13_ch 15 Mechanical Design budynas_SM_ch15

13_ch 15 Mechanical Design budynas_SM_ch15 - to the...

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Chapter 15 391 prerequisites, and how quantitative it was. The most important thing is to have the stu- dent think about it. The instructor can comment in class when students curiosity is heightened. Options that will surface may include: • Select a through-hardening steel which will meet or exceed core hardness in the hot- rolled condition, then heat-treating to gain the additional 86 points of Brinell hardness by bath-quenching, then tempering, then generating the teeth in the blank. • Flame or induction hardening are possibilities. • The hardness goal for the case is sufficiently modest that carburizing and case harden- ing may be too costly. In this case the material selection will be different. • The initial step in a nitriding process brings the core hardness to 33–38 Rockwell C-scale (about 300–350 Brinell) which is too much. Emphasize that development procedures are necessary in order to tune the “BlackArt”
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Unformatted text preview: to the occasion. Manufacturing personnel know what to do and the direction of adjust-ments, but how much is obtained by asking the gear (or gear blank). Refer your students to D. W. Dudley, Gear Handbook, library reference section, for descriptions of heat-treating processes. 15-12 Computer programs will vary. 15-13 A design program would ask the user to make the a priori decisions, as indicated in Sec. 15-5, p. 786, SMED8. The decision set can be organized as follows: A priori decisions • Function: H , K o , rpm, m G , temp., N L , R • Design factor: n d ( S F = n d , S H = √ n d ) • Tooth system: Involute, Straight Teeth, Crowning, φ n • Straddling: K mb • Tooth count: N P ( N G = m G N P ) Design decisions • Pitch and Face: P d , F • Quality number: Q v • Pinion hardness: ( H B ) 1 , ( H B ) 3 • Gear hardness: ( H B ) 2 , ( H B ) 4...
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