Patent Application
20140148327
The invention relates to a separation disc for a centrifugal separator and a method for manufacturing the separation disc. In particular the invention relates to a separation disc made of metal material and which is adapted to be compressed in a stack of separation discs inside a centrifugal rotor for separating a liquid mixture, the separation disc having a truncated conical shape with an inner surface and an outer surface and a plurality of spacing members extending a certain height above at least one of the inner surface and the outer surface for providing interspaces between mutually adjacent separation discs in the stack.
Separation discs of metal are used in connection with relatively robust and large-sized centrifugal separators for separating liquid mixtures; wherein the separation discs are of relatively large size and exposed to both high centrifugal and liquid forces.
The separation discs are stacked at a mutual distance to form interspaces between themselves. The liquid mixture to be separated in the centrifugal rotor is conducted through the interspaces, wherein the liquid mixture is separated into phases of different densities during operation of the centrifugal separator. The interspaces are provided by said spacing members arranged on the surface of each separation disc. There are many ways of forming such spacing members. They may be formed by attaching separate members in the form of narrow strips or small circles of sheet metal to the separation disc, usually by spot welding them to the surface of the separation disc. The separation disc may also be manufactured with spacing members formed in one piece with the material of the separation disc itself. Known techniques for manufacturing separation discs with integrally formed spacing members are disclosed in for instance WO 2007/055630 A1 and U.S. Pat. No. 6,526,794 B1.
The size of the interspaces between the separation discs depends on how much the spacing members extend or protrude from the surface, i.e. the height of the spacing members. Dimensioning the size of the interspaces or height of the spacing members involves different aspects to be considered. For instance, it will depend on the type and amount of solids (sludge) being suspended in the liquid mixture. In general, the height (or size of the interspaces) will be dimensioned somewhere in the range of 0.3 to 0.8 mm.
Furthermore, the centrifugal rotor provides a separation space which is designed with a given total height for the stack of separation discs. In order to maximize the separating capacity of the centrifugal separator, there is a de-sire to fit as many separation discs as possible into the stack within that given height. More separation discs in the stack means more interspaces in which the liquid mixture can be separated. An optimum height on each of the individual interspaces will however usually be given by (or depend on) the type of liquid mixture which is intended to be separated. Consequently, this leaves the option of making the separation discs as thin as possible to maximize the number of separation discs within said given total stack height.
However, there's a lower limit as to how thin the separation discs can be made. Present day manufacturing techniques and in particular the material of the separation disc will define this lower limit. The thickness of the separation discs (i.e. without counting the spacing members) will typically be somewhere in the range from 0.3 to 0.6 mm. A separation disc having a small size (diameter) may exhibit a thickness of 0.4 mm, whereas a substantially larger separation disc may exhibit a thickness as great as 0.7 mm. Hence, the separation disc is in general made thicker with the size (diameter) of the separation disc. The centrifugal rotor will rotate at high speeds, and accordingly the separation discs are exposed to high centrifugal forces and strains during rotation. If the separation discs are made too thin, such strains would lead to material failure or permanent deformation.
Prior to this happening, there may be other problems with very thin separation discs. As the separation discs are made thinner, they will exhibit a loss in rigidity and irregularities in their shape may begin to appear. The separation discs are furthermore compressed in the stack inside the centrifugal rotor to form a tight unit. The thin separation discs may thereby flex and/or because of their irregular shaping give rise to unevenly sized interspaces in the stack of separation discs. Accordingly, in certain parts of the interspaces (e.g. far away from a spacing member), the mutually adjacent separation discs may be completely compressed against each other to leave no interspaces at all. In other parts of the interspaces (e.g. in the vicinity of a spacing member) the separation discs will not flex much and accordingly provide an adequate height.
A high performing disc stack depends however, among other things, on the interspaces being equidistant. Having the same height all over means that the liquid mixture is evenly distributed in the interspaces of the stack. In this way, the interspaces all contribute to the separation of the liquid mixture. This is important for each of the interspaces separately and in relation to each other. Consequently, different sized interspaces along the stack would cause uneven flow distribution, whereby certain interspaces are overloaded with flow, while other interspaces barely receive any flow at all. Such uneven flow distribution will in turn cause a decrease in the separating efficiency of the disc stack. This problem may also appear in each of the individual interspaces, wherein compressed parts barely receive any flow at all and consequently do not contribute to separating the liquid mixture.
It is an object of the invention to provide a separation disc and a method for manufacturing such a separation disc which provides substantially equidistant interspaces in the compressed stack.
This object is achieved by the separation disc defined in claim 1. Hence a separation disc is provided for a centrifugal separator, the separation disc being of metal material and adapted to be compressed in a stack of se-partition discs inside a centrifugal rotor for separating a liquid mixture, the separation disc being of truncated conical shape with an inner surface and an outer surface and a plurality of spacing members extending a certain height above at least one of the inner surface and the outer surface for providing interspaces between mutually adjacent separation discs in the stack. The separation disc is characterized in that at least some of the spacing members are of such small size that each one of the small-sized spacing members has a width which is less than 2 mm along the surface of the separation disc, the surface of the separation disc being configured with a distribution pattern of the small-sized spacing members, in such a way as to provide equidistant interspaces in the compressed disc stack.
If small-sized spacing members in large numbers are introduced on the surfaces of the thin metal separation discs then equidistant spaces may be achieved using even thinner separation discs than today. Hence, the separating capacity of the centrifugal separator can in this way be further increased by fitting a greater number of the thinner metal separation discs into the stack and still maintain equidistant interspaces. The invention will in this way facilitate the use of separation discs as thin as possible to maximize the number of separation discs and interspaces within a given stack height. Furthermore, as previously mentioned, and in particular in large size centrifugal separators, the separation discs can run the risk of touching each other in the compressed state. This is a further reason why there is a minimal height (size) on the interspaces (such as 0.4 mm) in order to secure that the discs are not completely compressed against each other. The invention may hereby also make it possible to reduce this minimal size on the interspaces without risking that adjacent separation discs touch each other. This will also make it possible to provide more separation discs within a given stack height.
The invention makes it possible, due to the small width of the spacing members (i.e. small-sized spacing members), to arrange a distribution pattern in the form of a cluster or concentration of said spacing members in specific surface areas of the separation disc, where the previously mentioned problem of compression arises in the assembled stack of separation discs.
The spacing members may also—as an alternative to the clustered configuration—be configured in an evenly distributed pattern (i.e. the same distance between mutually adjacent small-sized spacing members) throughout the surface of the separation disc, and possibly at a greater concentration compared to “conventional” (large-sized) spacing members.
Finding a suitable distribution pattern may not only depend on the separation disc itself, but also on the design of the centrifugal rotor and the way in which the stack of separation discs is compressed inside the rotor. The deformation of the interspaces in the compressed disc stack may be calculated/simulated in a computer, or by inspecting the actual compressed disc stack. Such inspection could for instance be conducted by making a cast of a compressed disc stack, whereby any suitable casting material is introduced into the compressed disc stack (constituting the mold) inside which the casting material is allowed to solidify. The deformation areas may thereafter be identified, whereby the surface of the separation disc can be configured with (further) small-sized spacing members in the identified areas. Hence, the small-sized spacing members are distributed in a pattern such that equidistant interspaces are obtained in the compressed disc stack.
The small-sized pacing members may be distributed on the surface of the separation disc at a mutual distance in the range of 10-60 mm from each other.
The small-sized spacing members may have a width of 1 mm±0.5 mm, and preferably a width which is less than 1.5 mm, such as a width from 1 mm and smaller. Furthermore, the spacing members are preferably spot-formed, whereby the width of the spot-formed spacing member corresponds to its diameter. The spot-formed spacing members may be of either half-spherical or cylindrical shape as seen in the direction of its height. One advantage of the invention is that due to the smaller size, compared to the “conventional” large-sized spacing member, the spacing members may be provided in greater number without blocking the flow of liquid mixture. Furthermore, a greater number of small-sized spacing members may be arranged without reducing the effective separating area of the separation disc. It would however also be possible to provide small-sized spacing members of a somewhat elongated shape along the surface of the separation disc—even with lengths which are several times greater than said width of the spacing member. Such elongated spacing members must not be clustered too close together or oriented, in such a way that the liquid mixture is obstructed from flowing through the interspaces.
The spacing members may be integrally formed in one piece with the material of the separation disc. Accordingly, they may be formed in the material in accordance with the (previously mentioned) known techniques for manufacturing separation discs with integrally formed spacing members. The spacing members may be integrally formed by means of so called flow-forming, or they may alternatively be provided by means of any suitable press method—such as the press method disclosed in WO 2010/039097 A1. The small-sized spacing members in accordance with the invention provides an advantage in that only a small amount of the material of the separation disc needs to be displaced during this forming process. Hence, the volume of the displaced material in the integrally formed spacing member is very small, whereby the risk of producing an uneven surface (e.g. on the opposite side of the spacing member) is reduced. Furthermore, it's easier to displace a small amount of material, and thereby produce a more reliable form on the spacing members than with large-sized spacing members. For instance, a tool (or mandrel) used in the forming of the small-sized spacing members may be configured with only small-sized recesses (e.g. 1 mm±0.5 mm in width) into which the material of the separation disc is displaced, whereby a large number of exclusively small-sized spacing members is formed on the disc surface in a configuration to achieve the equidistant interspaces.
The separation disc may however further comprise large-sized spacing members of greater width than the small-sized spacing members. These may be in the form of separate pieces of narrow strips or circular blanks of sheet metal, which are attached to the surface of the separation disc. Hence, the separation disc is thereby provided with the integrally formed and small-sized spacing members, as well as large-sized “conventional” spacing members which are attached to the surface (by for instance spot welding). The “conventional” spacing members have a much greater width (e.g. a width of 4 mm or more), and may thereby support a greater portion of the forces in the corn-pressed disc stack. Accordingly, a reduced portion of the compressive forces is supported by the small-sized spacing members, which are distributed in order to secure or maintain an equidistant height on the interspaces between the large-sized spacing members.
The large-sized spacing members may be attached to the outer surface of the separation disc, wherein the integrally formed and small-sized spacing members may be formed in the inner surface of the separation disc. In this way, the large-sized spacing members may easily be attached to the outer surface of the separation disc, whereas the integrally formed and small-sized spacing members may be formed on the inner surface in accordance with the known techniques for manufacturing separation discs described in WO 2007/055630 A1 or U.S. Pat. No. 6,526,794 B1.
The height of the small-sized spacing members is the same as “conventional” large-sized spacing members (e.g. somewhere in the range of 0.3 to 0.8 mm). As previously mentioned, this height will be chosen in order to give a suitable size on the interspaces in view of the properties/composition of the liquid mixture which is intended to be separated.
As previously mentioned, the invention is particularly useful for maintaining equidistant interspaces in a stack of thin separation discs (e.g. separation discs having a thickness which is less than 0.6 mm). In order to maximize the number of separation discs in the stack, the invention would be even more useful in maintaining equidistant interspaces between very thin separation discs (e.g. separation discs having a thickness which is less than 0.4 mm). This is typically also the point where said problems of low disc rigidity and/or irregular shaping becomes an issue.
Hence, the invention makes it possible to use very thin separation discs, while equidistant interspaces are maintained by a great number of small-sized spacing members.
Furthermore, the invention relates to separation discs of metal material, which are compressed in relatively robust and large-sized centrifugal rotors for separating liquid mixtures. Accordingly, the separation discs are also of a relative large size. The separation discs will typically have an outer diameter of at least 200 mm, and in many cases above 400 mm. Hence, the small-sized spacing members are distributed in great number over a relatively large surface area on each separation disc. The invention is not however limited to very large separation discs. It may also be used for smaller separation discs, such as those having an outer diameter of 120 mm or above.
The invention further relates to a method as defined in claim 13. Hence a method is provided for manufacturing the separation disc with the small-sized spacing members formed in one piece with the material of the separation disc. The separation disc is manufactured by flow forming it from a metal sheet by means of a roller and a mandrel, the roller forming the separation disc over the mandrel which comprises a truncated conical support surface with recesses corresponding to the small-sized spacing members, the mandrel having a distribution pattern of said recesses to form the small-sized spacing members in one piece with the separation disc in such a way as to provide equidistant interspaces in the compressed stack of separation discs.
In the method it is also possible to make large-sized spacing members of greater width than the small-sized spacing members which are also flow formed by the roller forming the separation disc over the mandrel comprising recesses corresponding to the large-sized spacing members, whereby both small-sized and large-sized spacing members are integrally formed in one piece with the separation disc.
However, as an alternative to the above, small-sized spacing members may be flow formed on the inner surface of the separation disc, wherein large-sized spacing members in the form of separate pieces of narrow strips or circular blanks of sheet metal are attached to the outer surface of the separation disc. These may easily be attached by spot welding them to the outer surface of the flow formed separation disc. Obviously the separation disc should thereby not be provided with any further (or small-sized) spacing members on the opposite (inner) surface area to the large-sized spacing member, in such a way that a faulty double spacing is caused by directly abutting spacing members of mutually adjacent separation discs in the stack.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which
Furthermore, as can be seen in
It should be noted that the size of the spacing members 4 and 5 are greatly exaggerated in the drawings for the sake of clarity. In practice they would be of much smaller appearance on the separation disc surface and distributed at a much greater number on the surface. A separation disc 1 of the type shown in this embodiment would typically have an outer diameter 6 of much larger size than 200 mm, e.g. in a larger sized centrifugal rotor the separation discs' outer diameter 6 would be even larger than 400 mm. Accordingly, the spacing members 4 and 5 have a very small size (meaning the width of 1 mm along the surface of the separation disc) in relation to the size of the separation disc. Hence, a great number of these small-sized spacing members 4 and 5 are distributed on the inner surface 2 of the separation disc 1 in such a way as to provide equidistant interspaces in the compressed disc stack.
The shown separation disc 1 is further provided with distribution holes 7 for feeding and distributing the liquid mixture into the interspaces in the stack of separation discs. These distribution holes 7 are well known in the art of centrifugal separators and will not be further described here.
A roller 8′ is disposed at an axial level close to the apex end of the support surface 2′ and at a radial distance from the central axis X, the roller 8′ being rotatable about a central axis Y. The roller 8′ is supported by a shaft 10 which is itself supported for rotation by a retainer 11. The retainer 11 is movable vertically and horizontally by means of a motor (not shown), as indicated by two arrows pointing respectively upwards and downwards and two arrows pointing respectively left and right. The motor for moving the roller 8′ vertically and horizontally and guiding the position of the roller 8′ relative to the support surface 2′ may take many different forms which are well known and are therefore not described in more detail. A further second retainer 12 is arranged on the retainer 11. The second retainer 12 supports a tool 13 comprising a cutter 14. The tool 13 is movable as indicated by two arrows pointing respectively left and right relative to the retainer 12 so that the position of the cutter 14 relative to the surface of the metal sheet 6′ can be set in such a way as to achieve a desired cutting depth for the material-removing machining. Such material-removing may not be necessary however if for instance a desired separation disc thickness and smoothness on the outer surface 3 is achieved in the manufacturing process. Hence, the tool 13 and cutter 14 may not be necessary for achieving this.
The separation disc is manufactured by flow forming the metal sheet 6′ by means of the roller 8′ and the mandrel 1′. The roller 8′ forms the separation disc over the mandrel 1′ with the truncated conical support surface 2′ having the recesses 4′ and 5′ of relatively large size. The mandrel 1′ is also provided with small-sized recesses 4″ and 5″ (not shown in
As an alternative, the mandrel may be provided with only small-sized recesses 4″ and 5″ (shown in
Furthermore, small-sized spacing members 4 and 5 may be flow formed on the inner surface 2 of the separation disc 1, wherein large-sized spacing members in the form of said separate pieces may be attached to the outer surface 3 of the separation disc 1 (as previously mentioned).
| Number | Date | Country | Kind |
|---|---|---|---|
| 11177101.0 | Aug 2011 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/065439 | 8/7/2012 | WO | 00 | 2/4/2014 |
