DE102006051384A1 - Process for the pre-weathering of metal parts with a predominantly zinc surface - Google Patents

Abstract

The method for weathering of metal parts with a predominant surface consisting of zinc, comprises pickling the surface with an acid pickling solution, partly galvanizing the metal parts and dipping the galvanized metal parts into the solution for the duration of 30 seconds to 10 minutes. The picking solution contains ions of non-zinc metals in a concentration of 0.005-2 g/l, ions of lead and/or tin in a concentration of 0.005-2 g/l and zinc ions in the concentration of 5-50 g/l. The temperature of the solution is 20-55[deg] C. The method for weathering of metal parts with a predominant surface consisting of zinc, comprises pickling the surface with an acid pickling solution, partly galvanizing the metal parts and dipping the galvanized metal parts into the solution for the duration of 30 seconds to 10 minutes. The picking solution contains ions of non-zinc metals in a concentration of 0.005-2 g/l, ions of lead and/or tin in a concentration of 0.005-2 g/l and zinc ions in the concentration of 5-50 g/l. The temperature of the solution is 20-55[deg] C. The ions of the zinc and/or the non-zinc metal are added in the form of sulfates and nitrates, whose quantity ratio corresponds to the quantity ratio of the sulfuric acid and nitric acid in the solution. The solution is diluted on an acidity of 18 g/l and the concentration of the ions of the zinc or the non-zinc metals in the diluted solution is 0.02-0.3 g/l. The metal parts are activated before the pickling in an acid or alkali activation bath.

Description

The The invention relates to a method for the pre-weathering of metal parts with a predominantly zinc surface, in which the surface with an acid pickling solution is stained. In particular the invention with a method for the pre-weathering of piece galvanizing.

On the surface of zinc or of alloys containing zinc as the main component, is known to form by weathering over time Protective layer, the surface gives a high corrosion resistance. By a suitable choice the zinc alloy can be achieve that Surface after a certain weathering time a relatively uniform, dull gray Tint assumes because of its aesthetic appearance especially appreciated in construction engineering and therefore also referred to as "architect gray".

In EP 0 827 785 A2 For tinplate or strip (strip zinc) from Tintanzink a method of the above type is described, which can be achieved by pickling the surface in a relatively short time, the formation of a protective layer that is similar to the result of the natural weathering process. This has the advantage that the metal surface assumes the desired appearance more quickly and that the surface condition is less dependent on the current environmental conditions and more or less accidental environmental influences, so _that a uniform appearance of the surface can be achieved with improved reproducibility. In addition, the weathering-induced entry of zinc into the environment can be reduced by the pre-weathering. The pickling solution is a mixture of sulfuric acid and nitric acid with a certain content of zinc ions.

at hot-dip galvanized metal parts (zinc) However, so far could not be satisfactory by such a pickling treatment Results are achieved because the effect of the pickling process here through extra, hard to be controlled factors, i.a. through the respective geometric shape of the piece galvanizing material and the nature of the alloys used for hot dip galvanizing.

Another known method of surface treatment of galvanized metal parts is phosphating. For example, describes EP 0 713 539 B1 a method for phosphating single-sided galvanized steel strip.

Further describes EP 0 693 139 B1 a method for the substituted plating of zinc surfaces or surfaces of zinc alloys. In this process, the surface is treated with an organic acid containing, among other things, heavy metal ions. The surface layer obtained in this way is particularly suitable as a primer for later to be applied paint or varnish layers.

task The invention is to provide a method of the type mentioned, especially for Stückverzinkungsgut is suitable and with which largely independent of the particular composition The zinc alloy reproducibly an aesthetically pleasing color effect reach.

These Task is inventively characterized solved, that the pickling solution Ions of at least one non-zinc metal in one concentration from 0.005 to 2 g / l.

By the addition of metal ions other than zinc allows the pre-weathering process to be controlled so that both at band zinc as well as at zinc for all common Alloy types of the zinc base material with a uniformly colored surface with achieved high corrosion and abrasion resistance, giving the desired hue selectively influence by a suitable choice of the added metal ions leaves.

advantageous Embodiments and developments of the method are specified in the subclaims.

When pickling solution a mixture of sulfuric acid and nitric acid is preferably used, which has already been added with zinc ions to accelerate the reaction could be. In addition added ions of the non-zinc metals may be, for example to lead, tin, copper, nickel, cobalt, magnesium or sodium as well Combinations of these metals act.

The pickling is preferably carried out in such a way that the metal parts are immersed in the pickling solution for a certain time, which may be for example between 30s and 10 min. The pickling solution may be room temperature (20 ° C) or a slightly elevated temperature of for example 55 ° C ha ben. The higher the temperature of the pickling solution, the shorter the dipping time can be.

The Metal ions become the pickling solution preferably added in the form of metal salts. For better solubility it is useful if it is the salts of the same acids which also includes the pickling solution, for example Sulfates and nitrates, and if the proportion of these salts is about the ratio the acids in the pickling solution equivalent.

Especially in the pre-weathering of zinc it is useful with a diluted one pickling solution to work at the acidity For example, reduced to about 18 g / l. With increasing dilution of the pickling solution can the diving times extended which has the advantage of being different duration of action of the pickling solution less on the uniformity the surface impact. Such different exposure times can be especially with zinc from the fact that larger metal parts, which are lowered from above into the pickling bath, with their lower areas longer Be in the pickling bath as with their upper areas, or that depending on Geometry of the metal parts at certain points acid residues remain, the later during a flushing process be removed.

Farther It has proved to be advantageous, the metal parts after the hot dip galvanizing initially for about 30 to 90s in an acidic or alkaline activation bath, for example diluted Sulfuric acid or to dip a mixture of caustic soda and sodium carbonate solution to increase the reactivity of the surface before the actual pickling treatment takes place.

After the pickling treatment, the metal parts are rinsed or briefly immersed in an aftertreatment solution. Optionally, a protective film can also be applied to the surface after the pre-weathering, which reduces the subsequent detachment of metallic zinc, for example a film of polymers ( EP 0827 785 A2 ) or other organic molecules that can self-organize on the surface.

in the Following, the invention will be explained in more detail with reference to some examples.

1. Activating bath

To The hot dip galvanizing, the metal parts are first in an activation bath dipped to get a more reactive surface.

According to one embodiment is used as the activation bath 10% sulfuric acid. The activation is preferably carried out at room temperature (20 ° C), but can also at a slightly increased Temperature, for example at 50 ° C respectively. The immersion time should be between 3 and 90 seconds, preferably between 30 and 60 seconds. At room temperature is a dipping time of about 60 seconds is preferred.

Alternatively, an alkaline activation bath may also be used, for example a solution of 40 g / l NaOH (1 mol / l) and 28.6 g / l (0.1 mol / l) Na ₂ CO ₃ . The immersion times and the temperature are the same as those for the acidic activation bath.

2. pickling bath

Table I gives the compositions of various (undiluted) pickling solutions. These solutions are mixtures of sulfuric acid and nitric acid to which zinc salts are added according to the respective acid ratio. Each of these pickling solutions is added with various salts of one or more non-zinc metals. These metals are not listed in Table I, and their preferred compositions and concentrations will be discussed further below. Table I pickling solution 55/33 75/13 35/53 H ₂ SO ₄ (g / l) 55 75 35 ENT ₃ (g / l) 33 13 53 H ₂ SO ₄ (mol / l) 0.561 0,794 0,357 ENT ₃ (mol / l) 0.524 0.206 0.841 ZnSO ₄ × 7 H ₂ O (g / l) 68.75 93.75 43.74 Zn (NO ₃ ) ₂ × 4 H ₂ O (g / l) 37.5 14.77 60.22 ZnSO ₄ × 7 H ₂ O (mol / l) 0.239 0.326 0,152 Zn (NO ₃ ) ₂ × 4 H ₂ O (mol / l) 0.143 0.056 0.23 Zn total (g / l) 25 25 25

The amounts given for the zinc salts add up to a total content of zinc ions of 25 g / l. The ratio of the molar amounts of zinc sulfate (ZnSO ₄ × 7 H ₂ O) and zinc nitrate (Zn (NO ₃ ) ₂ × 4 H ₂ O) in the example shown corresponds approximately to the mass ratio of the acids, for example 55/33, 75 / However, the ratio of the amounts of salt can also deviate from this and should generally be chosen so that a good solubility of the salts is given.

Each of the pickling solutions listed in Table I are added to 0.1 to 2 g / l metal ions of one or more of the following non-zinc metals: lead, tin, copper, nickel, cobalt, magnesium, sodium. The addition of these metal ions is preferably carried out in the form of readily soluble metal salts or salt mixtures. Table II gives examples of suitable metal salts. The amounts are based on the pickling solution 55/33 from Table I and each give a total content of 1 g / l of the relevant metal ion. Table II metal Salt (s) Quantity (g / l) Quantity (mol / l) Lead (1 g / l) Pb (NO ₃ ) ₂ 1.598 0.00483 Tin (1 g / l) ZnSO ₄ 1.81 0.00843 Copper (1 g / l) CuSO ₄ 1.57 0.00983 Cu (NO ₃ ) ₂ × 3 H ₂ O 1.42 0.00588 Nickel (1 g / l) NiSO ₄ × 6 H ₂ O 3,097 0.0106 Ni (NO ₃ ) ₂ × 6 H ₂ O 1.68 0.00639 Cobalt (1 g / l) CoSO ₄ × 7 H ₂ O 2,981 0.0106 Co (NO ₃ ) ₂ × 6 H ₂ O 1,852 0.00636 Magnesium (1 g / l) MgSO ₄ .7H ₂ O 6,337 0.0257 Mg (NO ₃ ) ₂ × 6 H ₂ O 3,955 0.0154 Sodium (1 g / l) NaF 2.21 0.0526

at Copper, nickel, cobalt and magnesium, both as sulfate and can also be added as nitrate, the ratio of given moles again the mass ratio of sulfuric acid and nitric acid (55/33).

If the concentration of metal ions is to be varied, are the proportional proportions in Table II. For example multiply the salt quantities given by a factor of 0.1, if the concentration of the metal ion should be 0.1 g / l and they multiply by a factor of 2 when the concentration 2 g / l should be.

The Metals can lead and tin advantageously combined with each other, for example 1 g / l Lead and 1 g / l tin while in the case of the rest Metals preferably only a single metal is added.

After this the metal salts have been added and dissolved, the solution is preferably diluted, for example in relation to 1: 2, 1: 5 or 1:10, with the dilution in the ratio 1: 5 is preferred.

The from the activation bath removed metal parts are then in the so obtained and possibly suitably diluted pickling solution immersed. The temperature the pickling solution should preferably be about 20 ° C-55 ° C. The immersion times can depending on the desired Hue vary and are for example between 0.5 min and 10 min and are of the temperature as well as the dilution of the Pickling solution depends. ever higher the Temperature is shorter should be the dive time. In the case of the undiluted pickling solution, the preferred ones are Dive times between about 30 s and 90 s. At a ratio of 1: 2 diluted pickling solution the preferred dive times are between 60 s and 120 s. In the relationship 1: 5 dilute pickling solution lie in the range of 60 s to 240 s, and in the ratio of 1:10 diluted Pickling solution lie the preferred dive times are in the range of about 60 seconds to 360 seconds.

example 1

It become three different pickling solutions Type 55/33 according to the table I containing 0.1 g / l, 1 g / l and 2 g / l lead ions (Pb). The solutions then be in proportion Diluted 1: 5, so that the concentrations decrease the lead ions to 0.02 g / l, 0.2 g / l and 0.4 g / l, respectively. To activation in an acidic or alkaline activation bath the metal parts for three minutes at a temperature of 20 ° C (room temperature) into the pickling solutions immersed. At the concentration of 0.02 g / l, the surface takes on a bright Gray tone on. At the concentration of 0.2 g / l you get one very attractive medium gray tone (architect gray). At a Concentration of 0.4 g / l, the surface becomes very dark and the abrasion resistance decreases from.

Similar Results obtained one, if the pickling solution Tin (Sn) is added instead of Pb or in a solution with (Neat) 1 g / l Pb and Sn each.

Example 2

As Example 1, only with a pickling solution, the (diluted) 0.2 g / l of Cu instead of Pb or Sn. It turns out an easy greenish Hue.

Example 3

As Example 1, but with a pickling solution that (diluted) 0.2 g / l contains Ni instead of Pb or Sn. The surface is taking a relatively dark, slightly bluish Tint on.

Example 4

As Example 1, but with a pickling solution that (diluted) 0.2 g / l contains Mg instead of Pb or Sn. The surface is taking a gray shade.

Example 5

As Example 1, but with a pickling solution that (diluted) 0.2 g / l contains Co instead of Pb or Sn. The surface is taking a blue-gray hue.

Example 6

As Example 1, but with a pickling solution that (diluted) 0.2 or 0.4 g / l Na instead of Pb or Sn. The surface gets one light gray shade. The quality the surface decreases as the concentration of Na is further increased and exceeds a value of 0.6 g / l.

Claims (10)

A method of pre-weathering metal parts having a predominantly zinc surface in which the surface is pickled with an acidic pickling solution, characterized in that the pickling solution contains ions of at least one non-zinc metal in a concentration of 0.005 to 2 g / l. A method according to claim 1, characterized in that the pickling solution ions of lead and / or tin in a concentration of 0.005 to 2 g / l. Method according to claim 1, characterized in that that this Non-zinc metal one of the metals copper, nickel, cobalt, magnesium or sodium is. Method according to one of the preceding claims, characterized characterized in that Metal parts galvanized are and for immersed in the pickling solution for a period of 30 seconds to 10 minutes. Method according to claim 4, characterized in that that the Temperature of the pickling solution about 20 to 55 ° C is. Method according to one of the preceding claims, characterized characterized in that pickling solution a mixture of sulfuric acid and nitric acid is. Method according to Claim 6, characterized that the pickling solution Zinc ions in the concentration of 5 to 50 g / l contains. Method according to claim 6 or 7, characterized that the Ions of zinc and / or non-zinc metal in the form of sulfates and nitrates are added, the ratio of which is about the ratio of sulfuric acid and nitric acid in the pickling solution equivalent. Method according to one of the preceding claims, characterized characterized in that pickling solution on an acidity from about 8 to 45 g / L, preferably about 18 g / L and that the Concentration of the ions of the non-zinc metal or metals in the diluted pickling solution between 0.01 and 1.0 g / l, preferably between 0.02 and 0.3 g / l. Method according to one of the preceding claims, characterized characterized in that Metal parts before pickling in an acidic or alkaline activating bath to be activated.