BE1001732A6 - PROCESS FOR THE CHEMICAL TREATMENT OF METAL PARTS. - Google Patents

Abstract

Process for the chemical treatment of metal parts made of preferably iron-based materials in a solution of chromic acid, before metallization by hot immersion, characterized in that the metal parts having a surface which is pure from the metallic point of view are immersed in a solution having the following parameters: 3-34 g / l of CrO3, at least 0.06 g / l of ions (Cr) +++, at least 0.04 g / l of ions (Fe) ++ +, at a temperature of 310 to 355 K, for at least 60 seconds, and in that they are dried at a temperature of at least 350K.

Description

       

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  "Process for the chemical treatment of metal parts".
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  The present invention relates to a process for the chemical treatment of metallic parts, preferably of iron-based materials in a chromic acid solution, before metallization by hot immersion, in particular aluminization by hot immersion. This treatment is carried out between cleaning the surface and metallization by hot immersion to guarantee and improve the wetting capacity.



  It is known that metallic parts, which must receive a protective coating by hot-dip metallization, must be pure from the metallic point of view and that they must be subjected to a separate chemical treatment to increase the wetting capacity by the metallic melt.



  It is known, among other things, to treat metal parts in chromic acid solutions before hot immersion processes. Thus, a process of aluminization by immersion is described in the patent in the German Democratic Republic DD-223 730. According to this invention, immersed products based on iron and its alloys having a cleaned surface in a solution of chromic anhydride , they are then rinsed in water and they are introduced into a heated solution of sodium tetraborate, then they are dried and they are brought to the bath containing molten aluminum. Application of the process is certainly possible, but the quality obtained from the aluminum protective layer is unstable and therefore industrial application is not sustainable.



  The object of the invention is to develop the chemical treatment process for hot-dip metallization so as to obtain stable quality parameters from the metal protective layers by ensuring and improving the wetting capacity of the parts. metallic vis-à-vis the molten mass.

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   The object of the invention is to make the process sufficiently stable so that the protective layers obtained during metallization by industrial hot immersion of metal parts chemically treated according to a known state of the art correspond to technical standards.



   According to the invention, these problems are solved by the fact that the metallic parts, the surface of which has been cleaned in a "metallically pure" state according to a process known per se, are immersed in a solution of chromic acid having the following parameters:
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 3-45 g / liter of Croc at least 0.06 g / liter of ions Cr at least 0.04 g / liter of ions Fe, at a temperature of 310 to 355K, for at least 60 seconds, and they are dried at a temperature of at least 350K.

   The concentration of cor3 + and fic3 + ions in the freshly applied chromic acid solution can be obtained by a chemical reaction of metal parts made of unalloyed or weakly alloyed steel with the solution, or, when the solution is freshly supplied. chromic acid, part of a solution already used is added.



   The invention will be described in more detail with the aid of the examples below, without however being limited by the latter.
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  EXAMPLE I The metal parts, the surface of which has been cleaned to obtain the "metallically pure" state, are immersed in a solution of chromic acid, the concentration of Cr and Fe ions of which is obtained by a chemical reaction of the material. based on iron with the treatment solution and the composition of which is as follows: 4.0 g / l of Cr03 0.25 g / l of Cr3 + ions
0.14 g / 1 Fe ions
Solution temperature: 323 K
Immersion time: 270 s
Drying temperature: 360 K

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 Example 2 The metal parts pretreated in accordance with Example 1 are immersed in a solution of chromic acid containing 10.0 gil of Cru.



  The concentration of 0.05 gjJ of Cr3 + and 0.04 g / l of fie3 + is reached by the addition of an equivalent fraction of a treatment solution already used.



  Solution temperature: 310 K Immersion time: 90 s Drying temperature: 375 K


    

Claims (3)

 CLAIMS 1. Process for the chemical treatment of metal parts made of materials preferably based on iron in a chromic acid solution, before metallization by hot immersion, characterized in that the metal parts having a surface that is pure from the metallic point of view are immersed in a solution having the following parameters:  EMI4.1  3-45 g / i of CrO ,. at least 0.06 g / 1 of Cr ions at least 0.04 g / 1 of Fe3 + ions, at a temperature of 310 to 55 K, for at least 60 seconds, and in that they are dried at a temperature at least 350K.  2. Method according to claim 1, characterized  EMI4.2  1 "C 3+ F 3+ 'in that the concentration of Cr and e ions is reached by chemical reaction of iron-based materials with the applied chromic acid solution.  3. Method according to claim 1, characterized in that, when a new supply of chromic acid solution, part of the solution already used is added.