Joints and Pains of Hydraulic Cylinder

Joints and Pains of Hydraulic Cylinder
Mohan kumar L , Jayakeerthi S, Ganesh K C, Ramesh D.
Wipro Infrastructure Engineering Ltd.
Bangalore 58.
Abstract
"Enhanced solutions to achieve long painless life of Hydraulic cylinders and hence end equipment".
Hydraulic cylinder is the ‘muscle of fluid power’ linking load, structure and hydraulics. It will act like
rigid steel yet flexes like fluid accomplishing the duty and task like the knees and arms which do all
walking and working hydraulic cylinders perform their duty relentlessly straining and damaging
joints.
No other member in the machine experiences the modes a cylinder encounters viz.,
-
buckling
bursting
bending
bulging
twisting, shearing, tearing, tension compression ………….
The construction, cross-section, steel in all its composition and treatment along with functional
surfaces do call very high degree of super precision design and manufacturing – with culture of its
own.
Aptly over the years “Hydraulic Grade’ is established in terms of
-
material – castings, forgings, tubes, rods etc.
heat treatment
surface coating treatments
Hydraulic tolerances, forms & finish.
Anatomy of hydraulic cylinder reveals many critical members and joints.
-
impacting & high load motion surfaces
welded joints to resist hydraulic pressure shocks, peaks and mechanical impacts
prestressed threaded joints integrity and tactness under milli-second/fraction of m sec shocks and
peaks
friction welded joint survive tension, twisting, bending, compression and sheer loads
barrels – not just pressure vessels but under pressure hoop expansion maintains cylindrical bore for
piston operation
rods – take all the abuses direct/side loads
Each of these members or joints are subjected to both static and dynamic stresses – high or
low cycle fatigue leading to damage hence fatigue failure.
This paper describes various critical joints of hydraulic cylinder & discusses
-
joint construction
material and design aspects
static and transient loading aspects
joint analysis and
cyclic load testing of joints
Systematic approach in terms of understanding the loading, design, materials, stress analysis,
laboratory and field testing presented .Accelerated to Highly accelerated test methods are discussed
1.0
e. Aircraft's
Introduction
1.1 Muscle and Motion behind productive &
performing machines
Ever since Blaise Pascal, Joseph Brahma,
Bernoulli and others contributed to Fluid
Systems and Energy, it is in the last century we
saw host of machines and innumerable
applications
deployed
hydraulic
power
transmissions. Some of them (popular ones) are
Machines & Equipments that need power &
precision.
Civil
Military
f. Plant
a. Construction Machines
Steel Plant
Excavator
Backhoe Loader
Dumper
Cement Plant
Tractor
Grader
Injection Moulding
Fig. 1 - Machines
b. Industrial Equipments & Machines
In all the above the power conversion and
transmission from the engine / electric motor to the
point of application, completely fluid / oil linked.
This has made the entire design flexible with ease
of control of energy.
Forklift
Drill Rig
Crane
These machines operate in the pressure range
7 MPa (approx. 70 Kgf/cm2) to 42 Mpa (approx.
420 Kgf/cm2) & velocity range 0.1 to 1 m/sec max.
c. Truck Hydraulics
1.2 Elements of Hydraulic Power Transmission
Tipper Underbody
Garbage Compactor
Tipper Frontend
The typical power transmission system is illustrated
in the diagram.
Dumper Placer
The primary elements are :
• engine / electric motor driven pump
• control valves
• actuators (cylinders / motors)
Truck mounted crane Car Carrier
d. Agricultural
Tractor
Tractor
The secondary elements are
•
•
•
Harvestor
Forestry
2
conductors (Pipes, Hoses)
conditioners (Filters, Heat exchangers)
oil storage / tank with accessories
2.0
Hydraulic Cylinder & Working
Principle
Hydraulic cylinder consists of ¾ Barrel / tube mostly ‘stationary’ having
precision machined & super finished bore
(honed / burnished)
¾ Rod / Ram mostly ‘moving’ having precision
grinding followed by super finishing
¾ Piston and ram rod seals provide sealing
between chambers containing pressure yet
allowing motion – thus accomplishes Force &
Motion
¾ Bearings on piston & rod / ram facilitates the
necessary motion between bore-piston and
cover & rod.
¾ Hydraulic oil ports for extension & retraction
Fig. 2- Elements of hydraulic power transmission
1.3 Roll of Hydraulic cylinder
2.1 Working Principle
Tasks – each of the above machines demand
precise actions based on requirements viz.,
- lifting
- rotating
- turning
- steering
- digging
- swiveling
- hoisting
- pressing ……..
Hydraulic cylinder is a ‘linear actuator’ which
provides linear motion converting hydraulic energy
into mechanical power.
The pressure and flow in the chamber get converted
to force and motion at the load point.
Construction and elements of a cylinder shown
below
Fig. 4 - Construction of cylinder
2.2 Extension
During extension, the full area takes on the full
pressure and the rod side is connected to return line
having low pressure.
Fig. 3 – Applications
The oil flowing into the piston side increases the
pressure to equate the load and additional
pressurized oil flow pushes the piston imparting
motion
3
parts within the hydraulic cylinder that are
subjected to various kinds of loads and stresses. The
criticality of each of the joints along with stresses
are being discussed here.
The hydraulic cylinders consists of many sections
and joints that are critical to failure. The critical
joints include Cap cover tube weld joint, Cap cover
shear zone, piston shear zone, tube, piston rod Tube
HEC threaded joint, Piston rod-rod eye weld joint,
and rod eye.
The table shows what are the sections why these
sections are going to fail and what is the remedy for
the joint failure.
Fig5: cylinder crossection-completely in/retracted
-neutral
- completely extended
2.3 Retraction
What?
CAP cover- tube
weld joint
Tube
Pistonrod- rodeye
Piston nut thread
Tube –piston rod
During retraction, the rod side area (annular)
takes on the full pressure and hydraulicmechanical work is the same as explained in
extension.
Why?
Tensile - Crack
propagation SCF
Bursting
Shearing
shearing
Surface scoring
Remedy?
Tensile
stress,
Fatigue crack
Hoop stress
Shear stress
Shear stress
Side load
buckling
2.4 Action and Reaction
The above mention what –why joints are depicted
in the fig below.
The function of the cylinder is to give linear
actuation to an external mass. This is achieved
by inversion of the mechanism i.e., by fixing any
one end of the cylinder.
The cylinder experiences various kinds of forces
and reactions during extension and retraction
which is represented in the figure below.
Fig.7 - Hydraulic cylinder critical sections and stresses.
Fig. 6 - Hydraulic cylinder action and reaction
When oil builds the pressure inside the cylinder?
When there is an external load acting on the
cylinder end (Action) then the internal oil with
in the cylinder builds the pressure (Reaction
force) in order to oppose the push or pull, Then
it is said to be work done.
Fig.7a - Hydraulic cylinder critical sections and
stresses.
2.6 Force flow diagrams of Double acting
Hydraulic Cylinder
The basic function of a hydraulic cylinder is
performed with two functional end stages,
Extension and Retraction. Action and reaction
forces during the two stages are very complex and
dynamic in nature, for the purpose of theoretical
analogy force flow diagram during the two
2.5 Cross section and Critical areas in a
Hydraulic Cylinder
Hydraulic cylinders are most important and
critical members among the mechanical load
carrying members. There are various joints and
4
functional stages of hydraulic cylinder is in
figure(8) and figure(9).
Fig.8- Forces acting on Hydraulic Cylinder – extension
Fig.9-forces acting on Hydraulic Cylinder – Retraction.
Fig 11-Stress/ Force flow in a pipe
The forces acting within the Hydraulic Cylinder
pushes the piston rod which results in full
extension of the piston rod. When the Hydraulic
cylinder is completely extended a opposite
reaction force acts on the rod eye which allows
the cylinder to retract and return to its original
position.
2.7 Load and induced pressure levels in
Hydraulic cylinders
The pressure of the hydraulic fluid induces stresses
inside the hydraulic cylinder when extension and
retraction of the hydraulic cylinder takes place. The
back pressure inside the hydraulic cylinder induces
pressure induced stresses. The pressure developed
within the tube will give rise to hoop stress and
bending of piston rod when the critical buckling
load is being exceeded
When there is a force pulling the rod end during
full extension of cylinder as in fig (8) in an
unhealthy situation of hydraulic cylinder. In this
condition all the joints and connections will
experiences tension-tension forces that lead to
early failures which is shown in fig(9) there is an
external force that acting towards cap end cover
end of cylinder that grounds the forces by
building the pressure inside hydraulic cylinder
stated as healthy state of the hydraulic cylinder.
All these worst conditions are used to study joint
strength in this paper.
The below figure shows the force flow in a
typical telescopic cylinder. This type of cylinder
is used in front end tipper used to tip the tipper
body.
For the theoretical estimation of stress and life, the
dynamic time varying loads are simplified into load
spectrum that defines series of bands of constant
load levels and the number of times that each load
band is experienced. The typical load band
considered for analogy is as shown in fig below .
Fig 12 : Simplified load spectrum
2.8 Pressure Vessels - Thin Wall Pressure
Vessels
Fig 10 : Stress/ Force flow in Telescopic cylinder
Stress/ Force flow in the pipe: Pipe used to carry
hydraulic oil in to the cylinder.
Thin wall pressure vessels are in fairly common
use. We would like to consider two specific types.
Cylindrical pressure vessels, and spherical pressure
vessels. By thin wall pressure vessel we will mean a
container whose wall thickness is less than 1/10 of
the radius of the container. Under this condition, the
stress in the wall may be considered uniform.
5
We first look at a cylindrical pressure vessel
shown in Diagram 1, where we have cut a cross
section of the vessel, and have shown the forces
due to the internal pressure, and the balancing
forces due to the longitudinal stress which
develops in the vessel walls.
2.9 Columns and buckling
When we speak of columns (and buckling) we are
talking about members loaded in compression,
often axially loaded, although columns may be
loaded eccentrically. We also tend to think of
columns as vertical members, however, the
formulas we will utilize also apply to horizontal
compression members, or to compression members
in general. For instance, compression members of a
truss may be considered to be columns pinned at
each end point
Columns may be divided into three general types:
Short Columns, Intermediate Columns, and Long
Columns. The distinction between types of columns
is not well defined, but a generally accepted
measure is based on the Slenderness Ratio. The
Slenderness Ratio is the (effective) length of the
column divided by its radius of gyration.
Fig 13 : Thin walled pressure vessel.
To determine the relationship for the transverse
stress, often called the hoop stress, we use the
same approach, but first cut the cylinder
lengthwise as shown in fig 36.
3 Life cycle and fatigue considerations
Fatigue is the progressive localized permanent
structural change that occurs in materials subjected
to fluctuating stresses that may result in cracks or
fracture after sufficient number of cycles.
3.1 Fatigue life prediction :
Fatigue life of any specimen or structure is the
number of stress (strain) cycles required to cause
the failure.
3.2 Stress – strain diagrams:
The behavior of materials and their suitability for
engineering purposes can be obtained by
conducting tensile test and plotting the relationship
between stress and strain.
Fig 14 : forces in a pressure vessel
Hoop stresses:
σH= P R / t
P = internal pressure in cylinder;
R = radius of cylinder,
t= wall thickness.
We note that the hoop stress is twice the value of
the longitudinal stress, and is normally the
limiting factor. The vessel does not have to be a
perfect cylinder. In any thin wall pressure vessel
in which the pressure is uniform and which has a
cylindrical section, the stress in the cylindrical
section is given by the relationships above
Fig. 15 – stress strain diagrams for low carbon steel
and heat treated colddrawn steel.
3.3 Low cycle and high cycle fatigue :
In low cycle fatigue significant plastic straining
occurs. Low cycle fatigue involves large cycles
with significant amounts of plastic deformation
with relatively short life.
6
In high cycle fatigue stresses and strains are
largely confined to elastic region. High cycle
fatigue is associated with low loads and long
life.
3.6 Acceleration and high acceleration tests
Design of SN Test
Accelerated testing is great matter of interest in the
laboratories of various industries. After we are able
to achieve the accelerated failure of a specimen part
at a certain amount of load, we should be able to
extrapolate the results so as to know what will be
the approximate life corresponding to that particular
load.
When the graph is drawn where the amplitude of
stress forms the abscissa (S) and the life or the
number of cycles it can withstand for that particular
loading (N) forms the ordinate. This is known as a
typical S-N curve.
3.4 Factors affecting the fatigue strength
The value of endurance strength is dependent on
the condition of the surface of the specimen. The
endurance stress for ground and polished
specimens when no stress concentration is
present is frequently found out to be one half
ultimate strength.
The three factors on which the degree of
acceleration of the experiment depends are as
follows :
Working environment, sample size, testing time.
By the environment it is meant any operating
condition to which the part will be subjected to in
service and which may affect the performance and
durability. These factors are generally termed as
stress. A typical SN curve is shown below where
we can observe that the life of the specimen (N)
decreases as the amplitude of the stress (S)
increases.
Fig16: Relation between endurance limit and tensile
strength.
3.5 Constant amplitude Vs variable amplitude
stress
The loads and stresses in hydraulic cylinders are
always dynamic in nature, the figure below
shows the constant amplitude and variable
amplitude stresses.
Fig 19: Typical SN curve
Fig 17 : Constant amplitude stress
3.7 Endurance Limit
Certain materials have a fatigue limit or endurance
limit which represents a stress level below which
the material does not fail and can be cycled
infinitely. If the applied stress level is below the
endurance limit of the material, the structure is said
to have an Infinite life. This is characteristic of steel
and titanium in benign environmental conditions. A
typical S-N curve corresponding to this type of
material is shown Curve A in Figure 30.
Fig 18: Variable amplitude stress
7
The typical load data which is extracted from the
field sources is as follows.
The factors that influences the endurance limit
include Surface Finish ,Temperature Stress
Concentration
Notch
Sensitivity
,Size
,Environment Reliability.
3.8 Fatigue Ratio
Through many years of experience, empirical
relations between fatigue and tensile properties
have been developed. Although these
relationships are very general, they remain
useful for engineers in assessing preliminary
fatigue performance.
The ratio of the endurance limit Se to the
ultimate strength Su of a material is called the
fatigue ratio. It has values that range from 0.25
to 0.60, depending on the material
Fig 21 : Load data from the field
3.9 Mean Stress Effects
Most basic S-N fatigue data collected in the
laboratory is generated using a fully-reversed
stress cycle. However, actual loading
applications usually involve a mean stress on
which the oscillatory stress is superimposed, as
shown in Figure 31.
Two ways to accelerate the test :
3.11 To increase the number of cycles , retaining
the same load
In the case where the increase of load is not
feasible, the magnitude of load is retained the same
but the duration of the load is increased so that the
cumulative effect remains the same.
Fig 20 :Typical cyclic loading
Accelerated test technique.
Fig 22 : Step load histogram increased load cycles
This is actually simulated approach to achieve
fatigue and thus estimate the life of the specimen
when it is under service on the field.
One of the situations encountered frequently in
these kind of testing is the involvement of trade
off between the Sample size and testing time. If
the item is expensive, then the test can be
accelerated by extending the time of testing on
fewer items. For items which are easily
available, a large sample size is chosen thereby
reducing the test time.
The advantage of SN curve is that the life of the
part under service on the field can be predicted
and verified through lab tests.
3.12 To increase the load, retaining the same
number of cycles.
In the conventional S-N test the time can be reduced
by increasing the load. In the same manner the
preprogrammed load histogram can be intensified.
If the relation between the load intensity and life is
known, the number of cycles to failure under
increased load can be predicted.
So as mentioned the design of SN Curve is
absolutely essential in the area of simulated
accelerated experiments conducted in the labs to
predict the life of the part under service when
subjected to different loading conditions.
8
4.1 Theoretical life estimation :
Soderbergs-Goodmans approach :
Fig 23: stepload histogram with increased load
4 Theoretical estimation of stresses and life
evaluations:
Welded joint
The joining of two or more metallic components
by introducing fused metal(welding rod)into a
fillet between the components or by raising the
temperature of their surfaces or edges to the
fusion temperature and applying pressure is
called a welded joint.
Fig 25: soderberg and Goodmans approach
Soderberg line
If the point of the combined stress is below the
soderberg line then the component will not fail.
This is a very conservative criteria based on the
material yield point Syt.
To establish the factor of safety relative to the
soderberg criteria.
σmean
kfσamp
+
Se
Fig 24 : welded joints –types.
1
=
Syt
Nf
Goodman line
If the point of the combined stress is below the
relevant Goodman line then the component will not
fail. This is a less conservative criteria based on the
material ultimate strength yield point Sut.
Figure 33 shows three types of welded joints. In
a lap weld ,the edges of a plate are lapped one
over the other and the edge of one is welded to
the surface of the other. In a butt weld, the edge
of one plate is brought in line with the edge of a
second plate and the joint is filled with welding
metal or the two edges are resistance-heated and
pressed together to fuse. For a fillet weld ,the
edge of one plate is brought against the surface
of another not in the same plane and welding
metal is fused in the corner between the two
plates, thus forming a fillet. The joint can be
welded on one or both sides.
σmean
kfσamp
+
Se
1
=
Sut
Nf
Gerber's line
If the point of the combined stress is below the
Gerber's line then the component will not fail. This
is a less conservative approach based on the
material ultimate strength Sut.
To establish the fos relative to the Gerber's criteria.
Nfkfσamp
+
Se
9
(Nfσmean )2
=
(Sut)2
1
Nf
eye mountings. Clevis/ cap end side of the cylinder
is mounted to boom and rod eye to the arm of the
equipment. The figure below shows differential
cylinder mounted on to the backhoe loader.
Where Se= the modified fatigue strength
Sut = the ultimate tensile strength
Syt = the yield tensile strength
Nf = fos applicable for fatigue.
4.2 Basquin's relations
The theoretical life estimation is done by using
Basquin's relation. It is found to 68550 cycles
and experimental life of the specimen is 42000
cycles.
Theoretical estimation:
The life is calculated by using the relation.
Fig 26 : position of arm cylinder in
backhoe loader.
B= log(σe)-log(0.9σu)/3
Failure analysis.
The cap end cover and tube are joined by a Ugroove by welded technique. When there is a hoop
load is acting on the tube it tends to that cause the
crack and growth of pre existing crack.
A=σe/10(6B)
applying Basquin's equation
N=(σr/A)1/B
Where
N= No of cycles to failure
A and B= Basquin coefficients
σt= Tensile strength of the specimen
σe= Endurance limit of specimen
σu= Ultimate tensile strength
σt= Tensile strength of the specimen
σe= Endurance limit of the specimen
σu= Ultimate strength of the specimen
σr= Range stress stress
Fig27 : weld failure zone and 3d model
Analysis
Models considered are cap end cover, tube and the
weld joint as per the WIPRO standards.
Figure 20 shows the 3D model considered for
analysis. The model considered is a part of the
cylinder. The two halves of the weld grooves are
considered for analysis and comparison is being
made accordingly.
5. Stress and FEA of critical areas
Case studies of some of stress and FEA of
critical areas are discussed in the section.
The critical areas of hydraulic cylinder are as
depicted in picture shown in fig(7).
5.1 Analysis of Cap cover Tube welded Joint
In a hydraulic cylinder cap end cover and tube
are joined by a welding technique. This cap end
cover tube-welding joint is one such section that
affects the quality of a hydraulic cylinder.
Here an existing design for the welded section is
studied and an alternate design solution is found
to reduce the stresses coming on to the weld
groove and thus increases life of cylinder.
The function of an arm cylinder is to actuate the
arm of a Backhoe Loader for excavating
operation (Digging operation).
Arm cylinder is mounted on the structure of a
Backhoe loader with clevis/ cap end cover and
rod
Fig 28 : weld groove root joint
Conclusion
The two designs considered for analysis are
Case 1 Design 1.
Case 2 Design 2.
Maximum Von Mises stress values and its location
in each case is shown in table 1 below.
10
Problem definition
Failure considerations
In cylinders tube and head end covers are fastened
by threaded joint. This joint is prone fail due to
excess load coming onto the cylinder. Failure
pictures are as shown in figure 28 below.
What happens in the cylinder?
Table 1 : maximum stress values
Conclusion and results
From the above we can conclude that the results
of the validation and the theoritical results match
as per the stress values.
Fig 30 : Cylinder in fully extended condition.
There will be an axial pull on the HEC when the
cylinder is in fully extended condition. There will
be chances of external mechanical forces coming on
to the cylinder in an axial direction.
These forces tries to pull out the head end cover
fastened to tube, at that moment only first part of
the thread will take up the load and remaining part
of the tube will tend to flare off. This leads
to failure of cylinder.
5.2. Tube flaring analysis at HEC threaded
portion
In a hydraulic cylinder tube and head end cover
(HEC) are fastened by a threaded joint, thus help
in movement of piston rod through head end
cover. Due to the pressure load and mechanical
force the tube tend to flare off at this threaded
potion. This flaring of tube is studied and a
costeffective simple solution is presented here.
Model geometry
Components considered are tube and head end
cover, only a part of the tube length is considered.
Figure 31 shows the model considered for analysis.
Design (a) is as is design
Design (b) is addition of a strip at end of tube for
short length of thread.
Background
Analysis results
Von Mises stress fringes and deformation graphs of
the tube at threaded portion are extracted from
analysis. The figure in next coming pages shows
these fringes and graphs.
Results of design
with out strip - Stress fringes and deformation of
model
Fig 29 : stress concentration in threads
Figure 29 shows the stress concentration in the
threaded region of nut and bolt. Stress
concentration appears in the first threads, which
are heavier, loaded than the distant ones and
results in non-uniform stress distribution. This is
the case when the load applied on the bolt in the
downward direction as shown in the figure 27.
When the load is made upwards nut body will
flare off in the direction of "x", radial outward
direction. This indicates that the last thread
doesn't participate in taking the load due to
flaring of nut.
Fig 31: deformation of model with stress
11
Analysed for with and without strips optimal
placement and length the strip is found.
Fig 32 : Enlarged view of deformation of model
Fig 35 : Von Mises stress fringes of the entire model.
Fig33 : Deformation case without strip
Table 2 : showing the stress values
Conclusion
There is better stress distribution in radius values
between 1mm to 2.5mm, stress is distributed all
along the under cut region, also value of stress is
less. Hence with above, it is concluded that radius
values of 1mm, 1.5mm, 2mm, 2.5mm given better
results. Radius value is selected in between 1mm to
2.5mm.
Fig 34 : Deformation case with strip
Conclusions
Analysis study is conducted with two cases,
Design (a) without considering strip.
Design (b) with considering strip.
The flaring of tube is avoided by considering
case 2 i.e., Design (b) with strip case. It is
observed that even with application of load there
is a positive thrust on the HEC, so that flaring is
avoided.
Due to presence of positive locking between
tube and HEC, entire length of the thread will
take up the load hence shear of thread is
avoided.
5.4 Finite element analysis of cap end cover
Objective
To study the stress distribution in the model at the
cap end cover shear zone at different working load
conditions.
The maximum stress fringes are observer at the cap
end cover pin shear area. The Cap cover are
designed by considering this shear stress levels with
appropriate factor of safety and cost in mind.
5.3 Piston Rod thread under-cut analysis
Piston rod thread under-cut is one of the critical
areas of hydraulic cylinder that is prone to
failure. An optimum radius is required to reduce
the stresses at the undercut portion. Optimum
radius is found by considering different radius
values at the undercut portion to reduce stresses.
Results
Analysis is carried for seven radius values. The
radius values and corresponding stress values are
presented in the table
12
5.6 finite element analysis of rod buckling
Objective
To study the stress distribution of the piston rod. To
compare stress levels (wherever needed) between
different piston rod designs. Study of the stress
levels at different force levels. The study of the
piston rod
for buckling and find the stress
distribution acccordingly.
Fig 36 : Arm cylinder
5.5 Finite element analysis of rodeye:
Objective
To study the stress distribution in rodeye during
different working conditions of a hydraulic
cylinder (Extension and retraction).
Fig38 : Rod buckling
Conclusions
Analysis has been carried out in different
configurations of load.
The FEA of the capendcover, rodeye and rod for
buckling are performed at both the test pressure and
working pressure.
5.7 FEA of piston to optimize the critical radius.
Here the FEA of the swing cylinder piston is
considered. The optimum values of the radius and
thickness are being established which is around
2mm and thickness 9mm.
Fig 36 : FEA of the rod eye
The required stress levels are obtained with
proper rod eye geometry and optimal placement
of the grease nipple hole.
Fig 39 : piston FEA
13
6.2 Test specimens
The specimens are made as per IS 1608 from the
weld joints of a hydraulic cylinder
Fig 43 : rod & rod eye weld joint section
Fig 40 :piston radius and thickness
Fig44 : cap cover -tube weld joint specimen
Fig45: flange –tube weld joint specimen.
Fig 41: FEA of piston with optimal values
7. Design of life test laboratory experiments :
Results and conclusions
The results of the FEA match with the theoritical
calculations or results.
7.1. Pulse testing of Arm cylinder:
Objective:
Conduct Pressure Pulse test on Arm Cylinder to
evaluate CEC-Tube welding for Pulse durability.
Method of Testing:
1. Pump oil through the CE port such that the piston
is at fully extended condition.
2. Connect CE port to power pack (DC valve A or
B port) through intensifiers.
3. Adjust relief valve pressure so as to have
pressure on CE side as per table given
below.
4. Set timer counter to 4.2/1.2 ON/OFF depending
on the circuit to build sufficient
pressure.
5. Start applying pressure pulse.
Acceptance criteria :
- To check for Structural integrity
- No Leakage
7.2 Test setup:
Schematic
6. Fatigue Testing
To generate the fatigue data in case of hydraulic
cylinders various specimens are prepared with
different cross sections such as round and flat for
the welded joints.
6.1 Life test for welded joints
The purpose here was to devise a mechanism
which will bring about the fatigue of a specimen
by high frequency loading. Here a fatigue
tension compression test rig is designed to the
specimen and the number cycles to failure is
noted. figure (11).
Fig 42 : Test setup for fatigue testing
Fig 46 : schematic of test setup
14
8. Test setups
Test details
Above cylinder with new tube wherein OD is
increased from 131 to 135 and CEC Tube
Semi-Weld angle 7.5 degrees was subjected to
pressure pulse test as above. No external leakage
was observed during the test. After the test the
cylinder was subjected to internal leakage test @
50, 100, 150,200, 250, 300, 350 bar using hand
pump for 3 min by pressurizing the CE port
&pouring oil on other side of cylinder &
observing for any oil seepage through the
other HE port. Test was repeated for HE side.
No internal leakage was observed.
The below are the test lab facilities available at our
site.
Bell crank setup to test the hydraulic cylinder
under shock loads.
Dismantled cylinder
Fig 49 : Bell crank setup
Tilt test bench to simulate the fork lift tilt
function.
Fig 47: tube rod subassy with tube
Fig 50 : Tilt test bench
Hydrostatic simulation of steering cylinder.
Fig 48: tube with oring subassy
The above figures show the dismantled
hydraulic cylinder with tube rod subassembly
and tube. After the test the cylinder was
subjected to internal leakage test at different
pressures using hand pump by pressurizing the
CE port & pouring oil on other side of cylinder
& observing for any oil seepage through the
other HE port. Test was repeated for HE side.
No internal leakage was observed.
Fig 51 : steering test bench
7.3. Conclusion:
- No external leakage found.
- No internal leakage observed.
Hence the above cylinder has passed the test
successfully.
15
The stress and life estimation of the joints are
described with different case studies. The stress
estimation case studies involved, Cap cover tube
weld joint analysis, Piston rod radius optimization,
Piston critical section analysis, Tube-head end
cover flare off etc.,.
Pulse pressure durability on cylinder joints and
tubes by generating sudden pressure spikes
The paper involved two lab testing simulations
namely Fatigue testing of weld joints and Pulse
testing of Arm cylinder, All these tests are
conducted after proving the design theoretically.
Fig 52 : spike or pulse generation test
The different test setups developed in-house are
described in the last section for lab simulation of
different types of Hydraulic cylinder.
Stroke durability through pressure cycling
All these systematic approaches enhanced the life of
hydraulic cylinders and hence to an end equipment.
10. References
1. Andrew D. Dimarogonas, "Computer aided
Fig 53 : Back to back testing
machine design", Prentice Hall International,
Hot oil chamber with high critical work
conditions
Ltd. United states.
2. ASM Handbook on Fatigue and Fracture
Volume 19.
3. M F Spotts and T E Shoup, Design of Machine
Elements, Seventh Edition.
4. Wipro Company standards.
5. Paul M. Kurowski, Finite Element Analysis for
Fig 55: High temperature pressure spike
Design Engineers, SAE Publications.
9. Summary
6. Howard E. Boyer, Atlas of Fatigue curves,
ASM International, The materials information
A systematic approach to study the different
types of Joints and their pains in a hydraulic
cylinder are presented here. The study covered
detailed Joint construction, material, design,
static and dynamic loading aspects of different
joints.
Society.
We covered the basic working principle along
with applications, basic functional aspects and
cyclic - dynamic loading of joints of hydraulic
cylinder. The force flow at different working
stages in double acting and telescopic cylinders
are described for better understanding of stress
flow pattern.
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