Coating processes – With pretreatment of the base – Heating or drying pretreatment
Patent
1994-04-19
1995-09-05
Utech, Benjamin
Coating processes
With pretreatment of the base
Heating or drying pretreatment
427329, 427432, 4274342, 427436, B05D 300
Patent
active
054477549
ABSTRACT:
Steel alloys containing chromium may be hot dip aluminized in a bath having up to 15% silicon with improved wettability by using a bright preannealing practice in a box furnace having a substantially pure hydrogen atmosphere. The surfaces of the preannealed steel are easily coated if the box annealing furnace has a dew point of less than -60.degree. C. (-75.degree. F.). The preannealing should also include a minimum soak of at least 1 hour at a temperature of 675.degree. C. to 785.degree. C. (1250.degree. F. to 1450.degree. F.). It is important that the surfaces of the strip after preannealing are not removed prior to aluminizing. During the aluminizing operation, the strip temperature does not need to be heated to much above the bath temperature since the strip has already been preannealed. The furnace is maintained to avoid oxidation with an atmosphere which is typically a nitrogen, hydrogen or a hydrogen-nitrogen mixture. The surfaces of the steel prior to entering the aluminum bath have improved wettability and result in far less uncoated spots due to the improved surfaces provided by the preanneal in the dry box anneal. For ferritic stainless steels, such as Type 409, the surfaces have an iron enriched layer.
REFERENCES:
patent: 2197622 (1940-04-01), Sendzimir
patent: 3925579 (1975-12-01), Flinchum et al.
patent: 4675214 (1987-06-01), Kilbane et al.
patent: 5023113 (1991-06-01), Boston et al.
patent: 5175026 (1992-12-01), Bertol et al.
Armco Inc.
Bunyard Robert J.
Fillnow Larry A.
Johnson Robert H.
Utech Benjamin
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