A-FlameCorporation
Frequently Asked Questions (Arc Spray)
(Answered from the published papers on Metalizing)
1. How does arc sprayed metal differ from flame sprayed metal?
"The use of the electric arc process is often preferred to the flame process because
it results in higher deposition rates and bond strength."
Publication: AS/NZS 2312 - 1994, Section 6.3.2
2. How much faster than Plasma Spray is the Arc Spray Process?
"Consider a typical example in which conventional plasma equipment was used to
spray a paper roll measuring 3' in diameter by 20' long (.91 m by 6.1 m). In order to
complete the job quickly, the customer used six plasma guns to finish the job in 8 1/2
hours." (TAFA website).
3. Aren't thermally sprayed metal coatings porous?
"Porosity is sealed by normal aging, through formation of salts of the component
metals (oxides, hydroxides, carbonates, etc.). Sealing and/or painting can be used to
prolong the service life of a metal sprayed coating."
Publication: ISO 2063, Annex B, Section B.1
4. How much longer does a sealed metal sprayed system last?
"A duplex coating system (metal sprayed coating and sealing and/or painting) has a
longer service life than the sum of the service lives of the metal coating and the
paint system considered separately. The service life of the paint system is several
times greater than when not applied to an anticorrosive metalized coating."
Publication: ISO 2063, Annex B, Section B.3
"Organic sealers used in conjunction with metalized coatings form a synergistic
system that is reported to outperform the sum of its parts. This is especially true of
the anti-corrosive metalizing systems for marine and industrial atmospheres."
Publication: Journal of Protective Coatings & Linings, August 1989, Page 39.
"Performance of Selected Metalized Coatings and Sealers on Lock and Dam
Facilities" Author: Tim Race, Vince Hock and Al Beitelman, US Army Construction
Engineering Research Laboratory
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5. How does zinc protect steel?
"Both zinc and aluminum are anodic to steel. Zinc affords greater electrolytic
activity than aluminum, providing good galvanic protection to steel exposed in the
atmosphere. Breaks in the coating are protected by the galvanic couple, that is, the
zinc corrodes, rather than the structural steel."
Publication: Page 23, ROADS & BRIDGES, August, 1986.
6. How does aluminum protect steel?
"Aluminum is less active than zinc. Aluminum's protection of the substrate relies
more on a thin oxide film. This characteristic gives distinct advantages in low pH
(acidic) and chloride environments. Because aluminum is less active than zinc, it
cannot protect breaks in the coating."
Publication: Page 23, ROADS & BRIDGES, August, 1986.
7. What are the benefits of zinc/aluminum alloys?
"Independent research in Japan and Belgium has determined that a zinc-based
alloy containing 15 to 17% aluminum gives the advantages of both metals when in
sprayed coating form. The material produces a two phase coating. There is a
zinc-rich base, which protects galvanically, and an aluminum rich phase which
passivates and acts more like a barrier."
Publication: Page 23, ROADS & BRIDGES, August, 1986.
8. What is the expected life of a zinc/aluminum coating?
"The maintenance free service life of an unprotected zinc and aluminum alloy
metalized coating on a typical bridge is predicted to be 25-40 years. Using a sealer
and topcoat over the metalized primer is reported to extended the service life 15-20
years."
Publication: Journal of Protective Coatings & Linings, May, 1995.
Author: Eric C. Lohrey, PE, Connecticut Department of Transportation
9. What is the long term testing history of Thermal Sprayed coatings in marine
environments?
"Both 80 and 150 microns aluminum coatings showed no corrosion of the steel
substrate after 34 years exposure at the LaQue Centre (Kure Beach, North
Carolina) test site.
Bethlehem Steel Corporation documented the results of 25 years' experience with
Al/Zn alloy coatings, also at LaQue. The time to first rusting of the substrate was
15 years for severe marine (25 m from ocean) and 25 years for moderate marine
(250 m from ocean).
8175 Kroger Farm Road, Cincinnati, Ohio 45243 USA Tel 513-831-4284 Fax513-831-5237 E-Mail
The Norwegian Institute for Air Research published the results of metalized steel
exposed 14.5 years in a marine splash zone (Tanager, Norway). A 160 micron
aluminum coating had visible but insignificant damage.
Experience in the Soviet Union showed that a 120 micron aluminum coating could
perform effectively for 20 - 25 years in salt water. A 150 micron dual zinc/aluminum
coating could last 40 years or more in a humid environment.
Testing at SINTEF, Norway in natural seawater, gave free corrosion rates of 2 to 3
microns per year after 11 months of exposure for both Al and Al 5% Mg. This
would imply a service life of 60 years for a 200 micron Thermal Sprayed Aluminum
Coating."
Publication: Page 28, MP, April, 1995.
Authors: Karl P. Fischer, William H. Thomason, Trevor Rosbrook, Jay Murali
10. What is the structural integrity of sprayed metal coatings?
"The density of sprayed metals is typically 85% to 95% of the density of the wire
from which it is sprayed. The total oxide included in the sprayed film accounts for
only 0.5% to 3% of the reduction; the density reduction is due primarily to the
characteristic porosity of sprayed metal coatings."
Publication: Journal of Protective Coatings and Linings, August, 1989, Page 39.
Author: Tim Race, Vince Hock and Al Beitelman, US Army Construction
Engineering Research Laboratory
11. What are the economics of Thermal Spray (TS) Metal Coatings?
"Application of TS coatings shows considerable savings compared to
conventional coatings. Multiple coat systems require dry times between each
coat, and final cure time before parts can be handled without damage. TS
coatings can be sealed immediately after coating and, if a top coat is required, it
may be applied within 4 hours."
Dynamic Coatings Corporation Web Page
"Each process has different costs, materials flexibility and coating performance
capabilities. As a surfacing technology, however, thermal spray is compatible
with most materials, is affordable, rapid, and can produce relatively thick
(0.010" to 0.00110") protective coatings."
Drexel University Web Page (Philadelphia, PA, US)
12. How many types of metal can be sprayed?
Any metal which can be obtained in wire form can be sprayed, including copper,
stainless steel, hasteloy, inconel, and monel...even silver and lead!
8175 Kroger Farm Road, Cincinnati, Ohio 45243 USA Tel 513-831-4284 Fax513-831-5237 E-Mail
Both zinc and aluminum are anodic to steel and provide cathodic protection at the
economics of barrier coating.
Applied in Lenticular Splats, the molten metal is permanently bonded to the
substrate.
Utilizing electric arc methods, any substrate can be metalized including concrete,
fiberglass, wood, and clay.
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8175 Kroger Farm Road, Cincinnati, Ohio 45243 USA Tel 513-831-4284 Fax513-831-5237 E-Mail