EP0341433B1 - Solid bowl screw conveyor centrifuge - Google Patents

Description

The invention relates to a solid-bowl screw centrifuge, in particular a countercurrent centrifuge, for the separation of a suspension, for the supply of which from a stationary entry point outside the centrifuge into the separation space of the centrifuge formed between the screw and the shell, a stationary inlet pipe is provided, which is provided extends into an inlet space of the screw and is supported in its end region on a screw-fixed part via a bearing.

In centrifuges of this type, suspensions are separated into a solid and at least one liquid phase under centrifugal force. Such suspensions can consist of many different compositions; they can contain chemically aggressive substances and / or particles that cause high abrasion, such as sand. It is therefore endeavored, in the course of the supply of such suspensions, to use lines which are as continuous as possible up to the separating space of the centrifuge or a distribution space which opens into the separating space within the screw hub. Large pipe lengths often occur, which cause problems with regard to their mounting or their risk of producing strong radial vibrations. This is particularly the case with centrifuges of the type in question here, which operate in the so-called countercurrent principle, ie in which the suspension inlet into the separation space is provided far inside the centrifuge. Storage of such a long, stationary inlet pipe in its end region within the worm hub could indeed eliminate this problem, but such a bearing is within the Worm hub more exposed to dirt and difficult to access for maintenance work. Such storage is known from GB-A-2088255, in the form of a roller bearing protected with a seal within a housing. Due to the heavy stress on such a bearing due to suspensions to be separated, time-consuming and costly repairs and maintenance work are to be feared, quite apart from the relatively complicated multi-part construction.

From DE-U-8706954 plain bearings for pumps are known, the one bearing shell made of silicon carbide and the other bearing shell made of a material which cooperates well with this ceramic material as a bearing. An intermediate bush made of metal is arranged between the bearing shell made of ceramic material (silicon carbide) and the carrier for this bushing, which provides axially overlapping, annular-gap-shaped free spaces for absorbing the different thermal expansions. Furthermore, it is known - DE-A-3435821 - to provide plain bearings, one bearing shell of which is made of ceramic material and the other of which is made of hard metal, whereby operation in both dry and "wet" condition is to be made possible. To absorb vibrations, an elastic intermediate layer can be provided in the area of the bearing. In connection with this, it is also known to fix a bearing shell in a housing member by a shrink fit. Finally, it is known - EP-A-0195205 - to provide especially surface-treated sliding elements which are to be used in particular as sealing disks in mixer taps and sliding rings of mechanical seals.

The invention has for its object to provide a centrifuge of the type mentioned, in which the suspension is fed as far as possible into the separating chamber of the centrifuge via a fixed inlet pipe, even if the separating chamber is very far from the feed end of the Centrifuge jacket as seen in the longitudinal center area and beyond the centrifuge, as is the case with countercurrent centrifuges, without the long, fixed Inlet pipe can cause malfunctions due to large radial vibrations and without time-consuming and costly repair and / or maintenance work.

Starting from a solid-bowl screw centrifuge with the features mentioned above, this object is achieved according to the invention in that the bearing is designed as a plain bearing, the two bearing shells of which are made of a ceramic material in the sliding engagement area, and a hydrodynamic lubricating film builds up between their sliding bearing shell surfaces the suspension introduced through the inlet pipe into the separation space and / or is fed by means of a substitute liquid supplied through a separate line, and that the radially inner bearing shell is fixed with its inner lateral surface to a section of the outer wall of the component holding the bearing shell by means of an intermediate temperature-tension compensating body is.

According to the invention, the slide bearing is arranged correspondingly far inside the screw of the centrifuge in such a way that the two bearing shells in the sliding engagement area consist of a ceramic material. In the sliding attack area, the two ceramic bearing shells are acted upon by the suspension, which, however, poses no problems with regard to wear and / or maintenance, because such ceramic materials are extremely resistant to abrasion and corrosion, so that such a bearing with a ceramic bearing in the sliding attack area also can be used safely and permanently for suspensions with appropriate abrasion and corrosion properties. Tolerate such plain bearings high speeds and also withstand a pressure build-up, as can occur in a certain bearing arrangement from the separation space. In addition, such ceramic materials are highly heat-resistant and tolerate strong temperature changes.

There are a number of ceramic materials in question, and this or that ceramic material will be preferred depending on the application or suspension, such as Si₃N₄, Al₂O₃, MgO, ZrO₂; however, oxide-free ceramics are preferably used, and preferably SiC, in a sintered form, so that pure silicon carbide is contained without a free silicon content.

Basically, it is possible to fix the radially outer bearing shell of the slide bearing on one of the end boundary walls of the inlet space of the worm hub, while the radially inner bearing shell of the sliding bearing is fixed on the outer wall of the fixed or stationary inlet pipe. Another possibility is to hold the bearing shell of the slide bearing arranged radially on the inside on a bolt, also hollow bolt, fixed to the end wall of the inlet space and to fix the bearing shell of the slide bearing radially on the outside at the end edge of the end region of the stationary inlet pipe or an extension of this end region. The end region of the inlet pipe can also be supported indirectly, for example via a further concentrically inner pipe, on a partition of the screw body.

According to the invention, care is taken to ensure that a hydrodynamic lubricating film is present between the sliding bearing shell surfaces of the slide bearing due to the presence of a liquid medium builds up. This is due to the fact that the plain bearing is connected to the interior of the inlet pipe and is lubricated by the centrifugal medium introduced into the separating chamber of the centrifuge via the inlet pipe. However, a replacement liquid for lubricating the slide bearing can also be provided, which is automatically supplied when the addition of the centrifugal medium is interrupted. A separate line is provided for the supply of the lubricant to the slide bearing. Furthermore, the temperature of the slide bearing can be sensed with the aid of temperature sensors, so that when the temperature of the slide bearing rises above a certain value, the lubricant supply to the slide bearing is automatically switched on or the centrifuge is switched off.

In a conical area of the centrifuge, which is used to discharge the solid from the sump of the separation space, a cavity for the introduction of washing liquid can be provided in the screw body, the sliding bearing also being used as a seal in the transition area of a stationary supply line for the washing liquid to the rotating screw body is. In such a case, in that a washing liquid supply pipe is supported on the bearing on the worm hub body, the inlet pipe can be supported on the washing liquid supply pipe so that the end region of the inlet pipe is supported indirectly on the sliding bearing on the worm hub.

In a particularly preferred embodiment, care can be taken to ensure that an inspection of this ceramic bearing located inside the screw, ie in the area of the screw's inlet space, can be carried out in a simple manner without dismantling the centrifuge.

Figur 1

einen schematischen Schnitt durch eine Vollmantel-Schneckenzentrifuge nach einem ersten Ausführungsbeispiel;

Figur 2

eine vergrößerte Teilschnittdarstellung des Schneckenbereiches im Gebiet des Einlaufraumes nach einem weiteren Ausführungsbeispiel;

Figur 3

einen der Darstellung gemäß Figur 2 vergleichbaren Schnitt eines dritten Ausführungsbeispieles;

Figur 4

einen der Darstellung gemäß Figur 2 vergleichbaren Schnitt eines vierten Ausführungsbeispieles;

Figur 5

einen der Darstellung gemäß Figur 2 vergleichbaren Schnitt eines letzten Ausführungsbeispieles.

These and other preferred embodiments of the invention result from the subclaims, in particular in connection with the exemplary embodiments of the invention shown in the drawing, the following description of which explains the invention in more detail. Show it

Figure 1

a schematic section through a solid bowl screw centrifuge according to a first embodiment;

Figure 2

an enlarged partial sectional view of the screw area in the area of the inlet space according to a further embodiment;

Figure 3

a section comparable to the illustration of Figure 2 of a third embodiment;

Figure 4

a section of the fourth embodiment comparable to the illustration in FIG. 2;

Figure 5

one of the representation of Figure 2 section comparable to a last embodiment.

The solid-bowl screw centrifuge equipped with a jacket 1 and a screw 2 according to the exemplary embodiment is only shown with regard to the end face or storage located on the feed side of the suspension and in the inlet area into the separation space 3 formed between the casing 1 and the screw 2. The screw 2 is mounted at 4 on the casing, which in turn at 5 on a stationary component 6, which is viewed here as a bearing block. This embodiment shown in FIG. 1 is shown enlarged in the remaining figures only with regard to the inlet area area within the centrifuge.

The inlet pipe 31 for the supply of the suspension is led from the stationary entry point of the suspension, not shown, in the right connection area of FIG. 1 as a stationary pipe into the inlet space 32 of the screw 2 and is supported with its end area 34 on a bolt 35, which in turn is supported engages in a bore 37 provided in the end boundary wall 36 of the inlet space 32 facing away from the inlet side. Radially between the bolt 35 and the inner end wall of the end region 34 of the long, fixed inlet pipe 31, a slide bearing 12 with the two bearing shells 14 and 15 is arranged, so that there is a support between the bolt 35 and the end region 34 of the inlet pipe 31 against radial vibratory movements is. The suspension enters the long-shaped inlet pipe 31 in the direction of the arrow on the right and leaves it through the outlet opening 33, which leads into the inlet chamber 32 of the screw 2, from where the suspension in the usual way through openings in the screw hub into the separation chamber 3 reached. Due to the suspension given up through the inlet pipe 31 and its presence in the inlet chamber 32 of the screw 2, the slide bearing 12 is exposed to the suspension from both end faces. The suspension is used to form a hydrodynamic lubricating film for the plain bearing 12, on the other hand, its running surfaces are exposed to the stress emanating from the suspension. The two mutually sliding bearing shells 14 and 15 of the slide bearing 12 are made of a ceramic material, here in particular silicon carbide, so that abrasion and corrosion phenomena due to the lubricating effect of the suspension solids on the sliding surfaces does not occur or only occurs accordingly.

In the embodiment according to FIG. 1, it can be assumed that the inlet pipe 31 preassembled with the slide bearing 12 and the pin 35 is inserted into the position shown from outside the machine, which has been preassembled in this respect, in the longitudinal direction of the inlet pipe 31, the pin 35 having any configuration engages torsionally in the bore 37. The reverse assembly process makes it easy to inspect or replace the bearing without having to dismantle the centrifuge as such.

In the exemplary embodiment according to FIG. 2, the end region 34 of the inlet pipe 31 is held on a bolt 35 in a similar manner as in the exemplary embodiment according to FIG. 1. Here, however, a hexagon is provided which allows the bearing shell 14 to be removed from the bolt.

In the exemplary embodiment according to FIG. 2, a special lubricant supply is provided via a line 39 in the event that the suspension supply is interrupted. Thus, while the suspension entering the inlet space 32 through the outlet opening 33 forms the formation of the hydrodynamic lubricating film between the bearing shells 14 and 15 at the latest from the Ensures the end face facing away from the inlet, if the suspension supply is interrupted through line 39, a lubricant of whatever type is supplied which maintains the hydrodynamic lubricating film between the bearing shells 14 and 15.

In the area of the plain bearing, one or more temperature sensors can be provided, by means of which the special lubricant supply to the plain bearing is automatically switched on when the temperature of the plain bearing rises. Of course, you can also provide an emergency shutdown of the centrifuge here.

In the exemplary embodiment according to FIG. 3, the end region 34 of the inlet pipe 31 is supported via the slide bearing 12 or its bearing shells 14 and 15 in a similar manner as in the exemplary embodiment in FIG. 2, but the bolt on which the inner bearing shell 14 is, for example is held by a compensating body 16, formed as a hollow pin 38 which has an axially continuous bore. The opening of this through hole facing the inlet side is directed towards an inlet which is similar to that of the emergency lubricating fluid according to FIG. 2, but in the present exemplary embodiment according to FIG. 3 serves to supply a washing liquid, which thus ensures the lubrication of the bearing 12 and at the same time ensures a Feeds washing liquid into the interior of the screw, which adjoins the wall 36 of the inlet space 32 facing away from the suspension inlet. This space has small passage bores in the screw hub, through which the washing liquid enters the separating space of the centrifuge, specifically in its conical jacket area, in order to wash off solids.

The compensating body 16 serves to compensate for temperature-related dimensional changes; it is designed to be elastically flexible in the radial direction. This ensures that when the temperature increases, the more stretching jacket of the end region 34 of the inlet pipe 31 or - with respect to FIG. 1 - the diameter increase of the bolt 35 stresses the ceramic bearing shell, which expands much less at this temperature, while the ceramic material is sensitive. The tubular compensating body has a corrugated jacket wall in itself, with the wave shape seen in the circumferential direction, or also with the wave shape seen in the axial direction, as indicated in the drawing. The radially outer bearing shell is - depending on the embodiment on the inner jacket wall of the end portion 34 of the inlet pipe 31 or the wall 36 or 43 (Figure 5) of the screw body - fixed in that it is heated before inserting the bearing shell 15. When cooling, the different coefficients of thermal expansion of the inlet pipe or the screw body wall - for example steel - on the one hand and the ceramic body on the other hand mean that the bearing shell is fixed in position by shrinking and thus compressed, whereas the ceramic material is insensitive.

In the exemplary embodiment according to FIG. 4, the supply of washing liquid is made with the aid of a washing liquid supply pipe 40 which is rigid in itself and serves as a connection between the slide bearing 12 and the end region 34 of the inlet pipe 31 insofar as the inner wall of the end region 34 of the inlet pipe 31 over radial webs 42 is supported on the outer jacket wall of the washing liquid supply pipe 40. This support takes place in the vicinity of the slide bearing 12, which is in the passage area of the washing liquid supply pipe 40 is arranged through the end wall 36 of the inlet space 32 facing away from the inlet side. The outer bearing shell 15 is supported on the inner wall of a corresponding hole in the partition, while the inner bearing shell 14 is supported on the outer jacket wall of the washing liquid supply pipe 40. Accordingly, the slide bearing 12 forms a seal between the space into which the washing liquid is introduced and the inlet space 32, into which the inlet pipe 31 opens at the end.

In the exemplary embodiment according to FIG. 5, on the other hand, a very simple case of the suspension supply is again shown, in which emergency lubrication and washing liquid supply are not provided. In this case, the sliding bearing 12 is arranged in the passage area of the inlet pipe 31 through that end partition 43 of the inlet chamber 32 of the screw 2 which faces the suspension inlet. The outer shell of the slide bearing 12 is supported on the inner wall of a corresponding bore in the end partition 43, while the inner bearing shell 14 engages on the outer circumferential surface of the inlet pipe 31.

Claims (9)

1. A fully encased screw centrifuge, more particularly a counterflow centrifuge, for separating a suspension, for the supply thereof from a stationary delivery point outside the centrifuge into the separation area (3) of the centrifuge, formed between the screw (2) and the casing (1), there is provided a fixedly held inlet pipe (31) which extends into an inlet area (32) of the screw (2) and is supported, in its end region (34) there, via a bearing, on a part (36,35; 36,38; 36; 43) secured to the screw, characterised in that the bearing is constructed as a slide bearing (12) whose two bearing bushes (14, 15) are made of a ceramic material in the region of the sliding engagement, a hydrodynamic lubrication film being built up between the faces of the bearing bushes sliding against each other, which is supplied by means of the suspension passed through the inlet pipe (31) into the separation area (3) and/or by means of a substitute liquid delivered through a separate pipe (39; 40), and that the bearing bush (14) arranged radially inside is secured, by means of its inner wall face, via an interposed thermal stress compensating member (16), to a portion of the outer wall of the structural element retaining the bearing bush.
2. A centrifuge according to claim 1, characterised in that the ceramic material of the slide bearing (12) is oxide-free ceramics, more particularly made of or based on pure silicon carbide.
3. A centrifuge according to either claim 1 or 2, characterised in that the bearing bush (15) arranged radially outside is secured on its outer side so as to be acted upon by shrinkage pressure.
4. A centrifuge according to any one of claims 1 to 3, characterised in that the temperature-compensating member (16) is in the form of a radially resilient ring or tube section, in particular having a circumferential wall which, itself, is corrugated.
5. A centrifuge according to any one of claims 1 to 4, characterised in that the substitute liquid for lubricating the slide bearing is supplied automatically in the event of the delivery of the suspension being interrupted.
6. A centrifuge according to any one of claims 1 to 5, characterised in that one or a plurality of temperature sensors are provided within the region of the slide bearing (12) which automatically switch on the lubrication supply of the slide bearing or switch the centrifuge off, when the temperature of the slide bearing increases above a specific value.
7. A centrifuge according to any one of claims 1 to 6, characterised in that the screw member is provided, in the conical region of the centrifuge, with a cavity for introducing washing liquid, and that in the region, in which the stationary inlet pipe for the washing liquid passes over into the rotating screw member, the slide bearing (12) is arranged as a seal.
8. A centrifuge according to any one of claims 1 to 7, characterised in that the washing liquid inlet pipe (40) is mounted as a stationary pipe in the screw, via the slide bearing (12) with the ceramic bearing bushes (14, 15), and that the inlet pipe (31) which serves to supply the suspension is supported (42) on the washing liquid inlet pipe (40).
9. A centrifuge according to any one of claims 1 to 4, characterised in that the inlet pipe (31) is supported, via the slide bearing (12), in the separation end wall (43) of the inlet area (32) of the centrifuge.

Images