Oxyacetylene welding

In this process an intense flame is produced by burning a controlled mixture of oxygen and acetylene gas see Fig. 8.116. 

Welds are formed from the weld puddle created through contact of the flame, the work piece, and the welding rod. Oxyacetylene welding requires a high degree of skill to obtain high-quality deposits and the process is slow. The benefit of oxyacetylene welding is that it provides the least base metal dilution of any method. A one-layer deposit is usually sufficient to reach the desired hardness. 

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Fig. 2. (a) The shielded-metal arc-welding system, (b) The oxyacetylene welding process. 

Originally used as an illuminant, acetjiene [74-86-2] fiom carbide quickly found use ia oxyacetylene welding (qv) and cutting, ia the... 

In the United States calcium carbide-based acetylene is mainly used in the oxyacetylene welding market although some continues to be used for production of such chemicals as vinyl ethers and acetylenic alcohols. Calcium carbide is used extensively as a desulfurizing reagent in steel and ductile iron production allowing steel mills to use high sulfur coke without the penalty of excessive sulfur in the resultant steel (see Sulfurremoval and recovery). Calcium cyanamide production continues in Canada and Europe (see Cyanamides). 

The largest use for calcium carbide is in the production of acetylene for oxyacetylene welding and cutting. Companies producing compressed acetylene gas are located neat user plants to minimize freight costs on the gas cylinders. Some acetylene from carbide continues to compete with acetylene from petrochemical sources on a small scale. In Canada and other countries the production of calcium cyanamide from calcium carbide continues. More recentiy calcium carbide has found increased use as a desulfurizing reagent of blast-furnace metal for the production of steel and low sulfur nodular cast iron. 

Selected physical properties of oxygen are included in Table 9.24. It is a colourless, odourless and tasteless gas which is essential for life and considered to be non-toxic at atmospheric pressure. It is somewhat soluble in water and is slightly heavier than air. Important uses are in the steel and glass industries, oxyacetylene welding, as a chemical intermediate, waste-water treatment, fuel cells, underwater operations and medical applications. 

OH and Rexarc of West Alexandria, OH. These are small diameter nnits nsed mostly for oxyacetylene welding eqnipment. 

Oxyacetylene Welding gas welding in which the fuel gas is acetylene and which is burnt in an oxygen atmosphere. 

Self-Test 6.16A Calculate the standard enthalpy of formation of ethyne, the fuel used in oxyacetylene welding torches, from the information in Tables 6.4 and 6.5. 

A number of other deposition methods have been used for growing diamond, with varying degrees of success. These include oxyacetylene welding torches, arc jets and plasma torches, laser ablation and hquid phase crystallisation, but none of these yet reahstically compete with the hot filament or microwave systems for reliability and reproducibility. 

Uses In addition to the extensive use of acetylene in oxyacetylene welding it is used as a starting material for the manuf of inorg and org acetylides as well as many other compds. Some of them such as acetone, acetaldehyde, acetic acid, acetic anhydride, etc are indispensible in the manuf and testingof expls and ammo. Acetylene was also used to manufacture tetranitromethane by the method described in PATR 2510 (1958), p Ger 195, under Tetan... 

Oxyacetylene welding torches burn acetylene gas, C2H2(g). Use the information in Table 8.2 to calculate AH° (in kilojoules) for the combustion reaction of acetylene to yield C02(g) and H20(g). 

During transfer of the liquefied gas from a stock steel cylinder into smaller cylinders, the effective expansion caused cooling of the stock cylinder and a fall in pressure to occur. Application of a flame to the stock cylinder of the endothermic oxide led to decomposition and explosive rupture of the cylinder [1]. The explosive decomposition of the gas at 0.05—8 bar at ambient temperature after initiation by electric discharge can be prevented by addition of 30 vol% of air, nitrogen or oxygen [2]. Oxyacetylene welding repair work on or near to a 6 t tank of liquefied oxide led to a violent explosion... 

Alkynes are less common in nature than are alkenes. Alkynes are also less important in industry. The largest use of acetylene is as a fuel for the oxyacetylene welding torch, which burns at a very high temperature. 

Acetylene is by far the most important commercial alkyne. Acetylene is an important industrial feedstock, but its largest use is as the fuel for the oxyacetylene welding torch. Acetylene is a colorless, foul-smelling gas that burns in air with a yellow, sooty flame. When the flame is supplied with pure oxygen, however, the color turns to light blue, and the flame temperature increases dramatically. A comparison of the heat of combustion for acetylene with those of ethene and ethane shows why this gas makes an excellent fuel for a high-temperature flame. 

Among the carbides of the group 2 elements, calcium carbide is the best known. It reacts with water, liberating acetylene, and thus is called an acetyUde (equation 12). At one time, this reaction was the main source of HC=CH for oxyacetylene welding. Production of CaC2 peaked at 7 million toimes per year in 1960, bnt declined slightly to 6.2 million toimes in 1985 because acetylene now is obtained from petrochemical processing. 

Oxyacetylene welding is used to repair metal structures, including bridges, buildings, and even the Statue of Liberty. Calculate AS° for the combustion of 1 mol of acetylene (C2H2). 

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