technical insight
Power for a new era in rail transport Budd needed a power unit for his stainless steel train, to replace the hopelessly outdated steam engine. The expertise of no less than three firms was brought to bear on the problem of building a two-cycle diesel engine to meet the demands for train engines with increased horsepower. The work was led by the General Motors Co., which was aided by the company’s 1930 acquisition of the Winton Engine Co. and railcar builder Electro-Motive Co. A major turning point occurred in 1933, when the Kettering team’s eight-cylinder, 600-hp, 8-201 engine, with a weight-to-power ratio of only 20 pounds per horsepower, was chosen to supply power to the Chevrolet exhibit at Chicago’s “Century of Progress Exposition.” While visiting the fair, Ralph Budd came upon the display and immediately decided that the lightweight diesel engine would provide the power for his all-new, all- important passenger train. As Budd saw it, the diesel railroad was the railroad of the future and if any company could put the diesel engine in a train, it was General Motors. Approximately one year later, on May 26, 1934, the Pioneer Zephyr No. 9900 made its grand debut with a record-setting 1,000-mile dawn-to-dusk run from Denver to Chicago in 13 hours. Appropriately enough, the Zephyr was named after the Greek god of the west winds. It was designed for speeds of approximately 110 mph. Not only was the Pioneer Zephyr faster and lighter than its predecessors, but it also reduced Burlington’s cost of passenger train operation. A new era in railroading history had begun.
Austenitic stainless steels can be bent with ease. Even in the cold-worked condition, the material may be safely bent with a radius equal to twice its thickness. The formability of austenitic steels is strongly dependent on the initial condition of the material. Annealed material can be formed without difficulty, while the forming potential of cold-worked materials is limited. If material is to be formed, its final properties resulting from deformation may be considered for design. Three properties of austenitic steels are important for resistance welding - electrical resistivity, thermal conductivity, and the coefficient of thermal expansion. Compared to carbon steel properties, austenitic steels have a resistivity five times higher, thermal conductivity three times lower, and thermal co-efficient one-third higher. During welding, austenitic stainless steels do not undergo the y-a transformation, which ensures their good metallurgical weldability. A limited recrystallization occurs in the HAZ, leading to some softening. However, this has no consequence on the strength of resistance welds. The HAZ remains ductile in all cases. In either a peel or chisel test of spot welds, a well- defined button is always obtained. The high resistivity of austenitic steels allows for rapid obtaining and growth of the weld nugget. This is further enhanced by the low thermal conductivity, which limits heat sinking into the surrounding material. As a result, low amperages are required, and spot- welding multiple part combinations of a large total thickness are possible. The high coefficient of thermal expansion results in a tendency to produce nugget shrinkage discontinuities as well as high residual stresses in welds and distortion of assemblies. To prevent both occurrences, high forging forces are applied.
The interior revolution The high operating standards of the world’s first high-speed, diesel-propelled stainless steel three-car train were matched by the Zephyr’s painstaking interior furnishings. The first car held a diesel engine, an engineer’s cab, a 30-ft. railway post office, and space for baggage. The second car carried a larger baggage compartment, a buffet grill and, at the rear portion of the unit, a 16-ft.
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Issue 2 – 2024
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