Transcript Machine elements 2

BK50A2200
Design Methodologies and
Applications of Machine
Element Design
Lectures 7 and 8
Machine elements
D.Sc Harri Eskelinen
BK50A2200
Design Methodologies and
Applications of Machine
Element Design
Lecture 7
Machine elements
Shaft-hub-joints
D.Sc Harri Eskelinen
Feedback from exercise 5…
STRENGTH
WEAR
RELIABILITY
LIFETIME
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
Contact geometry
between the outer/inner
ring of the bearing and
the ball (roller element)
Size of
The
Overlapping
area of
two
distributions
1.Loading follows normal
Distribution.
2.Load bearing capacity
follows Weibull distribution.
MACHINE ELEMENTS
Main criteria dealing with
lifetime evaluation
* Key aspects
Reliability level
should be
expressed with the
desired lifetime
Strength calculations form
the basis for lifetime evaluation
* Key aspects
Wear rate is needed to
estimate the reliability level
Main criteria dealing
with strength
* Key aspects
Main criteria dealing
with reliability
Main criteria dealing
with wear
Shaft-hub-joints
Wear decreases the
strength of the component
* Key aspects
SHAFT KEYS
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
lifetime evaluation
• lifetime of the shaft is
critical
- fatigue failure
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
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
wear
• possible fretting
• corrosion (material
pairs)
SHAFT-HUB-JOINTS WITH CONICAL GEOMETRY
CONICAL SHAFT
AND HUB
Main criteria dealing with
lifetime evaluation
Lifetime
•based on the lifetime
of the shaft
•Failure due to
overloading
CONICAL FASTENING
RINGS
FASTENING HUB WITH
CONICAL STEPS INSIDE
Main criteria dealing with
reliability
Reliability
•utilization of fastening
screws or nuts
•distribution analysis of
torque transmission
ability Mv
•affecting axial loads
•loosering
Main criteria dealing with
strength
Main criteria dealing with
wear
Strength
•Allowed stresses in each
component and stress
concentrations
Wear
•adhesive/abrasive wear
during opening and
tighting
•possible sliding
•corrosion
•fretting
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
Conical shaft-hub joint
Spindle nut joints
Parallel shaft key joints
Fastening hubs with
conical steps inside
Interference fit
shaft-hub joints
Tapered key joints
Conical fastening rings
Splined shafts and hubs
Woodruff key joints
BK50A2200
Design Methodologies and
Applications of Machine
Element Design
Lecture 9
Machine elements
Belt and chain drives
D.Sc Harri Eskelinen
MACHINE ELEMENTS
Main criteria dealing with
lifetime evaluation
* Key aspects
Reliability level
should be
expressed with the
desired lifetime
Strength calculations form
the basis for lifetime evaluation
* Key aspects
Wear rate is needed to
estimate the reliability level
Main criteria dealing
with strength
* Key aspects
Main criteria dealing
with reliability
Main criteria dealing
with wear
Belt and chain
drives
Wear decreases the
strength of the component
* Key aspects
BELT DRIVES
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
Belt drives
Timing belt drives
Flat belt drives
V-belt drives
Main criteria dealing with wear
• abrasive wear
• friction wear (abrasive wear)
• ageing
• surface failures of the belt
• chemical failures of the belt
BELT DRIVES
• 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
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 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
reliability
Belt drives
Timing belt drives
Flat belt drives
V-belt drives
Main criteria dealing with wear
• abrasive wear
• friction wear (abrasive wear)
• ageing
• surface failures of the belt
• chemical failures of the belt
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
Stress due to centrifugal force
Stress due to torque
Stress due to intial tension
Bending stress
ROLLER CHAIN DRIVES
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
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
Main criteria dealing with
lifetime evaluation
Main criteria dealing with reliability
• 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
strength
• velocity of the chain
• centrifugal force
• radial force
• surface pressure on a link
• vibration phenomena
• speed ratio
• type of driven/driving machine
• required power transmission
capacity
• multiple chains
• adjusting the length /elongation
with a tensioner
• continuous lubrication
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)
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)
Exercises
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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.
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.
Table 1.
Table 2.
Shaft-hub-joint type
Power transmission system
Conical shaft-hub joint
Timing belt drives
Interference fit shaft-hub joints
V-belt drives
Parallel shaft key joints
Single roller chain drives