Galvanized Threaded Rods: Your Questions Answered

Galvanized threaded rods are used in various industries and for projects that require more stability or durability. You likely have many questions if you’re thinking of using galvanized threaded rods when building your own house. 

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This article will answer the most common FAQs.

What is Galvanizing?

Galvanizing, or galvanization, is a manufacturing process where a zinc coating is applied to iron or steel to offer better protection and resist rusting. The most common galvanizing process is called “hot-dip” galvanizing, but some manufacturers will use thermal diffusion.

Galvanized steel is a popular steel type because the galvanization process extends the overall durability of regular steel. Zinc acts as a protective barrier against corrosive elements. Due to its versatility, galvanized steel is used in several industries, such as construction and agriculture.

Does Galvanizing Make Steel Rust Proof?

Although galvanized steel is rust-resistant, it isn’t rust-proof. Galvanized steel in a wet or soaked environment will last 10 years or 34 years in conditions with a relative humidity of 100%. But most builders would use nylon in these conditions, as it’s non-corrosive and more cost-effective.

Galvanized steel works best in relative humidity below 60%, where the zinc layer won’t be consumed for 211 years. However, this assumes that the zinc coating is thick.

What are Threaded Rods?

Threaded rods are used to pin or fasten two materials together. Threaded rods are commonly used to stabilize structures or other objects in the ceiling or wall. In some cases, builders would use a threaded rod if they can’t pin or stabilize structures with the longest screw or bolt.

Threaded rods go by five other names: threaded stud, threaded bar, all-thread, all-thread rod, or screw rod, but they all describe the same thing. Most threaded rods have a helical structure, which is rotated during installation. This rotational movement will resist pressure.

What are Galvanizing Threaded Rods Used For?

Galvanized threaded rods are primarily used in structural and non-structural construction, plumbing and contracting, HVAC installation, metalworking, machinery, and oil and gas. 

Contracting and plumbing rely on threaded rods made of steel because they typically work with residential or commercial builds. HVAC installers often need galvanized threaded rods to enable quick level installation or sloping installation of heaters, air handlers, and ductwork.

Galvanized threaded rods may also hang suspended ceilings when they require proper alignment. You’ll also find them in medical and manufacturing machines.

What is the Difference Between a Threaded Rod and Bolt?

A threaded rod and bolt are similar. However, a bolt has a head and is threaded on one end, whereas a rod is threaded on both ends. Bolts are typically much shorter than rods at a few inches long. If you want to make a short threaded rod, you can cut it down using the equipment. 

Can You Galvanize High Strength Bolts?

Certain high-strength bolts like Fg55 and ASTM A572g50 low alloy steels can be galvanised. Medium carbon steel that’s been quenched and tempered, such as ASTM A449, can also be galvanized. However, things get tricky when we move to medium carbon alloy steel.

When a high-strength bolt is made of medium carbon alloy steel (quenched and tempered), it’s more likely to be susceptible to hydrogen embrittlement and shouldn’t be hot-dip galvanized. 

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What Types of Threaded Rods are Available?

There are five common types of commercially available threaded rods. These include:

• Fully Threaded Rods

A fully threaded rod has threads that run the entire length of the rod. These are used for walls and ceilings or sometimes as screws or bolts. 

• Double-Sided Threaded Rods

A double-sided threaded rod has threaded ends and a non-threaded middle. Both ends are secured with nuts. These are used for doors.

• Tap-End Studs

A tap-end stud looks like a double-sided threaded rod, but one side is longer. The shorter side has a chamfered point. These are used on cars.

• Internally Threaded Rod

An internally threaded rod provides a secure joint for another threaded rod. These are used in any industry that requires any type of threaded rod.

• Hollow-Inside Threaded Rod

A hollow-inside threaded rod looks similar to a fully threaded rod, except it’s hollow for wires to pass through. These are used in homes.

If you’re building a home, you will use fully threaded, double-sided, and hollow-inside threaded rods. As threaded roads are often cut in one-meter lengths, you may need a custom length for some projects. A cold cutting blade can provide a much quicker finish.

What Do the Color Codes Mean on Galvanized Threaded Rods?

Threaded rods are often colour coded on one end. These colours indicate the rod’s strength, with white being the strongest. As these colour codes are defined by the International Organization for Standardization (ISO), you can trust that a reputable supplier will code each piece properly.

Galvanized threaded rods belong to property classes 4.8 and 8.8 and are light blue, orange, steel grey, or purple. Out of the galvanized variety, purple and steel grey is the strongest.

The short answer is no, they don’t need to be galvanized but they can be. In some cases, they should be. You’ll want to consider galvanized anchor bolts if they are going to be in a corrosive environment or exposed to the weather. Galvanizing anchor bolts provide corrosion resistance to the bolt.

Instances where it is generally unnecessary, or you shouldn’t use galvanized bolts:

• If you are welding the bolt, the act of welding can release toxic fumes from the zinc coating and produce weld spatter. Welding should be performed prior to the galvanizing process.
• If the bolts are being used in a dry environment or indoors. The point of having the anchor bolts galvanized is to provide resistance to corrosion. If the bolts are being used indoors or are protected from the elements, it is generally unnecessary to have them galvanized.
• You are worried about aesthetics. The most common form of galvanizing is hot-dip galvanizing. This is the process of dipping the bolts into molten zinc. This is for utilitarian purposes and does not create a “pretty” looking bolt. However, anchor bolts are used in the ground so aesthetics typically should not be an issue.

ASTM Anchor Bolt Specification

The ASTM specification that covers anchor bolts is F. Within the specification, there are three grades which are F-36, F-55, and F-105. Each grade has different strength requirements. however, they all have the same coating options.

Allowable Coatings for ASTM F:

• Plain: This is also referred to as black or bare bolts. The plain coating is exactly as it sounds. This is the lack of a coating and just the bare steel.
• Hot-Dip Galvanizing: ASTM F covers the hot-dip galvanizing of fasteners. This is a form of zinc coating that offers a high degree of corrosion resistance and is an economical way to prevent rust and extend the life of your bolts. Hot-dip galvanizing is the process of dipping bolts in molten zinc which not only coats the steel but also bonds to the steel itself. This is one of the most common coatings. The expected service life of galvanized anchor bolts is more than 30 years.
• Mechanical Galvanizing: Mechanical galvanizing is similar to hot-dip galvanizing except the zinc is purely on the surface and does not metallurgically bond to the steel.

Anchor Bolt Configurations

ASTM F anchor bolts can come in multiple configurations. They can be headed anchor bolts, bent anchor bolts, or straight rods. Straight rods are typically threaded on each end. All thread rod is commonly used as epoxy anchors.

At Portland Bolt, we can manufacture any of the configurations above. We forge our headed bolts.

Process of hot-dip galvanizing anchor bolts

• If the bolts are headed, they are put in a wheelabrater to remove the hot forging scale.
• The bolts are dipped in caustic soda to remove grime or oil that has collected on the surface of the bolts during the manufacturing process.
• Next, the anchor bolts are dipped in sulfuric acid to etch the surface of the steel which allows the zinc to adhere easier to the bolts. The acid also removes any residual mill scale.
• After the bolts are rinsed with water, they are then submerged in Flux which assists the reaction that is about to occur with the zinc and steel.
• The bolts are then submerged in a tank of molten zinc until the zinc has bonded to the steel. The time in the tank varies and is dependent on the size and grade of steel.
• The bolts are then lifted out of the zinc tank and immediately put in a centrifuge which spins the bolts at a high speed to remove excess zinc.
• After the centrifuge, the bolts are then put in water to cool the bolts.
• Finally, each bolt is inspected to ensure quality and easy mating between the nut and bolt.

The challenge of galvanizing threaded anchor bolts

Portland Bolt manufactures and galvanizes anchor bolts in a 140,000-square-foot manufacturing facility in Portland, Oregon. Our hot-dip galvanizing line is designed exclusively for threaded fasteners to ensure a trouble-free nut fit. However, most anchor bolt manufacturers and suppliers rely on an outside company to galvanize their fasteners. These outside galvanizers are often not set up with the sophisticated equipment necessary to properly remove excess zinc from the threads during the galvanizing process. Consequently, many manufacturers resort to “chasing” the threads after the anchor bolts have been galvanized. This practice is strictly prohibited under the F hot-dip galvanizing specification. Chasing the threads is a process in which the anchor bolts are rethreaded, often removing all of the zinc in certain portions of the thread and leading to premature corrosion.

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