FR2978168A1 - METHOD OF EVALUATING, BY OBSERVING SIZES OF MICELLES, THE CAPACITY OF A CLEANING BATH TO PROVIDE A FUNCTION OF DEHUILING PARTS - Google Patents

Abstract

A method for evaluating the capacity of a cleaning bath containing at least one surfactant to perform a de-oiling function of parts, in which: - the size of micelles contained in the bath is evaluated, these micelles being at least partially formed of said surfactant; and the capacity of said bath to absorb oil according to the micelle sizes evaluated is evaluated.

Description

BACKGROUND OF THE INVENTION There are in the industry a large number of parts of different kinds of metal alloys coated with different types of oils and possibly pollutants. To clean these parts, it seeks to use chemicals as efficient as possible and is therefore generally used a suitable product for each pair of alloy to clean and oil to remove. This leads to using a large number of cleaning products that need to be stored. The storage of cleaning chemicals is particularly delicate because each of these products alone or in combination with one another may pose a risk to health and the environment. OBJECT OF THE INVENTION The object of the present invention is therefore to provide means for reducing the storage volume and possibly the number of chemicals to be stored while improving the cleaning of parts of different metal alloys. SUMMARY OF THE INVENTION The invention primarily relates to a method of evaluating the ability of a cleaning bath containing at least one anionic or ionic surfactant to provide a de-oiling function of parts. This method is described hereinafter as a "second method" and essentially consists of evaluating the bath's ability to perform its cleaning function according to the size of the micelles it contains. The invention also relates to a device for evaluating the capacity of a cleaning bath containing at least one surfactant to provide a de-oiling function of parts. This evaluation device which is adapted to implement the abovementioned evaluation method can be used alone or in combination with a bath regulating device described hereinafter. It is also proposed, in a first aspect of the invention a cleaning bath for metal alloy parts comprising aluminum and / or nickel and / or iron and / or titanium and / or copper, this bath comprising water, an anionic surfactant, a nonionic surfactant, a corrosion inhibitor adapted to form, on each piece of metal alloy leaving the bath, a layer limiting the corrosion of these parts, a pH agent adapted to limiting the variation of the pH of the cleaning bath, this bath having a mass concentration of anionic surfactant and nonionic surfactants of less than 3%.

With this first aspect of the invention, metal alloy parts containing aluminum and / or nickel and / or iron and / or titanium and / or copper are cleaned properly while avoiding degrading them when cleaning. Indeed the low concentration of anionic and nonionic surfactant associated with the presence of pH agent allows the bath to be effective without becoming corrosive. This bath can therefore be used on a variety of metals comprising at least aluminum and / or nickel and / or iron and / or titanium and / or copper which, as will be seen later, have the peculiarity of having a common area of immunity to corrosion between pH 8.5 to pH 9.5. The bath is therefore particularly suitable for cleaning such alloys which constitute the major part of the alloys of the industry. Thus, the cleaning bath of the invention makes it possible to have a single bath that can be used for a variety of alloys, which reduces the variety of cleaning products required and limits the need for storage of these products. It has been found that by limiting the concentration of anionic and nonionic surfactant below the mass threshold of 3%, the bath is satisfactory for degreasing the parts and does not present any risk of corrosion of the parts. Such a bath retains its characteristics over long periods thanks to the pH agent which prevents drift of the pH of the bath which would be a possible source of corrosion. Thus the bath is economical because it is rarely replaced and allows to treat with the same efficiency a large number of rooms. The simplicity of this bath of the invention (few components) facilitates the study of the wear rate of the bath (ie its ability to perform its cleaning function) and allows easy regulation of the bath components in the bath. during its use (few components / active ingredients are to be readjusted during the life of the bath and their readjustments are less frequent). In a preferred embodiment of the bath according to the invention, it is solely composed of water, a mass concentration of anionic surfactant which is SDS substantially equal to 1%, a mass concentration of nonionic surfactant. which is Tween 80 substantially equal to 1%, a mass concentration of corrosion inhibitor which is sodium metasilicate Na2SiO3 substantially equal to 1%, a mass concentration of pH agent which is sodium carbonate Na2CO3 substantially equal to 0.3% and possible traces of other components whose mass concentration is less than 1% and preferably without traces, the water being preferentially demineralised water. For the understanding of the invention, it is noted that: SDS denotes sodium lauryl sulphate (also known as sodium dodecyl sulphate); and Tween 80 is polysorbate 80 also known in the detergent field as polyoxyethylene (80) sorbitan monostearate.

In this ideal formulation, the specific bath of the invention does not comprise complexing agents, thickeners, fillers, salts, perfumes, anti-foaming agents and other coloring agents, but comprises only two surfactants, a single corrosion inhibitor. and a single known pH agent. This bath is specifically developed to: - degrease, without attacking / chemically corroding, a variety of alloy parts containing aluminum and / or nickel and / or iron and / or titanium and / or copper, these parts being greased with a variety of water-soluble and non-water-soluble oils; and - limiting the number of chemical molecules that can develop in the bath by recombination of pollutants carried by the parts with components of the bath; and allow a qualitative study of the bath by simple processes such as acid / base titration, conductivity measurement and / or measurement of micelle sizes (for example by dynamic light scattering: DLS). For this we limit the number of components of the original bath to the bare minimum necessary for its effectiveness. By limiting the number of chemical agents, the risk of having recombinant molecules is reduced, which facilitates the qualitative monitoring of the bath as well as its readjustment, which is thus achievable chemical agent by chemical agent.

By limiting the risk of occurrence of recombinant molecules is limited all the risk of degradation of parts by the bath. Another advantage of this bath is that it contains no solvent that can generate environmental risks or for the health of operators.

The bath according to the invention (in this case the ideal formulation presented above) was used to clean 1,200,000 pieces of steel of various alloys (316L, 30NCD16, 35NC6 laminated) each having an average of about 10cm2 surface to clean (rivets, bolts, barrels). This bath is heated to 60 ° C and mechanical agitation of the bath by bubbling is used only to mix the bath components. This agitation is stopped during the degreasing of the parts to avoid an overflow of the bath which would tend to foam. Despite the fact that no readjustment in surfactant was made during this test, it was found that all the parts were validly cleaned since no defect of coating adhesion (passivation, paint) on the parts was found . It is therefore demonstrated that the bath of the invention has the property of remaining effective despite a lack of regulation over a long period. According to two other aspects of the invention also satisfying the object of the invention, two methods of evaluating the capacity of a cleaning bath, containing at least one surfactant, to provide a de-oiling function of rooms. By allowing the operator to evaluate the real capacity of the bath to degrease parts it limits the risk that it prematurely replaces this bath, or on the contrary that it delays in replacing or readjusting it. Since the operator has factual information about the bath's ability to degrease, it reduces unnecessary use of products needed for degreasing and reduces the need for chemical storage. Indeed, the operator replaces the bath less often because he can simply readjust it by taking into account the information on the quality of the bath provided by the evaluation methods.

The operator is also not tempted to continue cleaning parts if the bath is no longer suitable for its function. This avoids the need to re-clean parts already partially cleaned in the bath and especially avoids having to reform parts because of defective surface treatment due to poor cleaning. In any case, these methods of bath evaluation can reduce the need for storage of chemicals while improving cleaning parts of different metal alloys. A first method relates to the evaluation of the capacity of a cleaning bath containing at least one anionic or ionic surfactant to provide a de-oiling function of parts. To carry out this first method: a sample of the bath to be evaluated is taken and at least one measurement of the quantity of acid necessary for this sample to reach a neutral pH is carried out. The oil content of the bath to be evaluated is evaluated. using: - predetermined calibration data expressing for various known baths having known oil contents, the amounts of acid respectively necessary for each of these respective baths to reach a neutral pH; and - said measured amount of acid; the surfactant content of the bath is evaluated using: said evaluated oil content of the bath to be evaluated; the measured conductivity of the bath to be evaluated; and - predetermined calibration data expressing for a plurality of known baths the evolution of the theoretical conductivity of these known baths as a function of the evolution of their respective oil contents and their respective contents of surfactant; then - depending on the evaluated oil content of the bath to be evaluated, the evaluated surfactant content of the bath to be evaluated and a predetermined rule, the current capacity of the bath to fix oil in the form of micelles to using surfactants it contains. This first method is particularly effective for knowing the anionic or optionally ionic surfactant content, as well as the oil content of the bath, which makes it possible to evaluate the amount of free surfactant and not yet loaded. This method has a limitation because it can only be used if the bath contains a single oil and comprises only one surfactant of anionic type or alternatively a single surfactant of ionic type. This first method, however, allows the efficient characterization of a bath comprising an anionic surfactant and a nonionic surfactant as is the case of the bath of the invention. The second method relates to the evaluation of the capacity of a cleaning bath containing at least one surfactant (possibly several surfactants optionally having anionic and / or nonionic and / or ionic types) to provide a de-oiling function of parts. To implement this second method: - the size of micelles contained in the bath is evaluated, these micelles being at least partially formed of said at least one surfactant; and the capacity of said bath to absorb oil according to the micelle sizes evaluated is evaluated. This method is advantageous because it allows to qualify a greater variety of baths than the first method, including baths containing multiple kinds of surfactants and polluted by multiple kinds of oils. According to another aspect of the invention, it also relates to a control device of a cleaning bath for metal alloy parts for regulating the composition of the bath using one and / or the other aforementioned bath evaluation methods.

The use of such a control device limits the need for replacement of the bath, which limits the consumption of chemicals and reduces the storage requirements of such products. Finally, according to another aspect of the invention, it relates to a device for treating parts to protect it against corrosion, this treatment device comprising the bath regulating device according to the invention. The invention in its various aspects makes it possible to meet the aforementioned object by developing a universal bath that can be used for a variety of alloys that are common in the industry and methods that make it possible to monitor and evaluate the wear of this bath. BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the invention will emerge clearly from the description which is given below, by way of indication and in no way limiting, with reference to the appended drawings, in which: FIG. 1 is a graph showing the zones of sensitivity to corrosion of different metals and a common zone of immunity Zi to these different metals Al, Ni, Fe, Ti, Cu; FIGS. 2a, 2b and 2c present steps of a first method of evaluating the capacity to degrease a bath, these stages making it possible to know the current concentration of the bath in oil by acid / base titration; - Figures 2d, 2e, 2f show the following steps of the first bath evaluation method to know its anionic surfactant content by conductivity measurement; FIG. 3 illustrates the evolution as a function of the number of parts cleaned of the bath content in free micelles (surfactants not associated with oil) and in loaded micelles (surfactants associated with oil); FIG. 4 shows a device for treating parts against corrosion using a passivation bath and allowing the implementation of the corrosion treatment method according to the invention; FIG. 5 shows the part cleaning device which is integrated in the piece corrosion treatment device shown in FIG. 4. DETAILED DESCRIPTION OF THE INVENTION A) CLEANING BATH ACCORDING TO AN ASPECT OF THE INVENTION A first aspect of the invention relates to a cleaning bath specifically developed for cleaning metal alloy parts comprising aluminum and / or nickel and / or iron and / or titanium and / or copper. This bath being characterized in that it comprises water, an anionic surfactant, a nonionic surfactant, a corrosion inhibitor adapted to form, on each piece of metal alloy leaving the bath, a layer limiting the corrosion of these parts, a pH agent adapted to limit the variation of the pH of the cleaning bath, this bath having a mass concentration of anionic surfactant and nonionic surfactant less than 3%. Preferably, the mass concentration of anionic and nonionic surfactant of the bath is between substantially 1% and 2.5% and preferably substantially equal to 2%. It has been found that by limiting the mass concentration of anionic and nonionic surfactants below the limit of 3% and preferentially by keeping it at 2%, it has a greater degreasing effect than one would have by adding more surfactant. . This limitation of the concentration makes it possible to optimize the efficiency of the bath while giving it an economic advantage (it requires few surfactants).

The anionic surfactant is used for its degreasing interest and good stability at high temperature and alkaline pH (it is in the alkaline pH that the immunity zone of the alloys to be cleaned), but it tends to generate foams. For this purpose combining 1% of anionic surfactant with a nonionic surfactant reduces the risk of occurrence of foam while retaining the advantages of the anionic surfactant. This mixture of anionic and nonionic surfactants is also more effective than a single surfactant. This synergy of the anionic and nonionic surfactants makes it possible to have a Critical Micellar Concentration lower than the Critical Micellar Concentrations of the same pure surfactants. It is partly thanks to this combination that one can have a degreasing efficiency of the bath while limiting the amount of surfactants. Preferably, the anionic surfactant is SDS, that is to say sodium lauryl sulphate, and the nonionic surfactant is Tween 80, that is to say polyoxyethylene-80-sorbitan monostearate.

These surfactants are chosen for their particularly important degreasing performance when combined in low concentrations in the bath. The ideal mass concentration of the bath in SDS is from 1% to +/- 0.2% and the ideal mass concentration of the bath in Tween 80 is from 1% to +/- 0.2%, this bath further comprising a mass concentration of inhibitor of corrosion, preferentially inorganic, substantially equal to 1% and a mass concentration of pH agent substantially equal to 0.3%. In this case, the mass concentration of the pH agent bath is 0.3% to +/- 0.05%. The selected corrosion inhibitor is sodium metasilicate Na 2 SiO 3 which is inorganic in nature and chemically inert to alloys. This inhibitor forms a protective layer on the surface of the alloys exiting the bath, this layer being easily removed in a post-cleaning passivation bath, for example a nitric acid bath.

The pH agent is chosen so that the bath has a pH stabilized around a pH value between 8.5 and 9.5. The pH agent selected is sodium carbonate Na2CO3 which is nontoxic to the environment.

It has been found that by choosing such a pH value one is in a zone of pH called zone of immunity Zi common to the most common metals in the industry that is to say the aluminum and / or the nickel and / or iron and / or titanium and / or copper (these domains of metal immunity are given by Pourbaix diagrams). In the immunity zone, these metals are not corroded by the bath. As can be seen in FIG. 1, the zone of specific immunity to iron extends over a pH range from 8.5 to 12, the zone of specific nickel immunity extends over a pH range from 8.5 to 12. , 5, the aluminum-specific immunity zone extends over a pH range from 4 to 9.5, the titanium-specific immunity zone extends in the range from 5.5 to 14, the Copper-specific immunity range extends in the range of 7 to 12.5. The common immunity zone Zi extends well over the pH range 8.5 to 9.5. The degreasing power of the bath according to the invention has been demonstrated by several tests for degreasing specimens in different alloys. Each test piece is covered with a given mass of oil and is immersed for 60 seconds in the bath of the invention heated to 60 ° C and without stirring to characterize the only bath.

After passing through the bath each test piece is dried and weighed to evaluate the mass of oil that has been removed by the bath. These tests were carried out with AU4G aluminum alloy test pieces, 316L stainless steel test pieces and NC22FeD iron and nickel alloy test pieces. For each selected alloy family, several series of tests were carried out, each test series using a known industrial oil. The selected oils are water-soluble oils and non-water-soluble oils. BacticoolO, SuperedgeO, ArdoxO and TurbonicoilO oils have been chosen which are widely used in the industry. Thus, the tested alloy / oil pairs correspond to the majority of cases of degreasing of parts occurring in the industry. The result of these tests shows, by type of oil tested, that the average percentage by weight of oil removed on the parts of different alloys is in all cases greater than 95% of the mass of oil spread on the part (despite the lack of agitation and the short residence time of the parts in the bath). This test demonstrates the effectiveness of the bath according to the invention and its ability to degrease a wide variety of couples alloys / oils. The ease of qualitative monitoring of the bath will be demonstrated later with reference to the first bath evaluation method. The corrosive impact of the bath according to the invention has also been studied on parts of the abovementioned alloys. It is found that the mixture with equal weight shares SDS and Tween80 is not very corrosive since the annual corrosion of this mixture is: - of 1.26 +/- 0.05 pm / year on a piece of AGSUC (which is an alloy of known aluminum); - 77 +/- 2 pm / year on a piece of alloy 316L 15 - 0.87 +/- 0.01 pm / year on a piece of alloy NC22FeD. The presence of the corrosion inhibitor associated with the pH agent makes it possible anyway to limit the risk of corrosion of the parts in the bath and at the bath outlet. It is also noted that the invention relates to a composition for preparing the bath according to the invention. To prepare / produce this bath a composition with a smaller amount of water than required in the bath is used. This composition is easier to transport to the place of use where it is diluted with water to form the bath. This composition comprises a mixture of SDS, Tween 80, sodium metasilicate and sodium carbonate, with dosages such that by diluting with a given amount of water the cleaning bath is obtained. B) PROCESS FOR TREATING CORROSION USING THE BATH OF THE FIRST ASPECT OF THE INVENTION According to a second aspect of the invention, there is provided a process for the corrosion treatment of at least one metal alloy part comprising aluminum and / or nickel and / or iron and / or titanium and / or copper. This treatment method comprises: a step of cleaning said at least one part by immersing it in a cleaning bath as defined previously according to the first aspect of the invention; and a step of treating this at least one cleaned part consisting in immersing it in a bath adapted to passivate at least one surface of this cleaned part, this bath being preferably acidic, and this acid being preferably nitric acid (for example example if the piece is steel) or sulfuric acid if the piece is anodized aluminum alloy. The fact of carrying out a step of cleaning the alloy part with the bath of the invention followed by a step of passivation of the part is particularly advantageous because the passivation of the part is more homogeneous and of better quality when the part is degreased without being corroded.

While most metal cleaning baths of the prior art corrode the alloy parts in an irregular manner, it is found that the bath of the invention allows to remove the oil from the room without corroding it. This gives a clean homogeneous surface and not corroded by the bath. Thanks to this homogeneous surface, homogeneous passivation of the part is promoted, in particular by acidic action. The corrosion of the part or the presence of oily zone on the part form obstacles to its passivation. By reducing the risk of corrosion or poor cleaning, the corrosion treatment process increases the chances of regular passivation of parts, thus statistically prolonging the life expectancy of the treated parts.

Ideally the cleaning bath in which is immersed said at least one part is heated to 60 ° C to +/- 5 ° C and the room is immersed in this bath for a period greater than 10 minutes and preferably less than 30 minutes.

The agitation of the bath is low to prevent the appearance of foam in the bath and avoid the need for anti foaming agents disturbing the analyzes. This method of treatment against corrosion is implemented using the coin processing device presented below with reference to FIG. 4. C) METHODS OF EVALUATION / STUDY OF THE CAPACITY OF A BATH, TO BE CARRIED OUT SA FUNCTION OF CLEANING PARTS BY REMOVING THE OIL POLLUTING THESE PIECES As indicated above it is also proposed according to the invention two methods particularly suitable for the evaluation of the bath of the invention presented above (see first aspect of the invention). invention). C-1) the first method of studying the capacity of the bath to degrease parts, this bath being contaminated by only one oil: This first method is applicable in particular to a bath comprising a single anionic surfactant or a single surfactant ionic and optionally containing a nonionic surfactant. This method is preferably applicable to cleaning baths polluted by a single type of oil which in the example below is Bacticool oil. Step 1: a sample of the bath to be studied is taken and at least one measurement of the amount of VegB acid required (ie, the amount of acid to be added to the sample) is made to reach this sample. a neutral pH (in this case, this quantity of acid is known by measuring the volume of acid poured up to the inflexion of the pH curve and knowing the concentration of the added acid); Step 2 the oil content% Mas estim of the bath to be studied is evaluated using: - predetermined calibration data expressing for various known baths having known oil contents (in this case this oil used for calibration is necessarily that present in the bath to be evaluated), the amounts of acid Veq respectively necessary for each of these respective baths to reach a neutral pH (in this case the neutral pH is 7 and is reached at the equivalent volume of acid); - the amount of acid measured VegB. The Coil curve ref of FIG. 2b is an expression of the variation of the equivalent volume Veq as a function of the mass percentage of oil. This curve Coil ref is therefore a predetermined calibration data allowing the implementation of this step 2. Step 3 (optional step) This oil content of the bath to be studied can also be deduced by carrying out several measurements. This reduces the risk of error of the acid titration measurement. For this purpose, several samples of the bath are used and several acid / base measurements are carried out in order to know the amounts of Veq of acid respectively necessary to reach the neutral pH of each sample of the respective bath. The average of these VegB acid quantities measured is then calculated and this average VegB and the calibration data are used to deduce the average MasMoy content of the bath in oil. It is noted that the pH can be observed using a pH meter or a pH indicator changing staining to pH 7. Step 4 the surfactant content of the bath is evaluated (this content comprises the free surfactants in the bath, that is to say surfactants not associated with oil to form micelles, and surfactants already associated with micelles and therefore no longer available to form new micelles and thus fix the oil in the bath) using: - the acid content of the bath evaluated in step 2 or 3; the conductivity K of the bath to be evaluated evaluated by at least one conductivity measurement of this bath; predetermined calibration data expressing, for a plurality of known baths, the evolution of the theoretical conductivity of these known baths as a function of the evolution of their respective oil contents and their respective contents of surfactant. To exemplify the realization of this step 4, reference will be made to FIGS. 2D to 2F. Thus, to evaluate the surfactant content in bath B is designated a point M1 having the oil content% Mas Moy previously evaluated (that is to say the measured oil content of the bath to be studied) and having a conductivity K equal to the conductivity evaluated by measurement of the bath to be studied (Figure 2D). Then we try to evaluate the original conductivity K of this bath to study while it did not yet contain oil (% Mas oil = 0). For this, a curve d1 is positioned as a function of the point M1 (the curve d1 is a typical curve of conductivity variation as a function of the oil content of the bath B). The shape of the conductivity curve d1 as a function of the oil content variation is known from previously stored tests which consist of changing the oil content in a standard bath while measuring the evolution of its conductivity as a function of this. variation in oil content (see for example curves C1, C2, C3). To position this curve d1 with respect to the point M1, we translate the shape of the curve C1 so that it passes through the determined point M1. Once this curve d1 is positioned, it is determined (FIG. 2F) the value of the original conductivity K of this bath when its oil content was zero. In this case, this value K corresponds to the point of intersection of the ordinate axis (0% of oil) with this curve d1 translated of conductivity variation passing through the point M1. It should be noted that the point determined as a function of M1 may be a point coinciding with M1 and / or a point made by calculating the mean conductivity value of the bath using several conductivity measurements (here it is necessary to evaluate the average conductivity of the bath at a given moment or over a given period during which the oil content in the bath has remained substantially constant, that is to say that the change in oil content of the bath for the time required for these Conductivity measurements must be less than 0.5% by mass of the bath, in this way it will be avoided to add parts to the bath to be cleaned at the moment when a measurement of the average conductivity of the bath is made. K of this bath to be studied while it did not yet contain oil (% Masoil = 0%), one can also make a first estimates of this value K according to the method described above using the curve of fo known as a variation of conductivity as a function of the oil content and to average this first estimate of K with at least a second estimated conductivity value K measured in a sample of the bath to be studied in which a known quantity has been introduced of oil to increase the oil content of the sample (this is illustrated with the curve C4 in Figure 2e which will be explained below). With the aid of the second conductivity value K measured in the sample containing the added oil and the oil content of this sample which is known, a second point M2 (visible in FIG. 2E) with a content of previously evaluated oil of the sample with added oil (that is to say the oil content of the bath to be studied to which is added the amount of added oil) and having a conductivity equal to the second conductivity value ( that is, the measured K conductivity of the test bath sample containing added oil). Then, depending on the point M2, a curve d2 of conductivity variation is set as a function of the oil content of the bath. In the same way as above, this operation is easily performed because the shape of the conductivity curve is known as a function of the oil content variation (this form is the same for d1 as for d2). It is enough to translate this form of curve so that it passes through a given point with M2 (in this case we chose to pass this curve by M2). It can be seen that there is a difference between the curves d1 passing through M1 and the curve d2 passing through M2, this sdK difference is due to several possible errors, such as an error in the estimation of the amount of oil in the bath to be studied. , an error in the amount of oil added to the sample of the bath to be studied, an error in the electrical conductivity measurements of the bath and the sample.

Once this curve d2 is positioned, it is determined (FIG. 2F) the value of the original conductivity K of this bath when its oil content was zero. In this case, an average conductivity value K is obtained by: - the value of K obtained at the point of the curve d1 corresponding to 0% of oil (intersection of d1 with the ordinate axis); and the value of K obtained at the point of the curve d2 corresponding to 0% of oil (in this FIG. 2F, it can be seen that the value of K given by d2 lies at the intersection of the curve d2 and 'Y axis). According to the example of FIGS. 2A to 2F, an average value of oil content of the bath which is 5% by weight is determined in FIG. This average value is derived from several acid / base titrations giving respectively an oil concentration of 4.8 and 5.2% by mass of the bath. The average concentration value is the sum of the concentration values evaluated by measurement and divided by the number of these concentration values, in this case (4.8 + 5.2) / 2 = 5% by mass of the bath. The difference between these concentration values is noted Delta% Mas estim. In Figure 2D we see several forms of curves C1, C2, C3 which are predetermined calibration data. Each of these curves shows the evolution of the conductivity (the conductivity is in mS / cm) as a function of the variation of the oil content of the bath (this content is expressed as a percentage by mass of oil in the bath% Mas oil ( % W / W)). In the present case, the oil is BacticoolO, the mass percentage of which has been varied in the bath from 0 to at least 12%. To obtain these curves C1, C2, C3, a bath with a known content of anionic surfactant is taken and its oil content is changed while measuring the evolution of its conductivity. Curve C1 shows the calibration curve obtained by mixing Bacticool O type oil with water without the presence of anionic surfactant and varying the oil content from 0% to at least 12%. Curve C2 shows the calibration curve obtained by mixing this same oil with water, but this time with 1% of surfactant which is in this case an anionic surfactant of SDS type. Curve C3 shows the calibration curve obtained by mixing this same oil with water, but this time with 5% by weight of anionic surfactant of the SDS type.

It should be noted that these curves C1, C2, C3 have identical shapes with each other because once the anionic surfactant content has been set, the conductivity changes only as a function of the oil content and according to a quasi-linear law of constant shape. The conductivity value of a bath containing no oil depends solely on its content of anionic surfactant. As will be seen in the example below, knowing the law of evolution of the conductivity K of the bath as a function of its mass percentage in oil% Mas garlic, and knowing the current oil content% Mas estimated or% Mas Moy, it is then possible to determine its current content of anionic surfactant or optionally ionic surfactant when replacing the anionic surfactant with an ionic surfactant.

As can be seen in FIG. 2d, a measurement of the conductivity of the bath to be evaluated and knowing also its oil content (known from FIG. 2c) is carried out, a point M1 is positioned at the intersection of the measured value of conductivity. (about 6 mS / cm) and the oil concentration value (about 5% by weight). Then, in FIG. 2E, the theoretical curve d1 is obtained which is an evolution curve of the bath to be evaluated if its oil content was only varied without modifying its current content of anionic surfactant. As has been seen previously, the shape of the conductivity variation curve as a function of the oil content is known from Cl, C2 or C3. By translating a curve C1, C2 or C3 parallel to the ordinate axis so that it passes through the point M1 defining the bath to be evaluated, a curve d1 is obtained which is a first estimation of the variation of the bath to be evaluated as a function of its oil content. To reduce errors in the study of the bath, a predetermined percentage of oil in the bath or in the sample of bath B to be studied is then added. The new conductivity value of the bath is measured with its added percentage of oil. Then a point M2 is positioned at the intersection of the oil content of the sample with the addition of oil (in this case the content of this sample with added oil has increased from 5% to 5.5% by weight of the sample) and the measured conductivity value of this sample (in this case 6.5 mS / cm). It is found that at the same content of surfactant the conductivity of the sample increases with its oil content (for respective contents evaluated in oil of 5% and 5.5% by mass respectively one has conductivities evaluated of 6mS / cm and 6.5 mS / cm). Then, as previously explained, the curve d2 passing through M2 is positioned by translating a curve of known shape C1, C2 or C3. It can be seen by reading the respective curves d1 and d2 that there is a standard deviation sdK between these curves corresponding to the measurement error that we wanted to reduce. It is also noted that the respective values of conductivity K for 0% of oil of each of these curves d1 and d2 are respectively estimated at 4mS / cm and 3.9mS / cm. The average conductivity value K of the bath to be evaluated if all its oil was removed and without modifying its anionic surfactant content is therefore estimated at 3.95 mS / cm (see FIG. 2F).

Knowing this average conductivity value K of the bath containing no oil, its total content of anionic surfactant is then determined by simple cross product, since it is known from curves C2, C3 that the conductivity of the bath does not contain any oil. oil is 2mS / cm for a bath containing 1% SDS surfactant and 10.2 for a bath containing 5% SDS. Thus, the current mass content of SDS surfactant in the bath is between 2.33% (4.9 * 5 / 10.5 = 2.33%) and 2.45% (4.9 * 1/2). It is noted that this same cross product can be realized with other values of conductivity K than those taken for a 0% oil content. For example, it may be decided to use the values of conductivities obtained when the bath has an oil content of 10% and we will still obtain substantially the same two mass contents of SDS namely 2.33% and 2.45%. It is therefore known that there is an anionic surfactant content of between 2.33% and 2.45% which is higher than the level of the ideal detergent bath which is 1% by mass of SDS. This first bath evaluation method therefore makes it possible to know whether the bath is able or not to fulfill its deoiling function of parts. It should be noted that this first method of studying the capacity of the bath only makes it possible to measure the level of anionic or optionally ionic surfactant (in the case where it is envisaged to replace the anionic surfactant with ionic surfactant) but does not make it possible to accurately measure the nonionic surfactant content that does not impact the conductivity of the bath.

However, it has been found that the level of anionic surfactant, or, where appropriate, ionic surfactant, evolves in the same proportions as the level of nonionic surfactant. Indeed, these surfactants both bind with the oil and form charged micelles which are removed from the bath so that these levels of anionic and nonionic surfactants evolve in parallel. Thus, knowing the level of anionic surfactant or, where appropriate, ionic, makes it possible to evaluate the level of nonionic surfactant. In addition, if, as is the case with the device of the invention, the surfactants are introduced into the bath by means of dosing means, such as dosing pumps, controlling the quantity of each of the surfactants that can be introduced. know and control the contents and evolutions of the bath surfactants. In summary, using the measurement of conductivity, the content of the anionic surfactant is known and knowing that the content of nonionic surfactant evolves in the same way as the anionic surfactant can therefore know the content of each of these surfactants in the bath. As will be seen below, if the concentration of free surfactant (a free surfactant is not combined with oil to form a loaded micelle) is considered too important, we will then seek to reduce this concentration so that it tends towards a predetermined target value which is in this case that of the ideal detergent bath of the invention: the target value is in the example of 1% of SDS. For this purpose, it is possible to: remove micelles loaded with oil from the bath because they comprise surfactants combined with oil (a De-Oil de-oiler is used for this purpose); and / or - adding water to the bath to reduce its surfactant concentration. In the opposite case, if the concentration of free surfactant is considered insufficient, we will then seek to increase this concentration so that it tends towards the predetermined target value.

For this purpose, a specific amount of surfactant is added to the bath (for this purpose an automatic surfactant doser is used, which can, as in the example of FIGS. 4 and 5, comprise a dosing pump P1 controlled by a central unit UC). Step 5 (optional step presented in step 4) The estimated surfactant content in the bath is obtained by averaging several bath conductivity measurements and / or bath samples.

Step 6 according to the evaluated oil content of the bath to be studied, the evaluated surfactant content of the bath to be studied and a predetermined rule, it is checked the current capacity of the bath to fix oil in the form of micelles to using free surfactants.

Depending on the evaluated bath oil content and the bath surfactant content evaluated, the ability of the surfactants present in the bath to form oil loaded micelles is determined. Several tests can determine if the bath is suitable for room cleaning. For example, knowing the estimated amount of oil present in the bath is determined according to a predetermined rule the minimum amount of surfactant necessary to form micelles containing any oil present in the bath. If the evaluated current amount of surfactant present in the bath is less than the minimum amount of surfactant necessary to integrate at least 100%, preferably at least 150%, of the oil present in the bath in micelles, then it is considered that the bath is no longer effective enough for degreasing parts. As will be seen below, it can also be decided that the bath is no longer effective from the moment when it is found that at least some loaded micelles exceed a predetermined critical size.

C-2) Second method of studying the bath's ability to degrease parts This method makes it possible to study a greater variety of baths than the first method allows, such as baths containing one or more oils and one or more types of surfactants of different types nonionic or ionic anionic. This method of evaluating the capacity of a cleaning bath containing at least one surfactant to perform a de-oiling function of parts essentially consists in: evaluating the size of micelles contained in the bath, these micelles being at least partially formed said surfactant; and - evaluating the capacity of said bath to absorb oil according to the micelle sizes evaluated. More precisely, from a given population of micelles whose size has been evaluated, the rate of these micelles belonging to a first set of small micelles and / or the rate of these micelles belonging to a second set of micelles of the same size is determined. large sizes compared to the said small micelles. Then when at least one of these rates passes a predetermined value, then it is considered that the bath is unsuitable for its cleaning function and the dosage is changed in surfactants or is replaced by another bath bath cleaning. By this method, the micelles size of the bath is estimated and the percentage of these micelles belonging to the first group (small micelles) and / or the percentage of these micelles belonging to the second group (micelles of large sizes) is calculated. . The micelles not yet saturated with oil and still able to capture bath oil and fatten belong to the first set of small micelles. The more a micelle is loaded with oil, the more its size, in this case appreciated by its apparent diameter, increases. Thus all large micelles micelles actually micelles already loaded with oil and therefore having a capacity to capture bath oil which is smaller than the capacity of small micelles. It can therefore be decided that the bath is adapted to perform its cleaning function as long as the micelle rate belonging to the first group is greater than a predetermined minimum value. According to a first example, it can be said that the bath is unsuitable for carrying out effective cleaning if the micelle level belonging to the first group falls below a threshold such as 40% of the micelles whose size has been evaluated. By way of illustration, by judiciously fixing the size limit differentiating the first and second groups we can then consider that the free micelles belong only to the first group and that the loaded micelles belong only to the second group. In the example of FIG. 3, this size limit is set at 12 nanometers because all the free surfactants SDS and Tween80 have a smaller apparent diameter and the Mi Lib free micelle population is thus clearly differentiated from the MiCrg loaded micelle population. . This FIG. 3 illustrates the evolution of these two populations as a function of the number of pieces P cleaned in this unadjusted / regulated bath B and without de-oiling. This figure 3 shows a line symbolizing the LIM limit of minimum percentage of free micelles acceptable to have a correct cleaning of the parts. This limit is here fixed at 40% of free micelles on the whole pop population of micelles observed. Thus, by observing the statistical size of the micelles, as soon as we go below the threshold limit we will order the readjustment of the bath. According to a second example, it can be said that the bath is unsuitable for performing a high performance cleaning if the micelle level belonging to the second group passes above a threshold for example 80% of the micelles whose size has been evaluated. In the case of the bath of the invention the micelles of the first group are: micelles free of SDS whose observed sizes are rays of the order of 3 nanometers; and - micelles free of Tween80 whose observed sizes are rays of the order of 5 nanometers.

The micelles of the second group are therefore micelles having a higher apparent radius such as micelles with radii greater than 10 nanometers. In another example, it can also be considered that the bath is unsuitable to perform its cleaning function when the rate or the number of very large micelles exceeds a predetermined value. According to this example, the second group can be defined as consisting only of very large micelles, for example with radii greater than 20 nanometers.

In this case, when it is seen that the rate or the number of micelles of very large sizes passes a threshold value and if the concentration of micelles of small sizes is less than a predetermined threshold then it is decided that the bath is unsuitable for its cleaning function and then the regulation of the bath (addition of surfactants and / or start of the de-oiler) or bath replacement is started. According to another example, usable when the quantity of oil contained in the bath is known (this quantity of oil can be measured, for example, using the assay of samples of the acid bath as described previously) it can be decided that the bath is unsuitable to fulfill its cleaning function when the evaluated current amount of surfactant present in the bath is less than a theoretical minimum amount of surfactant necessary to integrate at least 100%, preferably at least 150%, of the oil present in the bath in micelles. The amount of surfactant required to encompass a given amount of oil is known by calibration. So knowing the amount of oil in the bath can be deduced the amount of minimal surfactant to capture all this oil in micelles. To evaluate the sizes of these micelles we use the technique of Dynamic Light Diffusion known as the Dynamic Light Scattering whose acronym is DLS. The micelle size measurement means by dynamic light scattering comprise a probe S opti shown in FIGS. 4 and 5.

Unlike the first method which is inexpensive but which requires that the bath comprises anionic or ionic surfactants, this method is more expensive to implement but it is adaptable to a wider variety of baths containing for example anionic surfactants and / or or ionic and / or nonionic and one or more oils. It is possible to combine these two methods of bathing to refine the quality of bath evaluation.

One can indeed have a great advantage to combine these two methods, that is to say possibly to perform an acid titration to know the oil content of the bath (in the case where we use a de-oiler that maintains this constant oil content, this is known because it is set by the setting of the de-oiler and it is therefore not necessary to perform the acid determination), measure its electrical conductivity of the bath (first method) to know the content in anionic or ionic surfactant and also observe the size of the micelles (second method). As we have seen previously the first method does not measure the level of nonionic surfactant, against the second method allows to know the level of free surfactant and the level of surfactant loaded but does not allow to know the respective dosages different types of anionic or ionic and nonionic surfactants. The combination of these two methods makes it possible to know, for example, of the first method that one has a given anionic surfactant content and the level of charged surfactants is determined and, knowing the quantity of oil, the theoretical level of free anionic surfactant is determined. and the theoretical rate of charged anionic surfactant. However, it can happen when the baths contain several types of anionic and nonionic surfactants that the level of charged anionic surfactant is lower than the theoretical rate because part of the charged micelles is formed with nonionic surfactant. If the rate of loaded micelles observed with the second method is higher than the theoretical rate of anionic loaded micelles estimated with the first method, it is deduced while this difference (rate of loaded micelles given by the second method - theoretical rate of anionic loaded micelles). corresponds to the rate of micelles loaded with a nonionic surfactant. The combination of these two bath evaluation methods therefore makes it possible to know the rate of charged micelles formed with an anionic surfactant, the micelle content formed with the nonionic surfactant. Using this same reasoning for uncharged micelles, the combination of these two methods also allows to know the rate of free micelles (not loaded with oil) formed of anionic surfactants and the rate of free micelles formed with nonionic surfactant. The level of anionic surfactant which is still free and the level of nonionic surfactant which is still free are thus known, which makes it possible to better control the dosage of the bath with these surfactants and thus to have a finer evaluation of the bath's capacity to perform its cleaning function. by surfactant capture of the oil. For this reason the bath control device shown in Figure 5, is preferably adapted to implement one or other of these first and second evaluation methods and preferably to combine these two methods. It should be noted that these first and second methods are particularly suitable for estimating the cleaning capacity of a bath produced from the preferred bath of the invention (water, 1% of SDS, 1% of Tween 80, 1% of metasilicate of sodium Na2SiO3, 0.3% sodium carbonate Na2CO3). D) THE BATH REGULATION DEVICE B ACCORDING TO THE INVENTION According to another aspect of the invention, there is provided a control device 1 for a cleaning bath B for metal alloy parts P such as that presented in FIG. Figure 5. This device comprises the bath B comprising surfactants and a basin 2 in which is placed the bath to be regulated. This bath is preferably in accordance with the so-called ideal bath according to the invention and the objective of the regulating device is to reduce the composition drifts of this bath so that the pieces P are cleaned optimally.

The device 1 comprises a measurement system 3 of physical parameters of the bath representative of its capacity to form micelles with surfactants of the bath and the oil present in the bath is integrated in the device 1.

In this case, this measurement system 3 comprises: a measurement means adapted to estimate the current content of surfactant contained in the bath; and a measurement means adapted to estimate the current oil content contained in the bath B. The device 1 also comprises a means for assaying the surfactant 4 in the bath B adapted to control the delivery of a quantity of surfactants, occurrence of SDS and Tween80 in bath B as a function of: - measurements of physical parameters measured by the measuring system 3; and - pre-established dosage rules. More particularly, this means of dosing the surfactant in the bath controls the pouring of a quantity of surfactant into the bath as a function of: the current measured content of surfactant in bath B; and the current measured content of oil contained in bath B.

The bath regulating device 1 also comprises a de-oiler De-oil adapted to remove at least a portion of the oil contained in the bath at least when it is contained in micelles. The use of an oil separator makes it possible to maintain the oil content in bath B at a substantially constant level which is in this case 2 * 10-3% by mass of bath B. Thus, the combination: a bath of surfactant B to capture the oil present on the parts and fix it in the form of loaded micelles; and - a de-oiler for treating these loaded micelles to remove the oil from the bath; keeps the overall oil level in the bath relatively constant and thus facilitates the regulation of the bath despite the constant arrival of oil carried by the parts to be cleaned. The use of oil de-oiler is also advantageous because it prolongs the life of the bath and limits the discharges. It is noted that de-oilers are known in the field of effluent treatment, see for example the de-oilers of patent documents EP 2077160 or WO 2010072249. Other types of de-oilers that can be used are known in the trade under the names of "high-performance de-oiler TB 250 for emulsions & detergent "from the German company MKR-METZGER. De-oilers use eg centrifugation or flotation techniques to separate the oil from the water. The water leaving the de-oiler and optionally the free surfactants that it contains are then reintroduced into the bath to limit its volume decrease and thus limit its drying. This limits the increase in the concentration of the various constituents of the bath. The de-oiler is controlled so that it maintains a mass oil content in the bath of 0.02% oil at +/- 0.005%. In fact it is sought that the bath contains an oil mass equal to 1% of the mass of surfactant to promote the formation of micelles. Since the ideal concentration of the bath is 2% surfactant (see first aspect of the invention), the desired oil mass content will be from 0.02% to +/- 0.005%. By regulating the de-oiler so that it maintains a mass content of oil in the bath substantially constant, it is then found that the conductivity K of the bath is then almost no longer affected by the variation of the oil content which remains substantially constant, but it is essentially affected by its content of anionic or optionally ionic surfactant (for the less favorable case where the anionic surfactants would be replaced by an ionic surfactant). The regulation of the quantity of anionic surfactant to be introduced is then simply carried out as a function of the conductivity of the bath. For this purpose the dosing means comprise a pump P1 controlled by the control unit UC to regulate the content of surfactant SDS and Tween80 in the bath as a function of K conductivity measurements of this bath. The control unit UC preferably comprises an Affi display for displaying the values of the measured parameters and a human machine interface for programming this control unit UC and setting the desired concentration values of the various components of the bath. In the embodiment of FIGS. 4 and 5 the two surfactants are pre-dosed in a reserve and are introduced together into the bath, which reduces the need for surfactant dosage means. This is possible because these surfactants are consumed at substantially the same rate. It is also conceivable that each of these surfactants is dosed independently of the other surfactant. For this purpose, it is possible to use a specific dosing means for the determination of each surfactant, these dosing means being connected and controlled by the control unit UC. It should be noted that the device 1 comprises, in addition to the surfactant dosing pump P1: a conductivity probe Sk0; - a Sniv level probe - a SpH pH probe of the bath - a water dosing pump P2; a dosing pump of pH AgpH agent.

All the SkO, Sniv, SpH, Sopti probes are connected to the control unit UC in order to transmit to it results of measurements of bath parameters. All dosing pumps P1 for surfactants, P2 for water and P3 for the pH AgpH agent are also connected to the control unit but to be controlled and thus regulate the bath by dosing its various components. The H2O water supply is thus regulated according to the level measured by the Sniv level probe. This addition of water is necessary because the level tends to fall due to the evaporation of bath B which is heated to 60 ° C. In a particular embodiment of the invention, the corrosion inhibitor is dosed in the bath independently of the surfactant and pH agent dosage. This assay is performed with an automatic dosing means of the type used to assay the pH agent. However, the individual determination of the corrosion inhibitor is not mandatory. Indeed if it is found that the corrosion inhibitor disappears from the bath at the same time and in the same proportions as the surfactants then this inhibitor is mixed with the surfactants at a predetermined rate and in this case it is dosed at the same time as these surfactants, that is to say during the pouring of the pre-dosed mixture of surfactants and corrosion inhibitor. All these probes make it possible to study the current composition of the bath according to the first method or possibly to the second method or possibly by combining these two methods. The use of surfactant dosing means, water, the pH AgpH agent and optionally a corrosion inhibitor makes it possible to stretch the bath towards its ideal formulation.

In a particular embodiment of the regulating device 1, it is conceivable to have an oil content measuring means adapted to perform, in an automated manner, a measurement by acid / base titration of at least a part of the bath in accordance with FIG. the first method of determining the volumes of Veq acid required to have a neutral sample pH. But it has been found that with a de-oil deoiler performance maintaining the bath oil content constant and at a known level it is not necessary to measure this oil content of the bath. The means for measuring the current surfactant content is adapted to measure the anionic surfactant content by using the conductivity measurement K made by the SkO probe. Knowing that the oil content is kept constant by the de-oil de-oiler, the conductivity of the bath therefore increases linearly only as a function of the anionic surfactant content.

As has been seen above, it is also possible to evaluate the content of the different types of surfactants contained in the bath by combining the measurement of conductivity with the Sk0 probe and an optical measurement of micelle size. This optical measurement is performed by the Dynamic Light Diffusion technique. For this purpose, the means for measuring the current surfactant content comprises, in addition to the conductivity probe SkO, an optic probe S opti which measures at least the content of micelles of small sizes and consequently the content of free surfactants. By this method, the contents of free surfactants are evaluated and insofar as these surfactants have significant size differences (which is not the case for SDS and Tween80), it would also be possible to know the respective contents of each of the surfactants. surfactants present in the bath. The control unit UC is programmed so that depending on the contents of surfactants evaluated by measurements and according to the oil content which is set by adjustment of the de-oiler or possibly indicated by an acidic dosimeter base, this unit UC regulates the admission of the surfactants SDS and Tween80, H2O water, pH-AgpH agent and corrosion inhibitor to make the composition of the bath to a composition identical to that of said ideal bath according to the invention (see first aspect of the invention). 'invention). The control unit UC is programmed to control: the addition of anionic surfactant if the required level of conductivity K is lower than a desired value (for example less than 540p5 / cm) and if the level of the bath is too low ( that is to say less than a desired level value - the addition of water if the required conductivity level K is greater than a desired value and if the bath level is too low (ie less than one desired level) - the addition of the pH agent if the pH level indicated by the pH agent is too low compared to a desired pH value (in this case, to preserve the parts, wants the pH to be higher than 8.5) and - the addition of water if the pH is too high compared to a desired pH value (in this case, to preserve the parts, we want the pH is less than 9.5) E) THE PROCESSING DEVICE FOR METAL ALLOY PARTS According to another aspect of the inventio n, there is provided a device 5 for processing parts P metal alloy to protect them against corrosion. This piece processing device 5, visible in FIG. 4, integrates the bath regulating device 1 described above with reference to FIG. 5. This piece processing device 5 further comprises a BpassivHNO3 passivation bath containing nitric acid for passivating the metal alloy parts previously cleaned with the cleaning bath B. This part treatment device 5 also comprises several rinsing baths Br1, Br2, Br3 arranged between the cleaning bath B and the passivation bath BpassivHNO3 . One of these rinsing baths Br3 contains water and a corrosion inhibitor INHIB CORROS which is preferably sodium metasilicate Na2SiO3 whose concentration in the rinsing bath is at least equal to 1%. It should be noted that each of the cleaning baths B and rinsing baths Br1, Br2, Br3 can be supplied with corrosion inhibitor INHIB CORROS by specific dosing means. One of the dosing means regulates the corrosion inhibitor concentration of the rinsing bath Br3 about a predetermined concentration value specific to the rinsing bath Br3. This bath Br3 is the last rinsing bath through which the cleaned parts P pass before being passivated in bath B passivHNO3. These regulations of the corrosion inhibitor contents can take into account measurements of concentration of each of these baths in corrosion inhibitor in order to be relatively precise or simply to take into account estimations of concentrations depending on the amount of water, of surfactants, of pH agent introduced into the baths, respective measured levels of the baths and the mass of material removed by the de-oiler. It should be noted that in the example of FIG. 4, there are 3 rinsing baths BR1, Br2, Br3, but the number of these baths must be at least two if it is desired to rinse the parts effectively before introducing them. in the BpassivHNO3 passivation bath. The first of these baths allows a rough rinsing of the room to remove the surfactants and pH agent. The last of these rinsing baths is to protect the part against corrosion again before it is immersed in the Bpassiv HNO3 passivation bath. The use of such a Br3 rinse bath with pH inhibitor allows the cleaned pieces P to be stored in a Stk1 waiting stock while waiting for the volume of cleaned pieces to passivate to be sufficient to start the passivation. During this waiting at the Stk1 stock, the pieces P do not corrode, thus improving the homogeneity of the passivation.

These rinsing baths Br1, Br2, Br3 are in series so that each piece P passes successively through all these rinsing baths. Each of these respective rinsing baths is equipped with a clean conductivity sensor: respectively named Ski, Sk2, Sk3. The conductivity measurement of a rinsing bath makes it possible to know its pollution level and makes it possible to condition its replacement as a function of this conductivity. Finally, it can be seen that, once passivated, the pieces P treated against corrosion are stored in a second stock Stk2 waiting to be used.

Claims (8)

REVENDICATIONS1. A method for evaluating the capacity of a cleaning bath containing at least one surfactant to perform a de-oiling function of parts, in which: - the size of micelles contained in the bath is evaluated, these micelles being at least partially formed of said surfactant; and the capacity of said bath to absorb oil according to the micelle sizes evaluated is evaluated. 2. Evaluation method according to claim 1, in which: from a given population of micelles whose size has been evaluated, the rate of these micelles belonging to a first set of small micelles and / or the rate of these micelles belonging to a second set of large micelles compared to small size micelles; and when at least one of these levels passes a predetermined value, then it is considered that the bath is unfit for its cleaning function and the dosage of surfactants is changed or the bath is replaced by another cleaning bath. 3. The evaluation method according to at least one of claims 1 or 2, wherein the micelle sizes are evaluated according to the Dynamic Light Diffusion (DLS) technique. 4. A method of evaluating the capacity of a cleaning bath according to at least one of claims 1 to 3, wherein the bath evaluated is a cleaning bath for metal alloy parts comprising aluminum and / or nickel and / or iron and / or titanium and / or copper, this bath comprising water, an anionic surfactant, a nonionic surfactant, a corrosion inhibitor adapted to form, on each piece metal alloy bath outlet, a layer limiting the corrosion of these parts, a pH agent adapted to limit the variation of the pH of the cleaning bath, the bath having a mass concentration of anionic surfactant and nonionic surfactants less than 3%. 5. Evaluation method according to claim 4, wherein the mass concentration of anionic and nonionic surfactant is between substantially 1% and 2.5% and preferably substantially equal to 2%. 6. Evaluation method according to any one of claims 4 or 5 wherein: the anionic surfactant of the bath is SDS, that is to say sodium lauryl sulphate; and the nonionic surfactant of the bath is Tween 80, that is to say polyoxyethylene-80-sorbitan monostearate, the mass concentration of the SDS bath being substantially 1% and the mass concentration of the Tween 80 bath. being substantially 1%. 7. Device for evaluating the capacity of a cleaning bath containing at least one surfactant to provide a de-oiling function of parts, characterized in that it comprises: a measurement system (3) of physical parameters of the bath (B) representative of its ability to form micelles with bath surfactants and oil present in the bath (B); the physical parameter measuring system (3) comprising. measuring means (Sk0) adapted to estimate the current content of surfactant contained in the bath by observing the micelle sizes contained in the bath; and a measuring means adapted to estimate the current oil content contained in the bath; The device of claim 7, wherein the means for measuring the current surfactant content is adapted to evaluate micelle sizes according to the Dynamic Light Diffusion (DLS) technique.