Mike Bailey on Seams & Joints

Some customers—even dealers—may get mixed up between seams and joints due to a lack of understanding of big machines.  Vice President of Sales and New Product Development at Mestek Machinery, Mike Bailey, explains the difference between seams and joints.

Seams versus Joints

A seam goes along the length of the ducts.  It is how you mechanically close the piece of flat sheet metal that is wrapped into the final rectangular duct.  Seams are either Pittsburgh or Snaplock.  Joints are both ends of each duct section.  You can connect the joints of each duct section to elongate the ductwork.

How are joints formed?

Joints could be transverse duct connection (TDC) and transverse duct flange (TDF), or slips and drives.  All the flange types are produced in a 12 to 16 station bull form, whether it be standalones for fittings and straight ducts or in your coil lines.  Slips and drives are produced on a roll former via coil or pre-cut material.  They produce a 7/16th cleat edge.

How are seams formed?

Longitudinal seams are formed in two ways.  You have fittings, which would be on stand alone roll formers.  It could be a 20- or 16-gauge Pittsburgh; it could be a 20 gauge female Snaplock, or even a 24 gauge female Snaplock, which would be for your fittings, and/or straight duct if you don’t have coil processing equipment.  If you had a coil processing or coil line, then you would produce your longitudinal seams up front and then your transverse joints on the back half.  When it comes to the male seams, you can’t perform the straightedge on a break, however, female seams are always produced on roll forms.

What is a simple way to remember the differences between seams and joints?

Seams are longitudinal—the length of the duct. Length = longitudinal.  Joints are how you join or connect the two ducts together.


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