Sludge Ejecting Centrifuge

Abstract

A sludge ejecting centrifuge with an unbroken 360.degree. ejection slit which is opened and closed by an annular sealing device which is held in closed position by an annular spring arrangement that surrounds the rotor and which is held in open position by centrifugally generated hydrostatic pressure of injected control fluid.

Description

The invention pertains to a sludge ejecting centrifuge with an unbroken 360.degree. ejection slit which is opened and closed by an annuluar sealing device. It is known in the art to construct each centrifuges in such a manner that the sludge ejection slit is closed by means of spring pressure and opened with the help of the centrifugally induced pressure of a control fluid injected into the rotor. A known configuration of this type includes an annular sealing piston which is movably situated between an inner vessel including the centrifugation chamber, and an outer vessel containing springs, fluid channels, fluid chambers and the connection with a drive shaft which all together represent one half, in most cases the lower half, of a vertically rotating rotor, which furthermore includes an upper half, wherebetween are located a number of peripheral sludge ejection openings.

The drawbacks of this kind of construction are that relatively heavy vessels are needed which have to be fixed carefully in relation to each other in order to attain the necessary balance, that the vessels have to be drilled through to make long channels, that the annular piston between the vessels has to be sealed on both surfaces, that the individual springs cannot be replaced without dismantling the entire rotor which then has to be balanced again, that the springs may exert unequal pressures resulting in lopsided movements of the piston, that piston and springs are hard to get at, and that the upper edge of the piston is of metal which seals against a pliable gasket in the edge of the opposite half of the rotor. The latter arrangement has among others the weakness that the gasket must be placed in a groove which may catch sludge or fluid behind the gasket which then is pressed out of the groove and torn by the centrifugal stress. Further, there is not known any centrifuge of this type with an unbroken 360.degree. slit for the ejection of the sludge.

The purpose of the invention is to create a new centrifuge without the indicated drawbacks and with hitherto unknown advantages.

Thus, the invention comprises a centrifuge having only one vessel to form the centrifugation chamber and has no drilled channels or inner spaces to house the individual springs or the control fluid. The annular spring and relatively thin sheet piston cause no special balancing problems and lopsided pressures cannot occur. The piston may be thin because it is stressed only lengthwise by spring and control fluid while the centrifugally induced cross stresses exclusively are determined by the ratio of specific weight to material strength in the piston. Thus, the piston may be made of uncomplicated and cheaply passed sheet material. The gasket is exchangeable being fastened to an exchangeable ring which, for constructional reasons is fastened to the upper rim of the piston after the piston with inserted spring has been placed around the lower part of the rotor and before the upper part of the rotor is installed.

The invention may also have the spring helically coiled or comprising a number of disc-shaped elements.

The indicated types of springs are easy to handle and cheap because they are obtainable from stock. These springs can be used very well if the centrifuge is meant to work at a specific speed because in that case it is possible to calculate the hydraulic pressure inside the centrifuge and the fluid chamber and to define the spring's strength accordingly.

However, it may be necessary, especially with laboratory centrifuges, that the spring should be self-adjusting in relation to vary speeds which will be attained by a spring having non-compressible elastic rings between stiff wedge shaped rings which will be deformed progressively with increased speed and force the stiff rings away from each other.

The sealing member may comprise a sleeve formed part which extends into the centrifugation space and is fastened there. The piston is situated in a certain distance from the rotor vessel which distance may vary a little and thus it is necessary to make a sealing bridge, which must be elastical, across the gap between piston's upper rim and the rotor.

The piston preferably consists of plastic reinforced material such as epoxy compounds with glass fiber reinforcements which has great physical and chemical resistance in relation to its specific weight which, among other advantages, reduces balancing problems and the need to treat the surface of this part.

The spring chamber is preferably provided with at least one relief nozzle the importance of which is that the gap between the lower shoulder of the rotor vessel and the inner surface of the piston at that point near the control fluid chamber does not need to be specially water tight as long as the leakage has a lower through flow capacity than the relief nozzle.

In the following the invention will be described in detail in conjunction with the accompanying drawing which in

FIG. 1 shows an axial section through pertaining parts of a centrifuge with unbroken 360.degree. sludge ejection slit

FIG. 2 shows a detail of the same with a special bridge sealing gasket,

FIGS. 3 and 4 show another detail with a new spring type.

FIG. 5 shows another detail with a disc type annular spring, such as the type manufactured by Schnorr of West Germany.

The centrifuge rotor consists of an upper 1 and a lower 2 half with therebetween situated peripheral sludge ejection slit 3, all mounted on an axle 4 which, not shown, continues upwardly beyond the upper half 1 to facilitate the fixation and tightening of halves 1 and 2 in relation to each other. Around part 2 is in concentric relation a thin annular piston 5 furnished with an upper flange 6 and a lower chamber plate 7. Parts 5, 6 and 7 may be made in one piece. Between the piston 5 and rotor part 2 is a spring chamber 8 and in it an annular spring 9 which in the illustration is a helical spring. Between chamber plate 7 and the bottom of part 2 is an annular fluid chamber 10 which receives a control fluid from a stationary pipe 11. Fluid chamber 10 may be furnished with a number of relief nozzles 12. Spring chamber 8 may also be furnished with a number of relief nozzles 13 to eject whatever control fluid that may have entered chamber 8 from chamber 10. The flange 6 carries a separate reinforced ring 14 with attached rubber sealing gasket 15. The helical or disc spring keeps the centrifuge closed with a predetermined pressure force independently of the rotational speed of the centrifuge. Fluid chamber 10 is dimensioned in such a way that the fluid injected into chamber 10 generates a greater force than the spring force at a certain speed which opens the ejection slit 3.

In FIG. 2 the gasket 15 has a sleeve 16 which forms an elastic bridge over the gap between the ring 14 and rotor part 2 and which is fastened inside the centrifugating space in a known manner.

FIGS. 3 and 4 show an entirely new spring which consists of wedge shaped stiff rings 17 and interposed rings 18 of non-compressible elastic material. In FIG. 3 the elastic rings 18 ar slightly pressed between rings 17 which means that the centrifuge is slightly sealed when it stands still and at low speed. When a certain speed is attained the centrifuge is closed stronger as the elastic rings 18 force themselves more and more between rings 17. The higher the speed the stronger the sealing of the centrifuge. Rings 17 are forced progressively away from each other, as shown in FIG. 4. Fluid chamber 10 is dimensioned so that injected fluid generates a hydrostatic pressure which forces the elastic rings 18 along the wedge shaped surfaces of rings 17 back into their former position so that the centrifuge is opened. It is also possible to combine these special rings with an ordinary helical or disc spring arrangement.

Claims

What I claim:

1. A sludge centrifuge for the separation of fluids from sludge comprising a rotor having an upper half and a lower half, said rotor including at least one slit therein for ejecting sludge therethrough, said centrifuge further comprising an annular piston mounted coaxially with said rotor and surrounding at least a portion thereof, said piston having an upper flange reinforcement and forming an annular chamber between said piston and said rotor, at least one annular movable spring means positioned in said chamber in surrounding relationship with said rotor lower half, and spring means having an upper end pressing against the underside of said flange, said rotor further having a shoulder portion, said spring means further having a lower end pressing against said rotor shoulder portion, said piston having a lower end, said piston lower end including a chamber plate extending outside of and parallel with the bottom of said rotor lower half and forming together therewith a chamber for a control fluid, said control fluid chamber having at least one relief nozzle therein for said control fluid, said rotor sludge ejection slit being opened and closed by the cooperative action of said movable annular spring and said fluid controlled piston.

2. A centrifuge as in claim 1, characterized in that the spring is helically coiled.

3. A centrifuge as in claim 1, characterized in that the spring consists of a number of disc shaped elements.

4. A centrifuge as in claim 1, characterized in that the piston consists of reinforced plastic material such as epoxy compounds with glass fiber reinforcements.

5. A centrifuge as in claim 1, characterized in that the spring chamber is furnished with at least one relief nozzle.

6. A centrifuge in accordance with claim 1 wherein said sludge ejection slit is an unbroken 360.degree. slit in said rotor.

7. A sludge centrifuge for the separation of fluids from sludge comprising a rotor having an upper half and a lower half, said rotor including at least one slit therein for ejecting sludge therethrough, said centrifuge further comprising an annular piston mounted coaxially with said rotor and surrounding at least a portion thereof, said piston having an upper flange reinforcement and forming an annular chamber between said piston and said rotor, at least one annular movable spring means positioned in said chamber in surrounding relationship with said rotor lower half, said spring means having an upper end pressing against the underside of said flange, said rotor further having a shoulder portion, said spring means further having a lower end pressing against said rotor shoulder portion and comprising a number of wedge formed stiff rings placed on top of each other and of a suitable number of non-compressible elastic rings spaced between them, said piston having a lower end, said piston lower end including a chamber plate extending outside of and parallel with the bottom of said rotor lower half and forming together therewith a chamber for a control fluid, said control fluid chamber having at least one relief nozzle therein for said control fluid, said rotor sludge ejection slit being opened and closed by the cooperative action of said movable annular spring and said fluid controlled piston.

8. A centrifuge as in claim 1 further comprising a sealing member secured to said upper flange reinforcement, said sealing member having a sleeve formed part which extends into a centrifugation space and is fastened thereto.

9. A centrifuge in accordance with claim 8 wherein said sealing member is held in a position for closing said slit by said annular spring and is changed to a position for opening said slit by centrifugally generated hydrostatic pressure of said control fluid injected into said fluid chamber.