Organic phosphatizing composition and system for using it

Abstract: The composition comprises two or are mixed solvents having a flash point higher than 65°C and a vapor tension, at 20°C, lower than 2 mm Hg, which comprises 85 ÷ 99% of the composition. The composition also comprises polyphosphates, including acid phosphates and/or free phosphoric acid and possible surface active agents, in an amount of 1 - 15%. The phosphatizing system comprises a processing section (1), a blowing section (2) and drying section (3), as well as a solvent recovery section (4).

Description: BACKGROUND OF THE INVENTION The present invention relates to an organic phosphatizing composition and a system for using it, as well as methods for pre-processing and recovering solvents. As is known, the so-called single stage organic phosphatizing method is a very advantageous method for processing metals, which provides the possibility of degreasing and phosphatizing metals in a single step. This organic phosphatizing method is conventionally carried out by using a polyphosphate solution, diluted in suitable solvents, in which metal pieces are immersed for degreasing purposes. After the degreasing step, because of the acidity of the polyphosphate, an acid attack occurs followed, after the withdrawing of the piece and its drying for evaporating solvents, a deposition of a polymeric film which prepares the metallic surfaces for a subsequent painting step. The above mentioned process, in particular, is of a "permanent" type and, accordingly, for properly carrying out it, it is necessary to provide stable polyphosphates, which are stable in the presence of oils and fats and, moreover, are adapted to provide a film in the presence of these polluting substances. Inflammable and not inflammable chlorinated solvent based compositions and chlorinated solvent free inflammable compositions are usually commercially available. These products, however, are preferably used by an immersion process, since, if they would be used in spraying processes, then the evaporation loss of the solvent would be comparatively high with a consequent increase of the processing cost and environment pollution because of the varying conditions of the dry residue of the polyphosphate solutions. In this connection, it should be pointed out that, from an ec.ologic standpoint, the organic single-stage phosphatizing method does not present, unlike the conventional phosphatizing method, problems relating to the processing of the sewage polluted materials to be disposed. On the contrary, the mentioned organic single-stage phosphatizing method involves a release into the environment of solvent vapors, however in an amount less than that released from degreasing methods using chlorinated solvent vapours. Recentely, moreover, organic phosphatizing systems have been designed, which provide for the use of different formulation polyphosphates and which provide an improved resistance to corrosion and, moreover, can be also used for particular finishing operations such as, for example, by using polyester powders which could not previously be used in organic phosphatizing methods. The document FR-A-1450079 describes a cleaning and phosphating composition comprising 92-95% (preferably) of a solvent mixture of high boiling aromatic hydrocarbons and ethylene-glycol-ethers and 0.5-4% phosphoric acid. The composition can be applied by spraying or immersion of the metal to be treated. The document DE-A-3708909 discloses a cleaning and phosphating composition containing 0.07-2.5% phosphoric acid, 0.1-1% zinc phosphate and preferably more than 85% of a halogen free solvent or mixtures of such solvents. As solvents are mentioned: aromatic hydrocarbons, acetate esters, mono-di-, or tripropylene-glycolethers and mono-,di-, or triethyleneglycolethers with a C1-C5 ether group. The solution is applied by immersion of the metal substrate. The document GB 887 159 discloses an apparatus for cleaning and coating metal articles under an atmosphere of degreasing solvent vapour, comprising a treating vessel divided into three sections for the degresing, spray-panting and coalescing or smoothing of the sprayed coating in sequential order,said sections being divided by low partitions for the retention of liquid solvent and coating solutions containing said solvent,heating means for heating and boiling said solvent and solutions in said sections, pumps and sprays for treating the articles with the solvent and coating solutions retained in said sections, a conveyor for carrying the articles through the treating vessel, openings in the upper part of the vessel and coaling means for condensing solvent vapours. SUMMARY OF THE INVENTION The main object of the present invention is to provide such an organic phosphatizing composition which has all of the advantages of known phosphatizing compositions and which, moreover, is not inflammable, free of any chlorinated solvents, free of dangerous products to be specifically indicated in the composition formulations, as provided by enforcing rules, and which, moreover, is very satisfactory from a pollution-ecologic standpoint. Another object of the present invention is to provide such a single-stage phosphatizing composition which has a very high metal degreasing capability. Another object of the present invention is to provide such a composition which is adapted to solubilize both polyphosphates and oils and fats. According to one aspect of the present invention, the above mentioned objects, as well as yet other objects, which will become more apparent hereinafter, are achieved by an organic phosphatizing composition according to claim 1. The invention further relates to a method for applying such a phosphating composition on a metal piece and to a phosphating apparatus for phosphatizing metal pieces by using such a composition as claimed in claims 2 and 3. In particular, the solvents to be used in the composition of the present invention must have the following properties: 1) they must be high boiling solvents (having a boiling temperature higher than 125°C and preferably higher than 200°C), 2) they must have a very low vapor tension, less than 266Pa (2 mm Hg) at 20°C, and preferably much lower than this value, 3) they must have a high flash point, usually higher than 65°C and preferably much higher, 4) they must not comprise chlorinated solvents and, generally, halogenated solvents, 5) they must not comprise any substances classified as dangerous and, more specifically they must not be labeled as risk substances, according to the enforcing rules. Thus, by way of an example, the following solvents can be advantageously used: 1) Glycol ethers from propylene oxide, and preferably dimers or trimers such as, for example: Dipropylenglycolmonomethylether(DPM) Dipropylenglycolmonoethylether (EDP) Dipropylenglycolmono-n-butylether (DPnB) Dipropylenglycolmonoisobutylether (DPiB) Tripropylenglycolmonomethylether(TPM) Tripropylenglycolmono-n-butylether (TPnB) Propylenglycol phenylether (PPh) 2) High boiling aromatic solvents such as, for example: Solvesso 150(R), ShellsolAB(R) or the like (S150) Solvesso 200(R) or the like (S200) In the following description, the above indicated solvents will be identified with reference to the letters written within parenthesis. In this connection it should be apparent that the solvent mixtures must be formulated for meeting the above requirements of solubility, hydrogen binding properties and, moreover, the made mixture must be a good solvent both for polyphosphates and oils and greases. The above listed solvent mixtures have been experimentally tested with a great success even if they involve small differences in the corrosion resistance. In the following table have been identified at A the compositions in which prevails the first of the mixture solvents and at B the compositions in which prevails, as far as possible, the second solvent of the mixture. In actual practice, according to the invention, it is possible to prepare organic phosphatizing solutions which do not include any chlorinated solvents and which can be also spray applied because of the low vapour tension of the contained solvent substances and which compositions, moreover, are not inflammable (they are only combustible) since they have a flash point higher than 65°C, said compositions being prepared starting from the following solvent mixture: Glycolethers from propyleneoxide (DPM, EDP, DPnB, DBiB, TPM, TPnB, PPh, and so on) 25 - 75%; high boiling aromatic solvents (such as S150, S200 or the like), 75-25%; It should be apparent that it will be possible to prepare mixtures including three or more solvents, by mixing at will the above mentioned solvents. This procedure does not involve any formulation problems even if it does not provide further advantages and involves a less efficient control of the solvents which can be recovered and/or reused, as it will become more apparent hereinafter. The above mentioned products, in particular, do not require, according to the CEE'S standard, any risk labels and have TLV's which can not be practically achieved and, accordingly, can be used safely. The phosphatizing system as defined in claim 3, in turn, comprises a processing section, a blowing section and a drying section, as well as a solvent recovering section. BRIEF DESCRIPTION OF THE DRAWINGS Further characteristics and advantages of the phosphatizing composition and system, according to the present invention, will become more apparent from the following detailed disclosure of some preferred embodiment thereof, which are illustrated, by means of an indicative but not limitative example, in the figures of the accompanying drawings, where: Figure 1 shows an operating sketch of the phosphatizing system according to the invention; Figures 2 and 3 are respectively an elevation and top plan view of a static type of processing basin; Figures 4, 5 and 6 are respectively an elevation, top plan and side view illustrating an in-line processing basin; Figures 7 and 8 are respectively a front and cross-sectional view illustrating the drying section included in the system according to the invention; Figures 9, 10 and 11 illustrate three possible types of washing columns; Figure 12 is a schematic view illustrating the solvent recovering apparatus of the subject system; Figure 12a is a cross-sectional view illustrating a so-called Florentine separator. DESCRIPTION OF THE PREFERRED EMBODIMENTS With respect to the atmospheric pollution, it should be pointed out that the processing and blowing stages of the subject system, which will be disclosed in a core detailed way hereinafter, provide very reduced amounts of solvents emissions. In the drying step, on the contrary, are necessarily generated solvent vapours in an amount corresponding to about 20-25 g/processed m². These emissions are anyhow recovered. With respect to the phosphatizing system, and with reference to figures 1 and 2, it should be apparent that this system comprises respectively a processing section 1, a blowing section 2, a drying section 3 and a solvent recovery section 4. More specifically, the processing section can comprise a static or batch processing basin or tank 5, or a continuous processing or in-line basin or tank 6, which are substantially constructed like tanks or basins used for conventional organic phosphatizing processes. In particular, on the delivery side of the filtering circuit, indicated overally at the reference number 7, of the above mentioned static basin, there is advantageously arranged a manually movable sleeve 8 adapted to facilitate the mechanical cleaning operations on the pieces 9 to be processed which are driven by hoist device 10 provided for sliding along a single rail 11. The above disclosed basins are provided by a removable double bottom 13 for collecting sludges, as well as an output shut-off valve 14, an inlet shut-off valve 15, a ball valve 16, on the bottom discharge, and a discharge vessel well 17. In particular, the orientable jet from the sleeve provides an accurate cleaning of the critical points of the pieces to be cleaned. That same result, moreover, can also be achieved by using a plurality of nozzles (of the type which will be disclosed in a more detailed way hereinafter), so as to provide a mixed immersing/ spraying system. The nozzles, in particular, will be energized as the piece is withdrawn from the processing basin. Even when an in-line basin 6 is used, nozzles can also be arranged at the outlet of said basin, in order to facilitate the cleaning operations of difficult areas. In case a spraying nozzle ramp is used, the nozzles will be positioned so as to prevent polyphosphate aerosols to exit the processing tunnel, the outline of which is indicated at 12. Also in this case, it is indispensable to provide air blades at the inlet and outlet of the tunnel with a limited drainage which, after filtering-out of the aerosols, will be sent to a subsequent solvent recovering column. A possible modification of the in-line installation consists of a two-chain system which, with suitable lowering devices, enables to use processing tanks similar to those ones adopted for static installations. The above disclosed processing section 1 can also comprise a spray processing tunnel, with related ramps (not specifically shown), the construction of which is similar to that one used in conventional phosphatizing and/or phosphatizing-degreasing systems. Also in this case it is recommendable to prepare an organic phosphatizing material plenum chamber in order to avoid oil poliphosphate saturation due to the treatment of too oily and fatty articles. Like in the immersion processing, moreover, a filtering device will be provided, which can comprise a bag-filter and can be controlled by the same pump which supplies the spraying nozzles. With respect to the latter, any suitable nozzles used for conventional phosphatizing methods can be used, possibly made of a stainless steel material (for example AISI 303). In particular, it is preferable using nozzles having an opening angle of 60/90 with useful jets of 20-30 cm. With respect to the jet shape, it will be defined depending on requirements and on the pieces to be phosphatized and considering that: nozzles with a blade jet provide a greater pressure, with a consequent high mechanical cleaning effect; spraying heads with a solid conic jet efficiently cover broad surfaces of the piece. The operating pressure ranges usually from 0,5 to 1.51·10⁵Pa (0.5 to 1.5 atm). Downstream of the processing section there is the blowing section 2 installed to remove quickly the excess processing product remaining on the processed pieces. The blowing step, in particular, can be performed by using air circulation generated by centrifugal fans 18, with a high head of 980-1170 Pa or more (100-120 mm or more of water column), the airflow being adjusted so as to provide a flow output rate of at least 5 m/s. Alternatively, suitable spraying nozzles can be provided, as suitably arranged depending on the pieces to be processed and supplied by sources adapted to provide a high output speed of 8 ÷ 15 m/ sec. In this connection, it should be apparent that the nozzle must operate on the pieces from the top toward the bottom thereof, so as to accelerate the natural gravity draining process and they must operate with a sufficient power to remove any excess of the processing product. It should be apparent that the blowing step affords the possibility of: eliminating a long draining time; eliminating possible held by liquid materials which would be susceptible to cause painting defects; recovering of the polyphosphates and reduction of the consume due to an entraining of the product. On a suitably blown product, from 20 to 25 g/m² of diluted material should be held, with the exception of possible greater amounts on pieces having specific shapes. In this connection it should be pointed out that the mentioned blowing section is advantageously located inside a suitable casing (tunneling casing). At the inlet and outlet of the blowing section, moreover, are provided air blades of suitable strength, adapted to operate as pneumatic gates. The drying section essentially comprises an air circulating oven, consisting, for example, of a tunnel 19 defined, at the bottom and side portions thereof, by a box body 20 having through its inner walls, a plurality of slots 21. This box-like body is supplied with pressurized hot air, by means of the air source 22 and centrifugal fans 23 conveying the hot air through ducts 24. The hot air, which is "laminated" through the above mentioned slots, arrives into the tunnel 19 with a suitable turbulence, so as to impinge on the metal pieces 9 sliding on the rail 11 through the tunnel itself. In this connection it should be apparent that this hot air can be re-cycled with the exception of an air cage corresponding to 10 ÷ 15% which will be sent to the column for washing and recovering solvents. In particular, since it is preferably that the air sent to the subsequent washing column through the duct 25 arrives at this column with a temperature as low as possible, an air/air type of exchanger 26 can be advantageously provided for lowering the temperature of the air. In order to prevent losses of this hot air saturated in processing solvents, pneumatic doors 27 must be fitted at the input and output of the tunnel and are controlled by a centrifugal fan 28 which sucks air from the top portion of the section. In order to further limit the thermal losses, additional automatic mechanical doors can be provided and adapted to be opened only when the metal pieces to be dried pass therethrough. Moreover, it is recommendablethat the tunnel inlet and outlet doors have an extension as small as possible, that is just sufficient to allow for the smallest piece to pass therethrough. Downstream of the mentioned drying section will be arranged the above mentioned solvent recovery section 4. This solvent recovery procedure which can also be performed by a simple but expensive cooling(by thermal exchange of the hot air sent from the drainage of the drying section, because of the low vapor tension of the selected solvents), is preferably performed by sending the air to be processed to the washing column indicated at 29 in figure 1. More specifically, an absorbing column can be provided including a spray cyclone 30 and having a tangential air input, whereas the washing liquid is sprayed, as shown in the figure, for a height sufficient to wash air and cool it. According to an alternative embodiment, the washing column 31 can comprise a plurality of stacked plates 32, in any suitable number, and, in this case, the air to be washed, introduced from the bottom, will move in a counter-current relationship with respect to a washing liquid. According to a preferred embodiment, the washing column 33 is provided with an intermediate portion 34, defined by holding nets 35 and filled with a suitable inert material, the function of which is that of facilitating the contact of the air to be washed and cooled, introduced from the bottom and the washing liquid, introduced from the top with a counter current relationship. The mentioned inert material can consists, for example, of crushed stones, of round shape, ceramic material ring and/or ball members, polypropilene hollow balls or rings, of different diameters and the like. In this connection, it should be pointed out that to the washing column are conveyed the following air drainages: a drainage coming from the optional air blades of the processing section, at room temperature; a drainage coming from the air blades of the blowing section, at room temperature; hot drainages coming from the drying section and perimetrical air blades of that same section, The washing column, moreover, must be so designed and arranged as to allow the temperature of the air to be lowered to limit values 5 ÷ 10°C higher than the room temperature, so as to bring the vapor phase in equilibrium with the counterfed processing liquid. From the top of the column washed air 36 will exit. Since, as is known, based on the Raoult law which is valid for vapors following the ideal gas laws, the partial pressure of each component in the vapor is equal to the product of its molar fraction (X) in the liquid x the vapor tension (P) of the product under examination at the system temperature: p i = P i x X i where p i = partial pressure of the component (i) in the vapor P i = vapor tension of the component (i) at the temperature T of the system X i = molar fraction of the component (i) in the liquid, it follows that,since solvents here selected have a very low vapor tension, the concentration of these solvents will be very low, whilst the air will be moisture saturated. In actual practice, however, the solvent vapours are not ideal solvent vapors. Because of this it is necessary to amend the above mentioned law by including therein a multiplication factor which has a thermodynamic meaning of "activity coefficient" and the value of which, anyhow, is never such as to modify the above qualitative disclosure. From the above discussion, it will be apparent that the air exiting the washing column is substantially purified and only moisture saturated. In order to understand what occurs at the bottom of the washing column, it should be remembered that a ternary mixture, consisting of two organic solvents one of which is a hydrophylic solvent, pluswater, usually this mixture naturally separates into two distinct phases. The first defined for simplicity "aqueous phase" which mainly holdswater. The second defined for simplicity "solvent phase" which holdssolvents and a small amount of water. All of the disclosed solvents, with the exception of PPH are, in the liquid status, lighter than water; accordingly the solvent layering will usually occur with the aqueous phase at the bottom and the solvent phase at the top. By way of an example, in the diagram of figure 13 has been illustrated the case comprising water, indicated at A in the diagram, and a completely mixable solvent both in water and in the other solvent (TPM), indicated at B in the diagram, and, finally, a completely water not mixable solvent (S150), indicated at C in the diagram. A combination of A+B+C having a rate composition of %A = 100 x A A+B+C %B = 100 x B A+B+C %C = 100 x C A+B+C and pertaining to a straight line WA (for example the point P of the diagram) is mixed into the two phases, aqueous W and solvent S. The slopes of the straight lines WS are characteristic of each ternary system. It should be apparent that if we start from a point W and add a mixture of the solvents B and C so as to cause the point representative of the composition of the system A+B+C to be displaced substantially along the straight line WS, then we will have the formation of two phases: a solvent phase substantially holding B+C and a small amount of water and aqueous phase which is practically nearly equal to the starting phase the offset is due to the small amount of water which is present in the phase S). From the above it should be apparent that by selecting suitable ratios of B and C which can be determined on the basis of the cross point of the straight line WS and line segment BC, and with small amounts of added water, the system can be controlled in an equilibrium condition. Different solvent systems bring to conditions that can also differ from the shown condition but which can always conceptually brought back to the shown condition. At the base of the washing column will have substantially a liquid which is rich in the solvents restrained in the air to be washed or cleaned. Since the washing or cleaning liquid is always selected with a composition corresponding to the proper point W,it will be mixed into two phases. Thus it will be sufficient to convey it through a duct 37 to a Florentine separator 38 which is substantially formed by a vessel including two possible outlets,that is a bottom outlet 40 and a top outlet 41 provided with corresponding control gates 42. If the solvent phase is lighter than water (as shown in the figure),then the bottom outlet,or water phase outlet,will be coupled,through a pump 43 and an exchanger 44 with the head of a generic washing or cleaning column,whereas the top outlet will convey to the outside the solvent phase. The exchanger 44 is provided for introducing into the column 29 the washing liquid at a sufficiently low temperature to allow for the air to be cleaned to be cooled. During the operation it would be advantageous to hold the top outlet in a closed condition.At the end of the working day,a rest condition will provide a perfect separation or "layering" of the two phases. The separation interface will lower because of the evaporated water removed together with the cleaned air. Thus,it will be necessary: 1) to add water from the water supply system so as to bring the separation interface to the theoretical level. This operation will be facilitated by the provision of an ispection door or port 51. 2) to open the top outlet so as to cause the solvent recovered from the column to exit the Florentine separator. The recovered solvent,in particular,is alternatively sent to a first 45 and second 46 vessel which form an integrating portion of a subsequent dehydration section,indicated overally at the reference number 47. In order to facilitate a better phase separation,the Florentine separator can comprise a labyrinth path,as exemplary shown in figure 12a. It should be apparent that if the solvent has a weight greater than that of the water, then one has to work on the top outlet as indicated for the bottom outlet and on the bottom outlet as indicated for the top outlet. The solvents brought to the vessels 45 and/or 46 also hold a water fraction. If,as for example propylene oxide glycolethers are used, the presence of water is significative,then the use of such a solvent will bring to the so-called "flash-rust" effect which occurs at the drying step of the organig phosphatizing method. The developped brown color causes the processed piece to be discarded,even if the results, from the corrosion resistance standpoint would be acceptable. In these cases,accordingly,this solvent must be dehydrated,before reusing it. Because of this requirement,a dehydrating section has been provided which,as stated,must be actually provided only if the water amount held in the solvent phase is such as to originate the mentioned "Flash-rust" effect. This section comprises,in particular,a dehydrating apparatus 48 including a cylinder provided, at its end portions,with very fine mesh nets and made of a thermal resistant glass or steel,with a large inspection port. Within this cylinder there is arranged a dehydrating material,consisting of molecular sieves or highly water absorbing salts or, preferably,silica gel,holding an indicating or labeling substance to color the product in blue if it is anhydrous or in pale pink if it is water saturated. Owing to this provision,it will be practically possible,by a simple visual inspection,to evaluate the efficiency of the dehydrating product. In this connection,it should be further pointed out that the apparatus 48 must contain a sufficient silica gel amount,with a proper safety tolerance range,to recover or regenerate the product held in the vessels 45 and 46. For closing the cylinder there are provided two flanged covers supporting tubes for conveying the liquid to be dehydrated. There are moreover provided a passage in the bottom cover, with a related shut off valve for the air at 120°C coming from the drying air source, and an air outlet through the top cover, also provided with a shut off valve 50. The outlet air will be sent,as shown in the diagram of figure 1, to the air washing or cleaning column, From an operating standpoint,if the solvent held in the vessel 45 must be dehydrated,then the following method should be used: 1) the gate 52 is closed so as to prevent any solvent from entering; 2) the gates 53,54,55,56 and 57 are opened 3) the pump 58 is actuated and the solvent is circulated. A treatment for about two hours will be sufficient :however the silica gel loaded material must be held under control in order to detect a possible water saturation thereof.The solvent,at this time,is ready to be reused. 4) the pump 58 is stopped 5) the gates 53 to 57 are closed again. The dehydrated solvent can be stored in the vessel 45 and,as it must be reused,it can be removed through the gate 59. At this time, it will be necessary to regenerate the silica gel for the subsequent dehydration cycle and,to that end,the gates 49 and 50 will be opened and air will be blown into the apparatus 48, at a temperature of about 120°C, supplied by the hot air source of the drying section. In particular the outlet air of said apparatus will contain at the start the solvents which have wetted the silica gel and then the water stripped therefrom. In this connection it should be apparent that if the recovered solvent amount is small,then the solvent can also be dehydrated in a simplified way by arranging in the vessel 45 a bag containing a sufficient amount of silica gel.This silica gel,as water saturated,can be easily brought to the drying oven to be regenerated.

Claims: A combustible but not inflammable organic phosphatizing composition for degreasing and phosphatizing metal surfaces in a single stage, characterized in that said composition comprises two or more solvents, which do not comprise halogenated solvents, said solvents having a boiling temperature greater than 125°C, a flash point higher than 65°C, and being of a not toxic, harmful or irritating type, and with a vapor tension at 20°C lower than 266 Pa (2 mm Hg), in an amount of 85-99% by weight, and polyphosphates, acid phosphates and/or free phosphoric acid as well as surface active substances, in a total amount of 1-15% by weight, and that said solvents comprise propylene oxide glycol ethers in an amount of 25 to 75% by weight and aromatic solvents in an amount of 75 to 25% by weight. A method for applying a phosphating composition according to Claim 1 on a metal piece to be phosphatized, characterized in that said method comprises the step of spraying said composition on said metal piece or immersing said metal piece in a bath of said phosphatizing composition. A phosphatizing system comprising an apparatus for phosphatizing metal pieces and comprising the composition according to Claim 1, wherein said apparatus comprises a processing section (1), a blowing section (2), a drying section (3) and a solvent recovery section (4), said processing section (1) including tanks (5, 6) for batch or continuous treatment including a filtering circuit (7) on a delivery side of which there is provided a manually movable sleeve (8) for mechanically cleaning metal pieces (9) to be cleaned, said metal pieces (9) being driven by a hoist device (10) slidably supported on single rail means (11), said tanks being provided with a removable double bottom (13) for collecting processing sludges, with an output shut-off valve (14), an inlet shut-off valve (15), a ball valve (16) and a discharge vessel well (17). A phosphating system according to Claim 3, wherein said apparatus is a combined immersion/spraying apparatus including a plurality of spraying nozzles actuated as a said metal piece (9) os withdrawn from a said tanks (5, 6). A phosphating system according to Claim 4, characterized in that said spraying nozzles are arranged at an outlet side of said continuous tank (6). A phosphating system according to Claim 3, characterized in that said blowing section (2) includes air generating centrifugal high head fans (18) providing an adjustable air flow having a flow rate of at least 5m/sec. A phosphating system according to Claim 3, wherein said drying section (3) includes a hot air circulating oven (19). A phosphating system according to Claim 7, characterized in that said hot air circulating oven (19) is a tunnel oven including a bottom and side box-like body (20) having a plurality of slots (21), and a pressurized hot air generating fan assembly (23) adapted to generate pressurized hot air and convey said pressurized hot air through duct means (25) of said oven. A phosphating system according to Claim 3, characterized in that said solvent recovering section (4) includes an air washing column (29, 31, 33) holding said solvents and operating by an aqueous washing liquid. A phosphating system according to Claim 9, characterized in that said column (29) comprises spraying cyclone means (30) having a tangential air inlet. A phosphating system according to Claim 9, characterized in that said column (31) comprises a plurality of stacked plates (32), air to be washed being supplied from a bottom portion of said washing column (31) to move in counterflow against said washing liquid. A phosphating system according to Claim 9, characterized in that said washing column (33) comprises an intermediate portion (34) defined by holding nets (35) and filled with an inert material, adapted to facilitate the contact of air (36) to be washed and cooled, introduced from the bottom of said column (33) and the washing liquid, said inert material comprising round crushed stone particles, ceramic material ring and/or ball members, polypropylene hollow ball and ring members of different diameters. A phosphating system according to Claim 9, wherein the liquid from the outlet of said washing column (33) is conveyed (37) to a Florentine separator (38) comprising a vessel including two outlets (40, 41) provided with respective gates (42), one (40) of said outlets, that is the water phase outlet (40), being coupled through a pump (43) and exchanger (44) to a head portion of said washing column, and the other outlet (41) conveying to the outside the solvent phase, the latter being alternatively sent to a first and second vessels (45, 46) included in a subsequent dehydration section (47) of said apparatus. A phosphating system according to Claim 13, characterized in that said dehydration section (47) comprises a dehydrating apparatus (48) including a cylinder made of a thermal resistant glass or steel with a large inspection port provided with very fine mesh nets therein a dehydrating silica gel material is arranged and holding an indicating means adapted to color in blue an anhydrous product and in pale pink a water saturated product, through said dehydrating apparatus (48) passing both the solvent to be dehydrated and hot air for recovering the silica gel bed.

Inventors: GUIDETTI GIANLUIGI, GUIDETTI, GIANLUIGI
Applicants: PAI KOR SRL, PAI-KOR S.R.L.
Application year: 1989
Main classification: C23C22
IPC codes: C23C22