CA2022728C - Process of producing phosphate coating on metals - Google Patents
Process of producing phosphate coating on metals Download PDFInfo
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- CA2022728C CA2022728C CA002022728A CA2022728A CA2022728C CA 2022728 C CA2022728 C CA 2022728C CA 002022728 A CA002022728 A CA 002022728A CA 2022728 A CA2022728 A CA 2022728A CA 2022728 C CA2022728 C CA 2022728C
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
- C23C22/08—Orthophosphates
- C23C22/18—Orthophosphates containing manganese cations
- C23C22/182—Orthophosphates containing manganese cations containing also zinc cations
- C23C22/184—Orthophosphates containing manganese cations containing also zinc cations containing also nickel cations
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
- C23C22/08—Orthophosphates
- C23C22/12—Orthophosphates containing zinc cations
- C23C22/16—Orthophosphates containing zinc cations containing also peroxy-compounds
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
- C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
- C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
- C23C22/36—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates
- C23C22/362—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also phosphates containing also zinc cations
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
- C23C22/77—Controlling or regulating of the coating process
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- Chemical & Material Sciences (AREA)
- General Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Chemical Treatment Of Metals (AREA)
- Materials For Medical Uses (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
In a process of phosphating iron and steel surfaces according to the low-zinc technology, a nitrite-free aqueous acidic phosphating solution at 30 to 64 °C
is used, which contains 0.4 to 1.7 g/l Zn 7 to 25 g/l P2O5 2 to 30 g/l NO3 and in which the weight ratio of free P2O5 to total P2O5 is adjusted to a value in the range from 0.04 to 0.20, H2O2 or alkali perborate is added to the phosphating solution in such an amount that - being in working condition - the peroxide concentration is not in excess of 17 mg/l (calculated as H2O2) and the Fe(II) concentration respectively is not in excess of 60 mg/l (calculated as Fe).
It will be particularly desirable to control the addition of H2O2 and/or alkali borate in dependence on the electrochemical potential, which is determined by a redox electrode.
The phosphating solution may additionally contain Mn, Ni, Co, Mg and/or Ca and/or fluoroborate, fluorosilicate and/or fluoride.
The process can particularly be used to prepare metallic surfaces before they are painted.
is used, which contains 0.4 to 1.7 g/l Zn 7 to 25 g/l P2O5 2 to 30 g/l NO3 and in which the weight ratio of free P2O5 to total P2O5 is adjusted to a value in the range from 0.04 to 0.20, H2O2 or alkali perborate is added to the phosphating solution in such an amount that - being in working condition - the peroxide concentration is not in excess of 17 mg/l (calculated as H2O2) and the Fe(II) concentration respectively is not in excess of 60 mg/l (calculated as Fe).
It will be particularly desirable to control the addition of H2O2 and/or alkali borate in dependence on the electrochemical potential, which is determined by a redox electrode.
The phosphating solution may additionally contain Mn, Ni, Co, Mg and/or Ca and/or fluoroborate, fluorosilicate and/or fluoride.
The process can particularly be used to prepare metallic surfaces before they are painted.
Description
PROCESS OF PRODUCING PHOSPHATE COATINGS ON
METALS
DESCRIPTION
This invention relates to a process of phosphating iron and steel surfaces according to the low-zinc technology with phosphating solutions which are free of nitrite and contain phosphate and nitrate and to the use of that process in preparing iron and steel surfaces for painting.
The zinc phosphating process is used on a large scale in the metal-working industry. The phosphate layers produced by that process on the treated metal sur-faces serve particularly to facilitate sliding and non-cutting cold-working as well as to afford protection against corrosion and as a adhesion base for paint.
As a pretreatment before painting, phos-phating processes using low-zinc technology afford special advantages. The bath solutions used for that purpose contain zinc in concentrations of only about 0.4 to 1.7 g/1 and on steel produce phosphate layers having a high proportion of phosphyllite, which results in a better adhesion of paint and in a higher resistance to migration under paint than hopeite derived from phos-phating baths having a higher zinc content.
Nitrite, chlorate and organic vitro compounds have proved particularly satisfactory as ac-celerators in low-zinc phosphating baths and result in a formation of uniformly covering phosphate layers of high quality in a short time. It is also known to use peroxides as accelerators in low-zinc phosphating baths.
Whereas peroxides would be preferably to the above-mentioned accelerators for the sake of working place hygiene and protection of the environment, their accele-rating action is not sufficient under the previously employed treating conditions. A further disadvantage of the per compounds resides in that that even a treatment for a long time will result only in relatively thin phosphate layers, which afford only a moderate protection against corrosion.
It is an object of the invention to provide for the zinc phosphating of iron and steel, optionally together with galvanized, zinc alloy-coated and aluminized steel and aluminium by means of nitrite-free low-zinc phosphating solutions a process which does not have the known disadvantages, particularly those mentioned hereinbefore.
In the process of the kind described first hereinbefore that object is accomplished in accordance with the invention in that the surfaces are contacted at 30 to 65 °C with an aqueous acidic phos-phating solution which contains 0.4 to 1.7 g/1 Zn 7 to 25 g/1 P205 2 to 30 g/1 N03 and in which the weight ratio of free P205 to total P205 is adjusted to a value in the range from 0.04 to 0.20, and H202 or alkali perborate is added to the phosphating solution in such an amount that - being in working condition - the peroxide concentration is not in excess of 17 mg/1 (calculated as H202) and the Fe(II) concentration respectively is not in excess of 60 mg/1 (calculated as Fe).
The process in accordance with the invent-ion is intended for the surface treatment of iron and steel. But low-alloy steel, galvanized steel, zinc alloy-coated steel, i.e., e.g., steel coated with ZnAl, ZnFe and ZnNi, aluminized steel, aluminum and its alloys may be treated together with iron and steel.
Phosphating is affected at temperatures in the range from 30 to 65 °C. Below 30 °C the phosphat-ing rate will not be sufficient for modern series pro-duction. Temperatures above 65 °C will result in disad-vantages, e.g., in a stronger incrustation of the plant.
As is usual in processes of the so-called low-zinc technology, the weight ratio of Zn to P205 in the phosphating solution is preferably (0.075 to 0.015) :1.
The content of perioxide or Fe(II) in the phosphating solution is determined in a conventional manner, e.g., by a titration with potassium permanga-nate. In accordance with a preferred feature of the .
invention the surfaces are contacted with a phosphat-ing solution in which the addition of H202 and/or alkali perborate is controlled in dependence on the electrochemical potential determined by a redox elec-trode. For instance, a platinum electrode and a suit-able reference electrode, such as a calomel or a silver-silver chloride electrode, can be used for that purpose. Such an electrode system may be used for a continuous monitoring of the phosphating solution and peroxide may be added in such a manner that the steady-state concentration of Fe(II) ions and the steady-state concentration of hydrogen peroxide are maintained within the above-mentioned limits.
The kinds and quantities of the cations and anions contained in the phosphating solution used in the process in accordance with the invention are so selected that the ratio of free P205 to total P205 is :=:' ~i~ e~
,. , between 0~0~- and 0.20~ .As a rul8~ a higher bath tempe-rature and/or a higher zinc concentration will require.
that ratio to be selected in the upper part of th~
above-mentioned range and a lower bath temperature and/or a lower zinc concentration will require said ratio to be selected in the lower part of said ranges In accordance with a preferred 'feature of the process in accordance with the invention9 the surfaces are contacted with a phosphating solution to which H202 and/or alkali perborate have been added in such an amount that the maximum peroxide concentration is 8 mg/1 and the maacimum Fe(7CI, concentration respectively is 30 mg/1.
In accordance with a further preferred feature of the invention the surfaces nre contacted with a phosphatxng solution which in addition contains up to 3 g/l manganese, up to 3 g/1 nickel and%lor cobalt up t~ 3 g/1 magnesium and/or up to 3 g/1 calcium. The co-use of manganese and/or maginesium and/or calcium will result in phosphate coatiaags which in addition to zinc and optionally :.~ron(I~) contain also skid catione.
Such miaced phosphates dist3.nguish by a higher resistance to alkali and are particularly suitable as a adhesion base for paint. Nickel and/or cobalt are preferably added in order to increase the aggressiveness of the phosphating solution en steel and - where zinc surfaces are treated too - to improve the phosphating of zinc surfaces. An optional addition of small amounts of copper will increase the accelerating activity of the phosphating solution. Alkali and/or ammonium are mainly used for the adjustment of the desired acid ratio.
In another desirable embodiment of the invention the surfaces are contacted with a phosphating solution which contains up to 3 g/1 fluoro-borate (calculated as BF4) and/or up to 3 g/1 silico-fluoride (calculated as SiF6) and/or up to 1.5 g/1 fluoride (calculated as F). In general, the anions fluoroborate, silico-fluoride and/or fluoride act to increase the phosphating rate and, in addition, will be of advantage if a treatment of aluminum-containing zinc surfaces is intended. The presence of free fluoride (F ) is essential for the formation of crystalline phosphate coatings on aluminum and its alloys.
Chloride and sulfate may be used to adjust the phosphating solution to an electrically neutral state and, in special cases, to increase the agressiveness. An optional co-use of, e.g., polyhydroxy-carboxylic acids, such as tartaric acid and/or citric acid, will permit an influence on the thickness of the resulting phosphate coatings and/or their weight per unit of surface area.
~~~~~~,>~f~~ r~~-If the phosphating solution contains also manganese and/or nickel and/or cobalt and/or magrie- , sium, the weight ratio of Mn:Zn, of (Ni and/or, Co):Zn, of ~g:2n and/ofi Ca:Zn should not be in excess of 2:1 in each case.
In accordance w3.th a further desirable embodiment of the invention the surfaces are contacted with a phosphating solution in which the content of free P205 or the ratio of free P2 5 to total P~05 is ad~justed__during the processing by an addition of man ganese carbonate, zinc carbonate and/or zinc oxide.
In that case it will be desirable to add said components in the form of an aqueous dispersion.
The process in accordance with the invention may be carried out by spraying, dipping, spray, dipping or flooding.
In accordance with a further desirable embodiment of the invention the metal surfaces are con-tatted with a phosphating solution from which water is removed and the removed water is replaced by an addition o~'rinsing water from the succeeding rinsing stage or rinsing stages. hater can be removed from the phosphating bath, e.g., by evaporation, reverse osmosis and/or elec-trodialysis. Particularly if H202 is used as a peroxide component, these steps will permit the process in accord--ante with the invention to be carried out in such a manner J ~ ~~ fs!
that a sewage which is contaminated with phosphate will not. be obtained as an effluent from the rinsing step which succeeds the phosphating. The rinsing stages suitably constitute a cascade of rinsing water, which flows oppositely to the workpieces from each rinsing stage to the next and is then supplied to the phosphating bath. In the phosphating bath the water thus supplied replaces the water which has been removed from the phosp2~ating solwtion as mentioned above" The water which has been removed from the phos-phating bath, e.g., by reverse osmosis or electrodialy-sis, may be recycled to the rinsing stages.
In another desirable embodiment of the process in accordance with the invention the sur-faces are contacted with a phosphating solution which is replenished by an addition of phosphate in which the ratio of free P205 to total P205 is (-0,54 to +0~20):1.
In that definition of the ratio of free P205 to total P205, the minus sign means that there is no free P205 but a paxt of th~ phosphate consists of secondary phos-pha'te. for instance, a value of minus 0~19 means that 1~6 of the total P205 are present as a secondary phos-ph ate .
In accordance with another definition the phosphate comprnents during replenishing ~
limited by a content of SCr~ secondary phosphate and ,. t ..~ a~ x." <l r J . .
,.
~$J $~d ;~ fd~'!~. ~...
5096 priaaa.r;~ phosphate (calculated, as P20~), on the one hand, and by a content of 80~ primary phosphate and 20%
free phosphoric acid. (calculated as P20~) on the other hand, Because liquid replenishing concen-traces are.wot stable in the stated range of free P2C3~
to total F~~5, the replenishing is usually effected in the process in accordance With the invention by means of at least two separate concentrates.
The process in accordance with the invention9 particularly in its preferred embodiment in e~hich the coating phosphating solution is replenished' can be carried out for a long time~to form satisfactoz°y coatings not onl;~ on iron and steel but also on accom-panying surfaces, namely, gavanized, zinc alloy-coated and aluminized steel and aluminumo the process in accordance pith the invention is of special advantage in pretreating sur-.
faces bef ore-th.ey are painted9 particularly by dip electro-coating, and is of special significance for the cataphore-tic dip electrocoating.
The invention will be explained more in detail and by way of example in the follloeving ~,.,~' samples .
~~~~r~ , rJ
-lo-Example 1 A phosphating solution to be sprayed contained 0.8 g/1 Zn free X205 - 1.0~ g/1 1.0 g/1 Ni total P205 - 13 g/1 1.0 g/1 Mn free acid - 0.9 points 2.6 g/1 Na 13.0 g/1 p~05 total acid _ 23 points 2 .'1 g/ 1' LV03 The concentration of H202 in said solution was varied between 10 and 70 mg/1 H~02 by an addition of H2Q2 and in the absence of H202 the concentration of iron(II) was varied between 10 and 90 mg/1 Fe(II) by a processing of sheet steel.
Steel sheets which had been degreased with organic solvent were sprayed with said baths at 58°C. In Figure l9 the weight of the phosphate coating is plotted which had been formed after a fraying time of 3 minutes. Figure 2 indicates the minimum phosphating times which have been determined in said experix~entse i.e.y the phosphating times which were required to deposit uniformly covering phosphate coatings on the sheets. ,, ~3oth figures represent the desirable result which is achieved with the process in accordance with the invention.
sample 2 In a phosphating apparatus having a cubic capacity of 5 liters, previously degreased sheets of steel (80%) and electrolytically galvanized steel (20%) were phosphated in alternation with a phosphating solution having the following composition:
0.8 g/1 Zn free acid: 0.9 points 1.0 g/1 Ni total acid: 23 points 1.0 g/1 Mn 2.6 g/1 Na 13.0 g/1 P205 2.1 g/1 N03 The solution was at a temperature of 55 to 60°C.
The treatment was effected by spraying for 3 minutes. The throughput amounted to 3 m2/liter of bath volume at a throughput rate of 0.1 m2/h. The composition of the bath was maintained by an addition of zinc carbonate and a suitably composed replenishing solution throughtout the processing.
The replenishing concentrate contained, by weight, 23.4 % P205 1.89 % Na 1.74 % Mn 1.34 % Ni 3.39 % Zn 0 . O1 % Fe (III) 3.09 % N03 and for replenishing to constant points was required in a rS ~) c; ~f'1 ~t IvI id ~~ f~.Y
an amount of 1~ g per square meter of surface area.
To adjust the ratio of free P~ 5 to total P205, basic zinc carbonate (53~5 Zn) was added to the bath in an amount of 1.8 g%m2. That replenishment corre~onds to a ratio of free P205 to total P205 of (-0.18) :1 .
In dependence on 'the measured electro--chemical potential. hydrogen peroxide was supplied to such a rate that the steady-state concentration of Fe(II) ions and the H202 concentration in the bath were not in excess of 10 mg/1 each. The resulting phosphate coatings were uniform and closed throughout and had a weight of 2.0-r0:2 g/m2 for steel and of 2.5-~~0.2 g/m2 on electroly-tically galvanized steel.
sample 3 In a phosphating apparatus having a cubic capacity of 5 liters, previously degreased sheets of steel {60~,), electrolytically galvanized steel (30gb) and aluminum{1096) of the A,lMg3 grades were treated in alternation with a phosphat3.ng solution which contained 0.8 g/1 Zn free acids 1.1 1.0 g/1 Ni total acid: 23 1.0 g/1 Mn 3.2 g/1 Na 13.0 g/1 P205 2.l g/1 N03 0.5 g/1 P
rd '! ) f t j ~) 27 ~ t~e :~ r.a _13~
V~hen the conditions mentioned aboee and steady-state concentrations of Fe(II) and F3202 not in excess o~ 6 m~/1 were maintained, uni.~orm and. closed coatings were formed on all three materials and had the following vrei~hts:
Steel: ~ 2.10.2 g/m2 electrodeposited 2.60.2 g/m2 zinc:
AlSi: 2.9_+0.3g/m~
Al~g3 : 3 a Z+V ~/~~ .
.3
METALS
DESCRIPTION
This invention relates to a process of phosphating iron and steel surfaces according to the low-zinc technology with phosphating solutions which are free of nitrite and contain phosphate and nitrate and to the use of that process in preparing iron and steel surfaces for painting.
The zinc phosphating process is used on a large scale in the metal-working industry. The phosphate layers produced by that process on the treated metal sur-faces serve particularly to facilitate sliding and non-cutting cold-working as well as to afford protection against corrosion and as a adhesion base for paint.
As a pretreatment before painting, phos-phating processes using low-zinc technology afford special advantages. The bath solutions used for that purpose contain zinc in concentrations of only about 0.4 to 1.7 g/1 and on steel produce phosphate layers having a high proportion of phosphyllite, which results in a better adhesion of paint and in a higher resistance to migration under paint than hopeite derived from phos-phating baths having a higher zinc content.
Nitrite, chlorate and organic vitro compounds have proved particularly satisfactory as ac-celerators in low-zinc phosphating baths and result in a formation of uniformly covering phosphate layers of high quality in a short time. It is also known to use peroxides as accelerators in low-zinc phosphating baths.
Whereas peroxides would be preferably to the above-mentioned accelerators for the sake of working place hygiene and protection of the environment, their accele-rating action is not sufficient under the previously employed treating conditions. A further disadvantage of the per compounds resides in that that even a treatment for a long time will result only in relatively thin phosphate layers, which afford only a moderate protection against corrosion.
It is an object of the invention to provide for the zinc phosphating of iron and steel, optionally together with galvanized, zinc alloy-coated and aluminized steel and aluminium by means of nitrite-free low-zinc phosphating solutions a process which does not have the known disadvantages, particularly those mentioned hereinbefore.
In the process of the kind described first hereinbefore that object is accomplished in accordance with the invention in that the surfaces are contacted at 30 to 65 °C with an aqueous acidic phos-phating solution which contains 0.4 to 1.7 g/1 Zn 7 to 25 g/1 P205 2 to 30 g/1 N03 and in which the weight ratio of free P205 to total P205 is adjusted to a value in the range from 0.04 to 0.20, and H202 or alkali perborate is added to the phosphating solution in such an amount that - being in working condition - the peroxide concentration is not in excess of 17 mg/1 (calculated as H202) and the Fe(II) concentration respectively is not in excess of 60 mg/1 (calculated as Fe).
The process in accordance with the invent-ion is intended for the surface treatment of iron and steel. But low-alloy steel, galvanized steel, zinc alloy-coated steel, i.e., e.g., steel coated with ZnAl, ZnFe and ZnNi, aluminized steel, aluminum and its alloys may be treated together with iron and steel.
Phosphating is affected at temperatures in the range from 30 to 65 °C. Below 30 °C the phosphat-ing rate will not be sufficient for modern series pro-duction. Temperatures above 65 °C will result in disad-vantages, e.g., in a stronger incrustation of the plant.
As is usual in processes of the so-called low-zinc technology, the weight ratio of Zn to P205 in the phosphating solution is preferably (0.075 to 0.015) :1.
The content of perioxide or Fe(II) in the phosphating solution is determined in a conventional manner, e.g., by a titration with potassium permanga-nate. In accordance with a preferred feature of the .
invention the surfaces are contacted with a phosphat-ing solution in which the addition of H202 and/or alkali perborate is controlled in dependence on the electrochemical potential determined by a redox elec-trode. For instance, a platinum electrode and a suit-able reference electrode, such as a calomel or a silver-silver chloride electrode, can be used for that purpose. Such an electrode system may be used for a continuous monitoring of the phosphating solution and peroxide may be added in such a manner that the steady-state concentration of Fe(II) ions and the steady-state concentration of hydrogen peroxide are maintained within the above-mentioned limits.
The kinds and quantities of the cations and anions contained in the phosphating solution used in the process in accordance with the invention are so selected that the ratio of free P205 to total P205 is :=:' ~i~ e~
,. , between 0~0~- and 0.20~ .As a rul8~ a higher bath tempe-rature and/or a higher zinc concentration will require.
that ratio to be selected in the upper part of th~
above-mentioned range and a lower bath temperature and/or a lower zinc concentration will require said ratio to be selected in the lower part of said ranges In accordance with a preferred 'feature of the process in accordance with the invention9 the surfaces are contacted with a phosphating solution to which H202 and/or alkali perborate have been added in such an amount that the maximum peroxide concentration is 8 mg/1 and the maacimum Fe(7CI, concentration respectively is 30 mg/1.
In accordance with a further preferred feature of the invention the surfaces nre contacted with a phosphatxng solution which in addition contains up to 3 g/l manganese, up to 3 g/1 nickel and%lor cobalt up t~ 3 g/1 magnesium and/or up to 3 g/1 calcium. The co-use of manganese and/or maginesium and/or calcium will result in phosphate coatiaags which in addition to zinc and optionally :.~ron(I~) contain also skid catione.
Such miaced phosphates dist3.nguish by a higher resistance to alkali and are particularly suitable as a adhesion base for paint. Nickel and/or cobalt are preferably added in order to increase the aggressiveness of the phosphating solution en steel and - where zinc surfaces are treated too - to improve the phosphating of zinc surfaces. An optional addition of small amounts of copper will increase the accelerating activity of the phosphating solution. Alkali and/or ammonium are mainly used for the adjustment of the desired acid ratio.
In another desirable embodiment of the invention the surfaces are contacted with a phosphating solution which contains up to 3 g/1 fluoro-borate (calculated as BF4) and/or up to 3 g/1 silico-fluoride (calculated as SiF6) and/or up to 1.5 g/1 fluoride (calculated as F). In general, the anions fluoroborate, silico-fluoride and/or fluoride act to increase the phosphating rate and, in addition, will be of advantage if a treatment of aluminum-containing zinc surfaces is intended. The presence of free fluoride (F ) is essential for the formation of crystalline phosphate coatings on aluminum and its alloys.
Chloride and sulfate may be used to adjust the phosphating solution to an electrically neutral state and, in special cases, to increase the agressiveness. An optional co-use of, e.g., polyhydroxy-carboxylic acids, such as tartaric acid and/or citric acid, will permit an influence on the thickness of the resulting phosphate coatings and/or their weight per unit of surface area.
~~~~~~,>~f~~ r~~-If the phosphating solution contains also manganese and/or nickel and/or cobalt and/or magrie- , sium, the weight ratio of Mn:Zn, of (Ni and/or, Co):Zn, of ~g:2n and/ofi Ca:Zn should not be in excess of 2:1 in each case.
In accordance w3.th a further desirable embodiment of the invention the surfaces are contacted with a phosphating solution in which the content of free P205 or the ratio of free P2 5 to total P~05 is ad~justed__during the processing by an addition of man ganese carbonate, zinc carbonate and/or zinc oxide.
In that case it will be desirable to add said components in the form of an aqueous dispersion.
The process in accordance with the invention may be carried out by spraying, dipping, spray, dipping or flooding.
In accordance with a further desirable embodiment of the invention the metal surfaces are con-tatted with a phosphating solution from which water is removed and the removed water is replaced by an addition o~'rinsing water from the succeeding rinsing stage or rinsing stages. hater can be removed from the phosphating bath, e.g., by evaporation, reverse osmosis and/or elec-trodialysis. Particularly if H202 is used as a peroxide component, these steps will permit the process in accord--ante with the invention to be carried out in such a manner J ~ ~~ fs!
that a sewage which is contaminated with phosphate will not. be obtained as an effluent from the rinsing step which succeeds the phosphating. The rinsing stages suitably constitute a cascade of rinsing water, which flows oppositely to the workpieces from each rinsing stage to the next and is then supplied to the phosphating bath. In the phosphating bath the water thus supplied replaces the water which has been removed from the phosp2~ating solwtion as mentioned above" The water which has been removed from the phos-phating bath, e.g., by reverse osmosis or electrodialy-sis, may be recycled to the rinsing stages.
In another desirable embodiment of the process in accordance with the invention the sur-faces are contacted with a phosphating solution which is replenished by an addition of phosphate in which the ratio of free P205 to total P205 is (-0,54 to +0~20):1.
In that definition of the ratio of free P205 to total P205, the minus sign means that there is no free P205 but a paxt of th~ phosphate consists of secondary phos-pha'te. for instance, a value of minus 0~19 means that 1~6 of the total P205 are present as a secondary phos-ph ate .
In accordance with another definition the phosphate comprnents during replenishing ~
limited by a content of SCr~ secondary phosphate and ,. t ..~ a~ x." <l r J . .
,.
~$J $~d ;~ fd~'!~. ~...
5096 priaaa.r;~ phosphate (calculated, as P20~), on the one hand, and by a content of 80~ primary phosphate and 20%
free phosphoric acid. (calculated as P20~) on the other hand, Because liquid replenishing concen-traces are.wot stable in the stated range of free P2C3~
to total F~~5, the replenishing is usually effected in the process in accordance With the invention by means of at least two separate concentrates.
The process in accordance with the invention9 particularly in its preferred embodiment in e~hich the coating phosphating solution is replenished' can be carried out for a long time~to form satisfactoz°y coatings not onl;~ on iron and steel but also on accom-panying surfaces, namely, gavanized, zinc alloy-coated and aluminized steel and aluminumo the process in accordance pith the invention is of special advantage in pretreating sur-.
faces bef ore-th.ey are painted9 particularly by dip electro-coating, and is of special significance for the cataphore-tic dip electrocoating.
The invention will be explained more in detail and by way of example in the follloeving ~,.,~' samples .
~~~~r~ , rJ
-lo-Example 1 A phosphating solution to be sprayed contained 0.8 g/1 Zn free X205 - 1.0~ g/1 1.0 g/1 Ni total P205 - 13 g/1 1.0 g/1 Mn free acid - 0.9 points 2.6 g/1 Na 13.0 g/1 p~05 total acid _ 23 points 2 .'1 g/ 1' LV03 The concentration of H202 in said solution was varied between 10 and 70 mg/1 H~02 by an addition of H2Q2 and in the absence of H202 the concentration of iron(II) was varied between 10 and 90 mg/1 Fe(II) by a processing of sheet steel.
Steel sheets which had been degreased with organic solvent were sprayed with said baths at 58°C. In Figure l9 the weight of the phosphate coating is plotted which had been formed after a fraying time of 3 minutes. Figure 2 indicates the minimum phosphating times which have been determined in said experix~entse i.e.y the phosphating times which were required to deposit uniformly covering phosphate coatings on the sheets. ,, ~3oth figures represent the desirable result which is achieved with the process in accordance with the invention.
sample 2 In a phosphating apparatus having a cubic capacity of 5 liters, previously degreased sheets of steel (80%) and electrolytically galvanized steel (20%) were phosphated in alternation with a phosphating solution having the following composition:
0.8 g/1 Zn free acid: 0.9 points 1.0 g/1 Ni total acid: 23 points 1.0 g/1 Mn 2.6 g/1 Na 13.0 g/1 P205 2.1 g/1 N03 The solution was at a temperature of 55 to 60°C.
The treatment was effected by spraying for 3 minutes. The throughput amounted to 3 m2/liter of bath volume at a throughput rate of 0.1 m2/h. The composition of the bath was maintained by an addition of zinc carbonate and a suitably composed replenishing solution throughtout the processing.
The replenishing concentrate contained, by weight, 23.4 % P205 1.89 % Na 1.74 % Mn 1.34 % Ni 3.39 % Zn 0 . O1 % Fe (III) 3.09 % N03 and for replenishing to constant points was required in a rS ~) c; ~f'1 ~t IvI id ~~ f~.Y
an amount of 1~ g per square meter of surface area.
To adjust the ratio of free P~ 5 to total P205, basic zinc carbonate (53~5 Zn) was added to the bath in an amount of 1.8 g%m2. That replenishment corre~onds to a ratio of free P205 to total P205 of (-0.18) :1 .
In dependence on 'the measured electro--chemical potential. hydrogen peroxide was supplied to such a rate that the steady-state concentration of Fe(II) ions and the H202 concentration in the bath were not in excess of 10 mg/1 each. The resulting phosphate coatings were uniform and closed throughout and had a weight of 2.0-r0:2 g/m2 for steel and of 2.5-~~0.2 g/m2 on electroly-tically galvanized steel.
sample 3 In a phosphating apparatus having a cubic capacity of 5 liters, previously degreased sheets of steel {60~,), electrolytically galvanized steel (30gb) and aluminum{1096) of the A,lMg3 grades were treated in alternation with a phosphat3.ng solution which contained 0.8 g/1 Zn free acids 1.1 1.0 g/1 Ni total acid: 23 1.0 g/1 Mn 3.2 g/1 Na 13.0 g/1 P205 2.l g/1 N03 0.5 g/1 P
rd '! ) f t j ~) 27 ~ t~e :~ r.a _13~
V~hen the conditions mentioned aboee and steady-state concentrations of Fe(II) and F3202 not in excess o~ 6 m~/1 were maintained, uni.~orm and. closed coatings were formed on all three materials and had the following vrei~hts:
Steel: ~ 2.10.2 g/m2 electrodeposited 2.60.2 g/m2 zinc:
AlSi: 2.9_+0.3g/m~
Al~g3 : 3 a Z+V ~/~~ .
.3
Claims (17)
1. A process of phosphating iron and steel surfaces according to the low-zinc technology with phosphating solutions which are free of nitrite and contain phosphate and nitrate characterized in that the surfaces are contacted at 30 to 65°C with an aqueous acidic phosphating solution which contains 0.4 to 1.7 g/l Zn 7 to 25 g/l P2O5
2 to 30 g/l NO3 and in which the weight ratio of free P2O5 to total P2O5 is adjusted to a value in the range from 0.04 to 0:20, and H2O2 or alkali perborate is added to the phosphating solution in such an amount that- being in working condition- the peroxide concentration is not in excess of 17 mg/l, calculated as H2O2, and the Fe(II) concentration respectively is not in excess of 60 mg/l, calculated as Fe.
2. A process according to claim 1, characterized in that the surfaces are contacted with a phosphating, solution in which the addition of H2O2 and/or alkali perborate is controlled in dependence on the electrochemical potential determined by a redox electrode.
2. A process according to claim 1, characterized in that the surfaces are contacted with a phosphating, solution in which the addition of H2O2 and/or alkali perborate is controlled in dependence on the electrochemical potential determined by a redox electrode.
3. A process according to claim 1, characterized in that the surfaces are contacted with a phosphating solution to which H2O2 and/or alkali perborate have been added in such an amount that the maximum peroxide concentration is 8 mg/l and the maximum Fe(II) concentration respectively is 30 mg/l.
4. A process according to claim 1, characterized in that the surfaces are contacted with a phosphating solution which in addition contains more than zero to 3 g/l manganese, more than zero to 3 g/l nickel and/or cobalt, more than zero to 3 g/l magnesium and/or more than zero to 3 g/l calcium.
5. A process according to claim 1, characterized in that the surfaces are contacted with a phosphating solution which contains more than zero to 3 g/l fluoroborate, calculated as BF4, and/or more than zero to 3 g/l silico- fluoride, calculated as SiF6, and/or more than zero to 1.5 g/l fluoride, calculated as F.
6. A process according to claim 1, characterized in that the surfaces are contacted with a phosphating solution in which the content of free P2O5 during the processing is adjusted by an addition of manganese carbonate, zinc carbonate and/or zinc oxide.
7. A process according to claim 1, characterized in that the surfaces are contacted with a phosphating solution from which water is removed and the removed water is replaced by an addition of rinsing water from the succeeding rising stage or rinsing stages.
8. A process according to claim 1, characterized in that the surfaces are contacted with a phosphating solution which is replenished by an addition of phosphate in which the ratio of free P2O5 to total P2O5 is (-0.50 to +0.20):1.
9. A process according to claim 2, characterized in that the surfaces are contacted with a phosphating solution to which H2O2 and/or alkali perborate have been added in such an amount that the maximum peroxide concentration is 8 mg/l and the maximum Fe(II) concentration respectively is 30 mg/l.
10. A process according to claim 2, 3 or 9, characterized in that the surfaces are contacted with a phosphating solution which in addition contains more than zero to 3 g/l manganese, more than zero to 3 g/l nickel and/or cobalt, more than zero to 3 g/l magnesium and/or more than zero to 3 g/l calcium.
11. A process according to claim 10, characterized in that the surfaces are contacted with a phosphating solution which contains more than zero to 3 g/l fluoroborate, calculated as BF4, and/or more than zero 3 g/l silicofluoride, calculated as SiF6, and/or more than zero to 1.5 g/l fluoride, calculated as F.
12. A process according to claim 2, 3, 9 or 11, characterized in that the surfaces are contacted with a phosphating solution in which the content of free P2O5 during the processing is adjusted by an addition of manganese carbonate, zinc carbonate and/or zinc oxide.
13. A process according to claim 2, characterized in that the surfaces are contacted with a phosphating solution from which water is removed and the removed water is replaced by an addition of rinsing water from the succeeding rinsing stage or rinsing stages.
14. A process according to claim 2, 3, 9, 11 or 13, characterized in that the surfaces are contacted with a phosphating solution which is replenished by an addition of phosphate in which the ratio of free P2O5 to total P2O5 is (-0.50 to +0.20):1.
15. A process according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 11 or 13, used in preparing iron and steel surfaces for painting.
16. A process according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 11 or 13, used in preparing iron and steel surfaces for painting, by dip electrocoating.
17. A process according to claim 16, wherein the dip electrocoating is a catophoretic dip electrocoating.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3927614.7 | 1989-08-22 | ||
| DE3927614A DE3927614A1 (en) | 1989-08-22 | 1989-08-22 | METHOD OF GENERATING PHOSPHATURE SUPPLIES ON METALS |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2022728A1 CA2022728A1 (en) | 1991-02-23 |
| CA2022728C true CA2022728C (en) | 2000-02-01 |
Family
ID=6387566
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002022728A Expired - Fee Related CA2022728C (en) | 1989-08-22 | 1990-08-06 | Process of producing phosphate coating on metals |
Country Status (11)
| Country | Link |
|---|---|
| EP (1) | EP0414296B1 (en) |
| JP (1) | JP2992619B2 (en) |
| AT (1) | ATE91159T1 (en) |
| BR (1) | BR9004117A (en) |
| CA (1) | CA2022728C (en) |
| DD (1) | DD299662A5 (en) |
| DE (2) | DE3927614A1 (en) |
| ES (1) | ES2042199T3 (en) |
| PL (1) | PL286572A1 (en) |
| PT (1) | PT95053B (en) |
| ZA (1) | ZA906673B (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3219453B2 (en) * | 1992-03-17 | 2001-10-15 | 日本パーカライジング株式会社 | Manufacturing method of galvanized steel sheet with excellent blackening resistance |
| DE4243214A1 (en) * | 1992-12-19 | 1994-06-23 | Metallgesellschaft Ag | Process for the production of phosphate coatings |
| JPH0790614A (en) * | 1993-09-22 | 1995-04-04 | Elna Co Ltd | Aluminum or aluminum alloys and their chemical conversion treatment |
| BR9607700A (en) * | 1995-03-07 | 1998-07-07 | Henkel Corp | Aqueous liquid composition and process to form a phosphate conversion coating on a metal surface |
| US5888315A (en) * | 1995-03-07 | 1999-03-30 | Henkel Corporation | Composition and process for forming an underpaint coating on metals |
| DE19523919A1 (en) * | 1995-06-30 | 1997-01-02 | Metallgesellschaft Ag | Process for supplementing phosphating solution |
| DE19544614A1 (en) * | 1995-11-30 | 1997-06-05 | Metallgesellschaft Ag | Process for phosphating metal surfaces |
| US5797987A (en) * | 1995-12-14 | 1998-08-25 | Ppg Industries, Inc. | Zinc phosphate conversion coating compositions and process |
| DE19808755A1 (en) | 1998-03-02 | 1999-09-09 | Henkel Kgaa | Layer weight control for strip phosphating |
| WO1999048819A1 (en) * | 1998-03-25 | 1999-09-30 | Henkel Kommanditgesellschaft Auf Aktien | Treatment of waste water during phosphating |
| DE10118552A1 (en) * | 2001-04-14 | 2002-10-17 | Henkel Kgaa | Determination and optionally regulation of accelerator concentration in zinc phosphonating solution for steel, zinc (alloy)-plated steel and aluminum (alloy) uses biochemical hydrogen peroxide sensor giving electrical signal |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1796218B1 (en) * | 1968-09-23 | 1971-10-07 | Metallgesellschaft Ag | METAL PHOSPHATING METHOD |
| GB1585057A (en) * | 1976-06-28 | 1981-02-25 | Ici Ltd | Sensing concentration of coating solution |
| JPS5811513B2 (en) * | 1979-02-13 | 1983-03-03 | 日本ペイント株式会社 | How to protect metal surfaces |
| JPS6043491A (en) * | 1983-08-19 | 1985-03-08 | Nippon Denso Co Ltd | Formation of phosphate film on iron and steel surfaces |
| JPS63270478A (en) * | 1986-12-09 | 1988-11-08 | Nippon Denso Co Ltd | Phosphate chemical treatment method |
| DE3712339A1 (en) * | 1987-04-11 | 1988-10-20 | Metallgesellschaft Ag | METHOD FOR PHOSPHATIZING BEFORE ELECTROPLATING |
-
1989
- 1989-08-22 DE DE3927614A patent/DE3927614A1/en not_active Withdrawn
-
1990
- 1990-08-02 ES ES199090202104T patent/ES2042199T3/en not_active Expired - Lifetime
- 1990-08-02 DE DE9090202104T patent/DE59001884D1/en not_active Expired - Lifetime
- 1990-08-02 EP EP90202104A patent/EP0414296B1/en not_active Expired - Lifetime
- 1990-08-02 AT AT90202104T patent/ATE91159T1/en not_active IP Right Cessation
- 1990-08-06 CA CA002022728A patent/CA2022728C/en not_active Expired - Fee Related
- 1990-08-21 BR BR909004117A patent/BR9004117A/en not_active Application Discontinuation
- 1990-08-21 PL PL28657290A patent/PL286572A1/en unknown
- 1990-08-21 DD DD90343560A patent/DD299662A5/en not_active IP Right Cessation
- 1990-08-21 PT PT95053A patent/PT95053B/en not_active IP Right Cessation
- 1990-08-22 ZA ZA906673A patent/ZA906673B/en unknown
- 1990-08-22 JP JP2220940A patent/JP2992619B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| DE3927614A1 (en) | 1991-02-28 |
| JPH0387374A (en) | 1991-04-12 |
| DE59001884D1 (en) | 1993-08-05 |
| PT95053B (en) | 1997-04-30 |
| CA2022728A1 (en) | 1991-02-23 |
| ZA906673B (en) | 1992-04-29 |
| PL286572A1 (en) | 1992-02-10 |
| DD299662A5 (en) | 1992-04-30 |
| ES2042199T3 (en) | 1993-12-01 |
| EP0414296B1 (en) | 1993-06-30 |
| ATE91159T1 (en) | 1993-07-15 |
| PT95053A (en) | 1991-04-18 |
| EP0414296A1 (en) | 1991-02-27 |
| JP2992619B2 (en) | 1999-12-20 |
| BR9004117A (en) | 1991-09-03 |
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