CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    Not applicable.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to floor maintenance equipment and, more particularly, to a floor screening attachment and a dust collection system for a floor finishing machine.  
           [0003]    As a result of traffic induced wear, wood floors must be periodically refinished. Before the new finish is applied, the existing finish is sanded lightly or screened to promote adhesion of the new and old finishes. Screening is typically performed with a rotary floor machine of the type used for buffing, scrubbing, polishing, and a number of other floor maintenance operations. Referring to FIG. 1, typically, a floor machine  10  comprises a chassis  12  with an attached operator control handle  14 . To facilitate moving the machine  10 , a pair of wheels  16  is attached to the chassis  12  supporting the floor machine  10  when it is tipped in the direction of the handle  14 . A large diameter circular pad driver  18 , located under the chassis  12 , is connected to and rotated by a drive shaft  24  that is powered by a motor  20  and gear train  22  mounted in the chassis  12 . The pad  26  that performs the polishing, buffing, or other floor care operation is trapped between the pad driver and the floor. Friction between the pad driver  26  and the pad causes the pad to rotate with the pad driver  18 . For floor screening, the “pad” or screen  26  comprises an abrasive coated open mesh cloth having the appearance of window screen. Typically, the pad driver  18  used with a screen  26  is faced with felt to provide a resilient backing for the screen  26 . Slippage between the felt face of the pad driver  18  and the screen  26  erodes the abrasive coating of the screen  26 . The life of the abrasive on the side of the screen in contact with the pad driver  18  may be reduced by up to 50%. Since both sides of the screen  26  may be used to abrade the floor, slippage between the screen and pad driver results in a substantial increase in the cost of abrasives required to perform a screening operation.  
           [0004]    A second problem inherent in floor screening is the production of a large quantity of fine sanding dust. The dust can be controlled and collected with a wet screening process where water is spread on the floor prior to screening. The dust produced by screening mixes with the water to form a slurry that is removed from the floor by mopping. However, the slurry is difficult clean and its presence on the floor surface obscures the surface making it difficult to judge the progress and quality of the screening operation. For these reasons, floors may be screened while dry. However, the dry screening dust easily becomes airborne and must be cleaned from any horizontal or inclined surface in the vicinity of the screening project. Further, the fine airborne finish particles produced by screening may present a health hazard.  
           [0005]    To reduce the airborne dust produced by screening, specialized floor machines with dust collection systems have been devised. Typically, the dust collection system comprises an industrial vacuum cleaner connected to a shroud enclosing the top and the perimeter of the pad driver of the special machine. A special floor machine with a dust collection system may be justifiable for floor refinishing contractors, but many facilities have floor machines that are not equipped for dust collection and a special machine is not justifiable for periodic floor refinishing projects. Further, the quantity and fine nature of the dust produced by screening limits the effectiveness of the typical dust collection system. First, the felt pad driver used for screening comprises random fibers and has limited porosity. Air passages in the felt will quickly plug when air laden with screening dust is drawn through the felt. Since air cannot be drawn through the pad driver without frequent cleaning, the dust becomes trapped in the mesh of the screen and dust collection is only effective when the dust leaks from the edges of the screen disk. In addition, industrial vacuum cleaners rely on a dry filter element that traps particles on the surface of the element when air is drawn through pores of the filter medium. The fine dust produced by screening rapidly plugs the pores of the filter medium and the filter element must be frequently changed or cleaned if the vacuum cleaner is to continue to function.  
           [0006]    James et al., U.S. Pat. No. 5,922,093, disclose an ultra-filtration vacuum system that includes multiple liquid and dry filtering stages. Contaminated air drawn into the cannister of the vacuum is directed into a cyclonic air stream that separates large particles and debris from the air. The separated material collects in a first liquid filter medium in the bottom of the cannister. After cyclonic cleaning, the air passes through a labyrinth filter and is injected below the surface a second liquid filter medium. The air forms bubbles that rise to the surface of the liquid where many of the bubbles collapse. The air and liquid are then dispersed in a dispersion chamber. Particles entrained in the air are wetted by the liquid and a combination of cyclonic action and baffles in the dispersion chamber separate the mixture of liquid and wetted particles which flows back into the second liquid filter medium. Particulates remaining entrained in the air are filtered by a final dry filter element. While the vacuum system throughly filters the air, it is complex and not well suited to handling large quantities of fine dust produced by floor screening. Cyclonic cleaning relies on centrifugal force to separate heavy particles and debris from the air stream but is of limited usefulness for removing the fine, light weight particles produced by floor screening. When used for floor screening, the intermediate labyrinth filter would be exposed to essentially unfiltered air and subject to rapid plugging by the screening dust. Injecting contaminated air into a liquid filter media is an effective method of filtering out fine particles, but the volume of liquid in the second liquid filter stage is limited by the necessary equipment and the presence of the first stage filter in the cannister and would rapidly reach its capacity of particulate matter when exposed to the volume of dust produced by screening.  
           [0007]    If the finish is severely worn, floor screening may not be sufficient to prepare the floor for refinishing. In this case, as with newly installed floors, sanding the wood of the floor may be necessary to prepare the surface for the application of the finish. Floor sanding is performed with large belt or drum sanders. Like floor screening, floor sanding creates substantial quantities of dust. As is the case with floor screening, the large quantity of dust will rapidly plug a dry filter of a dust collection system. In addition, the presence of wood in the sanding dust causes foaming in a liquid filter medium severely limiting its effectiveness. Anti-foaming chemicals can reduce the foaming, but the chemicals are only partially effective. Further, adding chemicals to the liquid filter medium significantly increases the cost of floor finishing because the large quantity of dust requires the liquid medium and the anti-foaming chemicals be frequently replaced.  
           [0008]    What is desired, therefore, is an apparatus for converting a standard floor machine to a floor screening machine and an effective, large capacity dust collection system suitable for floor screening and sanding operations. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a perspective view of a floor machine.  
         [0010]    [0010]FIG. 2 is a perspective view of a floor machine with the floor screening attachment and an elevation view of a dust collection vacuum system.  
         [0011]    [0011]FIG. 3 is a perspective view of the floor screening attachment.  
         [0012]    [0012]FIG. 4 is a cross section of the floor screening attachment of FIG. 3 along line A-A.  
         [0013]    [0013]FIG. 5 is a plan view of the bottom of the facing of the sanding block of the floor screening attachment.  
         [0014]    [0014]FIG. 6 is a cross section of a floor screening attachment of an alternative construction.  
         [0015]    [0015]FIG. 7 is a schematic representation of a cross section of the dust collection vacuum system.  
         [0016]    [0016]FIG. 8 is a view of dust collection system including a dust collection unit for floor machine.  
         [0017]    [0017]FIG. 9 is a cross section of a dust collection unit of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    Referring to FIG. 2, the floor screening system  40  of the present invention generally comprises a floor machine  42 , a floor screening attachment  44 , and a dust collection vacuum system  46  connected to the floor screening attachment  44  by a hose  48 . The floor machine  42  comprises a chassis  50  enclosing a motor  52  and a gear train  54 . The chassis  50  also provides a connection point for a handle  56  for operator control of the floor machine  42 . Typically, floor machines are equipped with a pair of wheels  58  attached to the chassis  50  and arranged to engage the floor when the floor machine  42  is tipped toward the handle  56 . The wheels  58  provide a convenient support for the floor machine when moving between work areas. The floor screening attachment  44  is fitted with wheels  60  mounted for rotation and attached to the shroud  72 . Since the screening attachment  44  elevates the chassis  50 , the wheels of the floor machine  58  may not be useful for moving the floor machine when the screening attachment is in place. The wheels  60  can be used for moving the floor machine  42  when it is equipped with the screening attachment  44 .  
         [0019]    Referring to FIGS. 2, 3, and  4 , the floor screening attachment  44  comprises generally a pad driver  70  and a shroud  72  mounted for rotation independent of the pad driver. The pad driver  70  includes a pad driver shaft  74  having a first end providing an interface to the powered drive shaft  62  projecting from the gear box of the floor machine  42 . The interface between the pad driver shaft  74  and the drive shaft  62  of the floor machine is dictated by the design of the floor machine but, by way of example only, may be provided by intermeshing projections as illustrated in FIG. 4. A circular sanding block  76  is affixed to the second end of the pad driver shaft  74 . The sanding block comprises a backing plate  78  and a facing  80 . The backing plate  78  is a disk that supports the facing  80  and controls distortion of the facing which could cause unevenness of the screened surface. A bearing and seal  82  is affixed to the upper surface of the backing plate  78  and engages complementary bearing and sealing rings  84  and  86  attached to the shroud  72 .  
         [0020]    The shroud  72  of the screening attachment  44  includes a connector  88  for a hose  48  to the dust collection vacuum system  46 . The bearing and sealing ring  82 ,  84 , and  86 , in conjunction with the shroud  72 , form a plenum  75  around the periphery of the backing plate  78  in communication with the connector  88 . The pressure differential created in the plenum  75  by the vacuum source draws air through an approximately annular aperture between the shroud  72  and the backing plate  76  to move air entrained dust particles to the hose connection outlet  88 . The shroud  72  may be extended by a skirt  73 , such as a brush type screen or flexible element, to aid in confining dust expelled from the perimeter of the screen  90 . Preferably the skirt  73  comprises a flexible, non-porous material such as rubber or plastic that stops short of the floor to permit air to flow into the plenum  75 . However, the skirt  73  may comprise a brush or other porous material to permit air to flow into the plenum  75 .  
         [0021]    The screen  90  typically comprises an open mesh cloth coated with silicon carbide or another abrasive. When the sanding block  76  is rotated, friction between the facing  80  and the screen  90  causes the screen to rotate. To reduce slippage between the screen  90  and the facing  80  and resulting erosion of the abrasive from the screen  90  the present inventors concluded that facing should utilize a material having a high coefficient of friction with the mesh material. Further, the inventors concluded that when air is drawn through the prior art felt sanding block facing the passages in the felt quickly plug with dust limiting the effectiveness of the dust collection system. As a result, dust becomes trapped between the mesh of the screen and the felt facing. Since the vacuum system cannot draw air and dust through the plugged felt, the dust collection system is limited to collecting dust that migrates to the edge of the screen disk. The facing  80  of the sanding block  76  of the present invention comprises a plurality of spaced apart raised surfaces  92 . As illustrated in FIG. 5, the spaced apart, raised surfaces  92  are separated by surfaces  94  having a portion in relief of the raised surfaces  92  to create a pattern of channels through which air and entrained dust particles can migrate to reach the perimeter of disk for collection by the vacuum system. Rubber compounds, synthetic rubbers, plastics, and similar materials provide high friction between the screen  90  and the facing to reduce slippage and erosion of the abrasive, resilience to protect the sanded surface, and are moldable to form the plurality of spaced apart raised surfaces  92  useful in promoting air flow and dust collection.  
         [0022]    [0022]FIG. 6 illustrates an alternative construction for the floor screening attachment  44  of the present invention. The floor screen  202  is supported by a sanding block  201  (illustrated by a bracket) comprising a wooden backing plate  204  and a facing  80  as described above. To improve conformance of the screen  202  with the floor surface, a compliant pad  206  may be placed between the facing  80  and the wooden backing plate  204 . The sanding block is driven by a shaft  208  affixed to a flange  210  that is attached to the wooden backing plate with screws  212 . The opposite end of the shaft  208  is affixed to a second flange  214  that is attached to riser  216  and a clutch plate  218  by screws  220 . The drive shaft  62  of a floor machine  42  engages the clutch plate  218  to drive the sanding block  201 . A shroud  222  with a skirt  224  forms a plenum  226  about the exposed periphery of the sanding block  201 . A vacuum source (not illustrated) attached to the shroud draws air contaminated with dust from the plenum  226 . A pair of bearings having flanged outer cases  228  and  230  attached to the shroud  222  with screws  232 , permit the shaft  208  to rotate independent of the shroud  222 .  
         [0023]    Referring to FIG. 7, the vacuum system  46  of the present invention is connected to the screening attachment  44  by a hose  48 . The vacuum system  46  comprises generally a motor enclosure  100  and a container or cannister  102 . A vacuum source  104  (typically a motor and a fan) creates a pressure differential between the inlet  106  to the cannister and an air outlet  107 . A volume of liquid  108  (typically water) fills the cannister to a liquid level  110 . The inlet  106  for contaminated air drawn from the screening attachment is submerged in the liquid  108 . As the contaminated air  112  (indicated by an arrow) emerges from the submerged inlet  106  particles entrained in the air are wetted by and trapped in the liquid  108 . However, the surface tension of the liquid  108  also results in bubbles  114  and particles in the air trapped within the bubbles may not be wetted by the liquid. The bubbles  114  rise to the surface  110  of the liquid  108 . Particles within bubbles collapsing on the surface  110  of the liquid are wetted and trapped in the liquid  108 . Air and liquid are drawn up through a mixer  116  which further mixes the liquid and air further wetting entrained particles. The mixer  116  comprises a larger diameter tube concentric with the tube  118  leading from the hose to the inlet  106 . The mixture of air, liquid, and particles exits the mixing chamber  116  and enters a separator  118 . The separator  118  comprises a hollow toroid of generally circular cross-section surrounding the tube  118  leading to the inlet  106 . As the mixture of air and liquid is deflected by the curved walls of the separator and forced to change direction  120  (indicated by an arrow) additional bubbles are collapsed by the walls and additional particles are wetted by the liquid. As the moving mixture is further forced around the curved interior of the separator  118 , the heavier liquid and wetted particles are forced to the walls of the separator by centrifugal force. A slurry of liquid and wetted particles exits the mixing and separation chamber  118  at an exit aperture  122  and drops under the influence of gravity into the volume of liquid  108  in the bottom of the cannister  102 . Filtered air  124  exiting the separator chamber  118  is drawn to the outlet  107  by the pressure differential produced by the vacuum source  104 . Before exiting the cannister  102 , the air may also be filtered by a secondary dry filter  126  positioned in the air flow path. The large volume of liquid  108  in the cannister  102  provides substantial capacity to absorb dust produced by the screening operation permitting the work to continue without the need to change or clean filters. Liquid filtration avoids filter clogging encountered with industrial vacuums during screening.  
         [0024]    The vacuum system  46  provides substantial capacity for capturing dust produced by floor screening operations and can be used for other floor finishing operations, such as sanding. The wood of a new floor must be sanded to prepare the surface for finishing. Likewise, if an existing finish is severely worn sanding may be necessary to restore the surface for refinishing. Sanding can be performed with floor screening machines, drum sanders and belt sanders and produces as great or greater quantities of dust than floor screening. Further, the wood in the sawdust produced by floor sanding aggravates foaming of a liquid dust filter medium substantially reducing the effectiveness of liquid in trapping dust. Anti-foaming chemicals can be added to the liquid to reduce the foaming but the chemicals are only partially effective. In addition, the absorption of large quantities of dust requires frequent disposal of the liquid medium and the anti-foaming chemicals substantially increasing the cost of sanding. Referring to FIG. 8, to increase the dust containment capacity of the system and reduce problems created by foaming of a liquid dust filter medium during sanding operations, the floor finishing system of the present invention may include a dust removal unit  240  to remove a substantial portion of the dust from the air stream before reaching the vacuum  46 . The components of the system having counterparts illustrated in FIG. 2 and performing the same functions are assigned like numerals. The vacuum  46  draws dust laden air from the screening attachment  44  through the hose  242  into the dust removal unit  240 . A hose  244  connects the dust removal unit  240  to the vacuum  46 . A belt or drum sander may be used instead of a floor machine for sanding operations. Sanders and other floor finishing machines may include a fan to draw air from the vicinity of the working portion of the sanding or tool and expel it through the hose  242  to the dust removal unit  240  eliminating the need for the separate vacuum source  46 .  
         [0025]    Referring to FIG. 9, the dust removal unit  240  comprises generally a dust collection tank  250  sealed with a lid  252 . Sawdust laden air is drawn from the vicinity of the sanding element or tool of a floor screening machine, sander, or other floor finishing tool through the hose  242  to an inlet tube  254  of the dust removal unit  240 . Air contaminated with dust flows through the hose  242  into the dust removal unit  240  as a result of an air pressure differential between the inlet tube  254  and an outlet tube  256 . The air pressure differential can be created by an air moving device, such as a vacuum source  46  connected to the outlet tube  256  by a hose  244  as illustrated in FIG. 8 or by a fan at the floor finishing machine.  
         [0026]    Air including suspended dust entering the dust removal unit  240  is directed toward the underside of the top surface of the lid  252  into a first passage  258 . The first passage  258  is bounded by the underside of the lid  252  and an upper surface of a secondary chamber structure  260  suspended generally centrally in the lid  252  by attachment to the inlet  254  and outlet  256  tubes. The secondary chamber structure  260  is generally a hollow cylinder with a closed upper end. The velocity of the air is substantially reduced when the air flow is redirected by the surface of the lid  252  and diffused in the first passage  258  which has a cross-section substantially larger than the inlet tube  254 . As a result of the pressure differential between the inlet tube  254  and outlet tube  256  air flows to a second passage  264  in fluid communication with the first passage  258 . The second passage  264  has a cross-section greater the first passage  258  causing the dust laden air to further decelerate. As the velocity of the air decreases in the second passage  264  the dust particles can no longer be supported by the air and fall to the bottom of the tank under the influence of gravity. The air exiting the second passage  264  is further decelerated as its direction is changed to enter a third passage  266  defined by the interior surfaces of the secondary chamber structure  260 . The further reduction in velocity releases substantially all of the dust remaining suspended in the air. The air exits the third passage  266  through the outlet tube  256 .  
         [0027]    For floor refinishing operations, the system of the present invention provides a floor machine that can be quickly and conveniently converted to a floor screening machine. An effective dust collection system for the floor screening machine eliminates air borne contaminants and messy wet screening operations. The system can also include a dust collection unit to remove dust produces by floor sanding which can produce foaming of a liquid dust filter medium.  
         [0028]    All the references cited herein are incorporated by reference.  
         [0029]    The terms and expressions that have been employed in the foregoing specification are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims that follow.
Sanding and screening are steps in floor finishing that produce large quantities of fine dust which is difficult to remove and which plugs porous filter elements of dust collection systems. Dust collection is enhanced with a floor screening attachment for a floor machine. A vacuum system with a liquid filtering medium is provided to collect dust produced during screening. A dust collection unit is also disclosed to collect and separate sawdust produced by sanding which can cause foaming of a liquid filter medium.