×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# FORCE and TORQUE CALCULATION

## FORCE and TORQUE CALCULATION

(OP)
Hi,
Not done this sort of things since college days.
Some input would be much appreciated.

Please refer to the attached .pdf. The diagram is a schematic drawing only.

In order to determine the weld size, I need to calculate the force (N) at the diameter of the welds (888mm).

The inner flange is driven by a 250 kW motor which has a rotational speed of 42 rpm.
Given that motor power Kw=(T*rpm )/9552.4 where T=Torque (N m).

 T=(kW*9552.4)/rpm  T=(250*9552.4)/42  T=56859.5 N m

I calculate that the force at the weld diameter to be:-

force at weld=56859.5*((888/2)/1000)

 force at weld=128062 N

I deduce that the welds will be in shear.

### RE: FORCE and TORQUE CALCULATION

bretthydra, please check your kW to T*RPM conversion factor. I suspect you're off by a factor of 1000.

Also, please consider whether you have any thrust or acceleration in the application.

I used to count sand. Now I don't count at all.

### RE: FORCE and TORQUE CALCULATION

No that what I get going back to basics. That is a powerful motor to only do 0.7 reV per sec.

If the view you show is a section the force on a circular weld or weld's will be more like a shear stress not a force.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: FORCE and TORQUE CALCULATION

Shear stress yes. Over the thumb calc: if you take the 128062N as shear force it will act on a circular surface of app. 888*PI*8 = 22318 mm2 when the smallest weld width is 8 mm.
So shear stress is app. 5,7 N/mm2 which is a low value.

### RE: FORCE and TORQUE CALCULATION

(OP)
Thanks everyone,
As suggested by SANDCOUNTER, I am doubting the size of the force 128062N.
Take it a stage further from jlnsol:-
Circumference at the weld = 888*PI = 2789.7
Shear strength of weld material is 285N/mm2
Bearing in mind there are 2 welds.
So, area of weld required = 128062/285/2 = 224.7mm2
Width of weld = 224.7/2789.7 =0.08mm

All this of course is assuming that the motor is stalled by a force resisting rotation and no safety factors applied to the weld size.

### RE: FORCE and TORQUE CALCULATION

bretthydra, the force you calculated is correct, no doubt about that.
omega = 2*PI*n/60 = 2*PI * 42/60 = 4,398 rad/s
power is 250.000 Watt
torque is P / omega = 250.000 / 4,398 = 56844 Nm
force is torque / radius = 56844/0,444= 128027 N = 128 kN

### RE: FORCE and TORQUE CALCULATION

No. It's assuming that the 250kW motor is geared down to run at 42 rpm. A stalled motor torque might be a lot higher.

But yes you've discovered that welding is very strong.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: FORCE and TORQUE CALCULATION

Aside from all the rest, you want to be looking at the throat dimension, not the leg.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

### RE: FORCE and TORQUE CALCULATION

Stalled motor torquw might be higher..how much higher do you want it? times 2, no problem, times 4, no problem.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!