Oxyfuel cutting NCCER Welding Unit 2

intro Oxyfuel cutting is a process that uses the flame and oxygen from a cutting torch to cut ferrous metals. Flame is produced by mixing a fuel gas with pure oxygen. The flame heats the metal and then a flow of oxygen is used to cut the metal which produces dross. (The cut metal fragments) Fast and easy way to cut metal…Not the most precise

Protective equipment Always use safety cutting glasses with the proper shade. (shade filter of at least 3 to 6) Wear protective clothing…sleeves, leathers, and gloves Always wear 8’’ or taller high top safety boots.

Fire/explosion prevention Ake sure any flammable material in the work area is moved or shielded from the source of an open flame. ‘ Make sure fire extinguishers are in working order and located in an well seen area. Before cutting tanks or barrels, check to see if they have contained any flammable material. Always clean and fill with water, or purge them with a flow of inert gas to displace any oxygen.

Ventilation Always perform cutting operations in a well ventilated area. If the material contains any kind of mercury, lead, or zinc coating always wear an approved full face, supplied air respirator. This will prevent you from breathing toxic fumes.

Oxygen cylinders Oxygen is a colorless, odorless, tasteless gas that supports combustion. Combined with burning material, pure oxygen causes a fire to flare and burn out of control. Oxygen is stored at more than 2,000 psi in hollow steel cylinders. These cylinders must be tested every 10 years.

Acetylene cylinders Acetylene gas is a compound of carbon and hydrogen and is lighter than air. It is formed by dissolving calcium carbide in water. It has a strong, garlic like odor which is added so the gas can be detected. It is very unstable and will explode easily under pressure, this is why it must never exceed 15 psi when in a gaseous form. When combined with oxygen, acetylene creates a flame that burns hotter than 5,500 degrees.

Acetylene cylinders Because of its explosive nature, acetylene cannot be stored above 15 psi in a hollow cylinder. To solve this problem, acetylene cylinders are filled with a porous material that creates a solid, instead of a hollow cylinder. Acetylene cylinders must always be stored in the upright position and if one is ever tipped over, stand the cylinder upright and wait at least one hour before using. Acetylene cylinders have safety fuse plugs in the top and bottom of the cylinder that melt at 220 degrees. These prevent the tank from exploding.

Other gasses used Many fuel gasses other than acetylene can be used in oxyfuel cutting. They include natural gas, methylacetylene propadiene(MAP gas), propylene, and propane. Flames are not as hot, but may be cheaper or safer to use. MAP gas is mixture of acetylene and propane. Propylene mixtures are stable and shock resistant and burn at around 5,193 degrees.

Liquid fuel gas cylinders Liquified fuel gases are shipped in hollow steel cylinders. Can hold up to 225 pounds of liquid fuel gas. If high volumes of gas are removed from a liquid fuel gas cylinder, the pressure will drop, and the temperature of the cylinder will also drop. A ring of frost can sometimes form around the base of the cylinder.

Regulators Regulators are attached to the cylinder and reduce the pressure from the tank before it gets to the torch handle. Also helps maintain a steady flow of gas from the cylinder. Oxygen regulators have green markings and always have right handed threads. Will read up to 3000 psi on its high pressure gauge. Acetylene regulators are red and have left hand threads. A v-notch is cut on the nut for a reminder. The high pressure gauge will read up to 400 psi.

Cutting torches 2 types… One piece cutting torch and a combination torch Combination torch is what we use. Consists of a cutting torch attachment that connects to a welding torch handle. The fuel gas and oxygen valves are on the torch handle. These are used in light to medium duty jobs.

Cutting tips The cutting tip to be used depends on the base metal thickness and fuel gas being used. Special tips are also made for gouging or grooving. Rivet cutting heads are used to cut of rivets, bolts, and nuts.

Motor driven equipment A variety of fixed and portable motorized cutting equipment is available for straight and curved cuts. CNC machines like the Torchmate are used to cut metal using a computer driven system. Portable track cutting machines (track burners) can be used in the field for straight or curved cuts and beveling.

Testing for leaks As a safety precaution, always check equipment periodically for leaks before using. The torch should be checked before every use. We can use soapy water to check for leaks, if bubbles form… then a leak is present.

Oxidizing flames There are 3 types of oxyfuel flames: Neutral flame- burns equal amount of oxygen and acetylene. Used for all cutting operations Carburizing flame- has a white feather caused by excess fuel. Length of feather depends on amount of excess gas. Oxidizing flame- has an excess of oxygen, inner cone is shorter and much bluer in color, more pointed than a neutral flame

Shutting down the torch Once finished cutting, always remember to shut down the torch for safety reasons. First step in shutting down is to always close the fuel gas and oxygen valves. Once everything is shut down, always wrap up the hose to eliminate any tripping hazards.

Changing cylinders Once cylinders become to low to use, we should prepare them to be changed out. Remove the regulator and replace the cylinder cap on top of the cylinder. Mark MT(empty) and the date near the top of the cylinder using soapstone.

Cutting thin steel Thin steel is 3/16” thick or less. Distortion can be caused when cutting due to the heat and thinness of the steel. To minimize distortion, move as quickly as you can without loosing the cut. Hold the torch tip so that it is traveling in a 15 to 20 degree angle.

Washing Washing is a term used to describe the process of cutting out bolts or rivets. Washing tips can also be used to remove items such as blocks, angles, or channels that are welded onto a surface.

Gouging Gouging is the process of cutting a groove into a surface. Uses a special kind of cutting tip. Not as effective as washing tips but