According to standard machine design bands for pitch-line speed, over which peripheral velocity range are gears classified as medium-velocity gears?
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A1 – 3 m/s
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B3 – 15 m/s
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C15 – 30 m/s
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D30 – 50 m/s
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EAbove 50 m/s
Answer
Correct Answer: 3 – 15 m/s
Explanation
Introduction / Context
Gear classification by pitch-line speed (peripheral velocity at the pitch circle) guides material selection, heat treatment, lubrication strategy, and tooth form accuracy. Typical textbooks and standards group speeds into low, medium, and high ranges for preliminary design decisions.
Given Data / Assumptions
- Standard spur/helical gear practice for industrial machinery.
- Pitch-line speed v = π·d·n in consistent units.
- Conventional ranges: low, medium, high, with approximate thresholds.
Concept / Approach
In many design references, medium-velocity gears operate where hydrodynamic lubrication becomes more reliable and dynamic effects begin to influence accuracy requirements, yet speeds are not so high that special high-speed finishing becomes mandatory.
Step-by-Step Solution
1) Identify the common banding used in design guides.2) Low-velocity is typically up to about 3 m/s.3) Medium-velocity is broadly from 3 m/s to about 15 m/s.4) High-velocity regimes exceed roughly 15 m/s, with very high-speed applications going beyond 30–50 m/s.Verification / Alternative check
Machine design texts align on 3–15 m/s as the medium band, recognizing variations by author or application without altering the central value.
Why Other Options Are Wrong
- 1 – 3 m/s: characteristic of low-speed gears; boundary lubrication and wear dominate.
- 15 – 30 m/s and 30 – 50 m/s: these are high-speed domains requiring higher accuracy grades and improved finishing.
- Above 50 m/s: very high speed; special design and balancing are typical.
Common Pitfalls
- Using exact cutoffs rigidly; these are practical bands, not hard standards.
- Confusing angular speed with pitch-line speed; diameter matters via v = π·d·n.
Final Answer
3 – 15 m/s