Preload (engineering): Difference between revisions
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'''Preload''' is a [[mechanical engineering]] term with several meanings. |
'''Preload''' is a [[mechanical engineering]] term with several meanings. In the general sense, it refers to the internally application of stress to certain mechanical systems. |
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==Fastener preload== |
==Fastener preload== |
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Second, a nut which is correctly tightened will resist coming loose under the influence of vibration, temperature cycling, etc. |
Second, a nut which is correctly tightened will resist coming loose under the influence of vibration, temperature cycling, etc. |
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== |
==Bearing preload== |
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When it is provided an internal stress to a bearing in order to apply a negative clearance it is know as bearing preloading or just preloading. Advantages for preloading are to keep position in axial and radial direction for accurate displacements of angular movements; preloading increase rigidity in bearings; it prevent slinding by giroscope-like movements, specailly with high acceleration or speeds; keeping relative position of bearing elements. Preloading methods include position preload and constant presure preload |
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<ref> |
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{{cite web |
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| last = Motion and Control NSK |
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| first = |
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| title = Rolling Bearings preload |
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| url = http://www.nskamericas.com/cps/rde/xbcr/na_en/Preload.pdf |
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| accessdate = 3 February 2015 |
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| archiveurl = |
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| archivedate = }} |
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</ref>. |
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==Testing preload== |
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It is also used in testing a specimen, for a process where the [[crosshead]] moves to load the specimen to a specified value before a test starts. [[Data]] is not captured during the preload segment. |
It is also used in testing a specimen, for a process where the [[crosshead]] moves to load the specimen to a specified value before a test starts. [[Data]] is not captured during the preload segment. |
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When [[tensile]] specimens are initially placed into testing grips, they can be subjected to small compressive forces. These forces can cause specimens to bend imperceptibly, causing inaccurate and inconsistent results. Establishing a small preload as a part of the test method eliminates those compressive forces on specimens and improves the repeatability of results. |
When [[tensile]] specimens are initially placed into testing grips, they can be subjected to small compressive forces. These forces can cause specimens to bend imperceptibly, causing inaccurate and inconsistent results. Establishing a small preload as a part of the test method eliminates those compressive forces on specimens and improves the repeatability of results. |
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==Applications== |
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Preload become very important for large mechanical and high performance system such as Telescopes<ref>{{cite book |
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| last = Bely |
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| first = Pierre Y. |
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| authorlink = |
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| title = The Design and Construction of Large Optical Telescopes |
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| publisher = [[Springer-Verlag]] |
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| series = Astronomy and Astrophysics Library |
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| volume = |
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| edition = |
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| location = |
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| date = 2003 |
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| page = 508 |
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| doi = 10.1007/b97612 |
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| isbn = 978-0-387-95512-4 |
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| mr = |
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| zbl = }} |
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</ref>. In the general sense, it refers to the internally application of stress to certain mechanical system. By tensioning preloading increase the natural frequency of a structure avoiding resonance due to external disturbances; prevent buckling by different stress in different position on certain systems; as in the particulary case for bearing or fasteners it reduce or cancel backslash or dead zones and limiting loads to the system. |
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==See also== |
==See also== |
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* [http://www.smartbolts.com/fundamentals/ Fundamentals of Basic Bolting] |
* [http://www.smartbolts.com/fundamentals/ Fundamentals of Basic Bolting] |
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== Notes == |
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{{Reflist}} |
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[[Category:Bearings]] |
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[[Category:Materials testing]] |
[[Category:Materials testing]] |
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Revision as of 23:09, 3 February 2015
Preload is a mechanical engineering term with several meanings. In the general sense, it refers to the internally application of stress to certain mechanical systems.
Fastener preload
The most common usage is to describe the load applied to a fastener as a result of it being installed, before any external loads are applied (e.g. tightening the nut on a bolt). Preload in such cases is important for several reasons.
First, a tightened bolt experiences only a small fraction of any external load which is applied later when the joint is in service, so that a fully tightened bolt can (depending on the exact application) sustain a much greater load than loosely tightened bolt.
Second, a nut which is correctly tightened will resist coming loose under the influence of vibration, temperature cycling, etc.
Bearing preload
When it is provided an internal stress to a bearing in order to apply a negative clearance it is know as bearing preloading or just preloading. Advantages for preloading are to keep position in axial and radial direction for accurate displacements of angular movements; preloading increase rigidity in bearings; it prevent slinding by giroscope-like movements, specailly with high acceleration or speeds; keeping relative position of bearing elements. Preloading methods include position preload and constant presure preload [1].
Testing preload
It is also used in testing a specimen, for a process where the crosshead moves to load the specimen to a specified value before a test starts. Data is not captured during the preload segment.
When tensile specimens are initially placed into testing grips, they can be subjected to small compressive forces. These forces can cause specimens to bend imperceptibly, causing inaccurate and inconsistent results. Establishing a small preload as a part of the test method eliminates those compressive forces on specimens and improves the repeatability of results.
Applications
Preload become very important for large mechanical and high performance system such as Telescopes[2]. In the general sense, it refers to the internally application of stress to certain mechanical system. By tensioning preloading increase the natural frequency of a structure avoiding resonance due to external disturbances; prevent buckling by different stress in different position on certain systems; as in the particulary case for bearing or fasteners it reduce or cancel backslash or dead zones and limiting loads to the system.
See also
External links
Notes
- ^ Motion and Control NSK. "Rolling Bearings preload" (PDF). Retrieved 3 February 2015.
- ^ Bely, Pierre Y. (2003). The Design and Construction of Large Optical Telescopes. Astronomy and Astrophysics Library. Springer-Verlag. p. 508. doi:10.1007/b97612. ISBN 978-0-387-95512-4.