Questions buyers ask about large 15 kg reels of copper-coated mild steel MIG wire.
What does the ER70S-6 classification mean for this wire?
ER70S-6 is a public classification for solid, copper-coated mild steel wire used with gas shielding. The 70 refers to the minimum tensile strength class and the S-6 indicates a solid wire with higher levels of deoxidisers, namely manganese and silicon, which help the weld pool cope with a little surface contamination.
It is a general-purpose grade for mild and many structural steels. The classification does not fix every detail, so for the exact composition, diameter range and settings, check the wire maker's data sheet, and any inspection certificate if your work requires one.
Which polarity and shielding gas does this wire need, and how does the gas change the arc?
This type of wire is used with DC electrode positive (DC+), also called reverse polarity. It can run with 100 per cent CO2 or with argon and CO2 mixtures.
CO2 gives deeper penetration but a harsher arc with more spatter. An argon-rich mixture gives a smoother, more stable arc with less spatter, and higher argon contents are generally needed for spray transfer. Wire feed speed and voltage settings differ between gases, so follow the data sheet and your machine's settings chart.
Why is there more spatter with CO2 than with a gas mixture, and can I reduce it?
Straight CO2 gives a harsher arc and more spatter than an argon and CO2 mixture, which is why argon is commonly blended in. Switching from straight CO2 to a mixture is therefore the first thing to consider.
Whatever the gas, spatter is also reduced by matching voltage, current and wire feed speed correctly, keeping the correct gas flow and coverage, using clean dry material, and keeping the stick-out right. A worn or wrongly sized contact tip can cause spatter, and a nozzle clogged with spatter disturbs the gas flow and can lead to porosity, so keep both in good condition.
Does stick-out matter, and what is a sensible length?
Yes. Stick-out is the length of wire between the contact tip and the work. A longer stick-out preheats the wire and lowers the current for a given wire feed speed, and too long a stick-out gives a poor bead shape, shallow penetration and an unstable arc.
A range of about 6 to 13 mm is commonly given for short-circuiting transfer, and 13 to 25 mm for other transfer modes. The ideal length still depends on wire diameter, joint and settings, so follow the maker's guidance and keep it consistent from weld to weld.
What should I check first if the wire feeds unevenly or stalls?
Work through the feed path. Check the reel brake, then the drive rolls (the correct groove for the wire, and pressure no higher than needed), then the liner, and finally the contact tip.
Drive roll pressure set too high deforms the wire and causes poor current pick-up, and on copper-coated wire excess pressure or knurled rolls can make the coating flake, which builds up in the contact tip. The tip bore should be only slightly larger than the wire and the tip should be replaced when worn. Steel liners suit steel wire, and a dirty or kinked liner causes drag.
Who is a 15 kg reel of MIG wire best suited to?
A 15 kg reel suits regular, high-volume welding, such as production work, mechanised cells and busy fabrication shops. A bigger reel means fewer reel changes, which helps most on a stationary bench-type feeder.
A smaller spool is usually better where the feeder has to be carried about, such as site or field work. Think about how much wire you use between changes, whether your feeder can take the size and weight, and how you will lift the reel.