Design Considerations for Hot-Dip Galvanizing: Hole Sizes

Galvanizing

When the decision is made to hot-dip galvanize, it is important to consider all aspects of the project, down to the smallest hole. Because hot-dip galvanizing is a coating of zinc on bare steel, the original steel becomes slightly thicker. Typical galvanized coatings range from 3-8 mils (75-200 microns). When designing and detailing tapped holes, the increased thickness is important.

Hole sizes in certain fabricated steel products must be oversized to account for the zinc that bonds to the edges. If after galvanizing the hole is still not large enough, it can be retapped. Retapping will not necessitate regalvanizing. Because of the zinc coating’s cathodic properties, the coating on the mating fastener will protect chased or retapped nuts.

For holes that will be threaded after galvanizing, the hole should be drilled undersize before galvanizing so the threads can be cut after galvanizing.

Clearance holes must be designed to account for zinc pickup. Oversizing holes according to ASTM guidelines is usually sufficient to account for the thickness of the zinc coating.

Threaded assemblies must adequately accommodate galvanized fasteners. It is important to make sure the hole is undersized enough so that when cutting the threads, all zinc is removed and the hole is still accurately sized. If all of the zinc is not removed from the threaded hole, its relatively soft structure may become damaged when fitting the hole with a fastener. It is best to mate a galvanized fastener with threads solely composed of steel to ensure a quality bolted connection. When threads have been cut it will expose bare steel, but utilizing a hot-dip galvanized fastener in the threaded hole will cover the bare steel and give protection from corrosion for the bolted connection.

Uncoated fasteners should never be put in a galvanized threaded hole. Zinc’s cathodic protection characteristics cause it to sacrifice itself to protect the uncoated fastener, accelerating the rate in which zinc is consumed.

Minimize the use of very small holes that may become completely obscured by zinc. If small holes are unavoidable and become filled with zinc, the area may be heated after galvanizing in order to remove the excess zinc and open the hole.

Design considerations courtesy of American Galvanizers Association. The AGA also has the publication, The Design of Products to be Hot-Dip Galvanized After Fabrication, available for download. 

Galvanizing Applications: Agricultural Equipment

Galvanizing

Use Cases for Galvanized Steel in Agriculture

The simple answer is that almost anything on a farm or other agriculture operation can utilize galvanized steel. It can be used for stronger tractor parts, trailers, irrigation systems, fencing, tools, animal pens, barns, storage facilities, and more. Just about anything that sees heavy use, especially in an outdoor environment, can and should benefit from the power of galvanized steel.

At Cherry Creek Systems, the company works closely with customers to design and execute custom systems for greenhouse applications, using hot-dip galvanization to protect versatile, but hollow, steel tubing that brings strength to these systems. Galvanized solutions are also hygienic for use around animals and protect hollow parts and equipment in other areas of agricultural operations, such as conveyor castings, chains, supports, storage racks, irrigation equipment, refrigeration components to stand up to frigid temps and condensation, and much more.

In Agriculture, It’s Not Just Rust that Threatens Equipment

Other than the ever-present threat of rust and corrosion, equipment is exposed to other dangers, as well. Powerful storms and gusting winds fling debris at structures, machinery and fences, causing dents and more serious damage. Frequent use of equipment causes wear and tear, and extreme or changing temperatures can be dangerous, as well. The toughened zinc alloy coating of galvanized steel protects it from all of these things, repelling debris, shielding from abrasions, and maintaining overall structural integrity through the most extreme conditions.

Protecting the Budget

At first glance it might seem like all this extra protection makes galvanized steel a much more expensive investment than regular steel. However, not only is galvanized steel comparably priced, it also saves money down the road. The sturdiness of galvanized steel means it doesn’t need repairing or maintaining as often as other materials. That means less money spent on repairs and less downtime caused by maintenance. The abrasion-resistant surface makes it easier to clean and paint, and the rust-proof nature means it can go decades without needing to be replaced or patched up. 

Toughen Up 

Everybody should be aware of what they’re getting when choosing the best tools for the job. In almost every case, those tools are made with galvanized steel. The agriculture life will always be tough, but there’s no reason that equipment shouldn’t be up to the task.

To learn more, contact AZZ today.