Wire feed welder

I have found that if you must weld cast iron, the best way is to use DC reverse polarity.

You may look into a "buzz box" with AC/DC capability. Adding DC to a 225 amp welder is not that much more money and then you can do almost anything you want or need to do.

For the material thickness and potential stress that farm machinery sees a Millermatic 210 would be a more apropriate choice in my opinion. I have one of these machines too. It is rated a 3/8" material in a single pass. It would have no problem producing sound welds on 5/16" material. This machine is capable of outputting a high enough voltage so that you can leave the short arc mode of metal transfer and enter the globular mode , plus it is capable of running an All position gas shielded flux core wire. what these two amount to are deeper penetrating welds. For thick sections on farm machinery the gas shielded fluxcore is the way to go. It is the welding wire that is used on most heavy equipment. The only drawback to the MM 210 is the price $1100 +. Now the Ideal MIG would be a Millermatic 251, price is high though- $1700. This is the machine that I use at work. It is capable of all three modes of mig metal transfer; short arc, globular, and spray. Spray transfer is great for thick sections in the flat position. Spray transfer welds are the welds that you see on the hitch that goes under your truck.

In the end though if you are unable to fully clean your weld joints a stick welder might be a better choice. 6010 or 6011 rods can tolerate somewhat contaminated base metal. E70S-6 wire (MIG wire) can handle a small amount of rust though. No matter what though you should give it your best effort to get the metal as clean as possible. My 2 stick machines are 250 amp AC/DC Century welders, they are cheaper then Miller. I ve had them for 10 years now and no problems.If you look around you can pick up very good used stick welders for next to nothing. Who knows if you find one cheap enough you might even think about getting a HH 175 for everything 3/16 and thinner. I m not a big fan of stick so I always want some kind of MIG around for as thick of material as possible.
I would like to mention one more machine and that is it. My current MIG that I keep at my Dad's place for welding on his farm equipment is a CK Systematics 175. It is about the same size machine as the MM 210. Good machine I have had it for about 10 years now. Obviously the MM 210 is slightly better though. It is just that I ve only had the MM 210 since 12/01 and it is still my new baby. Don t want to take it out and put it through that abuse yet.

Any questions on anything above fill free to ask.

Now to you question. For welding your basic mild steel there is no real reason to use a low hydrogen rod like 7018,8018,9018, or 10018 these rods are mainly designed for using on high strength steels. The mechanical properties of 6011, 6013 ,7018AC or 7014 meet or exceed mild steel mechanical properties, and this is all you really need your electrode to do. A major reason for not using 7018 too, is the strict storage requirements of the rod. Once you break the container open on a low hydrogen rod you need to store it in a rod oven or bake it in your kitchen stove for 1 to 2 hours at 250 degrees prior to welding. The later is assuming that you are storing the rod in a dry enviroment and only using the rod on mild steel. Another reason that I ve mentioned above is arc blow 7018 contains a high (25% to 40%) level of iron powder in the rod coating this allows the rod to add more weld metal to the weld. However it also increases the intensity of arc blow. On to other rods. 6011 or 6010 is by far the most versitile rod. You can use either one on thick material, sheetmetal, out of position,to weld up a gap (open root) and on somewhat contaminated material. The later is going to apply to farm welding for sure, try welding on dirty material with 7018. these rods are also more forgiving to an inexperienced operator. The nature of there arc almost makes it impossible to have slag inclusions. This is getting quite long so so I think Ill just make a few final suggestions.

In my opinion, the best rods to have around the farm are 6011 and 7014 or 6013. In multiple pass welds, 6011 would be used for the root and then weld out with one of the others. This is assuming that the joint is 100% clean. If not 6011 all the way. Always remember though to get the base metal as clean as possible.