Surface cleaning method and machine - Patent Review 4096084

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BACKGROUND OF THE INVENTION

A method of scrubbing surfaces such as floors and pavements with a scrubbing machine wherein the same cleaning solution is recycled and reused after filtering out solid material from the recovered cleaning solution.

Experiments have been conducted with a hydrocyclone to try to clarify dirty scrub water for possible use in scrubbing machines; however, due to the fineness and low densities of the colloidal particles in the dirty scrub water, only a small fraction of the weight of the suspended particles are successively removed. As a result of the remaining particles of dirt the scrub water that outflows from the hydrocyclone is still too dirty for reuse.

In the prior art, filters, including reverse osmosis systems, have been tried in order to clarify water for recycling in a scrubbing machine. However, due to the small size of the dirt particles and large number of them in the dirty scrub water, the filters plug quickly and thus require frequent cleaning or changing. The filters must be extremely fine to remove the small particles and thus plug quickly, and require considerable power to operate. Centrifuges have also been tried for clarifying dirty scrub water for reuse in scrubbing machines, but the high cost of centrifuges and associated equipment together with high power requirements make centrifuges impractical in a scrubbing machine

The present day scrubbing process most frequently used involves providing at least two solution tanks on a scrubbing machine, one being a clean solution tank that contains clean water and detergent for scrubbing and a second being a dirty solution tank into which the recovered dirty scrub water is returned. When all the clean solution has been used for scrubbing, the machine is returned to a suitable refilling point where the dirty solution tank is emptied and the clean solution tank is filled, and thence the machine is returned to the point where the scrubbing operation is recommenced. The dirty water is usually dumped down the drain causing further problems for waste treatment facilities and causing pollution problems. It has been estimated that up to 30 to 50% of the machine use time with this type of operation is in the clean solution preparation, the emptying of the dirty solution tank and transport time back and forth from the work area to the fill and empty point. On scrubbers now in use only one half of the existing tank capacity is useful for containing cleaning solution because the other one half must be used to hold recovered dirty scrub water.

In scrubbing surfaces the fine particles of dirt become uniformly dispersed in the scrubbing solution on the surface and when the dirty water is picked up (usually with a squeegee,) the thin film of water that is left on the surface after squeegeeing also carries these fine dirt particles and when the residual water dries, a film of dirt is left on the surface, even with the most efficient squeeging system.

Frequently, it is necessary to go over the scrubbed surface a second time with clean rinse water in the clean solution tank in order to remove a part of the dirty film left on the surface after the first scrubbing operation.

In order to overcome problems such as the above, including minimizing the frequency of having to replenish the clean solution supply, reducing dumping and travel time as well as overcoming other problems, this invention has been made.

SUMMARY OF THE INVENTION

A process for wet scrubbing surfaces that includes adding a flocculating agent, with or without the addition of a detergent to the clean solution dispensed on the surface to be cleaned, agitating the cleaning solution dispensed on the surface to loosen dirt thereon and removing the dirty solution from the surface. In a scrubbing machine the process includes separating the formed flocs out of the cleaning solution removed from the surface, returning the separated solution directly to the surface or to a clean solution tank provided on the machine so the cleaning solution can be reused, if desired.

An object of the invention is to make the small dirt particles in scrub water to floc together into large enough flocs or agglomerates so that the flocs can be easily separated from the scrub water without the severe plugging previously encountered.

An object is to present a machine that can utilize scrubbing solution containing flocculation agents and recover solution containing the flocs and separate out the flocs so the recovered, clarified solution can be reused for additional scrubbing.

An object is to form large flocs on the surface before the solution is picked up. The large flocs are suspended and a film of clarified solution is left on the surface behind the pick up means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of one machine for carrying out the process of this invention;

FIG. 2 is a diagrammatic illustration of a second machine for carrying out the process of this invention; and

FIG. 3 is a schematic sectional view of a mobile scrubbing machine using a double brush scrubber and a form of separator for flocs which deposits clarified solution back on the surface for reuse.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Broadly this invention is directed to using polyelectrolytes in a scrubbing that is utilized in scrubbing a surface such as floors, pavements, walls, and the like to provide flocculation of the soilage right on the surface, and removing the flocculation dirty solution from the surface. In floor or surface scrubbing machines steps of filtering out the flocs and recycling the filtered solution to effectively use the solution more than once is included. In most scrubbing operations the polyelectrolyte is to be used in combination with a compatible detergent or soap. The normal small particles are made to floc together to form large flocs which can withstand mechanical action and which can be separated from the solution without constantly plugging filters or screens.

The inclusion of polyelectrolytes in the solvent (usually water) in the cleaning solution tank of a scrubbing machine, which solution is applied to the surface to be cleaned, together with agitation of the solution on the surface, results in the immediate formation of flocs on the surface. The flocs, because of air entrainment or other reasons tend to remain suspended or to float so that a film of clarified solution is left on the surface after the solution is removed to actually clean rinse the surface. The flocs may be readily separated out of the recovered solution. The clarified filtered solution is reused during the scrubbing operation. In the "Condensed Chemical Dictionary", 7th ed, 1966, published by Reinhold Publishing Company polyelectrolytes are defined as follows: "High molecular weight electrolytes of either natural origin (proteins, polysaccharides) or of a synthetic nature . . . They may be either weak or strong electrolytes. Since the polyelectrolytes in solution do not disassociate to give a uniform distribution of positive and negative ions, as do simple electrolytes, the ions of one sign are bound to the polymer chain. Thus for instance, the positive charges may be in the polymer chain, and only negative ions will be free to diffuse through the solvent".

The actual mechanics of flocculation with the aid of a high molecular weight polyelectrolyte is not fully understood. There have been papers written describing various theories, but the actual mode of action is not well understood, and descriptions are usually written in generalities. There are two basic actions that seem to be the starting points for most theories. When the polyelectrolyte is highly ionic in nature, it may work by charge neutralization on the charged particles in suspension, permitting them to agglomerate. Polyelectrolytes of very high molecular weight also may become physically adsorbed on two or more particles per molecule, which is called bridging. The neutralization of electrical charges on the adsorbed polyelectrolyte molecules then may cause it to coil and to become enmeshed with agglomerates of other molecules with similar particle holding characteristics.

With the wetting and emulsifying power of a detergent the following theory of flocculation with the aid of high molecular weight polyelectrolytes for use in scrubbers is offered as one plausible mode of action. The system that is to be described is one of a solution composed of water, high molecular weight polyelectrolyte and a compatible detergent. The detergent releases the particles from the soiled surface by emulsifying and wetting them. At this point on present scrubbing machines, the puddle on the surface has fine dirt particles dispersed throughout so that as the squeegee passes, it leaves a film of this dirt containing solution which dries and leaves a small portion of the dirt particles on the surface. With a high molecular weight polyelectrolyte in solution the dirt detergent micelles and colloids in the solution agglomerate and large flocs are formed. These flocs are then light enough to suspend in the solution or even float. The suspension or floatation does require agitation to be most effective. This suspension or floatation may be due to surface tension, air inclusions or other reasons, but in any event the flocs do not settle out rapidly so the area between the agitation means and the subsequently operable solution pickup means is rinsed with essentially clean solution. Also, in a machine, as the squeegee passes over the puddle, these large suspended or floating agglomerates are easily picked up with the cleaning solution. Because the solution left on the surface by the squeegee is of clarified water, when the film dries there are few, if any dirt particles left. A light penetrating process for comparing surface cleanliness illustrates the benefit of the film of clarified water on the surface and is described in detail subsequently in this specification.

It has been noted that some combinations of polyelectrolytes and detergents did not work until a metal salt flocculating aid, for example ferric chloride (Fe Cl.sub.3), was added to the solution. Immediately large tough flocs were formed that were easily removed leaving a well clarified scrub water. One explanation of this phenomena may be that the metallic salt ionically alters surface electrical charges to permit more effective action by the polyelectrolyte. In some examples the flocculating aid permits a reduction of the polyelectrolyte used, resulting in greater economy for similar results.

Water soluble synthetic polyelectrolytes usable in this invention comprise polymers having molecular weights of at least 5,000 including for example, polyacrylamide, copolymers of acrylamide with copolymerizable monomers such as acrylic acid, acrylonitrile, diacetone acrylamide and other N-substituted acrylamides, sulfonated polystyrene, polyethyleneimine, polymers of diallyl quaternary ammonium monomers, polyacrylic acid and its salts, polyamines, and polyethylene oxide. Since the water soluble synthetic polyelectrolytes disclosed in U.S. Pat. Nos. 3,345,841 and 3,492,224 may be used as well as others, a more detailed listing is not believed necessary.

Water soluble natural polyelectrolytes usable in this invention include guar gums (polysaccharides), starch derivatives and modified starches, carageen moss, sodium alginate and other natural polyelectrolytes well known in the art.

Usually it is desirable (although not necessary) to incorporate a detergent or soap in the cleaning solution. The type of detergents that are usable include for example an alkyl sulfate, an alkyl sulfonate, an alkyl-aryl sulfonate, sulfonated amide (all anionic); a fatty acid-polyethylene condensate, a phenol-polyethylene glycol condensate, an alcohol-polyethylene glycol condensate, a mercaptan-polyethylene glycol condensate (all nonionic); and quaternary ammonium and tertiary amines obtained after condensing ethylene oxide with fatty acids (all cationic). The chemical nature of detergents is vast, and the above list is for illustrative purposes to indicate the wide range of utility and not for limitation.

All detergents do not work well with all polyelectrolytes. However, generally a cationic polyelectrolyte works well with either a nonionic or anionic detergent, a nonionic polyelectrolyte works with a cationic or nonionic detergent and an anionic polyelectrolyte works with a cationic or nonionic detergent. With ampholytic detergents the pH of the scrubbing solution is the major factor in choice of polyelectrolyte. In addition to the compatability of the detergent and polyelectrolyte, other conditions influencing the selection of the particular detergent and polyelectrolyte to be used together include pH of the solution, the type and amount of soilage on the surface to be cleaned and concentrations of the detergent and polyelectrolyte.

A simple test to determine whether or not a given polyelectrolyte is suitable, or combination of polyelectrolyte and detergent or soap is suitable, for carrying out the invention comprises placing known quantities of each ingredient including water containing soil in different order in a glass container, covering the container, manually shaking vigorously for a few seconds, letting the container set a few seconds, and then visually observing to see if flocs are formed and if clarification of water results. For example, dirt, polyelectrolyte and detergent in known amounts can be added to 100 ml of water in the container; or in place of dirt and water, dirty scrub water from the area to be cleaned can be used.

If no detergent or soap is used, and the polyelectrolyte does clarify the water, or form flocs, it is suitable. If a particular polyelectrolyte in combination with a particular detergent did flocculate dirt from a dirty solution, then the particular combination of detergent and polyelectrolyte tested is considered suitable. If a particular combination of polyelectrolyte and detergent in dirty water resulted in most of the detergent coming out of solution with the flocs (usually apparent as a slime) or if the detergent comes out of solution without flocculating the soilage, then the detergent-polyelectrolyte combination is considered unsuitable. However, as previously indicated, for example, some combinations that are not suitable may become so with addition of a flocculant aid such as ferric chloride, incorporated in the solution.

The pH of a solution makes quite a difference in the effectiveness of a given polyelectrolyte and a range of pH is generally suggested by the manufacturer of the polyelectrolyte. Thus it is desirable but not necessary that the cleaning solution include a suitable buffering agent so that the filtered dirty scrub water maintains a fairly small range in pH value. The actual pH and pH range most suitable varies from one combination of detergent and polyelectrolyte to another.

Although the desirable concentration of polyelectrolyte in a cleaning solution for carrying the process of this invention varies from one polyelectrolyte to another and the concentration of and type of detergent or soap, if any, in the solution, and the concentration of and type of flocculating aid, if any, the useful limit range of polyelectrolyte is about 0.0002 to 5%, (by weight) of the solution with the usual desired range being 0.001% to 2%; while the desirable amount of detergent in solution, if used, usually will be in the range of about 0.5% to 15% (by weight) of the solution. Generally, if a given detergent is compatible with a particular polyelectrolyte, it is compatible at any reasonable and useful concentration of either the detergent or the polyelectrolyte.

It has further been found that the surface cleaning results from the use of a particular polyelectrolyte or a particular combination of a polyelectrolyte and detergent (or soap) may be enhanced with the addition of small amounts of metal flocculent aids. Examples are ferric chloride, alum and ferrous sulfate. These metal flocculant aids are generally polyvalent and are well known and used in water and sewage treatment plants to effect improved solids precipitation.

One diagrammatic illustration of a machine suitable for carrying out this invention for scrubbing surfaces is shown in FIG. 1 wherein a mobile scrubbing machine, generally designated 10, includes power source, such as an engine 10A or an electric drive motor mounted on a frame represented by the outline box 10B. The engine is used to power the components of the machine and also to propel the machine, if desired. Also an operators seat and steering controls may be provided. A power driven scrub brush 11 is rotatably mounted on the machine frame and driven from engine 10A. A solution tank 12, is mounted on the frame and a source of vacuum such as a motor driven vacuum pump or suction blower 13 is fluidly connected to the top of tank 12 by a line 14 to apply a vacuum to the tank. A squeegee 15 (or other suitable recovery apparatus) is mounted on the rear part of the frame and engages a surface 25 for collecting dirty scrubbing solution from the surface. A line 16 is connected to tank 12 and extends adjacent to or is connected to the squeegee for returning the dirty scrubbing solution collected by the squeegee to tank 12 under vacuum. A pump 18 and a strainer or filter screen 19 are connected in series in a line 20 that is connected between the bottom of tank 12 and discharge line 21. The line 21 is connected to a solution distributor line or nozzles 22 that discharge clean scrubbing solution onto the surface 25 to be cleaned, forwardly of the brush 11 in the normal forward direction of motion of the machine indicated by arrow 26. A control valve 23 is provided in line 21 to control discharge of clean solution onto surface 25.

When the solution is recycled several times between changes of cleaning solution in tank 12, the strainer must have capacity to permit several recycling operations. The strainer may be, for example, a loose woven cloth or throw away paper insert or a wire screen (for example 80 mesh wire screen) to separate out the large floc from the dirty solution. The screen 19 may be located in any number of desired locations, for example, right in tank 12, in line 16, at the squeegee 15 or as shown on the inlet of pump 18.

The drives for the machine are only illustrated schematically but could be belt, chain or hydraulic drives with remote motors. Scrubbing machines of the general type are well known in the art, but because of the essence of this invention, the formation of large flocs allows the use of a relatively open strainer in the circulation line permitting reuse of the clarified solution. The flocs can be separated out easily without plugging the strainer because the openings can be quite large, and the floc will readily fall off the screen after they are separated from the cleaning solution. A vertically oriented screen, for example could be vibrated and the large flocs collected in a bottom tray or compartment.

The brush illustrated for agitation is shown as a rotary brush extending across the machine but the agitation means could be disc type brushes, or reciprocating brush sections. The agitation also could be done with spray nozzles to agitate the solution carrying the polyelectrolyte with soilage on the surface to get proper flocculation. The term "agitation means" is therefore to be broadly construed.

With reference to FIG. 2, there is shown a scrubbing machine, generally designated 30, which instead of using only one tank has a clean solution tank 17 and a recovery tank 31. Dirty scrubbing solution collected by squeegee 15 is returned through line 16 to tank 31 while a vacuum from source 13 is applied through line 14 to tank 31. A pump 18 and strainer 19 are connected in series in a line 20 that extends between the recovery tank 31 and the clean solution tank 17. A line 21 connects the clean solution tank 17 to a solution distributor line 22 which has nozzles or openings to deposit solution on the surface.

Although the strainer 19 has been shown outside of the tanks, it may be physically located for example in either of tanks 31 or 17 or in line 16 or on squeege 15 as long as it is of a construction that material separated out of the solution passed therethrough is retained within a fixed space and the flocs separated out are not allowed to flow with the solution being discharged from the tank for application to the surface being cleaned. Thus, for example, in the first form of the invention line 16 may extend into tank 12 and a filter may be mounted on the discharge end of the line or in squeegee assembly 15 to retain the flocs within the interior of the filter.

A valve 32 in line 20 can be closed off and the unit used as an ordinary two tank scrubbing machine. One tank for clean solution and one for recovery of dirty scrubbing solution. The valve 32 is open for illustration of this invention.

A scrubbing machine showing agitation brushes, a solution tank, vacuum blower and the general arrangement for squeegees is shown in U.S. Pat. No. 3,197,798.

In carrying out the process of this invention, which is schematically illustrated in the drawings in connection with the machines, the cleaning solution tank 12 or 17 is filled with a cleaning solution, which by way of illustration will be considered to include a detergent and a compatible polyelectrolyte. Thereafter the machine 10 or 30 is moved to the area to be cleaned, the valve 23 is opened to apply the cleaning solution on the surface or on the brushes. The brushes, or other suitable agitation means, loosens the dirt and soilage on the surface; the detergent aiding in loosening and emulsifying the soilage. The polyelectrolyte in the solution together with the agitation causes the dirt to form strong large flocs which suspend or float in the solution on the surface between the brush and the squeegee 15. This stratifies the puddle on the surface into a suspension of flocs and a layer of clear solution on top of the surface being cleaned. The vacuum applied to the tank 12 or 31 results in the solution and flocs adjacent the squeegee to flow through line 16 to the tank 12 or 31. Because the film of solution on the surface is substantially clear and free of dirt, only a thin film of clarified cleaning solution remains on the surface behind the squeegee. The above mentioned agitation (brush) helps to clean the surface, aids in the flocculation process and may introduce air into the flocs. Solution can be removed easily from the floor or surface by various means, for example with the vacuum and rubber squeegee leaving a clean surface.

As the cleaning solution with suspended flocs flows through the strainer 19, regardless of its position and toward the discharge line 21, the flocs are separated out of the solution. If there is a screen or filter on either end of line 16, most of the flocs would be retained in this screen.

FIG. 3 illustrates the use of a double brush scrubbing unit for agitation and to illustrate another way scrubbing solution can be recirculated and reused in a machine for carrying out the process. A frame 40 rotatably mounts a pair of brushes 41 and 42 which extend transversely to the direction of movement of the unit shown by arrow 43. The frame can be mounted on wheels or supported by a power vehicle. A double brush scrubber of this type is disclosed in copending U.S. patent application Ser. No. 72,275 now U.S. Pat. No. 3,702,488, Filed Sept. 15, 1970. The brushes 41 and 42 may be rotated by power source 44 in a desired direction as indicated by the arrows on the brushes. The brushes may be rotated in opposite or same direction as desired. A solution tank 45 is provided as is a vacuum source 46 which applies a vacuum to tank 45 and draws solution from a squeegee 47 through a line 48 and a strainer or filter 49 in line 48 into the tank 45. The solution is pumped with pump 50 through a valve 51 in a line 52 to a solution distributor line 53. The solution is applied to the surface 54 and as the unit is moved in the direction of arrow 43 the brushes 41 and 42 agitate the solution, and actually pick up the solution on the surface and carry it up against a deflector 55 mounted on the frame. The deflector directs the major portion of the solution over brush 41. A screen trap trough 56 is mounted adjacent the brush 41 in the path of material carried by the brush and has a screen 57 dividing the trough so that solution flows onto the screen 57 and the flocs are held on the top of the screen while the liquid, which is clarified as it passes through the screen, is returned to the surface 54 for reuse directly without going back through tank 45 and distributor 53.

The squeegee 47 is used to collect the solution which remains on the surface after passage of the double brush unit.

The distributor line 53 is used to add sufficient solution to the surface to make up for the used solution picked up by the squeegee. The material which is picked up by the squeegee is strained through strainer or filter 49 and the clarified solution is recycled and reused.

The flocs again are large and either float or are suspended sufficiently so that the flocs are all picked up and a clear film or solution is all that is left on the surface after the squeegee has passed. Therefore the squeegee acts as a floc-solution separator to leave a clarified solution film on the surface without small dirt particles in the film.

As a result of providing the polyelectrolyte, the solution passed through the filter or strainer is clarified, but still contains detergent and polyelectrolyte. Thus the solution may be recycled a number of times, the number in part depending on the amount of solution left on the surface behind the squeegee. When the solution is all used the machine is returned to the filling point, the collected flocs carrying the dirt particles from the surface scrubbed being disposed of in a suitable refuse container rather than being discharged into the sewer system, and the clean solution tank is refilled with the solution containing flocculating agent and if desired soap or detergent.

Any suitable type of pump may be used for pumping the cleaning solution from the tank to be applied to the brush or surface; for example it may be electrically, mechanically or hydraulically powered, and it may be self priming. The pump is used to overcome the vacuum head in the tank. However, other pickup and recirculation systems can be used. For example, instead of using a vacuum to move the material from the squeegee to the tanks 12, 31, or 45, a suitable pump may be connected in the return line 16 or 48 and the liquid may feed from the tank (12, 31, or 45) to the surface by only gravity flow. The strainer trough of FIG. 3 is gravity flow for filtering and recycling of solution.

In place of a brush for furnishing agitation, the cleaning solution from the tank may be directed under high pressure by discharge nozzles, preferably discharging downwardly and forwardly in the normal direction of forward movement of the machine.

The manner of obtaining a cleaning solution containing a polyelectrolyte flocculating agent and a compatible detergent or soap can be varied. For example, a number of polyelectrolytes can be added in a concentrated form to a powdered detergent, next dried, then regranulated and thereafter mixed with water to form the cleaning solution. If the polyelectrolyte is of a type that it does not go into solution relatively rapidly, then desirably a concentrated aqueous solution is made ahead of time, and thereafter the concentrated solution and detergent are mixed with water to form the cleaning solution.

Also, dispensers may be provided to discharge metered amounts of the detergent and/or polyelectroly