Test case for primer Adhesion to Thermal Spray Coatings
As transportation industry facility owners look to protect their structures from corrosion while minimizing inconvenience to the public, many are turning to thermal spray coatings instead of traditional liquid paints. Thermal spray coatings have a historical duration from 30 to 50 years before any repair work was required; thus, the higher front-end cost of the TSC pays for itself, and less repair work is required, inconveniencing the public often.
The most widely used thermal spray material in the US transportation industry is 85/15 aluminum-zinc alloy. Either the TSC is exposed to the elements and forms a natural sealer through the zinc oxide and aluminum, or it is sealed with a penetrating sealer shortly after application of the TSC. Adhesion testing for TSC is usually specified in the test method ASTM D4541, Pull-Off Strength using a Portable Adhesion Tester. According to SSPC-CS 23 (I), Interim Specification for the Application of Thermal Spray Coatings (Metals) Aluminum, Zinc and Their Alloys and Composites, Steel for Corrosion Protection, Acceptance 85/15 Zinc-Al TSC is 700 psi Minimum Adhesion the value of. Here's a project that allows us to explore how TSC or osmotic sealers affect TSC adhesion value oxidation. Although the binding mechanism and improved adhesion time are not fully understood, our field trials show that the seal can improve TSC adhesion. MORE REMEMBER: We realize that when specifying adhesion testing at TSC, it should state whether the test is done on a sealed or unsealed coating.
project
In 2002, the Niagara Falls Bridge Commission set out to realize TSC's long-term interests in the seriousness of crossing the Rainbow Bridge, connecting Niagara Falls, New York, Ontario, USA, and Niagara Falls, Canada. The company operates 450,000 square feet (40,500 square meters).
The production job is in the hands of Clara Industrial Services, Inc. in Thunder Bay, IN. The Inspection Services Ltd in Picton, , provides contractor quality control. Item specifications called 8–12 ml of 85/15 zinc/aluminum throughout the structure, followed by 0.5–1.5 ml of penetration seal application of TSC within eight hours. The contract also stipulates that periodic bond testing is required by the resident engineer. While performing the adhesion test, the inspector noticed an apparent adhesion value after the test cart was placed on the surface to compare the values after sealing. While all values meet the stated minimum requirement of 700 lbs, we are curious and set up additional field tests
Subsequent Field Tests
The purpose of the field trial was to determine what effect, if any, the oxidizing agent or oxidizing agent penetrating the sealer had on the TSC adhesion value. Tested with three separate plates. All steel plates were blast cleaned to SSPC-SP 5, white metal blast cleaned with #20 nickel slag. The anchor shape is 4–4.5 ml. A two-part epoxy adhesive is used to set up the cart. Adhesion testing is performed with a Non-Magnet® at-m Self Adhesion Tester with ASTM D4541 method as plate #1 (Figure 1) has TSC applied to an average thickness of 12.8 ml; three carts are placed on the plate and pulled On Day 1a, the average adhesion value of the three was 733 PSI, the result of adhesion failure to the substrate and cohesive failure of the TSC coating. The board can withstand oxidation of the TSC for up to seven months at 65 to 80°F (18 to 27°C) and 50 - 70% relative humidity (3°C). Three carts are placed on plate #1 again and the next day reps 1B. Three average adhesion values of 767 psi in the TSC coating resulted in adhesion failure to the substrate and cohesive failure (Tables 1A and 1B). The adhesion value increased by only 5%, with no change in the failure mode, indicating that the native oxide sealer formed in the TSC has no direct effect on the adhesion of the TSC.
Figure 1 Plate 1 Fig. 1-3 Courtesy Randell Smith
Plate #2 (Figure 2) has been applied to TSC with an average thickness of 12 mils. Three carts are placed on the plate and pulled the next day to represent 2A. The three-average adhesion value was 620 psi, the result of coating adhesion failure to the substrate. The plates sat for three months (65–80 F 27 C–[18] and 50–70% RH), allowing the bands to oxidize. A penetrating sealer of corothane I prime (cured at 800 F [427] and 60% RH) to a thickness of 0.5–1.5 mils (13–38 microns) is then applied. Three carts placed on plate #2 put the day below to represent 2B. Three mean values of 1133 psi adhered to 100% adhesive failure (Tables 2A and 2B). These results indicated that the sealant was definitively effective for TSC adhesion, with an 83% increase in adhesion values.
Figure 2 Board 2
Plate #3 (Figure 3) had TSC applied in 10.4 ml. The plate is covered, dividing it into two parts. The sealer is 0.5–1.5 mL of TSC for exposure. After the sealer has been cured, three carts are placed on each segment to pull, the unsealed part representing 3A, and the sealed part representing 3B. The average adhesion value of the unsealed cross-section was 753 psi, with the coating failing in adhesion to the substrate. The mean value in the seal segment was 2127 pounds of adhesive bond failure (Tables 3a and 3b). Adhesion values increased by 183% in both seal and seal sections, indicating a substantial increase in adhesion values when TSC was applied soon after sealing.
Figure 3 Plate 3
what we learned
Our field tests have found that native oxides grown in the pores of TSCs do not affect their attachment values. Liquid sealants can affect TSC adhesion values even with minimal oxidation occurring after application. They also had an effect on the adhesion value when the TSC was applied shortly after, our tests found. Sealers with good wetting properties can penetrate loose areas (or cracks) and seal pores in TSC. It may be that when a penetrating sealer is applied to the TSC, the sealant penetrates the pores and voids of the TSC and creates a stronger bond.
When stem cells are considered for corrosion control, owners should benefit from applying a liquid-tight TSC. SSPC-CS 23 (me) recommends using sealers as soon as possible after work, or within eight hours. The increase in the adhesion values of the applied sealant to TSC in these parameters is evident and should be noted. When specifying an item for adhesion testing, be sure to state if the test is to be done on a sealed or sealed TSC.
references
Robert H. Unger, "The Bridge to Thermal Spray," Thermal Spray: Advances in Coating Technology, National Thermal Spray Conference, Orlando, FL, USA, Proceedings, September 14-17, 1988-8708-011.
Joseph T. Butler, Corrosion Control of Metals, Volume 1, Number 1 (January 2000.
SSPC-CS 23 (I), Interim Specification for Application of Thermal Spray Coatings (Metals) Aluminum, Zinc and Their Alloys and Composites, Corrosion Protection of Steel, SSPC Coating Handbook, Pittsburgh, PA, USA (March 2000.
Eric C. Lohrey metallizing steel bridges, in the field, jpcl (May 39–50 1995), p.
