Before galvanization, a masking material is frequently applied to steel. The masking agent inhibits galvanization on the steel surface to which it is applied. This can be useful for a variety of reasons. Masking materials are most commonly used on threaded bolts in Bee Dee Cycle. If a precise fit between the threading and its nut is required, the additional width created by galvanization within the threads can be an issue.
Masking material can be adhesive tapes, duct tape, or chemical compounds, such as Maskote Zinc Stop-off. Several products are available in each category; however, Bee Dee Cycle generally recommends and deals with Maskote Zinc Stop-off.
Why do we prefer Maskote Zinc Stop-off?
The AGA discovered in a 2010 study that adhesive tapes failed to prevent galvanization in most cases, mainly when used in conjunction with threaded bolts. In contrast, chemical compounds were successful, such as Maskote Zinc Stop off. Beedee Cycle prefers Maskote Zinc Stop-off because of its ease of use and low price. An additional benefit has been demonstrated to be effective when only an hour of curing time is provided.
How is Maskote Zinc Stop-off Used?
The key to successfully using Maskote Zinc Stop-off is to ensure that the steel surface is free of any debris or fluids, including dried fluids. Once clean, the steel substrate allows the Maskote Zinc Stop-off to adhere completely. This prevents galvanization between the zinc coating and the steel surface while still allowing the zinc to bond to non-covered areas.
Maskote Zinc Stop-off has a much lower per-ounce cost than other chemical competitors. Different chemical solutions that function similarly to Maskote can be up to 50% more expensive. While other materials, such as caulks are much less costly, they are not as easily applied.
Maskote Zinc Stop-off: Most dependable system to coat
We’ve discovered the best and most dependable system to coat the desired areas with Maskote Zinc Stop-Off. This is a heavy viscous paint designed to withstand all of the galvanizer’s preparation processes and remain present during galvanizing. Hot Dip Galvanizing aims to form a molecular bond between the zinc coating and the steel substrate. Zinc Stop-Off prevents zinc from bonding by remaining present throughout the process.
According to ASTM A-123 / A-153 specifications, hot-dip galvanizing is four-step. Each step is referred to as a “Bath.” The first bath is known as Degreasing, and it is performed in a hot alkali solution. The second method, Pickling, uses heated sulfuric acid or hydrochloric acid at room temperature.
There is usually a rinsing process in between baths. Fluxing, which uses a zinc ammonium chloride solution, is the third method. Most coatings would fail if immersed in these acids and solutions, but this is what makes Maskote Zinc Stop-Off so effective.
Understanding which type of surface preparation the galvanizer will employ is critical. Pickling, the second of the baths mentioned above, is intended to remove mill scale and iron oxides from the steel surface. Maskote Zinc Stop-Off is built to withstand the heated sulfuric acid bath pickling method. Abrasive cleaning is another method used by a Galvanizer to remove mill scale. Sandblasting, glass bead blasting, and metallic shot blasting are all options.
Any of these abrasive processes will erode and render the Zinc Stop-Off coating ineffective.
Maskote Zinc Stop-Off is initially a bright yellow coating. When the final step, immersion in molten zinc, is completed, the thick Maskote layer on the fabricated steel remains in place. Its purpose is to prevent molten zinc from bonding with steel. Because the zinc cannot bond, it will either run off or become embedded in the coating. The yellow layer has oxidized and turned into a thick, black residue.
The residual black ash crust will become brittle once removed from the Zinc kettle and cooled to room temperature. It’s simple to remove with a wire brush, wire wheel, or any other abrasive that wears through the coating. The ash will fall away from where the Zinc Stop-Off coating adhered to the steel surface, leaving the steel surface bare. The original coating application will now be visible.
DOT and bridge construction projects that require Maskote Zinc Stop-Off include Hot Dip Galvanized steel members that require field welding and are then embedded in concrete. Steel road plates with threaded holes for lifting hooks are also available.
If these plates are galvanized, zinc will settle in the internal threads, necessitating re-tapping. Internal threads present a problematic situation because they are tapped with cutting fluid, oil- or water-based. Each will leave a distinct residue and shavings from thread cutting. Zinc Stop-Off prevents this, but to adhere to the steel and avoid any zinc from clogging the internal threads, all shavings and residue film must be cleaned away. MEK (Methyl Ethyl Ketone) applied with a cylindrical brush is the best cleaning system in these cases.
Don’t hesitate to contact a BeeDee Cycle representative if you have any questions about masking material, Maskote Zinc Stop-off, or how to facilitate galvanization for your steel fabrication project best