LU82817A1 - CONTINUOUS PROCESS FOR MANUFACTURING SHEETS COATED ON A SIDE - Google Patents

Description

_C 2072-L 2.4379 Ö O D T ^ GRAND-DUCHY OF LUXEMBOURG Patent N ° ....... Q ..... L ..... Q ......... I / du l.a.r O.C.t.O. b.r.e 1.9.8 .0 fâïjÈÊ Minister for the Economy and the Middle Classes

Title issued ......................................... £ §% $ § Service of Intellectual property

LUXEMBOURG

Patent Application I. Application

The ..... C.ENTRE DE ..p..C.li.ER, C.tt.E $ ... <.. M.EIÂLL.UE.GI.D..U.ES.r. .C.EWI.RUM ..... V0.0.R ..... RESEARCH ..... IN (i) DE METALLURGIE, non-profit association, vereniging zonder wtristOOgineTki47ÿTue BTïïxëTrr ^ B '¥ TgTque7 .. .....................

represented ..... by ..... Sir ..... GharÎesH ^ unchenTConseil en breve ~ ts "" à .......... ^

Lux.emb..Qu: .r..g ..,. Ag.issan.t ... in quaLite of ... agent, ----------------- -----------------------------—.................... ......- 'deposit) this first October 1900 guatre-vints _________________________________________ (3) 1 at _______ 1 5:00 am, at the Ministry of Economy and Middle Classes, in Luxembourg: 1. this request for obtaining a patent for an invention concerning:, lP.ro.c.é.dë conti.ou ..... de ..... fabrication ..... de ..... ... on-one ..... fa-çe 2. the delegation of power, dated ...... ß.r..UX.ß..l..lSS .......... ................ on ... 3.0 ...... S..ep.t. £ ïïlh. ££ ..... 1-98 (3. the description in French ................................ of the invention in two copies; 4 .... ..... a .......... drawing plates, in two copies; 5. the receipt of the fees paid to the Registration Office in Luxembourg, on .... 1st .... .October ...... 1980 ......................................... ...................................... .................................................. .................................................. .....

declares (s) assuming responsibility for this declaration, that the inventor (s) is (are): M.Qn.sieur ..... V..lt.tor.in.Q ..... IU.SS.EI * ...... 6.9 ..., .... xu.e ..... J.ean.-Hub4.n., ...... B-.4 ..48Û ..... Oupeye— (5) in ..... Belgium .............................. .................................................. .................................................. .................................................. .................................................. ..

claim) for the above patent application the priority of one (s) application (s) of (6) ........... U .............. .................................................. ............ filed in (7) .............................. .................................................. .............................................

on _____________________ U ................................................ .................................................. .................................................. .................................................. .............................. (8) ______________________________________ U ................ .................................................. .................................................. .................................................. ................................................

in the name of ______________ // _______________________________________________________________________________________________________________________________________________________________________________________________________________________ (9) ♦> the elite (elect) for him (her) and, if designated, for his representative, in Luxembourg______________________________ _________________________ lia “boulevard Prince-Henri _____________________________________________________________________ (io) requests (nt) the delivery of a patent for the subject described and represented in the „appendices above ^^ -— with postponement of this issue to _____________________ /. / _________________________ months. (11) * "dd Deposit Report

The above patent application has been filed with the Ministry of the Economy and the Middle Classes, Intellectual Property Service in Luxembourg, on October 1, 1980 · ’” * s. Pr. The Minister at 1 StlQQ hours of Economy and the Middle Classes, r .., · '// ë® \\ pa · l -. "F (IkJw îj /" "· a connn 1. A" 5 ® # \ »f C 2072/8010.

“METALLURGICAL RESEARCH CENTER -CENTRUM V00R RESEARCH IN DE METALLURGIE,

Nonprofit organization -

Vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Continuous process for the production of coated sheets on one side.

The present invention relates to a continuous process for the production of sheets coated on one side, which is particularly advantageous in the case of galvanized sheets.

The production of coated sheets requires very careful surface preparation, not only for the adhesion of the coating, but also for the final appearance of the coated sheet. This surface preparation treatment is all the more important as its implementation often encounters difficulties / f »2.- r

When it comes to sheets coated on one side, the aforementioned difficulties are accentuated by the fact that one is confronted with the problem of two different sides for which the preparation treatment must be applied in a generally selective manner. A well-known technique in such a case consists in masking the coated face to avoid any degradation of the coating due to the treatment of the other face.

The subject of the present invention is a method making it possible to remedy these drawbacks and to continuously carry out the manufacture of coated sheets on one face without requiring selective treatment as a function of the differences presented by the faces to be treated.

This invention is based on the following considerations relating to the use, for the treatment of steel sheets, of a solution of at least one organic acid such as for example formic, acetic, citric acid, etc.

The pH of such a solution can be adjusted to a value suitable for satisfying the following two requirements: - on the one hand, a value low enough to ensure reaction kinetics such that the treatment time is relatively short, with the advantage in particular a reduced length of the treatment line, v - on the other hand, a value which is sufficiently high that the hydrolysis reaction of the organic salt can be carried out with the formation of a precipitate.

With regard to the temperature, it can be adjusted so as to adjust the reaction rate to the type of oxide to be treated.

Furthermore, the use of organic acid has the advantage of not leaving any traces liable to affect the quality of the surface of the treated sheets.

In the case of treatment with formic acid, the reactions are as follows, in the case of a layer of FeO pxxjj for example: j /) 3.- r

1) FeO treatment

/ .0] (, 0 \ v \ l I ° i formic acid ferrous formate 2) oxidation of ferrous formate to ferric formate f * 0) (<P \ 2 H - C Fe + 0 + 2 H - C s> 2 H - C Fe + H_0 l ^ \ l ° ° 3) hydrolysis of ferric formate (* ° \ ('° \ v H \ \ l -r- precipitated formic acid

These reactions 1, 2 and 3 clearly show that the formic acid contained in the solution when it is extracted from the treatment tank for recycling is completely regenerated. The only possible loss of formic acid can therefore only result from its mechanical entrainment by the sheet passing through the tank.

These reactions also show that ultimately only oxygen and water are consumed, only in small amounts.

In addition, during its tests, the applicant made the completely unexpected observation that the treatment of the sheet is much better when the solution already contains a certain amount of iron.

With regard to the operation of rinsing a sheet treated with organic acid, it is possible to use a reagent / capable of neutralizing or preferably destroying this acid ”4.- so as to allow the implementation of this operation continuously. In the case of treatment with formic acid, the rinsing of the sheet can be carried out with a solution containing hydrogen peroxide in the presence of a catalyst according to the reaction below: ^ 0 4) H - c '+ H_0 „catalyst c0 + 2 h_0.

-0 2 2 2 2

NOT

H

It can be seen that the products of this reaction, C02 and H20 have the advantage of not being troublesome for the continuation of the process.

In addition, the fact that rinsing can be carried out in a closed circuit eliminates the still important problem of the rejection of a polluted solution in the surrounding environment.

Consequently, the process which is the subject of the present invention for the production of sheets coated on one side is essentially characterized in that after having coated one side of these sheets with a protective layer based on a metallic material such as for example zinc, aluminum, nickel, etc., or of an alloy of these metals or based on a synthetic material, the other face being covered or not with an oxide layer, we put the said sheets in contact with a solution of at least one organic acid, the pH of which is maintained between a minimum value of 1.5 and a maximum value of 4, and the temperature of which is maintained above a minimum value T given by the formula: m T = 20 + (pH - 1.5) x 32, m where pH is the value at which the pH of the treatment solution is maintained and in that said solution contains iron in an amount greater than 50 milligrams per liter, and preferably / greater than 100 milligrams per liter. / Jm 5.-

According to the invention, the organic acid or acids making up the solution advantageously have the characteristics given below: - they do not have a halogen atom,

; - they have a pK less than 5. We know that pK = - log K

where K = acidity constant.

As already said in the preliminary considerations, the pH value must be greater than 1.5 to obtain a filterable precipitate of iron hydroxide and less than 4 so that the treatment speed is not too low, i.e. - say greater than 5 mg / m2 x sec. (weightloss).

In the case where the organic acid is formic acid, the pH of the treatment solution is advantageously maintained at a value between 1.5 and 4, and preferably between 2.6 and 3.6, and maintains the temperature of this solution above 40 ° C.

In the case of sheets which are normally covered with an oxide layer whose thickness is greater than 200 nanometers (Nm), it may be advantageous to carry out the treatment in several successive tanks by means of separate solutions, at least of which one has a pH between 1.5 and 4, a temperature above 40 ° C and an iron content above 50 milligrams. per liter. An advantageous method consists in circulating the solution from tank to tank in the same direction as the sheet, so that the last tank meets the conditions of the invention.

According to a first embodiment of the invention, the treatment solution is recycled by promoting the decomposition of the iron salt into hydroxide as well as its precipitation into Fe (OH) ^ and then eliminating this precipitate by a known operation,. such as decantation, evaporation or preferably filtration, / centrifugation. / y "6.- 9

According to a second embodiment of the invention, an oxidizing agent is added to the solution, preferably hydrogen peroxide (H ^ O ^) and the concentration of oxidizing agent in this solution is maintained between a lower limit equal to the value necessary for at least 80% of the ferrous ions contained in this solution to be oxidized to ferric ions and an upper limit equal to 10 times, and preferably 2 times, the value of said lower limit.

According to another embodiment of the invention, precipitation is facilitated either by the addition of a suitable coagulant-flocculant, preferably organic, or by electro-coagulation.

According to yet another embodiment of the invention, a wetting agent is added to the treatment solution.

It has also been found advantageous, according to the invention, to add a corrosion inhibitor to the treatment solution.

The oxide layer covering the surface of the steel sheet is possibly caused, at least in part, by heating in an open flame oven and / or by cooling with water, for example immersion in an aqueous bath. , preferably brought to a temperature higher than 75 ° C.

t

Before coming into contact with the treatment solution, the sheet is advantageously subjected, according to the invention, to a preheating operation.

It has also proved advantageous to use the treatment solution as a cooling medium, for example ξ i 7.-

With regard to the treatment solution purification operation, it can be noted that the marked preference for filtration or centrifugation is justified insofar as decantation is considered to be slow and requiring large volumes and where the evaporation is considered to produce deposits which are difficult to remove.

The choice between filtration and centrifugation can be determined by various factors including the cost of the investment, the cost of maintenance, the space available, etc.

'' It should be noted that the flow rate of the treatment solution to be purified for recycling depends on the conditions under which the heat treatment was carried out, on the pickling kinetics and on the admissible concentration of iron precipitate in the solution .

According to one embodiment of the invention, the rinsing of the sheet after treatment is carried out with recycling of the rinsing water continuously, by subjecting it to an operation of neutralization or chemical destruction of the residual acid.

According to another embodiment of the invention, the formic acid contained in the rinsing solution is chemically neutralized by adding to this solution a reagent such as hydrazine hydroxide with the formation of a soluble compound.

This reaction with hydrazine is instantaneous and the addition of a small amount of this reagent rapidly increases the pH value of the solution.

This method can be advantageous in the case where it is desired to rapidly decrease the content of organic acid. free without introducing an inorganic compound into the system.

According to yet another embodiment of the invention, the formic acid contained in the rinsing solution is chemically destroyed by adding to this solution hydrogen peroxide and a catalyst such as for example copper or iron.

As already said previously, this latter method has the advantage that the two compounds produced by the reaction, that is to say CO 2 and H 2 O, are not troublesome for the continuation of the process. 11 / 8.-

However, since hydrogen peroxide is a strong oxidant which can, under certain conditions, oxidize the sheet, it is advantageous to remove the excess hydrogen peroxide before recycling the treated solution.

To this end, according to the invention, the natural decomposition of hydrogen peroxide is accelerated by stirring in the presence of metal catalysts.

v To achieve this objective, it is possible to add to the destruction reactor by oxidation with hydrogen peroxide, an auxiliary reactor, which makes it possible to increase the yield of the oxidation reaction, to eliminate excess hydrogen peroxide and d '' obtaining greater ease of operation (possibility of switching off one of the reactors).

Also according to the invention, a little hydrogen peroxide is advantageously left in the recycled water, with a view to directly destroying the organic acid on the sheet without oxidizing the latter.

The present invention also relates to a sheet manufactured according to the method described above. This sheet has the advantages of having a high resistance to corrosion, without it being necessary to protect it by means of an oil film. The uncoated side has a high quality surface finish, without the coating of the other side being affected by the treatment.

The numerical applications below are given by way of nonlimiting example, to make clear the modalities of a processing operation in accordance with the present invention (the conforming examples are marked with an asterisk, the examples which are not conforming due to / conditions outside pH, temperature or iron content limits). / 1.

% »9.-

J

EXAMPLE 1: choice of acid.

Sheet steel heated in an open flame oven slightly oxidizing up to 550 °, then under H2 atmosphere) up to 750 ° C, maintained at 750 ° C for 1 minute. Cooling by quenching under water jets up to 60 ° C. Reheat to 280 ° C under the same gas and maintain at this temperature for 1 minute. Cooling under atmosphere to 120 ° C then quenching with water. Oxide thickness: 70 nanometers.

Treatment conditions s setting to have a treatment time of 10 to 15 sec; simple rinsing with water.

acid pH T in the bath_Notes

Hydrochloric 3 60 100 mgr / 1 yellow traces after rinsing

Sulfuric 3 60 "pitting corrosion during storage

Nitric 3 60 "immediate reoxidation of the sheet none of these mineral acids gives an acceptable surface.

Organic acids: bath tests maintained at 85 ° C.

PK iron content pH _

Name i · in the bath Remarks 20 ° C bath aans re oain X Form 3.75 2.65 250 mgr / 1 d Perfect surface sheet, X Acetic 4.75 2.4 "No corrosion in X Oxalic 1.23 2 , 9 "/ storage course

X Citric 3.14 2.7 "J

Methylamino "^ ^ ^„ insufficient treatment.

Benzoic

Trichloraceous - 2.85 2.8 "pits of tick corrosion during storage.

-T ^ i—

H

10.- t CONCLUSIONS: Sheets treated with conventional mineral acids are very difficult to rinse and have surface defects after storage. The same goes for organic acids having a halogen radical.

On the other hand, the sheets treated with organic acids do not exhibit any subsequent attack, but the pK of these acids must be less than 5 so that the treatment time remains reasonable.

"

Among the organic acids exhibiting these conditions, acetic acid and formic acid are the most common and of the lowest cost. Formic acid has an additional advantage, since it forms an azeotrope with water at 107.1 ° C, which means that even at boiling point, the vapor phase of a dilute solution is always richer in water than in acid.

The following examples were carried out with formic acid, but their extension to other acids, as claimed does not depart from the scope of the invention.

EXAMPLE 2: Effect of pH.

Sheet steel annealed at 900 ° C, under a protective atmosphere + 5% (^) and quickly cooled by immersion in a boiling water bath.

Thickness of the oxide layer: 80 nanometers (nm);

Processing speed (V) in a formic acid solution whose temperature is maintained at 100 ° C.

V = 4 mgr / m2 x sec. for pH = 4, 2 2 * 1 V = 6 mgr / m x sec. for pH = 4 Concentratxon in * V = 21.5 mgr / m2 x, sec. for pH = 3.5 iron maintained at x V = 40 mgr / m2 x sec. for pH = 2.9 around x V = 44 mgr / m x sec. for pH = 2.7 250 mgr / 1 / x V = 57 mgr / m2 x sec. for pH = 2.4 A /

X V = 98 mgr / m2 x sec. for pH = 1.85 d U

7 / en 11.- f EXAMPLE 3: Effect of the iron content in the solution.

Steel sheet annealed at 700 ° C under a protective atmosphere (N2 + 5% H2) and quickly cooled by immersion in a boiling water bath.

Thickness of the oxide layer: 30 nanometers, treatment in formic acid solution at pH 3.5 at 100 ° C.

Iron content in the bath Reflectivity of the treated surface in „% of that of the starting plate.

mgr / 1.

10 40% 20 60% 40 80% X 60 100% * 150 120% X 250 140% X 400 150% X 500 150% 1 (1

It is found that, unexpectedly, a minimum content of iron in the bath is required for the sheet obtained to be at least as bright as the starting sheet.

EXAMPLE 4: Effect of the bath temperature.

Sheet steel annealed at 850 ° C under a protective atmosphere (N2 + 5% H2) and quickly cooled by immersion in a boiling water bath.

Thickness of the oxide layer: 60 nanometers. /

Iron content in the bath maintained at around 100 mgr / 1. // »12.- f Bath temperature treatment speed value of the parameter

(° c) in mgr / m2 χ sec. 20 + 32 (pH - 1.5) J

1.85 15 4 31.2 * 1.85 41 6 31.2 2.5 43 4.5 52 * 2.5 60 10 52 3.5 75 3 84 * 3.5 90 15 84 2

It is found that the minimum processing speed of 5 mgr / m x sec.

is only reached if the temperature is both above 40 ° C and a value given by T. = 20 + 32 (pH - 1.5).

mm EXAMPLE 5.

Sheet metal covered with an oxide layer, the thickness of which is 10 micrometers.

Treatment in a solution at pH 1.86 and at 100 ° C; 400 mgr / 1 of iron in solution.

Processing speed 100 mgr / m ^ sec.

EXAMPLE 6.

Cold rolled steel sheet - thickness = 0.8 mm

Continuous annealing with open flame heating up to 500 ° C in 15 sec. and then with radiant tubes under N2 / 5% H2 up to 710 ° C in 40 seconds.

Holding for 40 seconds at 710 ° C under H2 / N2 (5% H2) Rapid cooling by immersion in an aqueous bath at 95 ° C, until the sheet is at 150 ° C.

Reheating to 450 ° C in 15 seconds under the same gas (H2 / N2)

Maintained at 450 ° C for 35 seconds under the same gas (H2 / N2) /

Cooling in a formic acid solution at 500 mgr / 1 h * 98 ° C for 15 seconds, pH = 2.9, iron content = 250 mgr / 1. IT · »13.- t

Rinsing and brushing.

The sheet was clean after treatment.

EXAMPLE 7.

Cold rolled steel sheet - thickness = 0.8 mm Continuous annealing with open flame heating, slightly oxidizing up to 600 ° C, then in a protective atmosphere (N2 + 5% H ^) up to 710 ° C in 30 seconds.

Holding for 40 seconds at 710 ° C under H2 / N2 (5% H ^) Rapid cooling by jets of atmospheric gas until the sheet is at 450 ° C

Maintain at 450 ° C for 180 seconds under (H2 / N2)

Cooling to 300 ° C in 20 seconds under Immersion in a formic acid solution at 98 ° C for 20 seconds, pH = 2.9 iron content: 400 mg / 1.

Rinsing and brushing.

The sheet was clean after treatment and showed no corrosion pitting after 2 months of storage.

EXAMPLE 8.

Cold rolled steel sheet - thickness: 0.8 mm Heating under N2 + 5% EL, up to 710 ° C Holding at 710 ° C for 40 seconds Cooling in water jets up to 80 ° C

Treatment for 5 seconds in a formic acid solution at pH = 3 and at a temperature of 80 ° C with an iron content of 300 mg / 1.

i

Rinsing and brushing. Then drying Reheating to 450 ° C under h2 / N2 Maintaining at this temperature for 1 minute Air jet cooling to 200 ° C

Immersion in cold water up to 40 ° C /

The sheet was clean after treatment and showed no corrosion pitting after 2 months of storage. / J / # 14.- EXAMPLE 9.

a) Pre-treatment conditions

Heating in an open flame oven Sheet speed · 0/1 m / sec.

Sheet width! 0.15 m.

Sheet temperature: 800 ° C at the cooling inlet Thickness of the sheet: 1.24 mm.

b) Internship conditions

Bath temperature: 98 ° C

Useful volume of the bath: 1500 liters

Sheet travel in the bath: 4.40 m pH of the bath: 2.9 by addition of 500 mg / 1. formic acid and iron content in the bath = 600 mgr / 1, stabilized by filtration and addition to H 2 O 2 at a rate of 200 mgr / 1.

Taking into account the conditions of pretreatment and treatment, it was observed that the l> ain remained stable in pH and in iron content by filtration of 2 liters / second with filters / mesh of 3 micrometers. / J

f! 15 .- Γ \

The appended figure, given by way of nonlimiting example, represents an embodiment of a continuous treatment installation in accordance with the present invention.

The oxidized sheet to be treated 1 passes through the treatment tank 2 and the rinsing tank 3 following a path imposed by the guide pulleys 4, 5, 6, 7 and leaves the tank 3 in the cleaned state by passing over a last guide pulley 8.

When it enters the treatment tank 2, the sheet passes between sealing rollers 9 and when it leaves between other sealing rollers 10. The upper wall 11 of the tank 2 is a double wall jacket and condensate fins. This double jacket is used for the circulation of cooling water which enters according to arrow 12 and exits according to arrow 13. The treatment using a formic acid solution is carried out by means of a series of nozzles 14, 15 , 16 and before leaving the tank 2 the sheet passes between wringing rollers 17.

The treatment solution to be recycled is extracted from the tank 2 along 18, passes into a tank 19 and from there is sent by the pump 20 in a double filtering installation 21 at the outlet of the laguelle, it is returned either to tank 2 along arrow 22, or in the tank 19 along arrow 23, using valves 24 and 25.

r

The reservoir 19 is equipped with an acid reserve 26, a device 27 for making up water, optionally from the rinsing, a pH meter 28 and a preheating system 29 to maintain optimum conditions. recycling.

t

After having left the treatment tank 2 passing between the sealing rollers read, the treated sheet enters the rinsing tank 3 where it passes successively between two series of nozzles 30, between two brushes 31 and again between two series of sprinklers 32. The sheet thus rinsed out of the tank 3 passing between two wringing rollers 33 / 'k # 16 .- and in an air drying battery 34 "before reaching the last guide pulley 8.

The rinsing solution to be recycled is extracted from the tank 3 along 35, passes into a tank 36 and part of this water is sent by the pump 37 to a double filtering installation 38, then to an elimination installation. formic acid comprising a tank 39 for destroying formic acid with oxygenated water introduced at 40 and an auxiliary tank 41 for removing excess oxygenated water, and finally in the tank 36. A pump 42 provides transport purified rinse water from reservoir 36 to tank 3 according to arrow 43.

The tank 36 is equipped with a preheating system 44 to maintain optimum recycling conditions.

In the installation described above, the contact of the steel sheet with the treatment solution is carried out by spraying by means of nozzles, but it can also be carried out by immersion in a suitable bath ^^ / 9 "

Claims (9)

1. Continuous process for manufacturing coated sheets on one side, characterized in that after having coated one side of these sheets with a protective layer based on a metallic material such as for example zinc, aluminum, nickel, etc. .., or an al-. bonding of these metals or based on a synthetic material, the other face being covered or not with an oxide layer, the said sheets are brought into contact with a solution of at least one organic acid of which the pH between a minimum value of 1.5 and a maximum value of 4, and the temperature of which is maintained above a minimum value T given by the formula: m T = 20 + (pH - 1.5) x 32 , m where pH is the value at which the pH of the treatment solution is maintained and in that said solution contains iron in an amount greater than 50 milligrams per liter. 2. Method according to claim 1, characterized in that the organic acid or acids making up the solution do not have a halogen atom. 3. Method according to either of claims 1 and 2, characterized in that the organic acid or acids making up the solution have a pK 5 (pK = - log K, K = acid constant). 4. Method according to either of claims 1 to 3, characterized in that the treatment speed is 2 greater than 5 mg / m x dry (weight loss). 1 Process according to either of claims 1 to 4, characterized in that the solution contains fefcn / in an amount greater than 100 milligrams per liter. f kf i 18.- 6. Method according to either of claims 1 to 5, characterized in that the organic acid is formic acid, in that the pH of the pickling solution is maintained at a value understood between 1.5 and 4 and preferably between 2.6 and 3.6, and in that the temperature of this solution is maintained at a value greater than 40 ° C. 7. Method according to either of claims 1 to 6, characterized in that the treatment is carried out in several successive tanks by means of separate solutions at least one of which has a pH of between 1.5 and 4 , a temperature above 40 ° C and an iron content above 50 milligrams per liter. 8. Method according to either of claims 1 to 7, characterized in that an oxidizing agent, preferably hydrogen peroxide (H „0j and in that l is added to the treatment solution) the concentration of oxidizing agent 4m of this solution is maintained between a lower limit equal to the value necessary for at least 80% of the ferrous ions contained in this solution to be oxidized to ferric ions and an upper limit equal to 10 times, and preferably 2 times, the value of said lower limit. * 9. Method according to one or the other of claims 1 to 8, characterized in that the treatment is followed by a rinsing of the sheet, and this rinsing is carried out with recycling of the rinsing water continuously by subjecting it to a neutralization or chemical destruction operation with residual acid. 10. Method according to claim 9, characterized in that, in the case where the organic treatment acid is formic acid, the acid is chemically destroyed for- / - r -—---— * f 19 .-. solution of hydrogen peroxide and a catalyst such as for example copper or iron. 11. Sheet metal coated on one side with high resistance to atmospheric corrosion and a surface finish of large qua-. lity, manufactured according to the process described in either of claims 1 to 10. Drawings: - boards pc.Crvs dc.:t ... Jf. · - - guard </ Ap ... «. ..: · description ....... 2>. ... c.i claims ........... ui-rîya descriptive Luxerntcu '. ,. J ;. -1 Charles München »