Coating processes – Spray coating utilizing flame or plasma heat – Metal or metal alloy coating
Reexamination Certificate
1995-12-18
2001-01-09
Beck, Shrive (Department: 1762)
Coating processes
Spray coating utilizing flame or plasma heat
Metal or metal alloy coating
C427S383700
Reexamination Certificate
active
06171657
ABSTRACT:
TECHNICAL FIELD
This invention relates to methods of coating yankee dryers to protect them against wear and to reduce paper production problems associated with yankee dryer wear. More particularly, the invention relates to obtaining smooth-wearing coatings for yankee dryers, the drum-like apparatus used to dry paper forming webs. The present invention yankee dryer coating combines great hardness for durability with excellent ductility against coating failure from fatigue as the dryer expands and contracts through cycles of temperature. More particularly, the invention is concerned with methods for providing yankee dryer drums with a coating which allows for longer runs of paper products with higher uniformity and fewer flaws, while requiring reduced downtime.
BACKGROUND OF THE INVENTION
Yankee dryers comprise large-scale drums, typically formed of cast iron, which are internally heated with pressurized steam and used to dry paper webs at the end of a paper-making line. These drums which expand and contract with the steam heat carry the moisture-containing paper web partway around their circumference to a take-off point marked by a blade which acts to separate the paper web from the drum for collection on a take-up roll. Yankee dryer drums are subject to wear from friction, i.e. tribological wear, and from chemical wear or erosion caused by chemical action, e.g. by chloride, fluoride and sulfite ion interactions with the drum surface as a concomitant of papermaking operations. Surface imperfections such as surface roughness then develop and this causes the separation blade to wear prematurely and irregularly and the paper quality is adversely affected. To avoid this, the yankee dryer drums must be periodically reground and repolished as surface imperfections become significant. Resurfacing of the dryer by grinding and polishing is costly in downtime, lost paper production, and in charges for overhaul of the dryer drum surface.
SUMMARY OF THE INVENTION
A successful coating for a yankee dryer will be hard so as to wear a long time, and resistant to erosive wear from chemical action over the long wearing period. Since there is continual wear, the capacity of the coating to maintain a high degree of uniformity of composition through the coating thickness, rather than have the coating composition vary with depth, becomes paramount. Loss of even one element from the coating alloy, for example molybdenum loss from a molybdenum-nickel-chromium coating containing too high levels of molybdenum, or a substantial decrease in its presence, as the coating wears, may allow chemically-induced erosion as wear progresses albeit not at the outset. As noted above, erosion and tribological wear will cause development of surface imperfections, manifested generally as roughness, loss of take-off blade efficiency, and deterioration in productivity.
It is accordingly an object of the invention to provide a method of coating yankee dryers with a hard but ductile coating composition and which provides a uniform coating composition through its effective depth so that wear resistance is substantially constant in progressing through the coating, to provide novel methods of papermaking with a yankee dryer, and to provide yankee dryer drums with a novel tribological and erosion wear resistant coating.
These and other objects of the invention to become apparent hereinafter are realized in the method of protectively coating against tribological and erosive wear a yankee dryer drum to be used for carrying a paper forming web in drying relation, including interposing between the surface of the yankee dryer drum and the paper forming web a coating comprising an iron alloy containing from about 20 to about 47 weight per cent chromium, about 2.5 to 6.5 weight per cent boron, about 1.7 to 2.7 weight per cent silicon, and less than 8 weight per cent molybdenum. In particular aspects the invention method includes selecting as the iron alloy an alloy containing no molybdenum, thermal, including arc spraying the alloy onto the dryer drum, selecting as the alloy an iron alloy having the composition:
Component
Weight Percent
Boron
2.5-6.5
Carbon
0.0-0.15
Chromium
20-47
Copper
0-2.5
Iron
45-60
Manganese
0.0-1.5
Molybdenum
0.0-8.0
Nickel
0.0-25
Phosphorus
0.035
Silicon
1.7-2.7
Sulfur
0.025
Titanium
0.0-0.3
and selecting as the alloy an iron alloy comprising about 55 weight per cent iron and about 20-45 weight per cent chromium and having a Rockwell C hardness of about 55 to 70.
The invention further contemplates the method of forming a coating on a yankee dryer drum against tribological and erosive wear by paper-forming webs passing over the dryer drum in drying relation, including spraying an iron alloy onto the web-contacting surfaces of the dryer drum, the iron containing about 20 to about 47 weight per cent chromium, about 2.5 to 6.5 weight per cent boron, about 1.7 to 2.7 weight per cent silicon, and less than 8 weight per cent molybdenum, and preferably comprising about 55 weight per cent iron and 20-45 weight per cent chromium.
In a further aspect of the invention, there is provided the method of papermaking with a yankee dryer, including passing a paper-forming web over a yankee dryer drum in drying relation, and interposing between the paper-making web and the dryer drum a tribological and erosive wear limiting coating consisting essentially of an iron alloy containing about 20 to about 47 weight per cent chromium, about 2.5 to 6.5 weight per cent boron, about 1.7 to 2.7 weight per cent silicon, and less than 8 weight per cent molybdenum, and preferably comprising about 55 weight per cent iron and 20-45 weight per cent chromium. In this embodiment as in previous embodiments, typically, the method further includes selecting as the iron alloy in the interposed coating an iron alloy containing less than 8 weight per cent of, and preferably free of, molybdenum and containing about 55 weight per cent iron and 20-45 weight per cent chromium.
The invention further provides a coated yankee dryer comprising a drum, the drum having a tribological and erosive wear limiting coating comprising an iron alloy containing about 20 to about 47 weight per cent chromium, about 2.5 to 6.5 weight per cent boron, about 1.7 to 2.7 weight per cent silicon, and less than 8 weight per cent molybdenum, e.g the iron alloy has the composition:
Component
Weight Percent
Boron
2.5-6.5
Carbon
0.0-0.15
Chromium
20-47
Copper
0-2.5
Iron
45-60
Manganese
0.0-1.5
Molybdenum
0.0-8.0
Nickel
0.0-25
Phosphorus
0.035
Silicon
1.7-2.7
Sulfur
0.025
Titanium
0.0-0.3
In this and like embodiments, typically, the drum comprises iron, the coating has a thickness of 20 to 60 mils, the coating has less than about 5% porosity, the coating has a Rockwell C hardness between about 55 and 70, the coating is free of molybdenum, and consists essentially of about 55 weight per cent iron and about 20-45 weight per cent chromium, or the coating has a thickness of 30 to 50 mils, and the coating is thermally sprayed onto the drum.
REFERENCES:
patent: 4064608 (1977-12-01), Jaeger
patent: 4160048 (1979-07-01), Jaeger
patent: 4389251 (1983-06-01), Simm et al.
patent: 4822415 (1989-04-01), Dorfman et al.
patent: 5292382 (1994-03-01), Longo
Bachand Louis J.
Beck Shrive
Bender Machine, Inc.
Chen Bret
Lee Jun
LandOfFree
Method of coating yankee dryers against wear does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of coating yankee dryers against wear, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of coating yankee dryers against wear will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2504853