Centrifugal separator

Abstract

 A centrifugal filter separator (1) includes a detachable tubular screen (44) disposed between an annu­lar filter (40) and the inner peripheral surface of a basket (21), the screen (44) having an annular flange (45) detachably connected to an open end of the basket (21) from the outside of the basket (21). The centrifu­gal separator (1) having such detachable screen (44) is applicable to centrifugal separation of various materials.

Description

[0001] The present invention relates to centrifugal sepa­rators for separating a solids-and-liquid mixture into solids and a liquid by means of centrifugal force, and more particularly to such a centrifugal separator which is equipped with a filter on which solid components remain after removal of liquid components.

[0002] An example of such centrifugal filter-type separa­tor is disclosed in U.S. Patent No. 4,193,874. The disclosed centrifugal separator, as shown here in Figure 7 of the accompanying drawings, includes a drive unit A, a filtration unit 8 and a cake-discharge unit C. The drive unit A includes an outer shaft D drivable by a motor (not shown) and rotatably supported by a bearing E, and an inner shaft F fixedly secured by a key, for example, to the outer shaft D for corotation therewith. The filtration unit 8 includes a basket G secured to the outer shaft D, and a rotor H disposed inside the basket G and secured to the inner shaft F so that the basket G and the rotor H are rotatable concurrently with each other. The basket G has formed in its peripheral wall a number of perforations or pores G′ for removing liquid components. The thus removed liquid components are col­lected at and then discharged from a discharge hole J in a casing I which contains the filtration unit B. The rotor H is slidably movable in a direction parallel to the axis of the basket G and includes a closure means for closing an open end of the basket G when the rotor H is received in the basket G. Extending between the bas­ket G and the rotor H is a tubular or hollow cylindrical filter K formed of a woven fabric or the like. The fil­ter K is overturned in response to the sliding movement of the rotor H in such a manner that the filter K is received in the basket G during filtration and when a cake is discharged, the filter K is forced into the cake-discharge unit C while being turned inside out. The filter K is rotatable together with the basket G and the rotor H. The basket G is provided with a screen L of a corrugated cross section fixedly secured to an inner peripheral surface of the basket G for providing passageways for liquid components and also for preventing the filter K from being withdrawn into the discharge hole G′.

[0003] In operation, the rotor H is received in the bas­ket G, then while keeping this condition, a solids-and-­liquid mixture to be separated is supplied into the filtration unit 8 through a feed pipe M which is dis­ posed along the common axis of the rotor H and the bas­ket G. The drive unit A is driven to rotate the basket G, the screen L, the filter K and the rotor H concurrently at high speeds, thereby removing liquid components from solid components by means of centrifugal force and subsequent filtration. In this instance, the liquid components are forced to flow successively through the filter K, the screen L and the pores G′ in the basket G into the dis­charge hole J of the casing I. The solid components (cake) remain on the filter K located inside the basket G. After removal of the liquid components, the rotor H is displaced from within the basket G to the cake-­discharge unit C during which time the filter K is inverted, thereby removing the solid components from the filter K. The thus removed solid components are then discharged from a cake-discharge hole N.

[0004] The conventional centrifugal separator described above is however not fully satisfactory in that the firm attachment of the screen L to the basket G inhibits a free access to a space between the screen L and the bas­ket G which is required for cleaning the space.

[0005] A further problem is that an improved effect to prevent withdrawal of the filter K into the screen L can only be attained by a double-layered screen L which is, however,complicated in construction.

[0006] With the foregoing difficulties in view, the pre­sent invention seeks to provide a centrifugal separator incorporating structural features which enable cleaning of the inside of a basket with utmost ease.

[0007] The present invention further seeks to provide a centrifugal separator, including a screen, which is simple in construction and detachable from the basket.

[0008] According to the present invention, there is pro­vided a centrifugal separator comprising: a rotatable centrifugal drum including a perforated basket having an open end, and a rotor slidably received within the basket and normally closing the open end of the basket, the rotor being rotatable in unison with the basket and reciprocally movable in a direction parallel to the axis of rotation of the drum into and out of the drum through the open end of the latter; a flexible annular filter extending between the basket and the rotor and adapted to be inverted in response to the reciprocating move­ment of the rotor; a water permeable tubular screen dis­posed between the filter and an inner peripheral surface of the basket and having an annular flange at one end thereof detachably connected to the open end of the basket; and spacer means disposed upon at least one of the screen and the basket for holding them in radially spaced relation to one another.

Figure 1 is a perspective view of a centrifugal separator according to the present invention;

Figure 2 is a longitudinal cross-sectional view of a processing head of the centrifugal separator;

Figure 3 is an exploded perspective view of a cen­trifugal drum of the processing head;

Figure 4 is longitudinal cross-sectional view of a portion of the centrifugal drum;

Figure 5(a) is a view illustrative of a screen and a filter according to another embodiment;

Figure 5(b) is a view similar to Figure 5(a), but showing a screen and a filter according to still another embodiment;

Figure 6 is a transverse cross-sectional view of a portion of the centrifugal drum; and

Figure 7 is a diagrammatical view showing a conventional centrifugal separator.

[0009] Certain preferred embodiments of the present invention will be described hereinbelow in greater detail with reference to the accompanying drawings.

[0010] Figure 1 shows a centrifugal separator 1 embodying the present invention. The centrifugal separator 1 includes a substantially rectangular frame 2 supporting thereon a processing head 3 for achieving a centrifugal separation, a drive shaft unit 4 for driving the proc­essing head 3, and a hydraulic power unit 5 for supply­ing a power to the processing head 3 and the drive shaft unit 4.

[0011] The processing head 3 includes a casing 10 constituting an outer shell of the processing head 3. The casing 10 has a tubular shape and is mounted at its one end to a head bracket 11 secured to an upper horizontal base of the frame 2. The other end or the front end of the tubular casing 10 is closed. A feed pipe 14 is connected to a central portion of the forward end of the casing 10 and extends into the casing 10 along the longitudinal axis of the tubular casing 10 for supplying therethrough a material to be subjected to centrifugal separation. The casing 10 is carried on a set of four wheels 16, 16 (two being shown) disposed in pairs at a lower portion of the casing 10. The wheels 16 are rollingly movable along a pair of parallel spaced rails of a horizontal sub-frame 15 projecting forwardly from an end of the frame 2 so that the casing 10 is mov­able toward and away from the head bracket 11, thus ena­bling inspection of the inside of the processing head 3. The sub-frame 15 is angularly movable in a horizontal plane while carrying thereon the casing 10 because one of the rails is pivoted by a hinge 17 to an end of the frame 2. The sub-frame 15 is normally held in contact with the frame 2 by means of a clamp 18 disposed on the frame 2 and lockingly engageable with the other rail of the sub-frame 15. The casing 10 houses a centrifugal drum 20 in which a centrifugal separation is achieved.

[0012] The centrifugal drum 20 generally comprises a bas­ket 21 and a rotor 22 disposed inside the basket 21 and rotatable in unison with the basket 21, the rotor 22 being slidably movable into and out of the basket 21. The basket 21, as shown in Figures 2 and 3, includes a boss 25 firmly fitted to one end of an outer shaft 24, an annular flange-like end plate 26 extending integrally and radially outwardly from the boss 25, and a tubular peripheral portion 27 connected at its one end to an outer peripheral portion of the end plate 26. The bas­ket 21 thus constructed is generally cup-shaped having an open end remote from the end plate 26. The tubular peripheral portion 27 has a number of perforations 28 (Figure 3) through which liquid components P2 of the material P are discharged from the basket 21. The rotor 22 is rotatable within the basket 21 and movable between a first position in which the rotor 22 is fully received in the basket 21, and a second position in which the rotor 22 is disposed outside the basket 21. The rotor 22 includes a boss 31 firmly fitted to one end of an inner shaft 30 extending concentrically through the outer shaft 24, an annular end plate 32 formed integrally with the boss 31 and extending radially out­wardly therefrom, an apertured tubular peripheral connector member 33 formed integral with the end plate 32 and extending perpendicularly from an outer periph­eral portion of the end plate 32, and an annular cover plate 34 extending parallel to the end plate 32 to close a front end of the tubular connector member 33. The cover plate 34 in constructed in such a manner as to substantially close the open end of the basket 21 when the rotor 22 is disposed in its first position in which it is fully disposed within the basket 21 as indicated by solid lines in Figure 2. The cover plate 34 has a central hole 35 for the passage therethrough of the feed pipe 14. The tubular connector member 33 has a number of elongate apertures or slots (not designated) circumferentially spaced at equal intervals.

[0013] The inner shaft 30 has in its central longitudinal portion an elongate keyway 37, while the outer shaft 24 has a key 36 slidably received in the keyway 27. With this interlocking engagement between the key 36 and the keyway 37, the inner shaft 30 is rotatable in unison with the outer shaft 24 and also slidable relative to the outer shaft 24.

[0014] The centrifugal drum 20 further includes a filter 40 of a woven fabric disposed between the basket 21 and the rotor 22 for filtrating liquid components P2 while blocking passage therethrough of solid components P1 of the material P. The filter 40 is secured at its oppo­site peripheral edges to the end plate 32 of the rotor 22 and to the open end of the basket 21. As shown in Figure 4, the open end of the basket 21 has a circular groove 41A for receiving therein a first peripheral edge of the filter 40. A presser ring plate 42A is secured by a plurality of screws 46 (only one shown) to the open end to firmly grip or hold the first peripheral edge of the filter 40 on the open end of the basket 21. Likewise, the end plate 32 of the rotor 22 has a circular groove 41B for receiving therein the second peripheral edge of the fil­ter 40. A presser ring plate 42B is secured by a plu­rality of screws (not designated and only one shown) to the end plate 32 to firmly hold said second peripheral edge of the filter 40 on the end plate 32 of the rotor 21.

[0015] According to an important feature of the present invention, there is provided a tubular screen 44 dis­posed between an inner peripheral surface of the basket 21 and the filter 40, the screen 44 having a water perm­eable structure.

[0016] As shown in Figures 3 and 4, the water permeable tubular screen 44 has a shape complementary in contour to the inner peripheral surface of the basket 21. The tubular screen 44 includes an end flange 45 secured to the open end of the basket 21. In this embodiment, the end flange 45 is disposed between the presser ring plate 42A and an annular flange 27A of the tubular peripheral portion 27 of the basket 21 and fastened to them by means of the screws 46. The circular groove 41A in the open end of the basket 21 is formed in one end face of the flange 45 of the screen 44 facing the ring plate 41A. The screen 44 has a number of openings 47 for the passage therethrough of the liquid components of the material to be separated. The opening 47 comprises three rows of axial slits circumferentially spaced at equal intervals. The slits 47 may be replaced with a number of circular holes of a small diameter. Alternatively, the slits may extend circumferentially along the peripheral wall of the screen 44 in either straight or zigzag formation. Yet, the screen 44 may be formed of a perforated plate bent into a tubular form.

[0017] The screen 44 is radially inwardly spaced apart from the basket 21 by a spacer means 49. The spacer means comprises a plurality of parallel spaced ribs 49 projecting from the inner peripheral wall of the basket 21. In the illustrated example, the ribs 49 extend circumferentially of the basket 21 but they may be arranged to extend parallel to the longitudinal axis of the basket 21. As an alternative, the ribs 49 may extend spirally along the inner peripheral wall of the basket 21. The ribs 49 may be continuous or interrupted into a series of rib segments. Yet, the ribs 49 may be provided on the screen 44 or on both of the basket 21 and the screen 44 provided that the ribs 49 do not hinder smooth fitting of the screen 44 into the basket 21.

[0018] As shown in Figure 5(a), there may be provided a further spacer means 51 disposed between the screen 44 and the filter 40 for holding the filter 40 out of con­tact with the screen 44 to thereby provide a space therebetween, which space serves to promote filtration of the liquid components. The spacer means comprises a mesh or net 51 of woven wires disposed on the inner peripheral surface of the screen 44. The wire mesh 51 may be replaced by a flexible fiber net 52 abutted to one surface of the filter 40 facing the screen 44, as shown in Figure 5(b).

[0019] A description will be given to a drive system of the centrifugal separator 1 with reference to Figures 1 and 2. the drive system includes a driven pulley 54 (Figure 2) secured to an intermediate portion of the outer shaft 24 and driven by an endless belt 57 trained around the driven pulley 54 and a drive pulley 56. The drive pulley 56 is secured to the drive shaft of a hydraulic motor 55. When the hydraulic motor 55 is driven to rotate the drive pulley 56, the outer shaft 24 and the inner shaft 30 keyed thereto are rotated concurrently. The inner shaft 30 is connected to a shift cylinder 59 (Figure 1) at one end thereof remote from the rotor 22. In response to operation of the shift cylinder 59, the inner shaft 30 is longitudinally reciprocated along the outer shaft 24 to thereby move the rotor 22 into and out of the basket 21. The shift cylinder 59 and the hydraulic motor 55 are connected with the hydraulic power unit 5 to receive therefrom a pressurized working oil. The hydraulic power unit 5 includes a hydraulic pump 60 driven by an electric motor M. The operation of the shift cylinder 59 is controlled by a shiftlever 61. In the centrifugal separator 1, various machine elements such as bearings, oil seals, etc. are disposed between rotatable component parts. These elements are conventional and do not constitute an essential part of the invention and hence will require no further description.

[0020] The centrifugal separator 1 of the foregoing con­struction operates as follows. The operation of the separator 1 begins with the rotor 22 disposed in its first position in which the rotor 22 is fully received in the basket 21. In this instance, the filter 40 is held taut between the open end 27A of the basket 21 and the end plate 32 of the rotor 22 and hence extends par­allel to the screen 44. After a predetermined amount of material (a solids-and-liquid mixture) P is supplied through the feed pipe 14 into the centrifugal drum 20, the hydraulic motor 55 is driven to rotate the outer shaft 24, thereby revolving the basket 21 and the rotor 22 in unison with each other at high speeds. The solids-and-liquid mixture P held in the rotor 22 is sub­jected to centrifugal force whereby liquid components P2 of the mixture P are removed through the filter 40 to the outside of the rotor 22. The thus removed liquid components P2 are then forced to flow radially outwardly successively through the screen 44 and the perforations 28 in the basket 21 to the outside of the centrifugal drum 20 from which the liquid components P2 are discharged from a liquid-components discharge hole 13 defined in the casing 10 below the centrifugal drum 20. Conversely, solid components P1 of the mixture P remain on the inner peripheral surface of the filter 40. A centrifugal separation of the solid and liquid compo­nents P1, P2 is thus achieved. Thereafter, the shift cylinder 59 is actuated to extend its piston rod, thereby moving the rotor 22 forwardly from the first position to the second position in which the rotor 22 is disposed outside of the basket 21 as indicated by phantom lines in Figure 2. With this movement of the rotor 22, the filter 40 is turned inside out so that the solid components P1 carried on the inner peripheral surface of the filter 40 is removed from the filter 40 and then discharged from a solid-component discharge hole 12 defined in the casing 10. When the rotor 22 is disposed in the phantom-lined second position, a dis­charge end portion of the feed pipe 14 is received in a central axial hole in the inner shaft 30.

[0021] When an inspection of the inside parts of the cen­trifugal drum 20, such as the filter 40 for example, is desired, the screws 46 are removed to detach the presser ring plate 42A from the open end of the basket 20, thereby releasing one end of the filter 40. Then, the presser ring plate 42B is detached from the end plate 32 of the rotor 20 in the same manner as done with the presser ring plate 42A, thereby releasing the other end of the filter 40. The filter 40 is thus removed from the cen­trifugal drum 20. With the detachment of the ring plate 42A, the flange 45 of the screen 44 is also released from locking engagement with the open end of the basket 20. Consequently, the screen 44 can be removed from the basket 20 by pulling the flange 45 forwardly away from the basket 20. The thus removed filter 40 and screen 44 are washed and then undergo inspection of damage. With the removal of the filter 40 and the screen 44, a clean­ing of the inside of the basket 21 can be achieved with utmost ease.

[0022] As described above, the screen 44 is provided with an annular flange 45 by means of which the screen 44 can easily be releasably attached by fasteners to the basket 21 from the outside of the centrifugal drum 20. With this detachable screen 44, the inside of the basket 21 can be washed easily and sufficiently. The centrifugal separator 1 having such detachable screen 44 is particularly suitable for the manufacture of foodstuffs, medical products or the like in which provision of a clean processing field is a major requirement. A fur­ther advantage attainable by utilisation of the detachable screen 44 is that different kinds of mixtures can be treated properly by replacing the current screen 44 with a different screen having a structure suitable for a mixture to be treated. Since the screen 44 is mounted on the basket 21 in radially spaced relation to the inner peripheral wall of the basket 21 by means of the ribs 49, the bas­ket 21 is rotatable smoothly without causing objectionable vibration which may occur due to unbalance produced when the screen is welded to the inner periph­eral surface of the basket 21. The screen 44 is per se simple in construction and can be manufactured at a low cost. The net 51, 52 disposed between the filter 40 and the screen 44 serves to reduce contact area between the filter 40 and the screen 44, thus improving the filtration capability of the centrifugal drum 20. The net 51, 52 further serves to facilitate smooth separa­tion of the filter 40 from the screen 44 when the rotor 22 is removed from the basket 21.

Claims

1. A centrifugal separator comprising: a rot­atable centrifugal drum (20) comprising a perforated bas­ket (21) having an open end, and a rotor (22) slidably received in said basket (21) and normally closing said open end of said basket (21), said rotor (22) being rot­atable in unison with said basket (21) and reciprocally movable in a direction parallel to the axis of rotation of said drum (20) into and out of said basket (21) through said open end of the latter; a flexible annular filter (40) extending between said basket (21) and said rotor (22) and adapted to be inverted in response to the reciprocating movement of said rotor (22); a water perm­eable tubular screen (44) disposed between said filter (40) and an inner peripheral surface of said basket (21) and having an annular flange (45) at one end thereof detachably connected to said open end of said basket (21); and spacer means (49) disposed upon at least one of said screen (44) and said basket ( 21) for holding them in radially spaced relation to one another.

2. A centrifugal separator according to claim 1, said tubular screen (44) having a number of slits (47) extending parallel to the longitudinal axis of said tubular screen (44) and circumferentially spaced at equal intervals.

3. A centrifugal separator according to claim 1 or 2, said spacer means comprising a plurality of ribs (49) projecting from said inner peripheral surface of said basket (21).

4. A centrifugal separator according to claim 3, said ribs (49) extending circumferentially over said inner peripheral surface of said basket (21).

5. A centrifugal separator according to claim 4, each said rib (49) extending continuously throughout the full circumference of said basket (21).

6. A centrifugal separator according to any pre­ceding claim, said annular flange (45) of said screen (44) having a first circular groove (41A) receiving therein one peripheral edge of said annular filter (40), said rotor (22) including an annular end plate (32) hav­ing a second circular groove (41B) facing away from said first circular groove (41A) and receiving therein the other peripheral edge of said annular filter (40), fur­ther including a pair of presser ring plates (42A, 42B) detachably connected to said annular flange (45) and said end plate (32), resectively, for holding said peripheral edges of said filter (40) in said first and second circular grooves (41A, 41B).

7. A centrifugal separator according to any pre­ceding claim, and further comprising an additional spacer means (51, 52) disposed between said filter (40) and said screen (44) for holding them in radially spaced relation to one another.

8. A centrifugal separator according to claim 7, said additional spacer means comprising a wire net (51) disposed on an inner peripheral surface of said tubular screen (44).

9. A centrifugal separator according to claim 7, said additional spacer means comprising a fiber net (52) abutted to one surface of said filter (40) which faces said screen (44) when said rotor (22) is disposed in said basket (21).

Drawing