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Hydraulic press/cylinder questions

fgrauch

Plastic
Joined
Sep 19, 2023
I am looking for some hydraulic press information. A press salesman didn't know the answers. Here goes. For this example there are no variables except the hydraulics.
I am pressing a dampened powder into pressed solids using a 20 ton press with a 2" cylinder.

1) If I press 3" high by 3" Dia. powder to 10 tons in a tube, will it have the same density as pressing 6" high by 3" Dia. powder to 10 tons in a tube?
2) If I press 4 different tubes 3" high by 3" Dia. to ten tons will they have the same density as if I had only pressed one?
3) If I have a 20 ton press with a 2" cylinder and press to 10 tons, and a 20 ton press with a 3" cylinder and press to 10 tons will they be the same density?
 
I am looking for some hydraulic press information. A press salesman didn't know the answers. Here goes. For this example there are no variables except the hydraulics.
I am pressing a dampened powder into pressed solids using a 20 ton press with a 2" cylinder.

1) If I press 3" high by 3" Dia. powder to 10 tons in a tube, will it have the same density as pressing 6" high by 3" Dia. powder to 10 tons in a tube?
Yes (with some limited exceptions that likely do not apply at that length to width ratio)



2) If I press 4 different tubes 3" high by 3" Dia. to ten tons will they have the same density as if I had only pressed one?
Yes within the tolerances of the equipment used



3) If I have a 20 ton press with a 2" cylinder and press to 10 tons, and a 20 ton press with a 3" cylinder and press to 10 tons will they be the same density? No the pressure inside a 2" cylinder under 10 tons is 6369 psi a 3" cylinder under 10 tons is 2830 psi Also you mention its a 20 ton press when you give a load of 10 ton the size of the press doesn't matter.
 
When compacting earth fill, it has to be done in thin layers called "lifts", to achieve maximum uniform density. I assume your powder will behave similarly
WHy a tall column or thick layer will not compact as much as a short/thin one under the same pressure, I can only speculat. T suspect there is literature on the subject
 
Powders are funny. I had to experiment with ground concrete powders and found that they can bridge and resist movement even in a pile. Other powders will flow like water. So some powders will compact consistently others wont, I will say most wont.
 
It all depends on the powder particle shape vs what results you want. Spheroidal particles won't lock together compared to something with a jagged particle.

I'm sure the press guy gave you the pressure cylinder calc. Press cylinder diameter squared times hydraulic psi times .7854 = pounds of pressing force. This is nice data but is also useless as you need to see results.

All bets are off on how your powder will behave. Mess around and find out.
 
If it is blackpowder,the theory is that the sulfur becomes plastic under pressure ,and the density of the material increases considerably.......with correct compression the powder can equal half weight equivalent with TNT..(47%)
 
This can be very complicated science. The 3 dimensional stresses that occur in powders and granular solids under compaction are difficult to predict without first quantitively characterizing the material being compacted as well as measuring how it interacts with its surroundings. When I was in college back in the last century, I worked for 6 months in the test lab of an engineering consulting firm that specialized in providing bulk solids storage and conveying system design guidance. Their laboratory was well equipped for measuring the behaviors of the materials under all environmental conditions they were likely to be exposed to. This provided data for characterizing the material which then went into proprietary formulas that would result in recommendations for environment, geometry, materials and surface finishes of the material handling equipment. For the process you describe, the tests would likely have included compaction at your desired pressure with an instrumented mold that would help determine the ratio of transverse stresses to vertical force, and how that affected the compaction at varying heights. For a simple test, you can weigh a known amount of powder and compact it. Measure the height of the result, then put twice as much powder in and see if the compacted height is more, less or equal to twice the original result. In general, you want the press platen to be a close fit to the cylinder (uniformly distributed vertical load), and the walls of the cylinder to be smooth and have low stiction with the material being pressed. A wet powder has the added challenge of a variable moisture content before and during the pressing operation as some moisture gets squeezed out of the mix.
 
If it is blackpowder,the theory is that the sulfur becomes plastic under pressure ,and the density of the material increases considerably.......with correct compression the powder can equal half weight equivalent with TNT..(47%)
thanks
 
I realize I have been asking the wrong question. When pressing black powder, 10 tons of pressure is giving me 1.79g/cc. I am pressing 3" dia. 3" height. If I am pressing 3" dia. 9" height will I need 30 tons of pressure to get the same 1.79g/cc? Wanted to add if the 10 tons 3" dia. 3" height has a 1.5 dia. piston, then would a 10 ton press with a 3" piston be able to press a 6" dia. 3" height the same density?
 
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Powders behave differently. With some powders at some height, the bridging and sidewall friction will absorb all your pressure, and the end of the cylinder could be uncapped. Do not expect linearity.
 
I realize I have been asking the wrong question. When pressing black powder, 10 tons of pressure is giving me 1.79g/cc. I am pressing 3" dia. 3" height. If I am pressing 3" dia. 9" height will I need 30 tons of pressure to get the same 1.79g/cc? Wanted to add if the 10 tons 3" dia. 3" height has a 1.5 dia. piston, then would a 10 ton press with a 3" piston be able to press a 6" dia. 3" height the same density?

I think we need to seperate your questions.
1: compression vessel, the thing your powder is going into, you are asking about how a longer cylinder will work, the answer is it depends on the powder and how it behaves you will need to experiment to find out.
2: you are asking about a 10 ton press with a 1.5" cylinder and a 10 ton press with a 3" cylinder. 10 tons is a force applied not a cylinder size. Putting a 3" hydraulic cylinder in place of a 1.5" hydraulic cylinder and operating it at the same hydraulic pressure the 3" cylinder will have about 4x the force so assuming we are talking about a 1.5" cylinder on your 10 ton press being replaced with a 3" one then you now have a 40 ton press if the frame can take the load.
3: changing the diameter of the compression vessel from 3" to 6" will increase the force needed to compress the powder in relation to the area of the
4: #3 could be wrong if your compression vessel is not using a piston that is smaller of the cylinder it is made of, think pushing a 1" rod into a 3" cylinder and the rod compresses the material into a cup shaped slug. I don't think this is what your talking about but I could be wrong.
 
Are you trying to make a traditional pucked and granulated product like 2FA ?

If so, it's usually pucked as thin wafers1/4 - 1/2". To facilitate ease of granulation. And uniform density

If you're just making large BP type comets. You don't need nearly the same amount of density.
 








 
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