Patent Application
20120273429
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The invention is explained in more detail below on the basis of exemplary embodiments, which are represented in drawings. The figures show the following:
In
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.
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.
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.
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
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.
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.
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
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.
As can be seen in
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.
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.
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
A second exemplary embodiment of a separating station according to the invention is represented in
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.
Fitted in the interior space between the two strands 33a, 33b 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.
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 33b 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.
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.
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.
To operate the separating station according to
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 33a 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.
The exemplary embodiment as provided by
In the case of the third embodiment according to
The configurations as provided by
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.
However, the method according to the invention may also be carried out in continuous operation. An example of this is shown in
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 73a of the belt conveyor 73 runs through under the inductor plate.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 054 076.8 | Nov 2009 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/065887 | 10/21/2010 | WO | 00 | 6/28/2012 |
