Chapter 36 Flashcards
Oxyfu gas welding
Welding processes that use the flame produced by combustion as a source of heat. Torch is used for this process
The torch has how many reactions
2
First reaction?
Oxygen and acetylene react to produce carbon monoxide and hydrogen. Occurs near the tip of the torch and generates intense heat
Second stage?
Combustion of CO and H2 and occurs just beyond the first combustion zone. Second stage produces a flame having two distinct regions, a light blue inner cone and a darker blue outer cone.
Putter flame?
Outer envelope of the flame preheats the metal and shields it from oxidation
Neutral flame.
More oxygen to acetylene. Most welding is done with a neutral flame, less chemical effect
Oxidizing flame
A higher ratio of oxygen produces an oxidizing flame, usually has a crackling sound. Flame temperature is not that great.
Mapp
Methyl acetylene propadiene (mapp) is an alternative for acetylene. Second hottest gas’s.
Propylene
Alternative gas, consists of propane and ethylene
Larger tip of flame
Greater heat input
Oxyfuel welding is primarily
Fusion welding
Filler metal
Can be added In The form of solid metal or rods.
Fluxes
Can be used to clean surfaces and remove contaminating oxide. Gaseous shield from flux can prevent further oxidation.
Issues with welds?
Heat source is not concentrated and can lead to distortion
Oxyflame pros?
Low carbon steel is typically welded. Portable and I expensive, extremely versatile.
Pressure gas welding
Uses a gas flame and then forces together the materials. This is a form of solid state welding. Coalescences is produced by pressure.
Arc
A concentrated heat source that can produce temperatures that’s re very high.
Electrodes
Carbon rod is one electrode, the work piece is the other.
Direct current electrode negative or straight polarity
The electrode is made negative and direct current is used. Fast melting of electrode and a shallow molten pool
Direct current electrode positive or reverse polarity
The work is made negative and the electrode positive. Metal deposition is lower, but deeper penetration happens.
Alternating currents and variable polarity
Alternates between dcen and dcep.
Consumable electrode processes
In one group of arc welding processes the electrode is consumed. No metal is needed to fill.
No consumable electrode processes
A tungsten or carbon electrode is used, but not consumed, except by slow vaporization. A delegate metal wire is required to supply filler metal.
Types of consumable arc welding
Shielded metal arc welding and gas metal arc welding
Shielded metal arc welding or stick welding
Versatile and low cost.
Shielded metal arc welding contains a wire with a coating that does:
Vaporize to protect the atmosphere. Provides ionized elements to stabilize the arc. Act as a flux to deodorize and remove impurities. Provide a protective slag to accumulate purities. Add alloying elements for strength. Add additional fillers. Affect arc penetration. Influence shape of weld bead.
How to shielded metal:
Operator touches the electrode to the workpiece and raises it to a stable state
Best used for what materials: shielded metal welding
Ferrous metals: carbon steels, alloy steels, stainless steels, and cast irons.
Gas metal arc welding
The electrode becomes uncoated, no flux is needed. Shielding is provided by the gas, no Slags or fluxes needed. Can be used for all metals.
Shielding gases for gas arc welding?
Have an effect on stability. Helium produces hottest arc and deepest penetration. CO2 is the opposite. Argon is heavier and requires lower flow rates. Helium is light and requires higher flow rates.
Pros of gas welding?
Fast and economical. Accounts for more than half of all weld metal deposition.
Advanced gas welding
Uses a second power source to preheat the filler metal
Gas tungsten arc welding knoe as he liard welding. Nonconsumable.
A nonconsumable electrode provides the arc but not the filler metal. Inert gas flows through the electrode holder to provide a shield.
Gas tungsten welding pros?
Most versatile of arc welding processes. No cleaning or slag must be removed. Many common metals and alloys can be welded.
Gas tungsten cons
Costs more and is slower, but produces a high quality weld.
