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tabs and hub for shaft of a pump

  • Thread starter Thread starter cugior
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cugior

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Hello my name is alessandro work in a shipyard.
Currently, despite not really my work, I am devoting myself to the sizing of a transmission shaft of the fire pump of our floating basin.
since I am a little rusty on these calculations I allowed myself to ask for your opinion on some details.

as the axis is about 8 m long I have the need to make joints (mancions) that transmit motion through tabs.

- note the torque, the diameter of the tree, the material of the tab, the section of the tab (table), how do you calculate the length? is it correct to obtain the minimum area of the tongue subject to cut due to the torque effect simply as a = f/tao, where f is the circumferential force that I echo from the couple and tao the tangential tension that I echo, through the criterion of mises, from the yielding sigma?
- if a joint consists of a cylindrical hub that presents the groove for the housing of the two keystrokes, how do I dimension the thickness of the hub?

I hope you can help me because I've been working for 3 days and I couldn't find anything about it.

thanks and soon
 
you should do cutting verification but also contact verification (use hertz).
do not use the yield, use the admin sigma, or take a safety coefficient on the admissible.
the tongue seat (not key, I imagine you're talking about tabs ... eye that size differently) is not a groove; is simply a seat!
the verification of the hub is torque, cutting, pressure (in the tongue area) and fatigue (as for the trees).
I hope you can help me because I've been working for 3 days and I couldn't find anything about it.
Click to expand...
Well, it's not exactly like that; on the tabs you find everything more but I also believe on the hubs!
Hi.
 
Thank you gerod,

You opened my eyes. I did the checks that you indicated me on the key both on the hub (in fact I did not run the one fatigued because my tree works vertically and therefore there are no variable efforts in time). I have only one problem. Does hertz not apply only for curved surfaces? My contacts are planary.
is it lawful to use the contact treatment between a cylindrical surface and a planar considering the diameter of the first very high or even infinite?
 
imho is wrong not to consider fatigue, I do not have it only with horizontal axis, but in any case where the load is variable over time. I imagine that the pump is not set in motion and then left there to work until it is replaced. the simple to turn it on and off is a fatigue cycle from 0
 
...for charity, it is true that a tree even if it works vertically is still subject to fatigue because it may vary the torque moment, but here we talk about a fire plant. statistically with what frequency and how long does it work?? ...I personally think that the fatigued dimensioning in this case is superfluous, but I'm not an activist.
I didn't understand, though, if you've got any keystrokes or tabs, you've cited them both.
the thickness of the hub is always function of the length of the tongue, or of the tau amm. and is automatically dimensioned once the tab itself is sized, unless materials with mechanical properties very different but at that point it is considered the material less resistant for the sizing, always with cutting safety load as suggested by gerod. or do you refer to any masses in rotation? It's just a joint, I don't think you're throwing a 300 wheel on a 20-wheeler, in case I worry about the tree. on 8 m, and I don't know what diameter of the tree, how many joints will you make? ?
I didn't understand why gerod suggested checking hertzian contact... However in case you consider the same formulas for linear cylinder-cylinder contact with an infinite radius, namely rm=r of the tree. here is a link of public utility:http://www.tribology-abc.com/default.htmGood lav!
 
you in fact a further verification I can do. You're right. in any case the pump will be operated periodically to verify the functionality of the plant.
a further question. .
what type of steel would you use, since periodically the axis will be immersed in sea water when the basin will be immersed in the maneuvers? I used, for my calculations, an aisi 304.
 
eek:
commercially speaking, put into account at least 316.
compared to 304 has a 2% molybdenum that increases corrosion resistance in marine environment (i.e. in presence of chlorides). once worked it is highly recommended to require a decapture treatment+passivation.
and know that however stainless, and however pre-passive it will still be subject to localized corrosion for pitting and crevice.
useless suggest to avoid geometries with small cracks etc for this second, which is so much anyway a type of corrosion **starda and autocatalytic that pits deep as a caries without you notice. much worse than generalized corrosion on c40 from the point of view of fatigue breaks.
useless to suggest also to use a super duplex stainless steel that so much does not find it and for 8 meters of material too costs you.
I add only, just to finish putting you anxiety (but you know, corrosion is my daily bread) that in this case you must also look after galvanic corrosion, that is to avoid using different metals and also inside the category of steels you must avoid using different alloys.
I tell you all this because I realize that the fire is one of the things you cannot afford to have out of service...:biggrin:
 
I would sincerely not use tongues but keystrokes.
If you tell me the diameter of the tree we can solve.
verification is very simple
4m/(hld) less than permissible voltage (snervation).
h is the useful height (so the height of the wrench minus the bevels),l is the length you need to look for, the diameter of the shaft.
Keep in mind that choosing the diameter of the aun 6604 provides you the width and height while the length you have to choose it in a certain range.
the cutting truth is already satisfied in this way.
be careful that if you use tabs the verification is no longer good, the value must be about 3 times so!!So if the tensions caused by the moment are high,use the key!
 
I don't think hertz's theory should be used.
I don't even agree with considering fatigue. attention that depending on the key you use you will cause a concentration of tensions due to the quarry and therefore you have to properly design the resistant section of the tree near the quarry!
 
In fact, I will use some tabs because, to couple the individual elements of the tree, I will use shell joints that are standardized according to din 115, and that make use, precisely, of the tabs. the diameter of the shaft in the coupling zone is bound to no less than 50 mm (I have to mate with the shaft section that is part of the pump that has d = 50 mm).
the torque to be transmitted is 410 nm. I have considered a standard tab, uni 6004 b 14x9x90 for which the length is well above my needs (I have checked at cutting and surface pressure even with hertz). I have no longer experienced fatigue because I have no variable loads in time that justify this verification.
I used (unfortunately yes!! it is necessary to look at the economic aspect) a 39nicrmo3 steel laminated and reclaimed because we decided to perform an anti-corrosion treatment (pitturation) in areas where the creeping bearings do not work. in those areas we will warm a stainless steel shirt.
This is in principle what we have predicted.
are open to comments or suggestions.
thanks to all
 
I have also done the verification of the tab.as you said the length is also beyond the need, but for safety this and other;)
Good, it works for me!
 

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