ABSTRACT
Now–a-days almost all the industries
are introducing the hydraulics and pneumatic process into their production. The
tendency of automation is spreading widely in the industries and one can’t
imagine the automation of process without hydraulics and pneumatics. Thus these
two processes are considered to be the backbone of any automation. It reduces
the cost of production, manual labour and time immensely.
It is often a good idea to
power-operate the claims and ejectors in a fixture. The choice of power comes
down to pneumatics or hydraulics power.
PNEUMATICS CLAMPING AND EJECTION HAS TWO DISADVANTAGES
1. It is low
pressure; therefore the cylinder must
be large
2. It is
springy, and when a load is released, the piston jumps.
3. Also should a blowout occurs, large amount of energy are
released and the efficiency decrease.
Hydraulics
power avoids these problems, but the normal power back is expensive. But the
amount of energy required is always small, what we need is large force.
Therefore it is in the field that the hybrid “HYDRO PNEUMATIC” system
finds its place. Now with the help of hydro-pneumatics we can solve many problems
faced in the industries by hydraulics and pneumatics alone. Now hydraulics
pneumatics can be used in various applications some of them are listed bellow.
CASE-I
By designing a suitable hydro-pneumatics circuit we can be
able to clamps the work piece pneumatically and by using air-water intensifier
to expand tubular parts of soft metal such as copper aluminum etc. into various
shapes by fluid pressure.
Probable Solution:
By using
hydro-pneumatics we can solve these problems in the following steps:
1. At first we place the work piece in fixture and shift the
handle of four-way valve (2). Air pressure is directed to blind end of the
clamp cylinder (3) and the piston of cylinder clamps the work piece.
2. When the pressure builds-up in line number (3) then the
valve (4) is opened and the air pressure is directed to blend-end of air-water
pressure intensifier. The piston of intensifier advances and the work piece is
expanded.
3. Then we shift the
handle of four-way valve to its original position. The piston of the
intensifier retracts rapidly, releasing water pressure. Then the piston of the
clamp cylinder retracts at a slow speed set by speed of control valve (6).
4. Then the finished work piece is then removed from the
fixture thus completing the cycle.
The use of
fluid pressure eliminates the need of expensive expanding mandrels and other
equipments, and water as the expanding fluid eliminates fire hazards and
reduces clean-up time. The inexpensive system shown has many uses.
CASE - II
By designing suitable in-expensive circuits for a press we
can do the press working operation with synchronization of two hydro-pneumatics
cylinders.
Probable
Solution:
- We operate loads work piece onto press platen.
- Then we shifts the handle of four-way, to position valve
(2). Air pressure is directed to ports ‘A’ and ‘C’ of air hydraulics(R)
cylinders (3) and (4). Pistons of these cylinders advance as oil is forced
from port ‘S’ to port ‘T’ and from port ‘U’ to port ‘R’. This action keeps
the pistons of (3) and (4) in synchronization.
- When the press is closed and work is completed, we
shifts handle of valve (2) to original position. Air pressure is directed
to ports ‘B’ and ‘D’. Pistons of 3 and 4 are retracted in unison, as oil
is directed form ‘R’ to ‘U’ and from ‘T’ to ‘S’.
- The use of air-hydraulics ‘R’ cylinders provides an
excellent means of providing synchronization. This system is quite
inexpensive to set up and has proven quite accurate.
CASE
- III
In a circuits
and air control valve, air oil reservoir and a sequence valve with build in
check one are used with and hydraulic cylinders. Rearrange all the items so as
to give hydraulics die-cushioning effect.
Probable
solution:
1.
We loads work pieces into press.
2.
We shift the handle of three-way air
controlled valve (2). The purpose of air control valve is to allow air pressure
to flow from pressure regulator (1) into port no 1 of air oil reservoir (4).
The air will force oil out of part no 2 into hydraulics bypass and check valve
(7). This oil will then flow through check of valve (7) into port no 3 of
hydraulics cylinder (3). Which will move the piston to its forward position?
The two-air release valves are to vent air that may accumulate in the close oil
circuits.
3.
As the load is applied to the rod end
of cylinder (3) pressure will built up causing a cushion for the die. By pass
valve (7) has an adjustable pressure setting that can be regulated so that the
cylinder will have a sufficient load as a die cushion.
4.
As the ram of cylinder (3) is depressed,
the pressure will increase, and the high-pressure oil will pass through by pass
valve (7) into oil tank.
5.
When the ram attached to the die is
returned to up stroke, the cylinder will raise due to the constant air-
pressure in air-oil tank. The oil flow through the by pass and check valve (7)
into hydraulics cylinder.
AIR OIL SYSTEM
Definition: The association of oil with pneumatics powered equipment
to give more precise control of linear motion.
LINEAR SPEED CONTROL PNEUMATICS
CYLINDER
The speed of standard pneumatics cylinder
can be fairly accurately controlled by metering exhausting air that is creating
a backpressure in the exhaust line. This type of control may be adequate for
lots of application; it would not be suitable for machine tool slides where
slow and accurate fee\d rates are required. This is because air is compression
fluid and would give a spongy action to the work feed table.
As all is practically and incompressible
fluid it can be more accurately metered in small quantity. Hydro-pneumatics
brings the advantages and simplicity of pneumatics cylinders for linear motion
with thrust together with the smooth step less control of an oil hydraulics
feed.
1. AIR OIL
SYSTEM
This system uses near standard pneumatics
equipments but has the work cylinder pressurized with Oil. Air is passed
through direction control valve to reservoir (1) to pressure the oil. Oil is
then forced through the free check of the flow control valve (3) and into the
end of the cylinder. The exhausting oil being pushed out of other end of the
cylinder is metered through the adjustable orifice of the flow control valve
(4) before passing into reservoir (2). Reversing the D.C valve pressurizes the
reservoir (2) to return the cylinder under control of flow control valve (3).
Disadvantages of air oil system:
1.
To reservoir required each larges in
volume then the work cylinder.
2.
Reservoir must always be mounted above
the work cylinder.
3.
Bulky and not a very neat assembly.
4.
Many fitting required with potential
leaks.
5.
Oil levels in reservoir must always be
kept balanced,
6.
Air absorption in the oil must be
avoided that is a floating piston is usually fitted in the reservoir.
INTENSIFIERS
Compressed air can be
used as a source of high-pressure hydraulics employing an intensifier cylinder.
This can be particularly attractive where elimination of the hydraulics pump is
desirable and relatively low flow rates are required on the hydraulics side the
base is of such set up is shown in fig.
Compressed air
is feed into the blind end of intensifier cylinder comprising the airside.
Forward movement of the piston rod now produce a plunger action in the smaller
(oil) end of the intensifier. A typical intensifier ratio would be 50:1, when
air is 80lbs/in would yield a fluid pressure of 4000lbs/in in the cylinder.
FUTURE
SCOPE
By using hydro-pneumatics system the
automation process becomes very easy we can make any complicated circuit into
an easy manual form by using hydro-pneumatics. Now days it is used in railways
it is try to be used in aeronautics also.
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