Shafts Flashcards
This is the component of all mechanical devices that transmits motion and power. Usually carries attachments such as gears, belt sheaves, or chain sprockets.
Shaft
This is a rotating device on which a wheel is mounted. Loaded transversely and are subject to bending.
Axle
This is a slender pin or rod which turns, or on which something else turns. Usually used to directly carry a tool for doing work. Must be very accurately installed.
Spindle
This is the part of the spindle, shaft or axle that rotates in or on a bearing
Journal
Shafting is available in various materials and finishes. These materials include low to high carbon steels as well as various stainless steels. Their finishes include: (4)
Hot and cold rolled, ground, and plated.
Selection of a material for a shaft is influenced by: (6)
Torque, speed requirements, components and their mounting methods, Compression and tensile limits, Contraction, bowing or expansion limits, Cost
This finishing process leaves a dark, rough, oxidized finish on steel. Size tolerance, concentricity and straightness have not been strictly controlled at the mill. For these reasons, bar stock is not intended to be directly incorporated into finished products and generally requires finishing by some machining process.
Hot rolling
Finished shafting has a smooth surface finish and is manufactured to close tolerances. They can be directly incorporated into finished products, however their costs can be greatly increased. What are the finishing methods used? (5)
Cold rolling, Machining, Centreless grinding, Grinding and polishing, Chrome plating
This is a basic cold finished steel in the low carbon range that welds readily. Used for general shafting purposes. Not recommended for high speed or high stress. Diameters maintained to a minus tolerance.
AISI C1018
The diameter of AISI C1018 is maintained to a minus tolerance. What does this allow?
Allows imperial size mounted bearings to be installed directly to the shaft.
To fit metric size mounted and unmounted, a larger size bore is selected and and a section machined to size.
AISI C1045/C1050 is also knows as:
Precision shafting
This shaft material is precision ground and polished. Made from medium carbon steels and distortion free. Can be used in high speed applications. Also available with a chrome plated finish for use as hydraulic piston rods and shafts.
AISI C1045/C1050
All sizes of _____ shafting and precision shafting over _____” are supplied in fibre tubes.
Chromed shafting and 1 1/4”
This alloy is hard, wear resistant and corrosion resistant
Chrome alloy
This alloy gives a long durability
High manganese alloy
This alloy has a high inherent strength
Nickel chrome steel alloys
These alloys are tough, corrosion resistant and wear resistant
Brass and bronze alloy
This alloy is a general purpose, medium carbon, chrome-molybdenum-steel alloy. It has high strength and is quite ductile, suitable for use as gears, axles and shafts.
AISI 4140
This shafting is used for power transmissions mostly on shaft mounted reducers. It’s easier to handle.
Hollow shafting
Hollow shafting has considerable weight loss while minimizing:
Strength loss
4” Dia. shaft with a 2” Dia. bore loses 25% weight but only 6.25% strength
This type of shafting is used where wear and corrosion are great
Alloy shafting
Shafts can be used to: (8)
- Transfer torque,
- Support equipment,
- Permit equipment to pivot to transfer motion,
- Permit a driven component to slide along shaft while transferring power,
- Extend the length of a drive,
- Change rotary motion to reciprocating motion,
- Provide supports for loads applied axially,
- Act as guides for slides
Proper labeling is the best way to identify shaft materials, but other methods are observing: (5)
- Surface finish,
- colour,
- weight,
- magnetic properties,
- results from spark tests, hammer and chisel tests and file tests
Stress can be defined as:
The internal resistance offered by a unit area of a material to an externally applied load
Normal stresses are either: (2)
Tensile or compressive
This stress tends to stretch or lengthen the shaft
Tensile stress
This stress tends to compress or shorten a shaft
Compressive stress
This stress is a combination of tensile and compressive stresses
Bending stress
This stress occurs when the applied force tends to cut through the shaft
Shear stress
An example of shear is the tendency of a key to shear off at the section between the shaft and hub
There is a direct relationship between the power, rotational speed and torque in a shaft transmitting power. When torque or twisting moment is applied, it tends to deform by twisting, causing rotation of one part of the shaft relative to another. When this stress is not distributed uniformly, this is:
Torsional shear
What can contribute to stress? (4)
- Weight of shaft,
- Components fitted to shaft
- loads applied to shaft,
- location of supporting bearings,
When a shaft is subject to many cycles of loading, stresses encountered are called:
Fatigue loading
The most fundamental type of fatigue loading is:
Reverse bending
The ability for a shaft to resist fatigue is called
Fatigue strength
_______ is produced when a load applied to a shaft bends it. The shaft is then rotated and bending continues, causing cyclic loading of the shaft.
Reverse bending
Another common type of fatigue loading is the repeated, one direction loading such as: (2)
Pulling or tensile loading
When a change in diameter occurs in a shaft______ _____ develop
Stress concentrations
In a shaft with a shoulder, the amount of stress concentrated at the shoulder can depend on what two factors? (2)
Ratio between the two diameters
The size of the fillet in the corner
Retaining ring grooves, holes and notches on a shaft can produce:
High stress concentrations
Any deviation from polished surface finish reduces the shafts:
Strength, fatigue strength
Which keyseat style has a lower stress concentration factor?
Runout keyseat
While you cannot eliminate stress, you can distribute it better. This results in:
Longer service life
Provide fillets whenever possible in a keyseat. When you do, what should also be done?
Edges of keys should be chamfered to match keyseat
When sections of shafting are to he turned down, the reduction in diameter should be no more than____. The fillet radius should be as large as possible to reduce stress concentrations
1.5:1
Is situations where the millwright has the choice of where to put the bearings, consideration should be given to:
Placing the support as close to the loaded components as possible.
There should be sufficient support on the shaft to prevent:
Shaft deflection causing fatigue stress
Failure to locate bearings correctly on a shaft can result in:
Changes in the clearance of mating parts
To maintain shafts in good working order, the millwright must attend to several factors: (4)
- Alignment
- runout
- shaft centers
- critical speed
Two or more shafts transmitting power from one to another must be:
Properly aligned to each other.
When aligning shafts, the axis of the shafts must be:
Parallel and in line, not offset
Shafts often require realignment because of: (4)
- settling foundations,
- heat
- vibration,
- bearing wear,
Some bearings and couplings can handle limited misalignment, but precise alignment reduces: (3)
- wear
- vibration
- fatigue loading
Many shafts have their ends:
Centre drilled
As a shaft rotates, small imbalances can:
Cause it to vibrate
For perfect running balance of a shaft, the center of gravity must be:
At the shaft centre
In most cases this is not so
Small imbalances on a shaft are normally tolerable, even at high speeds. As speed increases, a point is reached where there is excessive vibration. This speed is called:
The critical speed
Critical speed depends upon: (4)
- size of the load
- length of the shaft
- diameter of the shaft
- the kind of support bearings
The normal operating speed of a machine may or may not be higher than the:
Critical speed
Machines running close to their critical speed must be: (3)
- In precise alignment,
- balanced,
- have very little play in their bearings
A shaft and it’s attachments should maintain their relative position to the shafts center as they rotate. Any deviation (wobble) is called?
Runout
What are the 3 types of runout?
Radial
Circular
Axial
This runout occurs when the shaft and the attachments are not concentric in their rotation.
Radial runout
This runout occurs because of imperfections in the cross section of the part
Circular runout
This runout occurs because the attachments do not rotate perpendicularly to the shaft axis
Axial runout
Runout can result from?(4)
- Bent shaft
- Worn bearings
- Poor machining
- Poor assembly of components
Excessive runout can cause: (3)
- Vibration,
- premature wear,
- Possible seizing
Runout is usually checked by removing the shaft and attachments from the machine and rotating them:
Between fixed centers
A _________ is used to read the amount of deviation on the surface when looking for run out
Dial indicator
Shafts often develop this where they contact seals, bearings, and other components
Irregularities
The process of spraying a metal coating onto a metal object is called:
Metalizing
When metalizing, several types of coats can be applied including: (3)
Base coats
Corrosion resistant coats
Wear resistant costs
A method of repairing a damaged section of shaft is to machine the damaged section of shaft and:
Fit a sleeve over that section
When fitting a sleeve over a damaged shaft, what kind of a fit do you want?
Interface fit
Bent shafts wear out _____ and _____ and contribute to _________ and cause vibration
Bearings, seals, metal fatigue
What 3 steps are needed to fix runout in a shaft?
Remove the bearings and other attachments,
Locate the location with maximum runout
Straighten the shaft in a press, peening, or with heat
what are three factors that can lead to stress concentrations developing on a shaft? (3)
shoulders and other shaft modifications,
surface finish,
key seats
what are three ways we can reduce stress concentrations?
- maintainging surface finish,
- chamfered keys and matching fillets in key seats,
- reducing shaft diameter at shoulders by no more than 1.5:1
