Coating processes – Spray coating utilizing flame or plasma heat – Metal or metal alloy coating
Reexamination Certificate
1999-04-30
2001-04-10
Beck, Shrive (Department: 1762)
Coating processes
Spray coating utilizing flame or plasma heat
Metal or metal alloy coating
C427S449000, C427S456000, C118S313000, C118S315000, C138S145000, C138S146000
Reexamination Certificate
active
06214420
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for metallization of metal substrates and relates more particularly to the hot metallization of pipes, in particular cast-iron pipes which are obtained by means of vertical continuous casting.
Among the known processes for the hot metallization of pipes, the following are known:
customized hot-galvanization;
the continuous coating of steel plates with Zn or ZnAl;
methods for thermal spraying with Zn or ZnAl alloys;
zinc-coating of pipes.
The existing solutions based on galvanization have the following drawbacks.
Customized hot-galvanization coats the pipe internally and externally and the pipe undergoes an increase in temperature such that the results of other prior operations carried out on the pipe at lower temperatures risk being affected.
Hot galvanization by movement through a liquid poses the problem, currently unsolved, of tightness with respect to the liquid bath between the vertical pipe and the liquid metal, as well as the problem of maintaining a bath which is clean (without matte) and has a stable composition over time.
Cold metallization associated with annealing would ensure good distribution if rigorous conditions for preparation of the pipe surface are satisfied and would probably require heat treatment in an inert atmosphere.
The cost of such a treatment cycle would be considerable and as a result would offer limited advantages from an economic point of view.
The pipe to be coated, emerging after continuous casting, is not rough, which makes fixing of a cold coating impossible without carrying out surface preparation.
In order to obtain a well-distributed coating, a pipe without an oxide skin is necessary and the working temperature must be high or else the pipe handling time must be long.
SUMMARY OF THE INVENTION
The invention aims to provide a uniformly distributed coating which has a good impact resistance.
Moreover an object of the invention is to provide a coating which adheres very well to the outside of a pipe of varying position and diameter, continuously moving in a vertical direction and without undergoing rotation, while preventing the pipe from being subject to heat annealing.
Furthermore an object of the invention is to provide a coating which is “self-healing” in respect of any damage suffered.
Finally, an object of the invention is to provide a coating which contributes to corrosion resistance in underground conditions.
The invention therefore relates to a process for metallization of a metal pipe obtained by vertical casting and displaced vertically in a continuous manner with an upward movement, characterized in that it consists in:
cooling the pipe in an atmosphere which is inert with respect to oxidation up to a temperature of 700 to 900° C.; and
spraying onto the pipe, cooled beforehand to the aforementioned temperature, a zinc-based metallization alloy with the aid of a set of spray guns arranged so as to surround the path of the pipe to be metallized.
According to a particular characteristic feature of the invention, the spray guns are made to oscillate about the path of the pipe with a frequency and an angular amplitude adapted to the speed of displacement of the pipe with a view to obtaining a coating of uniform thickness.
The invention also relates to a plant for metallization of a metal pipe obtained by means of upward vertical continuous casting and displaced vertically in a continuous manner, characterized in that it comprises, along the path of the pipe, a metallization station comprising a passage for the pipe, a metallization enclosure, spray guns mounted inside the said enclosure on an oscillating plate surrounding the said path, means for supplying each gun with metallization material and means for causing oscillation of the support plate and for displacing the guns inside the said enclosure with an oscillating movement, the frequency and angular amplitude of which ensure the formation of a coating of uniform thickness.
The invention relates moreover to a metal pipe obtained by means of vertical casting, characterized in that it has a metallization coating obtained by the process defined above.
According to another particular characteristic feature, the spray guns are three in number and are arranged on the plate at 120° from one another.
According to another particular characteristic feature, the spray guns are flame guns or arc guns.
According to another characteristic feature of the invention, the metallization material is a wire of Zn
x
Al
1-x
alloy and the means for supplying metallization material comprise for each gun a wire store and an unwinding device operated by the oscillation movement of the plate supporting the guns.
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Girardin Denis
L'Huillier Joel
Lamouret Christophe
Beck Shrive
Calcagni Jennifer
Pont-a-Mousson
Sughrue Mion Zinn Macpeak & Seas, PLLC
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