DE2154938B2 - METHOD OF SURFACE TREATMENT OF STEEL BEFORE DIRECT WHITE ENAMELING - Google Patents

Description

The present invention relates to a multi-stage process for the surface pretreatment of steel, in particular of non-decarburized steel that can be enamelled, before enamelling using the direct whitening process.

It is known that direct whitening enameling of sheet steel requires particularly careful pretreatment which requires metal surfaces. This also applies to direct enamelling with light shades. the Sheet steel parts are therefore usually degreased in several alkaline stages before the enamel is applied, if necessary derusted in an acid bath, then intensively pickled and finally nickel-plated · To a The workpieces are cleaned between the individual pretreatment steps to prevent chemicals from being carried over rinsed with warm and / or cold water.

The known methods for Direktweißemaillieren are mainly for steels with ultra-low carbon content of about 0.001 to 0.015 ° / ₀ consideration. These "decarburized" steels are obtained by vacuum degassing the liquid steel or by annealing the already rolled metal in a reducing atmosphere. Depending on the type of production, these types of steel are referred to as VAC steels (vacuum decarburized) or OC steels (decarburized using the open-coil process). Special processes for direct white enamelling of normal steel with carbon contents of up to 0.15% have also become known.

However, direct white enamelling of normal steel has not yet generally entered series production found. A major obstacle to the general use of mild steel as a The basic material for direct enamelling is the occurrence of innumerable tiny imperfections in spots in the enamel layer, which are not recognizable as such to the eye. However, this appearance is for it responsible that the otherwise white enamel coating in the affected areas an undesirable Has a gray tone.

Also for the enamelling of OC and VAC steel are often observed email errors caused by

ίο the pre-treatment of the metal surfaces according to the previously known methods cannot be excluded. Most likely these will be disorders due to uncontrollable influences in the production and processing steps of the steel sheets caused.

It has now been found that the disadvantageous phenomena mentioned can be largely eliminated can if one uses the pretreatment procedure described below. In the inventive In this process, the metal surfaces are degreased, if necessary in an acidic bath derusted, then intensively pickled and nickel-plated. The method is characterized in that one the metal surfaces are treated with aqueous solutions prior to intensive pickling, which contain at least one, contain complexing agents that prevent the precipitation of heavy metal cations.

Suitable complexing agents for carrying out the process according to the invention are, for example water-soluble cyanides, such as sodium or potassium cyanide, and alkanolamines with at least three Hydroxyl groups in the molecule, such as triethanolamine, triisopropanolamine and N, N, N ', N'-tetrakis (2-hydroxyethyl) ethylenediamine. Further examples of suitable complexing agents are the following acids or their water-soluble salts, in particular their Sodium and potassium salts: oxalic acid, tartaric acid, citric acid, polyhydroxycarboxylic acids such as gluconic acid, Hexahydroxyheptanoic acid and saccharic acid, aminopolycarboxylic acids such as nitrilotriacetic acid and Ethylenediaminetetraacetic acid, l-hydroxyalkane-ljl-diphosphonic acids, like l-hydroxyethane-ljl-diphosphonic acid, 1 - hydroxyhexane -1,1 - diphosphonic acid and l-hydroxy-2-phenylethane-l, l-diphosphonic acid, l-aminoalkane-l ^ -diphosphonic acids, such as 1-aminoethane -1,1 - diphosphonic acid, 1 - aminobutane -1,1 - diphosphonic acid, l-Amino-l-phenylmethane-l ^ -diphosphonic acid and l-dimethylaminomethane-lJ-diphosphonic acid, and aminomethylene phosphonic acids, such as nitrilotri (methylene phosphonic acid) and ethylenediaminetetra (methylene phosphonic acid). The complexing agents mentioned are used individually or in a mixture.

Solutions have proven to be particularly effective

■ ^ had a complexing agent mixture from a Trialkanolamine, an aminopolycarboxylic acid and / or a polyhydroxycarboxylic acid or a mixture from one of the di- or polyphosphonic acids mentioned and a polyhydroxycarboxylic acid. The complexing agent solutions can be acidic, neutral or alkaline, which must be ensured. that the complexing agents used cause the precipitation of heavy metal cations in the pH range used impede.

The desired pH can be set by means of a suitable combination of acidic and alkaline Complexing agents or by adding hydroxides, carbonates, hydrogen carbonates, silicon

3 4

caten, borates, orthophosphates, pyrophosphates The sheets pretreated in this way left

and polyphosphates of the alkali metals, especially enamelling perfectly in direct white processes,

of sodium and potassium. Comparable enamel qualities were achieved when

In addition, such wetting agents can be added in the bath sequence described above instead of the other

are, the complexing agent bath given in the subsequent intensive pickling not 5 a solution of the

act as a pickling inhibitor. the following compositions were used:

The total concentration of the in the solutions _a ) 4.5 g / l NaOH,

existing complexing agent is expediently between 2.0 g / l Na ₂ SiO ₃ · 5H ₂ O,

see 0.1 and 5 percent by weight. Preferably ^ 5 φ Na ₆ P ₃ O ₁₀ ,

solutions are used that _{contain 0.3 to 1.5 g} 10 ^, 3 g / j triethanolamine,

contain weight percent complexing agents. The tem- o, 5 g / l sodium gluconate,

The temperature of the solutions can range from 15 to 0.2 g / l of the tetrasodium salt of the ethylene

90 ° C. The duration of treatment is expediently diamine tetraacetic acid;

moderately between 1 and 10 minutes. b) 8.0 g / l NaOH,

The inventive treatment of the tyletallober- 15 g / j triisopropylamine,

surfaces with solutions containing complexing agents 4.0 g / l nitrilotriacetic acid:

before the intensive pickling, an additional step in _c ) 2.0 g / l NaOH,

any standard bath sequence for the pretreatment of 40 g / l sodium gluconate,

4.0 g / l tetrasodium salt of the 1-hydroxy-

the. It is advisable after treatment with the 20 ethane-lj-diphosphonic acid. Complexing agent solution a rinse with water

to prevent chemical carry-over Example 2

in the subsequent acid bath for the intensive pickling to degreased until completely wettable with water

avoid. Vacuum decarburized steel sheets USt 12-03 VAC

By applying the new process to 25 (maximum carbon content 0.015 ° / ₀ ) were at

the direct white enamelling of normal steel is de-rusted at 55 ° C with 10% sulfuric acid, with

the appearance of gray spots in the white cold water and then rinsed at room temperature

Enamel layer largely avoided. / Treated in the direct with a 0.5 ° _o aqueous sodium cyanide solution,

White enamelling of OC and VAC steel brings this after an intermediate rinse with cold water

new process a significant quality improvement 3 ° were the sheets at 65 ° C with 20 ° / ₀ iger sulfur

the enamel layers with itself. intensely pickled with acid, rinsed again with cold water

From the German Auslegeschriften 1 2I6 066 and rinses and then at 8O ⁰ C in a solution that

1223 656 processes have been known, which contained about 1.5 ° / ₀ NiSO ₄ · 7H ₂ O, electroless nickel plated. It

enamelling sheet steel parts after pickling followed by rinsing with water at 75 ^° C.

The metal surfaces were treated with 35 ßend to remove disruptive surface deposits

Complexing agents are treated. These writings with a 0.5% sodium nitrite solution at 9O ⁰ C

However, no indication could be taken, passivated and finally ^{dried at 110 0} C,

that a treatment with complexing agents before the The entire pretreatment was in the immersion

Intensive stain to solve the frame part task procedure carried out. The average seduces. 40 dwell time in the individual baths was 6 minutes.

For all percentages in the following, the panels pretreated in this way were after

Examples are percentages by weight. enamelled using one of the common direct white processes, where flawless enamel layers were achieved.

Example 1 Similar results were obtained when one Perfectly degreased sheets made of cold-rolled 45 instead of sodium cyanide as a complexing agent

Steel of drawing quality USt 12 DIN 1623 / Sheet 1 (maxi- citric acid or oxalic acid used,

painter carbon content 0.1%) were at 7O ⁰ C with.

Derusted 8 ° / _o sulfuric acid and ^p cold iflit ^J

Rinsed with water. The sheets were danri OC (treated Openmit a solution decarburized 50 Coil method; maximum carbon content of 0.004%) at 50 ⁰ C decarburized sheets of steel 12 were included to complete water

1.5 g / l NaOH, wettability, degreased, at 8O ⁰ C with 10% sulfur

1.0 g / l triethanolamine, de-rusted rock acid solution and rinsed with cold water

1.0 g / l of the tetrasodium salt of Athyleu _rinse. Then the sheets were washed at 55 ° C

diamine tetraacetic acid _{55 a} complexing agent solution, the

contained and rinsed with cold water. The intensive

Pickling was done at 75 ° C with Seiger sulfuric acid Jg ^ aOH ^

performed. After an intermediate rinsing with ^CT . ..,. ·

1 tZ \\ r Jj- u ■ ^ Ci ₁ ΛλΚ »^ 5λ« _π 4 g / l triethanolamine

The stained steel lobes were ^bl

at 85 ° C with a solution containing nickel sulfate 60, or with a 1% 1-hydroxyethane

Electrolessly nickel-plated and 1,1-diphosphonic acid solution ^{with hot water (75 ° C.).} treated. After a

flushed. To passivate the sheets at 80 ° C, the sheets were rinsed with cold water

a solution used containing 0.5% of a mixture under the same conditions as in Example 2 intensively

from 3 parts of sodium nitrite and 1 part of borax. pickled, electroless nickel-plated, passivated and

Thereafter, the sheets at 11O ⁰ C were dried. The 65 dries.

Treatment took place in the immersion process. The direct white enamelling of the pretreated dwell time in the individual bathrooms was about 5 minutes - steel sheets resulted in flawless enamel, layers.

Claims (4)

Patent claims: 1. Process for the surface pretreatment of steel, in particular of non-decarburized, enamelling Steel, before direct white enamelling, in which the metal surfaces are degreased, if necessary derusted in an acidic bath, then intensively pickled and nickel-plated, characterized by that the! metal surfaces before the intensive stain with aqueous solutions treats at least one that prevents the precipitation of heavy metal cations Contain complexing agents. 2. Process according to claim 1, characterized in that the metal surfaces ^{are treated for 1 to 10 minutes at 15 to 90 °} C. with aqueous solutions containing 0.1 to 5 percent by weight, preferably 0.3 to 1.5 percent by weight of complexing agents contain. 3. The method according to claims 1 and 2, characterized characterized in that the metal surfaces are treated with solutions containing a complexing agent mixture from a trialkanolainine, an aminopolycarboxylic acid and / or a polyhydroxycarboxylic acid contain. 4. Process according to Claims 1 and 2, characterized in that the metal surfaces treated with solutions containing a complexing agent mixture of a di- or polyphosphonic acid and a polyhydroxycarboxylic acid.