Abstract:
A method of cleaning mineral-oil-based liquid cooling lubricants in which the cooling lubricants, which are continuously circulated in metal-working plants, are cleaned by a deposition filtration system. A continuous or discontinuous inoculation or introduction of filtering aid material is carried out in the filtration circuit during the filtration of the liquid cooling lubricant.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method for cleaning liquid cooling lubricants, especially those with a mineral-oil base, which preferably are in continuous circulation in metal-processing facilities, in which a deposition filtration system is provided. 
     Above all, liquid oil-based or emulsion-based cooling lubricants are used in metal-cutting facilities which cut off chips to cool and to lubricate cutting locations and to carry off abraded particles formed as a result. The liquid cooling lubricant is in continuous circulation, and to supply several metal-processing machines, the liquid cooling lubricant is re-introduced through a central supply facility into the individual machines. 
     To achieve ideal cross-sectional images of the workpiece, it is necessary to clean the liquid cooling lubricant after use. For this reason, continuously operating cleaning facilities are included in the circuit in which facilities the used cooling lubricant is freed, above all, from solid abraded metal particles by means of sedimentation facilities, magnets, or filters. 
     Deposition filters, in which a suspension is formed from the cooling lubricant together with a filtering aid and thereafter filtered through a carrier web with deposition of the filtering aid, are used especially for the extra-fine purification of the mineral-oil-based cooling lubricant. 
     Such a process is known from DE 25 37 384. In this process, highly surface-active, adsorbing, solid substances are used as filtering aids. Activated earth which has an average particle size of less than 0.06 mm is particularly preferred. 
     Systems are also known as deposition filters which work by deposition of internally-produced contamination. However, these processes do not offer a sufficient cleaning under high performance requirements. Under normal circumstances, therefore, filtering aids are deposited in a separate circuit before the actual filtration occurs by means of the interconnected second circuit. The contaminated oil or contaminated emulsion, which has been contaminated by grits and grinds, metal filings, or other types of contamination such as rolling scale or draw-in scale, travels from the metal-cutting machines or machine tools through a dirt return line into a dirty liquid buffer container. From there, the dirty liquid is conveyed via filter pumps through cartridge filters, in the process of which the contamination accumulates on the cartridges and forms a filter cake of dirt.. The oil purified by means of the filter cartridges travels into a clean tank and is once again transported from there to the machines or to sites of use. 
     One disadvantage of the known methods is that large quantities of the filtering aids are necessary. Disposal of these filtering aids is extremely difficult because this involves toxic substances which have to be disposed of following special disposal techniques. In addition, the filtration intervals are of relatively short duration since the filtering aid layer very quickly becomes loaded with the absorbed contamination, so only small amounts of liquid can be filtered. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to avoid the aforementioned disadvantages and to provide a method for cleaning liquid cooling lubricants in which the use of filtering aids is reduced and the filtration intervals are lengthened. 
     This object is achieved by the invention as described and claimed herinafter. 
     The substantial advantage of the invention is that the filtering aids are introduced into to the filter circuit in the form of an inoculation which takes place continuously or discontinuously. This has the advantage that the porosity of the deposits on the filter cartridges is increased and accordingly, the exposure time, i.e. the filtration interval, can be lengthened. In addition, this system provides the possibility of very precisely metering the amount of filtering aid applied and of increasing the quality of the filtration by means of the flow resistance of the liquid through the filtering medium. 
     One embodiment of the invention is designed so that the inoculation occurs by means of supplying the filtering aid in the contaminated liquid feed. The inoculation can thereby be performed directly in front of the deposition filter. In this way it is possible to achieve short flow paths for the filtering aid. It is also possible to carry out the introduction of the filtering medium on the suction side of the pump for the contaminated liquid. In this way, the pressure required for introduction is reduced. 
     In accordance with another embodiment of the invention, the inoculation is regulated in dependance on the openness of the porosity of the filter. A further reduction in the use of filtering aids is thus attained. 
     Of course, in addition to inoculation, there is the possibility of carrying out a base deposition of a filtering aid. This base deposition has a significantly thinner layer thickness, however, than was necessary for the previously known deposition filters. Cellulose or a coarse corn meal, for example, are suitable for the base deposition; cellulose is suitable for the inoculation. The deposition using diatomaceous earth used previously is thus no longer necessary. Diatomaceous earth is a health hazard which necessitates very high disposal costs. 
     Furthermore, the advantage in using cellulose or coarse corn meal as the inoculation or deposition material is that the material used can be disposed of thermally. The disposal costs are thus reduced considerably. 
     These and other features of the preferred embodiments of the invention also proceed from the description and the drawings as well as from the claims, whereby the individual features can be realized individually or together in the form of sub-combinations in embodiments of the invention and in other contexts and can represent advantageous embodiments which can be protected in and of themselves, for which protection is claimed here. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained below in further detail with reference to a working example shown in the accompanying drawing which is schematic representation of an installation for filtering cooling lubricants. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The FIGURE shows the schematic construction of a facility for cleaning liquid cooling lubricants. The cooling lubricant which is supplied by machine tools (not shown here) and which is loaded with shavings and contaminants is introduced through lines  10 ,  11 ,  12  into a dirty container  13 . From this dirty container  13  the liquid passes through line  14  and a pump  15  to a deposition filter installation  16 . Typically, several cartridge filters are located in a deposition filter installation. A deposition filter installation of this type is known, for example, from DE 29 08 625 A1. 
     The cleaned liquid leaves the installation through line  17  and then can be supplied to the machine tools once again through a clean tank and supplemental pumps which optionally may be provided. A line  18  and a valve  19  are arranged at the discharge opening of the deposition filter installation  16 . When the valve  19  is opened, the dirt and the filtering aid are conveyed into a container  20 . 
     A filtering aid for base deposition, for example cellulose, travels from a container  21  to a transport device  22 . This transport device has a metering device  23  and a screw conveyor device  24 . From here, the filtering aid is measured into a container  25  which is filled with oil or suspension. The filtering aid and the liquid are mixed with a stirring device  26 . This means that when the filter is started, initially the base deposition is prepared and is pumped to the filter. After the deposition of the base is completed, the deposition filter installation is ready for operation. During the normal circulation through the filter, oil-based infusion substance  28  from the inoculation container  25  is added to the filtration circuit continuously or discontinuously through line  27  and valve together with and simultaneously with the circulation through the filter; that is, oil-based inoculant is introduced continuously or discontinuously into the filtration circuit with an inoculation pump  29 . In order to avoid unnecessary energy consumption, this may advantageously be carried out by injecting the inoculant through pipeline  27  into pipeline  14 . 
     As a result of the inoculation process, the dirty liquid pumped through the filter cartridges is continuously also mixed with the inoculation substance, such that a mixture composed of inoculated deposition material and contamination forms on the filter cartridges. Because the inoculation deposition substance is injected continuously or discontinuously during the ongoing filtration, the porosity of the deposits on the filter cartridges, and respectively the property of the coating, increases, thus enabling a very effective and high caliber filtration quality. Likewise, a considerable increase in the exposure time is achieved through the inoculation. 
     To form a base deposit, the base deposition medium is provided in a container  30 , as shown in the figure, and is introduced from there into a transport device  31 , comprised of a measuring device  32  and a screw conveyor device  33 . The screw conveyor device feeds the base deposition medium into the container  34  in which oil or suspension is located. The base deposition material is mixed with the oil or suspension using the stirring device  35  and is introduced through line  36  and valve  37  into the deposition filtering device before a filtering process is begun. The base deposition medium thus deposits on the filter cartridges and forms a first filter layer. 
     As a result of the subsequent inoculation of the dirty liquid which is supplied, a better cooling lubricant material quality is achieved, meaning that the degree of purity of the cooling lubricants is increased.