Equipment and Materials
Cutting-torch, steel cutting, acetylene, propane, gasoline, hydrogen, demolition, scrap metal, rail cutting, underwater cutting, salvage, cutting torches, arc cutting, arc cutting torch, plasma arc cutting torch, cutting tip, cutting kit, lasers, industrial lasers, CO2 laser, high power lasers, high power CO2 lasers, laser cutting, lasercutting machinery, cutting tips, cutting links, cutting problems needing answers: these are some of the items presented here for the benefit of interested readers.
What is in here for me?
Why a Cutting-torch is a useful tool for metal construction preparation or for demolition? Because its principle of operation is simple, the technique can be learnt quickly, and its implementation isinexpensive if compared to mechanical cutting.
Why some metals do not lend themselves to torch cutting? Because they are rich in elements that prevent ready oxidation.
Is there a need for further preparation before welding of cut surfaces? Not really, if cutting is well performed.
Several techniques, derived from those developed for welding, permit using a Cutting-torch for cutting metals, even ofconsiderable thickness, as needed in preparation for further construction or, at the other end, for demolition.
In a sense it could be said that the process of cutting is the exact opposite of welding: while welding consists in uniting together two separate metal pieces by progressive local melting, cutting is the progressive severing (in two or more sections) of one piece by local heating and burningaway the metal.
In this presentation the main aspects of metal cutting with a Cutting-torch will be addressed for three most important methods, that is cutting using oxyacetylene flame, arc-cutting (with its variant, namely plasma-cutting) and laser cutting.
Tip!: Metal cutting by Cutting-torch is made possible by the tendency of certain metals to become readily oxidized under certain localconditions and burnt away by a powerful stream of oxygen gas.
The Cutting-torch using the oxyacetylene flame is a special piece of equipment designed to implement a process whereby the chemical reaction of a pure oxygen stream with steel at elevated temperature produces local separation along the line of advancement.
A small area must first be heated to the temperature of selfsustained ignition (less than iron melting point), then a concentrated stream of high purity oxygen is directed on the same spot rapidly changing the metal into its oxides which melt and are removed by the force of the impinging stream along with any present molten metal drops.
Tip!: For best quality cutting effects it is most important that the oxygen used be of high purity, at least 99.5%.
Itshould be noted that not all materials are easily sectioned by these methods: outstanding in this group are aluminum and copper which cannot be cut. However, for most of the constructional steels, these may be the most economical ways to perform manual or automated cutting according to lines or patterns as needed. Special variations can be used with special powders for stainless steels or otherdifficult to cut materials.
The Cutting-torch used is different from the customary welding torch (see Gas Welding Equipment): in one design the tip presents a crown of ports that supply the gas mixture employed to obtain the preheating flame, and a central channel through which the powerful pure oxygen stream is made to impinge on the heated spot to provide rapid oxidation and removal of oxides andmetal drops.
Once started the exothermic chemical reaction is self sustaining along the thickness of the metal (if the advancement speed of the Cutting-torch is not excessive), while the preheating flame is needed to bring new surfaces to ignition temperature. Critical to the success of the operation is the fact that iron oxides melt at lower temperature than the metal itself.