Welding Midterm
One BTU is defined as ____
the amount of heat required to raise one pound of water one degree Fahrenheit
Why is an inert shielding gas required for GTA welding?
To keep the air away from the hot tungsten and molten weld metal.
The useful life of a ceramic nozzle is affected by the _____________.
current level and proximity to the work
____ electrodes have a current-carrying capacity similar to that of pure tungsten, and may be used for both AC and DC welding currents.
Cerium tungsten
____ is magnetic and has very slight solid solubility, less than 0.02%, of carbon.
Ferrite
Stainless steels rely on ____________________ for their resistance to corrosion.
Free chromium
____ has the poorest heat resistance and electron emission characteristic of all the tungsten electrodes.
Pure tungsten
Tungsten electrodes that contain elements such as lanthanum or yttrium are referred to as _____.
Rare earth tungstens
Light that bounces off of a wall or ceiling is referred to as_________.
Reflected
____ is a gas that is produced by the ultraviolet light in the air in the vicinity of welding operations.
Ozone
____________________ is a metal used in large quantities in the manufacture of brass and is found in brazing rods.
Zinc
What is the difference between a tool with external grounding and a double-insulated tool?
A tool with external grounding has a wire that runs from the housing through the power cord to a third prong on the power plug. When this third prong is connected to a grounded, three-hole electrical outlet, the grounding wire will carry any current that leaks past the electrical insulation of the tool away from the user and into the ground. In most electrical systems, the three-prong plug fits into a three-prong, grounded receptacle. The green (or green and yellow) conductor in the tool cord is the grounding wire. Never connect the grounding wire to a power terminal. A double-insulated tool has an extra layer of electrical insulation that eliminates the need for a three-pronged plug and grounded outlet. Double-insulated tools do not require grounding and, therefore, have a two-prong plug. In addition, double-insulated tools are always labeled as such on their nameplate or case.
Define annealing.
Annealing, frequently referred to as full annealing, involves heating the structure of a metal to a high enough temperature, slightly above Ac3, to turn it completely austenitic. After soaking to equalize the temperature throughout the part, it is cooled in the furnace at the slowest possible rate. On cooling slowly the austenite transforms to ferrite and pearlite. The metal is now its softest with small grain size, good ductility, excellent machinability, and other desirable properties.
____ is the nonmagnetic form of iron and has the power to dissolve carbon and alloying elements.
Austenite
It is not safe to carry _________________ or _____________ in any pocket while welding because they can catch fire or explode.
Butane lighters, matches
How is a metal's hardness reduced?
By annealing
____________________ is a by-product of the natural gas industry. It is removed from natural gas as the gas undergoes separation for purification or refinement.
Helium
Explain how hydrogen is used in shielding gases, and why it is restricted to stainless steels.
Hydrogen is not an inert gas and is not used as a primary shielding gas. However, it can be added to argon when deep penetration and high welding speeds are needed. It also improves the weld surface cleanliness and bead profile on some grades of stainless steel that are very sensitive to oxygen. Hydrogen additions are restricted to stainless steels because hydrogen is the primary cause of porosity in aluminum welds. It can cause porosity in carbon steels and, in highly restrained welds, underbead cracking in carbon and low alloy steels.
Most paints containing ____________________ have been removed from the market; however, some industries, such as marine or ship applications, still use them.
Lead
The symptom of acute exposure to high concentrations of cadmium fumes is ____.
Lung Irritation
____________________ is the hardest of the transformation products of austenite.
Martensite
Argon and helium are _________________________ gases, which means they will not combine chemically with any other material, and will not affect the molten weld pool in any way.
Noble
____________________, when added in percentages of up to 0.6 percent to tungsten, improves its current-carrying capacity.
Thorium oxide, ThO2
____ is the property that allows a metal to withstand forces, sudden shock, or bends without fracturing.
Toughness
____ fire extinguishers are used for electrical fires.
Type C
The smallest identifiable group of atoms is the ____________________.
Unit Cell
If a nut or bolt is too tight to loosen with a wrench, ____.
Use a longer wrench
