Chapter6Gears(new)

# Chapter6Gears(new) - Chapter6Gears 1 Compute the forces...

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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 H9 & materials from which to make the gears, in order to provide adequate ±±±±±±±± ² performance for both strength and pitting .±± . resistance H9 & . 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 ± § ² ³ 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 L; ± friction force between meshing teeth Force in mesh Friction force Accessional L ; ± force ²oads 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 X ' & ± “7 ²² Tangential load .²² Radial load Normal load Nominal Torsion kW r/min N mm Direction of loads Fig6-10 p191 Driver Gear ( .²² -1 . ω

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Helical Gear 2 ˚ & ± 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 & ± ² 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 & ± ² ³ 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 6 ¤ & ± “7² 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 u 9 & or body of gear tooth----tooth breakage 2) skin-deep u9 & of gear tooth Fatigue failure occurs only on or in gear teeth

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tooth breakage 1 . Bulk % ¤ & ± or body of gear tooth----tooth breakage
1)skin-deep Q ¨ & ± of gear tooth abrasion Opening Gear Transmission----No lubrication is used Lubricating condition Enclosed ²²²²²²²² Gear Transmission---- using lubrication

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pitting Soft skin of teeth .&&& . 350HBW . —— H Ì ± ² Hard skin of tooth .&& & >350HBW . —— H Ì ± ² Only can be found in the enclosed gear boxes
scoring and scuffing .&&& High speed, Heavy load, or Low speed ,Heavy load

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plastic deformation
3 . Major influence factors of gear failures fluctuated Q ˚ & ± stresses .

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Chapter6Gears(new) - Chapter6Gears 1 Compute the forces...

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