Stone floors are conventionally ground by means of merely one guidable grinding machine. The operator is able to guide the machine in a desired direction by, with the handle, overlaying the net weight of the machine with a moment. Thereby, the angle between the axis of rotation of the grinding disc and the resultant of the pressure of the machine on the floor is altered so that the grinding disc will act as a kind of driving wheel for pulling the machine across the floor.

Typically, the grinding disc of the machine is quite simply composed of merely a single stiff disc on which are mounted for example grinding bodies based on diamond or carborundum.

The size of the grinding discs which can be used is limited by the stiffness. If the grinding discs are too big, they cannot follow unevennesses in the floor very well. However, stones of stone floors are often lying very unevenly, and large quantities of material must usually be ground off in order to get to grind the underlying areas of the floor as well which is necessary in order to give the finished floor the wanted uniform finish. Only grinding discs with relatively small diameters, for example between 350 mm and 430 mm, can therefore be used for this type of grinding machines.

The stiffness of the grinding discs furthermore put a limit for the rotational speeds which can be used without damaging the grinding bodies to between 150 and 400 rpm.

To this should be added that it is necessary to stop the actual grinding process at suitable intervals in order to remove excess grinding water with suspended slip from a just ground area of the floor.

All things considered, these conventional grinding machines therefore have a very low productive capacity, measured per man-hour. Normally, it would in this way only be possible to grind about 1 - 2 m2 stone floor per hour.

The object of the invention is to provide a grinding unit of the kind mentioned in the opening paragraph which has a much higher productive capacity than known per se.

The novel and unique features according to the invention, whereby this is achieved, is the fact that the grinding unit also comprises a number of handleless attached grinding machines which are mainly constructed in the same way as the control grinding machine and directly or indirectly are coupled to this whereby the capacity of the unit is increased proportionate to the number of attached grinding machines.

According to the invention, the productive capacity can be further increased by constructing each grinding disc of the grinding machine of an upper stiff disc connected to the output shaft of the motor, and a lower stiff disc for monting the grinding bodies of the machine, and an elastomeric intermediate disc for interconnecting the two stiff discs.

The intermediate disc, which for example can be made of foam rubber, now allows the lower disc with the grinding bodies to flexibly follow unevennesses in the floor. It is therefore not

necessary to grind large quantities of stone off the floor, as is the case with conventional machines, in order to give it a nice, uniform appereance. Thereby, the grinding time per grinding machine can be reduced by more than half compared to earlier when grinding uneven and badly laid floors.

The elastomeric intermediate disc furthermore has the effect of further reducing the grinding time per grinding machine as the flexibility of the intermediate disc permits increasing the rotational speed of the grinding discs to for example 800 rpm and the diameter of the grinding discs to about 500 mm without affecting the durability of the grinding bodies.

In consequence of the flexibility which the grinding disc obtains due to the presence of the elastomeric intermedite disc, diamonds can furthermore be used for the grinding bodies with advantage. For diamonds are precisely exceptionally effective at the above-mentioned high grinding speeds. The grit size of the diamonds can variate between finenesses of between 30 and 20.000. In the latter case, the floor will get a mirror-like finish. If a normal, good standard quality of the surface of the ground floor is wanted, diamonds of a fineness of up to 3,500 are used.

The different parts of the grinding discs, for example the grinding bodies are subjected to a not negligible wear during the working process. In order not to waste too much time when the worn parts are to be replaced, the mentioned parts can advantageously be assembled by bur-like assembling means of the kind which consists of two pieces of cloth with bur-like hooks on opposite sides for releasably interengaging when mounted. Thereby, for example worn grinding bodies can easily and quickly be replaced by new ones.

Stone floors are wet ground in order to avoid dust nuisances, to spare the grinding bodies and to obtain the wanted surface

finish, and it is therefore necessary to add water to the process. However, the grinding leaves rather large quantities of water with suspended slip from the floor. According to the invention, this excess water can be sucked away from the grinding discs without discontinuation of operations by means of a separate suction device. When a conventional grinding machine is used, the grinding process must per contra be stopped while the excess water is removed, and valuable working time is therefore gained by using a grining unit according to the invention instead.

The sucking away of the excess water can for certain be effectively done by placing a hanging skirt along the periphery of each cover plate. The bottom part of this skirt can advantageously be made of an elastomer, such as rubber, so that the skirt is able to follow unevennesses in the floor.

The skirt keeps the grinding water within the immediate working area of the grinding discs, and excess water with suspended slip can therefore easily and effectively be sucked away via an opening made in the skirt and connected to a suction hose which in its turn is connected to the suction device.

In an especially advantageous embodiment, the suction device comprises a water tank with a motor-driven ventilator placed above the water tank and serving for creating a negative pressure for via the suction hose sucking the excess water into the tank.

Furthermore, a centrifuge can be placed in the tank above the water surface, the sucked grinding water with suspended slip is made to pass this centrifuge before it, in filtered condition, runs into the tank reservoir.

The slip in the form of sludge is held back by the centrifuge where furthermore a filterbag advantageously can be placed for

collecting the sludge which therefore easily and quickly can be removed merely by removing the filterbag.

Finally, the filtered water in the tank can be recirculated to the grinding discs by means of a pump.

The above-described grinding water system is not only extremely labour-saving, but also profitable economically due to the saving of considerable quantities of expensive, fresh water, and because the grinding water essentially is recycled instead of being discharged into the public sewer system in a very polluted condition.

In an especially advantageous embodiment, adjacent grinding machines can be coupled by couplings which allow mutual vertical motion and angular displacement between the planes of the grinding discs. Each of the machines of the grinding unit can thereby follow unevennesses of the floor at the same time as the whole grinding unit is led mainly translatory across the floor as one concerted grinding unit.

The couplings can actually be of any kind as long as they allow the above-mentioned mutual vertical motions and angular displacements between the planes of the grinding discs. A simple and effective coupling which at the same time has an damping effect on the motion of the various grinding machines, can according to the invention consist of a vertically set spiral spring, the turnings of which are partially attached to a likewise vertically set bracket on each of the cover plates of two adjacent grinding machines.

This type of coupling is easiest to arrange when the cover plates have a polygonal contour and it is especially advantageous when the contour is hexagonal.

As will appear from the above stated, there is merely one handle on the grinding unit, the handle is only on the control machine. As mentioned earlier, guiding takes place by, with the handle, impressing the control machine a moment with a direction determining which direction the entire grinding unit is to follow. The moment will tilt the control machine in relation to the attached grinding machines, and this tilting is precisely possible because of the advantageous arrangement of the couplings which permit vertical intermotion and angular displacement between the planes of the grinding discs.

But the special arrangement of the couplings is in itself not enough to ensure a comfortable and safe guiding of the entire grinding unit. To obtain this effect, the number of attached machines must according to the invention be even, and the attached machines must in pairs have opposite directions of rotation. Thereby, the attached machines neutralise each others tendency to make the entire unit rotate and/or drive in the wrong direction.

The invention will be explained in greater details below, describing only exemplary embodiments with reference to the drawing, in which Fig. 1 is a schematic view of a single guidable control grinding machine which is led across a floor by an operator, Fig. 2 is a side view, partially in section, of the grinding machine shown in fig. 1 comprising an upper cover plate and a lower grinding disc made up of various parts, Fig. 3 is the same seen from below, Fig. 4 is a schematic view of a grinding unit comprised of the control grinding machine shown in fig. 1 - 3 now coupled to two attached grinding machines,

Fig. 5 is a schematic view of a second grinding unit comprised of the control grinding machine shown in fig. 1 - 3 coupled to four attached grinding machines, Fig. 6 is a schematic view of a third grinding unit comprised of the control grinding machine shown in fig. 1 - 3 coupled to four attached grinding machines as the one in fig. 5, but in another grouping, Fig. 7 shows a fourth grinding unit which corresponds to the one shown in fig. 6, but with hexagonal cover plates over the grinding discs.

Fig. 8 is a top view of a coupling for coupling the cover plates, which are only fragmentarily shown in the figure, of two adjacent grinding machines, Fig. 9 is the same, seen from the side, Fig. 10 is a schematic view and in perspective of the grinding unit shown in fig. 5 and a device for successively removing excess grinding water with suspended slip from the grinding process, and Fig. 11 shows a water tank with a motor-driven ventilator for via a suction hose successively sucking off the excess water from the grinding process, a centrifuge placed in the tank for separating the grinding sludge from the sucked water, and a submersible pump likewise placed in the tank for pumping the cleaned water back to be reused in the grinding process.

In fig. 1 is seen a single guidable grinding machine 1 led across a floor 2 by an operator 3 who controls the machine by means of a handle 4. In the following, it is assumed that the floor is horizontal. All directions are therefore, in the following, given from this assumption. In practise however,

the floor will usually have areas of big or small inclinations.

The handle 4 is pivotally mounted on a horizontal swing bed 5 on the grinding machine so that the operator can easily adjust the handle to a working position which suits his height and build. This adjustment is done by means of an adjusting rod 6 pivotally mounted on the grinding machine and an adjusting plate 7 fixed to the handle 4 and provided with a slit 8 extending in the longitudinal direction of the handle. The adjusting rod 6 forms an angle with the handle 4. A clamp bolt 9 driven through the slit 8 serves for, by means of a lever 10, clamping the adjusting rod 6 with the adjusting plate 7 and thereby with the handle 4.

When adjusting the handle, the operator loosens the clamp bolt and places the handle at an desired inclination, hereby slidingly displacing the clamp bolt in the slit. The clamp bolt is then tightened with the lever 10 after which the handle is tightly and firmly connected to the grinding machine.

The operator can now control the machine by, with the handle, tilting the grinding machine in a given direction. The friction of the grinding disc will be biggest on the spot where the machine subsequently is resting the heaviest against the floor, and the grinding disc will therefore act as a driving wheel for pulling the machine across the floor in the wanted direction.

In addition, two secondary wheels 11 are mounted on the grinding machine. By tilting the grinding machine backwards and down onto the secondary wheels, the operator can easily and quickly drive the grinding machine from one place to another without the grinding disc having to touch the floor.

In a way, the guidable grinding machine shown in fig. 1 could be a conventional grinding machine. However in the following description, it is assumed that the grinding machine is a control grinding machine according to the invention shown separately without attached grinding machines attached to it.

It has surprisingly turned out that an operator is able to control a grinding unit comprised of a control grinding machine with a number of attached grinding machines as easily as if there only was the control grinding machine. The invention is essentially built upon this realization, but in order to obtain the effect, a number of conditions which will be mentioned more explicitly later must be fulfilled.

The control grinding machine and the attached grinding machines are mainly constructed in the same way. Their construction will appear in more detail from fig. 2 and 3 which shows the control grinding machine shown in fig. 1.

The grinding machine is driven by a motor 12 with a output shaft 13. The motor is, by means of a flange 14, fixed to a cover plate 15 which i.a. serves for protecting the operator and other persons near by from coming into contact with the underlying grinding disc 16 which, during operation, rotates at a dangerously high speed, e.g. 800 rpm.

Conventional grinding discs only consist of one single stiff disc with mounted grinding bodies. The grinding disc 16 according to the invention consists of an upper stiff disc 17 connected to the output shaft 13 of the motor 12, a lower stiff disc 18 for mounting the grinding bodies 19 of the machine, and an elastomeric intermediate disc 20 for interconnecting the two stiff discs 17, 18.

According to the invention, the various parts 17, 18, 20, 22 of the grinding disc 16 are mutual assembled by means of

bur-like pieces of cloth 19 which in pairs work together for releasably assembling the two mentioned parts. One side of a pair of pieces of cloth is stuck to each of the two parts which are to be assembled. On the opposite side, each of the two pieces of cloth have a large number of bur-like hooks for releasably interengaging with corresponding hooks on the other piece of cloth. By means of this advantageous assembly method according to the invention, it is now possible to quickly and easily replace worn parts, e.g. the grinding bodies, without interrupting the grinding process considerably. The use of the assembly method overcomes a technical prejudice.

During operation, the grinding disc 16 is subjected to great stress in the form of i.a. bumps, impacts, and vibrations which, in deference to the durability of the grinding bodies, set narrow limits to how high a grinding speeds there can be used when conventional stiff grinding discs are used.

The elastomeric intermediate disc 20 is typically made of foam rubber of a thickness of e.g. 10 mm. In some cases, the intermediate disc can advantageously be made of several layers of foam rubber releasably assembled by the bur-like cloth pieces 19. The foam rubber damps the vibrations and absorbs yieldingly bumps and impacts which might affect the grinding disc during operation. The grinding disc can therefore work at far greater rotational speeds and with bigger diametres than known per se, for example at 800 rpm and with diametres of e.g. 500 mm without affecting the durability of the grinding bodies. Thereby, a substantial increase in the capacity of the grinding machine is obtained.

Diamonds are principally used as abrasive, these are set in grinding points 21 on the grinding bodies 22 which, in the shown case, are in the form of grinding segments 22. Diamonds are best at the above-mentioned high grinding speeds. Within

the scope of the invention, other kinds of abrasives can however also be used, for example carborundum.

A hanging skirt 23 is furthermore fitted along the peripheri of the cover plate, the skirt consists of an upper stiff ring 24 of e.g. iron and a lower elastomeric rubber ring 25 extending down to the floor. The significance and purpose of this skirt will be explained later.

By the aid of the above-mentioned means according to the invention, an unprecedented increase in the grinding capacity is obtained already in the case of just one grinding machine.

A further significant increase is obtained by coupling the control machine 1 to a number of attached grinding machines 26, for example as shown in fig. 4 - 7, by means of couplings 27 attached in mounting holes 28 in the cover plate 15.

In fig. 4, the control machine 1 is coupled with two attached machines 26 which are contra-rotating so that they jointly do not influence the entire grinding unit with any further torque than the torque of the control machine 1 itself which is absorbed by the operator. The operator can consequently control all three machines at the same time as easily as if there only were the control machine. As can be seen, the grinding capacity has been trebled.

With the arrangement shown in fig. 5 where the control machine 1 is coupled to two pairs of attached machines 26, a quintupling of the capacity is obtained.

The attached machines 26 can be grouped in different ways around the control machine 1. Fig. 6 thus shows an arrangement with two pairs of attached machines 26 attached to the control machine 1 just as the one shown in fig. 5, but grouped differently. In this case, the capacity has naturally also

been quintupled. The main difference is that the unit is narrower than the one shown in fig. 5.

In case of relatively confined spaces, the narrow unit shown in fig. 6 can advantageously be used. If there is enough room, it will in many cases be profitable to use the wide unit shown in fig. 5 which can grind a wide track at once. As can be seen, both the control machine and the attached machines all have mounting holes 28 for couplings 27. Thereby, a flexibility is obtained which allows for quick rearrangement from one type of grouping to another, and also for choosing the type of grouping most suited for the case in point.

The arrangement shown in fig. 7 corresponds quite to the one shown in fig. 6, the only difference being that the cover plates 29 are hexagonal with sides 30 presenting advantageously good possibilities for placing the mounting holes 28 with e.g. two holes along each of the sides of the hexagon. The hexagonal cover plates 29 furthermore gives the grinding unit a top side which makes it appear as a whole.

In the cases described above, the grinding unit was built of 3 and 5 grinding machines respectively, i.e. an uneven number which is necessary if the attached grinding machines in pairs are to cancel out each others moments. Depending on room, power supply, and manoeuvering possibilities, the number of grinding machines can easily be increased to for example 7 or 9, whereby a corresponding increase in the grinding capacity is obtained.

When the grinding unit is in operation, the control machine and the attached machine must be able to be led translatoric across the floor in one body. However, the floors are normally not even but on the contrary usually quite uneven. As the grinding unit exactly covers a relatively large floor space, the individual machines must separately be able to follow the

unevennesses of the floor, and each grinding machine must therefore be able to change angle and/or be displaced vertically in relation to the adjacent machines.

Fig. 8 and 9 show a coupling which allows such intermotion.

The main part of the coupling is a vertical set spiral spring 31 with windings 32 which along half of the spring turns in one direction and along the other half turns in the other direction so that the spring is torsion neutral.

The somewhat oblong windings of the spiral spring are along each of their two opposite sides tightened together by means of jaws 33. Each jaw is then with screws 34 screwed on a vertical set bracket 35 placed in a mounting hole 28 in one of two adjacent grinding machines 26.

In the shown case, each bracket 35 consists of a square pipe 36 on which is welded an angle 37. The square pipes 36 are fixed in corresponding square mounting holes 28 in the cover plate 15 and can therefore not turn in relation to this.

In fig. 7, the two sides of the mounting holes 28 are parallel to the sides 30 of the hexagonal cover plates 29. In this case, the geometry fits such that square pipes can be used without angle irons as brackets.

As can be seen, the only connection between the cover plates of two adjacent grinding machines is the spiral springs 31 which do not constitute a rigid, stiff connection but on the contrary a flexible connection which allows adjacent machines to alter angle and/or be vertically displaced in relation to each other which is necessary on the usually uneven floors which are to be ground. At the same time, the springs soften any vibrations which might be generated during the grinding process.

It must be noted that the above-described screw coupling only is an example. Within the scope of the invention, many other types of couplings with correspondingly flexible and softening properties can be used.

Grinding for example a stone floor is a hard process which require admission of grinding water. From e.g. a tap, the water is added to an area near the grinding disc inside the skirt 23 shown in fig. 2 and 3.

During the grinding process, large or small quantities of stone material in the form of fine dust are ground off and suspended in the water. The water filled with sludge is successively sucked away while the grinding unit is in operation by means of a suction device 38 via a suction hose 39 connected to an opening 40 made in the skirt 23.

This suction device 38 is shown schematically in perspective in fig. 10 where it serves five grinding machines grouped as shown in fig. 5.

Secondary suction hoses are led from the attached grinding machines to a manifold 42 on the control grinding machine 1.

The excess grinding water with suspended slip is successively sucked from there during operation to the suction device 38 via the suction hose 39.

The suction device 38 comprises a container 43 which, via a vacuum hose 44, is connected to, in this case, two vacuum pumps 45. When the vacuum pumps are in operation, the excess water with suspended slip is sucked into the container 43 where it is collected. The collected water and sludge is pumped by means of a submersible pump 46 via a pipe 47 to a waste pipe which for example is connected to the public sewer system.

Large quantities of water are used for the grinding of a floor and because of the high water prices, this will then represent a considerable part of the total costs for the grinding process. By using the suction arrangement shown in fig. 10, the used water with its content of sludge is discharged into the sewer system thereby polluting it.

Fig. 11 shows a second suction device 48 which is arranged in such a way that the sucked water or a considerable part of the water can be recycled and re-enter into the grinding process.

This variant comprises a container 49 with a detachable lid 50. On the lid, there is mounted a relatively high-speed motor 51 with an output shaft 52 on which is mounted an axial-flow ventilator 53 for generating a negative pressure in the container 49. By means of this negative pressure, excess water with suspended slip is sucked into the container at the top of this via a suction hose 54.

On the output shaft of the motor, there is furthermore mounted a centrifuge 55 into which the water from the suction hose 54 runs during operation.

The centrifuge separates the sludge from the water which, via holes 56 in the wall of the centrifuge, drains off into a water reservoir 57 at the bottom of the container 49.

The sludge can be very fine-grained. Therefore, a filterbag 58 is placed in the centrifuge for filtering off and collecting the sludge. Thereby, an advantage is obtained in that the sludge quickly and easily can be removed merely by taking the filterbag with its content of sludge out of the centrifuge.

In the water reservoir 57, there is placed a submersible pump 59 for via a water pipe 60 sending the cleaned water back into the grinding process.

As can be seen, substantial costs can be saved on the grinding water costs by means of this variant 48 of the suction device just as it is avoided that drain and sewer system are polluted unnecessarily. The water consumption is essentially reduced to the relatively small quantity of water used immediately during the grinding process. Fresh water can advantageously be added to the container 49.

The invention is described above and shown in the drawing on the basis of embodiment examples with an uneven number of grinding machines in each grinding unit. Within the scope of the invention, it is however also possible to have grinding units with an even number of grinding machines. For instance, the control grinding machine can pair with an attached grinding machine which is rotating in the opposite direction than the control grinding machine and counterbalance its torque. In this case, the operator is not loaded with any torque from the grinding unit.

When a conventional grinding machine is used for grinding stone floors, 1 - 2 m2 floor can typically be ground per hour.

If in stead a grinding unit according to the invention is used, there can, with for example seven coupled grinding machines, be ground up to 40 m2 per hour.