Bolt preload vs. transport screw torque

[blckwtr]

I have found several calculations and calculators regarding bolt preload for flanges etc, but I think this is different from the torque/tensile regarding a "free" transport screw or similar e.g. where the underlaying plates is NOT supporting the bolt preload.

Can anyone advise on this subject, formulas, links etc.

Regards

Tommy

 

[desertfox]

Hi blckwtr

I have heard of transport screws but not a free transport screw what is it? a sketch of what your talking about might help

desertfox

 

[blckwtr]

I'll try to explain first;

If you have a weight hanging from the screw this is the bolt load. Then you have a nut transporting this screw upwards. Then the preload in the bolt is then only the weight, and the moment transferred to the nut comes from friction between nut and bolt... This must differ from when you have something to squeeze between bolt head and nut...

 

[desertfox]

Hi blckwtr

Yes I think see what you mean, the nut is just run up the screw and supports the weight although the nut is not tightened up, so the weight can only transfer its load to the bolt via the nut.
The load in the bolt will only be the hanging weight and yes its different to tightening the nut hard up.
You need to check the threads on the bolt and nut for stripping.

desertfox

 

[CoryPad]

Leadscrews are screw threaded parts that do not clamp other parts. Equations are here:

http://en.wikipedia.org/wiki/Leadscrew

 

[desertfox]

Hi blckwtr

If its a leadscrew you mean then you can try this calculator:-

http://www.tribology-abc.com/calculators/e4_6.htm

desertfox

 

[unclesyd]

If I understand your problem the only things to be considered are the load, the friction factor between nut and threads, and last but not least is the friction between the nut and the nut landing area.

 

[blckwtr]

Thank's for all your good replies, just one more thing regarding nut landing area. is moment calculated on mean diameter or on diameter where inside or outside landing area is equal?

 

[unclesyd]

Here is a little information that may help.

http://www.hexagon.de/rs/k.htm

 

[desertfox]

Hi blckwtr

I think your talking about the torque applied to the nut to lift a component or weight if so trque is based on the pitch diameter of the thread.

look at this site:-

http://www.utm.edu/departments/engin/lemaster/Machine Design/Notes 27.pdf

desertfox

 

[blckwtr]

I am talking about the torque between the nut and the support for the nut. On the transport screw there are splines preventing the rotation. So total torque is torque between bolt and nut + torque between support and nut...

 

[desertfox]

hi blckwtr

Well I don't understand from your answer whether the link I gave you last is of any use, if it isn't of any use then put a sketch of your situation then we can see clearly what your trying to do instead of guessing.

desertfox