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.

Our Processes: Slitting

packaged slit coil at OFR MetalsIn part two of our processes series, we will discuss slitting. Slit coil is used for a variety of end products. Some of the more common include: HVAC duct, lighting fixtures, architectural trim, roof drain pipes, and many more.

So what does the slitting process entail? Well, the simplest definition is… slitting is a process where steel coils are fed through a slitting machine and cut into narrower widths.

But there is more to it than just making smaller coils.

Slitter Machines

slitting machine at work at OFR MetalsMachines used to create slit coil typically consist of stations for uncoiling, slitting, and recoiling. The thicknesses and widths that a coil can be cut to depend on the machine. Here is a list of our branch capabilities.

Machines used for the slitting process can run both ferrous and non-ferrous material and depending on the machine, may be used for sheet metal or rolled coils. At Metalwest, our machines process steel coils.

Blades used for slit coil vary depending on the job requirements. Different blades are used based on the gauge and type of material as well as the tolerances specified by the customer.

The Slitting Process

Quality check by our slitting team at OFR MetalsCoil slitting, or roll slitting, is the process in which a large master coil is uncoiled and sent through a set of two circular wheels, or shears. These shears are set at a predetermined width and cut the coil into a series of narrower rolls. The narrow rolls, now called strands, are then hand-measured by the teams on our slitter machines to ensure the customer specifications are met and tight tolerances are held.

After the quality check by our team, the strands are recoiled and packaged to produce customer-specific slit coils.

At Metalwest we can process slit material in a variety of gauges and widths to meet the demands of our customers. To find out which of our locations slit material and what the different tolerances are, contact your sales representative.

Check back to discover more about our processing capabilities.

Our Processes: Leveling / Cut-to-Length

Lately, we have discussed how many of our products are made and what they are used for. But we haven’t discussed how the coil from the mill becomes a swing set, an HVAC duct system, a food prep table, or a horse trailer. So, today we are going to talk about one of the many processes it takes to turn a coil into an end product. At Metalwest we process the coils we receive from mills and make them into ideal material for our customers. While it may not seem like much to most people, cutting a coil into smaller sheets can mean all the difference for customers who do not have the capability to handle large coils or need to save on processing times. That brings us to our first processing capability. This five-part series will delve into the different processes we offer our customers. The first is leveling / cut-to-length. The simple overview of a leveling / cut-to-length line is that it converts coil into sheet. But it does much more than that.

leveling lineLeveling

When a coil is run through a leveling / cut-to-length line the first step is to, well, level it. Metal can be easily bent, shaped, and formed-which is a good thing for many customers-but because of this, when the metal is wound into a coil at the mill it tends to hold that curved shape when the coil is unwound at a service center. So, the leveler’s job is to straighten the coil so it can later be cut into flat sheet.

cut to length / leveling lineTight Tolerances

The leveling technology we use is able to hold tight tolerances. This means we can process material to our customer’s specifications. The corrective levelers provide shape correction for squared cut-to-length material.

Reduce Overall Scrap

Because the technology we use can process tight tolerances it also means reduced scrap for not only us, but our customers as well. Reducing scrap costs is a top priority for many of our customers. Even a small reduction of those costs can have a large impact on our customers’ success. And we definitely believe our customers’ success is our success. Be sure to check back for more on our processing capabilities.