Living with Arc Welding Spatter
Spatter can originate from rapidly expanding gas bubbles in the weld puddle or in the metal drops that transfer from the end of the electrode. Expanding gases can cause drops to explode like an overinflated balloon. Spatter can come from the splash of molten metal drops as they hit the weld puddle, just like the splash of raindrops. It can come from electromagnetic motor forces that cause molten drops to rotate and whip around on the end of the welding wire. And spatter can come from the explosive fuse action that helps metal transfer from the tip of the welding wire.
Usually, it is the explosive fuse action that creates most of the spatter. The spatter from fuse action can be reduced by careful adjustment of the welding condition (voltage, amperage, shielding gas, etc.). By "tuning" in the power source, and with the correct equipment settings, the violence of the fuse action can be minimized.
Gas Shielding Problems
Spatter tends to cling to the inside surface and edge of gas shielding cups of welding guns. The spatter can build up until it interferes with the shielding gas flow. Operators must be careful and clean away the spatter buildup. However, this is not always done. Cleaning away spatter buildup is especially troublesome in the case of robotic welding systems.
On occasion, a ring of spatter will fall out of the gas cup while you are welding and will land in the weld puddle. When that happens, it may ruin the weld properties.
It is difficult for spatter to stick to clean, smooth surfaces. When a molten ball of spatter strikes a surface, it can instantly cool off and solidify. As it solidifies, the molten material molds itself into the scratches and microscopic grooves of the surface. It literally grabs onto the surface and won't let go.
When you use a sharp tool to remove spatter buildup, such as the end of a screwdriver, it can scratch the inside surface of a gas cup. That makes it easier for the spatter to stick to the cup the next time you weld. Some operators bang their welding guns against the work piece or against the floor, or other hard surface, to knock the spatter loose. That isn't a good idea because it can damage the gun. Some operators place the gas cup against a hard surface and whack it with a hammer or another heavy object to knock the spatter loose. That, too, is a no-no because it can damage the gun.
If you are very careful, you can use a sharp tool to remove the spatter by touching only the spatter. But don't let the tool touch the gas cup itself. Removing spatter is like remove a scab from a cut or sore. If you are careful, you can remove the spatter without scratching the surface of the gas cup. Sometimes it may be necessary to remove the cup from the gun, hold it with some type of clamp or pliers, and push the spatter out with a piece of wood. Wood will not scratch the inside of the cup.
It is possible to spray the inside of the gas cup with a protective coating before you begin welding. Using such sprays is similar to putting a coating of shortening on a pie plate before you bake the pie so that the pie can be easily removed. However, even these special sprays will not prevent some spatter buildup; sooner or later, you will have to remove the spatter yourself.
Some manufacturers of gas cups believe that certain materials make it more difficult for the spatter to stick to them. This is one reason why you will find a variety of metal and ceramic gas cups sold by the different manufacturers. To date, there is no known material that can eliminate or prevent spatter buildup. Just remember: A hard, clean, smooth surface will delay the spatter buildup and allow you to weld with a better shielding gas flow pattern.
Wire Feeding Problems
Spatter usually collects on the very tip of the contact tube from which the welding wire is fed. Just as with the gas shielding cups, spatter can stick to the metal from which the contact tip is manufactured. Some tips are threaded into the welding gun. As a consequence, some operators use pliers to grip the tip and turn it tighter. The gripping jaws of the pliers can leave marks and grooves on the tip. Spatter sticks to contact tips that are scratched and marked, for the same reasons it sticks to gas cups.
Once spatter begins to stick to the end of the contact tip, it can build up to where it begins to close off the wire feed hole. As the hole in the tip is closed off, wire feed forces are increased by the wire feeding system. Sooner or later, the increased wire feed force causes the wire to collapse inside the conduit leading from the wire feeding control to the welding gun, unless, of course, the spatter is removed.
Sometimes, while welding, an operator can see a ring of spatter pulled off the end of the contact tip by the welding wire as it is fed from the tip. These little chunks of spatter can cause a blip in the arc and may cause a small defect in the weld. You can slow down the buildup of spatter on a contact tip by keeping it smooth and coating it with one of the commercial anti-spatter sprays.
Occasionally, the buildup and release of spatter rings causes fluctuations in the wire feed speed, and consequently the welding current. Whenever you become aware of fluctuations in the arc, you should suspect the trouble is from a spatter-clogged contact tip. Keep the tip clean and smooth to reduce the chance of wire feeding problems.
Spatter Bridges
Welding guns are designed to electrically isolate metal gas cups from the current-carrying parts of the gun. That prevents accidental arcs between the edge of a gas cup and the work piece while you are welding. Such accidental arcs could result in defects in the weld zone.
However, when spatter builds up to the point where it completely bridges the gap between the inside wall of a metal gas cup and the contact tip, the gas cup becomes electrically hot. Current for an accidental arc-over between the edge of the gas cup and the work piece can flow from the contact tip, through the spatter bridge, into the gas cup. Such arc-overs can ruin welds and can cause accidents due to the reflex action of the operator. Spatter bridges should be avoided at all costs.
Spatter Removal Tools
Some companies market tools for removing spatter from the inside of gas cups. Those tools should be used with care and only as directed by the manufacturers of the tools. Incorrect usage can create scratches and marks inside the gas cup. Instead of correcting the problem, it will make it worse.
Gas Composition
In some cases, spatter can be reduced by changing the shielding gas composition. When it is possible to use different gases for making the weld, choose the one that gives the least amount of spatter. You may have to run an experiment to find the best shielding gas for use with the material you are welding, but the time will be well spent.
A Safety Reminder
As you know, spatter is hot. It can cause burns and start fires. But did you know it can bounce like a rubber ball? As it flies through the air, surface tension causes the little bits of molten spatter to become ball shaped.
While a ball is falling, the spatter cools off a bit. A thin skin forms on the surface like the skin on an apple. When the ball of spatter hits the ground, it can bounce, roll, and ricochet. It can travel as much as 35 feet, fall through cracks, etc. So you should protect the welding area in all directions from the hot spatter.
A few good safety references are:
- American National Standard, ANSI Z49.1, "Safety in Welding, Cutting and Allied Processes" (www.aws.org)
- OSHA General Industry Standard, 29 CFR 1910 Subpart Q (www.osha.gov)
- National Fire Protection Association, NFPA 51B, "Standard for Fire Protection During Welding, Cutting, and Other Hot Work" (www.nfpa.org)
Also, be sure to read and follow the instructional literature provided by the suppliers of your equipment and materials.
The bottom line: Follow the teachings of this article. Control of spatter will increase productivity, reduce expenses, and keep you safe.