Can Hydraulic Tonnage Be Added for Increased Press Capacity?

[hmc]

hydraulic tonnage question Help

I have a small machine shop. I need to build a 600 ton press. I have a 300 ton press now. Can I simply add a 300 ton cylinder to the other end of my existing press and get 600 tons on an object in the middle or is tonnage not additive?

 

[hmc]

I would really appreciate any help I could get. I was wanting to start on this in the morning buy I am perplexed. I'm sure the answer and explanation are simple and that I am over thinking this. But I do need help

 

[Averagesupernova]

Sure you can do that. But I won't guarantee it won't tear your press into two pieces.

 

[hmc]

I figured the yield and square inches of my press frame. The yield is 636 tons. The tensil is much higher. 1018 cold finish flat bar. 53700psi yield. I get 50/50 answers from everyone I talk to. Half say 300 tons because the cylinders cancel each other out. I realize that if one cylinder reaches it's full stroke then it is basically a stationary object and would no longer count. However with both cylinders pushing the same tonnage. I believe I will get 600 tons on the object in the middle. I would like someone to answer with some way of proving their reason to me because the material to build a 600 ton cylinder is very expensive and I would hate to waste the money.

 

[Averagesupernova]

So if you hook two cylinders in parallel you effectively double the piston area right? So why would it NOT double the force? It will certainly halve the speed of travel compared to one cylinder. Everything about it says it will double the push.

 

[hmc]

Not side by side. facing one another. The people on the general physics forum say 300 tons.

 

[Q_Goest]

I think you're saying you have one press acting downwards and another press you want to mount opposed to that, acting upwards. So as these two are actuated, they press from opposite sides acting toward one another. If that's the case, then you only get 300 tons of force.

They only double the force if they act in the same direction and parallel with each other, like your two legs. Think of squating down with both legs. Not too hard to bend all the way down and stand up again. But if you tried that with one leg it would be very difficult. Two legs in the same direction acting together in parallel you get twice the force. If you had two people laying on the floor with their feet together, you can only push as hard as one person can push. There's no increase in force.

Note also that if you had one bottle jack stacked on top of another bottle jack so they are acting in series, you would also not have any additional force created. The two bottle jacks have to act in parallel like your two legs.

 

[JasonD]

Wow, what a great question. I was completely convinced that I knew the answer until I started thinking about everyone else's reply.

If you compress an object on one side with a force it will experience that force. If you add another force to the opposite side, the object will now experience both compressive forces.

Lets say that only one cylinder is in use and the one on 180 degrees away is locked we would all agree that the object in the middle is experiencing 300 lbs of force. Now if the second cylinder (on the other side of the object) begins to extend and apply 300 lbs of force, the object in the middle should experience both compressive forces. Nothing happened to the first compressive force - it's still there. A second one was just added.

With that, I completely accept that I might be wrong! If you try this out, please let us know the answer.

 

[nvn]

hmc: Are these hydraulic cylinders you are referring to? If you have two hydraulic cylinders in parallel (side by side), you will double the applied force. But you have two hydraulic cylinders in series (end to end). Therefore, you will not increase the applied force. The force will be the same as one hydraulic cylinder.

Here is the proof you were asking for. If you have one hydraulic cylinder that outputs a maximum applied force of F, then the anvil it is pressing against already is pushing back with an equal and opposite reaction force F. Now if you replace the anvil with another hydraulic cylinder that outputs a maximum force F, then you simply replaced what the anvil was already doing (except you have replaced the anvil with a more expensive and weaker part). The pressure in the hydraulic fluid can go up to only p = F/A; otherwise, you will damage your control system, right? Therefore, you cannot obtain higher than F = p*A, regardless of how many hydraulic cylinders you place in series (end to end).

(Even if you can apply higher than p = F/A without damaging your control system, you cannot apply this to the hydraulic cylinder, because you will overstress and damage the steel in your hydraulic cylinder.)

Even if these presses are mechanical, instead of hydraulic, the answer is the same, because you are replacing the anvil with a second press, in series (end to end), that outputs a maximum force F, which is the same as the reaction force that was already applied by the anvil.

 

[Averagesupernova]

Two cylinders of the same size facing one another will not increase the push. I misunderstood.

 

[JasonD]

Looks like I was wrong, too...