Bolt Clamp Force 1

[somarp]

I need some help - I am working on a new design. I will tell you that I am not an engineer, but just a mechanical designer so please understand the basics of my questions.

I am designing a carriage that is rack and pinion drive. The carriage is being driven by 2 planteries with 2 Eaton motors driving them. The planeties are developing 30,000 pounds of force - 15,000 per each side.

The are 2 racks that are welded to a 8" x 8" sqaure tube and the carriage pinions run along the outside of the rack.

I am installing 2 prox switches at the end of the travel at one end of the tube. The first is a slow down and the switch is a stop.

My question is - I am wanting to design some mechanical stops to install to the side of the rack at the end of the tube. The stops would be there if in the event of a failure of either prox which would probably result in damage to the rack system.

I am thinking about using 2 square bars - 2" think and drilling thru holes in them and then drilling and tapping the rack on each side. Therefore I would mount the bars with bolts on each side of the rack. So in the event of a switch failure each bar would potentially see 15,000 force being applied to them. I know to design the bolts to withstand the shear force, but I am curious do I need to address the clamp force of the hardware to withstand the 15,000 force. I am thinking that I need too, but am unsure how.

I would appreciate any help. Thanks in advance.

 

[MikeHalloran]

I think you're on the right track, but I'm not getting a complete mental picture of what you've got and how many ways it could go wrong. It sounds like a failure could get real expensive.

Tell your boss that renting an engineer for a while is cheap insurance.





Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[Barry1961]

Just to give you an idea of what Mike is talking about.

A 30,000lb horizontal traveling carriage that is coasting, not driven, at a speed of 12" a second that hits a hard stop will require over 90,000lb of force to stop it. This is assuming that the "hard" stop deflects or is deformed .06".

With the same carriage traveling at 24" a second the force would be over 370,000lb. Don't even try to extrapolate it.

A very rough guess on the force to move the same 30,000lb carriage would be 6000 in-lb of torque.

A very rough guess on the force to accelerate or decelerate the same carriage at the gentle rate of 38 in-sec^2 would be around 18,000 in-lb of torque.

All of these a very rough guesses based on previous machines I have done. They may have nothing at all to do with your application. A skilled engineer may be able to save your enough money in your drive train to pay his wage.

Bigger is not always better. This is particularly true if you are running it into a hard stop or in a jam. What happens if one of your drives locks up and the other keeps running? Can your guidance take the twist/side load it would cause on the other rail?

Listen to Mike he knows what he is talking about.

Barry1961

 

[sreid]

How about some hydraulic snubbers.