US3339836A

US3339836A - Centrifuges

Info

Publication number: US3339836A
Application number: US429808A
Authority: US
Inventors: Robert J Mitchell; David E Bulpett
Original assignee: International Equipment Co
Current assignee: Thermo IEC Inc
Priority date: 1965-02-02
Filing date: 1965-02-02
Publication date: 1967-09-05
Anticipated expiration: 1984-09-05

Description

2 Sheets-Sheet l R. J. MITCHELL ETAL CENTRIFUGES Sept. 5, 1967 Filed Feb. 2, 1965 .Roeaf JTM Bale Filed Feb. 2, 1965 Sept, 5, 1967 R. J. MITCHELL ETAL 3,339,836

CENTRIFUGES 2 Sheets-Sheet 2 lieven/favs.- aw IMM, BvEZBuZpe-',

United States Patent Oce 3,339,836 Patented Sept. 5, 1967 chusetts Filed Feb. 2, 1965, Ser. No. 429,808 Claims. (Cl. 233-23) The present invention relates to apparatus having a chamber in which a rotor is supported by a driving member that is subject to an unwanted force due to an air ilow developed by its rotation.

The invention is discussed herein with particular reference to centrifuges when the driving mem'ber is sulllciently flexible to permit random low frequency excursions of the rotor. The use of such a driving member has substantial advantages both in construction and in use. Centrifuges incorporating such drives commonly have their useful speed ranges severely |limited because at speeds critical with each head and usually well below that for which that head was designed, vibrations develop that cannot be tolerated.

We have discovered that such vibrations are due to air ilow patterns which develop 'between the rotating head and the stationary walls of the chamber. At low rotor speeds, the air ilow is substantially laminar and relatively stable. The air flow becomes less stable as the rotor speed increases so that at intermediate speeds, the air currents have the effect of inducing the head to move oil center in a cyclical or vibrational manner akin to the whir effect which sometimes develops in a full fluid journal bearing. At yet higher speeds of the roten, the air flow is stronger and more critical with the air pressure being applied to the head, during its excursions, so unequally that the head vibrations or vibrational tendencies are abetted.

In accordance with our invention, we overcome these objectionable features by providing a stabilizing vertical air ilow such that the head, during its excursions, is not subjected to unequal air pressures of a magnitude that would induce or abet head vibrations. We effect that result by providing baille means within the chamber to intercept air currents and direct them inwardly towards the axis of the head both to avoid laminar flow and to create the turbulence necessary to avoid causing the head to vibrate during its excursions.

The baille means advantageously consists of a series of baffles and these may conveniently 'be carried by the cover and, in preferred forms, these baffles are equal-ly spaced spirals.

In the accompanying drawings, there is shown an illustrative embodiment of the invention from which these and other of its objectives, novel features, and advantages will be readily app-arent.

In the drawings:

FIGURE 1 is a fragmentary and partly sectioned view of a centrifuge, the section being taken vertically through the bowl assembly,

FIGURE 2 is a section taken approximately along the indicated lines 2 2 of FIGURE 1, and

FIGURE 3 is a section taken approximately along the indicated lines 3 3 of FIGURE 2.

The centrifuge sho-wn in the drawings has a casing 5 housing the generally indicated bowl assembly 6 and the generally indicated drive assembly 7. The bowl assembly 6 provides a cylindrical chamber 8 having an axial bottom opening 9.

The drive assembly 7 has a housing 10 which extends upwardly through the opening 9 and is sealed as by a grommet 11 attached to the bottom of the bowl. The drive assembly has a relatively small sha'ft 12 freely confined in the upper part of the housing 10 and fast on its upper end there is a support 13 dimensioned to fit the axial passage 14 of a head 15 and provided at its lower end with a supporting shoulder 16 therefor and at its upper end with threads 17 to receive the nut 18 by which the head 15 is locked to the shaft 12. The head 15 has a series of equally spaced and downwardly and outwardly inclined bores 19, each dimensioned to receive a tube, not shown, `containing liquid to be centrifuged.

A cover 20 is attached to the casing 5 as by a hinge 21 to swing downwardly into a receiver seat 22 and against a gasket 23. The cover 20 is also provided with a latch 24 movable by its handle 25 into and out of holding engagement with a striker plate 26.

In the operation of the centrifuge, as thus far described, air is driven outwardly by the head 15, as it rotates, towards the inner Wall of the bowl assembly. At speeds critical with each head, some tendency to vibrate exists and if the air llow is a regular pattern, any excursion of the head results in air being applied thereto with such pressure differentials that vibrations result, necessarily limiting the speed of operation of that centrifuge with that head. In any event, the flexibility of the drive results in speed-limiting vibrations developing at some critical speed which varies more or less directly with the weight and configuration of the head used. These Vibrations are often so severe as to limit the speed of the centrifuge to a speed considerably lower than that originally intended as the maximum centrifuge speed when that head was used.

In the embodiment of the invention illustrated by the drawings, the cover 20 includes a molded shell 27 provided With a pair of spiral =bailles 28. When the cover 20 is closed, the baflles 2.8 depend within the -upper part of the chamber 8 with their outer ends close to the inner surface of the bowl assembly 6. Each baille 28 is shown as surrounding the axis of t-he head 15 with its inner end spaced therefrom. The vertical dimensions of the ballles increase towards their inner ends.

In use, the bailles 28 intercept -air currents in the upper part of the chamber 8 and direct them inwardly to- Wards the axis of the head 15 with the air stream being vertical and ilowing downwardly against the head 15. As a consequence, excursions of t-he head 15 are not attended by the development of areas characterized `by such a pressure differential as would induce or abet head vibrations. As a consequence, the critical speed lrange may 'be passed throu-gh enabling the centrifuge to be brought up to the maximum speed for which the 4head was designed Iwithout troublesome vibrations resulting.

We claim:

1. A centrifuge comprising -an upwardly opening chamber, a rotor in said chamber of frusto-conic form, a drive to rotate said rotor including a driving member axially connected to said rotor within said chamber, said driving member lbeing sufficiently flexible to permit random, low "frequency excursions of said rotor, a cover closing said chamber, rotation of said rotor causing the air to flow outwardly from the rotor against the chamber wall and upwardly against said cover, and baille means in the chamber above the rotor to so intercept the upward air flow 3 and direct it inwardly and provide a downward vertical air ow towards the upper end of the rotor thereby to provide sufficient turbulence to avoid sustained pressure differentials on said rotor, during `excursions thereof, as would induce rotor vibrations.

2. The centrifuge of claim 1 in which the baffle means are secured to the undersurface ofthe cover.

3. The centrifuge of claim 1 in which the baie means comprises a series of equally spaced 'bafes extending beyond and laterally with respect to the rotor axis.

4. The centrifuge of claim 3 in which the bales dene air passages that decrease in width but increase in depth towards their inner ends.

5. The centrifuge of claim 3 in which the fbafes are spirals with the inner end of each extending part way about the axis of the rotor.

References Cited UNITED STATES PATENTS M. CARY NELSON, Primary Examiner.

H. KLINKSIEK, Assistant Examiner.

Claims

1. A CENTRIFUGE COMPRISING AN UPWARDLY OPENING CHAMBER, A ROTOR IN SAID CHAMBER OF FRUSTO-CONIC FORM, A DRIVE TO ROTATE SAID ROTOR INCLUDING A DRIVING MEMBER AXIALLY CONNECTED TO SAID ROTOR WITHIN SAID CHAMBER, SAID DRIVING MEMBER BEING SUFFICIENTLY FLEXIBLE TO PERMIT RANDOM, LOW FREQUENCY EXCURSIONS OF SAID ROTOR, A COVER CLOSING SAID CHAMBER, ROTATION OF SAID ROTOR CAUSING THE AIR TO FLOW OUTWARDLY FROM THE ROTOR AGAINST THE CHAMBER WALL AND UPWARDLY AGAINST SAID COVER, AND BAFFLE MEANS IN THE CHAMBER ABOVE THE ROTOR TO SO INTERCEPT THE UPWARD AIR FLOW AND DIRECT IT INWARDLY AND PROVIDE A DOWNWARD VERTICAL AIR FLOW TOWARDS THE UPPER END OF THE ROTOR THEREBY TO PROVIDE SUFFICENT TURBULENCE TO AVOID SUSTAINED PRESSURE DIFFERENTIALS ON SAID ROTOR, DURING EXCURSIONS THEREOF, AS WOULD INDUCE ROTOR VIBRATIONS.