Coating processes – With post-treatment of coating or coating material – Heating or drying
Patent
1998-07-06
1999-12-07
Cameron, Erma
Coating processes
With post-treatment of coating or coating material
Heating or drying
427409, 428461, B05D 138, B05D 302, B05D 714
Patent
active
059979550
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for treatment of the metal surface of a sheet, especially a steel sheet, for the purpose of preparing the said sheet for deep-drawing and/or protecting it against corrosion, wherein an aqueous solution of treatment product is applied to the said surface, the said surface is dried, then at least one operation of oiling of the said surface is performed.
European Patent 0 489 105 B1 describes a process of this type, wherein the treatment product comprises a water-soluble salt of an alkali metal, especially potassium phosphate.
Before a sheet is deep-drawn, therefore, a potassium phosphate solution is applied to its surface, then the applied solution is dried; the application and drying conditions are adjusted to obtain a phosphate deposit having a surface density of between 5 and 40 mg/m.sup.2.
Following this deposition process, at least one operation of oiling of the surface is then performed (to cover this deposit).
When a lubricating or deep-drawing oil has been used for oiling, the sheet treated in this way is then ready to be reloaded in the forming machine (for example, a deep-drawing press).
To be effective, this surface treatment (phosphating and oiling) must be performed on a clean metal surface, and it is sometimes necessary to clean the surface of the sheet before applying the treatment solution.
Such a surface treatment in preparation for deep-drawing allows the coefficient of friction between the sheet and deep-drawing die to be reduced substantially without having to resort to oils having high additive content, because sometimes such oils must be avoided, in particular for economic reasons.
The preliminary treatment of the metal surface by a phosphate solution therefore substantially improves the tribological properties of the said surface.
The preparation of a sheet for deep-drawing therefore comprises at least two operations, one being deposition of a treatment product (phosphate) and the other oiling.
Sometimes it is necessary to arrange for not one but two oiling operations after deposition of a treatment product, because in practice the sheets are stored, sometimes for a prolonged period, longer than one month, between fabrication and forming thereof.
During this storage period, it is therefore advisable to protect the sheets against corrosion.
After deposition of a treatment product (phosphate), oiling is performed first for temporary protection against corrosion, whereas oiling for lubrication is not performed until just before forming proper of the sheet.
Protective oils are generally different from lubricating oils: in general, therefore, a single oiling operation may not be sufficient.
After storage, the sheets can therefore be deep-drawn, generally by means of a second oiling operation, or re-oiling for lubrication.
In conclusion, the following disadvantages can occur between fabrication and forming of sheets: product+oiling), and possibly three in the case of storage (re-oiling after storage). this oiling operation was preceded by deposition of a phosphate-based treatment product, which reflects a problem of compatibility between the phosphate coat deposited to improve the tribological properties and the oil film deposited to protect against corrosion. deposition of a phosphate-based treatment product: as a result, it is more difficult to deep-draw sheets that have been kept in prolonged storage.
The object of the invention is to limit these disadvantages while providing a surface treatment that offers both good resistance to corrosion and good lubrication, even with a single oiling operation.
The object of the invention is a process for treatment of the metal surface of a sheet, especially a steel sheet, for the purpose of preparing the said sheet for deep-drawing and/or protecting it against corrosion, wherein an aqueous solution of treatment product is applied to the said surface, the said surface is dried, then at least one operation of oiling of the said surface is performed, characterized in that: derivatives, the said derivatives being sterol
REFERENCES:
patent: 4787995 (1988-11-01), Nichols et al.
Morand Claude
Pesarolo Roland
Cameron Erma
Sollac
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