Hydropneumatic intensifiers
are widely used on conventional machines, where hydraulic power
unit is not available
with the machine. Single acting elements are generally used with
hydropneumatic intensifiers.
Principle:
In the static condition, (Pressure
x Area) at air side is equal to (Pressure x Area) at oil side.
Description:
Hydropneumatic intensifier has one
oil cylinder and one air cylinder. The pistons of both these cylinders
are connected to each other. In single acting intensifier, the
air cylinder is single acting, spring return. In double acting
intensifier, the air cylinder is double acting. The air piston
is the driving piston and the oil piston is the driven piston,
in both the types.
Operation:
When air is allowed in the intensifier by
a D.C. valve, oil on the hydraulic side gets pressurised and is
forced out. The oil output operates the clamping cylinders and
the job gets clamped. After releasing the air pressure, due to
the spring in the intensifier (return air pressure in the double
acting intensifier), the air piston returns back and the job gets
declamped. Oil
is pushed back into the intensifier due the spring in the cylinder.
Note:
Selection of intensifier:
1. Intensification
Ratio : For 5 to 7 bar air pressure,
select an intensification ratio of 28 so as to get about 150 bar
hydraulicoutput. For 3.5 to 4 bar air pressure, select an intensification
ratio of 40 to get about 150 bar hydraulic output.
2. Oil
Output : Oil volume for every cylinder is given in the
catalogue. Sum up all the oil volumes of the cylinders to get
the total oil requirement. Intensifier output must be more than
the total oil volume required.
e.g. To use 2 cylinders of part no. 1510200 and 2 cylinders of
part no. 1540100 for clamping a job,
Oil required = (oil vol of 1510200) x 2 + (oil vol of 1540100)
x 2= (22 x 2) + (34 x 2) = 112 cc
Select the part no. 1128200 with 200 cc oil output.
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Leakage Compensation:
(Make up oil system)
This is an important feature of hydropneumatic
intensifier. The oil- side of the hydropneumatic intensifier,
hydraulic hoses and cylinders form a close loop system. Oil in
this loop is a confined fluid. There must be a leakage compensation
for the confined oil, if there is any leakage (across piston of
cylinder and through connectors). The make-up oil system, compensates
for leakage by adding small volume of oil at every stroke.
In the unpressurised mode, make-up oil is always connected to
the oil side. In the pressurisation stroke, as the piston movesup
and crosses the high pressure seal (Fig 1 page no. 1.3), the make-up
oil gets disconnected from the oil side. In case of leakage, when
the system pressure is released after operation, the hydraulic
piston moves down to the bottom. When it crosses the high pressure
seal, the make-up oil gets connected to the oil side. Any leaked-out
volume causes vacuum on the oil side and is automatically compensated
due to the atmospheric pressure.
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Selection of compressor:
Compressed air requirement can be calculated
as follows :
Compressed air volume required per cycle = Intensification ratio
x oil output.
e.g. For the intensifier of ratio 28 and oil output 100 cc,
air required per cycle = 28 x 100
= 2800 cc = 3 lit. approx.
If number of jobs per hour = 20 then
air required per hour = 3 x 20 =
60 lit / hour at 5 bar.
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Accessories:
1. FRL - Filter, Regulator
and Lubricator Unit. Filter to separate
water from compressed air,
Regulator to regulate air pressure to 5
bar, Lubricator for lubrication of
valves and the pneumatic seal of the intensifier.
2. D.C.Valve - Direction Control valve - (3/2
way valve).
On position - Job gets clamped.
Off position - Job gets declamped.
3. Q.E.Valve - Quick Exhaust
valve -
To increase declamping speed.
4. Pneumatic line
The hoses which should withstand
an air pressure upto 10 bar
5. Hydraulic line
The hoses of R2 grade or metallic
piping which should withstand an oil pressure upto
200 bar.
Copper washers or bonded seals must be used
for connectors.
6. Pressure gauge-
Use
glycerine filled gauges of 400 bar capacity.
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Safety elements
Hydraulic Pressure Switch - The clamping
force is directly proportional to the air pressure
in the intensifier. Precaution must
be taken to maintain this air pressure, and shut down the
machine if the pressure is not sufficient. The pressure switch
will shut down the machine,
if the oil pressure drops below the
preset value.
Points to remember while designing the system:
1. Keep
the system as simple as possible.
2. Keep minimum
no. of connections in the circuit to avoid possibility of leakage.
3. Try to minimise
the hose length and use a quick exhaust valve to get a quick return
stroke.
4. Use bonded seals
for leak proof connections.
5. Keep the intensifier
preferably at the highest points for easy bleeding.
6. In case of a
rigid piping, use a slant piping going towards intensifier for
easy bleeding.
7. For easier bleeding,
avoid loops in hoses or rigid piping.
8. In a hydropneumatic
system, a flow control valve with a check valve can be used to
achieve
a delay in butting and clamping cylinders as shown in figure.
Do not use more
than one
such valve in the circuit. Adjust the cracking pressure
of the check valve to less
than 0.3
bar.
9. A single
acting swing clamp should not be used after a sequence valve.
Two separate
intensifier
circuits can be used for better sequencing.
10. For hole punching, an external
spring force should be applied in the hydropneumatic
system as stripping
out force is not available.
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