The present invention relates to a floor wet-grinding method of the kind defined in the preamble of the following independent method Claim.

The invention also relates to floor wet-grinding apparatus of the kind defined in the preamble of the following apparatus Claim.

Thus, the invention relates to a wet-grinding method, preferably for wet-grinding of floors, particularly stone floors or floors comprised of a stone-like material, with the aid of a grinding tool, wherein liquid is delivered to the tool grinding area and a resultant mixture of particulate solids and liquid is sucked away and passed to filtering equipment in which the particulate material i.e. solids, is separated from the mixture and the liquid returned to the region of the grinding tool (EP-A1-0 549 202).

US-A-3,701,221 teaches a dry grinding machine for grinding terrazzo floors, said machine being coupled to a vacuum cleaner that separates the solids .

Wet-grinding is the only usable method in practice for grinding floors that are made of stone or stone-like material.

According to the known technique for wet-grinding floors, a stream of water is delivered to the working area of the grinding tool and it is endeavoured to transport the resultant mixture of liquid (water) and solids to a

collecting container that lies far away from the grinding area. For instance, it has been attempted to absorb the liquid with sawdust or the like upon completion of a working operation, and then shovel-up the wet sawdust and solids and carry the same to a container. This mixture of water and solids (and sawdust) in the container constitutes a serious dumping problem. Large quantities of water are involved and the container therefore quickly becomes very heavy. This water cannot simply be emptied into the sewage system, because it contains substantial quantities of suspended solids.

Accordingly, an object of the invention is to provide a method and apparatus that will enable the suspended solids to be separated by suction from a liquid/solids suspension, so as to enable the solids to be dumped as dry waste and the liquid to be recycled to the grinding machine.

This object is achieved by the inventive method according to the following Claim 1.

Further developments of the method are set forth in the dependent method Claims.

The aforesaid object is also achieved with an inventive apparatus according to the independent apparatus Claim.

Further developments of the inventive apparatus are set forth in the dependent apparatus Claims. An essential feature of the invention resides in the provision of a plurality of filter bags to which the mixture of liquid and solids is delivered sequentially from the grinding machine, wherein the

mixture is delivered to a bag or to a group of bags until the bag or bags has/have received a determined quantity of solids. The flow of solids and water is then transferred from the grinding machine to a fresh filter bag or group of filter bags, which are filled with water/solids until this bag or these bags has/have also received a predetermined quantity of solids.

Because solids form a filter cake on the inersurface of the filter bag as filtering progresses, de-watering of the water/solids mixture in the bag will take place more slowly with increasing quantities of solids received in the bag concerned. On the other hand, the filter bag will have a filtering capacity that will enable a very large proportion of solids to be separated by the filter bag. Consequently, there is found an optimum with respect to a practical balance between filtering capacity and surface area of the filter bag and the amount of solids that shall be received by respective filter bags, this optimum resulting, in practice, in a time requirement in the order of hours for the liquid to filter- out gravimetrically from one such filled bag.

By providing a plurality or a multiple of bags in accordance with the invention, some of the filled bags can be drained of liquid during the time in which at least one of the remaining bags receives a flow of liquid/solids from the grinding machine. The filtrate will preferably be led from the bags to a common disposable secondary filter and from there to a holding tank from which filtrate/liquid can be recycled to the grinding tool.

Subsequent to being drained of liquid, the filter bags can be sealed in a conventional manner and then dumped as dry waste.

Sequential filtering of the mixture in a plurality of groups of filter bags also ensures that the amount of circulating liquid can be maintained at a relatively low level, since the filtrate that can be returned to the grinding tool is reskirted in an essentially even flow. One important advantage afforded by the invention is that the filtrate returned to the grinding tool is essentially free from solids.

The filter bags may be comprised of conventional sackcloth, conveniently a sackcloth that will afford the desired filtering effect.

By allowing the filter bags to have the form of bags in which the solids can be dumped, and by also allowing the secondary filter to be comprised of disposable material, there is no need to clean the filter material in the filtering equipment.

The apparatus for collecting solids and for separating the filtrate may have the form of a trolley that is towed behind the actual grinding apparatus, or at least placed in the room in which the grinding apparatus operates. The trolley will preferably carry all peripheral equipment, such as pumps. Because the grinding tool of the grinding apparatus is shielded by a skirt-like device, and because the resultant mixture of solids and water is restrained inwardly of the skirt, the inventive grinding equipment can be used with a minimum of encroachment in the area in which floor grinding shall take place, for instance normal activities, and one of

normal skill in this art will realize that this possibility affords very important economical advantages. Furthermore, the skilled person will realize that regrinding of stone floors in dwelling entrance halls and the like can be carried out without needing to interrupt passage of people through the hall while the floor is being ground.

By placing all bags (and preferably also collecting trays and liquid containers for filter liquids) in a vacuum chamber, the flow of liquid and solids can be drawn by suction from area defined by the skirt, via the hose and the conduit system, to the bags that communicate with the skirt interior, with the aid of a vacuum pump that evacuates said chamber. When several bags are in communication with the skirt interior simultaneously, the flow will be directed primarily to the bag or bags that offers/offer the lowest flow resistance, i.e. the bag or bags that has/have the lowest load at that moment in time. The bags will therewith be filled uniformly, i.e. until it is time to switch the flow to the next group of bags. The time at which the flow shall be switched to a fresh group of bags (empty bags), can be determined by measuring the chamber subpressure.

The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawing, in which

Fig. 1 is a schematic, partially section side view of an inventive arrangement;

Fig. 2 is a schematic view from above, taken on the line II- II in Fig. 1; and

Fig. 3 illustrates the bags and the trays placed beneath a subpressure chamber.

Shown in Fig. 1 is a stone floor 30 that is to be ground with the aid of a grinding machine 1 that includes a motor-driven grinding disc 2 which is surrounded by a skirt 3 whose rim seals against the floor 30. Liquid is delivered to the interior space defined by the skirt 3 through a hose or conduit means 4 extending from a liquid storage means/water storage means 12 carried on a trolley 29. The conduit means 4 includes a pump 14. Dust and other solids that are produced as the floor is ground will be bound together by the water delivered to the skirt interior. This prevents stone dust from spreading outside the skirt 3. The mixture of water and particulate solids is withdrawn by suction through a suction conduit means 5 that includes a pump 6 carried on the trolley 29. The mixture of solids and water is transported from the pump 6 via a riser pipe 37 to a distribution conduit 7 and to branch pipes 8 via closure valves 27. The branch pipes 8 include stub pipes 9 which include closure valves 10. A filter bag 11, preferably a disposable filter bag, is fitted onto each pipe stub 9. A collecting tray 16 provided with a disposable filter 17 is placed beneath the bags 11.

The tray 16 has an outlet to a secondary tray 18, which is also provided with a disposable filter, referenced 19. The secondary tray 18 is emptied into the liquid container 12, from which the water is recycled to the interior of the skirt 3, via the conduit 4 and the pump 14.

The drive motors of the grinding machine 1 and the pumps 6 and 14 may be electrically powered by means of mains connected cables (not shown).

While the illustrated equipment is in operation, the valve 27 to one of the branch-conduits 8 may be open and the other two valves 27 of the two remaining branch conduits 8 initially closed. For instance, all valves 10 are open in the branch conduit 8 that can now receive the flow of particulate material and water via the hose 5, the pump 6, the riser pipe 37, the distribution pipe 7 and the open valve 27. After, e.g., an hour's work with the grinding machine, the loaded filter bags 11 will be filled to an extent at which they are no longer able to receive the flow from the pump 6. The open valve 27 is then closed and one of the earlier closed valves 27 is opened, so as to direct the flow into the previously unused bags 11. As these fresh bags are being filled, the water in the earlier filled bags 11 is able to run from the bags gravimetrically, so that the bags 11 containing solids can be disconnected from the connector pipes 9 and removed without liquid spillage, wherewith the bags filled with solids can be readily dumped in a refuse container, which may subsequently be emptied onto a public waste tip.

The filters 17, 18 may also be dumped and replaced with new disposable filters, at the end of a working period. The filter bags 11 are comprised of disposable bags that form both filters and storage bags for drained particulate solids.

Fig. 3 illustrates a subpressure chamber 50 that is evacuated with the aid of a vacuum pump 52 via a conduit 51. The conduit 8 carrying the pipe stubs 9, the valves 10, the bags

11, and the trays 16, 18 and container 12 are placed within the chamber 50. The chamber interior is accessible through sealed doors 55.

The pump 6 of the Fig.l embodiment can be omitted in the embodiment illustrated in Fig. 3, because the evacuation pump 52 will provide sufficient suction power through the bags 11 that communicate with the skirt interior 3. The flow is distributed uniformly between the bags, so that the bags will be filled generally to mutually the same extent. The subpressure in the chamber 52 can be measured to provide a basis for establishing when the connected bags can be considered as being full.