Mixture and process for fluxing metal components to be galvanized

Abstract

The mixture for fluxing metal components to be galvanized consisting of an aqueous solution comprising at least one inorganic halide salt, wherein it is substantially free of zinc chloride.

Description

[0001] MIXTURE AND PROCESS FOR FLUXING METAL COMPONENTS

[0002] TO BE GALVANIZED

[0003] Technical Field

[0004] The present invention relates to a mixture and a process for fluxing metal components to be galvanized.

[0005] Background Art

[0006] In the metallurgical sector, the coating of metal components, especially iron components, by hot-dip galvanizing is well known.

[0007] Hot-dip galvanizing generally involves a plurality of steps.

[0008] At first, a pre-treatment is carried out on the component to be coated, which is of considerable importance in order to ensure optimal galvanizing of the same.

[0009] The pre-treatment involves initially dipping the metal component in an acid or alkaline degreaser, pickling it in hydrochloric acid, washing it, and finally flushing it.

[0010] Next, the metal component is preheated to a temperature of approximately 100°C-120°C in order to dry it and prevent possible thermal shock during the next phase.

[0011] The pretreated component is then dipped in the galvanizing tank containing molten zinc at approximately 450°C.

[0012] Finally, the metal component is removed from the zinc tank and left to cool and, if necessary, passivated to preserve the shine thereof.

[0013] During pre-treatment, fluxing is a very important step, as it determines the correct adhesion of the zinc metal to the component to be coated and the thickness of the coating.

[0014] Known fluxing processes involve dipping the metal component in an aqueous solution of zinc chloride and ammonium chloride.

[0015] However, zinc chloride is a compound that is hazardous to the environment. In particular, it is considered highly toxic to aquatic organisms with long-lasting effects.

[0016] Therefore, galvanizing plants, and in particular fluxing plants, are subject to very stringent regulations regarding the management of fluxing baths.

[0017] Description of the Invention The main aim of this invention is to devise a mixture and a process for fluxing metal components to be galvanized that allows avoiding the use of zinc chloride.

[0018] Another object of the present invention is to devise a mixture and a process for fluxing metal components to be galvanized that ensure effective galvanization of the components subjected to fluxing.

[0019] Another object of the present invention is to devise a mixture and a process for fluxing metal components to be galvanized that allow the aforementioned drawbacks of the prior art to be overcome within the scope of a simple, rational, easy and effective to use as well as affordable solution.

[0020] The aforementioned objects are achieved by the present mixture for fluxing metal components to be galvanized having the characteristics of claim 1 and by a process for fluxing metal components to be galvanized having the characteristics of claim 6.

[0021] Other characteristics and advantages of the present invention will become more apparent from the description of a preferred, but not exclusive, embodiment of a mixture and a process for fluxing metal components to be galvanized.

[0022] Embodiments of the Invention

[0023] The mixture consists of an aqueous solution comprising at least one inorganic halide salt and, according to the invention, is substantially free of zinc chloride. In the context of this disclosure, the expression “substantially free of zinc chloride” indicates that the mixture is not completely free of this compound.

[0024] In fact, the possible presence of trace amounts of zinc chloride due to carryover or contamination cannot be ruled out.

[0025] Advantageously, the inorganic halide salt is selected from the list comprising: ammonium chloride, potassium chloride, magnesium chloride and calcium chloride or mixtures thereof. It cannot, however, be ruled out that the inorganic halide salt may be of a different type. Specifically, the halogen may be selected from fluorine, chlorine, bromine, and iodine, and the counterion may also be a metal or an inorganic cation other than those indicated.

[0026] According to a first embodiment, the aqueous solution comprises only magnesium chloride. Magnesium chloride is a relatively safe salt and is not subject to stringent safety regulations as is the case with zinc chloride.

[0027] Specifically, the aqueous solution comprises magnesium chloride in a concentration of between 50 g / L and 400 g / L with respect to the final volume of the mixture.

[0028] It cannot be ruled out from the scope of this disclosure that the aqueous solution may contain one of ammonium chloride, potassium chloride and calcium chloride.

[0029] As will be described in more detail below, flushing with magnesium chloride alone allows for uniform and effective galvanizing, similar to known mixtures containing magnesium chloride.

[0030] In accordance with a second embodiment, the aqueous solution also comprises at least one of either ammonium chloride or potassium chloride.

[0031] The use of mixtures based on ammonium chloride and potassium chloride salts is known, but not in combination with magnesium chloride.

[0032] The use of magnesium chloride allows the amount of the other two salts in the mixture to be reduced, which are known to be effective in fluxing metal components but at the same time give the fluxed piece less resistance to oxidation.

[0033] Specifically, the aqueous solution according to the second embodiment comprises magnesium chloride in a concentration of between 75 g / L and 200 g / L with respect to the final volume of the mixture.

[0034] It follows that the aqueous solution according to the second embodiment comprises: ammonium chloride in a concentration by weight of between 60% and 80% with respect to the total weight of the salts; potassium chloride in a concentration by weight of between 5% and 20% with respect to the total weight of the salts; magnesium chloride in a concentration by weight of between 10% and 30% with respect to the total weight of the salts.

[0035] Furthermore, it cannot be ruled out that the above salts may be present individually in the aqueous solution. According to a third alternative embodiment, the aqueous solution comprises ammonium chloride in a concentration of between 50 g / L and 1,000 g / L with respect to the final volume of the mixture.

[0036] Furthermore, according to a fourth embodiment, the aqueous solution comprises potassium chloride in a concentration of between 30 g / L and 300 g / L with respect to the final volume of the mixture.

[0037] Finally, according to a fifth embodiment, the aqueous solution comprises calcium chloride in a concentration of between 20 g / L and 200 g / L with respect to the final volume of the mixture.

[0038] According to a further aspect, the present invention also relates to a process for fluxing metal components to be galvanized.

[0039] According to the invention, the process comprises the following phases: preparing a dipping bath containing a mixture according to one or more of the embodiments described above; dipping a metal component to be galvanized within the dipping bath; picking the metal component from the dipping bath.

[0040] Specifically, the metal component is a piece of heavy or light structural steel made of iron.

[0041] The phase of preparation comprises a step of heating the mixture to a temperature of between 20°C and 60°C. The step of heating aims at increasing the solubility of the salts contained in the mixture and ensuring complete solubilization, thus preventing the deposit of salt aggregates on the metal component.

[0042] In addition, the heating step also serves to heat the metal component and prevent thermal shock during subsequent treatments and speed up drying. Conveniently, the process also comprises a dipping bath phase.

[0043] In fact, prior to fluxing, the metal component is pickled by dipping it in a hydrochloric acid bath and, despite subsequent washing with water, hydrochloric acid residues remain on the surface of the metal component.

[0044] As a result, frequent dipping of metal components leads to acidification of the mixture and solubilization of the iron ions making up the metal component.

[0045] The purification phase therefore comprises at least one step of iron ion precipitation by oxidation of the dipping bath.

[0046] Specifically, the precipitation step is performed using an oxidizing agent such as e.g. hydrogen peroxide.

[0047] In this way, the iron is oxidized from Fe(II) to Fe(III) and precipitates.

[0048] The precipitate is then filtered and removed from the bath.

[0049] The precipitation then causes the release of chlorine ions, which leads to a decrease in pH.

[0050] The purification phase usefully comprises a step of correcting the pH to a value of between 4 and 5, preferably pH 4.5. The purification step allows reducing the acidity of the dipping bath, which would otherwise prevent the iron from precipitating.

[0051] Usefully, the correction step is performed with at least one inorganic hydroxide, where the cation is the metal or inorganic ion of which the fluxing mixture is composed.

[0052] This restores the initial composition of the fluxing mixture.

[0053] Advantageously, the dipping phase is performed for a time of between 1 minute and 3 minutes.

[0054] At the end of this process, the metal component is transferred to further equipment for the execution of the additional steps required by the known hot- dip galvanizing technique.

[0055] Quality control shows that galvanizing metal components subjected to fluxing by means of the above-described process is fully compliant with regulations and free from imperfections.

[0056] The test to determine the thickness of the coating is performed using known techniques involving the use of a thickness gauge.

[0057] Similarly, adhesion tests have also yielded excellent results, demonstrating that the coating is well anchored to the metal component and that the iron / zinc alloying process has been carried out in a workmanlike maimer.

[0058] The test to check adhesion is also performed using known techniques, specifically by dropping a 1kg hammer at a 90° angle.

[0059] In actual facts, it has been ascertained that the described invention achieves the intended objects and, in particular, the fact should be emphasized that the mixture and the process according to the invention for fluxing metal components to be galvanized make it possible to avoid the use of zinc chloride.

[0060] Furthermore, the mixture and the process for fluxing metal components to be galvanized ensure effective galvanization of the components subjected to fluxing.

Claims

CLAIMS1) Mixture for fluxing metal components to be galvanized consisting of an aqueous solution comprising at least one inorganic halide salt, characterized by the fact of being substantially free of zinc chloride.2) Mixture according to claim 1, characterized by the fact that said inorganic halide salt is selected from the list comprising: ammonium chloride, potassium chloride, magnesium chloride and calcium chloride or mixtures thereof3) Mixture according to one or more of the preceding claims, characterized by the fact that said inorganic halide salt is magnesium chloride.4) Mixture according to one or more of the preceding claims, characterized by the fact that said aqueous solution comprises magnesium chloride in a concentration of between 50 g / L and 400 g / L with respect to the final volume of said mixture.5) Mixture according to one or more of the claims 1 to 2, characterized by the fact that said aqueous solution comprises ammonium chloride in a concentration of between 50 g / L and 1,000 g / L with respect to the final volume of said mixture.6) Mixture according to one or more of the claims 1 to 2, characterized by the fact that said aqueous solution comprises potassium chloride in a concentration of between 30 g / L and 300 g / L with respect to the final volume of said mixture.7) Mixture according to one or more of the claims 1 to 2, characterized by the fact that said aqueous solution comprises calcium chloride in a concentration of between 20 g / L and 200 g / L with respect to the final volume of said mixture.8) Mixture according to one or more of the preceding claims, characterized by the fact that said aqueous solution comprises at least one of ammonium chloride or potassium chloride.9) Process for fluxing metal components to be galvanized, characterized by the fact that it comprises the following phases: preparing a dipping bath containing a mixture according to one or more of the preceding claims; dipping a metal component to be galvanized within said dipping bath; picking said metal component from said dipping bath.10) Process according to one or more of the preceding claims, characterized by the fact that said phase of preparing comprises a step of heating said mixture to a temperature of between 20°C and 60°C.11) Process according to one or more of the preceding claims, characterized by the fact that it comprises a phase of purifying said dipping bath comprising at least one step of precipitating iron ions through oxidation of said dipping bath.12) Process according to one or more of the preceding claims, characterized by the fact that said phase of purifying comprises a pH correction step to a pH value of between 4 and 5. 13) Process according to one or more of the preceding claims, characterized by the fact that said phase of dipping is carried out for a time of between 1 minute and 3 minutes.