Applied Mechanics- Design of hinge support brackets for load in Pin axial direction 2

[Tejas123]

Hi all,
Actully in my current project ,I want to rotate the arm about vertical axis i.e. in horizontal plane. But while rotating it has to carry high gravitational load at its other end. This load is giving vertical reactions in hinge C bracket ( in which pin and arm is fixed ), which I want to design.

I was thinking to make C bracket by welding the plates together providing stiffeners and all .
But the main issue is how and what will be reactions in this C bracket.
How to go for it?

Thanks in advance.

design configuration- Arm is placed inside C bracket and pin is put vertically through both elements for locking and giving rotational motion only in horizontal plane

 

[desertfox]

Hi

Please provide a sketch with some figures regarding loading and its application.

thanks

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[SnTMan]

And perhaps dig out your Statics textbook.

Regards,

Mike

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

 

[rb1957]

I'd've thought you'd also be seeing large horizontal loads (offset moment).

read up on "free body diagram".

Sounds like you need a bearing surface between your arm and "the rest of the world", like at the lower hinge point, to react down load. If friction is a problem then maybe a ball bearing ?

another day in paradise, or is paradise one day closer ?

 

[chicopee]

Not only statics but also dynamics texbbook as you'll want to rotate the load which you will have some angular acceleration during startups andstarts and torque due to frictional force created during rotation.

 

[chicopee]

Son of a gun, my bad: "...during startups andstarts..." should be "... during startups and stops..."

 

[rb1957]

you know you can edit your posts ? (there should be an edit icon, between RF and delete)

another day in paradise, or is paradise one day closer ?

 

[Tejas123]

I am attaching a diagram with it....I hope it serves the purpoe intended.
pla check

 

[Tejas123]

actually I m really worried about is C bracket welds dosent break or C bracket should not open up bcoz of high load applied at other end.
so how will be the forces in Lower plate and upper plate and how to go for it

Its all sustainability of C bracket

 

[rb1957]

can you draw a free body diagram ? you need at least two (the arm and the C brkt), you could do one for the pin as well.

There is a natural loadpath for the vertical load out of the arm.

another day in paradise, or is paradise one day closer ?

 

[drawoh]

Tejas123,

Your hinge resists shear and moment. The shear load probably is minimal, and not worth worrying about. The moment will resolve into two very high loads at your pin interfaces, easily worked out by statics. The high friction forces could cause a lot of resistance to rotation. It will cause wear of your pin and the clearance holes. The shear forces on your pin might be significant.

Can you work out the forces and moments? Can you replace the plain bearing connection with ball bearings? Can you live with a short lifespan of your equipment? Can you make the pin soft and replaceable, and then harden all the other working surfaces? Are there any safety issues with this thing failing?

--
JHG

 

[Tejas123]

rb1957,

The same problem I am facing in free body diagram that "will pin oppose the moment created by load acting on arm or C brackets plates will oppose the same moment". As arm is precisely fit between the brackets with only manf clearance and also Pin and arm is connected by bushes even though pin is going to rotate with arm.

Then who will be taking moments??pin or bracket

 

[Tejas123]

drawoh,

Do you mean to say, even though there is no gap between arm and C bracket plates still the resisting moments will be opposed by pin only???

And yeah actually to avoid friction we have worked on it i.e.
The arm and pin is going to rotate together there is relative motion between them.
The pin and C bracket -in it we are putting ball bearing and Thrust bearing too to reduce friction and main purpose to increase the stiffness of joint as bushes flattens high loads with time.
actually motion of an arm is very less once we set it outwards it only has to take the high load at other end.

 

[drawoh]

Tejas123,

You are going to weld a bracket so accurately that there will be no gap between the arm and the C-bracket plates? I would like to see that. Increasing the radius to the friction face, increases the friction torque.

If this were my cantilevered arm, I would make the bearing section as tall as possible, to reduce the friction moments. Put a gusset between the bearing section and the beam.

--
JHG

 

[chicopee]

If it's a very high load, it is not a good design. The friction between the C clamp and the arm is going to be high and may even gouge the sharp corner at the entry side into the clamp.

 

[Tejas123]

Chicopee,
Actually there is very less amount of motion of arm like 3-4 times in a year but it has to take high load rest of the time. Its an outrigger to the vehicle. And load is not acting(except self weight) while in motion, once it is extended outward then it takes load
So still there be issue of friction or there is not much concern about it??

 

[chicopee]

You'll need sometype of a bearing surface as DRAWOH suggested.

 

[chicopee]

Being an outrigger, take a look at the designs of outriggers used on cranes and aerial lifts.

 

[IFRs]

Draw a free body diagram. The load resolves into shear forces in the pin, tension in the upper flange and compression in the lower flange. If there is zero clearance between the pin and the flanges and the pin and the long bar then there is no prying action. Since this is not the case, assume some clearance build-up and do another free-body diagram this time with the long arm at the downwards angle determined by the geometry of the gaps. This will resolve into a downwards force on the lower edge of the lower flange and an upwards force on the upper flange. The downwards force on the lower flange is resisted by bending in the lower flange and that is resisted by a moment in the weld and vertical leg of the C. If there is initial clearance between the long bar and the C then the pin may also see bending. Everything become visible and numerically evident when you make free body diagrams with dimensions and forces. Pick it apart one item at a time - it will be solved quickly...

 

[Tejas123]

IFRs,
So now as per suggested by "Drawoh" that its really difficult to weld C bracket plates by maintaining Zero clearance between arm and c beacket plates and additionally we are providing bushes between pin and arm so maintaining zero clearance between them.

So now as per your suggestion it is a case with clearance between Arm and C bracket plates with no clearance between Arm and pin.

I am attaching a free body diagram of this particular case. please see the attachment. and suggest me if I have done anything wrong as I m quite doubtful about it. And my doubt is
" In the pin (because of the force on arm) the reaction will be Only shearing action or we have to design pin for moment also. design criteria for pin ( shearing failure or Moment reaction or Both)

And if one says for moment also we have to design then moment of inertia section will be??
rectangular = bd^3/12= d*h^3/12
circular= pi* d^4/64

But I personally think pin will fil only by shear.
Thanks in advance