How is Spiral Duct Made?

Have you ever found yourself staring at exposed spiral duct work and wonder how it was made? If your answer was no I guess you can stop reading, but it is a pretty interesting process. If your answer was yes, continue reading to find out.

While spiral duct isn’t something we manufacture at Metalwest, HVAC is a common industry we service. So, why not delve into the process behind one of our serviceable industries?


To discover how spiral duct is made we must first cover the basics, or in other words, the materials.

Galvanized Steel

Galvanized steel is the most common material used for ductwork. Galvanized steel is ideal for ductwork because it is corrosion resistant and can withstand higher temperatures.


Aluminum sheet is used for ductwork because of its high strength and light weight. Lightweight pieces of duct can span longer distances without the need for supports. It is also flexible, which means it can be stretched and bent multiple times, but still hold an airtight seal.

Stainless Steel

Stainless steel ductwork is used more frequently in laboratories due to its sanitary benefits as well as its corrosion resistance to harsh substances. It also has greater strength than aluminum and is abrasion resistant.

The Spiral Duct Process

There are three parts to the spiral duct process. The first starts with the mill and the making of the raw steel (here are some posts on how galvanized, aluminum, and stainless steel are made).

The second part consists of Metalwest receiving coils from the mills and processing them into slit coils. Slit coils are narrower coils cut from a larger master coil (you can read more about it here).

These slit coils are sent to customers per the required specifications and processed into spiral duct, bringing us to the third part of the process.

The Spiral Duct Fabrication Process

Once a customer receives the slit coil it is placed on an uncoiler and sent through a rough leveler to flatten the material. It is then sent through an edge trimmer and formed.

The forming process sends the strip through an inner and outer welding stage that moves it in a circular motion to form a spiral. The edges are welded or pinched together to form the duct piece. It is then cut from the machine at the desired length, inspected, tested, and then sent on be installed.

Here is a video example of the spiral duct process.

The finished spiral duct (in some cases it goes on to be painted) is then installed in commercial buildings such as warehouses, medical facilities, restaurants, schools, etc. So the next time you find yourself staring at exposed ductwork while sipping on a caramel macchiato, you will know how it was made.

For more information about the materials used for spiral duct contact your local sales representative.

Our Processes: Stainless Steel Polishing

It is time to delve into another one of our processes, stainless steel polishing. We offer in-house stainless steel polishing out of our New Jersey facility. The process of polishing enhances the overall surface finish of stainless steel as well as increases the sanitary benefits of the material.

So, what does the process entail? Let’s find out.

Stainless Steel Polishing

O'Neal Flat Rolled Metals polishingThe process of polishing consists of smoothing the metal’s surface using abrasives. At OFR Metals, our polishing lines use abrasives that are attached to a flexible backing to provide a high-quality surface finish.

Our coil-to-coil polishing technology allows for various size coils to be processed. We offer different polished finishes, including No. 3, No. 4, No. 4 Fine, and No. 6 finishes. Custom-matched finishes are also available upon request.

The Metalwest New Jersey facility can process 18-60” wide and 0.016-0.120 thick coils on their two coil-to-coil polishers. The lines also provide two-sided PVC to protect the high-quality surface finish.

Polished Coil Uses

stainless steel polishing adds sanitary benefits to foodservice equipmentPolished stainless steel provides sanitary benefits which make it ideal for the food service and pharmaceutical industries.

You can expect to see polished stainless steel in kitchen equipment, including prep tables, warewashing equipment, sinks, refrigerators, ventilation systems, etc. It is also commonly used for pharmaceutical equipment such as lab carts and tables, as well as processing equipment and storage tanks.

For more uses on stainless steel check out our blog post “Stainless Steel: What it is Used For.” To learn more about our polishing processing and stocking capabilities contact your local sales representative.

Our Processes: Precision Blanking

Part three of our processes series delves into the precision blanking process.

Precision blanking can be looked at as a step beyond the tradition cut-to-length and slitting processes. It is a method for sheet metal, including slit coil, to be cut to a smaller size and prepared for further fabrication by our customers.

OK, so what does that mean?

Well, let’s take a look.

Precision Blanking Process

precision blanking lineThe precision blanking process allows slit or smaller coils to be leveled and cut-to-length in narrower widths and closer tolerances than compared to shearing or the standard cut-to-length line. It basically makes the material easier and more efficient for our customers to use.

A blanking line functions similarly to a cut-to-length/leveling line. The slit, or narrow, coil is sent through a leveler to straighten the bend in the coil that occurs from it being coiled. It is then sent through a set of shears to cut the material. Blanking lines have side trim capabilities and can maintain specific cut-to-length accuracies.

The blanking technology used at Metalwest produces tight tolerances regardless of material length and speed. We can also process various thicknesses and grades as well as surface-critical material. For a complete list of our blanking services check out our capabilities page.

Precision Blanks

precision blanking line 2After a coil is sent through a blanking process it is now called a blank. Precision blanks are flat metal pieces that are ready to be fabricated. Further fabrication processes may include stamping, roll forming, punching, bending, etc.

We have the capability to produce custom blanks in a variety of aluminum, carbon steel, and stainless steel material. If the material you need is surface-critical, we can also provide protective packaging to ensure you receive a high-quality material. Just tell your local sales representative you want it!

Look for the next part of our processes series, where we will focus on polishing, in the coming months.