How to Prevent Galvanization for Machining Processes

Galvanization is one of the most effective ways to combat rust. It involves chemically bonding zinc with the surface of iron or steel, creating a corrosion-resistant layer. Galvanized coatings provide cathodic protection, outperforming painting and powder coating. Zinc acts as an anode, giving up electrons during oxidation and sacrificing itself to keep the substrate intact. This metal also self-heals and repairs scratches on its own.

A thick galvanized coating can protect steel for 100 years from the elements, especially in rural and urban environments. However, leaving some parts of the material ungalvanized has merits on some occasions. Sealing 100% of the base metal with zinc before fabrication can be impractical since the protective layer may interfere with machining processes.

What Is the Machining Process and Its Types?

Machining is when a fabricator removes unwanted material from metal to achieve a desired shape. These are the most common machining processes:

  • Broaching: It involves a broach performing a series of successive deep cuts through a prepared leader hole at speeds ranging from 5 to 50 feet per minute. A fabricator uses this toothed tool to create spline and square holes. 
  • Electric discharge machining: It uses electric arcing discharges to rapidly cut hard materials and produce complex geometric shapes at close tolerances. It applies to ferrous alloys because the metal must be electrically conductive.
  • Electrochemical machining: It makes burr-free holes with high surface finishes in tough and exotic materials. A fabricator prefers this method to cut cavities, intricate contours and oddly shaped and small angles without putting thermal stress on the material.
  • Drilling: It feeds a rotating drill bit perpendicular to the plane of the material’s surface to create cylindrical holes.
  • Grinding: It eliminates small amounts of material from cylindrical holes and flat surfaces using various methods and grinding machines.
  • Milling: It refers to using rotating multi-point cutting tools to shape metal to add grooves or slots to the material, fabricate gears and machine complex shapes as well as flat and irregular surfaces.
  • Planing: It deals with large flat surfaces in preparation for finishing through scraping. 
  • Sawing: It refers to the use of vertical and horizontal band saws moving in continuous loops to shorten bars and extruded materials. 
  • Turning: It generates cylindrical shapes by rotating metal with a lathe and a cutting tool removes excess material linearly along the diameter.

Machining processes render newly cut iron and steel areas prone to rust by exposing them to oxygen and water in the environment. Moreover, fabrication methods are about precision.

A galvanized coating can skew machining output by increasing the material’s width, which can be a headache when hot-dipping metal in molten zinc. This galvanization process creates a protective layer that’s three times as thick as the one achieved when applying liquid zinc to straight sections of the material.

How Do You Prevent Galvanizing?

Masking enables you to prevent specific material areas from coming into contact with corrosion-inhibiting zinc, especially during a hot-dipped galvanization process. Zinc only reacts to clean steel or iron surfaces. Treating those you purposely want to remain ungalvanized to allow for machining should do the trick.

Masking isn’t foolproof, though. Zinc can slightly reach masked areas, so more work may be necessary to remove the unwanted coating.

How Do You Mask Galvanized Steel?

You can mask materials to prevent galvanization using various products, such as sealants, tapes, paints, gaskets, caulk and aerosols.

Some masking agents are more effective than others. A material doesn’t have to keep 100% of the masked area ungalvanized to be considered adequate. Galvanizers consider products that can prevent zinc coating on at least 90% of the masked area good enough.

Masking agent effectiveness also varies by material shape. Some products lack the fluidity to fit into threaded areas, limiting them to flatter and more accessible surfaces.

Removability matters, too. Allowing a masking material to cure as per its manufacturer’s instructions should make cleaning the covered areas and restoring the metal’s original finish painless. Lengthy curing times can affect fabrication, so fabricators may gravitate toward products that can harden more quickly.

Optimize Galvanization and Machining

Poor timing can diminish the benefits of galvanization. Applying zinc to a finished metal workpiece is generally a smart practice, especially if you prefer the hot-dipped method. This way, you can eliminate the need for masking, cut costs, streamline fabrication processes and reduce corrosion weak spots.