Welding Galvanized Steel
The photo shows a GMAW weld on a 22-ga. galvanized pipe made using 0.030-in (0.8 mm) SIL-WELD wire at 14V and 110 amps at a travel speed of approximately 40 in/min. With silicon bronze, low arc temperature, high travel speed and an ability to combine with zinc sharply reduce the amount of zinc lost to evaporation. The galvanized coating may become slightly darkened in the vicinity of the weld bead, but it's still protected. The silicon bronze itself is highly corrosion resistant.
with Wisconsin Wire Works SIL-WELD Silicon Bronze
Right now, you're probably thinking "Copper-base electrodes are expensive, and training my welders how to use them would cost me even more money! Besides, my jobs need the strength of steel weld seams."
Think again -- you're in for some pleasant surprises.First, let's take a closer look at those costs. Sure, a spool of Wisconsin Wire Works' SIL-WELD will run you about three to four times the cost of mild steel. In fact, you may even use a few more pounds of silicon bronze than steel for the same job because the bronze has a higher density.
But weld metal -- even silicon bronze -- is less expensive compared with labor costs. And if you're going to weld galvanized steel with mild steel electrodes, the largest portion of your labor costs occurs after welding.
Let's assume your job requires a 100-ft seam containing about 10 pounds of metal. In mild steel, the filler metal will cost less than ten dollars; in silicon bronze, it may cost as much as thirty. So, off the shelf, steel is ahead by twenty dollars.
Silicon bronze has a low (for copper alloys) thermal conductivity and heat loss to the base metal is generally low as a result. This means that joints can be made somewhat faster with Wisconsin Wire Works' SIL-WELD than with mild steel. However, because welding speed depends on several factors, we'll assume one hundred feet of weld seam should take about two hours with either metal. At twenty-five dollars per hour including fringes for labor, that's another fifty dollars. Now add another fifty for the two hours more it will take to clean up and paint the joint made with steel wire. We'll also have to pay for the paint. If you use SIL-WELD instead of steel electrodes, we don't have to add any extra time for cleaning and painting because the joint itself has plenty of corrosion resistance and the nearby zinc is still in good shape.
Here's how the costs add up:
WISCONSIN WIRE WORKS SIL-WELD SILICON BRONZE
|Cost Factor||Mild Steel Joint||SIL-WELD Joint|
|Labor (Welding, 2 hours @ $25/hr)||50.00||50.00|
|Labor (Cleanup % Re-coat, 2 hours @ $25/hr)||50.00||0.00|
|Materials (Cleanup % Re-coat)||5.00||0.00|
The bottom line is that the "more expensive" silicon bronze weld can cost about 30% less than mild steel when the costs of cleaning and re-coating are included. The bigger the job and the higher the labor costs, the more you save with thin-gauge galvanized sheet.
Welding parameters for common galvanized sheet gauges are listed in the following table. The values listed assume GMAW welding with 100% argon at a flow rate of 25 to 35 cfh, welding in the flat position.
SHEET STEEL WITH WISCONSIN WIRE WORKS SIL-WELD
|WIRE DIAMETER||SHEET THICK-|
|0.030 in (0.8 mm)||28 - 20 ga.|
0.018 - 0.039 in
(0.5 - 1.0 mm)
|14 - 15||100 - 110|
|0.035 in (0.9 mm)||24 - 14 ga.|
0.027 - 0.078 in
(0.7 - 2.0 mm)
|16 - 18||100 - 150|
|0.045 in (1.1 mm)||16 - 8 ga.|
0.063 - 0.168 mm
(1.6 - 4.3 mm)
GMAW welds can be made in all positions. Gas mixture and flow rates for GTAW are similar to those used with GMAW. For GTAW, use either 1/16-in, 3/32-in or 1/8-in filler rod.
Is silicon bronze strong enough? Yes, for most sheet metal welding jobs. With a minimum tensile strength of 50,000 psi (345 Mpa) and a Brinell hardness of 85 to 105 (500-kg load) in the as-deposited condition, silicon bronze is considered a moderate strength copper welding alloy. It is stronger than galvanized steel, and if failures do occur they generally take place in the base metal.
Should I consider any other copper-base welding alloys for galvanized steel? Galvanized mild steel sheet typically has a tensile strength between 35,000 and 50,000 psi (240 and 345 Mpa). Therefore, all copper weld metals listed in the table below except ER Cu deoxidized copper produce more than matching joint strengths. Occasionally, welders will use aluminum bronze to tack-weld large components. The higher strength of aluminum bronze ensures joint integrity during fit-up for final assembly. Welding is then completed with silicon bronze, which costs about 25 % to 35% less than aluminum bronze.
|ER Cu||25 Rockwell F||25,000||172|
|ER CuSi-A||80 to 105 (500 kg|
|ER CuAl-A2||130 to 150 (500 kg|
|Chemical compositions of several copper-base consumables are listed in Table 1.|
Is silicon bronze used for other galvanized-steel welding jobs? Millions of pounds of silicon bronze are used each year to assemble automobile and truck body components, many of which are now made from galvanized steel. Other galvanized steel products ranging from bicycle and motorcycle frames to heating, ventilating and industrial equipment -- even metal caskets -- all benefit from silicon bronze's easy weldability and good corrosion protection. Silicon bronze also has better electrical conductivity than steel. This property is useful when welding certain electrical connections, like bonding grounding-electrode conductors to antenna towers for radio/TV stations and cellular telephone service.