Abstract:
The invention relates to a plant for separating grinding slurry originating from grinding machines into metal chips and grinding oil. According to the invention, a carrier bowl ( 3 ) in a frame ( 1 ) is filled with a divided volume of the grinding slurry ( 10 ). The carrier bowl ( 3 ) has a perforated plate ( 4 ) having an edge ( 5 ) as a floor and a sieve-like intermediate floor ( 8 ). By means of a lifting device ( 2 ), the carrier bowl ( 3 ) is moved to the effective region of an inductor plate ( 9 ) serving as a heater. The induction heat heats the ferromagnetic steel or iron particles present in the grinding slurry ( 10 ). Said heating effects a reduction in viscosity of the grinding oil in the grinding slurry ( 10 ), from which substantial portions flow downward through the openings ( 6 ) or ( 7 ). In certain cases, the effect can be improved by placing a steel plate on the free surface ( 16 ) of the grinding slurry layer ( 10 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a method for separating grinding oil from grinding slurries and to separating stations for carrying out the method. A method and a separating station of this type are known from DE 196 00 505 A1. 
         [0002]    The known method is already designed for creating the preconditions for disposal or reuse of the individual grinding slurry components. Reducing the content of grinding oil in the grinding slurry to a sufficient extent allows the metal component to be reused in a steelworks or in a foundry, or the grinding oil may be separated with such a degree of purity that it can be reconditioned and reused. The known method pursued the aim of reducing the costs of the separating or purifying method, with low expenditure on equipment and process control. As provided by the proposal of DE 196 00 505 A1, for this purpose a method of mechanical separation is combined with a thermal process. To be specific, according to DE 196 00 505 A1, the mechanical separation is performed in a centrifuge and the grinding slurry is at the same time heated, in that electrical eddy currents are generated by magnetic induction in the finely divided metallic phase. The required magnetic field may be generated by permanent magnets or electromagnets, which are arranged in a stationary manner in the rotating drum of the centrifuge. 
         [0003]    The known method has the disadvantage that the components of the grinding oil that are freed from the grinding slurry rise in the drum from the bottom upward and, as they do so, to some extent have to pass through the slurry cake that is deposited on the inner wall of the drum and becomes increasingly thick in the downward direction as a result of gravitational force. Furthermore, in the case of such a centrifuge, the slurry cake has to be scraped off the inner wall of the centrifuge at regular intervals, which entails considerable work. With the known method, continuous operation is only likely to be possible by providing two centrifuges, which are alternately operated and serviced. 
       SUMMARY OF THE INVENTION 
       [0004]    Against this background, the invention is based on the object of providing a method of the type mentioned at the beginning in which there are clear physical conditions both for introducing the heat into the grinding slurry and for removing those grinding oil components of which the kinematic viscosity is sufficiently reduced, so that reliable continuous operation is possible with great effectiveness and good utilization of the energy that is used. 
         [0005]    The advantageous effects of the method according to the invention come about firstly by the grinding slurry being spread out on a carrier into a flat layer of low height. exposing the free surface of the flat layer of grinding slurry to the effective range of an inductor plate acting from above provides clear geometrical conditions for the heating up of the layer. Since the heating takes place from above, the grinding oil that is reduced in its viscosity can leave the grinding slurry in a downward direction, because suitable openings are provided in the carrier. The grinding slurry heated up still further is consequently freed immediately of the grinding oil components that have become mobile and is well able to undergo further heating. The removal of the grinding slurry reduced in its grinding oil content takes place outside the effective range of the inductor plate, whereas the application of the layer of grinding slurry to the carrier may take place either in or outside its effective range. This arrangement ensures good utilization of the heat generated by the inductor plate, which is produced directly in the metal components of the grinding slurry. The spreading out and heating of a pizza dough may serve as a graphic analogy for the approach according to the invention. If the grinding slurry is to be applied to the carrier in the effective range of the inductor plate, this may take place for example from the side obliquely downward onto the carrier, into the intermediate space between the inductor plate and the carrier. 
         [0006]    Particularly good experiences have been had with a layer of grinding slurry 2 to 30 mm thick on the carrier. However, this size range is in any case not obligatory; depending on the characteristics of the grinding slurry and the degree of kinematic viscosity of the grinding oil, advantageous results can also be achieved with greater layer thicknesses. 
         [0007]    The inductive heating of the grinding slurry is of course dependent on how pronounced the ferromagnetic properties of the metal chips and/or the metal dust in the grinding slurry are. The increase in temperature may take place to differing degrees, by the induction heating being switched on with differing degrees of intensity and duration. When there are weaker ferromagnetic properties, it is expedient to place onto the free surface of the flat layer of grinding slurry a steel plate, which is located in the effective range of the inductor plate between the latter and the free surface of the layer of grinding slurry. In this case, the inductor plate especially heats up the steel plate, which then gives off its heat to the layer of grinding slurry lying thereunder. 
         [0008]    In particular if the grinding slurry is still contaminated by further substances, it may also be expedient to place in the flat layer of grinding slurry a further steel plate, which is then located at a distance above the carrier, that is to say is arranged within the layer of grinding slurry. This additional plate may be formed as a perforated plate or as a screen and is likewise inductively heated by the inductor plate. This heat source located within the layer of grinding slurry allows the disadvantages of weaker ferromagnetic properties or of contamination of the grinding slurry to be balanced out. 
         [0009]    In a first refinement, the method according to the invention may be performed by divided portions of the grinding slurry being spread out on a carrier bowl, which is then brought into the effective range of the inductor plate from below. This leads to a comparatively simple plant that is suitable for separating not excessively great amounts of the grinding slurry. 
         [0010]    Another procedure involves forming the carrier as an endless conveyor on which there are formed at least three carrier bowls, which are fed one after the other to the operations of a) spreading, b) inductively heating by the inductor plate and c) unloading. The movement of the endless conveyor in this case takes place cyclically, and for the heating operation the inductor plate is respectively lowered from above onto the carrier bowl concerned. The endless conveyor may in this case be formed as a belt conveyor with a linear conveying direction or else as a circular conveyor. Further advantageous refinements are specified in dependent claims relating to the individual methods. 
         [0011]    In addition, however, a completely continuous procedure is also possible, in that the method is carried out with a continuously moved belt conveyor, the upper strand of which serves as a carrier for a continuously deposited layer of grinding slurry and takes it through below a constantly activated inductor plate. In this case, the running speed of the upper strand controls the introduction of heat into the layer of grinding slurry, with in addition to this the possibilities of influencing the inductor plate. 
         [0012]    The methods according to the invention that are presented here can be combined well with pretreatment stages, which may comprise mechanical separation of the grinding oil from the grinding slurry and a subsequent preheating of the grinding slurry. In this way it is achieved that the electrical energy of the inductor plate is only introduced and utilized in the last treatment stage, in a particularly cost-effective way. 
         [0013]    With the method according to the invention that is presented here it is possible to separate considerably more grinding oil from the grinding slurry and pass it on for reuse. The grinding oil especially represents a not inconsiderable cost factor in abrasive working. The higher the proportion of grinding oil that can be recovered, the more cost-effective the grinding method as a whole. With the method according to the invention that is described above, it is now possible to separate so much grinding oil from the grinding slurry that only small residual amounts remain in the grinding slurry. But even these small residual amounts may have the effect that the grinding slurry is regarded as hazardous waste and is not necessarily suitable for being reused, for example by melting the abrasively removed metal. According to a further refinement of the invention, it is therefore provided that, after the separation of grinding oil by reducing its viscosity, in a downstream method step the residual amount of grinding oil is burned. This may be achieved, for example, by the device for the inductive heating of the grinding oil being controlled such that its temperature is raised into the range of the combustion temperature and it is burned. However, it is also possible that an additional energy source is provided, by means of which the remaining grinding oil is burned. Such an additional energy source may, for example, also be a burner. 
         [0014]    The invention also relates to separating stations, with which the method according to the invention can be carried out in its distinct individual forms. The individual separating stations are described hereinafter and shown in the drawings. It should be emphasized here in particular that the base of the carrier bowl, which is formed as a flat plate, may if need be also consist of a ferromagnetic material. This again applies to the case where the ferromagnetic properties of the metal component in the grinding slurry are insufficient or where the grinding slurry is contaminated. In this case, the inductor plate acts up to the base of the carrier bowl and generates from there a thermal effect. This is based again on the layer thickness of the grinding slurry spread out in the carrier bowls being relatively thin. 
         [0015]    Finally, the invention also relates to a processing plant in which grinding oil is separated from grinding slurries, in that a mechanically acting separating device is combined with an inductive heating means. The particular feature of this plant is that the individual procedures are separate and are carried out in different treatment stations. After a mechanically acting separating device and a preheating, inductive separation with a separating station according to the invention may be performed as the third and preferably last treatment. This can therefore be optimized particularly well. A fourth treatment station is preferably provided, comprising a separating station with an additional energy source or with a controllable inductive device for burning residual amounts of grinding oil. 
         [0016]    The invention is explained in more detail below on the basis of exemplary embodiments, which are represented in drawings. The figures show the following: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  explains in a longitudinal section the principle of a separating station according to the invention in a first embodiment. 
           [0018]      FIG. 2  shows an additional detail of the separating station according to  FIG. 1 . 
           [0019]      FIG. 3  shows the representation of a multistage processing plant in which a separating station according to  FIG. 1  forms the final stage. 
           [0020]      FIG. 4  explains a second embodiment of a separating station according to the invention. 
           [0021]      FIG. 5  shows the representation of a separating station according to  FIG. 4 , in which a further treatment unit is added. 
           [0022]      FIG. 6  shows the principle of a third embodiment in a view of the separating station from above. 
           [0023]      FIG. 7  shows the partially sectioned side view associated with  FIG. 6 . 
           [0024]      FIG. 8  explains the principle of a fourth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    In  FIG. 1 , a separating station according to a first embodiment is represented. Arranged here in a frame  1  is a lifting device  2 , which is indicated in the form of an adjusting piston with a solid piston rod that is suitable as a supporting column. The lifting device serves the purpose of moving a carrier bowl  3  upward and downward, cf. the directional arrow  14  for the lifting movement. The carrier bowl comprises a flat plate  4  with a rising-up rim  5 , surrounding the flat plate  4 , and has a circular cross section. The flat plate  14  is provided with openings  6 , through which separated grinding oil can flow off, cf. the directional arrow  15  for the flow-off direction. The base of the frame  1  is also provided with openings  7  for the same purpose. 
         [0026]    Arranged at a distance above the flat plate  4  of the carrier bowl  3  is a permeable intermediate base  8 . It may be formed as a screen base or in the form of a perforated plate. The through-flow openings of the intermediate base  8  are small in relation to the openings  6  in the flat plate  4 . The permeable intermediate base  8  makes it possible for grinding oil components with reduced viscosity to flow or drip off unhindered from the layer of grinding slurry  10 . The mesh width of the screen or the hole diameter of a perforated plate depends on the characteristics of the grinding slurry and the kinematic viscosity of the grinding oil. 
         [0027]      FIG. 2  shows further details with which the function of the carrier bowl  3  can be improved. An abutting frame  11  may be placed onto the carrier bowl  3 , surrounding the rim  5  of the carrier bowl  3  in a slidable manner and being supported in an elastically yielding manner on the carrier bowl  3 . The elastic yieldingness may be brought about by a series of helical springs  13 , which are located between the rim  5  of the carrier bowl  3  and the abutting frame  11 . The abutting frame  11  has for this purpose an inwardly angled profile. 
         [0028]    The abutting frame  11  is intended for interacting with an inductor plate  9 , which is located above the carrier bowl  3  and covers with its surface area the surface area of the carrier bowl  3 . The carrier bowl  3  and the inductor plate  9  are arranged extending parallel to one another. During the operation of the separating station, there is on the carrier bowl  3  a layer of grinding slurry  10 , which contains grinding oil. The carrier bowl  3  is moved by means of the lifting device  3  up close to the inductor plate  9 , until the layer of grinding slurry  10  is in the effective range of the inductor plate  9 . At the same time, however, the free surface  16  of the layer of grinding slurry  10  must not come into contact with the inductor plate  9 , since induction heating is produced in any case without direct contact. When the carrier bowl  3  is brought up to the inductor plate  9 , the abutting frame  11  with sliding properties has the effect that the layer of grinding slurry  10  located on the carrier plate  3  is held together, so that none of the grinding slurry  10  can fall down. 
         [0029]    The carrier bowl  3  and the inductor plate  9  covering it may be of a circular or square form or of some other form, for example rectangular. The induction heating principle is not affected by this. 
         [0030]    In the case of a grinding slurry of ferromagnetic materials, the inductor plate  9  has the effect that the heat is produced directly in the steel or iron parts of the grinding slurry. If, however, the ferromagnetic properties of the material are only weak or are absent, the steel plate  13  that can be seen in  FIG. 2  is placed onto the free surface  16  of the layer of grinding slurry  10 . The inductively generated heat is then produced in the steel plate  13  and is given off to the layer of grinding slurry  10  lying thereunder. Since the carrier bowl  3  and the abutting frame  11  themselves are not to be heated up, they should generally not consist of ferromagnetic materials, but for example of heat-resistant plastics. A placed-on ferromagnetic steel plate can in any event contribute to the heating of the divided layer of grinding slurry  10 . 
         [0031]    If, however, the grinding slurry does not just consist of metal chips and grinding oil, but is contaminated quite a lot by other components, for example filtering aids and additives, the heating of the grinding slurry by the inductor plate may be greatly reduced in spite of ferromagnetic grinding chips. In these cases, it is advantageous if a further steel plate  24 , which is perforated or formed as a screen, is also placed in the spread-out flat layer of grinding slurry  10  in the layer of grinding slurry. This additional plate  24  with the through-openings  25  is then located within the layer of grinding slurry  10 . The plate  24  is consequently arranged above the flat plate  4 , which forms the base of the carrier bowl  3 , or above the permeable intermediate base  8 . The induction heating in this case has the effect of strongly heating the additional steel plate  24 , and this heat is transferred to the layer of grinding slurry  10 , in which the additional plate  24  is embedded. 
         [0032]    Such a desired additional heating effect may in certain cases also have the effect that the flat plate  4  of the carrier bowl  3  is advantageously formed at least partially from a ferromagnetic material. 
         [0033]      FIG. 3  reveals how the separating station according to the first exemplary embodiment described thus far can be inserted into a processing plant for separating the grinding oil from grinding slurry. The plant represented comprises three treatment stations, of which the first is formed by a magnetic roller  17 . It serves the purpose of removing relatively large metal parts from the grinding slurry, and consequently relieving the downstream separating operations. 
         [0034]    From the magnetic roller  17 , the grinding slurry passes into the second treatment station, which is formed by a tank  18 . The tank is heated by means of a heat exchanger  19 , which is indicated as a heating coil. The heating of the heating fluid may take place in a special unit (not represented here) by the waste heat of peripheral units that are present at the cooling-lubricant reconditioning plant and the grinding machine. This preheating has the effect that the grinding oil of the grinding slurry is already reduced in its viscosity, so that the grinding slurry can be conveyed better. With a feed pump  20 , the grinding slurry is then fed to the third treatment station, which comprises the separating station according to  FIGS. 1 and 2  and begins at the feeding station  21 . 
         [0035]    The plant described thus far and the associated separating station operate as follows: after passing through the magnetic roller  17  and the heated tank  18 , the preheated grinding slurry is fed by the feed pump  20  to the feeding station  21 . Here it is important to spread out the grinding slurry in a thin layer on the carrier bowl  3 . The measures for this are not represented in the figures. The analogy of spreading out a pizza dough may serve as a graphic example. A layer thickness of 2 to 30 mm has proven to be particularly advantageous. However, in many cases, a layer thickness differing from this may likewise lead to usable results; depending on the application, the characteristics of the grinding slurry and the kinematic viscosity of the grinding oil contained therein lead to different procedures. Excessively thick layers have the effect that it takes too long for the amount of grinding slurry  10  located on the carrier bowl  3  to heat up and for the grinding oil components of which the viscosity is reduced to be discharged from the grinding slurry  10 . 
         [0036]    As can be seen in  FIG. 3 , the carrier bowl  3  at the feeding station  21  is in its lowered position and has been moved laterally out of the machine frame  1  together with the lifting device  2  (representation in dashed lines). After the spreading out of the grinding slurry into a thin layer  10 , located on the carrier bowl  3 , the lifting device  2  is moved back again and under the inductor plate  9 . The lifting device  2  then comes into action and moves the carrier bowl  3  with the divided layer of grinding slurry  10  located on it upward into the effective range of the inductor plate  9 . The separating station is formed in such a way that the inductor plate  9  is only electromagnetically activated when the respective divided layer of grinding slurry  10  has reached the effective range of the inductor plate  9 . The operation may be controlled automatically, so that the induction heating is switched on or off of its own accord when the divided layer of grinding slurry  10  reaches or leaves the effective range of the inductor plate  9 . 
         [0037]    The layer of grinding slurry  10  is then heated up. The increase in temperature may take place to differing degrees, by the induction heating being switched on with differing intensity and duration. The process may be automatically controlled, and in this way serve for saving energy. The influence of the temperature on the viscosity of the grinding oil is considerable. For example, a typical grinding oil at a temperature of 40° C. has a kinematic viscosity of 10 cst and at about 95° C. only of 3 cst. At the same time, commercially available grinding oils can be heated up to 80 to 120° C. without their decisive properties changing or additives being destroyed. 
         [0038]    On account of its reduced viscosity, components of the grinding oil can leave the layer of grinding slurry  10  located on the carrier bowl  3  and pass via the permeable intermediate base  8  and the openings  6  in the flat plate  4  of the carrier bowl  3  downward onto the base of the machine frame  1 . This base for its part again has openings  7  (cf.  FIG. 1 ), which provide access to a grinding oil collecting tank  22  lying thereunder. In this way, the components of the grinding oil that are separated in the layer of grinding slurry  10  pass in the form of drips or trickles finally into the grinding oil collecting tank  22 . After collecting a sufficient amount, the grinding oil can be passed on for reuse or reconditioning via the emptying nozzle  23 . 
         [0039]    With careful process control, a residual oil content of 5 percent and less can be achieved in the way described. Lastly, the largely dried layer of grinding slurry  10  must be removed from the carrier bowl  3 . As provided by the exemplary embodiment according to  FIG. 3 , for this purpose the carrier bowl  3  is removed from the inductor plate  9  by the lifting device  2 , that is to say is lowered in the downward direction. For unloading the carrier bowl  3 , the lifting device  2  is moved out again laterally from the frame  1 . The carrier bowl  3  can then be unloaded underneath the feeding station  21  or at some other location. However, this procedure is not obligatory; the loading and unloading may also be performed within the frame  1 , if sufficient space is available underneath the inductor plate  9 . 
         [0040]    A second exemplary embodiment of a separating station according to the invention is represented in  FIG. 4 . This provides that two rollers  32  are rotatably mounted on a machine frame  31 , at least one of which rollers is motor-driven. An endless conveyor  33  runs over the rollers  32  on the belt conveyor principle. The endless conveyor  33  may be formed as a filter belt, fabric belt or link belt that is permeable to grinding oil. The upper strand  33   a  of the endless conveyor  33  is supported almost over its entire length on a perforated plate  34 , so that it cannot sag. The length of the upper strand  33   a  determines the length of a conveying section; the conveying direction  35  runs from left to right in  FIG. 4 . Formed at regular intervals on the outer side of the endless conveyor  33  are carrier bowls  36 , the rising-up rims of which can be seen in  FIG. 4 . Since the bases of these carrier bowls  36  must in any case be permeable, they can be formed well by links of a link belt, but also by the filter belt or fabric belt itself that primarily comes into consideration for the endless conveyor  33 . 
         [0041]    Over the longitudinal center of the endless conveyor  33  there is the inductor plate  37 . Its distance in height from the carrier bowls  36  can be varied by means of a lifting device  38 . The lifting device  38  is again indicated as a piston-cylinder unit. The inductor plate  37  is in this case guided on guiding rods  39 , and the direction of the lifting movement is indicated by the double-headed arrow  40 . 
         [0042]    Fitted in the interior space between the two strands  33   a,    33   b  of the endless conveyor  33  is a collecting trough  41 , which extends almost over the entire conveying length of the endless conveyor  33  and consequently can receive all the drips or trickles of the grinding oil that leave the grinding slurry  45  located on the endless conveyor  33 . The run-off for the grinding oil located in the collecting trough  41  is provided laterally, that is to say perpendicularly in relation to the plane of the drawing. 
         [0043]    Provided underneath the subassembly comprising the entire longitudinal conveyor  33 , the rollers  32  and the collecting trough  41  is a catching trough  42 . This serves the purpose of receiving remains of grinding slurry and grinding oil that fall from the lower strand  33   b  of the longitudinal conveyor  33  when it is running back empty in the running direction  48  and the emptied carrier bowls  36  are directed downward. 
         [0044]    Arranged upstream of the lifting device  38  with respect to the conveying direction  35  of the endless conveyor  33  is an inlet slurry tank  43 . Located in this tank is the preheated grinding slurry with a still high content of grinding oil. A divided portion of grinding slurry  45  is taken from the inlet slurry tank  43  via an automatically actuated metering valve  44  when an empty carrier bowl  36  is located under said tank. Again, application in a thin layer should be accomplished; as has been made clear by the analogy with the pizza dough. A fixed doctor blade  49  serves the purpose of eliminating major irregularities in the layer thickness of the layer of grinding slurry  45 . The doctor blade  49  comes into effect when the carrier bowl  36  passes by it. 
         [0045]    Provided downstream of the lifting device  38  in the conveying direction  35  is the emptying station of a very simple configuration. Since the way in which they are formed on the flexible endless conveyor  33  means that the carrier bowls  36  are likewise flexible, it is sufficient to pass them over the roller  32  present at the end of the conveying section, the carrier bowls  36  opening and turning upside down, so that a slurry discharge occurs at the location  46 . The grinding slurry  45  reduced in its grinding oil content falls into an outlet slurry tank  47 . 
         [0046]    To operate the separating station according to  FIG. 4 , the endless conveyor  33  is moved cyclically, that is to say intermittently. When an empty carrier bowl  36  arrives under the inlet slurry tank  43 , a divided portion  45  of the grinding slurry is automatically spread out in this carrier bowl  36  into a thin layer by means of the metering valve  44 . In the subsequent cycle movement of the endless conveyor  33 , this divided layer of grinding slurry  45  arrives under the inductor plate  37 . By means of the lifting device  38 , at the same time the inductor plate  37  is moved downward, until the divided layer of grinding slurry  45  is in the effective range of the induction heating. The induction heating then switches on automatically, i.e. the inductor plate  37  is electromagnetically activated. The same details that have already been presented with respect to the first exemplary embodiment apply to the heating operation. 
         [0047]    Those components of the grinding oil of which the viscosity has been reduced sufficiently by being heated up are then freed from the layer of grinding slurry  45  and make their way down in the form of trickles or drips through the upper strand  33   a  of the endless conveyor  33  and the perforated plate  34  into the collecting trough  41 . With the next working cycle, the induction heating is switched off, and the residual slurry is discharged from the endless conveyor  33  at the location  46  and passes into the outlet slurry tank  47 . 
         [0048]    The exemplary embodiment as provided by  FIG. 5  largely corresponds to that according to  FIG. 4 . Therefore, the most important details of the separating station according to  FIG. 5  are designated by the same reference numerals as in  FIG. 4 . A difference in  FIG. 5  is the arrangement of a blasting head  50 , which is fixedly connected to the lifting device  38  of the inductor plate  37 . The lateral distance from the inductor plate  37  is in this case fixed such that the following effect comes about: when the inductor plate  37  is located exactly over a carrier bowl  36  and covers it, the blasting head  50  is located exactly over the adjacent carrier bowl  36  that is further forward in the conveying direction  35  of the endless conveyor  33 . While the inductor plate  37  is heating up the divided layer of grinding slurry  45  located thereunder, a stream of air is directed by the blasting head  50  onto the layer of grinding slurry  45  located alongside it, which has already been heated up. Drips of grinding oil that already have a reduced viscosity but have not yet been freed from the layer of grinding slurry  45  are thereby likewise driven out from the layer of grinding slurry  45 . In order that these drips of grinding oil can also be caught, the collecting trough  41  in the configuration according to  FIG. 5  has been extended up to the roller  32 , which is located at the end of the conveying section. 
         [0049]    In the case of the third embodiment according to  FIGS. 6 and 7 , the endless conveyor is formed as a circular conveyor  51 . In  FIG. 6 , which corresponds to a section B-B through  FIG. 7 , the principle is only shown schematically. The circular conveyor  51  has the form of a flat circular disk that is rotatable about its center axis  63 , that is to say forms a carousel. The direction of rotation of the circular conveyor  51  is identified by the directional arrow  52 . On the circular conveyor  51  there are three circular carrier bowls  53  for receiving and treating divided layers of grinding slurry  54 , cf.  FIG. 7 . The way in which they operate is the same in principle as in the case of the separating station already described, with the belt conveyor which is moved cyclically in a linear direction. Each of the three carrier bowls  53  passes one after the other through the treatment units of a) loading and spreading, b) inductively heating and c) unloading. 
         [0050]      FIG. 7 , which corresponds to a section along the line A-A in  FIG. 6 , shows further details. Mounted on a frame  55  is a drive unit  56 , which sets the circular conveyor  51  in rotation in a cyclical manner. The circular conveyor  51  is permeable in the region of the carrier bowls  53 , for example by means of a fabric pad. Underneath the circular conveyor  51  there is a fixed drip trough  57  with the run-off opening  58  for the grinding oil that has left the divided layer of slurry  54 . Shown above the circular conveyor  51  are a lifting device  59  with an inductor plate  60  and also an inlet slurry tank  61  with a metering valve  62 . 
         [0051]    The configurations as provided by  FIGS. 4 to 6  show endless conveyors  33  or circular conveyors  51  with in each case three carrier bowls  36  and  53 , respectively. However, this number is in no way obligatory. The arrangement of the blasting head  50  according to  FIG. 5  may alone mean that, as a further treatment station, it also requires a further carrier bowl  36 . Similarly, it may be expedient to arrange upstream of the station with the inductor plate  37  or  60 , in the conveying direction  35  of the separating station as provided by  FIG. 4  or in the direction of rotation  52  of the circular conveyor  51  as provided by  FIG. 6 , a heating-up station, so that the divided layers of grinding slurry  45  or  54  are once again separately heated up before reaching the inductor plate  37  or  60 , respectively. In such cases, a further carrier bowl  36  or  53 , respectively, would also have to be accommodated on the conveying devices. General production-related technical reasons could also necessitate a greater number of carrier bowls. 
         [0052]    In the separating stations with endless conveyors described thus far, cyclical, that is to say discontinuous, operation of the conveying devices has been assumed. In these cases, the dwell time of the carrier bowls  36 ,  53  under the inductor plate  37 ,  60  has an influence on the amount of heat that is introduced into the layer of grinding slurry  45 ,  54 . 
         [0053]    However, the method according to the invention may also be carried out in continuous operation. An example of this is shown in  FIG. 8 . Mounted here on a frame  71  are two rollers  72 , over which a belt conveyor  73  runs in the manner of a conveyor belt. The belt conveyor has an upper strand  73   a  and a lower strand  73   b  and is again formed as a filter belt, fabric belt or link belt that is permeable to grinding oil. The upper strand  73   a  is supported on a perforated plate  74  and moves in the conveying direction  75 . It thereby runs through in continuous operation under the stationarily arranged inductor plate  77 . A lifting device  78  serves in the case of  FIG. 8  only for the one-off setting of the correct distance respectively from the upper strand  73   a  or for the carrying out of servicing work. When operation is in progress, however, the inductor plate is spatially fixed and constantly activated. The remaining structural formation corresponds to the representation according to  FIGS. 4 and 5 . Here, too, the layer of grinding slurry  85  is applied from an inlet sludge tank  83  via a metering valve  84  to the upper strand  73   a  of the belt conveyor  73 . At the location  86 , the discharge of the grinding slurry  85  from the upper strand into an outlet sludge tank  87  takes place. The components of the grinding oil that are freed from the layer of grinding slurry  85  pass through the belt conveyor  73  and the perforated plate  74  into the collecting trough  81 . In the catching trough  82 , remains of the grinding slurry that still stick to the lower strand  73   b  of the belt conveyor  73  during the discharge can be caught. 
         [0054]    The main difference is that the grinding slurry located in the inlet sludge tank  83  is continuously deposited via the metering valve  84  on the likewise continuously moving belt conveyor  73 . In this way, an endless and continuously moved layer of the grinding slurry is produced, running through under the inductor plate  77 . Apart from the controllable power output of the inductor plate, decisive here for the amount of heat that is introduced into the layer of grinding slurry  85  is the speed at which the upper strand  73   a  of the belt conveyor  73  runs through under the inductor plate.