Furnace Atmosphere

Air-assisted atomizer Air-atmosphere furnaces Air bag fabric Airbags... 

Air-Atmosphere Furnaces. These furnaces are appHed to processes where the workload can tolerate the oxidation that occurs at elevated temperatures in air. In some special appHcations, the oxidation is not only tolerable but is desired. Some furnaces heat the work solely to promote oxidation. Furnaces designed for air operation are not completely gas-tight which results in somewhat lower constmction costs. There are no particular problems encountered in selecting the insulation systems because almost all refractory insulations are made up of oxides. Heating element materials are readily available for the common temperature ranges used with air atmospheres. 

Protective-Atmosphere Furnaces. These furnaces are used where the work caimot tolerate oxidation or where the atmosphere must provide a chemical or metallurgical reaction with the work. In some cases, mainly in high temperature appHcations, the atmosphere is required to protect the electric heating element from oxidation. 

In sintering, the green compact is placed on a wide-mesh belt and slowly moves through a controlled atmosphere furnace (Fig. 3). The parts are heated to below the melting point of the base metal, held at the sintering temperature, and cooled. Basically a solid-state process, sintering transforms mechanical bonds, ie, contact points, between the powder particles in the compact into metallurgical bonds which provide the primary functional properties of the part. 

Fig. 3. Sintering of the green compact in a controlled atmosphere furnace.

Conventional Sintering Equipment. Like drying furnaces, sintering furnaces (29,76,85) can be periodic or continuous in nature. Periodic kilns offer greater flexibiHty continuous tunnel kilns are more economical. Advanced ceramics are typically siatered in high purity, controUed atmosphere furnaces by electric resistance heating. Ceramic furnaces used to fire traditional ceramic ware are generally heated with inexpensive natural gas, oil, wood, or coal. 

At temperatures in excess of 750°C the addition of water vapour accelerates the rate of growth of FeO (Fig. 7.10) by producing large pores in the FeO" . At much higher temperatures (1 200°C) Sheasby et have found that addition of steam to Oj-Nj, Oj-HjO-Nj and HjO-Nj, in a simulated reheating atmosphere furnace, caused increases in scale growth due to improved adhesion at the scale/metal interface. They concluded that water vapour enhances scale creep as previously reported by Tuck et... 

Air-atmosphere furnaces, 22 290-291 Air atomization, in spray coating, 7 70-72 Air-atomizing sulfur burners, 23 659-660 Airbags, nylon, 19 766 Air-based balanced vinyl chloride process, 25 637, 640, 641, 645 Air-based ethylene oxidation, 20 643-646 Air bioremediation... 

Wendlandt has provided an extensive compilation of conditions and requirements that influence the shape of DTA thermograms [18]. These can be divided into instrumental factors (furnace atmosphere, furnace geometry, sample holder material and geometry, thermocouple details,... 

Acid waste from petrochemical refinery processes is, for example, worked up under reducing conditions. The acidic tar or resin is converted into coke by heating in a reducing atmosphere (furnace gas, ca. 1000°C) in a rotary tube furnace. In a variant of this process the energy is produced by the burning of coke, which is supplied to the rotary tube furnace and burnt together with the coke formed. 

Kinetic Constant, g/cm s Atmosphere Furnace Efficiencies (Z) Mean Furnace Exit Temp Op Mean Net Heat Flux Btu/ft hr Maximum Net Heat Flux Btu/ft2hr Position of Maximum Heat Flux (ft) Maximum Flame Temp. (°F) Percent Unburned Fixed Carbon Percent Combustibles In Ash (Z)... 

Figure 323. Vapor atmosphere furnace for the Menler system.

In fuel-fired furnaces, the nature of the fuel may make a difference in the furnace design, but that is not much of a problem with modem industrial furnaces and burners, except if solid fuels are involved. Similar bases for classification are air furnaces, oxygen furnaces, and atmosphere furnaces. Related bases for classification might be the position in the furnace where combustion begins, and the means for directing the products of combustion, e.g., internal fan furnaces, high velocity furnaces, and baffled furnaces. (See sec. 1.2.4. and the rotary hearth furnace discussion on baffles in chap. 6.)... 

The general conformation of thermal analysis (TA) apparatus, consisting of a physical property sensor, a controlled-atmosphere furnace, a temperature programmer and a recording device, is illustrated in Figure 2.1. The most common forms of TA are shown in Chapter 1 (Table 1.1)... 

Applications include sulfur-bearing gas atmospheres, furnace parts, fire boxes, high-temperature containers, and heat-exchanger tubing. 

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