Chapter6Gears

# Chapter6Gears - Chapter6Gears 1 Compute the forces exerted...

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Chapter 6    Gears

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Objects of this chapter 1. Compute the forces exerted on gear teeth as they rotate and transmit power. 2. Describe suitable metallic 8 t & materials from which to make the gears, in order to provide adequate ±±±±±±±± X performance for both strength and pitting .±± . resistance 8 t & . 3. Use the GB as the basis for completing the design of the gears.
Chapter 6      Gears 1.Loads exerted on gear teeth 2.Failures of gears and design rules 3.Bending stress in gear teeth 4.Contact stress on gear teeth 5.Choice of spur gear parameters .&& 6.Structure ± u ² design of wheels and gears lubrication 7.CAD in design of gear pair

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1. Loads exerted on gear teeth   Hypothesis .&&& : Concentration force acting on the midpoint of tooth width Ignoring ±k W friction force between meshing teeth Force in mesh Friction force Accessional ± k W force Loads in mesh .&& &
6 1 1 9.55 10 P T n = × 2 1 cos t n n F F F α = = 1 1 2 1 2 t t T F F d = = 1 1 2 r t r F F tg F = = Spur Gear L t & “7 ±± Tangential load .±± Radial load Normal load Nominal Torsion kW r/min N mm Direction of loads Fig6-10 p191 Driver Gear ( .±± -1 . ω

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Helical Gear ¨ | 1 1 1 2 2 / t t F T d F = = 1 1 2 / cos r t n r F F tg F α β = = 1 1 2 a t a F F tg F = = /(cos cos ) n t n F F = Question: How to Judge the Axial Load Direction Acting on the Helical Wheel?
Principles of left or right hand (Driving H ˛u » Gear ) Determine the helical direction of driver gear teeth Put out your “ right ” hand and hold the axes, then make sure four fingers except the thumb H ˛F » ± to the direction of the rotation. At last, your thumb points the direction of the axial .&&& force. TRY BY YOURSELF!!

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Straight Bevel Gear ‚ u & “7± 1 1 2 m t d T F = 2 1 1 cos a t r F tg F F = = δ α 2 1 1 sin r t a F tg F F = = cos t n F F = Direction of Axial Load: point to large transverse plane
2.Failures of gears and  design rules 1) Bulk or body of gear tooth----tooth breakage

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1) skin-deep of gear tooth abrasion ‚ ˛F » pitting ‚ » scoring and scuffing ‚ » plastic deformation‚ » “7 pitting abrasion
scoring and scuffing plastic deformation Major influence factors of gear failures: Materials and their heating treatment; gear precision; lubrication P179~181—Please learn it by yourselves

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35 o& 931 & ± ² §»,& o&& & 70 & ± ——» * o& T | ¹ ª* T | % 1 . & 32.8 2 .&&& 19.5 3 4.3 4 4.6 5 20.3 6 13.2 7 u t | „ “7 5.3 Reference: ± ²e “7&& A ˘³»7&Q ¯l& » * 1992
1) Design Rules tooth breakage----Bending Stresses [ ] F F M W σ = Eq. ( 6-9) Pitting failure----Contact Stresses [ ] H H Question: 1. How to deal with other skin-deep fatigue? ---- GB/T 6413-1986 & ± & § » 7²² ³2 ´ “7²² µ ----Abrasive fatigue is considered by enlarging the value of m.

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Chapter6Gears - Chapter6Gears 1 Compute the forces exerted...

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