OXY-FUEL WELDING AND CUTTING

Transcription

1 OXY-FUEL WELDING AND CUTTING The xyfuel system is an auxiliary technique t welding develped since 1903 and used t date in many industrial applicatins. Flame cutting is used t make the edges f the wrk pieces and fr sheet cutting (films f metal frm 1 t 12 millimeters thin), pipes, steel bars, and ther ferrus elements in repairs, being versatile t handle different materials.

2 These systems can easily cut ferrus materials fr mre than 200 mm (8 inches) and is a ne f the preferred tls fr manual cutting f thick steel (mre than 38 mm r 1 ½ ), The system f xyfuel cnsists f: Tanks r cylinders with fuel and cmburent (the use f these tw highly inflammable gases and high pressure requires specific safety standards f maintenance, transprt and strage), pressure regulatrs (which reduce the pressure in the tank frm 150 atmspheres t pressures frm 0.1 atmspheres t 10 atmspheres) cutting trch (which mixes the gases), Return valves (which allw passage f gas in ne directin nly) Hse (leading t the gases frm the tanks t the trch and may be rigid r flexible).

3 Oxygen valves and fuel shuld be pened at all during use t allw unrestricted passage and act as a seal. The use f welding gggles is required every time t prtect eyes frm sparks and ultravilet and infrared light that can damage them. Tanks must be securely attached t a wall, pst r prtable cart t ensure stability. The cutting trch des the gas mixture which has bth hses cnnectin, cntrl keys, a mixing chamber with a cnduit fr circulating the gas flame heating and ne fr cutting (xygen), an injectr, and a nzzle.

4 The system perates in tw stages: (1) the steel is heated at high temperature (900 C) with the flame prduced by a fuel gas (cntained in tanks with acetylene, prpane, hydrgen r even gasline) in the presence f xygen (xidizing gas that allws the fcusing prcess). Their gal is nt t melt the metal, but take it t its ignitin temperature. An air-prpane flame may reach 2000 C, while an xygen-prpane flame up t 2500 C and an xygen-acetylene flame between 3200 C t 3500 C (althugh this is the cmbinatin f gas has a higher cst). (2) an fcused xygen stream is injected (cntained in high-pressure tanks) t prvide the heat f flame. Because heat is released mlecules cmbustin prduct has lwer energy state that the mlecules f fuel and xygen.

5 In the presence f xygen at high temperatures fcused, an exthermic xidatin ccurs in the irn which supplies all the heat required t burn it, transfrming it int ferric xide (Fe2O3), which melts in the frm f sparks because its melting is lwer than that f steel r is blwn acrss the surface. The xy-acetylene flame (acetylene is a hydrcarbn) can be set t be carbnizing (reductive, with excess f acetylene used fr peratins with hard surfaces that char metal), neutral (chemically neutral, with a clear blue cre flame and the surrundings with dark blue r transparent abut the mst cmmn and cutting r welding with ideal length f 8 mm) r xidizing (when there is an excess f xygen in the flame, but nt recmmended, nly slightly n surfaces requiring brnze welding). Very little xygen will make a slw ragged cut, while t much xygen will waste xygen and prduce a cncave cut, s special attentin shuld be paid t dsage, since the cutting xygen pressure must match the nzzle rifice.

6 Oxy-acetylene can nly cut lw carbn steel, medium carbn steel and wrught irn. High carbn steel is difficult t cut because the melting pint f the slag is clser t the melting pint f the parent metal, s the slag des nt cme ut as sparks but as mixtures with fused mass f the cut, which des nt allws xygen t reach the clean metal. In the case f cast irn, graphite between grains and grain shape interfere with the cutting actin. In the case f stainless steel cannt be cut because the material des nt burn easily. Fr these cases we recmmend using plasma cutting. Surce: