Thermal
Spray Metalizing - 85/15 Alloy
Metallines - The Corrosion Bulletin
November 1997
(continued)
The Benefits
Aside from the benefits of having a dual phase
coating and those described above, 85/15 can be
sprayed in both flame and in high deposition electric
arc equipment and is a denser coating. The maximum
service temperature of the alloy (600°F, 31
5°C) is greater than zinc (120°F).
Because the density of the material is greater,
the coating coverage per pound sprayed is also
increased. Zinc covers 3.5 sq. ft. per pound whereas
85/15 covers 4.3 sq. ft. per pound.
Caution:
There are applications where 85/15 either does
not work well or extra care should be taken when
using the alloy.
Those areas are:
Direct contact of an 85/15 coating with freshly
poured concrete. should be avoided until the concrete
is set. Because of the coating structure (see
above), the aluminum element of the coating is
very reactive with extreme alkaline conditions
like those encountered in fresh poured concrete.
Hydrogen gas will form and degrade the concrete
surrounding the coated steel.
Testing of the 85/15 coating on concrete to protect
steel reinforcing bars indicates that 85/15 does
not work as pure zinc performs on concrete. The
85/15 coating bubbles and disbond in the more
anodic areas. Platt does not recommend 85115 for
this application. Continued testing looks promising
using alloys with small amounts of aluminum and
studies are ongoing to determine the cause of
the 85/15 disbonding.
85/15 and the FHWA
Much has been said as to the effectiveness of
85115 over pure zinc in the ongoing FHWA studies.
Here are the facts from the FHWA Report, Environmentally
Acceptable Materials for the Corrosion Protection
of Steel Bridges, Publication No FHWA-RD96-058.
Metallizing systems (Zinc, Aluminum and 85/15)
provided consistently the best corrosion protection
performance. All metallized coatings tested showed
no corrosion failure in the aggressive salt rich
environments over the 5 to 6.5 year exposure periods.
In the 5 year tests, metallized systems have provided
excellent corrosion protection at all three locations.
There was exceptional overall appearance of the
85115 panel. 85115 was the only coating extended
with a 30 and 60 year life for life cycle cost
analysis.
Much of the report discusses metallized coatings
in general. However, the report does state;
"That
although the zinc provides good corrosion control,
the appearance of its own corrosion products
may be aesthetically unacceptable. Exposed zinc
metallizing produces highly visible white zinc
corrosion products. Alloying the zinc with small
amounts of aluminum maintains the sacrif cial
properties of the zinc while reducing the amount
of voluminous white zinc corrosion products.
Alloying also increases the hardness of the
coating. Aluminum metallizing is typically employed
in high-temperature areas where corrosion control
afforded by coatings would be jeopardized by
low melting temperature. All three of the alloy
systems can he either sealed or unsealed."
Information
from Equipment Manufacturers
There has been a great deal of discussion as to
the ability to spray the 85/15 alloy. Until the
development of high deposition electric arc equipment,
the 85/15 alloy was used in flame equipment such
as Sulzer Metco.  The
oxides inherent in the alloying of 85115 made
the wire difficult to spray in conventional arc
equipment, thereby reducing the number of contractors
able to use 85/15.
In the late 1980's came the development and use
of the high deposition arc equipment. Today, both
Tafa and Thermion Arc Systems manufacture equipment
that easily spray the 85/15 alloy.
The following are
statements and case histories directly from the
equipment manufacturers.
Thermion
Arc Spray Systems
P.O. Box 2136 Silverdale, WA 983383-2136
1-360-692-6656 • F 360-698-1539
Thermion's Bridgemaster "Big Wire"
Arc Spray System
Thermion's "Big Wire" Bridgemaster is
a heavy duty, light weight, low energy, high deposition
arc spray system with proven reliability in the
spraying of 3/16" (4.8MM) 85/15 Zinc/Aluminum.
Designed for shop or field applications, the Bridgemaster
is a proven workhorse in any environment. Controls
and meters are conveniently located on the feeder
module providing "et the work place"
control. The patented light weight front end is
a user friendly plus for the operator. this compact
wire feed module measures only 13" high and
10" wide and will fit through a 14"
diameter hole. The system can operate 150' from
the power supply and the control module.
 Thermion
has pioneered "Big Wire" Arc Spraying
of Zinc, Aluminum, and Zinc/Aluminum. Recent independent
evaluation of "Big Wire" 3/16"
(4.8MM) 85/15 and the smaller 1/8" (3.2MM)
wire shows a distinct improvement in deposit efficiency,
tensile strength and surface finish of 3/16"
(4.8MM) over 1/8" (3.2MM) wire. For instance,
in an evaluation of the Thermion system's performance,
1/8" 85/15 sprayed at 350 amps 29 volts had
a deposit efficiency of 63.9% while 3/16"
85/15 sprayed at the same parameters had a deposit
efficiency of 71%. Burn off rate for 1/8"
85/15 was 62.9 pounds per hour and 76.65 pounds
for 3/16". Tensile strengths were higher
for 3/16" 85/15 coating and surprisingly
the surface finish had a lower Ra than the 1/8"
85/15 coating. The evaluation included 21 different
sets of parameters where the advantages of the
"Big Wire" remained consistent.
Applicators have been arc spraying "Big Wire"
85/15 zinc/aluminum on several projects in Connecticut,
North Carolina, Indiana, Illinois and Ohio. Five
Thermion Bridgemasters were used on the first
phase of metalizing the Indianapolis Speedway
grandstands with 3/16" 85/15.
The ease of operation, portability and reliability
of the Bridgemaster was demonstrated again last
month. A painting company with only flame spray
metalizing experience completed an 8700 square
foot bridge metalizing project at Otway, Ohio
with a Bridgemaster using "Big Wire"
85/15. A one day, on the job indoctrination was
given by Thermion Metalizing Systems, Ltd. on
October 12, 1997. Set up of the equipment, indoctrination,
testing, spooling of wire, and the spraying of
approximately 200 pounds of wire was accomplished
that day. The bridge metalizing was completed
successfully by the applicator without further
assistance from Thermion.
Thermion
has developed a precision wire dispenser which
enables applicators to utilize the lower cost
of "Big Wire" 85/15 production pay-out
packs. Three of these systems were used on a recent
Illinois Bridge project. This project will be
the subject of a paper to be presented at SSPC
97 in San Diego.
The Thermion Bridgemaster spraying "Big Wire"
85/15 helps make this competitive long life metalized
coating the "coating of choice".
Tafa, Inc.
146 Pembroke Road
Concord, NH 03301
T- 603-224-9585 F - 603-225-4342
Tafa's 8860 for Corrosion Prevention Applications
The Tafa Model 8860 High Output Arc Spray System,
with high speed and high capacity capabilities
is designed specifically for the application of
aluminum, zinc and the 85/15 zinc/aluminum alloy.
With its 600 amp power source, reliable wire feed
drive and its ability to spray fan patterns, the
8860 is able to spray 100+ pounds per hour, 90
square feet per hour (8.2 sgm/hr) at an 8 mil
thickness.
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