Chapter #6 – Sheet Metal Joints

Rectangular Duct Joints

TDC – Transverse Duct Connector (SMACNA T-25A)

This traverse duct connector is fabricated from the same piece of metal as the duct (#3), and has a gasket (#10) inserted between the two joints of duct or fitting and is locked in place by a cleat (#9). Each corner will be bolted together. Watch the videos below to get a better sense of how this joint is assembled.

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Ductmate Duct Connectors (Slip on Flange)

The Ductmate duct connector is a proprietary connector manufactured by Ductmate Industries. One of the differences between this joint and the TDC joint above is that this is a slip on flange (#11) that is not fabricated from the piece of ductwork (#3) but is attached (slipped on) and secured to the raw end of the duct or fitting. This joint also requires a gasket (#10) between the flanges and cleats (#9) to fasten the two joints together. Watch the video below to get a better understanding of this proprietary joint.

Watch the following video for a better understanding of what Ductmate offers.

Duct Flange Rollformer Machine

This machine will make a slip-on flange to make duct joints. A fabrication shop that has this machine will be able to make their own flange instead of having to buy a proprietary flange like that manufactured by Ductmate.

The following video shows a demonstration of how the attached duct connector is assembled onto the end of a piece of ductwork.

The pieces that make up the TDC or Ductmate joint is comprised of the Flange (#4) on the end of the duct (#5) or fitting, the Gasket (#1) that provides an air tight seal, the Clip or Cleat (#2) that locks the two pieces together and the corner pieces (#3) that bolt together at each corner.

To ensure a proper sealing of flanged joints the use of gaskets with bolted corner pieces will make a tight fit that reduces the chances of leakage. The gasket is a continuous length of approved material with a minimum of 16 gauge corner pieces and 3/8” bolts. The clips are used to lock together the two adjoining pieces of duct and are a minimum of 6 inches in length.

In lieu of clips, screws can be installed at 6” maximum intervals starting at a maximum of 1” inch from the corners. Clips are to be spaced at a maximum of 15” inches on center for 3” static pressure and less, and at 12” centers for 4” static pressure and above.

Watch this video on how to install Cleats/Clips.

The sheet metal fabrication shop has several options when making a rectangular flanged connection. One is to use have the flange an integral piece make from the duct, or to add a proprietary flange (#1) on to the raw end of the duct such as the below from Hardcast, a Carlisle Company.

The flange (#1) has a piece for each side of the duct or fitting, and four corner pieces (#2). Cleats (#3) locks two adjoining sections of ductwork with each other or a fitting by using the Cleat Installing Tool (#4). Watch the video above to see how the cleat is attached.

TDC Corner Pieces

The corner of each section of duct will require a corner piece that allows separate sections of duct to be bolted together at their corners. The machine in the video below can do this automatically, otherwise they will be installed manually.

S & Drive Joint

Here is another method of attaching ductwork and fittings together using an Slip & Drive connector. This requires two (2) Slips and two (2) Drives for each connection.

#1 in the below image is the Drive portion that gets driven at the joint.

This joint can be used at any length when exposed to 2 inch static pressure and less, and up to 36 inches in length for 3 inch static pressure and less, or 30 inch maximum length for ducts exposed to 4 inches of static pressure. Not approved for any duct static pressure over 4 inches. In the image below you have the Drive Slip (#1) that gets driven down at the joint ends (#2) of the two pieces being attached together.

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And the S-Slip (#3) shown below holds the two pieces of duct (#2) in place on the other ends of the duct, so that you end up with two Drive-Slips and two S-Slips.

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There is another version of the S-Slip called a Hemmed S-Slip because as you can see circled in red below the Hemmed S-Slip (#4) has a hem at each end.

Watch the video below to see how the Slip and Drive is attached to the end of a piece of ductwork.

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This next video shows how easy this joint really is. As you will see, the sheet metal fabrication shop worker attaches two “S” slips to the end of two sections of ducts before pushing them together, then hammering the drives on each side to lock the two pieces together.

Watch the video below to see how a manual Drive Cleat/Slip is made in the shop. There are automated drive cleat machines that would produce these faster.

Below is an automatic cleat bender that is powered by a pneumatic operator.

Standing Drive Slip

Standing Drive Slip is similar to S and Drive except for the additional material and strength gained by a perpendicular extension of the Drive joint. This joint can also be reinforced with a bar for additional strength. This joint can be used at any length when exposed to 2 inch static pressure and less, and up to 36 inches in length for 3 inch static pressure and less, or 30 inch maximum length for ducts exposed to 4 inches of static pressure. Not approved for any duct static pressure over 4 inches.

Reinforced S-Slip

This joint uses a reinforced drive slip (#1) by using a 16 gauge angle (#2) that stands 1 inch in height. The angle slips within the drive section and is fasten in place with screws. This reinforced S-Slip is good on ductwork fabricated up to a maximum of 2” static pressure. The two sections of adjoining ductwork is shown by reference in the image below as (#3).

Standing S

The Standing S joint is similar to the reinforced S-Slip, except that the standing portion (#4) is fabricated from the same metal piece as the S connector. Below you can see that the two adjoining duct sections (#3) shown in red are inserted into the “S” section.

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Watch this video to see how a standing “S” lock is made.

Companion Angles

This is another way to reinforce the strength of the joint by adding companion angles (#6) on each end of a duct or fitting with a gasket (#7) between them. The companion angles can be attached to the duct or fitting by rivets (#8), screws or by tack welding, while the companion angles are secured together with bolts.

Welded Joints

Welded joints (#5) are attached by methods of welding various material types together. Most commonly welded in the HVAC industry would be Galvanized, Stainless Steel or Black Iron. This will necessitate having heavier gauge fittings and ductwork, as lighter gauges can’t handle the temperature of the welding process.

Black iron grease ductwork is a typically used for grease ducts. Two sections of ducts or a duct and a fitting are brought together and welded where their flanges meet. There are other methods of joining in welding, but the flanged joint is commonly used.

Bell Type Joint

The Bell type joint is also approved for use by the IMC (International Mechanical Code). The choice to use a particular joint is based on your sheet metal shop fabrication standards within the code approved methods. (See chapter on Grease Exhaust Systems for additional information)

Joint Length

The length of the duct will vary depending on which joint you use to fabricate your ductwork. As shown in the image below, the use of Ductmate (#1) a proprietary duct joint doesn’t require roll-forming as opposed to the other two joint types.

Remember Ductmate (#1) gets slipped onto the raw end of the duct, while the TDC/TDF (#3) flange is roll-formed from the same piece of sheet metal that the duct is made from. Since Slip & Drive (#2) and the TDC/TDF Flange (#3) are made from the same material as the duct, this cause the overall length to be shorter than one that made for the use of Ductmate.

Ductmate Joint Duct Length = 60”

Slip & Drive Joint Duct Length = 59”

TDC/TDF Joint Duct Length = 56”

What this means is that for every 100 feet for each type of joint there will be varying amounts of duct sections as shown below. There will be a quantity of 20 Ductmate pieces, 21 sections of Slip & Drive, and 22 sections of TDC/TDF joints. This is a great difference, but we want to make sure you understand that the roll-formers use some of the end of the duct to make the joints for TDC/TDF and the Slip and Drive joints.

Round Duct Joints

Flanged Round Duct Joints

There are various methods of attaching round duct and fittings together. Here is a proprietary system by Ductmate® called “Spiralmate”. The duct can come with the flanges already attached from the fabrication shop or can be field installed. Care must be taken not to damage the flange in transit or disturb the sealant that sits in the groove of the flange. If the sealant becomes damaged then more will need to be applied to ensure a proper seal when assembled onto the end of a duct or fitting.

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Here is another manufacture of a flanged round joint; the Spiral Pipe E-Z Flange System.

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And with this next video you can see how the roll former turns the end of a round duct until it is 90 perpendicular to its length thereby preventing the flange from slipping off, and allowing the two mating pieces to be clamped together.

Sheet Metal Combination Rotary

Preparing sheet metal for a wired edge, turning a burr, beading, and crimping are probably the most difficult of sheet metal forming operations to perform. Crimping the ends of round duct and fittings reduces the circumferences enough to allow the end to slip into its opposing duct or fitting.

This combination rotary is used for beading and crimping which in larger fabrication shops are produced by separate pieces of equipment.

Most low pressure round fittings will either have a crimped end or be coupling sized as shown below.

Crimped Ends

Crimped ends reduce the overall diameter just slightly so that the fitting or duct can slip into the next piece.

Round Couplings

Couplings slip inside the ends of two round ducts to be joined together and then sheet metal screws are fastened to hold it in place. Couplings could be required at a certain size such as connections 18” and larger. The shaded area in the image below is the coupling which has a beaded center so that each section of round ductwork slips over the coupling the same distance.

Slip/Coupling Joint

Spiral duct can slip over the end of a fitting that is made coupling size, so that crimping isn’t required. The spiral duct will slip over the fitting until it hits a beaded section preventing it from going any further. The fitting has a bead similar to the one shown at the center of the coupling above.

Welded Connections

The requirement for a welded duct connection can be found for kitchen grease exhaust systems or some industrial processes and laboratory exhaust systems. Some of the more commonly welded duct materials are galvanized steel, stainless steel and black iron. Joints are often butt welded or flanged.

Often welded kitchen exhaust systems will use stainless steel where exposed to view and black iron for the hidden duct to the grease exhaust fan. Grease exhaust ducts need cleanout doors every so often as required by code for access for cleaning. (See chapter on Grease Exhaust Systems)

DuraFlange This is a proprietary system that uses light weight flanges that are inserted into the ends of ducts and fittings in order to join two pieces together with a neoprene or butyl gasket between them. Screws are then placed every 6 inches around the perimeter to fasten the DuraFlange to the end of the duct or fitting. This is a three piece joint, with two flanges (#1 & #3) and a gasket (#2).

Watch the video below to see how this flange works.

Rectangular Duct reinforcement

Intermediate reinforcement goes between the joints to strengthen the section of duct of fitting. The construction standards, like those established by SMACNA will dictate where and when reinforcement is required. The reinforcement could be top and bottom or on all four sides.

Also, reinforcement can be around all four sides as shown below.

Tie Rods

Another method of reinforcing ductwork and fittings is with the use of Tie-Rods. Reinforcement can be at the joint (JTR) or mid-way (MPT) between the joints. You can see by looking at the image below that you can have Joint Tie Rods (#1) or Mid Panel Tie Rods (#2) for additional strengthening of the duct section. The Tie-Rods are shown in yellow, with one at each end (#1) of the duct section and two mid-way (#2) between the joint ends.

EMT or solid rods are used for Tie-rods. Steel rods in sizes 1/4” & 5/16” are used or 1/2” to 1-1/4” EMT based on static pressure and distance to Mid Panel Tie Rod from joint. If the steel rod exceeds 3 feet in length, then a 3/8” steel rod must be used for added stability and strength.

Mid Panel Tie Rods

The Static Press (#1), Sheet Metal Gauge (#2) and Mid Panel Tie Rod Distance (#4) will effect the Maximum Duct Width (#3) that can use a single toe rod for reinforcement when using a Mid Panel Tie Rod distance of 2-1/2’ (#4). As the table shows with the Red Arrow (#5) as the gauge of the duct gets thinner the maximum duct width (#3) decreases, and as the Static Pressure (#1) increases, the Maximum Duct Width (#3) decreases as shown by the red arrow (#6) although not as dramatically as with the reduction in sheet thickness.

Relationship Between Width, Gauge and Reinforcement

Duct Width (#1), Thickness (gauge)(#2), Reinforcement Spacing (#3) and Reinforcement size (#4) all relate to each other and changing one usually affects the others. When you increase the Duct Width (#1) this can increase the Sheet Thickness (#2), Reinforcement Spacing (#3) & Reinforcement Sizing (#4). Likewise when you change anyone of the other items it can have an inverse relationship to the others, such as if you increase the reinforcement spacing (#3) you might be able to reduce the Duct Thickness (#2).

Just remember that these factors are all related. Your Sheet Metal Fabricator will usually have a set of Duct Construction Standards that they use in most situation and only make adjustments in special situations.

Unreinforced Ductwork

Ductwork can be built without any additional reinforcement if it remains within SMACNA’s Table 2-47 “Unreinforced Duct (Wall Thickness)”. As can be seen in the image below, as the pressure class increases (#2), so does the thickness or gauge (#3) of the duct. The same applies to the dimension of the duct, so that as the duct gets larger, the thickness of the metal increases. In summary, if the pressure or the duct dimension increases, then the thickness of the material will also increase according to the below chart.

Aluminum and Reinforcement

Aluminum doesn’t have the same strength and rigidity as Galvanized steel for the same gauge or thickness. Any construction using aluminum would require an increase in the thickness of the metal and reinforcement in order to match the equivalent in strength and rigidity of that of galvanized steel. For example a 1” x 1” x 16ga Steel Angle would require a 1-1/4” x 1-1/4” x 1/8” aluminum angle to be similar in strength and rigidity (see reinforcement table below). Aluminum is 6061-T Strength.

Round Duct Reinforcement

Just like rectangular duct, round duct will require reinforcement under certain conditions. As can be seen in SMACNA Table 3-10 below, the requirements for stiffeners is based on duct size (#1) and stiffener spacing (#2). This table is for 2” Negative Pressure Spiral duct. The process would be that you would look up the size (#1) of the spiral duct required per the projects engineered drawings and then decide which stiffener spacing (#2) the duct will be fabricated at. This will determine the required gage or thickness of the metal and the reinforcement or stiffener type.

As example if we look at 54” spiral duct as shown on row #3 we can see our options are as follows starting with the Unstiffened Column #4. Here are your options;

54” Spiral

Unstiffened Gage = 16 gage, Stiffener = NR (Not Required)

Stiffener Spacing = Every 20 Feet, Gage Required = 22 gage, Stiffener Required = “B”

Stiffener Spacing = Every 12 Feet, Gage Required = 24 gage, Stiffener Required = “B”

Stiffener Spacing = Every 10 Feet, Gage Required = 24 gage, Stiffener Required = “A”

Stiffener Spacing = Every 6 Feet, Gage Required = 26 gage, Stiffener Required = “A”

Stiffener Spacing = Every 5 Feet, Gage Required = 28 gage, Stiffener Required = “A”

As you can see from the example above, as you increase the stiffener spacing (#2), you can reduce the thickness of the material, this is because the stiffener adds strength and rigidity to the duct allowing for a thinner material. Using an Unreinforced duct requires 16 gage material, while installing a stiffener every 5 feet allows you to use a much thinner and cheaper 28 gage duct.

The fabrication shop has to determine what their standard fabrication preference is and the cost for the various options based on stiffener spacing.

Now let’s look at chapter #8 on how to figure shop fabrication productivity.

Chapter #3 – Sheet Metal Coil Line

Those fabrication shops that have invested in a coil line will find it less labor intensive to fabricate straight pieces of ductwork.

Sheet metal coil lines are available with many optional pieces of equipment that can be added on to perform an additional function on the path to creating a fully sectional piece of ductwork.

The full capabilities of the coil line begins where several rolls of differing gauges of metal are housed in large heavy rolls and end where the sheet metal is bent. Between the beginning and end are various pieces of fabrication equipment that perform special functions in the process of making a piece of duct for the HVAC industry.

Standard coil widths include 48” and 60”, which can make anywhere from a 4 foot to a 5 foot long piece of duct. Also, as an option are coil widths of 72” for a duct length of 6 feet, minus flange allocation. Gauges will range from 16ga to 30ga.

Remember when watching some of the shop fabrication videos below that fabrication shops are very noisy at times when the equipment and workers are in full operation, as they are working with sheet metal.

This first video will animate the total process. We recommend that once you finish this chapter that you watch this video again to identify all the steps you are going to learn about in this chapter.

Sheet Metal Coil Line

The below image shows that a forklift is being used to load the sheet metal coil onto a coil machine. These coils are very heavy and require machinery or an overhead crane system to load them onto the coil line equipment.

The coil line process steps are outlined below and are covered in greater detail later in this course.

1. SHEET METAL COILS – Choose which coil width and gauge of sheet metal is required for the project.
2. STRAIGHTENER/LEVELER – The process of straightening the sheet metal.
3. BEADER – This stiffens the metal by putting a bead down the sheet metal
4. NOTCHER – The notcher will cut out (notch) small portion of the duct at its edge where it will be bent
5. SHEAR – This is when the sheet metal gets cut at the perfect point.
6. SEAMERS – This machine installs the Snaplock or Pittsburgh seam along its length at the point where it will attach to the other side. One seam will be a female seam and the other male for a perfect fit.
7. JOINT (Rollformer) – The metal has its end roll formed to create the ends of the duct that will join up to another piece of duct or a fitting.
8. LINER – If required liner will be added.
9. BREAK – This is the final step in the automated coil line. This last piece of the coil line will bend the sheet metal into either an L-Section (2-sided), U-Section (3-sided) or Full-Wrap (4-sided)

Watch the video below and see if you can identify the various coil line steps in the process of forming a section of duct.

We begin with the coil of a particular width and gauge, which gets fed into the straightener. The purpose of the straightener/leveler is to remove the metals tendency to want to remain curled up as it was within the coil from the manufacture. After this it goes through the beader, which puts several beads across the sheet metal to stiffen it in its finished form.

Then the metal gets notched at the points where the metal will be bend so as to allow for and easy bend along its longitudinal length. The next section will shear the duct, cutting it at the perfect point along its length. The seaming section is next where it will have a female seam on one side and a male seam installed on the other by their respective seamers, such as a Snaplock or Pittsburgh seam.

Then the metal goes through the roll former, which creates the joint end of the sheet metal duct, such as TDC, Drive Slip or completely raw for the attachment of a proprietary joint such as Ductmate. Next liner will be added if the specifications call for the duct to have internal liner. The automatic duct liner feeds from a coil of liner material while applying a liner adhesive to the sheet metal and then automatically pins the liner to the sheet metal.

And finally the metal is bent using the break to create an L-Section (2-sided), U-Section (3-sided) or Full wrap (4-sided) section. The brake is a heavy duty hydraulic sheet metal bending machine that will fold your duct in preparation for assembling.

Step # 1 – Sheet Metal Coil Line

Galvanized steel is defined as a carbon steel sheet coated with zinc on both sides. Hot Dipped Galvanized for the HVAC industry is usually specified to be coated either as G-90 or G60. The coating indicates the amount of zinc applied to each side of the carbon steel. The most common gages used are from 16 ga through 26 ga. The use of the lighter gages are not as common in commercial construction as it is in residential construction.

The most common width of the coils used in the HVAC industry is 36”, 48”, 60” and 72”, with the 60” width coil being the preferred width. The Wider the coil, the less joints you will need, as a 60” wide coil can make a 5 foot section of duct using Ductmate connectors, as opposed to only a 3’ foot section with a 36” coil width.

For example if you had 90 feet of straight duct, it would require;

1. 30 pieces of 36” (3 foot) sections of duct 3’ x 30 = 90’
2. 18 pieces of 60” (5 foot) sections of duct 5’ x 18 = 90’

It’s better to handle fewer pieces, in addition, the more pieces you have, the more it cost for gaskets, corner pieces and clips because you have 12 additional joints to make.

The coils are loaded onto the automated coil line using a forklift or overhead crane.

Step # 3 – Beading

The ductwork is Beaded or Cross Broken (#4) to provide strength across its surface area. Duct beading is the preferred method. The duct is run through a bead machine that puts a ridge or dimple across it transverse width every 12” or so. This will help reduce sagging of the metal.

The purpose of cross-breaking or beading ductwork is to provide support for large spans of ductwork. For ducts that are 19” and greater in width and 10 Ft2 of unbraced panel area will require cross-breaking or beading. This requirement is for duct classifications of 3” static pressure and down and 20 gauge or less thickness. Ducts built to 4” static pressure or greater don’t require cross-breaking or beading as the increased thickness and reinforcement requirements provide the added support benefit. Beading is spaced every 12” apart, running parallel with the joint of duct, but direction of bead can be random on fittings.

Step # 4 – Notcher

The machine will notch the duct at the points where they need to be folded. The below image shows a four sided piece of sheet metal ductwork notched (#1) at the points that it will be bent by the Brake. The yellow highlight shows the line of folding (#2) that will happen with the brake in order to make the four sided piece of duct. Notching is how sheet metal is allowed to go through the roll forming machine where the joint is made.

The notching allows the roll-formed edge (#4), such as a TDC/TDF or S & Drive the ability to avoid the interference from bending at the corners. There is no way to bend the metal after its been through the joint (#4) making process without having the corners notched (#1). Ductmate doesn’t require notching as it isn’t put through the roll former, as it is an added flange that gets put on after the duct is assembled.

The depth of the notch is determined by which joint type will be applied to the end, such as TDC or S and Drive. TDC requires a deeper notch then S&D (S & Drive). There are different types of notching but they all have the same goal in mind.

Step # 5 – Sheet Metal Shear

Another piece of shop fabrication equipment is the shear, which comes in various forms, from automatic to manual. The fully completed coil line uses an automatic shear. The shear cuts the sheet metal at the point needed to give the proper width of duct.

There are also hand held electric shears. Shown below is a manual stand-alone foot operated shear. Once the metal is position in the machine you push down with your foot on the long bar that near knee height.

Below are two videos, the first one is a short demonstration of a foot shear, the second is a longer video of the many steps in making a piece of sheet metal and the various tools used in marking and measuring.

This next video is a little over 8 minutes, but gives a good overview of the process of cutting a piece of sheet metal with a foot operated shear.

Step #6 – Sheet Metal Seams

Seams are created along the longitudinal length of the duct or fitting to fasten one section to another, as opposed to joints that connect one length of duct section to another, or a joint of duct to a fitting. Seams seal to make one section of duct or a fitting.

The longitudinal seam will be either Snap Lock or Pittsburgh Lock and is formed on a machine that will roll form the flat edges into one with a female and the other with a male end.

Pittsburgh seams are used on increased pressures, above those acceptable for Snap Lock.

The video below is a little grainy, but you can see that the rollers will bend the flat edge of the sheet metal, each successive roller bending the metal a little more until it reaches the shape required by the last roller. These machine is a stand-alone piece of equipment which in a complete coil line would be part of the automated process.

Step #7 – Roll Forming Machines

Depending on the seam type, the flat metal cut by the Coil Line or Plasma cutter will get  put through the roll former to form a Snap Lock Seam or a Pittsburgh Seam. These are the two most common seams, so they are the ones we will be using through-out this training program. The seam takes two pieces of metal and locks them securely together. The seam runs longitudinal and the joint runs transverse.

Step #8 – Liner

Duct is often provided with internal liner for mostly acoustical reason and for its thermal properties for air ducts installed outdoors where wrapping duct is not practical because of the cost. The video below is of a portable pinspotter machine that is not part of the automated coil line, but will show you how liner pins are fasten to the duct to hold the liner in place.

In an automated coil line with a liner station, the metal will be sprayed with adhesive before the liner is applied, followed by the pins. In non-automated systems there will be a table area where the metal will be sprayed with adhesive before the liner is attached to the interior of the duct or fitting.

In the below video you will see several methods used in the coil line process for attaching liner to the duct, in addition you will see another manual method of attaching the pins that hold the liner in place.

Step #9 – Duct Break

Before the sections of duct can be assembled they need to be bent to form an “L-Shape”, “U-shape” or 4-sided single piece which comprises the duct. The break is a machine that is used to bend sheet metal. The metal is inserted to a point where the bend is required and then the machine automatically activates the break to bend the metal.

Some shops still use a manual hand break (shown above) where the operator pulls a lever which causes the machine to bend the metal. With this portion complete you now have two “L” sections, or a “U-Shaped” section that will match up along a male and female companion seam. For smaller ducts it might be possible to make the duct section out of a single piece. The seam gets knocked together either as a snap lock or Pittsburgh seam as described previously.

Watch this video to see how metal is bent using a brake. These types of brakes go by various names such as Box Brake, Finger Brake or Pan Brake. Notice how the shop worker inserts the notched section of the flat metal into the machines notch guide to position it correctly for where the fold will occur.

Duct Reinforcement

Reinforcement provides for the strengthening of the ductwork under certain conditions as dictated by the construction standards. The construction standards are driven by many factors including the pressure class, the size of the duct or fitting, the length of the duct and the local code adopted construction standards table.

Reinforcement can be accomplished by adding angles, channels, and Condu-locks with EMT. There are various other methods depending on the construction standards that provide jurisdiction over the project location. The standard could be an adoption of the SMACNA standards or the jurisdictions own version of something similar.

Coil Line Feeding a Plasma Cutter

Instead of having the coil line feed a sheet metal duct making process, it can feed lengths of coil duct onto a plasma cutter. This avoids having to purchase flat sheet stock and material handle each piece onto the plasma cutter. Watch the video below to see how a coil line machine can feed a plasma cutter to save time and money.

A Simplified Coil Line

In the below video you can hear the loud notching of the metal as the machine punches (notches) out at the point where the duct will be bent and or cut. The coil line machine cuts the section while creating a longitudinal seam, the point at where the duct sections will attach. The machine provides all aspect of the duct section, including straightening, beading, notching, joint formation, cutting, seams and bending.

The only thing the machine doesn’t do is the final banging together the single or two piece sections of duct along the seam. It also doesn’t install the corners pieces where the sections are bolted together.

Duct Assembling

Ductwork can be made into one, two or four pieces. One piece duct or full wrap duct is fabricated with one continuous piece of sheet metal and is limited in size by the fabrication equipment. As the duct gets larger and larger, more pieces will be required to make the duct. Two pieces (aka “L” sections, half sections, knocked down) are easier to ship, but more costly for the field labor, as they have to assemble the sections before installing.

Check what an “L” Section looks like coming off an automated break.

The Pittsburgh seams are knocked together with a Tinner’s Hammer or an automated tool that accomplishes the same thing, that is to bend over the seam to lock the sections together.

Coil Line (Fast Time Lapse Video)

This next video shows a shop worker knocking together sections of duct, installing the corner pieces and using an automatic Pittsburgh seamer to bend over the seam and lock the sections in place.

Now that you have an idea of what happens from the coil line to the end product, see if you can identify some of the following steps in this sped up video of a coil line. You’ll notice that when the sheet metal first appears in the video it has already been straighten, beaded and notched.

The next step you will see is the application of the male and female seams which is done under the white/beige colored metal boxes that protect the roll formers. Then it moves down to the roll formers that put the joints on each end, before finishing by being bent. Replay the video until you notice each of the steps being performed.

One more quick video from coil line to end product.

And one more that shows you a 4-sided, one piece wrap.

Making Square to Rounds

Making a square to round requires that you make small bends along the length of the square to round to form the shape. Fabrication shops use various pieces of equipment such as the break to make these small creases incrementally along its length to make the square to round. This can be done faster with this NAMCOR Striker machine. See the video below to get an understanding of how the machine makes a square to round.

Now let’s look at chapter #4 to see how using a Plasma Cutter can save on material waste and labor.

• Chapter #1 – Introduction to Sheet Shop Fabrication
• Chapter #2 – Sheet Metal Materials
• Chapter #3 – Sheet Metal Coil Line
• Chapter #4 – Plasma Cutting Table
• Chapter #5 – Spiral Machine
• Chapter #6 – Sheet Metal Seams
• Chapter #7 – Sheet Metal Joints
• Chapter #8 – Sheet Metal Shop Fabrication Productivity
• Chapter #9 – Casings and Plenums