EP3925709B1 - Centrifugal separator with special separator wheel - Google Patents

Description

The invention relates to a centrifugal classifier.

TECHNICAL BACKGROUND

Centrifugal classifiers are known in different designs in the prior art.

The heart of every centrifugal classifier is a classifier drum that rotates at high speed within a drum-shaped classifier chamber.

The sifter drum is perforated, perforated or otherwise provided with a sieve structure on the shell side. Classifier air is sucked in from the fines outlet. This creates a continuous flow of classifying air. This usually enters the classifier room together with the material to be classified via the material inlet. There, the classifier air stream loaded with the material to be classified is swirled by the high-speed classifier drum to form a kind of cyclone flow. This initially circles around the outside of the sifter drum and finally enters the interior of the sifter drum through the perforated jacket of the sifter drum. From there, the classifier air flow flows into the fine material outlet on at least one end face of the classifier wheel.

In this process, the centrifugal classifiers take advantage of the fact that the larger, more massive particles of the material to be classified are finally thrown outwards by the centrifugal forces when the material to be classified is in the cyclone-like manner Flow circulates in the classifier room. In contrast, smaller, lower-mass particles and therefore only exposed to lower centrifugal forces at the same angular velocity are separated from the cyclone-like flow by the inwardly flowing classifier air and sucked into the interior of the classifier drum in order to then be discharged together with the classifier air flow.

The market is increasingly demanding sifters with increased throughput, whereby the quality of visibility should also be increased or at least maintained if possible.

One way to increase the throughput of a generic centrifugal classifier is to increase the diameter of the classifier wheel and thereby allow the classifier wheel to rotate at a higher speed - since simply increasing the classifier wheel diameter while maintaining the same nominal speed leads to the fines that can be recovered being coarser becomes.

However, the increase in speed means that the systems become technically more complex, have to be balanced even more precisely and are more expensive to maintain.

The DE 694 739 C discloses a centrifugal classifier according to the preamble of claim 1, it relates to an air classifier for classifying fine-grained or fine-gritty material with a spreading plate feed, with openings provided with flaps being arranged in the wall of the viewing chamber, ie the inner space located above the spreading plate, through which a Part of the dedusted air enters the viewing chamber from the separation chamber in a tangential direction.

The EP 1 004 366 A2 concerns an air classifier for classifying granular material into three fractions. The DE 25 51 457 A1 relates to a device for separating coarse material and fine material in the centrifugal field consisting of a cylindrical hollow body with a visible material fluid feed pipe which opens tangentially into a helical line at one end of the jacket, at least one axially arranged fine material outlet pipe and a tangentially attached one at the other end of the jacket emerging coarse material outlet pipe.

THE PROBLEM UNDERLYING THE INVENTION

The invention is dedicated to the problem of creating a centrifugal classifier that is easier or better balanced and easier to maintain and which offers the possibility of achieving a better quality of classifying.

THE SOLUTION ACCORDING TO THE INVENTION

According to the invention, the solution is achieved by means of a centrifugal classifier with the features of the first main claim.

It is a centrifugal classifier with a classifier housing - usually fixed relative to the foundation - and a classifier wheel that rotates in the classifier housing. The classifier housing has at least one classifying material inlet, at least one classifying air inlet, at least one coarse material outlet, and at least one, usually a first and a second, fine material outlet. As a rule, the classifier air is also drawn off via the latter(s), which is at least sucked in or fed in via the classified material inlet. The classifier air is preferably drawn through the centrifugal classifier by means of an external fan, which sucks in on the side of the fines outlet.

The classifier wheel is formed by a classifier drum and a classifier wheel shaft carrying the classifier drum. Ideally, the classifier wheel shaft rotates around an imaginary horizontal axis. The lateral surface of the sifter drum is perforated in such a way that, during operation, it causes the material to be viewed on the outside of the casing that hits the sifter drum to rotate, with additional aids possibly being available to generate the rotation. As a rule, one can say that the classifying material is set in rotation or further accelerated by the classifying drum, among other things. The visible material already has a certain basic translational speed when it enters the machine, with the direction changing as it enters. The lateral surface of the classifying drum is perforated in such a way that the classifying air flows through it in a radially inward direction.

The fine material outlets are arranged at the two front ends of the sifter drum, with the fine material-separated air mixture flowing from the interior of the sifter drum into the respective fine material outlet via the respective free end face of the sifter drum. The same applies if only one fines outlet is provided.

According to the invention it is provided that the classifier wheel shaft consists of two parts that are not directly connected to each other in a load-bearing manner. The first part of the classifier wheel shaft extends from a first hub, which carries the classifier drum in the area of its first end face, outwards, away from the classifier drum. The second part of the classifier wheel shaft extends from a second hub, which carries the classifier drum in the area of its second end face, in the opposite direction outwards, also away from the classifier drum.

For conceptual clarification, the following should first be noted:
In the context of the invention, the term “not directly connected to one another” means that there is no direct flow of force from one part of the shaft to the other - unlike shaft parts that are flanged, lugged or, for example, directly connected to one another. B. shaft parts directly coupled to one another by means of a Hirth toothing. The two shaft parts are therefore arranged at a spatial distance from one another. The sifter drum is located between them. The distance between the two shaft parts is usually at least 80% of the length of the classifying drum. This is self-supporting and bridges the distance between the two shaft parts by acting as a hollow shaft.

The term “ fine goods ” in its broader sense does not inherently have any size restrictions. However, the term " fine material " also has a narrower meaning - currently optional - and refers to such material made of ultrafine particles in which 98% of the particles have an average diameter of less than 6 μm and ideally even less than 3 μm.

The design according to the invention has the following consequences:
Because there is no longer a shaft running inside the sifter drum whose unbalance is different than the unbalance of the sifter drum, the sifter wheel can be precisely balanced more easily and better. It is therefore predestined for higher speeds and is less prone to vibrations.

In addition, with the elimination of the previously centrally running classifier wheel shaft inside the classifier drum, a significantly larger clear flow cross section is available for the mixture of classifier air and fine material. While the classifier air loaded with the fine material enters the interior of the classifier roller through the sieve structure at a speed of 13 to 17 m/s, the measure according to the invention slows the flow speed of the classifier air loaded with the fine material immediately in front of the fine material outlet to 2 to 6 m /s. This reduces the tendency of the fine material to agglomerate due to turbulence in the classifier air, i.e. H. to clump.

In addition, periodic maintenance of the classifier wheel becomes much easier. There is no longer a one-piece shaft, which is extremely cumbersome due to its long length - especially when it has to be manipulated to remove a one-piece or multi-piece sifter drum and reslide the replacement part and position it in order to finally fix it by tightening a screw connection, which is usually difficult to access in the annular gap between the classifier drum and the classifier shaft.

In addition, the design according to the invention usually also improves the quality of the sifting because the clear flow cross section within the sifting drum becomes larger. A usually associated effect is that the transport of the fine particles is improved. After passing through the sieve-like drum shell, the fine particles have more space inside the sifter drum, so less agglomeration occurs after sifting.

ANOTHER PROBLEM UNDERLYING THE INVENTION

In addition to what has been said above, the invention is also dedicated to the problem of creating a centrifugal classifier that achieves a qualitatively further improved classifying result.

THE FURTHER SOLUTION ACCORDING TO THE INVENTION

According to the invention, the solution is achieved by means of a centrifugal classifier with the features of the second main claim. On the one hand, independent protection is claimed for this, without reference to other claims. On the other hand, protection is also claimed for it in combination with the first main claim, making it a subordinate claim.

In its broadest form, the aforementioned claim proposes a centrifugal classifier as a solution, in which a one-part or multi-part guide element is arranged in the area of the at least one coarse material outlet. The guide element is arranged at a minimum distance X from the inner surface of the classifier housing section surrounding the classifier drum. It is designed in such a way that visible material, which flows along the said inner surface with a radial distance ≤ In addition, the guide element is designed in such a way that at least part of the material to be classified, which flows along the said inner surface with a radial distance >

For conceptual clarification, the following should first be noted:
The minimum distance X is measured in the radial direction. It refers to the distance that the front edge of the guide element, which is reached first by the inflowing material when it hits the guide element, is kept from the inner lateral surface delimiting the classifier space.

Undermining within the meaning of the invention occurs when visible material passes the guide element on its radially outward side without receiving an impulse from the classifier wheel that changes the trajectory or changes it significantly.

The design according to the invention has the following consequences:
Classified material that flows along the said inner surface with a radial distance ≤ It passes under the guide element and reaches the coarse material outlet undisturbed. Since the supporting effect of the inner surface is eliminated here, the incoming coarse material is discharged into the coarse material outlet by the centrifugal forces acting on it. Since the coarse material reaches the coarse material outlet on the flow-calmed side, ie on the leeward side of the guide element, there is no risk that part of the coarse material will be unintentionally carried back into the classifier space due to turbulence.

On the other hand, the part of the material that flows along the said inner surface with a radial distance > X is deflected in the direction of the classifying drum 14 and thrown back. This prevents material that has already come relatively close to the clear opening that leads to the coarse material outlet, but has not yet qualitatively completed the screening process, from being prematurely trapped by the centrifugal forces and the turbulences that occur in the vicinity of the said clear opening Coarse material is discharged. This would actually remove separable fine material from the screening process, which would worsen the screening result. Instead, a further sifting of the visible material thrown back towards the sifter drum takes place, during which the fine material that was previously entrained by the coarse material is given the chance to separate from it.

OPTIONAL FURTHER DEVELOPMENT POSSIBILITIES OF THE INVENTIONS

Preferably, the guide element partially covers the coarse material outlet or the clear cross section that branches off to the coarse material outlet. Preferably more than 35% and better yet more than 50% of said clear cross-sectional area is covered.

In this way, the guide element gives the leeward area already mentioned above an extremely effective size and essentially prevents visible material from being discharged prematurely into the coarse material outlet.

Particularly preferred are constructions in which additional classifier air is fed in at the coarse material outlet, which flows into the fine material outlet via the classifier drum. This additional classifier air could be described as supporting air acting in the area of the coarse material outlet, which - especially in conjunction with the guide element in question - ensures that classified material is not prematurely discharged into the coarse material outlet. It is particularly preferred if the said classifier air is not only sucked in passively, but is actively blown in using a corresponding blower or from a compressed air network.

It is favorable if the ratio NL/ND between the useful length NL of the classifying drum and the maximum useful diameter ND of the classifying drum is ≥ 2 and ideally ≥ 2.3. If the optimal case is NL/ND = 2.5, then a classifying drum whose usable length is 2,000 mm has a usable diameter of 800 mm. The useful length of the classifier drum is the length over which it extends freely through the classifier space parallel to the axis of rotation L. The useful diameter is the maximum outside diameter the drum. Structures that are not important in terms of flow and are locally positioned further out (e.g. flanges) are not included in the calculation of the maximum outside diameter.

By building an extremely long sifter drum, the throughput can be increased without increasing its nominal diameter. As the length increases, the passage area through which fine material can be sucked from the classifier chamber into the interior of the classifier drum increases. Since the nominal diameter of the sifter drum is not increased, the sifting result is not negatively affected. In particular, there is no increased entry of coarser grains into the fines obtained, which would have to be compensated for by other measures.

At the same time, a sifter drum that is longer in the axial direction, with otherwise the same parameters (diameter, speed and air volume), tends to result in a finer sift, since the radial passage speed of the air through the sieve-like jacket of the sifter drum decreases due to the larger flow inlet cross section. As a result, only finer particles tend to be able to be sucked in without overcoming the centrifugal forces acting on them.

It is particularly advantageous to design the centrifugal classifier in such a way that at least one, preferably both parts of the classifier wheel shaft are mounted outside the classifying material space. The rolling bearings that were previously arranged in the classifier room itself had to be protected at great expense from the turbulent and therefore highly invasive and abrasive atmosphere in the classifier room. Already an order outside the classifier room, e.g. B. in the area of the fine material outlet, which has a much less turbulent flow, brings an improvement here. The maximum improvement is achieved when the bearings are arranged completely outside any atmosphere contaminated with fine dust, i.e. also outside the fine material outlet, easily accessible on the side facing away from the classifier chamber. Here they achieve significantly longer average service lives, which is a decisive advantage at high speeds.

It has proven to be particularly advantageous if blades protrude radially inwards from the inner surface of the sifter drum, which influence the movement of the sifter air, in particular guide the sifter air and increase its rotation. In this context, it should be borne in mind that the rotation of the safety air inside the classifier drum reduces the pressure that is necessary to convey the fine product towards the front outlets.

It is particularly advantageous if the intermediate ring, which will be discussed in more detail later and is intended in particular for the center of the sifter drum, has blades of the type mentioned projecting radially inwards from its inner surface.

Ideally, self-contained support rings protrude radially inwards from the inner surface of the classifier drum in the circumferential direction. Such support rings support the sifter drum, which is often quite long and yet comparatively thin-walled, at certain intervals and thereby prevents it from expanding outwards like a drum at extremely high speeds and possibly even becoming overloaded or even failing.

It is particularly useful if the support rings in question are formed in pairs from flanges that extend radially inwards, with which the sifter drum elements mentioned in the next paragraph are flanged to one another.

The sifter drum preferably consists of several, preferably at least four sifter drum elements. These are arranged one behind the other along the common axis of rotation and connected to one another, preferably screwed together.

It is particularly favorable if the several sifter drum elements consist of two groups of identical sifter drum elements, since the production costs can be reduced by using identical parts. Under certain circumstances, cost-effective modularization can even be achieved for entire series, for example by equipping larger centrifugal classifiers with a classifier drum, which instead of two sets of two identical classifier drum elements consist of two sets of two and three identical classifier drum elements.

Ideally, an intermediate ring is installed in the middle of the sifter drum between two sifter drum elements. The intermediate ring has - preferably on its outer surface - one or more recesses for receiving a balancing mass body, usually in the form of at least one balancing groove.

Such an additional support ring can very effectively support the central area of the classifying drum, which is particularly stressed by centrifugal forces, and protect it from overloading.

Another possible further development of the invention is that the classifier drum has a deflector lip at its front ends, directly at the transition to the fine material outlet. This extends obliquely radially inwards - preferably in the Angle from 35° to 50°. The deflector lip prevents an undesired classifier air flow from occurring in the shortest possible way, almost in a kind of " short circuit " , which flows from the front side of the classifier drum, directly from its jacket into the fines outlet. Such an undesirable classifier air flow may only introduce incompletely screened material into the fine material outlet and thus lead to a kind of partial “short circuit”.

The wheel disks that connect the classifier drum to the classifier wheel shaft preferably consist of a rim that is connected to a hub sleeve via at least two, and better yet at least three, spokes.

It is particularly favorable if the rim rim forms an inner surface that widens conically towards the fine material outlet - not only in the sense of a chamfer common in mechanical engineering, but to at least 25%, better at least 45%, of the extent of the rim rim in the direction of the axis of rotation . This improves the guidance of the sifter air loaded with the fines where it exits from the front of the sifter drum at high speed into the fines outlet. This prevents strong turbulence from occurring due to an excessively abrupt change in the clear flow cross-section or a sudden deflection when the flow speed is too high. Excessive turbulence at this point could lead to part of the fine material carried by the outflowing classifier air precipitating prematurely and accumulating in a hindrance instead of being completely removed by the outflowing classifier air.

As part of a particularly preferred development, it is provided that the length of the hub sleeve in the direction of the axis of rotation is greater than the length of the rim of the wheel disc. In this way, a particularly strong and rigid anchoring of the classifier wheel shaft parts according to the invention can be achieved, which is not prone to permanent vibrations or at least temporary imbalances (for example when passing through the subcritical speed range during start-up). Ideally, the length of the hub sleeve in the direction of the axis of rotation is at least 30%, better at least 50% greater than the corresponding length of the rim.

Another, particularly favorable option is that the first and second parts of the classifier wheel shaft each form a disc flange that projects radially outwards. This disc flange preferably rests over its entire surface against the end ring surface of the hub sleeve assigned to this part of the classifier wheel shaft, which faces the interior of the classifier drum. The disc flange is preferably screwed to the hub sleeve, which not least provides additional bending rigidity.

Further design options, further technical effects and further advantages result from the exemplary embodiment, which is described below with reference to the figures.

FIGURE LIST

• The Figure 1 shows a perspective view obliquely from above and outside of a centrifugal classifier according to the invention.
• The Figure 2 shows a central longitudinal section perpendicular to the axis of rotation through the centrifugal classifier Figure 1 .
• The Figure 3 shows a section along the axis of rotation through the centrifugal classifier Figure 1 .
• The Figure 4 shows a front view of the sectional area of Figure 3.
• The Figure 5 shows a frontal view of the sectional surface of the Figure 2 .
• The Figure 6 shows an overall view of the centrifugal classifier according to the invention.
• The Figure 7 shows an enlarged section of the Figure 2 in the middle area, although here the intermediate ring is optionally equipped with blades.
• The Figure 8 shows an enlarged section of the Figure 5 .
• The Figure 9 shows a section of what a seal according to the invention can look like.
• The Figure 10 shows the same as that Figure 9 , frontal from the front.

EXAMPLE EMBODIMENT THE FUNCTIONING PRINCIPLE OF THE CENTRIFUGAL CLIFTER

The basic functional principle of a centrifugal classifier, according to which the centrifugal classifier according to the invention also works, has already been explained in the introduction to the description. Reference is made to this to avoid repetition.

THE CLIFTER HOUSING

The Figure 1 gives a first overview of a preferred embodiment of the centrifugal classifier 1 according to the invention.

The classifier housing 2 can be clearly seen here. One of the components rotates in it Fig. 1 Classifier wheel not shown.

The classifier housing 2 is preferably divided into an upper part 2a and a lower part 2b by a horizon flange 3. The upper part 2a can then preferably be detached as a whole and either completely removed or at least folded upwards around the hinges 4 and their hinge pivot axis S. This provides easy maintenance access to the classifier room, which should advantageously be cleaned regularly or in batch operation after each batch.

In the classifier space 10, which the classifier housing 2 delimits in its interior, a classifier wheel, which will be described in more detail, rotates about the rotation axis L. The classifier wheel is in good condition Figure 3 can be seen, it is marked there with the reference number 7.

As you can see, the centrifugal classifier is preferably designed as a horizontal classifier. This means that the axis of rotation L, around which the classifier wheel 7 rotates, runs horizontally when ready for operation.

This reduces the load on the rolling bearings on which the classifier wheel of this centrifugal classifier is mounted in order to keep the classifier wheel completely or essentially free of play. This is important at the high speeds to which the rolling bearings are exposed, since the classifier wheel preferably rotates at an external peripheral speed of between 50 m/s and 150 m/s. The reason for this is that the rolling bearings inherently carry essentially the same load on each side of the classifier wheel when the rotation axis L is horizontal. In contrast, when the classifier wheel rotates around a vertical axis, it is more difficult to achieve a uniform bearing load.

Above the classifier wheel, the classifier housing 2 has a classified material inlet 5. The classified material consisting of mixed coarse and fine material is fed to the classifier chamber via this classified material inlet 5 (large black arrow). As a rule, the visible material inlet 5 also functions as a visible air inlet. At least the majority of the classifier air therefore enters the classifier space via this material inlet 5. Due to the design of the classifier wheel according to the invention, which will be described in more detail and is particularly favorable in terms of flow technology, it is possible for the first time within the scope of the invention to adjust the product-to-air ratio increase. For classifiers according to the invention, it is ideally at least 0.5 kg, even better at least 0.75 kg of classified material per cubic meter of classifying air. The optional upper limit is 1 kg of visible material per cubic meter of visible air. The said mixture of visible material and visible air preferably flows in in a substantially tangential direction. Such a directed entry supports the circling of the material to be viewed in the classifier room, which creates the visual effect. As can be seen, the sifter inlet 5 extends over the majority of the length of the sifter space, viewed in the direction of the axis of rotation L.

The classifier housing 2 has a fine material outlet 6 at both front ends of the classifier chamber. The finished fine material is discharged via this. The discharge is usually carried out using the classifier air, which is also drawn off via the fine material outlet 6. As you can see, the fines are preferably discharged in a tangential direction, which is symbolized by the two small white arrows.

The classifier housing 2 has a coarse material outlet 8, which is usually arranged completely below the classifier wheel 7. This coarse material outlet is in Figure 1 symbolized by the large white arrow.

Preferably, a certain proportion of classifier air is additionally blown into the classifier space via the coarse material outlet 8 or the auxiliary air supply 9 arranged there, by means of a blower (not shown in the figure). This auxiliary air supply is in Figure 1 symbolized by the small black arrow. This means that particularly fine material that has unintentionally fallen into the area of the coarse material outlet or unintentionally falls into this area threatened to fall, transported back into the sifting room. This leads to a significant improvement in the quality of the screening results.

Further details are very good based on the Figure 2 to see, which shows a section in the vertical direction through the middle area of the sifter and which is viewed together with the Figure 3 is to be considered.

The cut part of the visible material inlet 5, the fine material outlet 6 behind it in the direction of the rotation axis L and the coarse material outlet 8 below, into the clear opening of which the guide element 28 protrudes, are clearly visible here. It can also be clearly seen how the classifier housing 2 forms a classifier space 10 in the shape of a substantially cylindrical drum, which runs horizontally here. The classifier wheel 7 rotates in this drum, at a considerable distance from the inner surface A of the drum. The distance A is preferably between 25% and 65% of the outer diameter of the classifier wheel 7.

In particularly preferred cases it is between 32% and 40% of the outer diameter of the classifier wheel 7.

THE SCREEN WHEEL

The classifier wheel 7 according to the invention and its exact structure can best be explained using the Figures 6 and 7 explain.

The classifier wheel 7 essentially consists of a classifier drum 14 with a classifier wheel shaft 11, which forms its axis of rotation.

How to immediately use the Fig. 6 recognizes, the classifier wheel shaft 11 is characterized by the fact that it does not completely pass through the classifier wheel 7. Instead, the interior of its classifier drum 14 remains free of it, over at least 80% of its length, measured in the direction of the axis of rotation L. In this area, the classifier drum 14 takes on the supporting function of the section of the classifier wheel shaft 11 saved here, which will be discussed in more detail shortly.

As you can see, the classifier wheel shaft 11 consists of a first and a second classifier wheel shaft part 12, 13. The two classifier wheel shaft parts each end in a wheel disk 15. This wheel disk 15 consists of a hub sleeve 16, which is connected to a rim rim 18 via at least three spokes 17 , preferably in one piece. The hub sleeve 16 has a length in the direction of the rotation axis L that is greater than the corresponding length of the rim rim 18.

As can be clearly seen, each classifier wheel shaft part 12, 13 forms a disk flange 19 at its end facing the interior of the classifier drum. This disk flange 19 rests against the inner end face of the hub sleeve 16 assigned to it. The respective disc flange 19 prevents the relevant classifier wheel shaft part 12, 13 from being pulled outwards from the hub sleeve 16. Preferably, the disk flange 19 is also screwed to the hub sleeve 16. The bolt heads 35 of the corresponding, preferably at least six, bolts are in Figure 6 can be seen on the disk flange 19 of the first classifier wheel shaft part 12.

As was already briefly mentioned above, the classifier drum 14 takes on the supporting function in the area in which the classifier wheel shaft 11 is exposed. For this purpose, the outer surface of the sifter drum is made with thick walls. Their wall thickness can essentially correspond to the wall thickness of a hub sleeve 16. It is particularly favorable if their wall thickness is greater than 20 mm and ideally lies in the range between 30 mm and 48 mm, +/- 0.3 mm. The classifier drum is additionally stiffened by the inwardly projecting annular disk-shaped support rings, several of which are provided at a distance from one another on the inner surface of the classifier wheel and which will be discussed in more detail shortly. The majority of the peripheral surface of the viewing drum is broken. It then forms a sieve-like or preferably grid-like or perforated structure through which it can be sucked in. A grid-like structure can be characterized in particular by the fact that its openings are longer in the direction parallel to the longitudinal axis by at least a factor of 7.5 and better by at least a factor of 10 than in the circumferential direction, which can improve the suction characteristics.

Each classifier wheel shaft part 12, 13 is preferably equipped as a stepped shaft with different diameters. Preferably where this stepped shaft has its largest diameter (apart from the disk flange 19), the hub sleeve 16 engages over it.

As you can see, the rim rim 18 of the wheel disc 15 is designed as a ring that is completely closed in the circumferential direction. One end face of this ring rests against a corresponding end face of the classifying drum 14 and is screwed to it. The screw connection is preferably carried out from the outside of the Wheel disc 15 ago. Accordingly, the receiving holes 20 for the bolt head in the rim 18 can be seen here, compare Figure 6 .

The Figure 6 shows how the inner surface 21 of the rim 18 widens conically towards the fine material outlet. This extension is more than just a bevel common in mechanical engineering. In the present case, it extends over the majority of the length of the rim in the direction of the rotation axis L.

On its outer peripheral surface, each rim has a type of toothing 22 or other blade-like structure. Together with the housing surrounding them, these form a type of impeller and/or mechanical deflector, which is arranged in the direction of flow in front of the sealing gap, for which it is effectively responsible, cf. Fig. 6 combined with Fig. 10 . It prevents particles from getting into this space - despite the air flushing of the gap between the rotor and the housing.

The rim is preferably provided on its outer peripheral surface with one or more sealing grooves 23, which form part of the labyrinth-like seal with which the classifier wheel is sealed on its end faces from the fine material outlet 6 - which will be discussed in more detail later.

The preferred design of the spokes 17 can be seen from the rear part of the Figure 6 comprehend. The spokes 17 preferably extend in a purely radial direction from the hub sleeve 16 to the rim rim 18. Each spoke 17 is just as long as the latter where it is connected to the hub sleeve 16, measured in the direction of the rotation axis L. Each spoke 17 tapers towards the rim 18. This means that each of the spokes usually protrudes into the interior of the sifter drum 14 and protrudes outwards on its opposite side in the direction of the axis of rotation L over the rim rim 18. In this way, the spokes have a relatively large area and can therefore effectively help to get the classifier air to rotate.

The sifter drum is preferably composed of several separately manufactured sifter drum elements 14a and 14b. These are arranged one behind the other along the common axis of rotation L and connected to one another, preferably screwed. Ideally, the classifier drum elements have a “ usable length (NL) to useful diameter (ND) ratio” that satisfies the following equation: NL/ND = 0.5 to 0.8. The usable length corresponds to the total extension parallel to the rotation axis L. A sifter drum element that extends 500 mm along the rotation axis L then has a diameter of 1,000 mm.

It is particularly favorable if each of the sifter drum elements 14a, 14b carries an annular disk-shaped fastening flange 24a, 24b, 24c on its two end faces. This extends, based on the inner surface of the sifter drum element, in a radially inward direction by an amount H. The ideal rule is: H ≥ 30 mm, cf. Fig. 7 , where the dimension H is drawn. Looking at this from another perspective, it can be said that the free area defined by the clear diameter XX (see Fig. 7 ), depending on the dimension H, must offer enough space so that the flow speed is below 30 m/sec falls. Nevertheless, the construction must of course have sufficient mechanical strength.

The fastening flange in question is located completely inside the sifter drum. It carries the screw connection that fixes two adjacent sifter drum elements to one another. It usually also forms a centering groove or a complementary centering projection 36, through the interaction of which adjacent sifter drum elements are precisely positioned relative to one another. A precise representation of such a centering groove and a centering projection marked with reference number 36 can be found in Figure 7 right, middle.

In this exemplary embodiment, a pair of annular disk-shaped fastening flanges 24a, 24b, 24c screwed together each form one of the support rings briefly mentioned above. These support rings prevent the sifter drum 14 from expanding outwards in a barrel shape in its middle area under the influence of the strong centrifugal forces caused by the high operating speed or even from being overloaded and failing.

Apparently the Figure 6 A special intermediate ring 25 is installed in the middle of the sifter drum between two sifter drum elements 14a. This intermediate ring 25 has one or more recesses on its outer surface for receiving a balancing mass body, preferably in the form of at least one balancing groove 37, cf. Fig. 7 .

In addition, this intermediate ring 25 is realized together with the annular disk-shaped ones blocked to it by the screw connection Fastening flanges 24a have a wider and therefore particularly heavy-duty support ring of the type already explained above. This has a particularly favorable effect, since the point of the classifying drum 14 that is most heavily loaded by centrifugal forces is located here.

Optionally, the intermediate ring 25 can be equipped with blades 26 that extend further inwards in the radial direction, which serve to move the classifier air without disturbing the pressure equalization explained below, see Figure 7.

In earlier designs, for reasons of strength, the sifter drum was supported by the safety shaft in the area of today's intermediate ring 25 with a disc wheel with narrow openings or swirling spokes. In contrast, the construction according to the invention results in a significantly better balance of the instantaneous pressure between the left half of the sifter drum, which communicates with the first fine material outlet, and the right half of the sifter drum, which communicates with the second fine material outlet located on the other side, via its maximum flow cross section .

The resulting lower pressure pulsations inside the sifter drum improve the sifting result, simply because fewer agglomerations occur.

As you can see, the radially inward end of each fastening flange 24a, 24b, 24c is beveled over its entire width, approximately like a lean-to roof, as shown by Figure 6 shown. Due to this, two fastening flanges screwed together form a gable roof-like configuration, which functionally forms a sliding slope for the visible goods. This reliably prevents a somewhat heavier part of the visible material from being permanently deposited at this point during operation and being held in place by the centrifugal forces - as could be the case due to a missing sliding slope on a surface that runs parallel to the axis of rotation L.

For the same reason, the radially inward end of the intermediate ring 25 is beveled like a gable roof and, where present, the inner ends of the blades 26.

Easy to recognize from the Figure 6 is that the sifter drum elements consist of two groups of identical sifter drum elements. As you can see, the two sifter drum elements 14a that meet in the middle of the sifter drum 14 are identical in construction and the two sifter drum elements 14b that close the sifter drum 14 to the outside are also identical in construction.

Finally, it shows Figure 6 that the sifter drum has a deflector lip 27 at its two front ends, directly at the transition to the fine material outlet 6, which extends radially inwards and at the same time obliquely towards the center of the sifter drum 14. This has the function mentioned in the introduction to the description.

It is worth considering designing the sifter drum elements 14a and 14b as cast parts, for example made of nodular cast iron, which are then subsequently precision turned. In this way, the large number of openings in the outer surface of the classifier drum 14 can be produced particularly efficiently. Regardless of whether the sifter drum is designed in one or more parts, applies that these openings are required for the entry of the classifier air into the interior of the classifier drum. In the case of a one-part or multi-part classifier wheel, they are preferably the sole or at least the predominant means of causing the safety air entering the classifier space and the material it carries to circulate in the classifier chamber in such a way that the centrifugal forces can develop their separation effect.

THE GUIDE ORGAN CONTROLLING THE COARSE GOODS OUTLET

The guide element 28 according to the invention, which controls access to the coarse material outlet, can best be described using the Figures 2 , 5 and 8th recognize and explain.

The guide element 28 according to the invention can be a blade or - in an optionally broader interpretation of the term blade - a guide element similar to a blade. Its main guide surface 29 is curved in such a way that material striking this main guide surface 29 is deflected or thrown back inwards towards the classifying drum 14. Fine material, which may previously have been mixed in with the material hitting the blade 26 and was carried along radially outwards by it, is given the chance to separate from the coarse material and then taken away by the classifying air flowing into the interior of the classifying drum 14 and to be entered into the interior of the classifying drum 14. This significantly improves the classification quality.

It should be noted that the said curvature is preferably a continuously concave curvature that extends towards the classifier drum 14 tends. The main guide surface 29 is preferably designed as a correspondingly curved sheet metal, which is held in shape at least by two edge plates 30 bordering it on both sides, cf. Fig. 5 and 8th . The main guide surface 29 is often also stabilized in its center (measured in the direction along the axis of rotation L) by an edge plate 30 of the type mentioned, which is welded on here as a rib-like reinforcement. The blade is preferably designed so that it does not cause any turbulence - at least no significant turbulence.

In the direction parallel to the axis of rotation L, the extent of the preferably one-piece guide member 28 according to the invention is usually so large that it covers the entire coarse material outlet in the direction along the axis of rotation L. Seen in the direction of rotation, the extent of the guide element 28 according to the invention is preferably so large that the guide element covers more than 45% and better 60% to 70% of the clear area with which the coarse material outlet opens into the inner surface of the drum designed as part of the classifier housing Sifter room 10 limited.

It is particularly advantageous if the position of the guide element is adjustable in and against the direction of rotation, ideally infinitely adjustable, so that if necessary it covers more or less of the clear area with which the coarse material outlet opens into the inner surface of the drum in question, which is not shown here is shown separately. In this way, the guide element according to the invention can be adjusted to the maximum average grain diameter of the fine material currently required by the classifier.

A special feature is that the guide element 28 is attached at a distance X from the inner surface of the drum, which delimits the classifier space 10. The distance X referred to here is preferably between 3 mm and 12 mm. Ideally it can be adjusted, usually continuously. In this context, the distance depends on the number of coarse particles contained in the visible material. If there are a lot of coarse particles, they need to be separated more quickly. The distance then tends to be set larger, resulting in faster ejection.

This positioning of the guide element 28 results in visible material (coarse material), which flows along said inner lateral surface with a radial distance ≤ Only the part of the material to be classified which flows along said inner surface with a radial distance >X and <Y is deflected in the direction of the sifter drum 14. The following preferably applies to the distance Y: (DSK-DSR)/2, where DSK is the inside diameter of the classifying chamber and DSR is the outside diameter of the classifying drum. Alternatively, it can be said that the distance Y " should be in the range between 1/2 DSR and 2/6 DSR

It is also worth noting that the guide element 28 is particularly effective in interaction with the auxiliary air supply 9, since these two improvements together have a synergistic effect.

This can be explained quite well using the Figure 5 recognize.

The guide element 28 increasingly forces the auxiliary air blown in via the auxiliary air supply 9 to enter the classifier space 10 in a tangential direction. It prevents or reduces the tendency of the auxiliary air to hit the classifier air rotating at high speed in the classifier chamber 10 at an obtuse angle and thus produce undesirable turbulence.

At the same time, the guide element 28 calms the air flow in the area in which the coarse material falls out after it has passed under the guide element 28. Because in this area, the guide element 28 creates a leeward space, at least essentially, compared to the classifying air circulating at high speed in the classifier room.

All of this leads to a significant improvement in visibility.

THE FRONT SEALING OF THE SIFTER WHEEL

Within the scope of the invention, the focus is also on sealing the transition between the classifier space 10 and the fine material outlet 6 on the front side of the classifier drum 14 as effectively as possible. This is important because sealing errors at this point lead to the fine material that has already been obtained with a high quality of screening being contaminated with screening material that has not yet been screened or has not been completely screened. This is to be avoided.

A non-contact seal is provided here for this purpose.

In order to be able to implement such a seal, the classifier housing 2 is in the area of the sealing point between the classifier chamber 10 and the fine material outlet 6 is designed as a double-walled area. This double-walled area is in Figure 3 identified by the reference symbol D.

Compressed air is brought to the sealing point via this double-walled area D.

The actual sealing point shows this Figure 10 in an enlarged view. First of all, a section of the rim rim 18 can be seen here. It has several, in this case preferably three, circumferential sealing grooves 23 on its outside, as have already been briefly mentioned above, cf. again Fig. 6 .

The double-walled area has a sealing insert 31 at its end, near the sealing point, see again Fig. 10 . The sealing insert 31 is preferably designed to be replaceable, although the seal works at least essentially without contact, since in the long term it is a wearing part in an atmosphere contaminated with fine dust. This sealing insert forms three raised, circumferential sealing rings 32. Each of these sealing rings 32 engages in a sealing groove 23 assigned to it on the rim rim 18.

Since the seal works without contact, the raised, circumferential sealing rings 32 and the sealing grooves 23 assigned to them form a kind of labyrinth. In order to give this seal a real blocking effect, the sealing insert 31 is equipped with one or preferably several compressed air injection openings 34, via which compressed air flows into the distribution channel 33 for the said seal labyrinth is blown in, which has been brought to the sealing point via the double-walled area, cf. Fig. 10 .

From the distribution channel 33, the majority of the blown-in compressed air flows into the classifier space 10 and keeps the path through which it flows out free of penetrating material. The smaller part of the compressed air blown in flows into the fine material outlet 6. The latter is because two baffles formed by sealing rings 32 and sealing grooves 23 stand in the way of this part of the blown-in compressed air, and not just one, which is why the flow is correspondingly lower.

Such a contactless seal is of great advantage for controlling the high speeds that occur on the classifier wheels according to the invention.

REFERENCE SYMBOL LIST

1

centrifugal classifier

2

Classifier housing

2a

Upper part of the classifier housing

2 B

Lower part of the classifier housing

3

Horizontal flange

4

Hinge for swinging open the classifier housing, which was previously separated into two halves

5

Visual goods inlet

6

Fines outlet

7

sifter wheel

8th

Coarse material outlet

9

Auxiliary air supply

10

sifter room

11

Classifier wheel shaft

12

first classifier wheel shaft part of the classifier wheel shaft 11

13

second classifier wheel shaft part of the classifier wheel shaft 11

14

Classifying drum

14a

Classifying drum element, type 1

14b

Classifying drum element, type 2

15

Wheel disc consisting of hub sleeve, spoke and rim rim

16

hub sleeve

17

spoke

18

Rim rim

19

disc flange

20

Locating hole for bolt head

21

Inner surface of the rim

22

gearing

23

sealing grooves

24a

ring-shaped mounting flange

24b

ring-shaped mounting flange

24c

ring-shaped mounting flange

25

Intermediate ring

26

shovel

27

deflector lip

28

guiding organ

29

Main guide surface

30

Edge plate

31

Sealing insert

32

sealing ring

33

distribution channel

34

Compressed air inlet openings

35

Bolt heads

36

centering projection

37

balancing groove

A

Radial distance between the inner surface of the classifier chamber and the outer surface of the classifier drum.

D

double-walled area

DSK

Inner diameter of the classifier space or the drum delimiting it

DSR

Outer diameter of the sifter drum

H

Amount of extension

L

Axis of rotation

ND

Usable diameter of the sifter drum

NL

Usable length of the sifter drum

S

Hinge pivot axis of hinge pair 4

X

smallest radial distance between the guide element 28 and the inner surface of the classifier space.

Y

Maximum radial distance that the material circulating in the classifier space may have to the inner surface of the classifier room in order to come into direct contact with the guide element 28

Y"

radial clearance between guide element 28 and the classifier wheel

XX

clear diameter inside an annular disk-shaped mounting flange

Claims (15)

1. Centrifugal separator (1) comprising a separator housing (2) and a separator wheel (7) which rotates in the separator housing (2), wherein the separator wheel (7) comprises a separator drum (14) and a separator wheel shaft (11) which forms its axis of rotation, and wherein the separator housing (2) has at least one coarse material outlet (8), characterized in that in the region of the at least one coarse material outlet (8) a guide member (28) is arranged,

   wherein the guide member (28) is arranged at a distance X from the inner jacket surface of the separator housing section which surrounds the separator drum (14),

   and the guide member (28) is configured such that material to be separated flowing along said inner jacket surface at a radial distance ≤X circumvents the guide member (28) and is then discharged into the coarse material outlet (8),

   and material to be separated flowing along said inner jacket surface at a radial distance >X is deflected in a radially inward direction toward the separator drum (14).
2. The centrifugal separator (1) according to claim 1, characterized in that the guide member (28) covers at least part of the coarse material outlet (8) in a flow direction.
3. The centrifugal separator (1) according to one of the preceding claims, characterized in that the at least one coarse material outlet (8) is arranged below the separator drum (14) and separation air which flows off via the separator drum (14) is fed in at the coarse material outlet (8).
4. The centrifugal separator (1) according to one of the preceding claims, characterized in that the ratio NL/ND between the usable length (NL) of the separator drum (14) and the maximum usable outer diameter (ND) of the separator drum (14) is ≥ 2.
5. The centrifugal separator (1) according to one of the preceding claims, characterized in that blades (26) project radially inwards from the inner jacket surface of the separator drum (14).
6. The centrifugal separator (1) according to one of the preceding claims, characterized in that supporting rings which are closed in the circumferential direction project radially inwards from the inner jacket surface of the separator drum (14).
7. The centrifugal separator (1) according to one of the preceding claims, characterized in that the separator drum (14) consists of several separator drum elements (14a; 14b) which are arranged one behind the other along the common axis of rotation (L) and are connected or screwed to one another.
8. The centrifugal separator (1) according to claim 7, characterized in that each separator drum element (14a; 14b) forms an annular disk-shaped fastening flange (24a; 24b; 24c) on each of its front faces which extends, in relation to the inner jacket surface of the separator drum element (14a; 14b), by an amount (H) in the radially inward direction.
9. The centrifugal separator (1) according to one of claims 7 or 8, characterized in that an intermediate ring (25) is installed in the middle of the separator drum (14) between two separator drum elements (14a, 14a).
10. The centrifugal separator (1) according to one of claims 7 to 9 in conjunction with claim 4, characterized in that the intermediate ring (25) has blades (26) that project radially inwards from its inner jacket surface.
11. The centrifugal separator (1) according to one of the preceding claims, characterized in that each of the wheel discs (15) consists of a wheel rim (18) which is connected to a hub sleeve (16) via at least two spokes (17).
12. The centrifugal separator (1) according to claim 11, characterized in that the first part and the second part of the separator wheel shaft (11) each form a radially outwardly projecting disc flange (19) which rests against the end ring surface of the hub sleeve (16) associated with this part of the separator wheel shaft (11), which end ring surface faces the interior of the separator drum (14), or is screwed to the hub sleeve (16).
13. The centrifugal separator according to one of the preceding claims, characterized in that the nominal speed of the separator drum is such that the target value of 160 m/s at the outer diameter of the separator drum is reached or exceeded.
14. The centrifugal separator (1) according to claim 2, characterized in that the position of the guide member can be adjusted in the direction of rotation and in the opposite direction of rotation.
15. The centrifugal separator (1) according to claim 8, characterized in that at least one fastening flange (24) of each separator drum element (14a; 14b) is bevelled over at least 25% of its radial extent.

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