shaft diameter

[gorkus]

How can I get de diameter of the shaft that you need in this aplication:

Speed 1100 rpm.
Prssure 7 bar

Flow 927 l/min

 

[HPost]

You need to calculate the torque based on the pressure, flow and speed.

Identify the material and it's maximum shear stress.

Identify what FOS you want

Then calculate the area of the shaft that can withstand the torque induced shear stress, with the necessary FOS.

The point being, you have to do some of the work yourself. You need to learn how to do it for yourself.

Regards

HPost CEng MIMechE

 

[HPost]

As a start...

Pump power @ 85% overall efficiency = 12.7 kW

Torque @ 1100 RPM = 110.5 Nm

 

[gorkus]

I've calculate the torqued:

M=225000/pi *N/n ( kg.m)

Where:
M= Torque kg*m
N= Power Cv = 25 ( taking account the viscoity value )
n = rpm = 1100

So the Torqued value is:

1627.71 kg*m

Then chosen material is Steel 1140

Where:

d= cubit rt [16*M/maximum shear stress *( pi)2*N/n]

But I'm not sure where I can get thes maximu shear stress value for steel f-1140

 

[gorkus]

Sorry the formula is


d= cubic rt(16*M)/PI* maximu shera strees

If if use this value, maximum shear strees , I work out the diameter of my shaft which is able to endure this torqued. Is it right??

 

[HPost]

I'm not sure what units you are using...

(Pressure x Flow)/510 = Power Required @ 85% OA Efficiency

@ 1100 RPM Torque = Power / Speed

You also need shear modulus of the material which is 77.8 GPa for your material

 

[rrguy]

I believe the length needs to be calculated in?
It would matter to me if you are trying to design a 1 piece application or production type relibilty factor you want. If weight or cost is an issue? If those are not factors then you can oversize. if weight is an issue then a hollow drive shaft would serve the purpose better.

 

[gorkus]

But The viscosity of the fluid is 14 cSt @ 20 ºC??


So once I have the torque I'm going to this formula in order to get the shaft diameter.

d= cubic rd [ (16*TORQUE)/(PI * MAXIMUM ALLOWED SHEAR STRESS OF F- 1140)]

Is it ok???
maximum shear strees is 77.8 GPA??

 

[HPost]

Viscosity is resolved in the pump pressure and mechanical efficiency losses.

77.8 GPa is the the shear modulus, not shear stress. You only need it if you are going to work out the angle of twist.

Shear stress of shaft is (Torque/Polar moment of area) x shaft radius

Polar Moment of Area = (Shaft Diameter^4 x PI)/32

As a guide, use 85% of tensile stress for shear stress.

 

[HPost]

Length of shaft is used for angle of twist, not shear stress.

 

[gorkus]

Then

First I need to calculate the Torque:
In order to get it I use the following formula.


Shear stress = 16 *T/pi d^3

Where T = Torque kg*m= (225000/pi)*(Power( cv)/rpm)=
rpm 1100
Power 12.7kw *1.36 = 17.272cv
I get a Torque of 1124,55 kg*m
Shear stress: 85% de tensile stress of F-1140 = 450 MPA
450 MPA= 4588.5591 KG/CM2

I get D diameter of my shaft. 49.97 MM


is it right??

Thanking you in advance

 

[racookpe1978]

Unless this is a homework problem: you need to either choose 50 mm, or buy the next larger pump/motor/gland seal/flange/vibration adapter (there were no margins or safety factors in your assumed values!) larger than 50 mm. 8<)