Weld symbol
Seam weld symbol
A circle with a bar through it calls for a seam weld - a continuous or closely overlapping resistance weld made by rolling wheel electrodes along the joint instead of stopping at each spot.
Reads asArrow side: seam weld, 1/4 size, 6 long, 1 pitch.
How to read it
The seam weld symbol is the spot weld circle with a straight bar drawn through it along the direction of travel. That bar is the whole distinction: it says the weld runs as a line rather than existing as isolated points. In practice the weld is made by wheel electrodes that roll along the overlapping sheets while current pulses through them.
The number to the left of the circle is the weld's width, meaning how wide the fused band is across the seam. A length to the right says how far the seam runs, and where the seam is not continuous a pitch after the length gives centre-to-centre spacing of the individual weld runs, which is how a roll spot pattern is called out.
Continuous seams are chosen when the joint has to hold pressure or keep liquid in, because a line of separate spots leaves paths between them. Intermittent roll spot seams are chosen when only strength is needed, since running the wheel continuously puts far more heat into thin sheet than the joint requires.
Like a spot weld, the seam forms between the sheets rather than on a visible face, so the symbol may sit centred on the reference line when the process determines access. Where it is drawn clearly above or below, read the side in the normal way. In every case the drawing rather than the symbol tells you which sheet the wheels run on.
Where each dimension goes
- Width (left of the symbol)
- How wide the fused band is across the seam, measured at the faying surface.
- Length (right of the symbol)
- How far the seam runs along the joint.
- Pitch (after the length)
- Centre-to-centre spacing where the seam is made as a series of runs rather than one continuous line.
- Bar through the circle
- The mark that separates a seam from a spot: it says the weld is a line, not a point.
Worked examples
Each one is a drawing, the sentence it comes out as, and then the mark-by-mark account of why. Read the sheet first and say the sentence yourself before you look down.
Example 1: Continuous seam on a tank lap
TitleContinuous seam on a tank lapRefSeam weldEx1 / 2Reads as
Run a continuous 3/8 wide seam weld the full six inches of the lap.
Which mark says so
- seam symbolBelow the reference lineA seam weld on the arrow side of the joint
- 3/8Left of the symbolSize of each weld - diameter for a spot, width for a seam
- 6Right of the symbolLength of each weld
The 3/8 to the left is the fused band's width and the 6 to the right is the run length. With no pitch, the seam is continuous rather than a series of separate runs.
And what it does not say
- No pitch follows the length, so the weld is continuous over that length.
- Nothing sits above the reference line, so the far face of the joint stays bare.
- There is no circle at the elbow, so the weld does not continue around the joint.
Example 2: Roll spot seam
TitleRoll spot seamRefSeam weldEx2 / 2Reads as
Make 1/4 wide seam runs one inch long on three-inch centres.
Which mark says so
- seam symbolBelow the reference lineA seam weld on the arrow side of the joint
- 1/4Left of the symbolSize of each weld - diameter for a spot, width for a seam
- 1Right of the symbolLength of each weld
- -3Right of the length on the symbolPitch - centre to centre spacing of an intermittent weld
Adding a pitch after the length turns the continuous seam into a series of short runs, which puts far less heat into thin sheet while still developing the required strength.
And what it does not say
- Nothing sits above the reference line, so the far face of the joint stays bare.
- There is no circle at the elbow, so the weld does not continue around the joint.
Common mistakes
- Missing the bar through the circle and reading a seam callout as a spot weld.
- Treating the width to the left as a nugget diameter rather than the width of a fused band.
- Making a continuous seam where a pitch says the weld should be intermittent, overheating thin sheet.
- Assuming a seam weld is automatically pressure-tight when the callout gives an intermittent pattern.