Abstract:
A grit classifier of the type used in a variety of industrial applications to separate grit or particulate matter from a feed slurry is disclosed, the grit classifier being unitarily-formed in one or two pieces of moldable plastic or plastic-like material which renders the grit classifier more easily and cost-effectively manufactured. The grit classifier of the present invention is also advantageously easy to transport to a site, thereby further reducing the costs of use. Also disclosed is an auger beating assembly for use in the unitarily-formed grit classifier tank of the present invention which is simply structured and adaptable to any screw auger type or size.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to classifier tanks used for separating particulates, or grit, from a liquid slurry and specifically relates to classifiers constructed to be easily transportable and economically made. 
     2. Description of Related Art 
     Grit classifiers are commonly used in a variety of industries, such as mining, municipal wastewater treatment and pulp and paper processing, to process liquid slurries for separation of the solids component from the liquid component of the slurry. More specifically, however, grit classifiers are employed to remove particulate matter or grit from such slurries. “Grit” typically includes inorganic particulates such as sand, dust or smaller mesh rocks or stones. Grit can also include organic material such as cinders, coffee grounds and other vegetal materials. It is important to the processing of industrial slurries to properly remove the grit from the slurry, and to do so in a manner which will avoid fouling the classifier equipment. 
     Grit classifiers generally comprise a tank or trough having a screw conveyor or auger positioned therein. The tank or trough is maintained at an angle to the ground. A slurry is introduced into the bottom, or lower, end of the tank, and the screw conveyor is operated to sweep the grit from the reservoir of fluid at the low end of the tank to a solids outlet positioned at the top, or elevated end, of the tank. Many classifier units thus described also act to dewater the grit as the grit is moved by the screw conveyor to the upper portion of the tank. Examples of grit classifiers are disclosed in U.S. Pat. No. 3,865,727 to Broling, et al., U.S. Pat. No. 4,871,449 to Lott and U.S. Pat. No. 5,368,731 to Pesotini. 
     Conventional grit classifiers are most typically made of a heavy and durable material, such as steel or concrete. They are also conventionally formed of over sixty separate pieces of metal which must then be welded together and secured by fastening means such as screws or bolts. Welding the parts together is very time consuming and, if done incorrectly, can compromise the integrity of the grit classifier. The formation of conventional grit classifiers may typically take about thirty man-hours and may cost several thousand dollars. In addition, the tanks are usually galvanized to increase durability and are then painted with two or more coats of erosion-resistant coating—all of which adds to the cost of manufacturing the grit classifier and increasing manufacturing time. 
     Another problem commonly encountered in conventional grit classifiers is that of transportation to a site. That is, grit classifiers are often used in industries where sludge processing systems must be brought to the site, such as in mineral and mining operations, and the transportation of conventional heavy metal or steel classifiers to a site is costly. Heavy lifting equipment (e.g., cranes) and large trucks must be employed to lift, transport and then position conventional grit classifiers at a site. To enable portability of grit classifiers, they have conventionally been manufactured in sections, which provides easier transportation of the parts, but which requires assembly at the site. An example of a grit classifier manufactured in sections is disclosed in U.S. Pat. No. 4,871,449. Assembling the grit classifier on site represents a loss of time and manpower. 
     Thus, it would be beneficial to the art to provide a grit classifier tank which is configured for simple construction, which is easily transportable to a site, which is resistant to degradation under conventional operating conditions and is economically made and used. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, a grit classifier is unitarily-formed from comparatively lightweight moldable materials which enable the grit classifier to be easily manufactured, easily transported to a site and implemented for use without time-consuming or costly assembly. The construction of the grit classifier of the present invention also renders it durable and corrosion-resistant and also provides beneficial improvements in the grit classifier art by facilitating attachment of a screw conveyor or auger to the grit classifier. 
     The grit classifier of the present invention comprises a unitarily-formed elongated tank having a bottom and upstanding, continuous wall, a fluid outlet formed at one end of the elongated tank for discharging fluid from the tank and a solids discharge outlet formed at the other end of the tank for discharging grit which has been removed from the fluid component of a slurry. The elongated tank is further structured to support a screw conveyor or auger within the tank for removing the grit or solids component from a slurry introduced into the elongated tank. The tank may be formed with an inlet for introducing a slurry into the tank. The grit classifier may include supports or legs unitarily-formed with the elongated tank, although legs may, alternatively, be added to the tank after formation. 
     The most beneficial aspect of the present invention is its unitary formation from comparatively lightweight, durable materials which render the grit classifier easily transportable and durable. As used herein, “unitary” or “unitarily-formed” means that the tank portion of the grit classifier is formed by means which produce a single component of substantially seamless construction. Depending on the embodiment of the grit classifier of the present invention, the unitarily-formed tank portion may be a single piece or two conjoinable pieces, each of which is unitarily-formed. The present invention thus provides a significant advantage over conventionally-constructed grit classifiers which are constructed of over sixty separate pieces. 
     The grit classifier of the present invention may be made by any suitable technique which produces a unitarily-formed structure as described herein. A particularly suitable example of such manufacturing means is a rotational molding process using high molecular weight plastics, such as polyethylene, or resinous materials. Rotational molding is a known process which involves introducing flowable plastic or plastic-like materials into a clamshell mold formed to the desired three-dimensional product design and continuously rotating the mold to assure the complete filling of the mold. The clamshell mold is then removed once the plastic has cured and hardened. Other suitable methods may be employed, however. By forming the grit classifier of the present invention in a unitarily-formed construction, there is a significant decrease in cost of manufacture, a significant decrease in manufacturing time (from weeks to days), an elimination of the need for coating the grit classifier because of the durability of the plastic material and a significant decrease in transportation costs and setup time at a given site. 
     One embodiment of the present invention comprises a single-walled tank of unitary formation which may have support legs additionally molded therewith or, in the alternative, secured to the bottom of the tank thereafter. In a second embodiment of the invention, the tank body is constructed with a double wall having a space therebetween which may be filled at the site with a weighted material, such as heavy-weight foam or cementitious material, to provide added stability to the grit classifier. The tank body may also be formed in two separate sections, generally comprising a pool section and grit discharge section with extension, which allows the discharge section of the grit classifier to be selectively sized for a particular application. 
     These and other advantages of the present invention will be better understood with reference to the detailed description of the illustrated embodiments disclosed hereafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention: 
     FIG. 1 is a plan view of a first embodiment of the unitarily-formed classifier tank of the present invention; 
     FIG. 2 is a side view in elevation of the embodiment shown in FIG. 1; 
     FIG. 3 is a plan view of the classifier tank shown in FIG. 1, with the cover removed to expose the interior of the classifier tank; 
     FIG. 4 is a view in cross section of the classifier tank shown in FIG. 1, taken at line  4 — 4 ; 
     FIG. 5 is a view in elevation of the fluid discharge end of the classifier tank shown in FIG. 3; 
     FIG. 6 is a view in elevation of the solids discharge end of the classifier tank shown in FIG. 4; 
     FIG. 7 is a view in lateral cross section of the classifier tank shown in FIG. 2, taken at line  7 — 7 ; 
     FIG. 8 is a view in lateral cross section of the classifier tank shown in FIG. 2, taken at line  8 — 8 ; 
     FIG. 9 is a view in lateral cross section of the classifier tank shown in FIG. 2, taken at line  9 — 9 ; 
     FIG. 10 is a view in lateral cross section of the classifier tank shown in FIG. 2, taken at line  10 — 10 ; 
     FIG. 11 is a perspective view of a second embodiment of the classifier tank of the present invention; 
     FIG. 12 is a view in cross section of the classifier tank shown in FIG. 11, taken at line  12 — 12 ; 
     FIG. 13 is a perspective view of a third embodiment of the classifier tank of the present invention; 
     FIG. 14 is a view in cross section of the classifier tank shown in FIG. 13, taken at line  14 — 14 ; 
     FIG. 15 is a perspective view of a fourth embodiment of the classifier tank of the present invention; 
     FIG. 16 is a view in cross section of the classifier tank shown in FIG. 15, taken at line  16 — 16 ; 
     FIG. 17 is a view in cross section of an exemplar auger bearing assembly configured for use in the classifier tank of the present invention; 
     FIG. 18 is an exploded view in perspective of the auger bearing assembly shown in FIG. 17 viewed from the end of the lip seal housing; and 
     FIG. 19 is an exploded view in perspective of the auger bearing assembly shown in FIG. 17 viewed from the end of the auger shaft. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment of the unitarily-formed grit classifier  10  of the present invention is shown in FIGS. 1-10, which also illustrate the general structural elements of the invention common to all embodiments. FIGS. 1,  2 ,  5  and  6  illustrate that the grit classifier  10  of the present invention is principally comprised of a unitarily-formed elongated tank body  12  having a bottom  14  and a continuous, upstanding wall  16  extending from the bottom  14 . The grit classifier  10  further comprises a first end  18  and a second end  20  of the elongated tank body  12 . That portion of the tank body  12  located toward the first end  18  defines a pool section  24  into which a slurry is introduced. That portion of the tank body  12  located toward the second end  20  defines a grit drainage section  26  for dewatering and discharging grit removed from the slurry. 
     As illustrated in FIGS. 1-10, the grit classifier  10  may optionally include a separate guard  28 , or cover, which registers with the elongated tank body  12  to provide a substantially closed tank system. The guard  28  may be fitted, however, with screen sections  30  to allow the release of gases from the tank  12  or to provide some aeration of the tank  12 . Notably, the embodiment of the grit classifier  10  shown in FIG. 1 does not strictly require a guard  28 , the presence or use of which is largely dictated by the application to which the grit classifier  10  is put. 
     In operation and use, the second end  20  of the grit classifier  10  is elevated above the first end  18  of the grit classifier  10  by means of supports or legs (not shown) which are of unequal height. (See FIGS. 11-16 for illustrative purposes.) The legs or supports located at the first end  18  are shorter in height than the legs or supports located at the second end  20 . Alternatively, the first end  18  may be devoid of legs or support such that the first end  18  rests directly on the ground or other supporting surface. The supports or legs may be unitarily-formed with the tank body  12  in a formation process (e.g., rotational molding), or the supports or legs may be separately formed and later secured to the tank body  12 . A slurry fluid is introduced into the tank body  12  in the pool section  24  thereof. The slurry may be introduced through the open top of the tank body  12  or through at least one feed slurry box  32  (two such feed slurry boxes  32  being illustrated in phantom in FIG.  1 ). The feed slurry box  32  or boxes may be unitarily-formed with the tank body  12  or, as suggested by FIG. 1, may be separately formed and secured to the tank body  12 . 
     The first end  18  of the tank body  12  may be configured with a weir extension  34  over which liquid flows, and a trough or launder  36  into which the overflow temporarily collects. The launder  36  is further structured with a fluid outlet  38  through which fluid from the launder  36  is discharged. A second underflow discharge outlet  42  may be formed in the bottom  14  of the tank body  12  in the pool section  24  through which fluid may be drained from the pool section  24 . 
     An auger shaft opening  46  is formed in the second end  20  of the tank body  12  to accommodate the positioning of an auger shaft  48  (shown in phantom in FIG. 2) therethrough. In use, the end  50  of the auger shaft  48  is secured to a motor (not shown) which provides rotation to the auger. A solids discharge outlet  54  is also formed at the second end  20  of the tank body  12 . Here, the solids discharge outlet  54  is formed through the bottom  14  of the tank body  12 . In use, the grit or solids component of the slurry pooling in the pool section  24  of the tank body  12  settles to the bottom  14  of the grit classifier  10  and the rotating auger lifts and moves the settled grit toward the second end  20  of the tank body  12 . The fluid moved with the grit will flow back toward the pool section  24  of the tank body  12  thereby causing a dewatering of the grit by the time the grit is moved and elevated to the solids discharge outlet  54 . 
     FIGS. 3,  4  and  7 - 10  more clearly illustrate the interior  60  of the grit classifier  10  and one example of the architectural configuration of the unitarily-formed tank body  12 . FIG. 3 illustrates the tank body  12  with the guard or cover removed so that the interior  60  of the tank body  12  may be viewed. The tank body  12  may be formed with a peripheral lip  62  against which the guard may register when a guard  28  is used. It can also be seen that the tank body  12 , in this exemplar design, is generally wider, or flared, in the area of the pool section  24  of the tank body  12  in comparison to the grit discharge section  26  which may be configured with more parallel-oriented walls. The pool section  24  need not be flared, however, and may have parallel-oriented walls as well. 
     FIGS. 3 and 4 show that the grit classifier  10  of the present invention may employ a weir  66  which, as shown, may be a separate and removable element of the grit classifier  10  and which is supported on the weir support  34  by weir brackets  68  unitarily-formed as part of the continuous wall  16  of the tank body  12 . Although shown as a separate and removable element, the weir  66  may optionally be unitarily-formed or molded as part of the tank body  12 . The weir  66  may be configured with a bearing channel  70  into which is slidably received a portion of a bearing assembly (suggested at  72 ) of an auger. An exemplar bearing assembly for an auger shaft which may be used with the present invention is disclosed more fully below. 
     FIGS. 3 and 4 further illustrate that feed openings  76  may be formed in the wall  16  of the tank body  12  to which a feed slurry box  32  (FIG. 1) may be unitarily-formed or attached. While two feed openings  76  are shown, only one, or more than two, may be employed in introducing slurry into the interior  60  of the tank body  12 . The tank body  12  may be configured, in the grit drainage section  26 , with a sluice water return channel  80  which runs longitudinally along the bottom  14  of the tank body  12 , as shown in FIGS. 3,  4  and  9 . The sluice water return channel  80  may be formed and defined by a ridge  82  (FIG. 9) running longitudinally in the bottom  14  of the tank body  12 . When grit is being moved upwardly through the grit discharge section  26  of the grit classifier  10  during operation, the sluice water return channel  80  and ridge  82  operate to keep the grit from settling and compacting in the bottom of the discharge section  26 . A sluice water nozzle  84  may be provided in the second end  20  of the tank body  12 , in alignment with the sluice water return channel  80 , through which sluice water is directed to flush grit and water back down into the pool section  24  of the tank body  12 . 
     While the shape and configuration of the tank body  12  of the present invention may vary, FIGS. 7-10 show but one example of how the grit classifier  10  may be shaped in cross section through the various portions of the tank body  12 . FIG. 7 is a lateral cross section view of the pool section  24  of the tank body  12  shown in FIGS. 1 and 2 and it can be seen that the tank body  12  in the pool section  24  is flared. That is, the upstanding wall  16  may comprise a first wall section  90  which is substantially vertical in orientation to the horizontal bottom  14  of the tank body  12 , a second wall section  92  which is oriented at a selected angle α to the first wall section  90  and a third wall section  94  which is oriented at a selected angle β to the second wall section  92  and at a selected angle δ to the bottom  14  of the tank body  12 . A flared configuration of the pool section  24  of the tank body  12  may be particularly suitable for facilitating the settling of certain types of grit or particulates in a feed slurry. Alternatively, however, it may be desirable to configure the pool section  24  of the tank body  12  with substantially more vertical side walls  16 , as suggested by FIG.  8 . 
     FIG. 8 shows the lateral cross section of the tank body  12  at the point of entry of the feed slurry through the feed box openings  76  formed through either wall  16  of the tank body  12 . It can be seen that the first wall section  90  has been extended in depth, thereby resulting in the shortening of the second wall portion  82 . Again, this configuration of the tank body  12  in the vicinity of the slurry introduction may facilitate pooling of the slurry in the pool section  24 . FIG. 9 shows a lateral cross section of the tank body  12  taken through the grit discharge section  26 . The figure illustrates how the slurry water return channel  80  and ridge  82  are configured in the bottom  14  of the tank body  12 . The first wall section  90  is also greater in depth such that the side walls  16  of the grit discharge section  26  are substantially parallel. The same is true with respect to the cross section of the tank body  12  shown in FIG. 10 which is taken near the second end  20  of the tank body  12 . Again, the configuration of the tank shown is only exemplary and is not intended to imply the only means of configuring the grit classifier tank of the present invention. 
     The first embodiment of the invention illustrated in FIGS. 7-10 is a single wall, unitary construction which facilitates manufacture of the grit classifier and enables easy transportation to a site. FIGS. 11-16 illustrate alternative embodiments of the invention, the common feature of which is a double wall configuration. As shown in FIGS. 11 and 12, the grit classifier  10  of this embodiment is comprised of two, unitarily-formed sections, the first being the pool section  24  and discharge section  26  of the tank body  12  and the second being a tank extension  100  of the discharge section  26  of the tank body  12 . The tank extension  100  is secured to the tank body  12  by securement members  98 , which may be unitarily formed as part of the tank body  12  and tank extension  100  structures. The pool section  24  of the tank body  12  includes a front support  102  and a back support  104  which are different in relative height to each other so that the second end of the tank body  12  is elevated above the first end  18  of the tank body  12 , thereby facilitating the formation of a pool of liquid in the tank body  12 . It can be seen that the tank body  12  of this embodiment has all of the configurational features of the single-wall embodiment previously described, including a launder  36 , a fluid discharge outlet  38 , weir brackets  68  to hold an insertable weir, feed openings  76  and a slurry water return channel and ridge  82 . In this embodiment, the feed slurry boxes  32  may be unitarily-formed with the tank body  12  during the molding or formation process. Alternatively, the feed slurry boxes  32  may be separately formed and secured to the tank body  12  as shown. This embodiment differs from the single-wall embodiment in having the solids discharge outlet  54  positioned in the tank extension  100 . 
     As more clearly seen in FIG. 12, the tank body  12 , and optionally the tank extension  100 , is configured with a double wall  104  which provides a void  106  between the two walls. The void  106  may be filled, as shown, with a variety of ballasting materials, such as heavy foam or cementitious material. The double wall configuration is formed during the molding process by, for example, using mated clamshell forms which are of disparate sizes. At least one aperture  107  is provided in the tank body through which the ballasting material may be placed or flowed to fill the void  106 . The double wall configuration of the present invention provides a significant advantage over conventional grit classifiers in enabling the device to be easily and less expensively transported to a site for use because of its lessened weight, whereafter the void  106  can be filled with ballasting material to stabilize it in place. Construction costs are also significantly reduced. 
     FIGS. 13 and 14 illustrate a further embodiment of the present invention where the tank extension  108  is of greater length and is configured with its own support leg  110 . The tank extension  108  of this embodiment secures to the tank body  12  by securement means  98 , as previously described, and includes the solids discharge outlet  54  therein. Similarly, as shown in FIGS. 15 and 16, the tank extension  114  may be of even greater length and includes its own unitarily-formed support leg  116 . FIGS. 11-16 demonstrate that a variety of tank extensions  100 ,  108 ,  114  can be sized and configured for attachment to the same size tank body  12 , thereby enabling selective sizing of the grit classifier  10  to accommodate a give application and to enable the selection of an appropriate screw auger size as dictated by the particular application. 
     Each of the tank bodies  12  and associated tank extensions  100 ,  108 ,  114  of various sizes are configured to employ a screw auger of selected size, as shown. Additionally, the configuration of the tank body  12  enables the lower end  120  of the screw auger  122  to rest on the bottom  14  of the interior  60  of the tank body  12 , thereby eliminating the need for conventional lift-out mechanisms. The ability to rest the screw auger  122  in an elevated manner above the floor  130  of the tank body  12  is particularly facilitated by using an auger bearing assembly  200  of the type described hereinafter and illustrated in FIGS. 17-19. 
     FIG. 17 illustrates an auger bearing assembly  200  which is generally comprised of an auger shaft adaptor  202 , a lip seal housing  204  and a lip seal  206 . This auger bearing assembly  200  has particular advantages over conventional bearing assemblies used in grit classifiers in having very simple construction (three parts) and being very durable in the abrasive conditions to which such bearings are exposed in the operation of grit classifiers. The auger bearing assembly  200  is easily constructed and inexpensively manufactured, thereby rendering it easily and inexpensively replaced if worn. 
     The auger shaft adaptor  202  is configured with a depression  208  sized in depth and diameter to receive the flange  210  of an auger shaft  48  therein. A plurality of apertures  212  are formed through the thickness of the auger shaft adaptor  202  through which bolts  216  are secured to firmly attach the flange  210  of the auger to the auger shaft adaptor  202 . The auger shaft adaptor  202  may also be formed with a raised landing  218 , the diameter of which is sized to be received in the bore  220  of the auger shaft  48  to securely engage the auger shaft  48  therewith. 
     The auger shaft adaptor  202  is also configured with a shaft  224  which is sized to be received into a bore  226  (FIG. 19) formed in the lip seal housing  204 . The bore  224  of the lip seal housing  204  is surrounded by a recessed shoulder  230  the internal diameter of which is greater than the internal diameter of the bore  224 . A lip seal  206  is provided for positioning in the recessed shoulder  230  of the lip seal housing  204 . The external diameter of the lip seal  206  is comparable to the internal diameter of the recessed shoulder  230  and the internal diameter of the lip seal  206  is sized to be receivable about the shaft  224  of the auger shaft adaptor  202  to provide a snug fit therebetween. As the auger shaft  48  rotates, the lip seal  206  moves with the auger shaft  48  and rotates in the recessed shoulder  230  of the lip seal housing  204 , which is stationary. The auger shaft adapter  202  and lip seal housing  204  are preferably made of an ultra high molecular weight (UHMW) plastic which imparts durability to the bearing assembly  200 . The lip seal  206  is preferably made of graphite or a similar material. The lip seal housing  204  may preferably be structured with a lift-out handle  234  oriented toward the top of the lip seal housing  204  which may be grasped for removal of the bearing assembly  200  from the tank body. The lift-out handle  234  may also be formed with an eye  236  through which a hook or finger may be positioned to help leverage the bearing assembly for lifting. The auger shaft adaptor  202  described and illustrated herein is but one exemplar configuration for such as adaptor, other designs or configurations being possible. 
     The grit classifier of the present invention is structured to be easily and cost-effectively manufactured to reduce the overall cost of construction and to reduce the cost of transportation of the grit classifier to a site. The grit classifier of the present invention has significant advantages over conventionally-made grit classifiers, as described previously. The grit classifier can be adapted in size, shape and configuration to meet the specific requirements of any number of industrial applications. Hence, reference herein to specific details of the structure and function of the invention is by reference only and not by way of limitation. Those skilled in the art will recognize that changes may be made to the invention to adapt it to a variety of applications.