EP0104458A2 - Centrifuge sieve and process for its production - Google Patents

Abstract

In a centrifuge sieve drum, wherein the inner surface of the drum is lined with a support arrangement carrying wear-resistant sieve or screen rods, there is obtained a compensation of the different thermal expansions of the sieve rods and the support arrangement in that, the sieve rods comprise an axially extending web and the support arrangement comprises identically shaped grooves or slots engaged by the webs. Each web and its associated groove or slot may be designed, for example, as a dovetail guide. Thus, while the sieve rods may expand or contract in longitudinal direction or in the direction of the lengthwise axis of the drum, the sieve rods are, however, immovable in radial direction and in circumferential direction. Such a support arrangement can be efficiently manufactured by simultaneously cutting, such as by milling the grooves or slots and sieve openings or slots in a convex outer surface using a triple cutter, such as a milling cutter, and by subsequently bending the supporting arrangement to form a concave surface and inserting the same into the drum.

Description

The invention relates to a centrifuge sieve with a supporting structure provided on the inside of a centrifugal drum, which carries sieve bars made of wear-resistant material running in the axial direction of the centrifugal drum, and a method for its production.

In such, e.g. Centrifuge sieves known from DE-A 28 30 388 or US Pat. No. 4,259,136, the sieve rods protecting the centrifugal drum from wear are fastened to the drum supporting structure by means of adhesive bonds. To compensate for the different thermal expansion of the sieve bars and the support structure consisting of a material with a different coefficient of thermal expansion, elastic intermediate layers are provided in these connections, e.g. Rubber intermediate elements. However, these are not sufficiently durable in operation. In addition, they allow mobility in several directions, which allows undesired and impermissible deformations of the sieve bars and support structure against each other. Another disadvantage is the poor manufacturability, in particular the difficult and unsuitable for mass production assembly of the sieve bars on the inside of the centrifugal drum or the support structure.

The centrifuge described in US Pat. No. 3,100,746, in which the sieve bars rest loosely in a groove at least at one end, has similar disadvantages, since here too an uncontrolled movement and deformation of the sieve bars is possible, and moreover, to prevent the sieve bars from falling out to prevent, only operation with a vertical axis is possible, and only if the centrifugal drum is conical.

Also the proposal according to the older priority EP-A 71 012, the sieve bars only fixed in one place, but in other places e.g. There are drawbacks to connecting them to the supporting structure by means of slots in the axial direction, especially the replacement of defective or worn sieve bars is tedious, and the production of such a centrifuge sieve is complicated and labor-intensive.

The invention has for its object to avoid the above-mentioned disadvantages of the prior art, and in particular to create a centrifuge sieve in which the sieve rods permanently, temperature and corrosion resistant, movable in a defined manner against the supporting structure and connected to it and easy to assemble are, the sieve rods are easily exchangeable without the operation and shape of the centrifuge being restricted. Such a centrifuge sieve should also be easy and inexpensive to manufacture in mass production.

According to the invention, this object is achieved in that either the sieve bars or the support structure have webs which engage in grooves or slots of the same shape in the other part, so that the sieve bars can only be moved in the axial direction with respect to the support structure.

A particularly advantageous solution is obtained if the sieve bars on the support surface with the support structure have dovetails running in the axial direction of the centrifugal drum and the support structure has slots in the form of a geometrically corresponding dovetail guide.

Such a support structure can be produced in a particularly advantageous manner by milling oblique slots with parallel side faces that run into the starting material for the support structure that is curved into a convex surface and that have parallel side faces, in that slots with opposite obliquity with respect to the axis more slots with parallel side surfaces are milled, and that the support structure is then bent into a concave surface corresponding to the inside of the centrifugal drum.

• Figur 1 zeigt ein Zentrifugensieb in Perspektive
• Figur 2 zeigt einen Axialschnitt dieses Zentrifugensiebes
• Figur 3 zeigt einen Ausschnitt der Trommelaussenwand dieses Zentrifugensiebes
• Figur 4 zeigt einen Ausschnitt der Trommelaussenwand eines anderen Zentrifugensiebes
• Figuren zeigen verschiedene Beispiele der Verbindung 5 - 9 von Siebstäben und Stützwerk
• Figuren erläutern ein Verfahren zur Herstellung des 10 + 11 in Figur 7 dargestellten Stützwerkes anhand von zwei Schnittbildern
• Figur 12 erläutert ein abgewandeltes Herstellungs-Verfahren anhand eines Schnittbildes

The invention is explained on the basis of the exemplary embodiments shown in the figures:

• Figure 1 shows a centrifuge sieve in perspective
• Figure 2 shows an axial section of this centrifuge sieve
• Figure 3 shows a section of the drum outer wall of this centrifuge screen
• Figure 4 shows a section of the drum outer wall of another centrifuge sieve
• Figures show various examples of connection 5 - 9 of sieve bars and support structure
• Figures explain a method for producing the 10 + 11 support structure shown in Figure 7 using two sectional images
• FIG. 12 explains a modified manufacturing method using a sectional view

The centrifuge sieve shown in FIGS. 1, 2 and 3 has a centrifugal drum T with a drum diameter from the decimeter to the meter range, on the inside of which a sieve-like support structure 1 rests, on the inside of which a plurality of, for example made of a hard material or a, is in turn used as wear protection other suitable material Sieve bars 2 with a thickness of a few millimeters and a length of up to approximately 30 cm in the axial direction of the centrifugal drum are fastened at a small lateral distance from one another.

The support structure 1 is made of a suitable metal, e.g. Steel, and has sieve slots 3 or holes for the passage of the filtrate when centrifuging. Instead, however, the support structure can also consist of a framework of rings which are connected to one another by axially parallel rods, so that the required sieve slots are created between the rods. On the inside of the drum T, annular webs_4 are provided, on which the supporting structure 1, which may also have annular webs 7 on the outside, possibly rests on spacers 8, a path for the filtrate to pass through the spaces 5 between the sieve bars 2 and the ones below Slots 3 of the support structure 1, the space 9 between the support structure and the drum, and the slots 6 offset from the sieve bar spaces are formed in the drum T. If the slots are not or only slightly offset from one another, the spacers can also be dispensed with.

The sieve bars 2 can be made of a wear-resistant hard material, for example melt basalt or sintered material, such as sintered ceramic or cemented carbide, for example aluminum oxide or tungsten carbide. If the requirements are somewhat lower, a suitable wear-resistant steel can serve as the material, or a particularly wear-resistant plastic, for example plastic reinforced with glass or carbon fibers, or another suitable material. Since temperature fluctuations of up to 100 ° C can occur during operation of the centrifuge, the materials of the sieve bar, for example tungsten carbide, and the Support structure, for example steel, when fastening the sieve bars 2 to the support structure 1, precautions are taken for a length compensation in order to avoid deformations and breakage of the sieve bars. For this purpose, 2 dovetail-shaped webs 10 are provided on the support surface of the sieve bars, which engage in corresponding, identical grooves or slots 11 in the support structure.

The described arrangement and guidance of the sieve bars causes the sieve bars 2 to be immovable in the radial direction, but a length compensation is possible in the longitudinal direction, that is to say in the axial direction of the centrifugal drum. Movement in the circumferential direction is made impossible by the axial alignment of the grooves 11.

Due to the arrangement described, a defined mobility of the sieve bars against the supporting structure is only possible in the main direction of expansion, i.e. reached in the longitudinal direction of the sieve bars, using only very durable and temperature and corrosion resistant materials. Compared to known centrifuge sieves with elastic rubber or plastic connecting elements, the arrangement described could multiply the service life in practical operation and significantly improve the corrosion resistance. Another advantage is the much easier interchangeability of the sieve bars, since the webs of the sieve bars only have to be inserted into the corresponding dovetail guide, and that opened bars are held in their entire length by the special guide.

FIG. 4 shows another example in which a plurality of layers of sieve bars 2 ¹ , 2 ² are arranged one behind the other at a small distance in the axial direction, wherein the connection of sieve bars 2 ¹ , 2 ² and supporting structure 1 again takes place by means of webs and slots 11 ¹ and 11 ^2, for example in the form of a dovetail guide. Between the sieve bars 2 ¹ , 2 ² several rows of sieve slots 3 ¹ , 3 ^{2 are} provided in the support structure 1, through which the filtrate can flow off. In comparison to the first example, the use of several layers of sieve bars allows a longer length of the sieve drum, up to several meters. This is particularly advantageous for sintered materials that only allow a limited rod length. In this embodiment, the support structure can also consist of several parts arranged one behind the other in the axial direction, each support structure part, for example, carrying only one sieve bar layer, but it is also readily possible to provide several, for example two, layers, the introduction of the sieve bars into the slots can be done from both sides.

It should be noted that, instead of providing a support structure 1 separate from the drum T, this can be firmly connected to the drum, or the inner part of the drum T can serve as a support structure on which the sieve bars 2 rest directly, and that is provided with the required grooves or slots 11.

FIGS. 5-9 show various expedient, geometric shapes of the webs 10 and slots 11.

In the example according to FIG. 5, the sieve bars 2 have webs 10 with a rectangular cross-section on their support surface 12 on the supporting structure 1 which extend in the axial direction. Corresponding slots 11 are provided in the supporting structure 1, into which the webs 10 fit exactly and are possibly clamped.

Conversely, as shown in FIG. 6, the webs 10 can also be provided on the supporting structure 1, while the sieve bars are provided with corresponding slots 11.

In order to prevent the rods 2 from falling out with a rectangular cross section of the webs 10 if the narrow dimensional tolerances required here are not complied with, the cross section of the webs 10 and slots 11 according to FIG. 7 is expediently chosen to be trapezoidal, i.e. in the form of a dovetail guide.

Securing the rods against falling out is also possible with a different geometric shape of the webs, e.g. As shown in FIG. 8, with a rounded shape with a constriction 13 near the support surface 12 and a corresponding design of the slot with an inward expansion.

As shown in FIG. 9, a plurality of parallel webs 10 ¹ , 10 ² can also be provided on the same part, for example on the sieve bars ² .

Furthermore, the slots can be designed as deeply limited grooves, as shown in the examples described above, or as deep slots, e.g. the support structure consists of separate bars, which are connected at the ends at most.

In the examples described and possible further modifications within the scope of the inventive idea, it is ensured that the sieve bars can expand and contract practically unhindered in the direction of the drum axis, but are immovable in the circumferential and radial directions. The assembly and replacement of the sieve bars is extremely easy.

In principle, the screen slots 3 and the grooves 11 can indeed be produced in a conventional and known manner, for example using suitable milling tools. In the design as a dovetail guide according to FIG. 7, however, the use of a particularly simple, rational and inexpensive manufacturing process is possible by first bending the material of the support structure into a convex surface, then using a milling tool from the outside to make a slot or a groove with parallel side surfaces or Flanks are milled into the convex surface, the application direction of the tool and thus the direction of the flanks obliquely with respect to the axis of the supporting structure, ie on one side of the axis at a certain distance from it. After completing this process step, a milling tool is attached to the same point on the surface, but with an opposite slope to the axis, i.e. with an application direction running on the other side of the same, and an additional slot is milled obliquely to the existing slot, so that a dovetail groove is formed. The support structure is then bent in the opposite direction to a concave surface which corresponds to the shape of the inside of the centrifugal drum. The dovetail grooves come to rest on the inside of the support structure.

A particularly advantageous development of this method can be achieved if the dovetail grooves and the sieve slots are milled in one operation or in the same method steps. As shown in the sectional images shown in FIGS. 10 and 11, a tube 14 is used as the starting material, the diameter of which corresponds approximately to the inner diameter of the centrifugal drum and the zones lying one behind the other in the direction of the axis A. has a smaller wall thickness 15 and a larger wall thickness 16, and the zones 16 of greater wall thickness form beads or webs 17 on the inside, while the outside 18 of the tube 14 is smooth and has a uniform diameter. The machining is carried out from the outside using a milling tool 19 with three parallel milling cutters 20, 21 and 22, for example with three circular saw blades, or a central circular saw blade 20 and two outer side milling cutters 21 and 22. The penetration depth of the central milling cutter 20 is selected or set in this way that this cuts through the entire wall when milling a slot along a surface line of the tube 14, that is to say in the axial direction, in the zones 15 of smaller wall thickness, so that here there is a continuous slot from the outside, a later sieve slot 3, while in the Zones 16 of greater wall thickness only a non-continuous groove is milled, and a continuous ring remains, the later annular web 17. The depth of the two outer milling cutters 21 and 22, on the other hand, is selected or set so that during milling the wall of the tube 14 is not completely penetrated in either of the two zones 15 and 16, so that only grooves are formed.

The three cutters 20, 21 and 22 work simultaneously during the milling process. While the middle milling cutter produces the later screen slots 3, the outer milling cutter 21 mills a groove, the side surfaces of which run obliquely to the axis A. After this operation, the tube is rotated through an angle M 14, which is selected such that the other outer cutter 22 comes to the position where the cutter 21 is already an oblique _N ut generated. In the now following operation, this milling cutter 22 then mills a flank into the groove already pre-milled by the milling cutter 21, which flank also extends obliquely to the axis with opposite inclination, so that a dovetail groove 11 with a trapezoidal cross section is created, at the same time a new slot is milled by the central milling cutter 20, and a new groove is prepared by the milling cutter 21. The tube 14 is then rotated again by the angle o (.) And the operations are repeated until the entire surface of the tube 14 is provided with slots 3 and grooves 11. After the milling operations, the tube 14 is slit open at a point 23 , bent into a concave surface with an opposite curvature, and inserted into the inside of the centrifugal drum, so that the dovetail grooves 11 now come to lie on the inside. The insertion of the sieve rods into the dovetail grooves can be done either immediately after the end of the Milling process, or after the support structure has been bent into its final shape, if necessary also only after insertion into the centrifugal drum.

Modifications of the method are possible within the scope of the inventive concept. Thus, FIG. 12 demonstrates a method in which the tube 14 is rotated between the work steps by an angle β, which is selected such that a prepared groove 24 only becomes a finished dovetail groove 25 in the third subsequent work step.

In any case, a centrifuge sieve can be produced in an extremely simple and efficient manner, even in mass production, using the starting material mentioned and the method described.

Claims (10)

1. Centrifugal sieve with a support structure (1) provided on the inside of a centrifugal drum (T), which carries sieve bars (2) which run in the axial direction of the centrifugal drum and are made of wear-resistant material, characterized in that either the sieve bars (2) or the support structure ( 1) have webs (10) which engage in grooves or slots (11) of the same shape in the other part, so that the sieve bars can only be moved in the axial direction with respect to the supporting structure. 2. Centrifuge sieve according to claim 1, characterized in that the webs (10) on the sieve bars (2) and the grooves or slots (11) are provided on the support structure. 3. Centrifuge sieve according to claim 1 or 2, characterized in that the webs (10) have a rectangular cross section. 4. Centrifuge sieve according to claim 1 or 2, characterized in that the webs (10) have a constriction (13). 5. Centrifuge sieve according to claim 4, characterized in that the webs (10) have a trapezoidal cross-section and form a dovetail guide with the grooves or slots (11). 6. Centrifuge sieve according to one of claims 1-5, characterized in that the sieve bars (2) or the support structure (1) have a plurality of webs (10) or grooves or slots (11) running parallel to one another. 7. Centrifuge sieve according to one of claims - 6, characterized in that the sieve bars (2) consist of sintered material, in particular sintered ceramic, such as aluminum oxide, molten basalt or sintered carbide, such as tungsten carbide. 8. centrifuge sieve according to one of claims 1-7, characterized in that the supporting bars (1) carrying the sieve bars (2) is formed by the inner part of the centrifugal drum (T). 9. A method for producing a centrifuge sieve according to claim 5, characterized in that oblique grooves or slots with parallel side surfaces that are milled into the grooves or slots with parallel side surfaces are milled into the starting material for the supporting structure, which is curved into a convex surface, for the supporting structure opposite obliquity with respect to the axis, further slots with parallel side surfaces are milled, and that the support structure is then bent into a concave surface corresponding to the inside of the centrifugal drum. 10. The method according to claim 9, characterized in that a material with zones lying one behind the other in the axial direction with alternately smaller and larger wall thickness is used as the starting material for the support structure, that three to each other in each step in the curved starting material for the support structure in a convex surface parallel grooves or slots are milled with parallel side surfaces, the central slot extending in the axial direction and having a depth that it penetrates all the material in the zones of smaller wall thickness, and wherein the two outer grooves run on different sides of the axis of the support structure and have a depth such that they do not penetrate the material even in the zones of smaller wall thickness, and that for the following work step the convex support structure is rotated about its axis so that a The grooves prepared by an external milling cutter come to rest on the opposite side of the axis at the point of application of the other external milling cutter tool, that the operations are repeated until the entire surface of the supporting structure is provided with grooves or slots, and then the supporting structure is closed the predetermined concave surface is bent.

Images