ES2620302T3 - Flow compositions for galvanizing steel - Google Patents

Abstract

A flow composition for treating a metal surface, comprising: (a) more than 40 and less than 70% by weight zinc chloride, (b) 10 to 30% by weight ammonium chloride, (c) more 6 and less than 30% by weight of a set of at least two alkali metal chlorides including sodium chloride and potassium chloride, (d) 0 to 2% by weight of lead chloride, and (e) 0 to 15% by weight of tin chloride, (f) at least one non-ionic surfactant, provided that the weight ratio of KCl / NaCl of said set of at least two alkali metal chlorides ranges from 3.0 to 8 , 0.

Description

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DESCRIPTION

Flow compositions for galvanizing steel Field of the invention

The present invention relates to the field of galvanization, more specifically hot-dip galvanization or hot-dip zinc coating. In particular, the present invention relates to the galvanization of ferrous materials such as, but not limited to, iron, cast iron, steel and cast steel. More particularly, the present invention relates to a range of flow compositions for treating the surface of a ferrous material such as iron and steel before immersing it in a zinc-based molten bath. The present invention also relates to (1) galvanization processes, in particular hot dip galvanization, making use of the flow compositions in at least one process stage, and (2) galvanized products, including galvanized ferrous products (by for example, long and smooth steel products), formed by a process in which the surface of the product is treated with new flow compositions.

Background of the invention

The importance of providing corrosion protection for ferrous articles (for example, iron or steel) used outdoors such as protections, wires, screws, cast iron elbows and automobile parts is well known, and the coating of a material Ferrous with zinc is a very cost effective and effective way to achieve this goal. Zinc coatings are commonly applied by immersion or by passing the article subject to coating through a molten metal bath. This operation is called "galvanization", "hot galvanization" or "hot dip galvanization" (HDG) to distinguish it from zinc electrometallization processes. In this process, a solidified zinc layer is formed on the surface of the article and the zinc coating layer formed as a result adheres strongly to the surface of the article by means of an intermetallic iron / zinc alloy that is shape during galvanization. Oxides and other foreign materials ("dirt") on the surface of the steel article interfere with the chemistry of the galvanization process and prevent the formation of a uniform, continuous and void-free coating. Accordingly, various techniques and combinations of techniques in the industry have been adopted to reduce, eliminate, or at least accommodate, oxides and dirt as much as possible.

The improvement of the properties of galvanized products can be achieved by zinc alloy with aluminum and / or magnesium. The addition of 5% by weight of aluminum produces an alloy with a lower melting temperature (eutectic point at 381 ° C) that exhibits improved drainage properties with respect to pure zinc. In addition, galvanized coatings produced from this zinc-aluminum alloy have greater resistance to corrosion, improved conformability and better paint performance than those formed from essentially pure zinc. However, zinc-aluminum galvanization is particularly sensitive to surface cleaning, so that many difficulties are often encountered, such as insufficient wetting of the steel surface, when zinc-aluminum alloys are used in galvanizing .

Many techniques and combinations thereof have been adopted in the industry to reduce, eliminate or at least accommodate rust and dirt as much as possible. In essentially all of these processes, organic dirt is removed first (ie, oil, grease, compounds that prevent corrosion), bringing the surface under coating into contact with an alkaline wash (alkaline cleaning). This can be achieved by means of additional techniques such as brush washing, ultrasonic treatment and / or electro-cleaning. Then the rinse occurs with water, contacting the surface with an acidic aqueous wash to remove the fine iron materials and the oxides (pickling with acid) and finally rinse again with water. All these acid-rinse pickling procedures are common for the majority of galvanization techniques and are carried out industrially in a more or less precise manner.

Another pre-treatment method used for high strength steels, steels with high carbon content, cast iron and cast steels is a mechanical cleaning method called shot blasting. In this method, corrosion and dirt is removed from the steel or iron surface by projecting small impacts or gravel on this surface. Depending on the shape, size and thickness of the parts to be treated, different shot blasting machines such as a drum blasting machine, a tunnel blasting machine for automobile parts, etc. are used.

There are two main galvanization techniques used on clean metal parts (for example, iron or steel): (1) the flow method, and (2) the annealing oven method.

The first galvanization technique, that is, the flow method, can in turn be divided into two categories, the dry flow method and the wet flow method.

The dry flow method, which can be used in combination with one or more of the cleaning procedures, acid pickling, rinsing or shot blasting, creates a layer of salt on the surface of the ferrous metal by immersing the metal part in an aqueous bath containing chloride salts, called "pre-flow". Subsequently, this layer dries before the galvanization operation, protecting the surface of the steel against

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upon re-oxidation until its entry into a molten zinc bath. Said pre-flows normally comprise aqueous zinc chloride and optionally contain ammonium chloride, the presence of which has been shown to improve the wettability of the surface of the article and, thus, favor the formation of a uniform, continuous and lacking coating. of holes.

The concept of wet flow is to cover the galvanization bath with an upper flow that also normally comprises zinc chloride, and usually ammonium chloride, but in this case these salts are molten and are floating on top of the galvanization bath . The purpose of the upper flow, such as a pre-flow, is to provide zinc chloride and preferably ammonium chloride to the system in order to contribute to the wettability during galvanization. In this case, the surface oxides and the dirt that remain after the acid-rinse-pickling with acid-rinsing are removed when the steel part passes through the upper flow layer and is submerged inside the galvanizing boiler. The wet flow has several disadvantages such as consumption of much more zinc than the dry flow, production of many more vapors, etc. Therefore, the majority of current galvanizing plants have adapted their processes to the dry flow method.

A summary of the annealing oven method is presented below. In continuous processes using zinc or zinc-aluminum or zinc-aluminum-magnesium alloys as a galvanizing medium, annealing is carried out under a reducing atmosphere such as a mixture of nitrogen and hydrogen gas. This not only eliminates the re-oxidation of previously cleaned, acid-stripped and rinsed surfaces, but also removes any residual oxides and dirt that may be present. The majority of steel coils are currently galvanized in accordance with this technology. A very important requirement is that the coil is leaving the annealing furnace continuously and goes directly into the molten zinc without any contact with the air. However, this requirement makes it extremely difficult to use this technology for shaped parts, or steel cables since the cables break too often and the annealing furnace method does not allow discontinuity.

Another technique used for the production of galvanized zinc-aluminum coatings comprises electro-coating of steel articles with a thin layer (ie 0.5-0.5 pm) of zinc (hereinafter "pre-layer "), oven drying with an air atmosphere and subsequent immersion of the pre-coated article inside the galvanization boiler. This is widely used for hot-dip coating of the steel tube in continuous lines and, to a lesser extent, for the production of a steel strip. Although this does not require processing in reducing atmospheres, it is disadvantageous since an additional metal coating step is required.

Galvanizing is carried out either in a batch operation or continuously. Continuous operation is normally carried out on articles susceptible to this type of operation such as cables, plates, strips, tubes and the like. In a continuous operation, the transfer of the items between successive treatment stages is very fast and is done continuously and automatically, the operation personnel being present to control the operations and fix the problems in case they occur. Production volumes in continuous operations are high. In a continuous galvanizing line that involves the use of an aqueous pre-flow followed by drying in an oven, the time that elapses between the removal of the article from the pre-flow tank and the immersion inside the galvanizing bath is usually approximately 10 to 60 seconds, instead of 10 to 60 minutes for a batch process.

Batch operations are considerably different. Batch operations are favored when production volumes are low and galvanized parts are more complex in shape. For example, various fabricated steel parts, structural and tubenic steel forms are advantageously galvanized in batch operations. In batch operations, the parts to be processed are transferred manually to each stage of successive batch treatment, with little or no automation involved. This means that the time that each piece resides in a particular treatment stage is much longer than the continuous operation, and even more significantly, the time between successive treatment stages is much wider in variation than in the continuous operation. For example, in a normal batch process for galvanizing a steel tubena, a batch of 100 tubenas is transferred after joint immersion in a pre-flow bath, by means of a manual operating crane to a feeding table, one by one, inside a galvanization bath.

Due to differences in scale and procedure between continuous and batch operations, particularly useful techniques in one type of operation are not necessarily useful in the other. For example, the use of a reduction furnace is restricted to continuous operation on a commercial or industrial scale. Similarly, high production rates in continuous processes make preheating a valuable aid in providing heat of formation to the galvanization bath. In batch processes, the delay times are much longer and also the production rates, and also the rate of depletion of the thermal energy of the galvanization bath is much lower.

There is a need to combine good conformability with improved corrosion protection of the ferrous metal article. However, before the zinc-based alloy coating with high amounts of aluminum (and optionally magnesium) can be introduced into the general galvanization industry, the following drawbacks have to be resolved:

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- Zinc alloys with high aluminum contents can be produced using the conventional zinc-ammonium chloride flow. The flows with metallic deposits of Cu or Bi have been proposed in a preliminary way, but the possibility of leaching copper or bismuth inside the zinc bath is not attractive. In this way, better flows are required.

- High aluminum alloys tend to form explosions of the intermetallic zinc-iron alloy that are negative at a later stage of galvanization. This phenomenon leads to very thick, uncontrolled and coarse coatings. Explosion control is absolutely essential.

- Moisture fitness issues were previously presented in Zn-Al alloys with a high aluminum content, possibly due to a higher surface tension than pure zinc. In addition, bare spots are easily formed due to poor wetting of the steel, and also a need for a lower surface tension of the melt.

- there was a poor control of the coating thickness in Zn-Al alloys with high aluminum content, which possibly depended on parameters such as temperature, flow composition, immersion time, steel quality, etc.

WO 02/42512 describes a hot dip galvanization flow comprising 60-80% by weight zinc chloride; 7-20% by weight of ammonium chloride; 2-20% by weight of at least one alkali metal or alkaline earth metal salt; 0.21-5% by weight of at least one of NiCh, CoCl2 and MnCh; and 0.1-1.5% by weight of at least one of PbCl2, SnCl2, SbCl3 and BiCh. Preferably, this flow comprises 6% by weight of NaCl and 2% by weight of KCl. Examples 1-3 show flow compositions comprising 0.7-1% by weight of lead chloride.

WO 2007/146161 describes a galvanization method with a molten zinc alloy comprising the steps of (a) immersing the ferrous material being coated in a flow bath in a separate container, thereby creating a ferrous material coated by flow, and (2) subsequently immerse the ferrous material coated with flow in a molten aluminum-zinc alloy bath in a separate container object coated with an aluminum-zinc alloy layer, in which the aluminum alloy molten zinc comprises 10-40% by weight of aluminum, at least 0.2% by weight of silicon and the balance being zinc and which optionally comprises one or more additional elements chosen from the group consisting of magnesium and an earth element rare In step (1), the flow bath comprises 10-40% by weight of zinc chloride, 115% by weight of ammonium chloride, 1-15% by weight of alkali metal chloride, a surfactant and an acid component such that the flow has a final pH of 1.5 or less. In another embodiment of step (1), the flow bath can be as defined in WO 02/42512.

JP 2001/049414 describes the production of a hot dipped Zn-Mg-Al base alloy coated steel plate, with excellent corrosion resistance, by hot dipping in a flow containing 61-80% by weight of zinc chloride, 5-20% by weight of ammonium chloride, 5-15% by weight of one or more of an alkali metal or alkaline earth metal chloride, fluoride or silicafluoride, and 0, 01-5% by weight of one or more chlorides of Sn, Pb, In, Tl, Sb or Bi. More specifically, table 1 of JP 2001/049414 discloses various flow compositions with a weight ratio of KCl / NaCl ranging from 0.38 to 0.60 which, when applied to a steel plate in a bath of molten alloy comprising 0.05-7% by weight of Mg, 0.0120% by weight of Al and zinc being the equilibrium, provides a good metallizing capacity, no stippling, no slag and smooth. In contrast, Table 1 of JP 2001/049414 discloses a flow composition with a weight ratio of KCl / NaCl of 1.0 which, when applied to a steel plate in a molten alloy bath comprising 1 % by weight of Mg, 5% by weight of Al and zinc being the equilibrium, provides a good metallizing capacity, dotting defect, some slag and poorly smooth.

Chinese patent application No. 101948990 shows an electrolytic flow for hot-dip galvanization of a steel cable, comprising 30-220 g / l of zinc chloride, 2-90 g / l of ammonium chloride, 0 -150 g / l potassium chloride, 0-150 g / l sodium chloride, 0-100 g / l boric acid, 0-70 g / l acetic acid, 1-25 g / l sodium fluoride , 2-50 g / l of cerium chloride, 0-50 g / l of potassium fluorocirconate, 0-50 methanol, 0-5-20 g / l of hydrogen peroxide and equilibrium water. Hydrogen peroxide is used as an antioxidant and, since the pH value is maintained within the range of 4.5-5 by means of boric and acetic acids as buffering agents, Fe (OH) 3 is precipitated from the solution, eliminating the unwanted influence of Fe2 + on the electrolytic flow. All exemplary embodiments of document CN101948990 include fluoride salts and volatile organic substances that are prohibited by the legislation (safety, toxicity) of industrial galvanizing units.

Thus, the common consideration of the prior art is a preferred weight ratio of KCl / NaCl below 1.0 in the flow compositions with major proportions (more than 50% by weight) of zinc chloride. However, the prior art has not yet resolved the majority of the technical problems highlighted above. Therefore, there is a need in the art for improved flow compositions and galvanization methods that make use of them.

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GB 1 040 958 A refers to a galvanization flow comprising at least 65% zinc chloride, up to 30% by weight of ammonium chloride and a surfactant. The preferred composition comprises 75% zinc chloride, 10-20% ammonium chloride, up to 5% surfactant, up to 20% sodium chloride and up to 25% potassium chloride. The surfactants can be non-ionic such as ethylene oxide condensates with fatty alcohols or with alkyl substituted phenols such as, for example, condensate of ethylene oxide and nonyl phenol; anionic surfactants such as alkyl arene sulphonates and sulfated alcohols; cationic surfactants such as long chain quaternary ammonium salts or higher alkylamine salts such as dimethyl ammonium chloride and cetyl ammonium chloride. Saporin can also be used as a surfactant.

EP 1 209 245 A1 refers to a flow and its use in a hot dip galvanization process. The hot dip galvanization flow comprises from 60 to 80% by weight of zinc chloride ZnCl2, from 7 to 20% by weight of ammonium chloride NH4Cl, from 2 to 20% by weight of fluidity modifying agent comprising at least one alkali metal or alkaline earth metal, from 0.1 to 5% by weight of at least one of the following compounds: NiCh, CoCl2, MnCh and from 0.1 to 1.5% by weight of at least one of the following compounds: PbCl2, SnCl2, BiCl3 and SbCl3.

EP 0 905 270 A2 refers to a steel plate metallized with Zn-Al-Mg by hot dipping good in terms of resistance against corrosion and surface appearance which is a steel plate metallized by hot dipping with base Zn, obtained by forming on a surface of the steel plate a layer of Zn-Al-Mg metallized by hot dipping formed by Al: 4.0-10% by weight, Mg; 1.0-4% by weight and the balance of Zn and unavoidable impurities, the metallized layer having a metal structure that includes a [primary crystal Al phase] or a [primary crystal Al phase] and a [phase Zn individual] in a matrix of [ternary eutectic structure of Al / Zn / Zn2Mg].

"Next Level HDG Technologies", Fontaine Technologie, July 25, 2012 (2012-07-25), XP 002719188, retrieved from internet: URL:
http://fontaine-technologie.net/index.php/next-level-hdg-technologies [retrieved 2014-01-22] refers to different commercial galvanization processes called DUROZINQ®, MICROZINQ® and ECOZINQ®.

Summary of the invention

The objective of the present invention is to provide a flow composition that makes possible the production of continuous, more uniform, softer and hollow coatings on metal articles, in particular iron or steel articles, of any shape and size by means of galvanization. by hot dipping with pure zinc or zinc alloys, in particular zinc-aluminum alloys and zinc-aluminum-magnesium alloys of any composition. Surprisingly, it has been proven that this can be achieved by providing flow compositions comprising potassium and sodium chlorides in a weight ratio of KCl / NaCl well above 1.0. The problems discussed above are solved by means of a flow composition as defined in claim 1 and a galvanization process as defined in claim 6. The specific embodiments of the present invention are defined in dependent claims 2-5 and 7-14. In addition, a galvanized iron or steel product is provided as defined in claim 15.

Detailed description of the invention

As defined in claim 1, the essential feature of the present invention is the recognition that enormous improvements can be obtained in the galvanization of metals, in particular iron and steel, when starting from a flow composition having a set of at least two alkali metal chlorides including sodium chloride and potassium chloride, with the proviso that the weight ratio of KCl / NaCl of said set of at least two alkali metal chlorides ranges from 2.0 to 8.0. This feature is associated with specific amounts of other flow components.

Definitions

The term "hot dip galvanization" is intended to designate the corrosion treatment of a metal article such as, but not limited to, an iron or steel article by immersion in a molten bath of pure zinc or a zinc alloy, in a continuous or batch operation, for a period of time sufficient to create a protective layer on the surface of said article. The term "pure zinc" refers to zinc galvanizing baths that may contain trace amounts of certain additives such as for example antimony, bismuth, nickel or cobalt. This is in contrast to "zinc alloys" that contain significant amounts of one or more other metals such as aluminum or magnesium.

Next, the different percentages refer to the weight ratio (% by weight) of each component with respect to the total weight (100%) of the zinc-based flow or bath composition. This implies that not all maximum and minimum percentages can be present at the same time, so that the sum is 100% by weight.

In one embodiment of the present invention, the weight ratio of KCl / NaCl specified is associated with the presence of lead chloride in the flow composition. The proportion of lead chloride can be at least

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0.1% by weight, or at least 0.4% by weight, or at least 0.7% by weight of the flow composition. In another embodiment of the present invention, the proportion of lead chloride in the flow composition may be a maximum of 2% by weight, or a maximum of 1.5% by weight or a maximum of 1.2% by weight. In a specific embodiment of the present invention, the proportion of lead chloride in the flow composition is 0.8 to 1.1% by weight.

In one embodiment of the present invention, the weight ratio of KCl / NaCl specified is associated with the presence of tin chloride in the flow composition. The proportion of tin chloride in the flow composition may be at least 2% by weight or at least 3.5% by weight or at least 7% by weight. In another embodiment of the present invention, the proportion of tin chloride in the flow composition is at most 14% by weight.

In one embodiment, the combined amounts of lead chloride and tin chloride represent at least 2.5% by weight, or at most 14% by weight of the flow composition. In another embodiment, the flow composition may also comprise other salts of lead and / or tin such as fluoride, or other chemical substances that are unavoidable impurities present in commercial sources of lead chloride and / or tin chloride.

In one aspect of the invention, the specified weight ratio of KCl / NaCl is combined with specified proportions of other chlorides that make it possible to produce continuous, more uniform, softer and void-free coatings on the metal, in particular iron or steel, galvanizing articles, in particular hot dip galvanization, processes with molten zinc or zinc-based alloys, especially in batch or continuous operation.

For example, the weight ratio of KCl / NaCl specified in the flow composition is combined with more than 40 and less than 70% by weight zinc chloride. In one embodiment of the present invention, the proportion of zinc chloride in the flow composition is at least 45% by weight, or at least 50% by weight. In another embodiment, the proportion of zinc chloride in the flow composition is at most 65% by weight or at most 62% by weight. These selected proportions of ZnCh are capable, in combination with the weight ratio of KCl / NaCl specified in the flow composition, to ensure a good coating of the metal article to be galvanized and to effectively prevent oxidation of the metal article during the stages subsequent processes such as drying, that is, before the galvanization itself.

In one aspect of the present invention, the weight ratio of KCl / NaCl in the flow composition is combined with 10-30% by weight of ammonium chloride. In one embodiment, the proportion of NH4Cl in the flow composition is at least 13% by weight or at least 17% by weight. In another embodiment, the proportion of ammonium chloride in the flow composition is at most 26% by weight or at most 22% by weight. The optimal ratio of NH4Cl can be determined by the skilled person, without extensive experimentation and depending on parameters such as the galvanized metal and the weight proportions of the metal chlorides in the flow composition, simply using the experimental evidence shown in the following examples, to achieve a sufficient chemical attack effect during hot dipping to remove residual corrosion or poorly pickled acid spots, while avoiding the formation of black spots, that is, uncoated areas of the metal article . In some circumstances, it may be useful to replace a minor part (for example, less than 1/3 by weight) of NH4Cl with one or more quaternary alkyl ammonium salt (s) in which at least one alkyl group is 8 to 18 carbon atoms such as those described in EP 0488,423, for example, an alkyl trimethylammonium chloride (for example, trimethylauryl ammonium chloride) or a dialkyl dimethylammonium chloride.

In one aspect of the present invention, the weight ratio of KCl / NaCl specified in the flow composition is further combined with the presence of appropriate amounts of alkali metal or alkaline earth halides, in particular optional halides of alkali metals and alkaline earths different from K and Na. These halides are preferably or predominantly chlorides (bromides and iodides may also be useful) and other alkaline or alkaline earth metals (classified in descending order of preference in each metal class) can be chosen from the group consisting of Li, Cs, Mg, Ca, Mr and Ba. Preferably, fluorides should be avoided for safety and / or toxicity reasons, that is, the flow compositions should be fluoride free salts. In one embodiment, the set of at least two alkali metal chlorides, optionally together with alkali metal or alkaline earth metal halides other than K and Na, represents 6-30% by weight of the flow composition. In another embodiment, the set of at least two alkali metal chlorides includes sodium chloride and potassium chloride as main components or single components. In another embodiment, the set of at least two alkali metal chlorides (for example, which includes sodium chloride and potassium chloride as main components or single components) represents at least 12% by weight or at least 15% by weight of the composition of flow. In another embodiment, the set of at least two alkali metal chlorides (for example, which includes sodium chloride and potassium chloride as main or single components) represents a maximum of 25% by weight, or a maximum of 21% by weight of the composition of flow. NaBr, KBr, MgCh and / or CaCl2 may be present as secondary components in each of the aforementioned embodiments.

In one aspect of the present invention, the weight ratio of KCl / NaCl specified in the flow composition is further combined with the presence of appropriate amounts of one or another metal chloride (for example, a transition metal or a metal of the rare earths) such as, but not limited to, nickel chloride, cobalt chloride, manganese chloride, cerium chloride and lanthanum chloride. For example, some examples below demonstrate that the presence of up to 1% by weight (even up to 1.5% by weight) of nickel chloride is not negative for

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behavior of the flow composition of the present invention in terms of coating quality obtained after hot dipping galvanization. Other metal chlorides that may be present include bismuth chloride, antimony chloride and the like.

In order to solve the above problems and achieve the stated advantages, the weight ratio of KCl / NaCl is important. In any embodiment of the present invention, the weight ratio of KCl / NaCl may, for example, be 3.5 to 5.0, or 3.0 to 6.0.

In other aspects of the present invention, the weight ratio of KCl / NaCl specified in the flow composition is further combined with the presence of other additives, preferably additional additives that participate in the adjustment or improvement of certain desirable properties of the composition of flow. These additives are presented below.

For example, the flow composition of the present invention may further comprise at least one non-ionic surfactant or wetting agent which, when combined with the other ingredients, is capable of achieving a predetermined desirable surface tension. Essentially any type of non-ionic surfactant can be used, but preferably soluble in liquid water. Examples thereof include ethoxylated alcohols such as nonyl phenol ethoxylate, alkyl phenols such as Triton X-102 and Triton N101 (eg, from Union Carbide), block copolymers of ethylene oxide and propylene oxide such as L-44 (from BASF) and tertiary amine ethoxylates derived from coconut, soy, oleic and tallow oils (for example, Ethomeen from AKZO NOBEL), polyethoxylated and polypropoxylated derivatives of alkylphenols, fatty alcohols, fatty acids, aliphatic amines or amides containing at least 12 carbon atoms in the molecule, alkylarene sulphonates and dialkyl sulfosuccinates, such as derivatives of polyglycol ether or aliphatic and cycloaliphatic alcohols, saturated and unsaturated fatty acids and alkylphenols, so that said derivatives preferably contain 3-10 ether groups of glycol and 8-20 carbon atoms in the rest of hydrocarbon (aliphatic) and 6-18 carbon atoms in the alkyl residue of alkylphenol, soluble adducts in a gua of poly (ethylene oxide) and polypropylene glycol, ethylene-diaminopolypropylene glycol containing 1-10 carbon atoms in the alkyl chain, whose adducts contain 20-250 ethylene glycol ether groups and / or 10-100 ether groups of propylene glycol, and mixtures thereof. Such compounds normally contain 1-5 units of ethylene glycol (EO) for each unit of propylene glycol. Representative examples are nonylphenol-polyethoxyethanol, polyglycolic ethers of castor oil, poly (propylene oxide-ethylene) adducts, tributyl-phenoxypolyethoxy ethanol, polyethylene glycol and octylphenoxypolyethoxyethanol. The fatty acid esters of polyethylene sorbitan (such as polyoxyethylene sorbitan trioleate), glycerol, sorbitan, sucrose and pentaerythritol, and mixtures thereof, are also suitable non-ionic surfactants. Low foaming wetting agents such as ternary mixtures described in US Patent No. 7,560,494 are also suitable. Commercially available non-ionic surfactants of the aforementioned types include those marketed by Zschimmer & Schwarz GmbH & Co KG (Lahnstein, Germany) under the trade names of OXETAL, ZUSOLAT and PROPETAL, and those marketed by Alfa Kimya (Istanbul, Turqrna) with The trade name of NETZER SB II. Different qualities of appropriate non-ionic surfactants are available under the trade name of MERPOL.

The hydrophilic-lipophilic balance (HLB) of said at least one non-ionic surfactant is not a critical parameter of the present invention and can be chosen by the skilled person within a wide range of 3 to 18, for example from 6 to 16, by For example, the HLB of MERPOL-A is 6 to 7, the HBL of MERPOL-SE is 11 and the HLB of MERPOL-HCS is 15. Another characteristic of the non-ionic surfactant is the cloud point (i.e. the temperature of phase separation as can be determined, for example, by means of the conventional test method ASTM D2024-09; this behavior is characteristic of non-ionic surfactants containing polyoxyethylene chains, which exhibit an inverse solubility against temperature in water and by both "experience turbidity" at the same point as the temperature rises; glycols that demonstrate this behavior are known as "cloud point glycols") that should preferably be higher than the processing temperature of flow defined below with respect to the use of a flow bath in a hot dip galvanization process. Preferably, the cloud point of the non-ionic surfactant should be greater than 90 ° C.

Appropriate amounts of non-ionic surfactants are well known to the skilled person and usually range from 0.02 to 2.0% by weight, preferably 0.5 to 1.0% by weight, of the flow composition. , depending on the type of compound selected.

The flow compositions of the invention may further comprise at least one corrosion inhibitor, that is, a compound that inhibits the oxidation of steel, in particular under oxidative or acidic conditions. In one embodiment, the corrosion inhibitor includes at least one amino group. The inclusion of said amino derivative corrosion inhibitors in the flow compositions can significantly reduce the rate of iron accumulation in the flow tank. By "amino acid corrosion inhibitor" is meant herein a compound that inhibits the oxidation of steel and contains an amino group. Aromatic alkyl amines and quaternary ammonium salts (which preferably contain 4 independently selected alkyl groups with 1-12 carbon atoms) such as quaternary alkyl dimethyl ammonium nitrate are suitable examples of this type of amino compound. Other suitable examples include hexamethylenediamines. In another embodiment, the corrosion inhibitor includes at least one hydroxyl group, or both a hydroxyl group and an amino group and is well known to those skilled in the art. The appropriate amounts of the inhibitor of

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Corrosion is well known by the skilled person and usually ranges from 0.02 to 2.0% by weight, preferably 0.1-1.5% by weight, or 0.2-1.0% by weight, depending of the type of compound selected. The flow compositions of the invention may comprise at least one corrosion inhibitor as well as a nonionic surfactant or wetting agent as defined above.

In any of the above embodiments, the flow compositions of the invention are preferably free of volatile organic substances, for example, acetic acid, boric acid and methanol, especially those prohibited by legislation for galvanizing units (safety, toxicity).

The flow compositions of the invention can be produced by various methods. They can simply be produced by mixing, preferably thoroughly (for example, under high shear) of the essential components (for example, zinc chloride, ammonium chloride, alkali metal chlorides) and, if necessary, the optimal ingredients ( that is, lead chloride, stannous chloride, quaternary alkyl ammonium salt (s), other transition metal or rare earth chlorides, other alkali metal or alkaline earth halides, corrosion inhibitor (s) and / or surfactant (s) non-ionic (s)) in any possible order in one or more mixing stages. The flow compositions of the invention can also be produced by means of a sequence of at least two stages, in which one stage comprises the dissolution of lead chloride in ammonium chloride or sodium chloride or a mixture thereof, and in which in a further stage the solution of lead chloride in ammonium chloride or sodium chloride or a mixture thereof is subsequently mixed with other essential components (i.e. zinc chloride, potassium chloride) and, if necessary, the Optional ingredients (listed above) of the composition. In one embodiment of the last method, the dissolution of lead chloride is carried out in the presence of water. In another embodiment of the last method, it is useful to dissolve an amount ranging from 8 to 35 g / l of lead chloride in an aqueous mixture comprising 150 to 450 g / l of ammonium chloride and / or sodium chloride, water being the equilibrium. In particular, the last dissolution stage can be carried out at a temperature ranging from 55 ° C to 75 ° C for a period of time ranging from 4 to 30 minutes and preferably with stirring.

A significant advantage of a flow composition of the invention is the wide field of applicability (use). The present flow compositions are particularly suitable for batch hot-dip galvanization processes using a wide range of zinc alloys but also pure zinc. In addition, the present flow can also be used in continuous galvanization processes using either pure zinc or zinc-aluminum or zinc-aluminum-magnesium baths, for galvanizing a wide range of metal parts, for example, cables, pipes or coils (sheets), especially formed by ferrous materials such as iron and steel (for example, long and flat steel products).

According to another aspect, the present invention thus relates to a flow bath for galvanization, in particular hot dip galvanization, in which an appropriate amount of a flow composition is dissolved according to any one of the above embodiments in water or an aqueous medium. Methods for dissolving in water a flow composition based on zinc chloride, ammonium chloride, alkali metal chlorides and optionally one or more chlorides of a transition metal or rare earth metal (e.g., lead, tin, nickel , cobalt, cerium, lanthanum) are well known in the art. The total concentration of components of the flow composition in the flow bath can vary within very wide limits such as 200-750 g / l, preferably 350-750 g / l, most preferably 500-750 g / l 600 -750 g / l. This flow bath is particularly suited for hot-dip galvanization processes using zinc-aluminum baths, but also with pure zinc galvanizing baths, either in continuous or batch operation.

For use in hot-dip galvanization processes (either continuous or batch), the flow bath of the present invention should be advantageously maintained at a temperature within a range of 50 ° C-90 ° C, preferably 60 ° C-90 ° C, most preferably 65 ° C-85 ° C. The process comprises a treatment (flow) stage, for example immersion, of a metal article in a flow bath according to any one of the above embodiments. Preferably, in the batch operation, said treatment step is carried out at a speed performance within the range of 1-12 m / min or 2-8 m / min, for a period of time that varies from 0.01 to 30 minutes, or 0.03 to 20 minutes, or 0.5 to 15 minutes, or 1 to 10 minutes, depending on the operating parameters such as the composition and / or bath temperature of flow, the composition of the metal (for example, steel) object of galvanization, the shape and / or the size of the article. As is well known by the skilled person, the treatment time can vary widely from one article to another: shorter times (next or even below 0.1 minutes) are appropriate for cables, while longer times lengths (close to 15 minutes or more) are more appropriate for example for rods. In continuous operation, the metal treatment stage, that is, immersion in the flow bath, can be carried out at a speed of 0.5 to 10 m / minute, or 1-5 m / minute. You can also achieve much higher speeds of 10-100 m / min, for example 20-60 m / min.

In practice, any metallic surface susceptible to corrosion, for example any type of iron or steel article, can be treated in this way. The shape (smooth or not), geometna (complex or not) or the size of the metal article are not critical parameters of the present invention. The article object of galvanization can be called a long product. As used herein, the "long product" refers to products with a dimension (length) that is at least 10 times higher than the other two dimensions (as opposed to

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smooth products in which two dimensions (length and width) are at least 10 times higher than the thickness (the third dimension), such as cables (coiled or not, to manufacture screws and protections), rods, coils, bars reinforcement, tubes (welded or seamless), branches, structural shapes and sections (for example, I-beams, H-beams, L-beams, T-beams and the like) or tubenas of any dimension, for example, for use in construction civil, mechanical engineering, january, transport (rail, tram), domestic environment or furniture. The galvanized metal article may also be, without limitation, in the form of a smooth product such as sheets, sheets, honeycombs, hot and cold rolled strips (either 600 mm wide and more, or narrow below 600 mm, provided in regular winding coils or superimposed layers) that are rolled from plates (50-250 mm thick, 0.6-2.6 m wide, and up to 12 m long) and which are useful in automotive, heavy machinery, construction, packaging and electrical appliances.

It is important in any galvanization process that the surface of the galvanized object is cleaned properly before carrying out the flow stage. Techniques for achieving the desired degree of surface cleaning are known in the art, and can be repeated, such as alkaline cleaning, followed by aqueous rinsing, acid pickling and finally aqueous rinsing. Although all these procedures are well known, the following description is presented for integrity purposes.

Alkaline cleaning can be carried out appropriately with an aqueous alkaline composition that also contains phosphites and silicates as additives as well as various surfactants. The free alkalinity of such aqueous cleaners can vary widely. Thus, at an initial stage of the process, the metal article is subjected to cleaning (degreasing) in a degreasing bath such as an alkaline ultrasonic degreasing bath. Then, in a second stage, the degreasing article is clarified. Next, the metal article is subjected to one or more acid pickling treatment (s) by immersion in a strong aqueous acidic medium, for example, hydrochloric acid or sulfuric acid, usually at a temperature of 15 ° C to 60 ° C and for 1-90 minutes (preferably 3-60 minutes) and optionally in the presence of a ferrous and / or ferric chloride. Acid concentrations of about 5 to 15% by weight are usually used, for example 8-12% by weight, although more concentrated acids can be used. In a continuous process the pickling time with acid is usually 5 to 30 seconds, more usually 10 to 15 seconds. In order to avoid acid pickling, one can include at least one corrosion inhibitor in the acid pickling bath, usually a cationic or amphoteric surfactant, usually in an amount ranging from 0.02 to 0, 2% by weight, preferably 0.05-0.1 percent by weight. Acid pickling can be achieved simply by immersing the article in an acid pickling tank. Additional processing steps can also be used. For example, the article can be agitated, either by mechanical or ultrasonic means, and / or electric current can be passed through the article for electrode etching with acid. As is well known, these additional processing means normally shorten the pickling time with acid significantly. Clearly, these pre-treatment stages can be repeated individually or in cycles if desired, until the desired degree of cleaning is reached. Then, preferably immediately after the cleaning steps, the metal article is treated (subjected to flow), for example, immersed in a flow bath of the invention, preferably under conditions of total salt concentration, temperature and time specified above. , in order to form a protective film on its surface.

The metal article subjected to flow (for example, iron or steel), that is, after immersion in the flow bath for an appropriate period of time and at the appropriate temperature, is then preferably dried. Drying can be carried out, according to prior art conditions, by transferring the metal article subjected to flow through a furnace having an air atmosphere, for example a forced air stream, in which it is heated to a temperature of 220 ° C to 250 ° C until its surface exhibits a temperature between 170 ° C and 200 ° C, for example, for 5 to 10 minutes. However, it has also been surprisingly found that milder heating conditions may be appropriate when using a flow composition of the invention, or any of its particular embodiments.

Thus, it has been found that it may be sufficient that the surface of the metal article (for example, steel) exhibits a temperature of 100 ° C to 200 ° C during the drying stage. This can be achieved, for example, by using a heating temperature ranging from 100 ° C to 200 ° C. This can also be achieved using a poorly oxidative atmosphere during the drying stage. In one embodiment of the invention, the surface temperature of the metal article may vary from 100 ° C to 160 ° C or from 125-150 ° C or 140-170 ° C. In another embodiment, drying can be carried out for a period of time ranging from 0.5 to 10 minutes, or 1-5 minutes. In another embodiment, drying may be carried out in specific gas atmospheres such as an air atmosphere devoid of water, a nitrogen atmosphere devoid of water, or an atmosphere of nitrogen enriched air and devoid of water (e.g., in which the nitrogen content is above 20%).

At a later stage of the galvanization process, the dried and flow-molded metal article is immersed in a galvanized bath based on molten zinc to form a metallic coating thereon. As is well known, the immersion time can be defined depending on a set of parameters that include the size and shape (for example, smooth or long) of the article, the desired coating thickness, and the exact composition of the zinc bath, in particular its aluminum content (when a Zn-Al alloy is used as a galvanization bath) or magnesium content (when a Zn-Al-Mg alloy is used as a galvanization bath). In one embodiment,

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The zinc-based galvanizing bath can comprise (a) from 4 to 24% by weight (for example from 5 to 20% by weight) of aluminum, (b) from 0.5 to 6% by weight (for example from 1 at 4% by weight) of magnesium, and (c) the remainder being essentially zinc. In another embodiment, the galvanized bath based on molten zinc may comprise minor amounts (i.e., below 1.0% by weight) or trace amounts (i.e. unavoidable impurities) of other elements such as, but not limited to , silicon (for example, up to 0.3% by weight), tin, lead, titanium or vanadium. In another embodiment, the galvanized bath based on molten zinc can be agitated during a part of this treatment stage. During this stage of the process, the zinc-based galvanization bath is preferably maintained at a temperature ranging from 360 ° C to 600 ° C. Surprisingly, it has been found that with the flow composition of the invention it is possible to lower the temperature of the immersion stage while obtaining layers of good quality protective coating, that is, being able to maintain its protective effect during a extended period of time such as five years or more, or even 10 years or more, depending on the type of environmental conditions (air humidity, temperature, etc.). Thus, in one embodiment, the galvanized bath based on molten zinc is maintained at a temperature ranging from 350 ° C to 550 ° C, or 380-520 ° C or 420-520 ° C, depending on the optimum temperature of the aluminum and / or magnesium content optionally present in the zinc-based bath. In another particular embodiment of the galvanization process of the invention, the immersion is carried out at a temperature ranging between 380 ° C and 440 ° C, and said galvanized bath based on molten zinc comprises (a) from 4 to 7% by weight of aluminum, (b) from 0.5 to 3% by weight of magnesium and (c) the remainder being essentially zinc.

In one embodiment, the thickness of the protective coating layer obtained by carrying out the immersion step of the metal article, for example, an iron or steel article, which has been treated with the flow composition of the present invention may vary from 5 to 50 pm, for example from 8 to 30 pm. This can be chosen appropriately by the skilled person, depending on a set of parameters including the thickness and / or shape of the metal article, the tension and the environmental conditions that the metal article is supposed to be able to withstand during its useful life, the expected durability over time of the protective coating layer formed, etc. For example, a 5-15 pm thick coating layer is suitable for a steel article that is less than 1.5 mm thick, and a 20-35 pm thick coating layer is suitable for a steel article which has a thickness greater than 6 mm.

Finally, the metal article, for example of iron steel, is removed from the galvanization bath and cooled. This cooling stage can be carried out conveniently by immersing the galvanized metal article in water or simply allowing it to cool in the air.

It has been proven that this hot-dip galvanization process allows the continuous or batch deposition of thinner, more uniform, softer and hollow protective coating layers on iron or steel articles (both smooth and long products ), especially when using a zinc-aluminum or zinc-aluminum-magnesium galvanization bath with no more than 95% zinc. With respect to the roughness, the coating surface quality is equal to or better than that achieved with the conventional HDG zinc layer in accordance with EN ISO 1461 (that is, with no more than 2% of other metals in the bath of zinc). With respect to corrosion resistance, the coating layers of the present invention achieve approximately 1,000 hours in the salt spray test of ISO 9227 which is much better than the approximately 600 hours achieved with a conventional HDG zinc layer of according to EN ISO 1461. In addition, pure zinc galvanizing baths can also be used in the present invention.

In addition, the process of the present invention is well adapted to galvanize steel articles of any shape (smooth, cylindrical, etc.), such as cables, sheets, tubes, rods, reinforcing bars and the like, forming from a wide variety of steel grades, in particular articles formed from grades of steel having a carbon content of up to 0.30% by weight, a phosphorus content between 0.005 and 0.1% by weight and a silicon content between 0.0005 and 0.5% by weight, as well as stainless steel. The classification of steel grades is well known to the skilled person, in particular through the Society of Automotive Engineers (SAE). In one embodiment, the metal can be chrome / nickel or chrome / nickel / molybdenum steel susceptible to corrosion. Optionally, this quality of steel may contain other elements such as sulfur, aluminum and copper. Suitable examples include, but are not limited to, grades of steel known as AISI 304 (* 1.4301), AISI 304 l (1.4307, 1.4306), AISI 316 (1.4401), AISI 316 l (1 , 4404, 1.4435), AISI316Ti (1,4571) or AISI 904 l (1.4539) * 1, xxxx = according to DIN 10027-2]. In another embodiment of the present invention, the metal may be a steel grade referenced as S235JR (according to EN 10025) or S460MC (according to EN 10149) or 20MnB4 (* 1.5525, according to EN 10263).

The following examples are provided for the compression and illustration of the invention and should not be construed as limiting the scope of the invention, which is defined only by the appended claims.

Example 1 - general procedure for galvanizing at 440 ° C

A plate (2 mm thick, 100 mm wide and 150 mm long) formed by the quality of S235JR steel (weight contents: 0.114% carbon, 0.025% silicon, 0.394% manganese, 0.012 % phosphorus, 0.016% sulfur, 0.037% chromium, 0.045% nickel, 0.004% molybdenum, 0.041% aluminum and 0.040% copper) according to the following sequential pre-treatment procedure:

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- first alkaline degreasing by means of SOLVOPOL SOP (50 g / l) and a mixture of EMULGATOR SEP surfactant (10 g / l), both available from Lutter Galvanotechnik GmbH, at 65 ° C for 20 minutes;

- rinse with water;

- first acid pickling in a bath based on chlortedric acid (composition: 10% by weight HCl, l2% by weight FeCh) at 25 ° C for 1 hour;

- rinse with water;

- second alkaline degreasing for 10 minutes in a degreasing bath with the same chemical composition as the first stage;

- rinse with water;

- second pickling for 10 minutes in a pickling bath with the same chemical composition as before;

- rinse with water;

- flow in a flow composition as described in one of the following tables for 180 seconds at a concentration of 650 g / l and 0.3% by weight of Netzer 4 (a non-ionic wetting agent commercially available from Lutter Galvanotechnik GmbH);

- drying at 100-150 ° C for 200 seconds;

- Galvanizing for 3 minutes at 440 ° C at an immersion rate of 1.4 m / minute in a zinc-based bath comprising 5.0% by weight of aluminum, 1.0% by weight of magnesium, trace amounts of silicon and lead, zinc being the balance; Y

- air cooling.

Examples 2 to 17 -treatment according to illustrative flow compositions of the present invention before galvanizing at 440 ° C

The experimental procedure of Example 1 was repeated with various flow compositions in which the proportions of the chloride components are shown in Table 1. The coating quality was assessed by a team of three people who evaluated the percentage (expressed on a scale of 0 to 100) of steel surface that was perfectly coated with the alloy, the value indicated in the last column of table 1 below being the average value of these three individual annotations. The quality of the coating was assessed while maintaining the flow bath at 72 ° C (examples 1 to 10, without asterisk) or at 80 ° C (examples 11 to 17, marked with asterisk).

Table 1

 Ex.

 ZnCl2% NH4Cl% NaCl% KCl% SnCl2% PbCl2% Coating quality

 one*

 59 20 3 12 4 1 75

 2

 60 20 3 12 4 1 90

 3*

 52.5 17.5 3 12 13 1 75

 4

 53 18 3 12 13 1 80

 5*

 52 21 4 17 4 1 70

 6

 52.5 21.5 4 17 4 1 60

 7

 60.5 12 4.5 18 4 1 60

 8

 57 19 3 12 8 1 85

 9

 59 20 4.5 11.5 4 1 70

 10

 59 20 2.5 13.5 4 1 70

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 eleven

 61.3 20.4 3.1 12.3 2 1 CD cn *

 12

 55 25 3 12 4 1 CD cn *

 13

 56.1 25.5 3.1 12.2 2 1 90 *

 14

 50 30 3 12 4 1 * or CD

 fifteen

 54.1 18 2.7 20.7 3.6 0.9 70 *

 16

 62.5 20.8 3.2 12.5 0 1 * O 00

 17

 57.3 26 3.2 12.5 0 1 00 cn *

* The flow compositions of Examples 1, 3 and 5 additionally contain 1% by weight of NiCl2 to adjust to 100% by weight.

Comparative Example 18

The experimental procedure of Example 1 was repeated with a flow composition comprising 60% by weight of zinc chloride, 20% by weight of ammonium chloride, 10% by weight of sodium chloride, 5% by weight of potassium chloride and 5 % by weight of tin chloride. The quality of the coating was evaluated by means of the same methodology as in the previous examples and it was found to be 20%. This comparative example demonstrates that when the 1/3 KCl / NaCl weight ratio is used as in the prior art, then the coating quality is significantly lower for examples 1 to 17.

Example 19 - general procedure for galvanization at 520 ° C

The sequential procedure of Example 1 was repeated, the treatment stage being carried out with a flow composition at 80 ° C, except that the penultimate galvanization stage was carried out at 520 ° C at a immersion rate of 4 m / minute in a zinc-based bath comprising 20.0% by weight of aluminum, and 1.0% by weight of magnesium, trace amounts of silicon and lead, the balance being zinc.

Examples 20 to 25 - treatment according to illustrative flow compositions of the present invention before galvanization at 520 ° C

The experimental procedure of Example 19 was repeated with various flow compositions in which the proportions of various chloride components are collected in Table 2 below. The coating quality was evaluated by means of the same methodology as in the previous examples.

Table 2

 Ex.

 ZnCl2% NH4Cl% NaCl% KCl% SnCl2% PbCl2% Coating quality

 twenty

 60 20 3 12 4 1 95

 twenty-one

 57 19 3 12 8 1 80

 22

 61.3 20.4 3.1 12.3 2 1 85

 2. 3

 55 25 3 12 4 1 80

 24

 56.1 25.5 3.1 12.2 2 1 85

 25

 54.1 18 2.7 20.7 3.6 0.9 75

Example 26 - general procedure for galvanizing at 460 ° C

The sequential procedure of Example 1 was repeated, the treatment stage being carried out with a flow composition at 80 ° C, except that the penultimate galvanization stage was carried out at 460 ° C at a immersion speed of 4 m / minute in a zinc-based bath comprising 11.0% by weight of aluminum, 3.0% by weight of magnesium, trace amounts of silicon and lead, the balance being zinc.

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Examples 27 to 29 - treatment of steel with illustrative flow compositions of the present invention before galvanizing at 460 ° C

The experimental procedure of Example 26 was repeated with various flow compositions in which the proportions of various chloride components are as set forth in Table 3 below. The coating quality was evaluated by means of the same methodology as the previous examples.

Table 3

 Ex.

 ZnCl2% NH4Cl% NaCl% KCl% SnCl2% PbCl2% Coating quality

 27

 61.3 20.4 3.1 12.3 2 1 95

 28

 55 25 3 12 4 1 95

 29

 56.1 25.5 3.1 12.2 2 1 95

By way of summary, examples 20-25 and 27-29 demonstrate that the present invention achieves exceptional coating quality whatever the composition of the zinc-based galvanizing bath.

Example 30 - galvanizing steel plates at 510 ° C

A steel plate (thickness 2.0 mm) from a quality steel S235JR (composition as defined in example 1) was treated according to the following procedure:

- first alkaline degreasing at 60 ° C by means of SOLVOPOL SOP (50 g / l) and a mixture of Emulgator Staal surfactant (10 g / l), both available from Lutter Galvanotechnik GmbH, for 30 minutes;

- rinse with water;

- first acid pickling in a bath based on hydrochloric acid (composition: 12% by weight of HCl, 15% by weight of FeCh, 1% by weight of FeCh, 2 ml / l of HM inhibitor and 2.5 ml / l from Emulgator C75 from Lutter Galvanotechnik GmbH) at 25 ° C for 60 minutes;

- rinse with water;

- second alkaline degreasing at 60 ° C for 5 minutes in a degreasing bath with the same chemical composition as the first stage;

- rinse with water;

- second acid pickling in an acid-based bath with the same chemical composition as the first pickling step with acid at 25 ° C for 5 minutes;

- rinse with water;

- flow of a steel plate at 80 ° C for 3 minutes in a flow composition (comprising 60% by weight zinc chloride; 20% by weight ammonium chloride; 3% by weight sodium chloride; 12% by weight of potassium chloride; 4% by weight of tin chloride and 1% by weight of lead chloride) with a total salt concentration of 750 g / l and in the presence of 1 ml / l of Netzer 4 (a wetting agent from Lutter Galvanotechnik GmbH), using an extraction speed of 4 m / min or more;

- drying until the surface temperature of the steel plate reaches 120 ° C;

- Galvanizing the steel plate subjected to flow for 3 minutes at 510 ° C in a zinc-based bath comprising 20.0% by weight of aluminum, 4.0% by weight of magnesium, 0.2% by weight of silicon, trace amounts of lead, zinc being the balance; Y

- cooling of the galvanized steel plate in the air.

It was found that this procedure provided a superior coating quality similar to example 20. The following variants of the present process also provide a superior coating quality:

• Same as 650 g / l of total salt concentration, 2 ml / l of Netzer 4 in flow and galvanization in the zinc-based bath at 490 ° C, •

• Same as 650 g / l total salt concentration, 2 ml / l Netzer 4 in flow and galvanization in the bathroom

zinc based at 500 ° C for 1 minute,

• The same but 650 g / l of total saline concentration, flow for 5 minutes with 2 ml / l of Netzer 4 in flow and galvanization in the zinc-based bath at 510 ° C for 10 minutes,

• The same but 650 g / l of total saline concentration, flow for 5 minutes with 2 ml / l of Netzer 4 in flow and galvanization in the zinc-based bath at 530 ° C for 5 minutes, and

• Same as 650 g / l of total saline concentration, flow for 5 minutes with 2 ml / l of Netzer 4 in flow and galvanization in the zinc-based bath at 530 ° C for 15 minutes.

Example 31 - galvanizing steel plates at 520 ° C

A steel plate (thickness 2.0 mm) from a quality steel S235JR (composition as defined in example 1) was treated according to the same procedure as in example 30, except for the following operating conditions:

- at the flow stage, a total salt concentration of 650 g / l in the presence of 2 ml / l of Netzer 4, and

- a 3 minute galvanization step at 520 ° C in a zinc based bath comprising 20.0% by weight of aluminum, 2.0% by weight of magnesium, 0.13% by weight of silicon, trace amounts of lead, the balance being 15 zinc.

It was found that the process provided a superior coating quality similar to example 20.

Claims (14)

5 10 fifteen twenty 25 30 35 40 Four. Five 1. - A flow composition for treating a metal surface, comprising: (a) more than 40 and less than 70% by weight zinc chloride, (b) from 10 to 30% by weight of ammonium chloride, (c) more than 6 and less than 30% by weight of a set of at least two alkali metal chlorides that include sodium chloride and potassium chloride, (d) from 0 to 2% by weight of lead chloride, and (e) from 0 to 15% by weight of tin chloride, (f) at least one non-ionic surfactant, with the proviso that the weight ratio of KCl / NaCl of said set of at least two alkali metal chlorides ranges from 3.0 to 8.0. 2. - A flow composition according to claim 1, wherein said combined amounts of lead chloride and tin chloride represent at least 2.5% by weight of said composition. 3. - A flow composition according to claim 1 or claim 2, which further comprises at least one corrosion inhibitor. 4. - A flow bath for hot-dip galvanization comprising a flow composition according to any one of claims 1 to 3 dissolved in water. 5. - A flow bath according to claim 4, wherein the total concentration of the components of the flow composition in water ranges from 200 to 750 g / l. 6. - A process for hot dipping galvanization of a metal article, comprising a step of treating said article in a flow bath according to claim 4 or claim 5. 7. - A hot dip galvanizing process according to claim 6, wherein said metal article is an iron or steel article. 8. - A hot dipping galvanization process according to claim 6 or claim 7, wherein said treatment step consists in immersing said article in said flow bath for a period of time from 0.01 to 30 minutes 9. - A hot dip galvanizing process according to one of claims 6 to 8, wherein said treatment step is carried out at a temperature ranging from 70 ° C to 90 ° C. 10. - A hot dip galvanizing process according to any one of claims 6 to 9, wherein the treated article is further dried until its surface temperature ranges from 100 ° C to 200 ° C. 11. - A hot dip galvanization process according to any one of claims 6 to 10, which further comprises a step of immersing the treated article in a galvanized bath based on molten zinc. 12. - A hot dip galvanizing process according to claim 11, wherein said galvanized bath based on molten zinc comprising (a) from 4 to 24% by weight of aluminum, (b) from 0, 5 to 6% by weight of magnesium and (c) the remainder being essentially zinc. 13. - A hot dip galvanization process according to claim 11, wherein the immersion is carried out at a temperature between 380 and 440 ° C and wherein said galvanized bath based on molten zinc comprising (a) from 4 to 7% by weight of aluminum, (b) from 0.5 to 3% by weight of magnesium and (c) the remainder being essentially zinc. 14. - A pre-treated galvanized iron or steel product with a flow composition according to any one of claims 1 to 3, which has a protective coating layer with a thickness ranging from 5 to 30 pm and obtained from according to a hot dip galvanization process according to any of claims 12 or 13.