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.

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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

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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.

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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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