The present invention relates to a method of disinfecting a metalworking cooling and lubricating fluid by pumping said fluid from a collection sump of a machine tool to a reservoir of a disinfection system and back to the collection sump, whereby disinfection is performed in the disinfection system by means of an ultraviolet radiation unit in which said fluid flows downward in the form of a film under the influence of gravity over an internal longitudinal wall along which an ultraviolet radiation source is arranged.

Within the machining industry, cooling lubricants are used to cool machining processes and to lubricate the cutting tools. The cooling lubricants are mostly an emulsion (mixture of oil and water) in a ratio of 6-12% oil and the rest water. Previously, various additives and chemicals have been added to the liquid, e.g. to inhibit bacterial growth and fungus. However, newer EU legislation has banned a number of essential additives, which the oil companies have been forced to remove from the products and as a result there are major problems in the industry with bacteria and inappropriate side effects. The cooling water turns into a smelly swamp of fungus and bacteria and this is a huge problem in the industry. It is a problem in terms of health, since pathogenic bacteria now have good growth conditions, but it is also a problem in that the lubricating properties of the liquid are reduced, which has negative effects in terms of lifetime and economy of the machine tools.

US 3,264,055 discloses a method for treating fluids employed as coolants and lubricants in metalworking operations whereby said metalworking fluid is subjected to the action of ultraviolet radiation to prevent an increase in microorganism population. The fluid is continuously pumped from a collection sump of a machine tool and then flows downward under the influence of gravity over the interior walls of a vertical tube in the form of a relatively nonturbulent contiguous film. A source of ultraviolet radiation is positioned within the tube, thus subjecting the peripheral film of metalworking coolant to the influence of the ultraviolet radiation. The fluid then flows from the lower end of the tube into a collecting chamber which surrounds lower edge of the tube. From the collecting chamber, the metalworking coolant and lubricant liquid is pumped directly back to the machine tool in which a metal workpiece, during the working thereof, is subjected to spray of the metalworking coolant and lubricant liquid. After contacting the work piece, the coolant liquid is collected in a drain and eventually discharged into the collection sump of the machine tool.

However, known solutions based on ultraviolet radiation such as the one described just above are in reality not able to efficiently disinfect metalworking cooling and lubricating fluids and, furthermore, those solutions consume far too much energy.

It is a challenge that oil-based cooling lubricant appears milky white, because for this reason, it is very difficult for light to penetrate. In the known solutions, it has therefore been necessary to use extremely strong ultraviolet lamps, but nevertheless, in practical use, the results in terms of inhibition of the growth of bacteria and fungus have not been satisfactory. Moreover, the use of such extremely strong ultraviolet lamps results in an excessive consumption of electricity.

Therefore, it has proved difficult to use known solutions incorporating UV disinfection of the oil-based cooling lubricant.

The object of the present invention is to provide a method of disinfecting a metalworking cooling and lubricating fluid which is more effective in terms of disinfection than known solutions and which is also more energy efficient than known solutions.

In view of this object, the disinfection is performed in consecutive batch operations, whereby in each batch operation, a batch of fluid in the form of a part of the fluid contained in the collection sump of the machine tool is pumped to the reservoir of the disinfection system, the batch of fluid in the reservoir of the disinfection system is treated by circulating it through the ultraviolet radiation unit and back to the reservoir of the disinfection system for a certain period of time, and the treated batch of fluid in the reservoir of the disinfection system is pumped back to the collection sump of the machine tool. Surprisingly, it has been found that efficiently disinfecting consecutive relatively smaller batches of the metalworking cooling and lubricating fluid contained in the collection sump of the machine tool and returning each treated batch of fluid to the sump, result in a significantly more effective process both in terms of disinfection and in terms of energy consumption as compared to known continuous disinfection methods.

Without wishing to be bound by this explanation, it is believed that the reason for the effectiveness of the present invention as compared to known solutions is as follows. Many relevant types of pathogens are able to regrow to pre-treatment levels within hours of UV- exposure, if the dosage (effect x time) is insufficient to deactivate the DNA replication ability of the bacteria. Therefore, by continuously recirculating and disinfecting a large quantity of metalworking cooling and lubricating fluid, bacteria may be able to recover if it receives too low a dose of ultraviolet radiation and too much time passes before it is illuminated again. On the contrary, according to the present invention, by separately recirculating a relatively smaller batch of fluid, the individual bacteria may be exposed again and again within short time intervals whereby they may receive a sufficient dose so that they can no longer form colonies. By treating such relatively smaller batch of fluid for a sufficient time, the batch of fluid may in practical terms get completely disinfected which may result in a huge difference. The relatively smaller, but practically completely disinfected batch of fluid may be returned to the collection sump of the machine tool, thereby diluting a relatively large amount of fluid with a high bacteria content. However, as long as the disinfection process is faster than the bacteria's ability to form colonies, the total bacteria level in the collection sump of the machine tool will be gradually lowered.

Consequently, as a result of the present invention, the lifetime of metalworking cooling and lubricating fluid may be significantly extended, thereby saving large amounts of oil, water and further resources. Furthermore, significant health benefits may be achieved for operators exposed to such fluids on a daily basis. In a preferred embodiment, the volume of each batch of fluid to be treated corresponds to less than 30 per cent, preferably less than 15 per cent, more preferred less than 10 per cent and most preferred less than 5 per cent of the volume of fluid which may be contained in the collection sump of the machine tool. Thereby, an even more effective process both in terms of disinfection and in terms of energy consumption may be achieved.

In an embodiment, an amount of fluid corresponding to the amount of fluid contained in the collection sump of the machine tool is pumped to the reservoir of the disinfection system for disinfection and back to the collection sump at least once per day, preferably at least twice per day, and most preferred at least three times per day. Thereby, an even more effective process both in terms of disinfection and in terms of energy consumption may be achieved.

In an embodiment, the amount of fluid of each batch in the reservoir of the disinfection system is circulated through the ultraviolet radiation unit and back to the reservoir of the disinfection system at least 20 times, preferably at least 40 times, and most preferred at least 60 times before said batch is pumped back to the collection sump of the machine tool. Thereby, an even more effective process both in terms of disinfection and in terms of energy consumption may be achieved.

In an embodiment, the duration of each batch operation is at least 30 seconds per litre, preferably at least 40 seconds per litre, more preferred at least 1 minute per litre, even more preferred at least 2 minutes per litre, and most preferred at least 3 minutes per litre of fluid of each batch in the reservoir of the disinfection system. Thereby, an even more effective process both in terms of disinfection and in terms of energy consumption may be achieved.

In an embodiment, when treating the batch of fluid in the reservoir of the disinfection system, the fluid is circulated through the ultraviolet radiation unit by means of a pump which is pumping fluid from the reservoir of the disinfection system to the ultraviolet radiation unit and also directly to a fluid outlet arranged in the reservoir of the disinfection system. Thereby, the fluid in the reservoir of the disinfection system may be agitated appropriately without the use of a propeller or the like. Appropriate agitation may ensure a homogeneous disinfection of the fluid in the reservoir of the disinfection system and thereby a generally more effective disinfection process of the metalworking cooling and lubricating fluid in the collection sump of the machine tool.

In an embodiment, said pump is also pumping fluid from the reservoir of the disinfection system directly to an ejector adapted to suck fluid from the collection sump of the machine tool to the reservoir of the disinfection system when initiating treatment of each batch of fluid. Thereby, a separate pump for pumping fluid from the collection sump of the machine tool to the reservoir of the disinfection system may not be necessary.

The present invention further relates to a disinfection system for metalworking cooling and lubricating fluid, the disinfection system being adapted to pump such fluid from a collection sump of a machine tool to a reservoir of the disinfection system and back to the collection sump, the disinfection system including an ultraviolet radiation unit adapted to disinfect said fluid, the ultraviolet radiation unit having an internal longitudinal wall and an ultraviolet radiation source arranged along the internal longitudinal wall, the internal longitudinal wall being arranged in such a way that fluid entering the ultraviolet radiation unit may flow downward in the form of a film under the influence of gravity over the internal longitudinal wall.

The disinfection system is characterised in that it is adapted to perform disinfection of said fluid in consecutive batch operations so that in each batch operation, a batch of fluid in the form of a part of the fluid contained in the collection sump of the machine tool is pumped to the reservoir of the disinfection system, said batch of fluid is treated separately by circulating fluid from the reservoir of the disinfection system, through the ultraviolet radiation unit and back to the reservoir of the disinfection system for a certain period of time, and the treated batch of fluid in the reservoir of the disinfection system is pumped back to the collection sump of the machine tool. Thereby, the above- mentioned features may be obtained. In an embodiment, a pump is arranged to pump fluid from the reservoir of the disinfection system both to the ultraviolet radiation unit and to an ejector, the ejector is arranged to suck fluid from the collection sump of the machine tool through an inlet valve to the reservoir of the disinfection system, an outlet of the ejector is arranged to lead fluid through an outlet valve to the collection sump of the machine tool, and a control system of the disinfection system is adapted to control operation of the inlet valve and the outlet valve. Thereby, a separate pump for pumping fluid from the collection sump of the machine tool to the reservoir of the disinfection system and back again may not be necessary. The pump may run continuously and the duration of the batch process may be controlled by the control system and control valves.

In an embodiment, the volume of the reservoir of the disinfection system corresponds to less than 30 per cent, preferably less than 15 per cent, more preferred less than 10 per cent and most preferred less than 5 per cent of the volume of the collection sump of the machine tool. Thereby, an even more effective process both in terms of disinfection and in terms of energy consumption may be achieved.

The invention will now be explained in more detail below by means of examples of embodiments with reference to the very schematic drawing, in which

Fig. 1 illustrates a side view of a collection sump of a machine tool and a disinfection system for metalworking cooling and lubricating fluid according to the present invention, during filling of a reservoir of the disinfection system;

Fig. 2 is a view corresponding to that of Fig. 1, whereby the reservoir of the disinfection system has been filled with fluid, and during disinfection of fluid in the reservoir of the disinfection system;

Fig. 3 is a view corresponding to that of Fig. 1, during emptying of the reservoir of the disinfection system; and

Fig. 4 is a top view of the reservoir of the disinfection system of Figs. 1 to 3. Fig. 1 shows a collection sump 2 of a not shown machine tool and a disinfection system

4 according to the present invention for disinfection of metalworking cooling and lubricating fluid 1 present in the collection sump 2 of the machine tool. A wide variety of machine tools, such as CNC machines, incorporates, in a manner known perse, a collection sump for metalworking cooling and lubricating fluid which is used for cooling of machining processes and for lubrication of the cutting tools of the machine tools. The skilled person will understand that not shown tubing is used to lead metalworking cooling and lubricating fluid 1 from the collection sump 2 to the machine tool and back again to the collection sump 2.

The disinfection system 4 is adapted to pump the metalworking cooling and lubricating fluid 1 from the collection sump 2 of the machine tool through an inlet pipe 17 to a reservoir 3 of the disinfection system 4 and through an outlet pipe 18 back to the collection sump 2 again. As seen, the inlet pipe 17 has an inlet end provided with a floating intake device 30 adapted to lead fluid into the inlet pipe 17 only from just below the surface area of the fluid 1 where the concentration of oxygen is high and growth of bacteria is also high. The floating intake device 30 may be of a type well known in the art.

The disinfection system 4 includes an ultraviolet radiation unit 5 adapted to disinfect said fluid. The ultraviolet radiation unit 5 has an internal longitudinal wall 7 and an ultraviolet radiation source 8 arranged along the internal longitudinal wall 7. The internal longitudinal wall 7 is arranged in such a way that fluid entering the ultraviolet radiation unit

5 may flow downward in the form of a film 6 under the influence of gravity over the internal longitudinal wall 7. As seen, in the illustrated embodiment, the internal longitudinal wall 7 is formed on the inside of a vertically arranged tube 19. The ultraviolet radiation source 8 may have the form of a UV lamp, such as a fluorescent tube, which extends along a central axis of the vertically arranged tube 19. The length of the ultraviolet radiation unit 5 corresponds preferably to at least 80 per cent, and most preferred to at least 90 per cent, of the length of the vertically arranged tube 19. The tube 19 does not need to be arranged vertically, but could alternatively be arranged at an oblique angle. As an alternative to the vertically arranged tube 19, an obliquely arranged trough could be used with the ultraviolet radiation source 8 arranged above the trough.

As seen, in the illustrated embodiment, a lower end of the vertically arranged tube 19 is fixed in a hole of a lid 20 of the reservoir 3 of the disinfection system 4. An upper end of the vertically arranged tube 19 is provided with an inverted funnel 21 which has an outer diameter which is only slightly smaller than an inner diameter of the vertically arranged tube 19 and which is inserted into the upper end of the vertically arranged tube 19, thereby creating an inlet chamber 22 above a ring-formed inlet gap formed between an outer edge of the funnel 21 and the inside wall 7 of the vertically arranged tube 19. A feed tube 23 for the ultraviolet radiation unit 5 has an outlet end opening into the inlet chamber 22 of the vertically arranged tube 19. An inlet end of the feed tube 23 is connected to a pump 10 arranged to pump the metalworking cooling and lubricating fluid 1 from the reservoir 3 of the disinfection system 4. The inverted funnel 21 and the ring- formed inlet gap formed thereby between the inlet chamber 22 and the inside wall 7 of the vertically arranged tube 19 may cause the fluid entering the inlet chamber 22 to flow as a film downward along the inside wall 7 of the vertically arranged tube 19. The inverted funnel 21 and the ring-formed inlet gap formed thereby between the inlet chamber 22 and the inside wall 7 of the vertically arranged tube 19 is understood to be a separate invention which is independent of whether the disinfection system is batch operated or continuously operated. In the illustrated embodiment, the pump 10 has the form of a submersible pump.

The disinfection system 4 is adapted to perform disinfection of said fluid in consecutive batch operations so that in each batch operation, a batch 9 of fluid in the form of a part of the fluid 1 contained in the collection sump 2 of the machine tool is pumped to the reservoir 3 of the disinfection system 4, said batch 9 of fluid is treated separately by circulating fluid from the reservoir 3 of the disinfection system 4, through the ultraviolet radiation unit 5 and back to the reservoir 3 of the disinfection system 4 for a certain period of time, and the treated batch of fluid in the reservoir 3 of the disinfection system 4 is pumped back to the collection sump 2 of the machine tool. As seen, in that the feed tube 23 for the ultraviolet radiation unit 5 is provided with a Double Tee fitting 24, the pump 10 is arranged to pump fluid from the reservoir 3 of the disinfection system 4 both to the ultraviolet radiation unit 5 and to an ejector 12. The ejector 12 is arranged to suck fluid from the collection sump 2 of the machine tool, through the inlet pipe 17, through an inlet valve 13 arranged in the inlet pipe 17, and to the reservoir 3 of the disinfection system 4. An outlet 14 of the ejector 12 is arranged to, via a Tee fitting 25, lead fluid through an outlet valve 15 to the collection sump 2 of the machine tool. A control system 16 of the disinfection system 4 is adapted to control operation of the inlet valve 13 and the outlet valve 15. As seen, the Tee fitting 25 furthermore connects the outlet 14 of the ejector 12 to a discharge valve 26 which may lead fluid through a discharge tube 27 to the reservoir 3 of the disinfection system 4. The discharge valve 26 is also controlled by the control system 16.

As further seen, by means of the Double Tee fitting 24 provided in the feed tube 23, the pump 10 is also arranged to pump fluid from the reservoir 3 of the disinfection system 4 directly to a fluid outlet 11 arranged in the reservoir 3 of the disinfection system 4. The fluid pumped to the fluid outlet 11 may be regulated by means of a manual valve 31 arranged in a tube 32 connecting the Double Tee fitting 24 and the fluid outlet 11. Thereby, the fluid in the reservoir 3 of the disinfection system 4 may be agitated appropriately without the use of a propeller or the like. Fig. 4 illustrates the reservoir 3 seen from above. As seen, in the illustrated embodiment, the reservoir 3 has an octagonal cross-section in order to minimize dead spaces at corners, thereby ensuring better agitation. Of course, the reservoir 3 could have other suitable forms, such as a circular crosssection.

As seen, the outlet valve 15 controlled by the control system 16 is a three way valve that may optionally lead fluid to a first and/or a second tube 28, 29. Each tube 28, 29 may be positioned at a different location in the collection sump 2 of the machine tool, preferably at the bottom of the collection sump 2. In this way, disinfected fluid may dilute the fluid in the collection sump 2 at different locations for each batch of disinfected fluid being led back to the collection sump. This may be advantageous in order to obtain the best disinfection of the entire volume of fluid in the collection sump. More than two different tubes 28, 29 may be employed and arranged at different locations in the collection sump.

As seen, the reservoir 3 of the disinfection system 4 is provided with a level switch 33 adapted to give input to the control system 16 about the level of fluid in the reservoir 3. The control system 16 may use this information when filling and emptying the reservoir 3 as explained in the following.

Preferably, the volume of the reservoir 3 of the disinfection system 4 corresponds to less than 30 per cent, preferably less than 15 per cent, more preferred less than 10 per cent and most preferred less than 5 per cent of the volume of the collection sump 2 of the machine tool.

Preferably, the volume of each batch 9 of fluid to be treated corresponds to less than 30 per cent, preferably less than 15 per cent, more preferred less than 10 per cent and most preferred less than 5 per cent of the volume of fluid which may be contained in the collection sump 2 of the machine tool.

Preferably, an amount of fluid corresponding to the amount of fluid contained in the collection sump 2 of the machine tool is pumped to the reservoir 3 of the disinfection system 4 for disinfection and back to the collection sump 2 at least once per day, preferably at least twice per day, and most preferred at least three times per day.

Preferably, the amount of fluid of each batch 9 in the reservoir 3 of the disinfection system 4 is circulated through the ultraviolet radiation unit 5 and back to the reservoir 3 of the disinfection system 4 at least 20 times, preferably at least 40 times, and most preferred at least 60 times before said batch 9 is pumped back to the collection sump 2 of the machine tool.

Preferably, the duration of each batch operation is at least 30 seconds per litre, preferably at least 40 seconds per litre, more preferred at least 1 minute per litre, even more preferred at least 2 minutes per litre, and most preferred at least 3 minutes per litre of fluid of each batch 9 in the reservoir 3 of the disinfection system 4.

The operation of the disinfection system 4 is controlled by the control system 16 as follows. It is noted that electric cables 34 generally illustrate connections between the control system 16 and the illustrated controlled valves 13, 15, 26, the pump 10, the level switch 33 and the ultraviolet radiation source 8. The flow of fluid in the tubes is generally indicated by means of arrows.

In Fig. 1, the reservoir 3 of the disinfection system 4 is being filled with metalworking cooling and lubricating fluid 1 from the collection sump 2 of the machine tool through an inlet pipe 17. This is achieved by the control system 16 by maintaining the pump 10 on, maintaining the valve 15 closed, maintaining the valve 13 open, maintaining the valve 26 open. Furthermore, optionally, the ultraviolet radiation source 8 is maintained on during filling in order to initiate disinfection already before the reservoir 3 has been filled which may shorten the batch period.

Turing now to Fig. 2, when the level switch 33 indicates that the reservoir 3 of the disinfection system 4 has been sufficiently filled, the control system 16 closes the valve 13 in order to stop the filling operation. Disinfection is now continued as illustrated in Fig. 2 until a set period of time has elapsed. A suitable period of time may be determined, by calibration, when first starting up the disinfection system 4, by testing disinfection during different time periods and measuring the level of bacteria in the fluid.

Turing now to Fig. 3, when the set period of time has elapsed, emptying of the reservoir 3 of the disinfection system 4 is initiated in that the control system 16 opens the valve 15, closes the valve 26 and closes the valve 13. Furthermore, optionally, the ultraviolet radiation source 8 is maintained on during emptying in order to continue disinfection during emptying which may shorten the batch period.

Typically, the volume of the collection sump 2 of the machine tool is 300 to 1500 litres, however, other sizes are possible. As an example only, the volume of the reservoir 3 of the disinfection system 4 could be 20 to 30 litres, however, other sizes are possible. As an example only, the batch processing time could be between 15 and 90 minutes, however, other batch processing times are possible, depending among other things on the size of the collection sump 2 and on the size of the reservoir 3 of the disinfection system 4.

The person skilled within the art will understand that although the method of disinfecting a metalworking cooling and lubricating fluid and the disinfection system for metalworking cooling and lubricating fluid according to the present invention has been de- scribed and illustrated by means of a system operated by a control system, one pump, an ejector and several valves, the method and system according to the present invention can be employed in many different ways. For instance, separate pumps may be arranged for each of the following operations: Filling of the the reservoir 3 of the disinfection system 4, circulation of fluid through the ultraviolet radiation unit 5, and emptying of the reservoir 3. Thereby, some or all of the illustrated valves may be superflous, but in some such embodiments valves may nevertheless be employed.