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Loctite and Preload
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Posted by: Aztek

06/27/2006, 05:11:21

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Hello,

As it is known, preload is applied to the fasteners to prevent loosening. Also there are some loctite products to be applied to the fastener threads for the same purpose.

I would like to ask, if preload is needed or not for the fasteners that we have applied loctite? If yes, should we apply the preload as if we did not apply loctite?

As it is known, applying preload weakens the fastener also. So I do not want to apply preload to the fastener.

Thank you!








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Re: Loctite and Preload
Re: Loctite and Preload -- Aztek Post Reply Top of thread Forum
Posted by: Kelly_Bramble

06/28/2006, 09:13:04

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Preload is applied to fasteners for more reasons than to prevent them from loosening. Fatigue (cyclic) loading causes the fastener to change stain (more and less stretch). The thread interface actually moves a little during the change of loading. Thread locking materials, like Loctite are used to help prevent the fastener from loosening during load cycling due to vibration, thermal, fatigue, or a combination of the factors. Somtimes, Loctitie or other thread compound is applied to seal the threads from the environment, helping the corrosion resistance of the interface.

Applying a preload to a fastener does not weaken the fastener, however it does effect the working load. Normally the fasteners used are so much stronger than required. Grade 5 and 8 fasteners are brutally strong. Your design should include some sort of preload to ensure the parts are properly secured together. You should determine the working load required for your assembly and design for fasteners that are size appropriate. It is not uncommon for fasteners to be 100 times stronger than required even with preload.

Other problems associated with loose fasteners:
Thread galling
Burnishing
Thread Fatigue and failure

FYI: A survey was done in the US of automobile repair and service managers which found that 23% of all car service problems were traceable to loose fasteners. 12% of new automobile and trucks where found to have fasteners loose.









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Re: Re: Loctite and Preload Agree
Re: Re: Loctite and Preload -- Kelly_Bramble Post Reply Top of thread Forum
Posted by: Aztek

06/29/2006, 02:55:39

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Thanks for your help!
I'll consider your words








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