rotor is terminated, the gap between the armature 36 and the conductor 27 of the magnetic suspension is such that the lift produced by the magnet 26 limits the pressure exerted by the spindle 56 on the stepbearing 75 to the predetermined value. The electric motor 4 is then started so as to rotate the rotor 2 to centrifuging speed which is continuously measured by the tacho-generator 63. Oscillations of the rotor 2, e.g. during its acceleration, are transmitted via the spindle 56 and bearing 75 to the sleeve 72 and are damped in the oil in which the sleeve is mounted. The amplitude of oscillations caused by strong accidental disturbances is limited by contact of the armature 36 with a plastics ring 38, Fig. 2, mounted at the lower end of the member 29 and of the projection 60 with the disc 61. During operation, variation of the pressure exerted by the spindle 56 on the step-bearing 75 causes the diaphragms 90 to bend and move the bar 88 with the disc 93 up and down. This causes the gap between the disc 93 and the cores 87 of the coils 85 to vary and this in turn causes changes in the inductive reactance of the coils which are sensed by a measuring system. This measurement of pressure on the step-bearing makes it possible to check for correct initial assembly of the centrifuge and its condition during operation.