Abstract:
Cyclones having abrasion resistant liners with a system and method for replacing the liners when they worn out due to the destructive nature of the materials being classified in the cyclone. The cyclone includes segmented inlet housing liners which are separately removable through the opened top of the cyclone housing. A lifting ring in the bottom of a conical housing has an apex cone and plural cone liners supported in a stacked array thereon within the conical housing and hoisting straps are used to lift the lifting ring, the apex cone and the array of cone liners out of the opened top of the cyclone housing without having to remove the cyclone from its operating position and completely disassemble the cyclone. Wear detector bolts attach the inlet head liners and a cage-like conical housing allows direct viewing of wear detecting weep holes provided in the liners mounted therein.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates in general to cyclones and more particularly to especially configured cyclones with a liner system and method by which worn liners are replaced with a minimal expenditure of time and labor and without having to remove the cyclones from their mounting bases.  
         [0003]     2. Description of the Prior Art  
         [0004]     Cyclones are mechanisms that are used in various industries to separate different sized particles that are fed as a mixture into the inlet of the cyclone. In the mineral processing industries such as for example in the processing of copper, iron ore, lead/zinc, gold, coal and the like, a plurality of large cyclones are typically carried in mounting bases arranged in a cluster over a “tub”. Each of the cyclones are in circuit with grinding mills and a slurry of water and the mineral to be classified is fed into the inlet of the cyclone. The heavier materials in the slurry exit the cyclone through an underflow outlet at the bottom of the cyclone and are returned to the grinding mill. The lighter materials are carried upwardly in a vortex created within the cyclone and exit through an overflow outlet nozzle at its upper end. The primary components of a cyclone include an inlet housing having a feed duct and a cylindrical head section, a head section cover plate, a downwardly tapering conical housing depending from the head section, an apex cone at the lower end of the conical housing with the course material underflow outlet at the lower end of the apex cone, and an internal vortex finder coupled to the fine materials overflow outlet nozzle.  
         [0005]     The feed duct of cyclones is often referred to as an involute which receives the slurry at high velocity from the grinding mill and directs it tangentially into the cylindrical head section of the cyclone. As the slurry swirls around in the head section the weight of the slurry, and particularly the large particles, will tend to fall downwardly into the conical housing of the cyclone. The larger particles and the water carrying them will move downwardly through the apex cone and will exit the cyclone through the underflow outlet. A vortex consisting of smaller particles and the water carrying them is created within the apex cone and moves upwardly through the center of the conical housing into the vortex finder and exits the cyclone through the overflow outlet.  
         [0006]     The feed duct, inlet head section, head section cover plate, conical housing, apex cone and the vortex finder of large cyclones of the type used in mineral processing are provided with liners which protect these components from the destructive forces imparted by highly abrasive slurries as they move through the cyclones.  
         [0007]     As disclosed in a paper entitled “Krebs Elastomer Liner Installation Instructions”, which is available on the internet at the krebs.com web site, gum rubber is the most commonly used liner material and synthetic rubber materials are also used in applications where gum rubber is not well suited. Such synthetic rubber-like materials include Neoprene, Nitrile/bunaN, Butyl, urethane and the like. Elastomeric liners are molded structures which historically are provided with annular flanges that are secured between the mating flanges of the different cyclone housing components to hold the liners in place. It is a common practice to affix these molded liners to the interior walls of the cyclone components by means of a suitable adhesive. The liners are designed to be a form fit within their respective components and compressive forces are used to install and fit the liners within each of the housing components and these forces must be maintained while the adhesive cures. In large cyclones, such as those having head section diameters of 26, 30, 33 inches, the conical housing is an assembly usually formed of two or more cone shaped housings which are bolted together at their mating flanges, and the conical housing assembly is similarly bolted to the lower end of the cylindrical head section after the large one piece liner is installed in the head section. The apex cone is bolted to the lower end of the conical housing assembly in some cyclones while others are attached by a quick release clamp as disclosed in my U.S. Pat. No. 4,541,934. In liner replacement operations involving these elastomeric liners, the cyclone housing must be disassembled, that is, the apex cone, the two or more cone shaped housings which form the conical housing assembly and the inlet housing are separated from each other and the head section cover plate is removed. This provides the access needed to peal the worn liners out of the several cyclone housing components and subsequently to apply the adhesive, install the new liners and exert the compressive forces needed to fit new liners.  
         [0008]     As hereinbefore discussed, gum rubber is the most commonly used liner material and this is due to it providing the longest possible wear life in most applications. Alternative liner materials are used in applications where natural gum rubber is unsuitable. Synthetic rubber is used when temperature or the slurry constituents do not allow the use of natural gum rubber. Reinforced highly resilient urethane in used in applications in which rubber liners are torn rather than worn. Ceramic and silicone materials are typically used in high wear areas of the cyclone and, for example, in the coal industry such liner materials are used throughout the entire cyclone. As was the case with the replacement of rubber liners, the entire cyclone must be disassembled to accomplish replacement of the liners formed of these alternate materials. Typical installation of such liners is discussed in a paper entitled “Installation of Ceramic Parts into Krebs D-Series Cyclones” which is available on the internet at the krebs.com web site. These types of liners are molded or cast and are assembled and fit individually into the disassembled housing components which form the cyclone. The inlet head section liner is a large one piece structure which is inserted into the inlet head housing and rubber wedges are used to center the liner in the head section. The cover plate and cover plate liner is then mounted on the inlet housing which is turned upside down. The liners are inserted into the cone shaped sections and gaskets and spacer rings are then inserted sequentially between the flanges which join the inlet head section to the uppermost cone portion, and between the flanges which join the two or more conical sections to each other. The gaskets are sized so that the abutting edges of the liners are in contact with each other and a bead of silicone sealant is applied to the abutting edges to aid in sealing the joints. The liner is then inserted into the apex cone and it is then connected to the lowermost cone section of the conical housing. The cyclone is then set on its side and the feed duct and vortex finder are then attached to complete the reassembly of the cyclone.  
         [0009]     Disassembly of large cyclones for the purpose of replacing worn liners is very labor intensive and time consuming. The first problem associated with such operations is the need for removal of the cyclone from its mounting base in the cluster of cyclones and transporting it to a dedicated repair facility or simply laying it on its side in a suitable maintenance area away from the cluster. Cyclones of this type are very awkward and can weigh up to about 5,000 pounds. Thus, the operator of the crane needed to remove and transport the cyclone must be careful not to damage the cyclone or adjacent equipment and must be skillful to precisely align the cyclone for reconnection to the material handling pipes when it is being returned to its operational position. The second problem in such operations is removal of the multiplicity of nuts and bolts which hold the various cyclone components together and typically the nuts and bolts will number between 50 and 75 depending on the size of the cyclone. There are some places on cyclones where power tools will not fit and in all cases the cyclones which are laying on their sides during this phase of the replacement operation must be moved to provide the needed access. Further, due to the hostile environment in which cyclones operate, the nuts and bolts are often rusted and must in many instances be heated or cut off to remove them.  
         [0010]     The traditional way to determine when cyclones are in need of liner replacement is to periodically inspect the liners until accurate records of the wear characteristics are collected at which time replacement schedules can be established based upon operating time. Conducting periodic inspections of the liners is labor intensive in that access to the interior of the cyclones is needed to conduct the inspections and of course operation of the cyclone must be interrupted during the inspections.  
         [0011]     Therefore, a need exist for a new and useful cyclone with a special liner replacement system and method which overcomes some of the problems and shortcomings of the prior art.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention discloses cyclones having a special liner arrangement for in-situ replacement of worn out liners which eliminate the need for completely disassembling the cyclone housing during a liner replacement operation. Also disclosed is a method for accomplishing the in-situ liner replacement.  
         [0013]     The special liners each include a rigid substrate formed of suitable material such as metal, rigid urethane or the like, with an abrasion resistant material such as rubber, high energy (soft) urethane, ceramic or other suitable liner material bonded to the substrate. The substrates are manufactured so as to conform to the shape of the particular interior wall section of the cyclone housing adjacent to which they will be placed, and the abrasion resistant materials are bonded to the interior surfaces of the substrates.  
         [0014]     The slurry inlet housing of the cyclone includes a transition duct portion which converts the slurry flow from a round in-cross-section flow provided by a supply pipe from the product grinding mill to the square in-cross-section flow within a feed duct section of the inlet housing. The feed duct, is sometimes referred to as an involute due to its shape and it feeds the slurry to be processed tangentially into the cylindrical head section of the inlet housing. The liner used in the transition duct section of the slurry inlet is especially configured to produce the change in flow configuration and is a one piece structure having a flange which is disposed between the flanges of the supply pipe and the transition duct section. At least three separate liner segments are used in the feed duct and the cylindrical head section of the inlet housing, rather than the prior art one piece liner, to facilitate installation, fitting and subsequent removal. The liner segment used in the feed duct is configured in the involute shape of the duct and is of upwardly opening U-shape in-cross-section so that when installed it will line the bottom and side walls of the feed duct. The liner segments used in the cylindrical portion of the head section of the inlet housing are of arcuate configuration to line the interior side walls of the cylindrical head section of the inlet housing. The open top of the feed duct and the head section are closed by a cover plate and a cover plate liner which is located in the upper end of the inlet housing below the cover plate.  
         [0015]     The cyclone housing also includes a cylindrical vortex finder mounted in the cover plate so as to extend axially down into the head section of the inlet housing. The vortex finder is fabricated with a rigid urethane substrate to which suitable abrasion resistant exterior and interior liners are bonded. When the vortex liners are worn out, replacement is accomplished by removing attaching bolts an pulling the finder axially out of the cover plate.  
         [0016]     The feed duct liner and the arcuate liner segments used in the inlet housing of the cyclone are held in contiguous engagement with the interior surfaces of their respective sections of the inlet housing by special fasteners. In addition to securing liners in place the special fasteners act as wear detection devices which provide an indication that liner wear is nearing the point that a replacement operation should be scheduled. The head section housing is provided with an opening at each location that a special fastener is to be used, and a bolt is positioned to extend through the opening into threaded engagement with a captive nut mounted on the interior surface of the rigid substrate of the liner. The nut is affixed to the substrate prior to bonding of the abrasion resistant material on the substrate and the bolt is sized so that its inner end is at a predetermined depth within the liner material. The bolt has an axial bore formed there through so that when the bonded liner material wears to a point where the inner end of the bolt is exposed, a small amount of the slurry will leak out through the bolt and thus provide a visual indication on the exterior of the cyclone housing that liner replacement will soon be needed.  
         [0017]     The cyclone housing further includes a conical housing assembly which tapers downwardly from its relatively large upper end to its smaller lower end and is dependingly attached to the open lower end of the head section of the inlet housing. The liners used in the conical cyclone housing include an upper cone liner, a middle cone liner and a lower cone liner and a apex cone. The upper and middle cone liners are preferably made with a high energy (soft) abrasion resistant material such as urethane bonded to the rigid substrate as described above and may be described as “drop-in” structures which fit in their proper positions within the conical housing due to the matching tapered configurations of the housing and the liners. The lower cone and the apex cone are preferably provided with ceramic liner materials which together taper from the upper end of the lower cone to a cylindrical outlet at the bottom of the apex cone. The rigid substrates of the lower cone and the apex cone are of special configuration by which the upper, middle, lower cone liners and the apex cone can be extracted from the conical cyclone housing by a lifting device which will be described below. The upper end of the outer surface of the rigid substrate of the lower cone liner is of conical configuration with the lower portion thereof being cylindrical. A radially extending annular flange is formed on the apex cone and is positioned to circumscribe the open upper end thereof. The lower end of the apex cone is cylindrical and has an annular groove in its outer surface. When installed in the conical cyclone housing, the lower end of the lower cone rests on the annular flange of the apex cone and they cooperatively form a cylindrical configuration at the junction of the lower cone and the apex cone. The conical cyclone housing is especially configured to provide a cylindrical lower end the open lower end of which is circumscribed by an inwardly extending ring-shaped shelf. The cylindrical configuration formed at the junction of the lower cone and the apex cone is located in the cylindrical lower end of the conical cyclone housing when the lower cone and the apex cone are mounted therein.  
         [0018]     A cylindrical anti-splash skirt of tubular shape is mounted so as to depend from the lower end of the apex cone. The cylindrical body of the skirt is formed of high energy (soft) urethane and an inwardly extending flange circumscribes the open upper end of the skirt. The inherently resilient nature of the skirt material allows it to be installed and subsequently removed by snapping it onto the cylindrical lower end of the apex cone with the flange of the skirt being disposed in the annular groove of the apex cone. An optional snap-in liner of resilient material can be installed inside the anti-splash skirt.  
         [0019]     A circular lifting ring is supported on top of the ring-shaped shelf provided at the lower end of the cyclone housing with the flange of the apex cone resting on the lifting ring. The body of the apex cone and the splash skirt extend axially downwardly through the lifting ring and depend from the open lower end of the conical housing. The lower, middle and upper cones are arranged in an axially stacked array on the upper surface of the flange of the apex cone and will move as an entity when the lifting ring is moved upwardly toward the inlet section of the cyclone housing.  
         [0020]     A pair of hoisting straps are attached to diametrically opposed sides of the lifting ring and extend upwardly therefrom between the exterior of the axially stacked conical liner array and the inner surface of the conical cyclone housing. The upper ends the hoisting straps each pass through a different one of a pair of diametrically opposed slots formed proximate the lower end of the head section of the inlet housing so that the upper ends of the straps are stored outside the cyclone housing until needed to accomplish a liner replacement operation.  
         [0021]     The method of the present invention for in-situ replacement of cyclone liners includes the initial step of disconnecting the slurry supply and overflow pipes from the cyclone to be serviced followed by the step of removing the cover plate and cover plate liner. Prior to removing the cover plate and cover plate liner, the optional step of removing the overflow nozzle and vortex finder may be accomplished or they can be left in place and removed along with the cover plate. Then the segmented inlet head liners and the feed duct liners are removed, followed by fishing the upper ends of the hoisting straps through the slots formed in the head section of the cyclone housing to move them into the interior of the cyclone head section. Then the upper ends of the hoisting straps are connected to a suitable bail that is coupled to a crane which pulls the hoisting straps, and the lifting ring and the stacked liner array and apex cone upwardly in the cyclone housing. The next step is interrupting the upward movement of the lifting ring when the upper cone liner clears the open upper end of the cyclone housing and removing the upper cone liner manually from the stacked array of liners. The next step is restarting the upward movement of the lifting ring until the middle cone liner clears the open upper end of the cyclone and halting the upward movement so that the middle cone liner can be manually removed from the stack. The next steps includes repeating the step of restarting and subsequently interrupting the upward movement of the lifting ring until the lower cone and the apex cone have been removed from the cyclone housing. The cyclone liner replacement operation is completed by the steps of inspecting the liners and replacing those showing excessive wear with new liners and installing them in the cyclone housing by performing the above recited steps in the reverse order.  
         [0022]     In addition to the special liner arrangement and method for in-situ replacement of worn out liners, a modified cyclone housing is disclosed as having a one piece open-sided cage-like conical housing with the cone liners contained therein being in plain view. This allows wear indicators provided at various locations in the cone liners and the apex cone to be inspected for indication of wear without interrupting operation of the cyclone. The wear indicators are in the form of weep holes having their inner ends buried beneath the inner surfaces of the abrasion resistant materials so that when the inner ends of the weep holes are opened into the interior of the cyclone as a result of material wear, the slurry liquid will seep out of the weep holes and provide a visual indication that a liner replacement operation should be scheduled. Also, modifications of the cyclone assembly techniques are disclosed to replace the prior art bolted assembly technique.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is an elevational view of a cyclone incorporating the features of the present invention.  
         [0024]      FIG. 2  is a top view of the cyclone shown in  FIG. 1 .  
         [0025]      FIG. 3  is an enlarged fragmentary sectional view taken along the line  3 - 3  of  FIG. 2 .  
         [0026]      FIG. 4  is an enlarged fragmentary sectional view taken along the line  4 - 4  of  FIG. 2 .  
         [0027]      FIG. 5  is an enlarged fragmentary sectional view taken along the line  5 - 5  of  FIG. 1 .  
         [0028]      FIG. 6  is an enlarged fragmentary sectional view taken along the line  6 - 6  of  FIG. 1 .  
         [0029]      FIG. 7  is an enlarged fragmentary sectional view taken along the line  7 - 7  of  FIG. 6 .  
         [0030]      FIG. 8  is a perspective view showing the cover plate, cover plate liner, the feed duct liner and the inlet head liners exploded from open top of the cyclone.  
         [0031]      FIG. 9  is an enlarged elevational view partially broken away to show the various features of the conical housing, the apex cone and the splash skirt of the cyclone.  
         [0032]      FIG. 10  is an enlarged fragmentary sectional view of the encircled portion  10  of  FIG. 9 .  
         [0033]      FIG. 11  is a sectional view taken along the line  11 - 11  of  FIG. 9 .  
         [0034]      FIGS. 13   a  through  13   c  are perspective views of the cyclone housing illustrating some of the steps of the method of the present invention.  
         [0035]      FIG. 14  is a top view similar to  FIG. 2  but showing a second embodiment of a cover plate attachment arrangement.  
         [0036]      FIG. 15  is an enlarged fragmentary sectional view taken along the line  15 - 15  of  FIG. 14 .  
         [0037]      FIG. 16  is an enlarged fragmentary sectional view taken along the line  16 - 16  of  FIG. 14 .  
         [0038]      FIG. 17  is an elevational view of the cyclone showing it mounted in an angular disposition with the second embodiment of the cover plate shown in  FIG. 14  being open to serve as a ramp in aiding the handling of the cone liners during a liner replacement operation.  
         [0039]      FIG. 18  is an elevational view similar to  FIG. 1  showing another embodiment of the cyclone of the present invention with the cyclone being partially broken away to show the various features thereof.  
         [0040]      FIG. 19  is an enlarged sectional view taken along the line  19 - 19  of  FIG. 18  with portions of the view being broken away to show the various features thereof.  
         [0041]      FIG. 20  is an enlarged view of the encircled portion  20  of  FIG. 19 .  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0042]     Referring more particularly to the drawings,  FIG. 1  shows a typical cyclone which is indicated in its entirety by the reference numeral  14 . To insure a clear understanding of the present invention, the basic components and features the cyclone  14  will now be described. Briefly, the cyclone  14  includes an inlet housing  15  having a feed duct section  16  and a cylindrical head section  17 . The top of the inlet housing  15  is closed by a removable cover plate  18  having an overflow nozzle  19  mounted thereon which is in communication with a vortex finder  20  that depends from the cover plate  18  axially into the cylindrical head section  17  of the inlet housing  15 . A conical housing  22 , which is usually an assembly including two or more truncated conical housings, depends axially from the cylindrical head section  17  and is disposed so that its small apex end  24  is at the lower end of the conical housing. The conical housing  22  shown in the accompanying drawings is not typical in that it is especially configured for reasons which will become apparent as this description progresses.  
         [0043]     The material to be processed in the cyclone  14  is in the form of a slurry which is a mixture usually of water and a range of different sized particles which are to be classified in the cyclone. The particles can be various minerals such as iron ore, coal and the like which are delivered from a grinding mill (not shown) to the cyclone by a suitable supply conduit  26  which is shown in dashed lines in  FIG. 2 . The slurry received from the conduit  26  passes through a transition duct section  28  located at the inlet end of the feed duct  16 . The feed duct  16  is sometimes referred to as an “involute” in that, as best seen in  FIG. 6 , it directs the slurry in a curved flow path to an outlet which is tangential to the cylindrical head section  17  of the inlet housing  15 . The slurry enters the cyclone  14  at high velocity and swirls around the vortex finder  20  in the head section  17  of the inlet housing  15 . Due to the weight of the swirling slurry, peripheral portions of it, and particularly the larger particles, will tend to fall downward from the head section  17  into the conical housing  22  of the cyclone  14 . The larger particles contained in the slurry will move downwardly through an apex cone  30  of frusto-conical configuration and a splash skirt  32  located at the apex end  24  of the conical housing  22  and will exit the cyclone  14  through an underflow outlet  34  provided at the open lower end of the splash skirt. A vortex is created within the apex cone  30  which carries a slurry of classified particles and water upwardly through the center of the conical housing  22  and the head section  17  of the inlet housing  15  and through the vortex finder  20  and the outlet nozzle  19  into a discharge duct  36  that is shown in dashed lines in  FIG. 1 .  
         [0044]     In the mineral processing industry, large cyclones such as those having inlet head diameters of 26, 30 an 33 inches are normally used and due to the highly abrasive nature of the slurries, such cyclones are provided with abrasion resistant liners to prevent destruction of the cyclone housings. As will now be described in detail, the special liner system of the present invention significantly reduces, and in some instances eliminates, the previously described problems associated with replacing worn out prior art liners.  
         [0045]     Reference is now made to  FIGS. 3 through 8  wherein the multiple liners  38 ,  40  and  42  are shown as being used in the inlet housing  15  instead of the prior art one piece liner. The liner  38  used in the feed duct  16  includes a rigid substrate  44  to which an abrasion resistant material  46  is bonded. The rigid substrate  44  is formed of any suitable material such as metal, fiberglass, rigid urethane or the like, and the abrasion resistant material  46  is preferably a high energy (soft) material such as gum rubber, synthetic rubber or soft urethane. The liner  38  is configured to conform to the involute shape of the feed duct  16  and is of upwardly opening U-shape in-cross-section so as to line the bottom and side walls of the feed duct  16 . The involute liner  38  is demountably fixed in the feed duct  16  by attachment means in the form of special fasteners  48  which will hereinafter be described in detail. The liners used in the cylindrical head section  17  of the inlet housing  15  are shown as being the two liners  40  and  42 , however, more than two can be used. Both of the liners  40  and  42  have a rigid substrate  50  to which an abrasion resistant material  52  is bonded to the inner face of the substrate, with the substrate and abrasion resistant material preferably being the same as that used in the involute liner  38 . The liners  40  and  42  are of arcuate configuration so as to conform to the interior surface of the cylindrical head section  17  of the inlet housing  15 , and the previously mentioned special fasteners  48  are used to demountably secure the arcuate liners  40  and  42  in place. The involute and arcuate liners  38 ,  40  an  42  are formed with beveled end edges  54  at each location where the liners form a junction with each other to seal the joints at those locations.  
         [0046]     In addition to mounting the involute and arcuate liners  38 ,  40  and  42  within their respective parts of the inlet housing  15 , the special fasteners  48  briefly mentioned above act as wear detection devices that provide an indication that liner wear is nearing the point that a replacement operation should be scheduled. A typical one of the fasteners  48  is seen best in  FIG. 7  as securing the arcuate liner  40  in contiguous engagement with the interior wall of the head section  17 , and it will be understood that the following description will apply to each of the special fasteners. Aligned openings  56  and  58  are provided in the head section housing  17  and in the rigid substrate  50  respectively, and a bolt  60  extends through those openings into threaded engagement with a captive nut  62  that is welded or otherwise affixed to the interior surface of the rigid substrate  50  of the liner. The nut  62  is affixed to the substrate  50  prior to bonding of the abrasion resistant material  52  thereto and when the bonding is accomplished, the nut is buried in the material  52 . The bolt  60  has an axial bore  64  formed there through and the bolt is sized so that when in threaded engagement with the nut  62 , the inner end of the bolt  60  is at a predetermined depth below the inner surface of the abrasion resistant material  52 . When the abrasive resistant material  52  wears to a point where the inner end of the bolt  60  is exposed, a small amount of the slurry will seep out through axial bore  64  of the bolt and thus provide a visual indication on the exterior of the inlet housing  15  that liner replacement will soon be needed. The axial bore  64  formed in the bolt  60  is preferably tapered with its small end located at the inner end of the bolt to prevent clogging of the axial bore by particles carried in the slurry. The buried depth of the inner end of the bolt  60  is such that when slurry leakage is seen, a sufficient thickness of the abrasion resistant  52  remains so that immediate liner replacement is not needed and can be scheduled at a convenient tine.  
         [0047]     A special liner  66  is provided for use in the transition duct section  28  of the feed duct  16 . The transition duct liner  66  is a one piece structure molded or otherwise formed of a suitable abrasion resistant material which is preferably the same as the material used in the liners  38 ,  40  and  42 . The transition duct liner  66  is configured to change the flow of the incoming slurry from the round-in-cross-section configuration provided by the supply conduit  26  into the square-in-cross-section configuration of the feed duct  16 . The transition duct liner  66  is formed with a flange  68  at its inlet end and the liner is held in place by its flange  68  being interposed between the flanges of the feed duct  16  and the supply conduit  26 .  
         [0048]     As seen best in  FIG. 5 , the vortex finder  20  is preferably formed with a rigid tubular substrate  70  having a flange  72  at its upper end. An inner ceramic liner  74  is bonded to the inner surface of the tubular substrate  70  and an outer ceramic liner  76  is bonded to the exterior surface of the tubular substrate to provide the vortex finder with an extended life. The vortex finder  20  is demountably secured within an opening  78  formed in the cover plate  18  by having the flange  72  of its rigid substrate  70  located between the outer surface of the cover plate  18  and the flange  80  of the overflow nozzle  19  which is bolted to the cover plate. A liner  82  of suitable abrasion resistant material can be bonded within the bore  84  of the overflow nozzle  19 .  
         [0049]     The involute liner and the arcuate liners  38 ,  40  and  42  respectively, do not extend all the way up to the opening at the top end of the inlet housing  15 . A cover plate liner  86  as seen best in  FIG. 8 , is preferably formed with peripheral metal band  88  and an internal frame  89  for supporting a suitable molded abrasion resistant material  90  having a depending peripheral lip  91 . When the cover plate  18  and the cover plate liner  86  are in their assembled positions, the depending lip  91  of the cover plate liner  86  exerts a downward force on the top edges of the liners  38 ,  40  and  42  to seal the joint there between. The cover plate liner  86  may be simply placed in the open top of the inlet housing  15  or can be attached to the underside of the cover plate  18  by suitable fasteners( not shown).  
         [0050]     The conical housing  22 , which is customarily an assembly of two or more housings of truncated conical configuration, depends axially from the cylindrical head section  17  of the inlet housing  15  and is disposed so that its small apex end  24  is at the lower end of the conical housing. In the embodiment shown best in  FIGS. 1 and 9 , the conical housing  22  has an upper cone housing  92  and a lower cone housing  94  with the latter being of special configuration which will hereinafter be described in detail. The liners used in the conical housing  22  are of truncated conical configuration and include an upper cone liner  96  which is used to line the inner wall of the upper cone housing  92  and a middle cone liner  98  which is used to line the inner wall at the upper end of the lower cone housing  94 . The upper and middle cone liners  96  and  98  are preferably made with a high energy (soft) abrasion resistant liner material  100  such as high energy urethane which is bonded to a rigid metallic substrate  102 . The upper and middle cone liners  96  and  98  may be described as “drop-in” structures which fit in their proper positions within the conical housing  22  due to the matching tapered configurations of the cyclone housing and the liners. The inner wall at the lower end of the lower cone housing  94  is lined with a lower cone liner  104 . The apex cone  30  and the splash skirt  32  depend axially from open apex end  24  of the conical housing  22 . The lower end of the lower cone housing  94 , the lower cone liner  104  and the apex cone  30  are especially configured to facilitate replacement of the liners  96 ,  98  and  104  along with the apex cone  30  and splash skirt  32  when those components become worn out.  
         [0051]     The lower cone housing  94  is of downwardly tapering conical configuration for most of its axial length and deviates from conventional conical cyclone housings by being formed with a cylindrical lower portion  106 . An annular ring-shaped shelf  108  extends inwardly into the opening at lower end of the cylindrical portion  106  of the lower cone housing  94  and a lifting ring  110  is supported on the upper surface of the shelf  108 . The function and structural details of the lifting ring  110  will hereinafter be described in detail. The apex cone  30  has a rigid substrate  112  formed of a suitable material such as rigid urethane with a bonded liner  114  which is preferably formed of ceramic to better withstand the severe abrasive forces that occur within the apex cone  30 . An annular flange  116  is formed on the substrate  112  and is disposed to circumscribe the open upper end of the apex cone  30 . The apex cone is of tapered configuration for most of its axial length and has a cylindrical lower end  118  in the outer surface of which an annular groove  120  is provided. The annular flange  116  of the apex cone  30  is supported on the lifting ring  110  so that the apex cone depends axially through the opening at apex end  24  of the cylindrical portion  106  of the lower cone housing  94 . The lower cone liner  104  has a rigid substrate  122  formed of a suitable material such as rigid urethane with a bonded liner  124  which is preferably formed of ceramic to better withstand the severe abrasive forces that occur in that area of the cyclone. The bonded liner  124  of the lower cone liner  104  is cone shaped as is the inner surface of the substrate  122 , however, the lower portion of the outer surface of the substrate is cylindrical to provide a thickened wall  126  at the bottom end of the lower cone liner  104 . The thickened wall  126  of the lower cone liner  104  is supported on the upper surface of the annular flange  116  of the apex cone  30 .  
         [0052]     The anti-splash skirt  32  has cylindrical tubular body  128  and is mounted so as to depend from the lower end of the apex cone  30 . The tubular body  128  of the skirt  32  is formed of high energy (soft) urethane and has an inwardly extending flange  130  that circumscribes the open upper end of the skirt body. The inherently resilient nature of the skirt material allows it to be demountably attached to the cylindrical lower end  118  of the apex cone  30  by snapping the flange  130  of the skirt body  128  into the annular groove  120  of the apex cone. An optional snap-in elastomeric liner  132  can be installed inside the anti-splash skirt  32 , and will be supported by an inwardly extending circular flange  134  formed at the bottom end of the skirt body  128 .  
         [0053]     As seen in  FIG. 11 , the lifting ring  110  has a pair of notches  136  formed at diametrically opposed sides thereof with a pair of up standing tabs  138  each located in a different one of the notches and attached to the lifting ring  110  such as by welding. The tabs  138  extend upwardly from the ring  110  and the lower ends of a pair of hoisting straps  140  are each attached to a different one of the tabs. The hoisting straps  140  extend upwardly between the inner walls of the conical housing  22  and the periphery of the cone liners  96 ,  98  and  104 . The upper ends of the hoisting straps  140  enter the lower end of the cylindrical head  17  of the inlet housing  15  and pass through slots  142  in the housing to the exterior of the cyclone  14 . The hoisting straps  140 , which have suitable connecting hardware such as D-rings  144  on their upper ends, are stored on the outside of the cyclone housing and are used in liner replacement operations as will be described below.  
         [0054]     As previously mentioned, mounting of the cover plate  18  on the inlet housing  15  exerts a downward force which seals the joint between the depending lip  91  of the cover plate liner and the upper edges of the liners  38 ,  40  and  42 . That same force is transmitted downwardly to seal the joints between the cone liners  96 ,  98  and  104 . As seen in  FIG. 12 , wherein the joint between the upper and middle cone liners  96  and  98  is best seen, the integrity of the seal formed at that joint is assured by forming an annular groove  146  in the top edge of the lower cone liner  98  and installing an O-ring  148  in the groove. It will be understood that the groove  146  and O-ring  148  shown in  FIG. 12  are intended to be typical of the seal configuration provided at joint between each of the liners  38 ,  40 ,  42 ,  86 ,  96 ,  98  and  104 .  
         [0055]     The cyclone liner replacement method of the present invention includes the initial step of disconnecting the cyclone  14  from the discharge duct  36  and, if the transition duct  28  is to be inspected and possibly replaced, slurry supply conduit  26  should be disconnected. The next step, which can be seen best in  FIG. 8 , includes removing the cover plate  18  and the cover plate liner  86 . Then the special fasteners  48  are removed and the feed duct liner  38  and the arcuate liner segments  40  an  42  are lifted out of the inlet housing  15 . In that there are three separate liners used in the inlet housing  15  each is relatively light and can be removed by hand. Referring now to  FIGS. 13   a  through  13   c,  the next steps include fishing the hoisting straps  140  through the slots  142  into the interior of the inlet housing  15  followed by the step of connecting the D-rings  144  of the straps to the opposite ends of a bail  150 . A suitable lifting mechanism, such as a crane (not shown), is then operated to move the bail  150  and axially pull the stacked array of liners  96 ,  98 ,  104 , the apex cone  30  and the anti-splash skirt  32  to a first position wherein the upper cone liner  96  is clear of the open top of the inlet housing  15  as seen in  FIG. 13   b.  Upon reaching this first position, operation of the lifting mechanism is interrupted and the upper cone liner  96  is manually removed from the stacked array. Operation of the lifting mechanism is then sequentially resumed and interrupted to move the stacked array into second and third positions (not shown) wherein the cones  98  and  104  are in turn removed manually form the stacked array. Final operation of the lifting mechanism raises the apex cone  30  and the anti-splash skirt  32  clear of the housing  22  as seen in  FIG. 13   c.  The liner replacement operation is completed by a reversed sequence of the above described steps of the method of the present invention.  
         [0056]     In view of the disclosed liner replacement system of the present invention, it will be noted that the only disassembly now required is removal of the cover plate  18  and the bolts securing the cover plate. Reference is now made to  FIGS. 14, 15  and  16  wherein clamping means  152  and hinges  154  are shown which attach a cover plate  18   a  to the inlet housing  15 . As seen in  FIG. 14 , a plurality of the clamping means  152  are used to secure the cover plate  18   a.  The clamping means  152  can be over-center latches, however, the swing bolts  152  as seen in  FIG. 15  are preferred. The swing bolts  152  are mounted to the side of the inlet housing  15  by a clevis  156  which supports an axle  158 . A sleeve  162  is provided on the lower end of the bolt  160  and the sleeve is mounted on the axle  158  so that the bolt  160  is pivotable between the solid and dashed line positions. In the solid line position, the bolt  160  extends upwardly through outwardly opening slots  164  formed in the flange  166  of the inlet housing  15  and in the cover  18   a.  A nut  168  is threadingly mounted on the bolt  160  to hold the cover in the mounted position, and loosening of the nut allows the bolt to be swung into the dashed line position. The cover  18   a  can be attached to the inlet housing  15  by using only the swing bolts  152 , however it is preferred that the hinges  154  be used for reasons which will be described. The hinges  154  may be mounted in the position shown or any other suitable position with the structural details being shown in  FIG. 16 . A gusset  170  is mounted on the side of the inlet housing  15  and a hinge pin  172  extends oppositely from the gusset. A hinge plate  174  is mounted fast on the upper surface of the cover plate  18   a  and a spaced apart pair of L-shaped arms  176  are carried on the hinge plate. A sleeve  178  is mounted between the depending ends of the L-shaped arms  176  with the hinge pin  172  positioned in the bore  180  of the sleeve to allow the cover plate  18   a  to be moved from the closed position to an opened position as indicated by dashed lines.  
         [0057]     In some installations cyclones are mounted in an inclined position as shown in  FIG. 17 . In such positions, the cover plate  18   a  can be swung into the open position so that it rests on the cyclone supporting structure  182 . When in this position, the cover plate  18   a  acts as a ramp to aid in the handling of the cone liner  96  and the other cone liners handled during replacement operations. In some installations opening the cover plate  18   a  in this manner may not be possible and complete removal of the cover can be accomplished by removing the hinge pin  172 .  
         [0058]     When retrofitting existing cyclones to include the in-situ liner replacement system of the present invention, no changes need to be made in assembling a cyclone housing by bolting the plurality of housing components to each other. However, as a direct result of the liner replacement system of the present invention, new and improved cyclone housing assembly techniques and design will now be disclosed.  
         [0059]     In a first embodiment, a change in the assembly technique is made by welding the separate components to each other as shown best at  184  in  FIG. 9 . In addition to eliminating the use of bolts, washers and nuts, using gaskets between the mating flanges will also be eliminated and the chances for developing leaks at the joints will be substantially reduced if not eliminated.  
         [0060]     In a second embodiment as seen in  FIGS. 18 and 19 , a modified cyclone housing  186 , as hereinbefore described, includes the major components of an inlet housing  188  having a head section  190  and a feed duct  192 . The open upper end of the inlet housing  188  is closed by a cover plate  194  having an apron  195  with an overflow nozzle  196  mounted on the cover plate, and a conical housing  198  depends axially from the open lower end of the head section  190  of the inlet housing  188 . In addition to a modified assembly technique, which will hereinafter be described in detail, the major differences between the cyclone  186  and those hereinbefore disclosed are in the conical housing  198 . The conical housing is provided with a flange  200  which circumscribes its open upper end and a sleeve  202  is provided at its lower apex end. The flange  200  and the sleeve  202  are interconnected by a plurality of struts  204  which may vary in number with it being preferred that at least four of the struts be provided. In addition, the struts  204  may be tubular as shown or they may be beams of any suitable shape such as I-beams. The struts  204  are disposed to taper downwardly from the flange to the sleeve and are radially spaced relative to each other to form the housing  198  into a cage-like structure having openings  206  about the periphery of the housing. A ring-shaped shelf  208  is provided at the open lower end of the sleeve  202  and the lifting ring  110  with its upwardly extending hoisting straps  140  (one shown in  FIG. 18 ) is restingly supported on the shelf. The annular flange  116  of the apex cone  30  is in turn supported on the lifting ring  110  so that the apex cone  30  and the anti-splash skirt  32  depend axially from the conical housing  198 . The cone liners  96 ,  98  and  104  are supported on the annular flange  116  of the apex cone  30  in a stacked array which is removable in the manner set forth in the previously described liner replacement method of the present invention.  
         [0061]     The open-sided conical housing  198  provides a clear view of the cone liners  96 ,  98 , and  104  so that weep holes  210  formed at various locations in the cone liners are in plain view. It will be understood that the following description of the weep hole  210  shown in  FIG. 19  will apply to all of the weep holes. The weep hole  210  is formed in the rigid substrate  102  of the cone liner  98  and extends into the abrasive resistant liner  100  a predetermined distance so that the inner end of the weep hole is buried below the inner surface of the liner  100 . The abrasive nature of the slurry being processed in the cyclone will wear down the liner material  100  to a point where the inner end of the weep hole  210  becomes open to the inside of the cyclone. When this occurs a small amount of the slurry liquid will seep out through the weep hole  210  and provide a visual indication that a liner replacement operation should be scheduled.  
         [0062]     The cyclone housing  186  has a plurality of swing bolt assemblies  212  each including a clevis  214  that is mounted on the flange  200  of the conical housing  198 . An elongated bolt  216  having a nut  218  threadingly carried on its upper end is pivotably mounted in each clevis  214 . Each of the bolts  216  extends upwardly from its clevis  214  through an outwardly opening slot  220  formed in a load-bearing plate  222  mounted on top of the cover plate  194 . When in the position shown, the swing bolt assemblies  212  clamp the cover plate  194  on the inlet housing  188  and clamp the conical housing  198  to the bottom of the head section  190  of the inlet housing  188 .  
         [0063]     As previously mentioned, the upper and middle cones  96  and  98  have a soft abrasion resistant liner  100  such as rubber or high energy urethane bonded to their substrates  102  and the lower cone  104  has a ceramic liner  124  bonded to its substrate  122 . Those liner materials are preferred due to their different characteristics which enable them to best withstand the different percussion and abrasion forces that occur within their particular areas of the cyclone. The different wear characteristics of the two dissimilar materials can cause a turbulence problem in the cyclone. The liner of soft material wears faster than the ceramic liner and when the soft material liner  100  reaches a thickness that is less than the thickness of the ceramic liner  124 , the top edge of the ceramic liner will protrude into the cyclone further than the soft material liner. This is referred to in the industry as a “reverse step” and it produces turbulence by deflecting the downwardly moving slurry into the center of the cyclone which disrupts the flow of slurry and classified materials being carried upwardly by the vortex. This problem is eliminated, or at least substantially reduced, by forming a curved surface  224  on the inner edge of the top surface of the ceramic liner  124  as seen best in fig,  20 . The curved surface  224  is intended to anticipate the wearing down of the soft material liner  100  and may be a segment of a circle or an irregular curve as determined by the wear characteristics of the cyclone and the materials being classified therein. It will be understood that a curved surface similar to the surface  224  can be formed at any junction between dissimilar cyclone liner materials where turbulence resulting from a reverse step could occur.  
         [0064]     While the principles of the invention have now been made clear in illustrated embodiments, many modifications will be obvious to those skilled in the art which do not depart from those principles. The appended claims are therefore intended to cover such modifications within the limits only of the true spirit and scope of the invention.