Hand Calculations (Design verification)

[CarlosEstinos]

Hello All,

I have a drive interface that i have attached in a drawing. The green component is a splined rotational drive shaft from a hydraulic actuator. This drives the silver shaft which is a valve. Ive been trying to get my head around FEA recently, but have come to the conclusion that it would be safer to verify my design by using hand calculation as im not fully proficient at FEA yet!. Im currently studying (part time) a Mechanical engineering degree which i am 2/3rds of the way through so i have some a fairly good understanding of basic prinicples along with the Maths thats required.

The drive components in my design are meshed with a key. The red and blue flanges would be bolted toghether with 4 bolts and this is what connects the valve and actuator. There would be a rotationlal reaction force(torque) between theses two flanges.

Im just after some feedback on what route i would need to take to verify that the torque delivered on the green drive gear would not shear the silver stem or the bolts that bolt the red and blue flanges together.

Any help is gratefully recieved.

 

[desertfox]

For the keyway go here:-

http://www.roymech.co.uk/Useful_Tables/Keyways/key_strength.html

 

[zekeman]

Looks like homework.
And a 2/3 complete engineer should easily handle this.

 

[CarlosEstinos]

Thanks for the encouraging words zekeman! It most definitely isn’t Homework I can assure you that. It’s to do with my line of work. I am a Project Engineer. Being 2/3 rds of a complete engineer takes much more than just having a degree. But I do agree that I probably should be able to solve that kind of problem but this isn’t something I do day in day out so I felt it necessary to confer to the engineering community!
I always like to gain as much feedback as possible when trying to solve any task. My main uncertainty is how you mathematically model such a system. Surface contact area between initial and final drive must surely be important ,as is what key you use(dimensions along with all tolerances) . Thanks for the link Desertfox, i didn’t think to look at roymech , i will have a look now.

 

[rb1957]

"Surface contact area between initial and final drive must surely be important" ... are you implying friction between the red and blue plates ?

but aren't the initial and final drives connected by the key ? so what torque is transferring across the red/blue interface ?

in any case, if there are fasteners between the red and blue plates, these would take the torque, F = torque/(PCD/2)/n

 

[CarlosEstinos]

[/quote Surface contact area between initial and final drive must surely be important" ... are you implying friction between the red and blue plates ?]

No I’m not implying the friction between the red and blue plates. They would be static and would be fixed with 4 fasteners.
I was referring to the surface area in which the initial and final drive interact with each other

 

[Cockroach]

Possibly we could answer two threads on key ways with one solution. Problem here is that I need some design inputs like shaft size and material. What about the Hub? Nice to have material. Sizing a key from first principles is easy, given the proper information. Bet you a few regulars to this forum do it in their sleep.

Regards,
Cockroach

 

[rb1957]

"I was referring to the surface area in which the initial and final drive interact with each other"

I'd count the key as loadpath between the drives, unless you've used an interference fit between the drives (which i doubt).

 

[CarlosEstinos]

I had been delayed in replying as the manufacturer of the actuator had taken a while to get back to be with the material specification of the drive coupling.

Material of the input drive is SS 2142
The material of the shaft is A182 F51 (Duplex) Outside diameter is 50 mm
I haven't chose a key material yet but will assume it to be Standard key steel something like EN9 The Key is DDIN6885 14x9x80 . The tolerance on the shaft 14JS9
There are three things I am trying to work out here.
is the key strong enough? (rb1957 you are correct in that it isn't an interference fit. So considering that I guess the key would be a load path, this was something I was little unsure of) Would I be calculating the maximum allowable shear stress? Along with the actual shear stress?
is the shaft strong enough? When will it shear?
Also from this I want to calculate the maximum allowable stem torque. The point at which the shaft will begin to deform

I've attached a page from Roark's Formulas for Stress and Strain
Example28. I believe this is the profile I'm talking about. Am I right in saying K is the polar moment of inertia?

Also for my example the ratio of b(key intrusion into shaft) and the radius would be 4.25÷25 = 0.17
The ration between a/b would be 7 ÷4.25 = 1.64 . This figure does not fall into the range specified in this example 0.3 ≤ a/b ≤ 1.5 . If it did fall into that range how would I calculate that the key is fit for purpose and that the shaft wont shear. Also the maximum allowable stem torque(the point that it begins to deform)

This is a real scenario! and any help would be fantastic. If anyone has other recommendations for literature that I should buy to assist me on these problems that would also be most appreciated.

Carlos