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BK50A2200 Design Methodologies and Applications of Machine Element Design Lectures 7 and 8 Machine elements D.Sc Harri Eskelinen.

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Presentation on theme: "BK50A2200 Design Methodologies and Applications of Machine Element Design Lectures 7 and 8 Machine elements D.Sc Harri Eskelinen."— Presentation transcript:

1 BK50A2200 Design Methodologies and Applications of Machine Element Design Lectures 7 and 8 Machine elements D.Sc Harri Eskelinen

2 BK50A2200 Design Methodologies and Applications of Machine Element Design Lecture 7 Machine elements Shaft-hub-joints D.Sc Harri Eskelinen

3 Feedback from exercise 5… Contact geometry between the outer/inner ring of the bearing and the ball (roller element) Effecting compression stress vs. Materials compression strength Deformation of the geometry: 1. Changes of the motion type * Rolling vs. sliding 2. Changes of the active wear phenomenon * Adhesive vs. abrasive 1.Loading follows normal Distribution. 2.Load bearing capacity follows Weibull distribution. Size of The Overlapping area of two distributions STRENGTHWEARRELIABILITYLIFETIME

4 Main criteria dealing with lifetime evaluation * Key aspects Main criteria dealing with reliability * Key aspects Main criteria dealing with strength * Key aspects Main criteria dealing with wear * Key aspects MACHINE ELEMENTS Reliability level should be expressed with the desired lifetime Wear rate is needed to estimate the reliability level Wear decreases the strength of the component Strength calculations form the basis for lifetime evaluation Shaft-hub-joints

5 Main criteria dealing with reliability starndardized dimensioning performance range (= power transmission capacity) - component failures - loosening assembly errors consequences of the failure (fault tree analysis) dimensional tolerances key types Main criteria dealing with strength surface pressure in the hub surface pressure on the shaft shear stress of the key combined loading cases - axial forces - torque - dynamic loading stress concentrations of the shaft SHAFT KEYS

6 Main criteria dealing with lifetime evaluation lifetime of the shaft is critical - fatigue failure Main criteria dealing with reliability starndardized dimensioning performance range (= power transmission capacity) - component failures - loosening assembly errors consequences of the failure (fault tree analysis) dimensional tolerances key types Main criteria dealing with strength surface pressure in the hub surface pressure on the shaft shear stress of the key combined loading cases - axial forces - torque - dynamic loading stress concentrations of the shaft Main criteria dealing with wear possible fretting corrosion (material pairs) SHAFT KEYS

7 SHAFT-HUB-JOINTS WITH CONICAL GEOMETRY CONICAL SHAFT AND HUB CONICAL FASTENING RINGS FASTENING HUB WITH CONICAL STEPS INSIDE Strength Allowed stresses in each component and stress concentrations Lifetime based on the lifetime of the shaft Failure due to overloading Reliability utilization of fastening screws or nuts distribution analysis of torque transmission ability Mv affecting axial loads loosering Wear adhesive/abrasive wear during opening and tighting possible sliding corrosion fretting Main criteria dealing with lifetime evaluation Main criteria dealing with reliability Main criteria dealing with strength Main criteria dealing with wear

8 Highlight! Importance of the: 1)Stress analysis of each component of the construction 2)Clearance and/or fit analysis 3) Reliability of power transmission capacity

9 Conical shaft-hub jointConical fastening ringsFastening hubs with conical steps inside Interference fit shaft-hub joints Woodruff key jointsParallel shaft key joints Tapered key joints Spindle nut joints Splined shafts and hubs

10 BK50A2200 Design Methodologies and Applications of Machine Element Design Lecture 9 Machine elements Belt and chain drives D.Sc Harri Eskelinen

11 Main criteria dealing with lifetime evaluation * Key aspects Main criteria dealing with reliability * Key aspects Main criteria dealing with strength * Key aspects Main criteria dealing with wear * Key aspects MACHINE ELEMENTS Reliability level should be expressed with the desired lifetime Wear rate is needed to estimate the reliability level Wear decreases the strength of the component Strength calculations form the basis for lifetime evaluation Belt and chain drives

12 Main criteria dealing with strength diameters of pulleys (wheels) distance between pulleys (shafts) angle of wrap of the pulley (contact area covered by the belt on the pulley) centrifugal force belt tensions due to torque (driven vs. driving pulley) friction between the belt and pulley intial tension belt cross-section Main criteria dealing with wear abrasive wear friction wear (abrasive wear) ageing surface failures of the belt chemical failures of the belt BELT DRIVES Belt drives Timing belt drives Flat belt drives V-belt drives

13 Main criteria dealing with lifetime evaluation belt failure may cause serious consequences visual inspection pre-set time for changing the belt (e.g. running hours/years) Main criteria dealing with reliability standardized design guidelines multiple belt drives proper belt drive type - vee belt (v-belt) - flat belt - timing belt elastic creep of the belt friction and sliding power transmission capacity adjusting the tension Main criteria dealing with strength diameters of pulleys (wheels) distance between pulleys (shafts) angle of wrap of the pulley (contact area covered by the belt on the pulley) centrifugal force belt tensions due to torque (driven vs. driving pulley) friction between the belt and pulley intial tension belt cross-section Main criteria dealing with wear abrasive wear friction wear (abrasive wear) ageing surface failures of the belt chemical failures of the belt BELT DRIVES Belt drives Timing belt drives Flat belt drives V-belt drives

14 Highlight! Importance of the: 1)Different stress components of the belt 2)Friction (V- and flat belts) 3) Different cross-section shapes of the belts and different materials Bending stress Stress due to intial tension Stress due to torque Stress due to centrifugal force

15 Main criteria dealing with strength velocity of the chain centrifugal force radial force surface pressure on a link vibration phenomena speed ratio ROLLER CHAIN DRIVES

16 Main criteria dealing with strength velocity of the chain centrifugal force radial force surface pressure on a link vibration phenomena speed ratio Main criteria dealing with wear abrasive wear adhesive wear tribochemical wear lubrication required number of links vs. teeth (multi-corner effect) environmental aspects material pairs (chain vs. sprocket) ROLLER CHAIN DRIVES

17 Main criteria dealing with lifetime evaluation wear rate usually an unexpected failure failures of the locking mechanisms chain failure may cause serious consequences pre-set time for changing the chain minimum number of teeth of sprockets Main criteria dealing with reliability type of driven/driving machine required power transmission capacity multiple chains adjusting the length /elongation with a tensioner continuous lubrication Main criteria dealing with strength velocity of the chain centrifugal force radial force surface pressure on a link vibration phenomena speed ratio Main criteria dealing with wear abrasive wear adhesive wear tribochemical wear lubrication required number of links vs. teeth (multi-corner effect) environmental aspects material pairs (chain vs. sprocket) ROLLER CHAIN DRIVES

18 Highlight! Importance of the: 1)Allowed ultimate strength of the chain under static and dynamic loading 2)Allowed surface pressure of the chain and possible wear phenomena 3) Vibration problems (velocity analysis)

19 Exercises Exercise 7. Exercise 7. Select any industrial applications in which the shaft-hub joint types given in Table 1 are used. Form the approach for the lifetime analysis of the joints and their components by integrating the viewpoints of strength, wear and reliability analysis. Select any industrial applications in which the shaft-hub joint types given in Table 1 are used. Form the approach for the lifetime analysis of the joints and their components by integrating the viewpoints of strength, wear and reliability analysis. Exercise 8. Exercise 8. Select any industrial applications in which the power transmission systems given in Table 2 are used. Form the approach for the lifetime analysis of these systems and their components by integrating the viewpoints of strength, wear and reliability analysis. Select any industrial applications in which the power transmission systems given in Table 2 are used. Form the approach for the lifetime analysis of these systems and their components by integrating the viewpoints of strength, wear and reliability analysis. Table 1. Table 2. Table 1. Table 2. Shaft-hub-joint type Conical shaft-hub joint Interference fit shaft-hub joints Parallel shaft key joints Power transmission system Timing belt drives V-belt drives Single roller chain drives


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