Chapter 8 – Cutting Processes Part 2

Typical Oxygen-Acetylene Rig

Oxygen Cylinder

Oxygen Regulator

Acetylene Cylinder

Because liquid acetone is used two special precautions must be followed when using these cylinders. First, an acetylene cylinder should always be stored and used in an upright position. Second, there is a limit to the amount of acetylene that can be drawn out of a cylinder. Because liquid acetone is used two special precautions must be followed when using these cylinders. First, an acetylene cylinder should always be stored and used in an upright position. If a cylinder is laid down the liquid acetone will flow into the valve. When the cylinder is used the liquid acetone will flow into the regulator, hose and torch. This will cause the flame to be erratic and negatively affect the torches performance. Second, there is a limit to the amount of acetylene that can be drawn out of a cylinder. If the withdraw rate is to high liquid acetone can be pulled into the valve. The maximum withdrawal rate is determined by the size of the cylinder (see torch manufactures specifications). If higher withdrawal rates are required a larger cylinder must be used or several cylinders will need to be used, using a manifold system. The manifold system allows multiple cylinders to be used at time. This is done by attaching a regulator to each cylinder. The output gas from each regulator is then coupled into a larger diameter gas line. This allows each cylinder to supply a safe amount of gas and not surpassing its withdrawal limitations. When done correctly each cylinder should supply an equal amount of gas with total volume equaling the required amount.

Acetylene cylinders should never be exposed to high temperatures or flames.

Acetylene Regulator

Check Valves and Flashback Arrestors

Check Valves Foreign material can become lodged in the valve causing it to malfunction. It is recommended that the valves be checked periodically to insure that they still operate properly.

Flashback Arrestors The mesh screen does have the negative effect of reducing gas flow. Flow rates may need to be increased to compensate. The flashback arrestors should also be checked periodically to insure that they are still functioning correctly.

Hoses

Torch Handle The universal torch handle allows the welder to switch between these different operations without having to disconnect the gas lines. This is a huge benefit in a shop where all three processes are used. The drawback of the universal handle is that there are more connections thus there is always an increased chance of gas leaking.

Integrated Torch Handle

Torch

Tip The size and type of cutting tip is determined by several different factors: Type of fuel gas – Each fuel gas burns at a different temperature and operate at different flow rates and pressures. These differences make it necessary to have different tips for cutting. Figure 10- shows different examples of tips for different fuel gases. Thickness of steel – As the steel thickness increases the flow rate of the oxygen and fuel gas must increase to provide greater heat input in order to raise the increased mass to its kindling temperature. Type of operation (scrapping, demolition, general cutting or heavy construction) – A tip that is designed for general cutting will not last very long in a scrapping or demolition operation. Tips being used for these operations are exposed to more spatter, heat and physical damage, thus the tips must be designed to withstand the abuse. Type of cutting process – The versatility of the process allows it to be used to gouge and scarving. The tips for each of these processes are different then the standard cutting tip. Condition of the steel’s surface (clean, rusted, painted or coated) – The cleaner the steel the easier and faster it is to cut. Iron oxide (rust) does not transfer heat as well as steel thus it takes longer to reach the kindling temperature. Paint and coatings (galvanized or aluminized) also slow the rise in temperature. As a safety note coatings can also produce gases and vapors that can be harmful to the welder.  

Friction lighter

Caution: Only use chain to secure cylinders Step 1: Secure cylinders   Caution: Only use chain to secure cylinders

Step 2: Crack oxygen valve

Step 3: Attach oxygen regulator

Step 4: Attach acetylene regulator

Step 5: Attach flashback arrestors on oxygen and acetylene regulators

Step 6: Attach gas hoses.

Step 7: Attach torch.

Step 8: Turn out flow pressure adjustment screw then open oxygen valve

Step 9: Turn out flow pressure adjustment screw then open acetylene valve

Step 10: Set Oxygen operating pressure (always consult manufactures recommended pressure settings)

Step 10: Set Acetylene operating pressure (always consult manufactures recommended pressure settings)

Step 11: Put on personal protective equipment

Step 12: Purge oxygen and acetylene lines Step 12: Purge oxygen and acetylene lines. Then double check pressure settings.

Step 13: Open acetylene torch valve and light torch.

Step 14: Open torch oxygen valve Step 14: Open torch oxygen valve. Adjust acetylene and oxygen valve until a neutral flame is achieved.

Torch Shut Down Step-By-Step

Step 1: Turn off torch acetylene valve (consult manufactures recommendations)

Step 2:Turn off torch oxygen valve first (consult manufactures recommendations)

Step 3: Close Oxygen and Acetylene cylinder valves.

Step 4: Purge oxygen and acetylene lines.

Step 5: Turn out flow pressure adjustment screws.