Chapter 7 Flame Cutting Flashcards
What is the kindling temperature of a material?
The temperature at which rapid oxidation can begin.
What is rapid oxidation?
Combustion.
What is OFC?
OFC or oxyfuel gas cutting is a group of oxygen cutting processes that use heat and a high pressure stream of oxygen to cut metal.
What is a good oxyfuel cut?
A cut that is straight, square and requires little to no post cut clean up.
Name the three types of OFC processes used in industry.
Manual, Mechanized, Automatic.
Why are flame characteristics of different gases hard to measure?
Different flame conditions will affect the temperature making it hard to measure accurately.
What are the 3 conditions of a flame?
Carbonizing (carburizing) - too much fuel; Oxidizing - too much oxygen; Neutral - equal amount of oxygen and fuel.
What are the 5 main fuel gases used in Oxyfuel Cutting?
Acetylene, MPS (Methylacetylene-Propadiene), Natural Gas, Propane, Propylene.
They are all hydrocarbon gases.
Why is hydrogen not commonly used?
Hydrogen has no smell and can leak easily. The flame is invisible and the gas is very expensive.
What are the two separate chemical reactions in oxyfuel cutting gases?
- Primary combustion (inner cone of flame); 2. Secondary combustion (outer envelope [feather]).
What are the final products of all clean-burning hydrocarbon flames?
Water Vapor (H²O) and Carbon Dioxide (CO²).
What is the combustion rate (rate of propagation) of a flame?
The rate of speed at which the flame burns, measured in feet per second or meters per second.
What can cause the burn rate to increase or decrease?
Oxygen. More Oxygen increases the burn rate; less decreases the burn rate.
What combustion rate of an Oxyfuel can be more prone to backfire or flashback?
Higher.
How is Acetylene produced?
Mixing calcium carbide with Water in an acetylene generator.
What is the smell of Acetylene?
A strong garlic smell.
When is acetylene unstable?
At pressures above 30 psig or temperatures above 1435°F (780°C).
MPS gases are mixtures of what gases?
Propane, butane, butadiene, methalyne and propadiene.
What is the role of a piccolo tube?
Helps keep gases mixed during use by agitating the liquid in a cylinder.
Why are MPS gases better for preheating than Acetylene?
Their secondary combustion (outer envelope) produces twice the amount of heat than acetylene.
Why are Natural Gas and propane frequently used more in the welding industry?
Most shops use natural gas or propane for heating so these gases can be piped through the shop easily.
What metals can Oxyfuel cutting NOT be used on?
Non-reactive metals - stainless steel, cast iron, brass, copper, aluminum. Most nonferrous metals.
What nonferrous metals can be used in oxyfuel cutting and why are they seldom used?
Titanium, zinc and magnesium can be cut but require extensive post cut clean up and may give off excessive hazardous fumes.
What is the metal most used for oxyfuel cutting and why?
Low carbon steels (0.3% or less carbon) because there is little to no oxide left on metal making for easy post cutting clean up and can be easily welded.
What are the two types of hand torches?
- Combination torch; 2. Cutting torch.
What are the benefits of a combination torch?
A combination torch can be used for preheating, cutting, or welding by switching the tip.
What must happen to oxygen and the fuel gas before they leave the tip of a torch to create the flame?
They must be completely mixed.
What are the two methods used to mix gases in a hand torch?
- Mixing chamber; 2. Injector chamber.
What are mixing chamber torches known as and why?
They are known as equal pressure torches because the gas and oxygen enter the chamber at the same pressure causing turbulence, mixing the gases thoroughly.
When does an injector chamber torch have to be used?
Injector chamber torches must be used if the gas supply is low pressure.
What are cutting tips made of?
Copper alloy. Chrome - chrome plating prevents splatter from sticking to the tip, thus prolonging its usefulness.
What is a standard or high speed tip used for?
Straight cutting.
How can you determine the thickness of metal a torch tip can cut?
The diameter of the center cutting orifice determines the thickness of metal that can be cut with that tip.
Is there a standard numbering system for oxyfuel cutting tips?
No. Each manufacturer uses its own system.
What tool can be used to determine the cutting capabilities of a torch tip?
Tip cleaners.
Why must tips only be used with the fuel they were designed for?
Certain tips for different fuels have a different number of preheating holes. Without the proper number of preheating holes, enough heat might not be produced to heat the metal.
What is the role of a pressure regulator?
Reduce the pressure to the proper working pressure and maintain a constant working temperature through changing flow rates.
What can be used to detect leaks in torches and hoses?
Leak detection solution. Will bubble where there is a leak.
How does a regulator work?
A regulator works by holding the forces of both sides of a diaphragm in balance.
What are the two gauges on a regulator?
Working pressure gauge - shows pressure at regulator; Cylinder pressure gauge - shows pressure of cylinder.
What is line pressure drop?
The drop of pressure from the regulator to the torch that occurs in the line from resistance to the gas flow.
Tips for better cut with a hand torch?
Be a SLUT! S- steady yourself in a comfortable position; L - lean your torch 5°-10° for a slight angle; U - utilize torch guides or your gloves for stability; T - Travel at an appropriate speed for thickness of metal.
What is a coupling distance?
The distance from the inner cone of a flame to the workpiece
What should be done when piercing a plate to start a cut?
Increase your coupling distance when depressing the cutting lever to avoid blowing slag back onto the tip.
What is drag?
The distance by which the bottom of a cut lags behind the top.
What causes the top edge of a plate to be melted and rounded off with excessive hard slag to remove?
Too much preheat flame.
What causes a melted top and gouges in a metal plate?
Too slow travel speed.
What happens when you travel too fast while torch cutting?
An incomplete cut.
What are the characteristics of a good oxyfuel torch cut?
Square top edge, smooth face, slightly slanted backwards drag lines, square bottom edge, little to no slag post cut clean up.
Why do most mechanized cutting equipment have two oxygen supplies and regulators?
Separate oxygen systems allow for better control of the preheating flame and cutting flame.
What are the two types of slag seen on oxyfuel cuts?
- Soft slag - very porous and brittle and can easily be removed
- Hard slag - 30-40% or more unoxidized iron making it very difficult to remove.
Where should a hole be started on sheet metal?
The hole should be started near the center and work around the inner circumference of the hole.
What is it called when the metal bends or twists out of shape from being heated?
Distortion.
What are two methods for controlling distortion?
Making two parallel cuts on the same plate at the same speed and time; Start cut a short distance from the edge of the plate periodically leaving small tabs.
What happens when cutting pipe and what can be done?
Sparks shooting out at the end nearest you. Plug up the end of the pipe closest to you or stand to one side of the material being cut.
What is the difference between oxyfuel cutting and oxyfuel gouging?
Oxyfuel cutting goes through the metal where gouging does not.
What is oxyfuel gouging used for?
Preparing grooves in preparation for welding or to remove defects in welds to make repairs.
How are gouging tips different from cutting tips?
Gouging tips have a slight bend 1/3 of the way down.
What can be done to increase the depth of a gouge?
Increase the tip to work angle.
What sound does a backfire make?
A loud pop.
What sound does a flashback make?
A high-pitched whistle.
Which torch has a longer body?
Dedicated cutting torches - allows operator to be further away from heat and sparks.
Why does a technician need to be called when a flashback occurs?
Usually indicates there is something wrong with the system.
What is a reverse flow valve?
Ensures that gases cannot accidentally flow from the torch to the wrong hoses.
What is a flashback valve?
Usually attached in-between the hoses and the body of the torch. It acts as a reverse flow valve and will also stop the flame of a flashback.
What is a Siamese hose?
Hoses that are molded together in one piece.
If Siamese hoses are not used, what needs to be done?
They must be taped, but not entirely to reveal what type of gas is in the hoses.
What should be done when hoses are not in use?
Gases should be turned off and the pressure bled from them.
When lighting a torch, how can you determine there is too much oxygen in the preheating flame?
There is a visible oxygen line in the flame when the cutting lever is not depressed.
What is a chill plate?
Thicker piece of metal clamped to thin metal to absorb heat.
What is an example of slow oxidation?
Rusting.
