Chapter 7 Review Questions & Answers Flashcards
What elements make up all hydrocarbons?
The gases are made up of hydrogen (H) and carbon (C) atoms.
What are the separate parts that make up an oxyacetylene flame?
Primary combustion and secondary combustion.
Why is a neutral flame the most commonly used oxyacetylene flame?
It adds nothing to the metal.
A neutral oxyacetylene flame burns at approximately what temperature?
5589°F (3087°C).
What are methylacetylene-propadiene fuel gases used for?
As fuel gases for oxyfuel cutting, heating, brazing, metallizing, and, to a limited extent, welding.
Which fuel gas has the strongest odor and is easiest to detect?
MPS at 100 ppm.
What is the major advantage of using propane or natural gas?
The major advantage of propane and natural gas is that they are often used for heating the shop. Therefore, a supply of these gases is readily available.
Use Table 7-6 to determine which fuel gas would be best for cutting material thicker than 5 in. (125 mm).
MPS.
Use Table 7-6 to determine which fuel gas would be best for powdered metallizing.
Acetylene.
Use Table 7-6 to determine which fuel gas would be best for stack cutting.
MPS.
What two major safety problems does hydrogen present?
First, hydrogen has no smell, which makes it difficult to detect leaks. Second, the molecule is extremely small so that it leaks easily.
What metals can be cut with the oxyfuel gas process?
Low-carbon steels with carbon contents up to 0.3%, nonferrous metals, titanium, zinc, and magnesium.
State one advantage of owning a combination welding and cutting torch as opposed to just having a cutting torch.
More flexibility because a cutting head, welding tip, or heating tip.
State one advantage of owning a dedicated cutting torch as compared to having a combination welding and cutting torch.
Dedicated cutting torches are usually longer and have larger gas flow passages than the combination torches. The added length of the dedicated cutting torch helps keep the operator farther away from the heat and sparks and allows thicker material to be cut.
What is a mixing chamber?
It is used to mix the gases.
Where is the mixing chamber located?
The mixing chamber may be located in the torch body or in the tip.
Define the term equal-pressure torch.
Equal-pressure torches because the gases must enter the mixing chamber under the same pressure.
How does an equal-pressure torch work?
The mixing chamber is larger than both the gas inlet and the gas outlet.
How does an injector-type mixing chamber work?
The injector allows the oxygen to draw the fuel gas into the chamber even if the fuel gas pressure is as low as 6 oz/in.2 (26 g/cm2).
State the advantages of having two oxygen regulators on a machine cutting torch.
One for the preheat oxygen and the other for the cutting oxygen stream.
Why are combination welding and cutting torches considered to be more versatile?
Combination torch sets are often used in schools, automotive repair shops, auto body shops, and small welding shops or with any job where flexibility in equipment is needed.
What determines the amount of preheat flame requirements of a torch?
The amount of preheat flame required to make a perfect cut is determined by the type of fuel gas used and by the material thickness, shape, and surface condition.
Why are some propane and natural gas tips made with a deep, recessed center?
The flame burns at such a slow rate that it may not stay lit on any other tip.
What types of tip seals are used with cutting torch tips?
Metal-to-metal and fiber packing.
If a cutting tip sticks in the cutting head, how should it be removed?
Tap the back of the head with a plastic hammer.
What do the two pressure gauges on a regulator show?
One pressure gauge shows the working pressure, and the other indicates the cylinder pressure.
What is the material used to manufacture oxygen cylinders?
High-strength metal slug.
How are cylinders hydrostatically tested?
Cylinders are hydrostatic tested by filling it with water, lowering it into a water-filled tank and pressurizing the water to a pressure 150% higher than its designed working pressure. Water is used for the test because liquids are noncompressive, meaning their volume does not change even under high pressures.
What liquid is used inside an acetylene cylinder to absorb acetylene?
A porous material and acetone.
LP fuel tanks cannot be filled more than _____%.
80%.
What can the improper handling of cryogenic liquids cause?
Improper handling of these liquids can cause serious injury or death.
Why does the high-pressure gauge on a regulator not always indicate the amount of gas in the cylinder?
It shows cylinder pressure only; cylinders containing liquefied gases, such as CO2, propane, and MPS, must be weighed to determine the amount of gas remaining.
Why must the gas pressure be released, and the adjusting screw backed out when welding is finished, and the cylinders are turned off?
This is required both by federal regulation and to prevent damage to the diaphragm, gauges, and adjusting spring if they are left under a load.
What should be done to the valve packing if the valve knob does not turn freely after it has been tightened to stop a leak?
If it does not, or if the leak cannot be stopped, replace the valve packing.
What should be done if the torch flashes back?
Close the oxygen valve at once and then close the fuel valve.
What is the purpose of a reverse flow valve?
It is to prevent gases from accidentally flowing through the torch and into the wrong hose.
What type of piping can be used for a manifold system?
Piping for the high-pressure side of a manifold must be steel, stainless steel, or alloyed copper. Piping for the low-pressure side, except acetylene, can be stainless steel, copper (type L or K), brass, steel, or wrought iron. All acetylene piping must be steel or wrought iron.
How can a hose be checked for leaks?
To test a hose for leaks, adjust the regulator to a working pressure with the torch valves closed. Wet the hose with a leak detecting solution by rubbing it with a wet rag, spraying it, or dipping it in a bucket. Then, watch for bubbles, which indicate that the hose leaks.
Why is the oxygen valve turned on before starting to clean a cutting tip?
Turn on a small amount of oxygen. This procedure is done to blow out any dirt loosened during the cleaning.
Why is a slight forward torch angle helpful for cutting?
A slight forward torch angle helps the flame preheat the metal, keeps some of the reflected flame heat off the tip, aids in blowing dirt and oxides away from the cut, and keeps the tip clean for a longer period of time because slag is less likely to be blown back on it.
Why should cans, drums, tanks, or other sealed containers not be opened with a cutting torch?
The heat, sparks, and oxygen cutting stream may cause even nonflammable residue inside to burn or explode.
Why is the torch tip raised as the cutting lever is depressed when cutting a hole?
By raising the torch tip away from the metal, the amount of sparks blown into the air is reduced and the tip is kept cleaner.
Why are the preheat holes not aligned in the kerf when making a bevel cut?
If the preheat flame is directed at the edge, it will be rounded as it is melted back.
What is the best way to set the oxygen pressure for cutting?
While holding the cutting lever down, increase the oxygen regulator pressure slightly. Readjust the flame, as needed, to a neutral setting by using the oxygen valve on the torch.
Why is it important to have extra ventilation and/or a respirator when cutting some used metal?
Some metals release harmful oxides when they are cut.
What factors regarding a cut can be read from the sides of the kerf after a cut?
Preheat flame, cutting speed, and oxygen pressure.
What is hard slag?
There is 30% to 40% or more unoxidized iron in hard slag.
Why is it important to make good-quality cuts?
Poor-quality cuts require more time to clean up than is needed to make the required adjustments to make a good weld.
Describe the methods of controlling distortion when making cuts.
One method involves making two parallel cuts on the same plate at the same speed and time. The second method involves starting the cut a short distance from the edge of the plate, skipping other short tabs every 2 ft (0.6 m) to 3 ft (0.9 m) to keep the cut from separating.
List three things that can become a problem when cutting and affect your ability to make a quality cut.
Changing positions, sparks, hot surfaces, tip cleaning, and blowback.
How does cutting small-diameter pipe differ from cutting large-diameter pipe?
On small-diameter pipe, usually smaller than 3 in. (76 mm), the torch tip is held straight up and down and moved from the center to each side. For large-diameter pipe, 3 in. (76 mm) and larger, the torch tip is always pointed toward the center of the pipe.
