Stitched Elbows (Stitched Halves)
US Duct has a full line of elbows in galvanized, SS and carbon steel in ALL duct gauges and radii. Stitch Welded elbows, while only available in Galvanized metal, are a main category of these elbows.
The name basically tells it all. These are elbows formed by stitch welding halves that have been stamped out using mechanical presses and forming dies. The stitch weld is virtually a continuous weld although a visual examination would lead one to think that the weld was an intermittent weld. HOWEVER, there is another weld on the reverse side welding the 'skipped space' from the other side. The result is a very tight elbow.
However, the mechanical stamping process places limits on the gauge that can be used limiting them to a maximum of 22 gauge. The result is that these elbows, while available in sizes 3",4",5",6",7",8",9",10" and 12" in 90,60,45 and 30 degrees, are good all around elbows for air or dust up to 8". Larger than that their application should be limited to light dust or air as the gauge is too light for heavy particle.
The stamping process also limits the elbow to fixed radii* of 1xD, 1.5xD.
The ends of the elbow can be fitted with flanges or rolled lips.
*Radius means the height of the elbow and is a direct reference to the length of sweep- an important factor when considering the impact of air flow, static pressure and wear. Typical radii are 1xD (short radius), 1.5xD (Standard Radius) and 2.5xD (Long Radius). A 1.5xD radius means that the a 4" dia. elbow has a 6" (1.5x4) radius. Another way to think of this is to set a 90 degree elbow on the floor and measure from the floor to the center line of the elbow. (Be sure to subtract any straight portion of the elbow.) Divide this height by the diameter and you have the radius.