US3424375A - Continuously operating screenless screw-type centrifuge - Google Patents

Description

F. MAURER 3,424,375

IIJOUSIJY OPERATING SCREENLESS SCREW-TYPE CENTRIFUGE Jan. 28, 1969 Z of 2 Sheet Filed Oct. 9, 1957 I/vl E/ rvR FRITZ H/HARER United States Patent U.S. Cl. 23320 Int. Cl. B04b 9/10, 11/00 7 Claims ABSTRACT OF THE DISCLOSURE A continuously operating screenless screw-type centrifuge for removing solids from liquid and including a centrifuge drum and a screw-type conveyor coaxially mounted in a housing at a fixed distance apart, the difference in speed of the drum and the screen being variable in predetermined time intervals.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a continuously operating screenless screw-type centrifuge, and, more particularly, to such a centrifuge for removing abrasive solids from cooling liquids.

Prior Art In order to remove finely divided solids or larger solid particles from a vehicle liquid, screw-type centrifuges are generally used. These centrifuges consist essentially of a drum and of a discharge screw arranged within the drum. The drum has predominantly the shape of a hollow conical frustrum within which the discharge screw is arranged with a slight distance being provided between the screw threads and the inner wall of the drums.

Under the action of the centrifugal force, the solidscontaining vehicle liquid forms within the drum a hollow cylinder and the solids, clue to their higher specific gravity, are accelerated against the inner wall of the drum by the action of the centrifugal force. The discharge of these solid particles is then effected in the direction towards one end of the drum by the relative movement of the discharge screw with respect to the drum.

The distance of the screw threads from the inner wall of the drum and, in particular, the value of the difference in speed of rotation between drum and screw must be adjusted in accordance with the nature, particle size, and quantity of the solids to be removed from the vehicle liquid.

In order to obtain the generally relatively small difference in speed between the outer drum and inner screw, various devices have already been proposed. For instance, it is known to drive the centrifuge drum and the discharge screw via a planetary gearing in which one of the two drive shafts extends in the other shaft, which is hollow. Planetary gearings, however, represent extremely cumbersome and expensive constructions which considerably increase the overall cost of such an installation.

Thus it has also been proposed to produce the difference in speed between the discharge screw and the centrifugal drum by arranging the discharge screw in free-wheeling manner in a directly driven drum rotating with constant speed and being braked by electrical means, such as an eddy-current brake, or the like.

A similar braking by means of a hydrostatic transmission during the centrifuging has also already been pro- "ice posed. The importance of this concept lies in the fact that the difference in speed of the drum and the discharge screw can be adapted to the nature of the material being centri fuged during operation. This, however, is only of interest and importance when, aside from the best possible separation of the solid components from the vehicle liquid, the solid component must have a predetermined density of consistency.

Further problems exist in the separation of solids from cooling liquids for industrial machining, since the solids consist practically exclusively of metal chips, grinding wheel emery, lapping pastes and grinding dust which must be removed from the circuit of the coling liquid so as to make the latter suitable again for cooling and to prevent a clogging of the liquid conduits and damage to them. Also, it has been found that emery and lapping paste exert an extremely abrasive and destructive action on the inner wall of the drum so that, without counter-measures, the wearing down of the screw threads of the discharge screw and of the drum is so great after a relatively short period of operation, that replacement is necessary.

In order to solve this latter problem, a screw-type centrifuge has been proposed in which a coupling is arranged between a gearing and the discharge screw and which can be engaged and disengaged during the centrifuging. This coupling is preferably in the form of an electromagnetic clutch which is engaged and disengaged by means of a time-switch.

In this latter arrangement, however, the drive of the discharge screw is effected by a friction drive which is maintained by the solids depositing on the inner wall of the centrifuge drum between the centrifuge drum and the discharge worm. The operating properties, including the acceleration of the discharge screw, are therefore dependent on the nature of the solids to be separated, as well as on the thickness of the layer in which the solids particles deposit on the centrifuge drum. In addition to this, a driving of the discharge screw only commences upon the placing in operation of the centrifuge when, after a certain period of time, solids have already deposited on the inner wall of the centrifuge drum, so that the required frictional engagement with the discharge screw has been brought about. This operational behavior is extremely unsatisfactory, especially when abrasive solid particles are encountered, as discussed above.

SUMMARY OF THE INVENTION A screw-type centrifuge particularly for separating abrasive solid particles from cooling liquids for the machining industry in which the centrifuge drum and the discharge screw are coupled directly with the drive device, and the differential speed between the two rotating elements is periodically varied automatically between zero and a given predetermined difference in speeds.

The centrifuge drum and the discharge screw are connected with each other via a freewheel and have a common drive which can be braked periodically during operation.

The periodic braking may be achieved by controlled reversal of phase of an electric drive motor, the control being effected by a timing relay, or by a mechanical brake acting directly on the drive.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in further detail below with reference to the accompanying drawings in which:

FIGURE 1 is a longitudinal section through a screwtype centrifuge in accordance with the invention;

r, FIGURE 2 is a cross-section along the line IIII of FIGURE 1; and

FIGURE 3 is a cross-section along the line III-III of FIGURE 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring specifically to the drawings, the reference numeral 1 refers to a centrifuge housing 1, within which a centrifuge drum 2 is arranged for rotation about a vertical axis. The centrifuge drum 2 has approximately the shape of an upward widening conical frustrum with an attached cylindrical portion. The upper wall of the centrifuge housing 1 bears a stationary hollow hub 3 which extends vertically downwardly into the inside of the centrifuge drum 2 and has bearings 4 and 5 supporting drum 2. Within the hollow hub 3 there extends a main drive shaft 8 which is supported in the upper housing wall at 6 and in the drum at 7, and is fixed to a discharge screw 9 to rotate same within the centrifuge drum 2.

Between the discharge screw 9 and the centrifuge drum 2 there is provided a unidirectional freewheel coupling 10 so that the two rotating elements, namely, the centrifuge drum 2 and the discharge screw 9 can be driven jointly in the same direction by an electric motor 11 via a toothed belt 12.

The discharge screw 9 has, toward its bottom, a funnel-shaped extension 13 the inside of which has runner blades 14 in the manner of a flow pump.

The centrifuge housing 1 is arranged directly over a tank 15 into which the cooling liquid from which the solids are to be removed continuously flow so that a liquid level designated 16 is continuously maintained. The funnel-shaped extension 13 of the discharge screw extends into the liquid level 16 so that, upon rotation of the discharge screw 9, the liquid is conveyed into the centrifuge drum 2 by the runner blades 14.

As shown in FIGURE 2, the screw threads of the discharge screw 9 are borne by a spider 17 between the arms of which the cooling liquid, conveyed by the funnelshaped extension 13, is passed into the inside of the drum.

The operation of the centrifuge is as follows. By starting the electric motor 11, the main drive shaft 8 and the discharge screw 9 are placed in rotation via the toothed belt 12, while at the same time the centrifuge drum 2 is placed in rotation in the same direction via the unidirectional freewheel coupling 10. In this way, liquid is conveyed out of the tank 15 by the runner blades 14 into the inside of the drum as shown by the upwardly extending arrows in FIGURE 1, wherein the solids of the cooling liquid deposit on the inner wall of the centrifuge drum 2 as a result of the centrifugal force and their greater specific gravity. The cleaned cooling liquid itself is forced through bore holes 18 in the drum into an upward separating chamber 19 of the centrifuge drum 2 from which it is withdrawn under pressure.

A change in phase is now effected on the electric motor 11 which is periodically controlled by a timing relay 20 and which causes a periodic delaying or braking of the rotation of main drive shaft 8, and therefore discharge screw 9. Since the centrifuge drum 2 is connected with the drive via the freewheel coupling 10 only in one direction of rotation it is not affected by this delay in rotation, but rather rotates with practically constant speed due to its inertia. Therefore, the rotation of discharge screw 9 periodically lags behind the centrifuge drum 2, and as a result of this periodically varied difference in speed, the solids which have deposited on the inner wall of the centrifuge drum 2 are conveyed by means of the relative movement of the discharge screw with respect to the centrifuge drum 2 in the direction towards the discharge end of smaller diameter of the latter, from which they are thrown out through edge grooves 21 as shown by the downwardly extending arrows in FIGURE 1. The

dry to sludge-like solids then fall through a shaft located within the tank 15 into a drawer 22 which can be emptied at certain time intervals.

The switching times of the timing relay 20 can be lengthened or shortened, depending on the degree of solids in the liquid, so that the discharge screw 9 accordingly shows a difference in speed of rotation from the rotating centrifuge drum 2 only during the corresponding time intervals.

In principle, it is immaterial which of the two rotating elements rotates with constant speed and which with periodically variable speed. Advisedly, however, the drum will always be allowed to rotate with constant speed, since, in view of its larger mass, a greater force would have to be exerted on the drive device to slow it down.

As can be noted from FIGURE 3, spring-loaded cone valves 23 are arranged in the drum wall of the centrifuge drum 2 both below and in the separating chamber 19. At the operating speed, the valve bodies 24 of these valves are pressed against their valve seat by the centrifugal force, so that the cone valves 23 are closed during operation. However, in order to prevent the liquid present in the space of the drum from flowing back downward into the drawer 22 upon the shutting off of the centrifuge, the strength of the valve springs 25 is so designed that at about /a the operating speed the spring force of the valve springs 25 pushes the valve bodies 24 inwardly against the action of the centrifuge force and the cone valves 23 are thereby opened. In this way, the cleaned liquid present within the drum gushes under high pressure through the valve opening so that, upon the final stopping of the centrifuge, the inner spaces of the drum are free of liquid. Due to the intensive flow through these valves, a depositing of solids and a clogging of the valves is prevented.

Of course several variations in the structure and arrangement of the above are possible within the scope of the invention. For example, a device may be provided which controls the braking frequency of the main drive shaft as a function of the quantity of solids removed or to be removed in such a manner that the frequency increases with an increase of the solids in the cooling liquid.

I claim:

1. A continuously operating screw-type centrifuge for separating solids from a liquid, comprising a drive shaft rotatably mounted in said housing, means to drive said drive shaft in a predetermined direction, a housing, a tank disposed below said housing to initially receive said liquid, a centrifuge drum mounted for rotation within said housing, a discharge screw mounted for rotation within said housing and extending within said drum in a spaced relationship thereto, said discharge screw being fixed to said drive shaft for rotation therewith and extending into said tank for delivering the contents thereof into said housing for separation to solids and liquids, freewheel means operatively connecting said drum and said drive shaft during rotation of said drive shaft in said predetermined direction, and braking means for periodically braking said drive shaft during operation so that the speed of rotation of the said discharge screw lags at periodic time intervals behind the speed of rotation of the said drum.

2. The centrifuge according to claim 1, wherein said freewheel means is in the form of a unidirectional coupling member.

3. The centrifuge according to claim 1 wherein said freewheel means is mounted on said discharge screw.

4. The centrifuge according to claim 1, wherein said braking means is in the form of a periodically controlled mechanical braking device acting on said drive means.

5. The centrifuge according to claim 1, wherein said discharge screw includes a lower funnel-shaped cylindrically terminating extension extending into the liquid in said tank.

6. The centrifuge according to claim 1, further comprising at least one spring-loaded cone valve provided in the wall of said drum and adapted to be closed under the action of a predetermined centrifugal force during operation and to open automatically at a given speed of rotation below the operating speed.

7. The centrifuge according to claim 1 wherein said drive means is in the form of an electric motor; and wherein said braking means includes means for selectively reversing the phase of the electric motor, and a timing relay for controlling the frequency of reversal of said phase.

References Cited UNITED STATES PATENTS ROBERT W. JENKINS, Primary Examiner.

US. Cl. X.R.

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