Computing
Lab Press Force
The
force that a press can generate is a function of
the hydraulic fluid pressure and the effective area
of the piston or cylinder on which pressure is being
exerted by the compressed hydraulic fluid.
Generally,
hydraulic presses are designed to generate their
rated force or tonnage capacity when the hydraulic
fluid has been compressed to a pressure of 10,000
psi, which is the maximum pressure that the hydraulic
lines in most hydraulic systems are designed to
tolerate. Presses with higher tonnage ratings have
larger diameter pistons. For example, our 12 ton
EZ Press™ has a piston area of 2.4 square
inches while the
20 ton EZ Press™ and 20 ton AirEZ™ have
piston areas of 4.0 square inches, and all reach
their rated capacities when the pressure of the
hydraulic fluid is at 10,000 psi. In addition to
the obvious differences in capacity, this means
that a user of a manual 20 ton press will have to
generate significantly less line pressure to reach
10 tons of force than will a user of a 12 ton press.
Example
1: A 12 ton EZ Press™ with a 2.4 square
inch cylinder operated at 8,000 psi will generate
what force?
FORCE
= 8,000 psi x 2.4 in^{2}
= 19,200 pounds or 9.6 U.S. tons (8.72 metric tons)
per square inch
Example
2: A 20 ton EZ Press™ with a 4.0 inch^{2}
cylinder operated at 5,000 psi will generate what
force?
FORCE
= 5,000 psi x 4.0 in^{2}
= 20,000 pounds or 10 U.S. tons (9.1 metric tons)
per square inch

Computing
the Pressure Applied To The Sample
When
we use the term “force” in describing
a laboratory press, we are describing the load that
is driving the ram or platen. The force of a press
does not change based upon sample size, but the
pressure being applied to the sample does change.
For example, if the press is generating 10 tons
of force on the ram and the sample is one (1) square
inch, then the pressure on the sample will be the
same as the force on the platen – 10 tons.
But when the sample is smaller or larger than one
square inch, the formula is:
For
example, when there is a load of 10 tons on the
ram and a 1.25" diameter die is being used,
then the sample area is 1.227 square inches and
the pressure being applied to the sample is 8.15
U.S. tons.
When
a 1/2" (13mm) die set is in use, the sample
area is 0.1963 square inches and the same 10 ton
load on the ram produces 50.9 tons per square inch
of pressure on the sample.
Press
operating manuals contain charts showing pressures
corresponding to a range of both sample sizes and
loads. Copies are available on request.
