In other words we can say a hydraulic cylinder is a device which converts the energy of fluid which is in a pressure form into linear mechanical force and motion. Single action cylinders. Double action cylinders. Single action cylinder can be defined as "Cylinder in which displacement in one direction is by working fluid pressure and in the other direction by external force. Single action cylinder can take power-stroke only in single direction.
That is either it can develop necessary force in forward stroke of cylinder or return stroke of cylinder, depending on its construction. The non-productive direction of cylinder stroke is achieved by various means such as self-weight gravity , spring, auxiliary cylinder etc. Double action cylinders are those in which forward as well as reverse strokes are actuated by fluid pressure.
Double action cylinder can develop power-stroke in both forward and reverse direction. In figure 8. Return stroke is achieved by gravity and spring. While in figure 1. Figure No. Piston Rod: When diameter of piston rod is almost equal to piston diameter then generally it is called as RAM.
But in general all large size of piston rods are called "RAM". Piston rod is a mechanical member, which transmits kinetic energy, which got developed at piston, to the work-piece. It is circular in cross-section in case of double action cylinder, as hydraulic sealing is required between piston rod and guide bush.
In ram type of single action cylinder, piston rod is also circular in cross action, while in piston type single action cylinder in which sealing is not required between piston rod and guide bush, piston rod may be of any type of cross section. For example in case of lock nut type of single action jack, piston rod has thread on its entire length. Piston-rod is also called as plunger. It could extend from both the end of cylinder, and it could be hollow also.
Piston-rod could be attached to other component by means of threading, eye bolt type arrangement, or groove and split coupling arrangement etc. Wiper Seal: These are used to avoid entry of dust particle in cylinder. When these seal softly wipe the rod then it is called wiper seal and when they are stiffly and forcefully rub the piston rod to avoid entry of dust particle in cylinder then they are called scraper.
Gland-Bush: Gland-bush is used to retain gland seal, accommodate wiper seal, and provide guide to piston rod. It is an optional component; it could be merged with Guide-bush.
That means guide-bush can also accommodate rod seal, wiper seal and can provide guide to piston rod. We provided separate gland-bush for convenience in manufacturing, controlling dimension accurately, and stronger design. Making grove in Guide-bush and maintaining tolerance and surface finish is too difficult, so by using gland bush we make an open step for accommodating seal and solve this problem.
Guide-bush is made from mild steel, while guiding piston rod requires bearing material. So instead of making complete guide bush of bearing material we make gland-bush of bearing material, Which is smaller in size as compared to guide-bush, and hence we save money. Strips and bush could be used to provide guide to piston-rod in Guide bush, instead of making separate gland bush.
But long guides provided by gland-bush which are made from bearing material are much stronger and gives long life as compared to thin and short bushes and strips Filled in guide-bush. Rod Seals: These are also called as Gland seals.
It is a device which is used to avoid the leakage of working fluid or air from the periphery of piston-rod, Generally it is used to stop leakage between piston rod and guide-bush of cylinder. This gives additional guide to Piston - Rod. It is also called sleeve guide or collar guide. This is a cylinder end enclosure, which covers the annular area or the differential area between the cylinder bore area and piston rod area.
In addition to functioning as end-closer, it also could be used for mounting cylinder, providing oil-port, accommodating bleeding and cushion arrangement, and providing guide to piston rod.
Oil Port: - A port is an internal or external terminus of air or fluid passage in hydraulic or pneumatic component. In hydraulic cylinder, oil ports are provided to feed pressurised oil. It may be threaded or bolted type, and its size depends on the flow of oil thought these oil ports and inside diameter of cylinder 8. Cylinder-Tube-Flanges: These are circular or rectangular rings, threaded and welded to the outside diameter of cylinder tube.
When this is fixed at front-end of cylinder then it is called Front-Tube-Flange. It may be used for bolting of guide-bush and cylinder mounting, in case of Front-Tube-Flange mounted type of cylinder. When it is fixed to the rear-end of cylinder end-plug side , then it is called Rear-Tube-Flange of cylinder.
It may be used for bolting of End-Plug and cylinder mounting in case of Rear-TubeFlange mounted cylinder. Stopper Tube: When cylinder has long stroke, and in fully extended condition of Piston-rod, if there is a chance of buckling of piston-rod or any damage to cylinder, then piston-rod is always kept sufficiently Design and Manufacturing of Hydraulic Presses.
A piece of pipe, which floats freely between piston and guide-bush, and stop ram from taking its full stroke, is called stopper-tube. Air-Bleed-Off-Port:Air may get trapped in cylinder. This air may be due to cavitations and de-aeration in oil, or air present while assembling and commissioning of cylinder.
Trapped air gives spongy operation, jerks, and loss of control on cylinder movement. To remove trapped air small tapped holes are provided in end-plug and guide-bush, which always remains plugged. To release air these plugs are loosened allowing air to escape to atmospheres. When air is completely removed then oil started leaking-out from these plugs, then plugs are tighten again.
This process of removing air till oil starts coming out is called bleeding and the port provided for this purpose is called air-bleed-off-port. Main Shell: It is also called cylinder-tube, or cylinder-pipe, or cylinder-body. It has circular inside crosssectional area. It receives, confines, and direct the fluid under pressure to piston or ram so that the pressure energy in fluid gets converted into kinetic energy of the moving piston or ram.
The crosssection area of cylinder-tube withstands radial as well as longitudinal stress developed due to the fluid-under-pressure. It also provides guide to ram or piston. Seal Plates: These are round rings or plates, used to retain piston-seal on piston. Piston Seal: These are hydraulic seals used to avoid leakage between piston and inside diameter of cylinder tube.
Piston: Piston is circular in cross-section. It slides in main shell, and provides guide to piston rod at oneend piston-end. Piston has provision and means to avoid leakage between cylinder and piston, and because of this feature, when fluid-under-pressure when enters in main shell in one direction, piston gets pushing force in other direction.
Hence it assists in conversion of pressure energy in fluid to kinetic energy Lock Nut:To avoid losing of piston from piston-rod these lock nuts are provided.
Guide-Ring: These are flat rings of plastomeric material. And used in piston, guide-bush, and gland-bush to avoid metal to metal contact, and act as guide. All mechanical property of guide-rings are similar to bearing material. Cushioning:As per the requirement of hydraulic system, piston-rod may travel at extremely high speed in its stroke range.
On completing its stroke if piston hits guide-bush or end-plug with same high speed then it will damage the whole cylinder. Hence special arrangements are made in piston and endcovers to reduce the speed of piston-rod as it completes its stroke. This process of deceleration of piston or piston-rod is called cushioning.
Cushioning is achieved by throttling the rate of exhaust or return of oil, from cylinder. Cushioning may be fixed type or variable type; Detail about arrangement of cushioning will be discussed in design of cylinder. End-Plug: It is also called as Cap-End Cover - End or Rear - End of cylinder this is a cylinder-end enclosure which completely cover the cylinder-bore-area.
In addition to providing end enclosure, end plug also could be used for mounting of cylinder, providing oil port, making arrangement for bleeding, and cushion etc. Design and Manufacturing of Hydraulic Presses.
For more knowledge about terms used for hydraulic cylinder, and other items kindly refer IS which describes about terms related to oil hydraulic. These two principal types of hydraulic cylinders have been modified in so many ways as per requirement of industry, convenience in manufacturing, economy and duty cycle.
Some of them are described as follow. Tie - Rod Construction. Threaded Construction. Bolted Construction. One Piece welded construction. Costume Build Cylinder with combination of above mentioned constructions.
ISI standard also generally refers to one of this type of construction. As all the components are only machined and assembled together and not welded. Hence planning manufacturing, quality control, assembly, and maintenance are more convenient than other types of construction. As long tie rods are used to hold all the component together hence special care required to tighten them, and safe guard against loosening in operation.
Like standard valves and pumps, these types of cylinders are also manufactured as standard hydraulic component, and used for low to medium pressure and low to medium duty operation for general purpose, and machine tool industry. In this design both ends are assembled with cylinder tube by threading, as shown in following design. These are used for medium to heavy-duty operation, and widely used in earth moving machinery. Similar to tie rod construction these are also designed and manufactured as standard hydraulic component and widely used in industry.
These are economical but cannot be repaired. There are used for low pressure; agriculture machinery application. One of the most widely used combination is welded cap-end cover, bolted head-end cover, with front tube flange mounting. In case of high capacity cylinder when it is steel cast or machined from solid steel forging, then end cover and front flange may be integral part of cylinder tube.
Cylinder with this type of construction widely used in hydraulic press. In this type of cylinder, ram or piston-rod have such construction that their displacement in one direction is by fluid force and in other direction by external force. Gravity return single action cylinder Figure No.
In this type of design the stroke of piston rod in forward as well as in reversed direction is due to fluid pressure, as shown in figure 2. When differential cylinders are connected to regenerative hydraulic circuit then it gives same equal forward and return speed. As annular area on both ends are same, hence it moves with same speed in its forward and return stroke. Sometime piston is made hollow to pass the work-piece or another machine element through it.
Total stroke length may be as much as four to six times longer than collapsed length of the cylinder. Telescopic cylinders are single as well as double action. The force out-put varies with stroke. We get maximum force on first stage when full piston area is used, while minimum force at the end of stroke. These types of cylinders are used in dumper-truck, hydraulic mobile crane, and. For example, in three-position cylinder as shown in following diagram, on pressurizing the cap-end-oil port the cap-end piston-rod forces against the head- end-piston, and moves it to some portion of its stroke generally about half of its total travel.
Three-position cylinders are often used to actuate multi position valves or to shift gears in machine tools. They are frequently used as pneumatic actuators in food and drug industries because they require no lubrication and do not exhaust a contaminating oil dust.
Spring- return models shown in figure should not be pressurized in the reverse direction because reversals can pleat the diaphragm and shorten its life. Double-acting actuators with twin diaphragm are available for application requires pressure in both directions. Diaphragm Piston. They are often used to actuate rotating chucks on turret lathe. In this type of cylinder, complete cylinder assembly may rotate along with mating components.
Special journals, thrust bearing etc. Fluid is supplied through special stationary distributor. But with low RPM they can have relative rotary motion. Hydraulic rotating cylinder and hydraulic torque motor are two different units. Hydraulic rotating cylinder only imparts liner motion to a rotating device. While torque motor impart rotary motion to a device to be rotated. Rotating body Stationary distributor.
Rotating Cylinder Figure No. The slot is sealed with a spring-steel strip that is threaded through the piston assembly. So far sloteded cylinders are available for pneumatic system but not hydraulic system. Out put member Moulded seal. Cross - section of a simple of compound cylinder is shown in following figure. In this cylinder we can have three forward speeds and pressing force.
Which is used to boost the pressure of working fluids. Intensifier may be a part of hydraulic circuit, in which pump initially supplies hydraulic fluid at low to medium pressure to carry out all the operation and function of a hydraulic system and when high pressure required then with the help of medium pressure hydraulic fluid and intensifier, high pressure is developed. Piston pump can develop up to Bar. Some sophisticated pump can also develop up to Bar. But when oil at Bar or bar pressure is continuously required then such type of intensifier is used.
In following example using low pressure pump very high pressure oil can be supplied to cylinder. E] Operation Principle: I When direction control valve Actuated to A piston, oil from pump passes to return side of cylinder.
Spring of check valve No. Cylinder gets fully retracted. II After full retraction of cylinder , oil passes from check valve 5 and enters in upright 3 , which cause plunger 2 to retract.
III In fully retracted condition of cylinder and plunger 2 system is ready for forward stroke cylinder. IV When solenoid is activated to B-position. Oil from pump is directed to forward port of intensifier cylinder. This cause plunger 2 to more down and transfer oil in upright 3 to port for forward stroke of V If area of intensifier cylinder 1 in A1 and pump pressure is P1, Area of upright 3 is A2 , them pressure P2 got developed in up-right will be By this simple method method very high pressure could be developed by using simple low pressure.
Pneumatic cylinder is completely made from non-magnetic material such as aluminum, brass or non-magnetic stainless steel. Piston ring of pneumatic cylinder consists of an additional magnetic ring. Out side cylinder tube two "Proximity switches" are provided at both ends of cylinder tube.
When piston with magnetic ring passes near the proximity switch, it actuate. Proximity switch closes the electrical circuit and supply of current to the coil of pneumatic direction control valve to actuate it. Pneumatic direction control valve is detention type, that is once it get energized it changes its position, and even after its coil gets de-energised, it remain in same position, and do not changes its position, unless other side of coil is energised to changes it's direction.
In operation, pressurized air is supplied to four-way-two-position pneumatic direction control, which operates cylinder, as cylinder takes its stroke, and piston with magnetic ring moves across the "Proximity switch" it temporarily energies coils of direction control valve for the reverse direction of cylinder. As reverse stroke progress, even though direction control valve get deenergized but do remain in same position due to its detention characteristic. When reverse stroke reaches its end, piston passes through the other "Proximity switch", it get operated for a very short period of time.
But in that short period it energies coil of direction control valve for forward stroke and again change the direction of cylinder.
That is how it changes direction of stroke and cylinder keep on reciprocating. This reciprocating pneumatic cylinder connected to a single action type of hydraulic cylinder, with two-check valve, which on its retraction stroke suck oil, and on its forward stroke deliver oil under pressure.
The simple system we have described is by using magnetic ring, Proximity switch and detention type Direction control valve.
Reciprocating pumps are also available which are with out Proximity switch, and use only special pneumatic direction control valve. In one such system, pneumatic cylinder has cushion like arrangement at its both end. When piston reaches the end of its stroke the pressure of air trapped between piston and end-cover increases slightly more than supplied air pressure. This extra pressure is used to change the direction of detention type direction control valve.
In operation spool of direction control valve get equal air pressure at its both end and remain in balance, but at the end of stroke increase in pressure of the air-trapped in cushion chamber off balance it and changes its direction. So on this principle cylinder keeps on reciprocating and keep on pump flanged at pressure as reciprocating pump. Refer figure. Primary cylinder is similar to convention at double action cylinder, but with hollow ram. A tube freely float in this hollow ram, and held freely at some distance from inlet oil port.
Oil is injected through a nozzle at high velocity in the tube. When oil come out from other end of tube inside hollow ram at high velocity, as velocity decreases, pressure increases. This pressure forces tubes out of hollow ram, and presses it firmly on the opening of nozzle.
This allows all the oil injected by nozzle to pass on to hollow ram and force it out at high speed. As ram take its stroke at high speed the volume of cap end cylinder is filled by oil through a large size of pre-fill valve, to avoid cavitations. As main ram hollow ram reaches its full stroke, some arrangement is made to leak the pressurized oil getting injected in hollow ram to main cap-end area of cylinder, to develop full pressure and force.
This may be achieved by providing a side hole in tube or making it taper at the end and increase the clearance. This cylinder gives very high speed with very small capacity pump and motor. Speed ram is developed by Mr. Broughton Redman Engineering Ltd. Birmingham is Licensees to manufacture these cylinder commercially. Pre-filliag by Carend oil-port. Bred bury speed ram Figure No.
Indian standard has also defined various nominal bore diameters. And instead of classifying each nominal bore into ten schedules, they have classified it in to three categories, namely light duty, medium duty, and heavy duty. In Annexure we have also described pipes as per Indian standard. If we design and select the inside diameter of cylinder and its wall thickness as per the standard pipes available in market, and ma- chine it as per preferred series or advice by ISI Standard, then manufacturing and maintenance of hydraulic cylinder will be much more convenient and economical.
Care should be taken that the final dimension of cylinder is also as per the availability of standard seal. Seals of odd dimension also could be made, but than keeping spare, and maintenance will be always a problem. Constraint about size of cylinder, and its design. Working medium. If size of cylinder has to be reduced keeping the tonnage pressing capacity same. Then working pressure has to be increased. As working pressure increase corresponding hoop stress also increase.
To cope up with higher stress either wall thickness has to be increased or material with higher allowable stress has to be selected. To reduce over all size mostly material with higher allowable stress are selected. Such as plain carbon steel or low or medium alloy steel. But these materials are difficult to weld. If working medium of hydraulic cylinder is of corrosive in nature, then brass or stainless steel seamless pipe are used.
If there is no constraint about size, and working fluid is also not corrosive, then for such standard working condition seamless pipe of low carbon steel is used, in which carbon percentage is be- tween 0. Indian standard, and standard of other countries such as ASTM, DIN, BS and other standards have defined more than 10 various groups of materials for seamless pipe, with varying percentage of carbon and other element.
But most widely used material is ASTM. A grade B. For more detail refer chapter "Material used in Hydraulic Presses". Machining: - For manufacturing of hydraulic cylinder tube, we cut pipe to the length, then machine it by turning, and boring its inside diameter on lathe machine.
Then hone it on honing machine. As per IS by honing it is possible to control tolerance limit up to H4 to H5. But the requirement Design of Hydraulic Cylinders Khan Design and Manufacturing of Hydraulic Cylinder of fitting tolerance in cylinder is that cylinder tube inside diameter and piston outside diameter should have normal to easy running fits. Hence inside diameter of cylinder tube is made as per H7 to H9 tolerance grade and piston outside diameter as per f8 to e8 tolerance grade.
Selection of tolerance grade depend upon inside diameter, length of cylinder tube, working pressure, duty cycle, and how critical the system is. By honing operation we can achieve surface finish up to 0.
Roughness should not be less than 0. Because hydraulic seal rubs the cylinder inside diameter under pressure, if roughness is more friction will be more and seals will fail due to wear and tear. But if roughness is too less, then such smooth surface do not retain oil film which can cause increase in friction between seal and cylinder due to dry running, which again cause heat generation and seal life get reduced.
Surface of cylinder must retain some oil film for seal lubrication. Surface roughness 0. Extra Protection of Cylinder Tube Inside Surface: - Piston rubs against the cylinder inside diameter, which is honed surface. Piston also has bearing material lining hence do not damage the honed surface.
Hence for general purpose, and common hydraulic application cylinder tubes are only honed, and used. But in those cases when cylinder may not be used for long period, then the honed surface may get damage due to atmospheric mois- ture and corrosion. In such case it is hard-chromplated.
Pneumatic cylinders are also chrome plated as air contains moisture. In those cases where honed cylinders tube may or may not be used for hydraulic cylinder. But has to under go most server service condition, then to protect its honed surface it is nitrated. Nitrating make skin of cylinder inside diameter very hard, and corrosion resistance. For example gun-barrels, Barrel's of plastic extrudes etc.
But for nitrating material of cylinder should be of capable of getting heat treated. For example alloy steel EN41B is used for barrel for plastic extrusion.
For further detail about hard-chrome plating and nitrating refer chapter on "Surface Protection " and "Heat Treatment". Welding of Hydraulic Cylinder: - Most critical welding in hydraulic press is a welding of end plug of hydraulic cylinder. Hence we will particularly study welding procedure of end-plug. Design And Welding Procedure: - Step 1. Calculate and decide the thickness of end-plug by equation. Step 2. First end-plug is threaded and fitted in cylinder then welded. Calculate the number of thread required to takes the full load coming on end-plug.
Make threading and fit end-plug in cylinder Step 3. For welding, prepare the welding joint while machining the end-plug and cylinder. Step 4. Tighten the thread to maximum extent. So that end-plug do not have clearance for move- ment under pressure. Threads are for taking load, and welding though can take load, but use them only for making joint leak proof. Step 5.
Heat the joint and cover remaining portion of cylinder to avoid heat loss. Step 6. Use low hydrogen electrode for welding. Bake welding electrode before welding. Step 7. Run first weld as shown in figure. Step 8. In case of large cylinder use penning to over come pulling of end-plug on one side due to shrinkage in weld deposit.
For penning, weld a small portion, clean the flux, take a blunt chisel, and hammer the weld deposit with such a blow that it flatten the weld deposit. Do all this when weld deposit is still at sufficient high temperature. Repeat this till welding completed.
Step 9. When welding gets completed cover the whole cylinder, so that full cylinder get slowly cooled. In no condition cold water or any thing fall on heated welding joint. Neither it should left in cool breeze for air cooling. By natural cooling fine-grain structure will get produce, which are ductile and soft. Even if coarse grain get produced which has less strength, then also it does not matter, as load is t a k e n by thread and not welded joint.
All cylinders expand when pressurized and contract on releasing pressure. If rate of cooling al- lowed to be vary fast then martensite grain structure will get produced in welded joint, which are very hard, brittle and welding will crack on cylinder pressurization. Step Next day when cylinder get cooled downed clean welded joint, and inspect for any crack developed.
Test it and if it is found OK them said cylinder can be used for further operation. If welding cracks than remove all weld deposit, check chemical composition of cylinder tube and end-plug, and select welding electrode and welding procedure as per the requirement of that grade or type of material. Any welding done on a cracked weld deposit tends to crack again hence it is better remove all old crack weld deposit before welding again.
Use low hydrogen-electrode of grade E for welding. As these electrode are for welding high alloy steel to un alloy so in majority of cases cracking problem get solved by using them. Khan Design and Manufacturing of Hydraulic Cylinder Some fact and figure to be remembered while calculating the force developed by cylinder.
Back pressure may be intentionally developed by counter-balance value or check-valve or it may get developed naturally due to throttling, checked return line etc. Back pressure will counter-act the force developed by cylinder. Under pressure they get energised and further pressure against mating parts. Hence after resistance against motion between cylinder piston, and piston-rod.
This resisting force reduces the effectiveness of force developed by cylinder. Khan Design and Manufacturing of Hydraulic Cylinder Piston rod transfers the force developed at piston to work piece. This force may be pushing or pulling. Piston rod is designed to transfer these forces along its central axis.
It is not designed or expected to take any side bending load. As the force acts through its central axis only, hence when length of piston rod is shorter, then the cross-section required to transfer force within safe stress limit can be calculated using basic simple formula such as. As piston rod fails at much lower stress value by buckling. For calculating various parameters of long piston rod, following formulas could be used.
Taking into consideration manufacturing process of cylinder, its rigidity required in service, installation condition and other factors, it is advisable to keep the ratio of the piston-rod length to it's diam- eter less then Factors affecting the selection of size of piston-rod: - By means of engineering formulas and graphs we can find the minimum diameter required for the piston rod.
But actual size must be decided after referring to following factor. Up-to 70mm size of piston rods are available in ground and hard chromplated condition in market 2. Availability of Seals: - If Rod size could not be selected as per ISI, then rod size should be selected as per standard seal available in market. For example on calculation if we got piston rod diameter as , which is much higher than and much less than , in such case if should be rounded off to Nowadays machined seals are also available by which we can make any size of seal within few minutes.
So we can keep any size of piston-rod, then also keeping some standard in design is always better. Rod size required for pulling load: - Sometime cylinder has to perform pulling operation. Khan Design and Manufacturing of Hydraulic Cylinder cylinder-bore and piston rod should be more.
Keeping inside diameter of cylinder minimum pos- sible, for larger annular area diameter of piston rod has to be small. Keeping the pulling load same, if diameter of rod has to be reduced, then piston rod should be of alloy steel. Hence before selecting diameter, pulling force, required strength of alloy steel to be used, and heat- treatment of alloy-steel has to be studied and selected carefully.
Integral type of piston-rod and piston assembly: - When piston and piston rod are integral type. Then keeping larger size of piston rod is more advis- able, as raw material selected is of piston diameter.
We machine it, and remove material to reduce diameter to make piston-rod as per calculation. If diameter is kept higher then time of machining will be saved, strength of piston-rod will increases. As annular area between piston-rod and cylin- der will decrease, return speed of cylinder will also increase.
Only precaution is to be taken that the annular area of piston which is between piston-rod and cylinder inside diameter, and which will presses against guide-bush and apply full load in case of fully extended stroke, must be sufficiently large.
This ensures that the compressive stress devel- oped remain in safe limit. If annular area is less and compressive stress crosses the safe limit then both piston and guide-bush will yield, and guide-bush may grip the piston-rod and damage its outer smooth surface. Material used for piston rod: - Generally ground and hard-chrome plated rod of C40 or EN8-B grade material and in standard size is available in market and widely used for piston-rod.
Piston-rod can also be made from, cast-iron for larger size and short length of piston-rod under compressive load mild steel, alloy steel, stain- less steel, etc, depending upon application and various parameter. Nowadays stainless steel of grade in ground and polished condition are also available, which are much better than C40 grade piston rod.
Manufacturing of piston rod: - a Raw materials of higher size made by forging etc. It is also tested ultrasonically for internal crack etc. Hardness of coating about RC. Depending precision it also could be machined as per g8 or h8 tolerance grade. No sharp groove should be provided to avoid stress concentration. Threading etc. Hence in case of precise equipment, piston rod should be ground again after plating. More chromium get deposited at both end of piston rod, hence when grinding after plating is not required, then at both end, diameter should be reduced by 0.
I In general C grade material in use for making piston-rod. In British standard it is D grade En-8 material, which contains 0. J Bent piston-rod should not be used. It accommodate hydrau- lic seals to avoid leakage between cylinder and piston. It is also fitted with guide-ring, wear rings, or piston itself may be made from bearing material to protect the honed inside surface of cylinder.
Piston withstands the full load developed by pressurized oil and transfers it to the piston rod. It is the first member, which bear and transfer the load, hence it should be designed accordingly for its satisfactory performance.
Design of Piston: - According to the attachment with piston rod, piston can be classified in two categories. Integral type of piston rod: - Integral type of piston and piston rod arrangement is generally used for large size of piston rod, and high capacity cylinder. And in any cylinder this arrangement will be more economical where length of piston rod is short and diameter of piston rod is very close to inside diameter of cylinder.
This arrangement is more sturdy than supported type. Perfect alignment also always remain between piston, piston rod, cylinder tube, guide-bush, hence more life to seal and less wear and tear to guides. Simply supported type of piston or assembled type of piston: - This type piston is attached to piston rod by means of threads or simply assembled on end of piston rod and retained by check-nut.
This type of assembly is most-widely used in industry, as it is convenient for mass-produc- tion of piston of standard dimension. Piston rod is also mass produce as straight ground and hard- chrome plated rods. As Inside Diameter of cylinder, Outside Diameter of piston rod and seals etc.
Hence a good quality cylinder of standard dimension could be produce in very short time. Outside Diameter of piston is as per the Inside Diameter of cylinder tube, and machined generally with f8 grade of tolerance. If piston is of simply supported type then Inside Diameter of piston should be machined as per H7 to H9 standard and surface finish also should be good as o- ring rub against it.
Thickness of piston depends upon the load which has to be transfer. Under load piston may fail in two way. First by bending load and second by shear stress. We will study how to calculate the thickness of piston to withstand these two types of load satisfactorily as follow. Thickness of piston subjected to bending: - Outside diameter of piston is as per inside diameter of cylinder. The oil under pressure applies uniform load on its complete projected area. While piston is supported on its other side only at small annular area of piston-rod.
As there is large un-supported areas, hence piston is subjected to bending stress, which tends to bend piston and make it a dish like structure. Value of C can be selected from following table. Hence thickness of piston should be sufficient to resist the failure by shearing. Minimum thickness of piston required to resist them could be calculated as fallow. Piston is supported by piston rod. The annular area of contact between piston and piston rod withstand compressive load.
Piston-rod couldbe attached to other component by means of threading, eye bolt type arrangement, or groove andsplit coupling arrangement etc. Wiper Seal: -These are used to avoid entry of dust particle in cylinder. When these seal softly wipe the rodthen it is called wiper seal and when they are stiffly and forcefully rub the piston rod to avoidentry of dust particle in cylinder then they are called scraper.
Gland-Bush: -Gland-bush is used to retain gland seal, accommodate wiper seal, and provide guide to pistonrod. It is an optional component; it could be merged with Guide-bush. That means guide-bushcan also accommodate rod seal, wiper seal and can provide guide to piston rod. We providedseparate gland-bush for convenience in manufacturing, controlling dimension accurately, andstronger design. Making grove in Guide-bush and maintaining tolerance and surface finish is too difficult, so byusing gland bush we make an open step for accommodating seal and solve this problem.
Guide-bush is made from mild steel, while guiding piston rod requires bearing material. Soinstead of making complete guide bush of bearing material we make gland-bush of bearingmaterial, Which is smaller in size as compared to guide-bush, and hence we save money.
Strips and bush could be used to provide guide to piston-rod in Guide bush, instead of makingseparate gland bush. But long guides provided by gland-bush which are made from bearingmaterial are much stronger and gives long life as compared to thin and short bushes and stripsFilled in guide-bush. Rod Seals: -These are also called as Gland seals. It is a device which is used to avoid the leakage of workingfluid or air from the periphery of piston-rod, Generally it is used to stop leakage between pistonrod and guide-bush of cylinder.
This gives additional guide to Piston - Rod. It is alsocalled sleeve guide or collar guide. This is acylinder end enclosure, which covers the annular area or the differential area between the cylin-der bore area and piston rod area. In addition to functioning as end-closer, it also could be used for mounting cylinder, providingoil-port, accommodating bleeding and cushion arrangement, and providing guide to piston rod.
Oil Port: - A port is an internal or external terminus of air or fluid passage in hydraulicor pneumatic component.
In hydraulic cylinder, oil ports are provided to feed pressurised oil. It may be threaded or boltedtype, and its size depends on the flow of oil thought these oil ports and inside diameter ofcylinder8. Cylinder-Tube-Flanges: -These are circular or rectangular rings, threaded and welded to the outside diameter of cylindertube.
When this is fixed at front-end of cylinder then it is called Front-Tube-Flange. It may beused for bolting of guide-bush and cylinder mounting, in case of Front-Tube-Flange mountedtype of cylinder. When it is fixed to the rear-end of cylinder end-plug side , then it is called Rear-Tube-Flangeof cylinder. It may be used for bolting of End-Plug and cylinder mounting in case of Rear-Tube-Flange mounted cylinder.
Stopper Tube: -When cylinder has long stroke, and in fully extended condition of Piston-rod, if there is a chanceof buckling of piston-rod or any damage to cylinder, then piston-rod is always kept sufficiently. A piece of pipe, which floats freely between piston and guide-bush, and stop ram from taking itsfull stroke, is called stopper-tube. Air-Bleed-Off-Port:-Air may get trapped in cylinder.
It is designed by the following steps. Specification of function The main function of the frame is to withstand the force developed by the hydraulic cylinder. Frame is used mounting and housing the press accessories like hydraulic cylinder, die block, ejection system etc.
Pgs: 2. Determination of forces The weight of the cylinder and the cylinder load is the major forces acting on the frame structure. Selection of materials The mild steel IS is selected for the frame because it is soft and ductile they can be easily welded and machined. Determination of dimensions The frame consists of many number of plates fabricated to support the structure.
Design modifications The of the machine element are modified from assembly and manufacturing considerations. The allowable fillet radius of 5mm is provided to reduce the stress concentration. And isotropic That is, it is same material throughout and of equal elastic properties in all the direction. Specification of function The main function of the cylinder is to convert hydraulic energy into mechanical energy and to withstand the pressure and force during the operation.
Determination of forces The free body diagram of the hydraulic press is constructed to determine the forces acting on cylinder.
Selection of materials The mild steel IS is selected for the cylinder because it is soft and ductile they can be easily welded and easily machine for structural applications.
Determination of dimensions The shape of the machine element depends on two factors that are operating conditions and the shape of the adjoining machine element. Pgs: Length : mm Inner diameter : mm Outer diameter : mm 5.
The analysis of hydraulic press structure is needed to increased their performance and productivity. The deformation of press structure during the loading condition is analysed to change the dimensions of plates.
For the hydraulic cylinder, the loading condition is defined with applying the pressure to the inner surface of the cylinder.
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