Some thoughts on basic metal working

Discussion in 'Back to Basics' started by Tully Mars, Jan 28, 2015.


  1. kellory

    kellory An unemployed Jester, is nobody's fool. Banned

    We use them as well.
     
  2. KAS

    KAS Monkey++

    can someone please explain a/c ,d/c welding ... difference and advantages and disadventages...
     
  3. Airtime

    Airtime Monkey+++

    Direct current (DC) is the kind of electrical current you get from a battery. There is a positive terminal and a negative terminal and current flows from the positive to the negative.

    Alternating current (AC) is the kind of electricity you generally get from generating machinery where one terminal is positive, then it switches to negative, then positive then negative, etc. This is the kind of power that comes through the grid. One of the great things about AC is the voltages can be increased way up or down with transformers. Can't do that easily with DC.

    Now, here is the interesting thing about current, it is actually electrons flowing through a wire, much like water flowing through a garden hose. HOWEVER, electrons have a negative charge, so when they are moving through a wire left to right, "current" is considered as flowing right to left. In other words, electron flow is the flow of negative current, or current flows opposite of electron flow. Why does this matter for welding?

    With the very high currents in welding, often hundreds of amps, electrons are busting loose from one metal item and jumping to the other metal item. As they do this, the metal giving up the electrons tends to melt faster. Some of the molten metal will even get carried along with the electron flow. So, if the base metal is negative and the welding electrode is positive (often called reverse polarity) current flows from the electrode to the base metal. However that means electrons themselves are actually flowing the other way and will cause base metal to melt faster and hence deeper, resulting in more weld penetration.

    Alternatively, with electrode negative (often called straight polarity) DC welding, current flows base to electrode but the electron flow will be from the electrode to the base metal. This melts the electrode welding rod/wire faster and there will be more deposition of the welding electrode into the weld.

    AC welding basically splits the difference with the electrode being positive half the time and negative half the time. The simplist/cheapest welders are just AC as they don't need the very high current capable diodes to convert AC into DC. There are some fancy welders like TIG welders that even let you control the percentage of time the electrode is negative vs positive. There are welding rods (sticks) that are designed with different coatings to work better with AC, DC reverse and DC straight polarities.

    That help?
    AT
     
    Last edited: Feb 4, 2015
    Tully Mars and kellory like this.
  4. Tully Mars

    Tully Mars Metal weldin' monkey

    Kell, is your buzzbox one of the Lincoln AC225 "Tombstone" welders by chance? If so, they make a GREAT little TIG welder for steel with a little bit of work. A person can get a scratch start TIG torch, a bottle of argon with a regulator, the required collets,holders and tungsten and you're pretty well set. If interested I can help with what/where to get and the set up.
     
    KAS and kellory like this.
  5. kellory

    kellory An unemployed Jester, is nobody's fool. Banned

    I will check it's specs
     
  6. Tully Mars

    Tully Mars Metal weldin' monkey

    Airtime and kellory like this.
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