10/04 COVER 1 zaida

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Specifications	10/04 COVER 1 zaida
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WELDING RESEARCH -S283WELDING JOURNAL ABSTRACT. In order to optimize lance performance, a nonreactive, nonmelting layer to co

Specifications	10/04 COVER 1 zaida
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Content	WELDING RESEARCH -S283WELDING JOURNAL ABSTRACT. In order to optimize lance performance, a nonreactive, nonmelting layer to cover the wire-core thermal cut- ting lance has been tried. The layer stabi- lized the lance combustion (aluminum- hybrid iron wire-core lances). Lances cov- ered by this layer produced a highly con- vergent stream of cutting oxygen and did not suffer from major radial leakage of cutting oxygen typical of commercial ther- mal lances. The layer also improved the cutting continuity by avoiding the solder- ing effect and lance extinction. A novel lance, Sharp-Fire (O)TMhas been devel- oped. Experimental data indicate that the new lance cuts steel or iron two times faster than conventional commercial ther- mal lances. The cost of cutting with the new lance is also economical. The cutting data reveal that the savings can be in the range of $1–$10/ft of material cut. Introduction The thermal lance process represents the oldest commercial use of oxygen cut- ting or piercing of massive objects (metal- lic materials and concrete) (Ref. 1). The invention of the oxygen lance was based on an exothermic reaction of iron pro- vided by the lance and a gaseous oxygen supply (Ref. 2). There are plenty of oxygen lance designs; however, the wire-core lance is the most common lance design in the industry, because it provides more iron for combustion and is easy to fabricate. In the thermal lance cutting process, the lance rod, which is made of low-carbon steel tube with several iron wires (Fig. 1), reacts with a supplied flow of oxygen. The oxidation reaction generates a large amount of heat, melting the target. Excess oxygen is used to oxidize and blow out the molten target (the slag). The process has always been regarded as a crude method of cutting and severing, since it relied on the evolution of a large amount of heat at the point of cutting/piercing (Ref. 1). The oxygen cutting jet plays an impor- tant role in the design of a thermal lance because most of the heat is provided by the burning of the cutting plate. This oxygen also helps to blow out the unreacted ma- terials to make a cut. In the process of heavy cutting, the pressure of the cutting oxygen entering the cutting tip is of para- mount importance, because of the dis- tance the cutting jet must traverse through the kerf (Ref. 1). As opposed to oxyfuel cutting technology, the cutting tip of the thermal lance can always touch the cutting spot to avoid this problem. The efficiency of oxygen is therefore increased in the thermal lance cutting process. In the past, research and inventions were focused on questions like A) how to change the lance design in order to get a better lance performance; B) is it possible to replace the iron fuel by other metals to achieve a higher lance burning tempera- ture (Refs. 1, 3, 4); or C) how to apply chemical flux processes for increased per- formance (Refs. 5, 6). In this paper, we focused our attention on a nonmelting, nonreactive layer modi- fication of the wire-core thermal lance. This layer is applied around the thermal lance and serves as a flame-focusing ele- ment and consequently improves the lance cutting efficiency. Although it is well known that plastic and ceramic layers are applied for the insulation purpose of elec- tric-aided cutting rods (Refs. 4, 7), we did not find any previous report on the flame- focusing effect of an inert layer. Experiment Setup The setup of a commercial thermal lance system is depicted in Fig. 1. The principle of the experimental ther- mal lance system is described as follows: oxygen comes from the cylinder, through the oxygen hose and the torch, and finally reaches the lance rod. Oxygen flow rate is controlled by both the cylinder regulator and the torch trigger. The iron wire-core lance rod, commercially produced, has been made of low-carbon steel tube with several low-carbon steel wires along the inside surface of the tube (some steel is re- placed by aluminum, in aluminum-hybrid iron wire-core lances). There are hollow areas inside to allow the oxygen to pass through — Fig. 1, upper-right corner. In the modified lance design, this assembly was surrounded by a nonmelting, nonre- active inert jacket. By scrubbing the lance tip on the striker plate, sparks are generated on the lance tip. The sparks initiate the lance burning. By adjusting the oxygen flow, the lance burning propagates by itself. The burning lance targets the cutting plate to start the cutting. In our experimental test- ing, we have measured the flow rate of oxygen, time of cutting, consumption of the lance, and length of the cut. This in- formation made it possible to calculate the cutting speed. The experiments have been repeated several times and the values re- ported here represent a reliable average value. Four types of lances were tested: commercially available iron wire-core lances (CAL), aluminum-hybrid lances, and inert-layer modified lances of both CAL and aluminum-hybrid types. Flame Focusing, Flame Stability Theory, and Lance Modification Combustion of metals in oxygen is a strongly exothermic process. It is well known that strongly exothermic processes feature all types of instabilities occurring both in space and in time. Typical time in- stability is represented by a longitudinal oscillation of the flame, and the tempera- ture in the flame can oscillate by several hundred °C. We have observed this type of behavior for the flame produced by alu- minum or titanium lances. The angular os- cillation of the flame results in the rim burning at different speeds. We observed that after lance extinction the lance rim looked jagged. In addition to flame instability, there is another problem brought by the wire-core Flame-Focusing Modification of a Wire-Core Thermal Lance Improvement shown to double cutting speed BY H. WANG, P. PRANDA, AND V. HLAVACEK H. WANG is a graduate student, Depart- ment of Chemical Engineering,The State University of New York at Buffalo. P. PRANDA is at Department of Chemical and Biomolecular Engineering, University of Notre Dame, Ind., and V. HLAVACEK is at The State University of New York at Buffalo. KEYWORDS Thermal Cutting Lance Exothermic Processes Soldering Effect Flame Stability wang qwkcorr 8/27/04 8:40 AM Page 283
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