10/04 COVER 1 zaida

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Specifications	10/04 COVER 1 zaida
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WELDING RESEARCH OCTOBER 2004-S286 (4500°F) (Ref. 12). There are studies that report that aluminum burns as vapor or bot

Specifications	10/04 COVER 1 zaida
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Content	WELDING RESEARCH OCTOBER 2004-S286 (4500°F) (Ref. 12). There are studies that report that aluminum burns as vapor or both as liquid and vapor (Refs. 13–15). Be- cause aluminum has a higher adiabatic tem- perature, it is widely used to replace iron to increase the flame temperature. Due to in- stability of aluminum combustion, a stable self-propagating lance flame is possible only if a small part of iron is substituted by alu- minum (Refs. 4, 16). We have tested the performance of aluminum metal in the design of a wire- core lance, and the results have been com- pared with the performance of the com- mercially available lance (3⁄8-in. OD CAL) with the same dimension and design. In the experiments reported below, we used Fe wires of 0.09 in. (2.29 mm) and alu- minum wires of 0.08 in.(2.03 mm). The re- sults of the test are reported in Table 1. Aluminum wires or aluminum tubing, if used in proper relation to the iron ma- terial of the lance, can substantially in- crease the cutting speed compared to CAL performance. However, this increase of the cutting speed is at the expense of the combustion stability of the lance. Alu- minum metal melts in the flame, the small droplets of liquid aluminum are carried away by the oxygen stream, and after- burning of aluminum takes place. The self-propagating combustion regime is ex- tinguished as the oxygen flow rate in- creases above 80 L/min. An application of an inert jacket on the aluminum lance is very important for a stable combustion. Experimental observations indicated that the absence of the nonreactive, nonmelt- ing jacket would result in highly unstable combustion, resulting in the flame extin- guishing. The implementation of the inert jacket improved the flame stability of the hybrid Fe-Al lance. Discussion Application of other metals to a regular iron lance can have positive results if the rela- tion between iron and the additional metals is kept in a certain range. Ex- periments de- scribed above re- vealed that a hybrid Fe-Al lance does not burn in a stable mode, and a stable combustion can be achieved only if the iron material is in excess and the lance is protected by an inert jacket at the low oxygen flow conditions. In particular, a combination of iron wires and aluminum 6061 tubing turned out to be a very effective lance with a high cutting speed if an inert jacket was applied. The inert jacket has the effect of flame stability improvement. The follow- ing qualitative explanation of the im- proved flame stability can be presented. It is known in the theory of strongly exother- mic, strongly nonadiabatic flames that the behavior of the flame shows major longi- tudinal oscillation that eventually results in flame extinction. The theory also indi- cates that the decrease of heat loss from the flame improves stability behavior. Ob- viously, the unreacted piece of the sleeve, before being broken off, represents a ra- diation mirror, and the radiation flux in the radial direction is smaller. Conse- quently the flame is hotter and more alu- minum evaporates. A homogeneous flame usually exhibits higher stability compared to a flame-consuming fine spray of drops. The thermal conductivity of graphite is also much less than that of aluminum. These facts reduced the energy loss and heat dissipation to the environment. The flame was therefore stabilized. As the experimental results of 3⁄8-in. OD wire-core iron lances show, the inert jacket modified lance cuts faster than the commercially available lances under the same oxygen flow rates. With increasing cutting plate thickness, the difference be- tween CAL and modified lances increases. In cutting procedure, the lance flame heats up the plate surface first. After the plate is heated up to the ignition temper- Fig. 5 — Relative cutting speed index as a function of oxygen flow rate (1.2 cm/s = 0.472 in./s). Fig. 6 — Overall cutting-cost comparison of CAL and modified lances at 50 lb/in.2(345 kPa). Fig. 7 — Overall cutting-cost comparison of CAL and modified lances at 80 lb/in.2(552 kPa). Relative Cutting Speed Index RCSI 0.8 0.6 0.6 1.0 0.8 0.4 0.4 0.20.2 0.00.004080120160200 CAL RCRI 1/4 inch OD lance (CAL, Modified) cutting on 1/2 inch thick steelCost/ft Cut Cost ($) at 50 PSI CAL CAL Modified Modified Cost/ft cut ($) at 80 PSI Modified wang qwkcorr 8/27/04 8:40 AM Page 286
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