Want to know what is the best in terms of friction

[victor2006]

i want to use a 100 cm diameter piston witch will have 4000 kg of pressure on it.
Questions
-how thick does the piston have to be to hold that much weight if it is made of metal?
-what material should i use to make a seal to the cylinder wall and should the cylinder wall be another material then metal?
-what is the static friction on the cylinder wall and seal if lubricated?

thank you for your time

 

[mfb]

4000kg is not a pressure, it is a mass.

-how thick does the piston have to be to hold that much weight if it is made of metal?

Which metal?

-what material should i use to make a seal to the cylinder wall and should the cylinder wall be another material then metal?

Without any special requirements, steel is probably a good choice for the cylinder wall. The next question: which type of steel.

-what is the static friction on the cylinder wall and seal if lubricated?

Hard to tell without more details about the setup.

 

[fedaykin]

http://en.wikipedia.org/wiki/Friction#Approximate_coefficients_of_friction has some static friction coefficient values for lubricated steel on steel. I would not trust these values for any serious work though.

The coefficient of static friction gives you an approximation of static friction as a portion of the normal force. The normal force is basically how hard your surfaces are pressing against each other.

 

[victor2006]

What i want to do is have a cylinder that is made of steel (don't know what types there are but i guess regular)
with a height of 20 ft or so, filled with water. for the bottom of the cylinder i want a piston that would move 6 inches.

the volume of the water on top of the piston is about 4000 liters
i was wandering if you could tell me how thick the steel would have to be so that it would support that weight.