Abstract:
A centrifuge screen clamp comprises a body and a screen retaining portion connected to the body. The screen retaining portion comprises a pressure fitting surface and a clamp interface member engaging surface. In one embodiment, the pressure fitting surface is a substantially planar surface disposable on a screen portion of a centrifuge screen and the clamp interface member engaging surface is disposable on a clamp interface member disposed on the screen. The clamp interface member engaging surface operates to apply a counteractive force against the clamp interface member, which counteractive force is substantially coplanar with an inertial sliding tendency direction of the screen during rotation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to co-pending U.S. patent application Ser. No. 09/978,840, which was filed on Oct. 16, 2001, which claims benefit priority under 35 U.S.C. §119 to provisional patent application No. 60/240,784 filed on Oct. 16, 2000 and are both herein incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This present invention relates to filtering devices and clamps. More particularly, the invention relates to centrifuges which utilize a screen to separate a solid from a liquid and for clamps to secure the centrifuges. 
     2. Description of the Related Art 
     A conventional sugar refining process employs a centrifuge to separate sugar crystals out of raw molasses. The centrifuge includes a spinning drum having a truncated conical basket, which tapers towards its bottom. The walls of the truncated conical basket are lined with a screen material. In a typical sugar refining process, a raw molasses product containing sugar crystals is poured into the center of a centrifuge spinning at a very high rate—e.g. 1750 rpm. As the raw product containing sugar crystals is poured into the center of the centrifuge, inertia pushes the raw molasses through the screen material, through the basket, and out of the centrifuge. However, the sugar crystals are too big to pass through the screen and are left behind. As the raw molasses pass through the screen, the spinning of the centrifuge forces the sugar crystals up the walls of the centrifuge. The sugar crystals work their way up the screen, eventually passing up and over the perimeter of the screen. In this way, sugar crystals are filtered out of liquid raw molasses product and are collected as they pass over the lip of the spinning screen. 
     To separate sugar crystals from raw product, the screen employed must be very fine. That is, the openings in the screen must be very small to prevent the sugar crystals from passing through the screen along with the liquid, raw molasses. Conventional sugar processing screens have been formed by “etching” a very thin metal plate. A metal plate may be etched with openings sized small enough to separate sugar crystals from liquid molasses. For example, a metal plate may be etched with a laser to form very small slits in the plate. The plate is then formed into a conical shape which fits within the walls of a centrifuge basket. 
     The greater the number of slits cut into a conventional sugar processing screen, the greater the “open area” of the screen. A large number of slits, spaced closely together, produces a relatively large “open area” in the screen, which increases the screen&#39;s production. However, the slits in a typical sugar processing screen weaken the overall screen and subject it to fatigue. Additionally, sugar crystals may lodge in the slits of a conventional sugar processing screen, thereby reducing its performance. A sugar processing device having a screen which is durable and has a fine opening, high open area would be welcomed by those in the sugar processing industry. Additionally, other industries that utilize such processes as coal dewatering and driller mud dewatering, etc. would welcome a fine opening, high open area centrifuge screen. 
     Typically, the conventional sugar processing screen is secured in the truncated conical basket by a clamping ring. A conventional centrifuge  200  is shown in FIG.  12 . In particular, FIG. 12 shows a partial cross sectional perspective view of a sugar processing screen  202 , a conical basket  204  and a clamping ring  206 . The clamping ring  206  is constructed to clamp a lower portion  208  of the conventional sugar processing screen  202  to the truncated conical basket  200  while an upper portion  210  of the conventional sugar processing screen may move freely. In this arrangement, the frictional force created by the clamping ring holds the conventional sugar processing screen in place in the centrifuge. However, a problem associated with the sugar refining process occurs while the centrifuge is spinning at a very high rate of speed. Specifically, the forces created by the centrifuge overcome the clamping force of the clamping ring. At this point, the conventional sugar processing screen begins to slide out of the clamping ring and subsequently flings out of the truncated conical basket, which may cause damage to the equipment or injury to nearby personnel. 
     There is a need, therefore, for an improved clamping ring arrangement that will secure a screen in conical basket. There is a further need for a clamping ring arrangement that will prevent the screen from falling out while the centrifuge is spinning at a very high rate of speed. There is yet a further need for a more reliable centrifuge screen. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a centrifuge screen clamp is provided. 
     One embodiment provides a centrifuge screen clamp. The clamp comprises a body adapted to be secured to a centrifuge and a screen retaining portion connected to the body. The screen retaining portion comprises a pressure-generating-centrifuge-screen engaging surface adapted to engage a centrifuge screen and apply a force thereto to create a pressure fit; and an interface member engaging surface adapted to engage a corresponding interface portion disposed on the centrifuge screen and create an interference fit therewith, whereby the clamp interface member engaging surface and the clamp engaging surface create equal and opposite forces coplanar with a sliding tendency direction of the screen during rotation. 
     Another embodiment provides a centrifugal refining device. The centrifugal refining device comprises a rotatable support basket, a screen disposed in the basket for filtering a liquid during rotation of the drum, a clamp interface member rigidly disposed on the screen and defining a clamp engaging surface, and a clamp to secure the screen with respect to the rotatable support basket. The clamp comprises a body and a screen retaining portion connected to the body. The screen retaining portion comprises a pressure-generating-centrifuge-screen engaging surface disposed against the screen and applying a force thereto to create a pressure fit; and a clamp interface member engaging surface disposed against the clamp engaging surface to create an interference fit therewith, whereby the clamp interface member engaging surface and the clamp engaging surface create equal and opposite forces coplanar with a sliding tendency direction of the screen during rotation. 
     Yet another embodiment provides a centrifugal sugar refining device. The centrifugal sugar refining device comprises a rotatable drum defining an interior space, a rotatable support basket disposed at least partially in the interior space, a screen disposed in the basket for filtering sugar crystals from molasses during rotation of the drum, a clamp interface member rigidly disposed on the screen and defining a clamp engaging surface and a clamp to secure the screen with respect to the rotatable support basket. The clamp comprises a body and a screen retaining portion connected to the body. The screen retaining portion comprises a pressure-generating-centrifuge-screen engaging surface disposed against the screen and applying a force thereto to create a pressure fit; and a clamp interface member engaging surface disposed against the clamp engaging surface to create an interference fit therewith, whereby the clamp interface member engaging surface and the clamp engaging surface create equal and opposite forces coplanar with a sliding tendency direction of the screen during rotation. 
     In one embodiment, a clamp of the present invention secures a screen comprising a series of fine filter wires spaced closely together and mounted generally perpendicularly to a series of underlying support rods. In particular embodiments, the filter wires have a V-shaped profile with a width of approximately 0.020 inches. The mating points of the support rods also have a V-shaped profile with a width of approximately 0.060 inches. The filter wires are spaced approximately 0.0035 inches apart and the support rods are spaced approximately 0.38 inches apart. However, it will be understood by one of ordinary skill in the art that different dimensions may be used to create a fine opening, high open area centrifuge screen used, for example, to separate crystalline sugar from liquid raw molasses. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description particularly refers to the accompanying figures in which: 
     FIG. 1 is a perspective view of a centrifuge screen in accordance with the present invention within a sugar processing device having a centrifuge drum; 
     FIG. 2 is a top view of the screen of FIG. 1; 
     FIG. 3 is a plan view of one segment of the screen of FIG. 1; 
     FIG. 4 is a side view of the screen of FIG. 1; 
     FIG. 5 is a perspective, detailed view of a section of the screen of FIG. 1, with portions broken away; 
     FIG. 6 is a perspective view of the section of screen of FIG. 5, including pieces of rubber being positioned between support rods of the section; 
     FIG. 7 is a side view of the pieces of rubber being positioned between the support rods of FIG. 6; 
     FIG. 8 is a side view of the pieces of rubber positioned between the support rods of FIG. 6; 
     FIGS. 9A-B are partial cross sectional views of a centrifuge with a clamp according to one embodiment of the invention; 
     FIG. 10 is a partial cross sectional view of a centrifuge with a clamp according to another embodiment of the invention; 
     FIG. 11 is a partial cross sectional exploded view of clamp and interface member of FIG. 10; and 
     FIG. 12 is a partial cross sectional view of a centrifuge with a clamp according to the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIG. 1, a fine opening, high open area screen  10  in accordance with the present invention is shown in a sugar processing or refining device  100 . The screen  10  is generally conical and has an upper rim  12 , a lower rim  14 , and a sidewall  16  extending from the upper rim  12  to the lower rim  14 . The sidewall  16  has an inner surface  18  and an outer surface  20 , best seen in FIG.  4 . Referring back to FIG. 1, the conical shape of the screen  10  dictates that the sidewall  16  taper from the upper rim  12  to the lower rim  14 , with the circumference of the upper rim  12  being approximately two and a half times the circumference of the lower rim  14 . 
     The screen  10  is nested within a centrifuge drum  22  of the sugar processing device  100 . The drum  22  includes a perforated, conical basket  26  (hidden from view in FIG. 1, shown in FIG. 8, as will be discussed below) underlying and supporting the conical screen  10 . During sugar processing, liquid, raw molasses containing sugar crystals (not shown) are poured into the center of the centrifuge drum  22 . The molasses are poured into the centrifuge drum  22  while it is spinning rapidly. In this way, the raw molasses are forced outward against the inner surface  18  of the sidewall  16  of the screen  10 . The molasses are first forced against the sidewall  16  near the lower rim  14  of the screen  10 . However, because the inner surface  18  is slanted from the lower rim  14  to the upper rim  12 , the molasses “crawl” their way up the inner surface  18  as they are forced outward and through the screen  10 . As the centrifuge drum  22  spins, the liquid raw molasses are forced through the screen  10 , leaving sugar crystals behind. Because not all of the liquid, raw molasses can flow through the screen instantaneously, some of the molasses crawl up the inner surface  18  of the screen  10  before being forced through the screen  10 . The greater the open area of the screen  10 , the quicker the molasses flow through the screen  10  and the less they crawl up the inner surface  18 . In any case, at some point between the lower rim  14  and the upper rim  12 , the liquid raw molasses will have been filtered entirely through the screen  10 , leaving only crystalline sugar on the inner surface  18  of the screen  10 . The spinning of the centrifuge drum  22  causes the sugar crystals to continue to ride up the inner surface  18 . While the liquid molasses can flow through the screen  10 , the sugar crystals are too large to pass through. When the sugar crystals reach the upper rim  12 , they are ejected out of the drum  22  and are collected around the perimeter of the drum  22 . 
     As mentioned above, the screen  10  allows a liquid, for example raw molasses, to pass though it, while filtering out fine particulate matter, for example crystalline sugar suspended in the molasses. As best seen in FIG. 5, the screen  10  is constructed of filter wires  28  in close, generally parallel relation to one another mounted on support rods  30 . The filter wires  28  and support rods  30  are each a V-shaped profile wire, connoting that they each have a generally triangular-shaped cross-section. The filter wires  28  are mounted generally perpendicular to the support rods  30 . Each filter wire  28  includes a face surface  32  and two side surfaces  34  which converge to a point  36 . The filter wires  28  are aligned, side-by-side, with their face surfaces  32  lying in a plane  38 , which, as will be further discussed below, creates the inner surface  18  of the screen  10 . 
     The screen  10  is constructed by inserting a number of support rods  30  into a series of notches equally spaced around the circumference of a specially designed wheel (not shown). In the case of the V-shaped profile rods  30 , the notches in the wheel would also be generally triangular in shape. In this way, the support rods are secured around the wheel and extend substantially perpendicularly to the wheel to create a cylinder of support rods  30 . The wheel, and thus the cylinder of rods  30 , is then rotated and a filter wire  28  is continuously and spirally wrapped around the rotating cylinder of rods  30 . At each point where the filter wire  28  intersects a rod  30 , an electrical charge is conducted through the intersection and the wheel, thereby welding the filter wire  28  to the rod  30 . The result is a screen cylinder formed with longitudinally extending rods  30  spirally-wrapped in a filter wire  28 . To create flat sheets of the screen material  10 , the resulting cylinder is cut between two support rods  30 , along the length of the cylinder. In this way, the spirally-wrapped filter wire  28  is cut at each revolution around the cylinder. The cylinder is then flattened, resulting in a sheet of screen  10 , a portion of which is shown in FIG.  5 . 
     As shown in FIG. 5, in the resulting screen  10 , the filter wires  28  are welded generally perpendicularly across the support rods  30  to create a filtering lattice material. In the illustrated embodiment, the face surfaces  32  of the filter wires  28  are 0.020 inches wide and are positioned 0.0035 inches apart from each other to create a filtering gap  42  between consecutive face surfaces  32 . However, it will be readily understood by one of ordinary skill in the art that other dimensions may be employed which produce the desired sugar filtering results. The position of the filter wires  28  in relation to the support rods  30  in the complete screen  10  can be seen with reference to FIG. 4, wherein a left screen portion  54  includes the support rods  30  along with the filter wires  28 , while a right screen portion  56  illustrates only the filter wires  28 . As seen in FIG. 4, the support rods  30  are positioned generally perpendicular to the filter wires  28 . 
     Referring again to FIG. 5, a filter channel  44  is created between opposing side surfaces  34  of consecutive filter wires  28 . Because of the triangular shaped cross-section of the filter wires  28 , the filter channels  44  between consecutive filter wires  28  open away from the plane  38  defined by the face surfaces  32  of the filter wires  28 . Put another way, the filter channels  44  do not have parallel walls, but instead flare from the face surfaces  32  to the points  36  of the filter wires  28 . 
     As shown in FIGS. 1-4, the screen  10  is constructed of three arcuate-shaped segments  46 . The arcuate-shaped segments  46  are cut out of larger, flat sections of the filtering lattice material constructed as described above. As shown in FIG. 3, in this way, the filtering wires  28  run parallel to each other and toward the upper rim  12  of the segment  46  of screen  10 . It will be readily apparent to one of ordinary skill in the art that, while the filter wires  28  extend generally radially in the screen  10 , they do not extend truly radially from the lower rim  14  to the upper rim  12  of the screen  10 . Truly radially aligned wires would diverge as they extended away from the lower rim  14  of the screen  10 . In contrast, the filter wires  28  of the screen  10  of the present invention remain generally parallel, producing filtering gaps  42  of uniform width. 
     After being cut out of larger portions of the filtering lattice material, the arcuate-shaped screen segments  46  are rolled to match the curvature of the centrifuge basket. Then, the edges  48  of the three segments  46  are joined at screen joints  50  to form the truncated conical shape of the screen  10 , as best seen in FIG.  4 . The joints  50  are formed by welding the ends of the support rods  30  of one segment  46  to the ends of the support rods  30  of the adjacent segment  46 . However, additional arrangements for coupling adjacent segments  46  may be used. For example, a rectangular bar joint (not shown) may be welded down the joint  50  between two consecutive segments  46 . Alternatively, a T-bar (also not shown) may be used to hold down the edges  48  of consecutive segments  46 . The vertical member of the T-bar may be coupled to the basket which holds the screen  10 . The horizontal member of the T-bar would then hold down and guide the edges  48  of the segments  46  and protect the unsupported ends of the filter wires  28 . The T-bar may act as a clamping mechanism to hold the screen  10  against the basket. An angle-shaped joint (not shown), oriented as an inverted “L,” may also be used to form joints  50 . Each screen segment  46  may have one edge  48  welded to the vertical segment of a piece of angle iron. In this way, the horizontal segment of the angle iron overlaps, holds, and protects the edge  48  of the adjacent screen segment  46 . 
     Referring to FIG. 1, a collar (also referred to herein as a “clamping member”, or simply “clamp”)  49  is used to secure the screen  10  within the drum  22 . The lower rim  14  of the screen  10  is clamped between the collar  49  and the conical basket  26 , shown in FIG.  8 . As shown in FIGS. 6-8, to increase friction between the screen  10  and the basket  26 , pieces of rubber  51  may be applied between the support rods  30  in those locations directly beneath the collar  49 . It will be readily understood by those of ordinary skill in the art that any material that is compressible and has a high coefficient of friction may be used instead of rubber. The pieces of rubber  51  may include adhesive on one or more sides to hold them in place. Referring to FIG. 7, the uncompressed thickness X of the rubber  51  is slightly greater than the exposed height Y of the support rods  30  to ensure that the rubber  51  is in compression when the collar  49  clamps the screen  10  to the basket  26  (FIG.  8 ). Embodiments of the collar  49  will be described below. 
     With the screen  10  formed and shaped as discussed above, at a center  52  of each screen segment  46 , the filter wires  28  are generally aligned with the flow of product as it crawls up the inner surface  18  created by the face surfaces  32  of the filter wires  28 , and the support rods  30  run generally transverse to the flow. At the joints  50  between the segments  46 , the filter wires  28  are less aligned with the flow path of the product because of the way in which the screen segments  46  are cut out of flat sections of the lattice material and roll formed, as described above (See FIG.  4 ). As liquid product is forced against the screen  10  in the spinning centrifuge drum  22 , the liquid, raw molasses flow past filtering gaps  42  and through filtering channels  44 . From there, the liquid, raw molasses flow through an annular space created by the support rods  30  between the filter wires  28  and the perforated basket  26  that holds the screen  10 . The liquid molasses then continue through the perforations in the perforated basket and out of the sugar refining device  100 . 
     The sugar crystals work their way up the inner surface  18  created by the face surfaces  32  of the filter wires  28 . Because of their size, the sugar crystals cannot pass through the filtering gaps  42  between the filter wires  28 . Instead, the sugar crystals pass up the inner surface  18  of the screen  10  and are ejected over the upper rim  12  of the screen  10 , where they are collected. 
     As will be readily apparent to those of ordinary skill In the art, the present invention as described above and illustrated in FIGS. 1-8 may be used in a number of applications in which a fine opening, high open area centrifuge screen is used to separate a solid from a liquid, such as, but not limited to, sugar processing, coal dewatering, driller mud dewatering, etc. 
     FIGS. 9A-B (collectively referred to as FIG. 9) are partial cross-sectional perspective views of the refining device  100  of FIG. 1 illustrating one embodiment in accordance with the present invention. Accordingly, FIG. 9A generally shows the conical basket  26 , the screen  10 , a clamping member  49  and a clamp interface member  60 . In part, the screen  10  may be held in place by the friction created between the basket  26  and the clamping member  49 . To this end, a friction member may be disposed between the screen  10  and the comical basket  26 , such as the rubber  51  described above. The screen  10  is further secured by the cooperation of the clamping member  49  and the clamp interface member  60 . Embodiments of the clamping member  49  and the clamp interface member  60  will now be described in detail. 
     In the embodiment of FIG. 9, the clamp interface member  60  is a generally annular member connected to the lower rim  14  of the screen  10  and adapted to engage with a portion of the clamping member  49 . In one embodiment, the clamp interface member  60  is welded to an inner portion of the lower rim  14 . However, other connection means may be employed, so long as, the connection means is able to secure the clamp interface member  60  on the lower rim  14 . In another embodiment, the clamp interface member  60  may be an integral portion of the screen  10  itself. For example, a portion of the lower rim  14  may be bent upward to form the clamp interface member  60 . 
     In the embodiment of FIG. 9, the clamping member  49  is an annular member generally comprising a body  62  and a screen restraining portion  47 . A lower end of the body  62  may be secured to the refining device  100  according to any variety of techniques, including those well-known in the art. By way of example, the clamping member  49  is secured to the refining device  100  by fasteners  80  (e.g., bolts) disposed through a flange  82  of the clamping member  49 . Illustratively, the screen restraining portion  47  is a hook-shaped member defining a screen engaging surface  64  and a clamp interface member engaging surface  66 . The screen engaging surface  64  is shown in mating abutment with the lower rim  14  of the screen  10 , whereby a downward pressure is exerted by the screen engaging surface  64  on the lower rim  14 . In this manner, the inertia of the spinning screen  10  in operation produces a counteracting friction force to resist any sliding (slippage) of the screen  10 . However, because the direction of the slippage is generally parallel to the planar screen engaging surface  64 , once the frictional force is overcome, the screen  10  may slide out from between the clamping member  49  and the basket  26  without the provision of further restrictions. In the present invention, any sliding tendency of the screen  10  is further inhibited by the clamp interface member engaging surface  66 , which creates an interference fit with the clamp interface member  60 . In particular, the clamp interface member engaging surface  66  is shown in mating abutment with an upper clamp engaging surface  68  of the clamp interface member  60 , as best shown in FIG.  9 B. The resulting equal and opposite forces produced by the surfaces  66 ,  68  are shown as F 1  and F 2 , respectively. In the illustrative embodiment, the forces are substantially normal to the planar surfaces  66 ,  68 . However, the embodiment of FIG. 9 is merely illustrative and other embodiments are contemplated in which opposing forces between the clamping member  49  and the clamping interface member  60  are generated in response to any sliding tendency of the screen  10 . 
     For example, illustrative alternative embodiments of the clamping member  49  and the clamping interface member  60  are shown in FIGS. 10 and 11. FIG. 10 shows a partial cross-sectional perspective view of the refining device  100  and FIG. 11 shows a partial exploded cross-sectional view of the refining device  100 . For convenience, like numerals identify the same or substantially similar components described above. In this embodiment, the clamping member  49 , and in particular the screen retaining portion  47 , has a stepped profile. The stepped profile is defined by an annular shoulder  70  which defines the clamp interface member engaging surface  66 . The annular shoulder  70  is sized to be received in a notch  72  formed in the interface member  60 . The notch  72  is, in part, defined by a ledge  74  on which the surface  66  rests. In operation, the ledge  74  is urged against the surface  66  of the shoulder  70  as a result of the inertia of the screen  10 . Because the shoulder surface  66  is oriented to prevent the clamp interface member  60  from sliding over the ledge  74 , the shoulder  70  and the clamp interface member  60  achieve a cooperative hooking action to prevent movement of the screen  10 . 
     In addition to the hooking action achieved by the shoulder  70  of the clamping member  49  and the clamp Interface member  60 , the clamping member  49  creates a frictional force by applying a pressure downward on the screen  10 . The pressure is applied, at least in part, by a lip portion  78  of the screen restraining portion clamping member  49 . The lip portion  78  extends from the body of the clamping member  49  and is positioned over the screen  10 . The clamp interface member surface  64  formed on the lip portion  78  is placed in mating abutment with the lower rim  14  of the screen  10  ( shown in FIG.  10 ). When the clamping member  49  is secured to the refining device  100  (e.g., in a conventional manner), a pressure is exerted by the lip on the screen  10 , thereby “sandwiching” the screen  10  between the clamping member  49  and the basket  26  (as shown in FIG.  10 ). 
     It should be understood that while various surfaces disclosed herein are described as being in mating abutment, direct physical contact between the surfaces (e.g., surfaces  66  and  74 ) Is not necessary. For example, intermediary materials or films may be disposed between the surfaces for various purposes (e.g., to minimize wear of parts). Alternatively, such intermediary materials may themselves be understood as defining the various surfaces disclosed herein, in which case direct physical contact between the surfaces exists. 
     In the foregoing embodiments, the clamping member  49  and the clamp interface member  60  are described in shown as annular members. However, persons skilled in the art will recognize that a variety of geometries and configurations are possible. For example, either or both the clamping member  49  and the clamp interface member  60  need not be singular monolithic components. Instead it is contemplated that individual discrete members may collectively make up the clamping member  49  and/or the clamp interface member  60 . For example, the screen restraining portion  47  of the clamping member may comprise a plurality of fingers each engaging the clamp interface member  60 . Such embodiments may be desirable, for example, where it is advantageous to minimize weight. 
     To ensure sufficient strength, the clamping member  49  and the clamp interface member  60  may be made of metal. For example, in one embodiment the clamping member  49  may be made of stainless steel 303 or 304 and the clamp interface member  60  may be made of stainless steel 316L. However, the foregoing materials are merely illustrative and persons skilled in the art may recognize other suitable materials. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.