Butt welding is a welding technique used to connect parts which are nearly parallel and don't overlap. It can be used to run a processing machine continuously, as opposed to having to restart such machine with a new supply of metals.
Usually, the seams (or abutment sections) are cleaned and prepared, and set on an automated piece of equipment which then welds the two materials together. Afterward, the material is usually ground down to a smooth finish and either sent on its way to the processing machine, or sold as a completed product.
This type of weld is usually accomplished with an arc or MIG welder, but can also be accomplished by brazing. With arc welding, after the butt weld is complete, the weld itself needs to be struck with a hammer forge to remove slag (a type of waste material) before any subsequent welds can be applied. This is not necessary for MIG welds however, as a protective gas removes any need for slag to appear. Another advantage with a MIG welder is that a continuous copper wire is fed onto the stock, making the weld virtually inexhaustible. [1]
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Butt welding can also be achieved through traditional blow torches in the most common form of butt joints, a process that uses some variety of flux, usually a tin based solder and precise hand eye coordination that is common for hand made boxes of copper, brass, and silver.
The process consists of 2 desired strips of metal that are lined with flux that is lightly dried with a blowtorch until it's a sticky consistency, followed by cutting a strip of solder that is generally 20% of the full joint's size. Applying heat gently makes the gel like flux now appear white and powdery which now is primed to be welded in which the blow torch is arched so that the "heat cone"; the bluest and hottest part of the flame, is now directly upon the sauter melting the joints together evenly.
The joint is then cooled and cleaned in a solution of sulphuric acid diluted in 20 parts water – commonly known as "pickle" – to remove imperfections. Sanding and polishing then achieves the desired finish.
EN 1993-1-8, which covers the design of joints in the design of steel structures, defines a set of provisions for welding structural steel.