Example of tubular combustion chamber liner, which consists of multiple, contoured tubes running along the length of the liner. (Courtesy of Pratt & Whitney Rocketdyne.)
Long description of figure 1.
Tubular main combustion chambers (MCCs) have been used for many years as an alternative to milled wall liners, such as the one used in the Space Shuttle Main Engine. Examples of prior and current engines to use tubular designs are the Douglas PGM-17 “Thor” missile (ref. 1) first deployed in September 1958, the Pratt & Whitney RL-60 engine (ref. 2), and the Pratt & Whitney Advanced Expander Combustor developed under the Integrated High Payoff Rocket Propulsion Technology initiative (ref. 3). Tubular liner designs, such as the one shown in the preceding photograph, offer the potential for considerable increases in rocket engine life over conventional milled channel liners (ref. 4). Additional benefits in tubular liner performance and life could be gained from utilizing the advanced copper alloy GRCop-84, recently developed by the NASA Glenn Research Center, which has a balance of improved strength and temperature capability combined with high thermal conductivity in comparison to competing alloys. Prior efforts to draw GRCop-84 into tubing successfully demonstrated feasibility, but the manufacturing methods were not suitable for large-scale production. Therefore, Glenn undertook an effort with LeFiell Manufacturing of Sante Fe Springs, California, to improve the production.
The first step was to eliminate gun drilling of small-diameter solid bars to make the starting stock. Instead, 300 lb of powder were consolidated into a large solid cylinder, a small hole was gun drilled into the cylinder, and the cylinder was extruded through a die and over a mandrel to produce 15 m (45 ft) of tubular starting stock. This change increased the yield by approximately 50 percent. The second step was to maximize the amount of reduction prior to annealing and to minimize the required annealing temperature. A design of experiments was conducted with three drawing reductions and three annealing temperatures as the independent variables. Room-temperature tensile properties were used to establish any difference in tubing after drawing to 9.5-mm (0.375-in.) outside diameter (OD) by 1.0-mm (0.040-in.) wall. The results indicated that GRCop-84 exhibits a wide processing window with all three annealing temperatures and two of the drawing reductions resulting in tubing with statistically identical tensile properties. The third and most aggressive drawing reduction resulted in failure of the tubes during drawing because of tensile overload and was abandoned. From the remaining conditions, the optimum processing parameters were selected.
To validate the optimized production parameters, over 330 m (1100 ft) of 9.5-mm OD by 1.0-mm wall GRCop-84 tubing was produced. A portion of the finished tubing is shown in the following photograph. The optimized conditions required approximately one-third fewer drawing steps than the original drawing conditions did and reduced the annealing temperature by 200 °C (360 °F). Along with the improved starting stock, these changes will result in large cost and time savings for GRCop-84 tubing. Further details can be found in reference 5.
Finished 9.5-mm OD by 1.0-mm wall GRCop-84 tubing.
Long description of figure 2.
Last updated: December 14, 2007
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