Welding
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Welding is a way of heating pieces of metal using electricity or a flame so that they melt and stick together. There are many kinds of welding, including arc welding, resistance welding, and gas welding. The most common type is arc welding. Anyone who is near arc welding needs to wear a special helmet or goggles because the arc is so bright. Looking at the arc will hurt your eyes, maybe forever. It is also important to cover all your skin because it can give you something like a sunburn. Hot sparks from the weld can burn any skin that is showing. One kind of welding that does not use an arc is Oxy-fuel welding (OFW), sometimes called gas welding. OFW uses a flame to heat up the metal. There are other kinds of welding that do not use an arc.
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[change] Arc Welding
Any kind of welding that uses an electric arc is a kind of arc welding. There are different processes of arc welding too— shielded metal arc welding (SMAW) is a common type. Sometimes SMAW is called stick welding. Another common one is gas metal arc welding (GMAW). It is sometimes called wire welding or metal inert gas welding (MIG welding). Another type of arc welding that is less common is gas tungsten arc welding (also known as tungsten inert gas welding or TIG welding). Before there were many kinds of arc welding, SMAW was called just 'arc welding'. Sometimes it is still called that today, but it's better to call it by it's real name instead. Arc welding heats metals by making an electric arc between the piece of metal and something called an electrode. An electrode is the part of the welder that the arc touches.
Sometimes the electrode is used up by the welding, sometimes it is not. In SMAW, GMAW, and some other kinds, the electrode is used up. The electrode is made of the same kind of metal that is being welded, and melts into the weld and becomes part of it. Because it is used up, it must constantly be fed into the weld. In SMAW, the electrode is a rod of metal with flux on it. There is more information on flux further down. The person doing the weld feeds the rod into the weld. In GMAW, the electrode is a thin wire that might be as thin as 0.635 millimeters. Really big welds might use a 4 millimeter electrode, but the biggest common electrode size is around 2 millimeters. The welding machine has a motor in it that pushes this wire into the weld.
In welding that does not use up the electrode, the metal that makes up the weld does not have any electricity flowing through it. The most common type of welding like this is called gas tungsten arc welding. It is also called TIG welding or GTAW. The electrode is made of Tungsten, so it will not melt even though it is touching an arc. The extra, or filler, metal to make up the weld is added from a thin rod.
Almost all welding uses filler metal to fill in the small gap between the metal. The extra metal helps to make the weld strong. Sometimes welds need to be made without any filler metal. Welding with no filler metal is called autogenous welding.
[change] Shielding in arc welding
All types of welding require that the hot metal have protection. If it didn't, things on the metal or things in the air could cause problems in the weld. Things on the metal that could cause problems might be rust, grease, or dirt. Oxygen in the air will cause big problems in a weld. There are two main ways to shield an arc weld, they are flux and shielding gas.
Flux can be made of many things, but is always a solid or a paste. During welding, the flux will melt and some of it will evaporate. This makes a small pocket of gas around the weld as long as there is flux. It is much easier for an electric arc to flow in this gas pocket than through normal air. Without this gas pocket the arc would not be usable. This pocket of gas prevents air, especially oxygen, from getting into the weld. Melted flux around the weld also helps clean up dirt and other things on the metal. The liquid flux will cool down and turn into a solid again. This layer of solid flux is called slag, and it will stay on the finished weld until it is removed. Slag helps protect the weld while it cools down. One type of welding that uses flux is shielded metal arc welding. Shielded metal arc welding is used to build things, like buildings or pipes. It is also used to repair things. It works best for welding steel.
Shielding gas protects the weld by being a pocket of gas around the weld. The purpose of this gas is to keep normal air out, especially oxygen. It is different from flux because there is no liquid on the weld. There is only a gas around the weld. Because there is no liquid, it will not clean up dirt and other things on the metal. This means that the metal has to be clean before it is welded. If it isn't, the dirt and other things could cause problems. The gases that are usually used are argon, helium, and a mixture that is 3 parts argon and one part carbon dioxide. Other mixtures of gases can have nitrogen, hydrogen, or even a little bit of oxygen in them. One kind of welding that uses shielding gas is gas metal arc welding. It is usually used in factories to make things.
Welding that uses flux is easier to do outside when it is windy. This is because the liquid flux is protecting the hot metal and it will not blow away. Also, the flux is always making the pocket of gas which keeps the electric arc from going out. Welding that uses shielding gas usually cannot be used outside because the gas would blow away if there were any wind.
[change] Other kinds of welding
Some kinds of welding do not use an electric arc. They might use a flame, electricity without an arc, an energy beam, or physical force. The most common type of welding that does not use an arc is called gas welding. In gas welding, a flammable(meaning it will burn) gas and oxygen are combined and burn at the end of a torch. Gas welding does not need any special shielding because a flame which is adjusted right has no extra oxygen in it. It is still important to make sure the metal is clean. The flame heats up the metal so much that it melts. When both the pieces of metal are melted at the edge, the liquid metal becomes one piece.
The other kind of welding that does not use an arc still uses electricity. It is called resistance welding. With this kind, two pieces of thin metal are pinched together and then electricity is made to go through them. This makes the metal get really hot and melt where it is pinched together. The two pieces melt together at that place. Sometimes this is called spot welding because the welding can only happen at one small place(or spot) at a time.
Forge welding is the first kind of welding that ever was used. Forge welding needs the two pieces of metal to so hot that they almost melt. Then they are beat together with hammers until they are one piece.
The other kinds of welding that do not use an arc are hard to do, and usually new. They are expensive too. Most of these kinds of welding are only done where specially needed. They might use an electron beam, laser, or ultrasonic sound waves.
[change] Energy welding
Every kind of welding needs to use energy. This energy is usually heat, but sometimes force is used to make a weld. When heat is used, it can be from electricity or from fire.
[change] Power supplies for arc welding
A lot of electricity is used in arc welding. Some kinds of welding use alternating current like the electricity that buildings use. Other kinds use direct current like the electricity in a car or most things with a battery. Almost all kinds of welding use a lower voltage than the electricity that comes from a power plant. Arc welding requires using a special power supply that makes the electricity from the power plant usable for welding. Things that a power supply does are to lower the voltage and control the amount of current. The power supply usually has controls on it that allow these things to be changed. For kinds of arc welding that use alternating current, sometimes the power supply can do special things to make the electricity alternate differently. Some power supplies do not plug into a power plug, but instead generate their own electricity. This kind of power supplies have an engine that turns a generator head to make the electricity. The engine might run on gasoline, diesel fuel, or propane.
[change] Energy for other kinds of welding
OFW uses a flame from burning fuel gas and oxygen to heat up the metal. This fuel gas is almost always acetylene. Acetylene is a flammable gas that burns very hot, hotter than any other gas. That is why it is used most of the time. Other gases like propane, natural gas, or other industrial gases can be used too.
Some kinds of welding don't use heat to make the weld. These kinds of welding can get hot, but they do not make the metal melt. Forge welding is an example of this. Friction stir welding is a special kind of welding that does not use heat. It uses a very powerful motor and a special spinning bit to mix the metals together at the edge. This seems odd because metals are a solid. this is why it takes a lot of force to do and is very hard. The energy for this kind of welding is mechanical energy from the spinning bit.
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