In-Line Measurement of Nitrite Content in Metalworking Fluids

Abstract

An apparatus for in-line monitoring of nitrite content in a metalworking fluid is provided, the apparatus comprising a sample inlet for receiving a sample of a metalworking fluid, a dilution inlet for receiving a dilution fluid, a reagent inlet for receiving a photoactive reagent, a reaction volume for containing a sample mixture in fluid communication with the sample inlet, dilution inlet and reagent inlet, a photometer for monitoring the sample mixture, and a flow control system for controlling fluid flow in the apparatus, to: selectively introduce the sample, the dilution fluid and/or the photoactive reagent from the respective inlets to the reaction volume to form the sample mixture, retain the sample mixture in the reaction volume and discharge the sample mixture from the reaction volume.

Claims

1. An apparatus for in-line monitoring of nitrite content in a metalworking fluid, comprising: a sample inlet for receiving a sample of a metalworking fluid; a dilution inlet for receiving a dilution fluid; a reagent inlet for receiving a photoactive reagent; a reaction volume for containing a sample mixture in fluid communication with the sample inlet, dilution inlet and reagent inlet; a photometer for monitoring the sample mixture; and a flow control system for controlling fluid flow in the apparatus to: (a) selectively introduce the sample, the dilution fluid or the photoactive reagent from the respective inlets to the reaction volume to form the sample mixture; (b) retain the sample mixture in the reaction volume; and (c) discharge the sample mixture from the reaction volume.

2. The apparatus of claim 1, wherein the reaction volume comprises a reaction vessel and a photometer flow path for providing the sample mixture from the reaction vessel to the photometer.

3. The apparatus of claim 2, wherein the flow control system comprises a first pump for providing the sample mixture from the reaction vessel to the photometer flow path, and for discharging the sample mixture from the reaction vessel.

4. The apparatus of claim 3, wherein the flow control system comprises a first valve for selecting whether the first pump provides the sample mixture to the photometer flow path, or discharges the sample mixture from the reaction volume.

5. The apparatus of claim 2, wherein the flow control system comprises a second valve for selecting whether the sample mixture is discharged from the reaction vessel or the photometer flow path.

6. The apparatus of claim 1, wherein the flow control system comprises a sample pump for introducing the sample into the reaction volume, a dilution pump for introducing the dilution fluid into the reaction volume, or a reagent pump for introducing the photoactive reagent into the reaction volume.

7. The apparatus of claim 1, wherein the reaction volume comprises a first discharge flow path for discharging the sample mixture from the reaction volume and a second discharge flow path for only partially discharging the sample mixture from the reaction volume to leave a pre-defined volume of the sample mixture in the reaction volume.

8. The apparatus of claim 7, wherein the flow control system comprises a t valve for selecting whether the sample mixture is discharged through the first or second discharge flow path.

9. The apparatus of claim 7, wherein the first pump is arranged to discharge the sample mixture through the first and second discharge flow paths.

10. The apparatus of claim 6, wherein the sample pump comprises a multichannel pump for introducing the sample and the dilution fluid into the reaction volume at the same time, for example a dual channel pump in fluid communication with the sample inlet and the dilution inlet.

11. The apparatus of claim 1 further comprising a controller configured to operate the apparatus to: (i) provide a first volume of the sample of a metalworking fluid to be tested from the sample inlet into the reaction volume; (ii) provide a second volume of the dilution fluid from e dilution inlet into the reaction volume to form a diluted sample mixture; (iii) provide a third volume of the photoactive reagent from the reagent inlet into the reaction volume to form an activated sample mixture; and (iv) obtain a photometry measurement of the activated sample mixture using the photometer, wherein the photometry measurement provides an indication of the nitrite content of the sample.

12. The apparatus of claim 11, wherein the controller is configured to operate the apparatus to provide the first volume by introducing a volume of the sample greater than the first volume into the reaction volume, and discharging metalworking fluid from the reaction volume to leave the first volume of the sample.

13. The apparatus of claim 11, wherein the controller is configured to operate the apparatus to circulate the diluted sample mixture and/or the activated sample mixture within the reaction volume.

14. The apparatus of claim 13, wherein providing the second volume of dilution fluid and/or providing the third volume of photoactive reagent, is at least in part simultaneous with the circulating of the diluted sample mixture and/or the activated sample mixture within the reaction volume respectively.

15. The apparatus of claim 1, wherein the controller is configured to obtain a photometry measurement of the diluted sample mixture before introducing the photoactive reagent.

16. The apparatus of claim 11, wherein the controller is configured to periodically obtain measurements that provide an indication of the nitrite content of different samples of metalworking fluids.

17. The apparatus of claim 16, wherein between measurements the controller is configured to operate the apparatus to empty the reaction volume of sample mixture and/or to flush the apparatus with dilution fluid or the sample.

18. The apparatus of claim 11, wherein the controller is configured to record the photometry measurement or nitrite content of the sample in a database, or to provide an indication when the nitrite content of the sample is outside a threshold range.

19. The apparatus of claim 11, wherein the controller is configured to provide an indication and/or a control signal to adjust the nitrate content of a metalworking fluid based on the indication of the nitrite content of the sample.

20. A method for in-line monitoring of nitrite content in metalworking fluids using an apparatus as defined in claim 1, the method comprising: (i) withdrawing a sample of a metalworking fluid to be tested from a metalworking fluid stream and providing a first volume of the sample from the sample inlet into the reaction volume; (ii) providing a second volume of a dilution fluid from the dilution inlet into the reaction volume to form a diluted sample; (iii) providing a photoactive reagent from the reagent inlet into the reaction volume to form an activated sample; and (iv) obtaining a photometry measurement of the activated sample, wherein the photometry measurement provides an indication of the nitrite content of the sample.

21. The method of claim 20, wherein the dilution fluid is water and the metalworking fluid is an aqueous metalworking fluid, and/or wherein the photoactive reagent comprises sulfanilamide and N-(1-naphthyl)ethylenediamine.

22. The method of claim 20, wherein the apparatus further comprises a controller, and wherein the method comprises the controller operating the apparatus.

23. A computer program product comprising program instructions configured to program a computer system to perform the method of claim 20.

24. A control system for an apparatus, comprising a processor and computer memory comprising program instructions according to claim 23.

25. Use of an apparatus according to claim 1 for automatically monitoring, and optionally recording, the nitrite content of a metalworking fluid periodically.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0085] The present invention will now be described by way of example and with reference to the accompanying FIGURE in which:

[0086] FIG. 1 illustrates an example of an apparatus for in-line monitoring of nitrite content in a metalworking fluid.

SPECIFIC DESCRIPTION

[0087] FIG. 1 shows a schematic representation of an example apparatus in which sample inlet 2, which is in use connected to a source of metalworking fluid to be monitored, is connected via valve V5 to sampling volume/flow path 42, which is connected via valve V6 to a vent 4 and an outlet 6, which may be arranged as a return line to return fluids to the source of metalworking fluid from which the sample is obtained. Valves V5 and V6 are operable to hold a volume of sample in the sample volume 42.

[0088] An inline filter separates valve V5 from calibration valve V4, which is operable to direct the sample via flow path 16 for offline calibration, or to direct the sample via flow path 14. Flow path 14 is connected via dual channel sample pump P2 to an inlet of reaction vessel 18. Therefore, the dilution fluid may be introduced by pump P2 into the reaction vessel 18 at the same time as the sample.

[0089] Dilution inlet 8 is connected to a source of dilution fluid, for example water, and the dilution inlet 8 may be opened or closed by operating a valve V7. The dilution inlet 8 is connected via flow path 12 and the dual channel sample pump P2 to an inlet of reaction vessel 18. The dilution inlet is also connected via flow path 10 and dilution pump P3 to a flow path 30 from a first outlet 20 of the reaction vessel, whereby dilution fluid can be introduced into the reaction volume independently of the sample.

[0090] Reagent pump P4 and optional second reagent pump P5 are also connected to flow path 30 for introducing photoactive reagent into the reaction volume. Reagent pumps P4 and P5 may be connected to respective reagent reservoirs for storing the photoactive reagent or components thereof.

[0091] Reaction vessel 18 comprises an outlet 20 that is connected via flow path 30, third valve V3, flow path 34, and second valve V2 to an inlet of first pump P1. The outlet of the first pump P1 is connected by flow path 38 to a first valve V1, where the first valve V1 is connected, via flow path 40 to the outlet 6. Thus, the first pump may be operated to discharge sample mixture from the reaction vessel through the outlet 6.

[0092] The first valve V1 is also connected to photometer flow path 24 comprising a photometer 26 arranged to monitor fluids that are provided to the photometer 26 by the photometer flow path 24. The photometer flow path 24 comprises a flow path 28 that connects to an inlet of the reaction vessel 18. Thus, the first pump P1 may be operated to circulate the sample mixture from an outlet 20 of the reaction vessel 18, via the photometer 26 and back to the reaction vessel 18 via flow path 28.

[0093] Second valve V2 is additionally connected directly to the photometer flow path 24 via flow path 36. Thus the photometer flow path 24 may be connected via the second valve V2 to an inlet of the first pump P1, and the first pump may be operated to discharge sample mixture in the photometer flow path through the outlet 6 via first valve V1.

[0094] The reaction vessel 18 comprises a second outlet 22, which is connected via a flow path 32 to the third valve V3. The second outlet 22 is arranged to only partially withdraw sample mixture that is present in the reaction vessel 18. Thus, third valve V3 is operable to select which of the first outlet 20 and second outlet 22 of the reaction vessel 18 are connected via first pump P1 to the outlet 6.

[0095] Although not shown in FIG. 1, the components of the apparatus shown in FIG. 1 may be connected to a controller configured to control flow within the apparatus and operation of the photometer. With reference to the apparatus of FIG. 1, an example of the operation of the apparatus in use will be described.

[0096] Valves V5 and V6 may be operated to connect sample inlet 2 to outlet 6 so as to flush sample through the sampling volume 42. Valves V5 and V6 are then closed to retain a sample to be monitored in sampling volume 42.

[0097] Before introducing the sample mixture into the reaction vessel 18, the reaction vessel 18 may first be emptied by operating the valves V1, V2 and V3 to connect the first outlet 20 of the reaction vessel 18 to the outlet 6 via flow paths 30, 34, 38 and 40, and operating the first pump P1 to discharge sample mixture from the reaction vessel 18 to the outlet 6.

[0098] The apparatus may then be flushed with fresh sample mixture by introducing sample from sampling volume 42 to the reaction vessel via flow path 14 by operating valves V5 and V4 and sample pump P2, and at the same time introducing dilution fluid from dilution inlet 8 via flow path 12 by operating valve V7 and pump P2. In general, when sample is introduced into the reaction vessel from sampling volume 42, valve V6 may be operated to open to vent 4. The sample mixture is also circulated from the first outlet 20 back into the reaction vessel 18 via flow paths 30, 34, 38, 24 and 28 by operating valves V1, V2 and V3 and pump P1, and sample mixture may also be discharged through flow path 40 to the outlet 6. Following this, the reaction vessel 18 may be emptied of sample mixture as described previously.

[0099] A partially diluted sample mixture is introduced into the reaction vessel 18 from sample volume 42 by operating valves V5 and V4 and sample pump P2 to introduce sample along flow path 14, and at the same time introducing dilution fluid from dilution inlet 8 via flow path 12 by operating valve V7 and pump P2.

[0100] The volume of partially diluted sample mixture in the reaction vessel 18 is then controlled by operating valves V3, V2 and V1 to connect second outlet 22 to outlet 6 via flow paths 32, 34, 38 and 40 and operating the first pump P1 to partially discharge the partially diluted sample mixture from the reaction vessel.

[0101] Dilution fluid from dilution inlet 8 is then introduced via flow path 10 by opening valve V7 and operating dilution pump P3. The dilution fluid is provided to the reaction vessel 18 via flow paths 30, 34, 38, 24 and 28, and at the same time the diluted sample in the reaction vessel 18 may be circulated from the first outlet 20 to the flow path 28 by the same flow path as the dilution fluid introduced from flow path 10.

[0102] The diluted sample mixture may then be homogenised by circulating the diluted sample within the reaction volume from the first outlet 20 of the reaction vessel 18, via the photometer 26 and back into the reaction vessel 18 via flow paths 30, 34, 38, 24 and 28, by operating valves V1, V2 and V3 and pump P1.

[0103] The pump P1 is turned off to stop the circulation of the diluted sample to provide a substantially static sample at the photometer 26, and the photometer 26 is operated to obtain a background photometry measurement of the diluted sample.

[0104] The reagent pump P4 is then operated to provide the photoactive reagent to flow path 30, and the sample mixture circulated from first outlet 20 to flow path 28 as described previously, to provide the photoactive reagent to the reaction vessel 18. Where present, the reagent pump P5 may be operated in substantially the same way to introduce a second component of the photoactive reagent and this may be done simultaneously or sequentially with respect to introduction of a first component of the photoactive reagent using pump P4.

[0105] The sample mixture may then be homogenised to form the activated sample mixture by circulating the sample mixture including the photoactive reagent within the reaction volume from the first outlet 20 of the reaction vessel 18, via the photometer 26 and back into the reaction vessel 18 via flow paths 30, 34, 38, 24 and 28, by operating valves V1, V2 and V3 and pump P1.

[0106] The pump P1 is turned off to stop the circulation of the activated sample mixture and the photometer 26 is operated to obtain a photometry measurement of the activated sample.

[0107] The photometry measurement and the background measurement may be recorded in a database along with the time, for example the date, that it was measured and/or with another identifier for the metalworking fluid that was sampled and measured such as a batch identifier. The photometry measurement and the background measurement may be compared to provide an indication of the nitrite concentration in the sample, and the nitrite concentration in the sample may be recorded instead of or in addition to the photometry measurements. The nitrite concentration may be determined in real time with the collection of the photometry measurements, and an alert signal recorded or sent to a user in real time if the nitrite concentration is outside a threshold range. An indication of a nitrite concentration outside a threshold range may alternatively or additionally trigger a control signal to adjust the nitrite content of the metalworking fluid source from which the sample was taken. The threshold range for issuing an alert signal may be different from the threshold range for triggering a control signal, for example the threshold range for issuing an alert may be narrower (in respect of the upper and/or lower limits) than the threshold range for issuing a control signal. An alert signal or control signal may in some cases only be issued based on more than one measurement, for example at least two measurements taken sequentially, where a first nitrite content measurement outside the threshold range may trigger a second measurement, where the trigger to issue an alert or control signal is dependent on both measurements. Alternatively or additionally, the more than one measurement may comprise more than one measurement taken at periodic time intervals, for example so that the measurements can be analysed to determine the presence of a pattern of nitrite contents outside a threshold range over time.

[0108] It will be appreciated that the volume of sample, dilution fluid and photoactive reagent introduced to the reaction volume will be set so that concentration of nitrites in sample can be calculated from the absorbance measured by the photometer, for example using a previously determined calibration function. The exact volumetric ratio of the different components and the total volume may suitably vary based on the particular system. In one example, where for example the dilution fluid is water and the photoactive reagent comprises sulfanilamide and N-(1-naphthyl) ethylenediamine, about 1 to 2 ml of sample, about 40 ml of water, and about 5 ml of photoactive reagent solution may be introduced into the reaction volume for measurement. Following a measurement, the photometer flow path 24, including the photometer 26 and flow path 28, may be emptied of sample mixture by operating second valve V2 to connect the photometer flow path 24 to the inlet of the first pump P1 via flow path 36, and operating first valve V1 to connect flow path 38 to flow path 40 and the outlet 6. The reaction vessel 18 may also be emptied of sample mixture by operating the valves V1, V2 and V3 to connect the first outlet 20 of the reaction vessel 18 to the outlet 6 via flow paths 30, 34, 38 and 40, and operating the first pump P1 to discharge sample mixture from the reaction vessel 18 to the outlet 6.

[0109] Finally, the reaction volume may be rinsed with dilution fluid by introducing dilution fluid via flow path 10 by opening valve V7 and operating dilution pump P3. The dilution fluid is provided to the reaction vessel 18 via flow paths 30, 34, 38, 24 and 28, and at the same time the dilution fluid is circulated from the first outlet 20 of the reaction vessel 18 to the flow path 28 by the same flow path as the dilution fluid introduced to the reaction vessel 18 from flow path 10. The reaction vessel 18 and the photometer flow path 24 may then be emptied as described previously, and the cycle of rinsing and emptying the reaction volume repeated, for example repeated three times, with the final emptying step performed either immediately or before performing a further sample measurement.

[0110] In certain examples a controller described herein may be configured to perform any of the methods, or particular steps of said methods. A controller described herein may refer to a single controller and/or processor or control may be distributed between multiple controllers and/or processors, which may physically form part of the apparatus or may be a remote controller communicatively coupled to the apparatus. The activities and apparatus outlined herein may be implemented using controllers and/or processors which may be provided by fixed logic such as assemblies of logic gates or programmable logic such as software and/or computer program instructions executed by a processor. Other kinds of programmable logic include programmable processors, programmable digital logic (e.g., a field programmable gate array (FPGA), an erasable programmable read only memory (EPROM), an electrically erasable programmable read only memory (EEPROM)), an application specific integrated circuit, ASIC, or any other kind of digital logic, software, code, electronic instructions, flash memory, optical disks, CD-ROMs, DVD ROMs, magnetic or optical cards, other types of machine-readable mediums suitable for storing electronic instructions, or any suitable combination thereof.

[0111] The above embodiments are to be understood as illustrative examples. Further embodiments are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

[0112] Other variations and modifications of the apparatus will be apparent to persons of skill in the art in the context of the present disclosure.