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19 Cards in this Set
- Front
- Back
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Name the types of bearings and their general use |
Plain bearing - sliding motion, Rolling elements bearing - rolling motion |
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Explain two issues that arise from bearing use |
Sliding inside the bearing causes friction, which then causes wear and heat (leading to inefficiency and failure) |
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List the types of lubrication |
Partial: Boundary, Dry, None Film fluid: Hydrostatic, Hydrodynamic |
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Describe the features of boundary lubrication |
A grease or oil film is applied, which carries a portion of the load. However, the surfaces are still in contact which leads to wear. For moderate loads and speeds. |
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Describe the features of dry lubrication |
Usually something like graphene powder which is easily retained by the part. The surfaces are still in contact which causes wear. For low load and speed |
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Describe the features of no lubrication |
When a polymer is used as the bearing surface, there is no maintance required. But surfaces are still in contact, causing wear. For low loads and speed. |
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Describe the features of hydrodynamic lubrication |
When a wedge of film of lubricant holds surfaces apart there is no wear generated. Pressure of the film is increased by rotational speed. Good for high loads and speed. |
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Describe the features of Hydrostatic lubrication |
Film pressurised by an external pump holds surfaces apart causing no wear. Good for high load and low/moderate speed. |
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Define Embeddibility (EM) |
The ability of a material to safely embed contaminant particles onto its surface and minimise damage. |
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Describe how to calculate the PV value of a bearing and why it is used |
PV = Pressure x velocity x 2 If this value is exceeded the bearing will heat up and fail through melting or warping. |
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What materials would be used for a plane bearing? |
Soft materials like: White metals, Copper alloys, Aluminium alloys, Polymers, Porous sintered metals, |
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Give an example of White metals used in plane bearings and its advantage |
Tin or lead based alloys, as they have good EM |
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Why would copper alloys be used over white metals in a plane bearing? |
They are stronger and have better thermal conductivity |
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Give the features of using aluminium alloys in a plain bearing |
Good strength, but poor EM |
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Why would you use Polymers in a plain bearing? |
No lubrication required |
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Why are Porous sintered metals used in plain bearings? |
They can retain oil in pores in the surface of the metal |
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What material might be used for a shaft (which will have a plain bearing attached) |
Hard materials, like hardened steel |
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List the advantages of plain bearings over roller contact bearings |
Smaller overall diameter, Cheaper, Quieter, More tolerant of foreign particals if lubricated externally, No fatigue life, Better at withstanding shock |
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List the advantages of roller contact bearings over plane bearings |
Lower starting friction, Easier to lubricate than hydrodynamic or hydrostatic lubrication, Less axial space required, Can withstand axial and radial loads, Standard items in many different configurations |
