Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-06-25
2003-03-04
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C072S039000, C072S041000, C072S042000, C148S246000, C148S270000, C205S316000, C205S477000, C205S496000, C205S508000, C423S544000, C428S659000, C428S469000, C428S688000, C428S689000, C428S702000, C428S908800
Reexamination Certificate
active
06528182
ABSTRACT:
The invention concerns the pre-lubrication of the zinc coated surface of plates coated with zinc or zinc-based alloy and the treatment of these plates in aqueous solutions containing sulphates.
The document entitled “The influence of some sulphur-containing anions on the anodic behaviour of zinc in an alkaline medium”, written by S. S. Abd El Rehim et al., published in “Journal of Electroanalytical Chemistry”, 401 (1996) 113-118, describes, in an alkaline medium (|NaOH|=0.1 M, therefore pH=13), the oxidation of zinc into zinc hydroxide Zn(OH)
4
=
ion in a first step, then the oxidation of this hydroxide ion into zinc oxide ZnO
2
in a second step; this document also describes the influence of sulphur-containing species in solution, in particular of sulphate SO
4
=
ions, on the second oxidation step.
According to this document, if the concentration of Zn(OH)
4
=
ions attains the product of solubility, the zinc hydroxide Zn(OH)
2
precipitates and forms a passivating film on the surface.
With reference to
FIGS. 2 and 4
, this document (cf. page 115) teaches that the presence of SO
4
=
anions stimulates the dissolution of the zinc; this effect might come from the adsorption of these anions on the zinc-coated surface which facilitates oxidation of the zinc of this surface by these adsorbed anions.
With reference to
FIGS. 2 and 5
, this document (cf. page 115) also teaches that too high a concentration of anions in the alkaline solution provokes rupture of the passivation film formed after the first oxidation step.
The domain of concentration studied in this document covers the range 0.05 to 1.7 mole SO
4
=
per liter.
Documents JP 61-60915, 63-46158, 63-46159 and EP 0 339 578 describe anodic treatments of zinc-coated steel plates in aqueous solutions containing sulphates and the use of these treatments to colour the zinc-coated surfaces of these plates.
The concentration of electrolyte in the treatment solution is included between 70 and 200 g/l; the concentration of sodium sulphate is for example 150 g/l, i.e. about 1 mole/liter.
Document JP 63-274797 describes the use of a treatment of the same type for improving the aptitude to phosphatisation of steel plates coated by electrodeposit of a zinc-based alloy containing nickel.
The treatment solution then contains, in addition to sulphates (for example: magnesium, sodium or aluminium sulphate at 150 g/l), carboxylic acids (for example citric, maleic, salicylic at 30 or 40 g/l).
The pH of the treatment solution is included between 4 and 5.5.
The anodic treatment is conducted under a current density included between 30 and 200 A/dm
2
until the quantity of electricity consumed is included between 50 and 500 C/dm
2
of surface to be treated.
According to this document, this treatment improves the aptitude to phosphatisation because it results in the elimination of the superficial traces of zinc hydroxides —Zn(OH)
2
— and makes it possible to improve the surface reactivity.
The plates resulting from these treatments under anodic polarisation in aqueous solutions containing at least 0.05 mole of sulphate ions per liter, particularly more than 10 g/l of sulphate ions, pose problems in deep-drawing and forming.
Patent EP 0 489 105 describes a method of treating the metallic surface of a plate, particularly a steel plate, intended for preparing said plate for deep-drawing and/or for protecting it against corrosion, in which:
there is applied on this surface an aqueous solution of a water-soluble salt of an alkaline metal, particularly potassium phosphate,
said surface is dried,
then at least one operation of oiling of said surface is carried out.
The conditions of application and of drying are adapted in order to obtain a deposit of phosphate of surface density included between 5 to 40 mg/m
2
.
The oil used may be an oil for temporary protection against corrosion and/or a lubricating oil for forming, particularly deep-drawing.
Thus, before storage and/or transport, a first oiling for protection may be effected; after taking from stock, a second oiling for lubrication may be effected, for preparing forming, particularly by deep-drawing.
According to this document EP 0 489 105, the phosphatisation treatment, prior to oiling, makes it possible substantially to improve lubrication at the moment of forming: it is therefore question of a pre-lubrication treatment.
The zinc-coated plate obtained is provided with a pre-lubricating deposit based on phosphate.
The lubricating effect of this phosphatisation treatment sometimes proves to be insufficient on zinc-coated plates; furthermore, this treatment generates effluents containing phosphates, which it is desired to avoid.
The invention has for an object to provide a pre-lubricated zinc-coated plate with higher performances than those obtained by phosphatisation and to offer a treatment of pre-lubrication of zinc-coated plates more efficient than a treatment of phosphatisation and more respectful of the environment at the level of the effluents that it generates.
To that end, the invention has for its object a steel plate coated with a metal layer based on zinc, characterized in that:
said metal layer is itself coated with a layer based on zinc hydroxysulphate,
the surface density of sulphur corresponding to said layer of hydroxysulphate is more than 0.5 mg/m
2
.
Other advantageous characteristics of the plate according to the invention are indicated in the dependent Claims.
Several methods of hydroxysulphation make it possible to arrive at the pre-lubricated zinc-coated plate according to the invention.
The invention therefore also has for an object a first method of obtaining a plate according to the invention from a steel plate coated with a metal layer based on zinc comprising the steps consisting in applying on the zinc-coated surface of the starting plate an aqueous treatment solution containing more than 0.07 moles of sulphate ions per liter, in polarising in anodic manner said surface so as to cause a polarisation current to circulate, then rinsing said surface, then drying it, characterized in that
the pH of said solution is greater than or equal to 12 and less than 13,
the quantity of electric charges, circulating during the treatment through said surface and generating on said surface the deposit of a layer including sulphur, is adapted so that the quantity of sulphur obtained in said layer of hydroxysulphate exceeds 0.5 mg/m
2
.
Other advantageous characteristics of the first method of obtaining the plate according to the invention are indicated in the dependent Claims.
In practice, it is possible to determine, for predetermined conditions of use of the treatment solution, the minimum quantity of charges that should be circulated in order to obtain a deposit presenting a sulphur content of 0.5 mg/m
2
, to carry out this method, the quantity of charges used must in that case be greater than this minimum quantity.
The plate obtained by this method, then oiled, offers very good tribological properties well adapted to forming, particularly by deep-drawing: this hydroxysulphation treatment therefore has an effect of pre-lubrication.
By optimalizing the thickness of the layer of hydroxysulphate deposited, the pre-lubricating effect obtained is greater than that contributed by a treatment in a solution of phosphate as described in EP 0 489 105.
It is observed that this effect of pre-lubrication comes from the nature of the deposit: the infrared reflection spectrum of the deposit obtained is shown in
FIG. 3
(reflectance in % as a function of the wave number in cm
−1
); here it is essentially a question of a layer of zinc hydroxysulphate, also called basic zinc sulphate; this hydroxysulphate would correspond to the general formula:
[Zn
x
(SO
4
)
y
(OH)
z
, tH
2
O],
where 2x=2y+z, with y and z different from zero; preferably, z is higher than or equal to 6, and more preferably z=6 and 3≦t≦5; according to the spectrum of
FIG. 3
, x=4, y=1, z=6 and t=5.
In ord
Bello Alain
Petitjean Jacques
Rossi Armand
Wajda Sylviane
Koehler Robert R.
Sollac
Sughrue & Mion, PLLC
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