Other Flashcards
(48 cards)
What is Se,mod and Se?
Se,mod is the endurance strength as measured in an experimental setup.
Se is the actual endurance strength for which the differences between actual and experimental setups are taken into account.
For which reason are flat belt pulleys crowned?
To prevent the belt from sliding off the pulley sideways
Describe how a function-means-tree can be used in a product development process
A FMT is a decomposition of functions (what must be done) into means (how one might do it). The means can be further decomposed into secondary functions that would result from implementing the means.
What is the main reason for roller chains having a limited life?
Chain life is limited by wear between the pins and bushings.
What is the purpose of the roller in a roller chain?
The rollers prevent sliding when the chain is entering the sprockets.
Compare the shaft diameter calculations of ANSI and von Mises
The ANSI equation is used to design the shaft against fatigue. The input load should be effective mean load.
The von Mises equation is used for designing a dhaft against yield. The input load is then the maximum load.
Why should not only one bearing be used and why shouldn’t three or more be used?
- One shouldn’t be used because most bearings cannot hold the torque alone
- Three or more shouldn’t be used because of tolerance errors in e.g. the bearing seats would induce high unexpected loads on the bearings
What happens if the load of an induction motor is suddenly disengaged and the motor runs without external load?
The motor accelerates to nominal speed (where Tm=0)
Function of keys/keyseats?
Transmit torque between gear and shaft
Function of spacer?
Bearing inner rings location (A spacer or standoff is a fixed size component designed to separate two other parts by a known amount.)
Function of a shim?
A shim is a component used to fill up an unwanted gap. Shims may be flat or tapered, and are often specified as “select to fit” parts, rather than as a part with a predefined thickness.
Function of washer?
A washer is a part used to spread the load between the two components, e.g., between a bolt- or screw-head and whatever the bolt or screw is fixing.
Give the main reasons for making a bearing arrangement where one bearing is designed to be axially locating and the other non-locating
If both were locating, thermal expansion and/or tolerances would create axial load
What are Wöhler diagrams used to study?
Fatigue properties of a material
What properties are Wöhler diagrams showing the relation of?
- Load level
- Number of cycles to failure
Explain why the stress concentration factor is only used in the first term of ANSI’s shaft diameter equation
Because stress concentrations are very bad for bending but less harmful for static loads
Give two advantages for using splines as a shaft-hub connection
- Can transmit higher torque
- Allows axial movement of the hub or shaft under load
The right way of pressing a bearing into a housing’s bearing seat
The press force should never go through the rolling elements since this will cause permanent indents and result in premature failure.
Give three examples of how a deep groove ball bearing can be axially locked on a shaft
- Nut
- Retaining ring
- Screw and washer
- Step on the shaft
Hub reducers are often used as the last speed reduction step in truck drive lines. What is the main reason for using them?
Reducing torque through the driveline
Explain the reason for using the modified endurance strength in the first term and the yield strength in the second term in ANSI’s shaft diameter equation
- The first term is bending which causes a pulsating stress
- The second term is torsion which causes a constant stress
What is the main advantage using a spring compared with using a nut for creating the preload?
It is easier to achieve the correct preload when using a spring, since the thread that is used with a nut makes load applied uncertain
The figure below shows a typical torque speed curve of an induction motor. Explain what is happening when n/ns > 1
The motor is forced to run faster than the synchronous speed (ns). The torque then becomes negative and the motor generates electric power (generator mode)
Define constraints and objectives
Constraints: Essential condition that must be met (e.g. maximum temperature 60 degrees)
Objectives: Quantity for which an extreme value is sought (e.g. minimize cost, minimize weight)