5

“DESIGN AND FABRICATION OF HYDRAULIC SCISSOR LIFT”

CHAPTER 1

INTRODUCTION

In modern automated and robotized production lines the hydraulic drive has found an

ever-increasing application. This drive supersedes the mechanical, pneumatic and electric drives

in realizing straight-line translational and rotational motions of actuator. A confined fluid is one

of the most versatile means of modifying motion & transmitting power. fluid can move rapidly

in one part of its length and slowly in another. No other medium can combine the same degree of

positive ness, accuracy & flexibility while maintaining its ability to transmit maximum power in

minimum bulk & weight.

The advantages of the fluid have been integrated with the speed and flexibility to produce

hydraulic platform lifter. This machine developed is used particularly for lifting the load in

industrial lines where now a day the labor is higher . the machine finds wide applications in the

industries where load transmission from one place to another at particular height is to be done.

now days the hydraulic power is used in wide field of industries such as automobile hoist,

machine tool, fork lift, construction equipment, mining equipment etc

The hydraulic platform lifter consists of hydraulic power pack which is the source of

storing the hydraulic oil and for cooling of oil after the circulation of oil through the cylinders.

The base structure is made up of standard c channels which is capable of handling greater loads.

The hydraulic actuator consisting of cylinder, piston and all the other parts of the cylinder.

FUTURE TECHNOLOGY’ DESIGN, FABRICATION, ANIMATION Page 1


CHAPTER 2

OBJECTIVES OF PROJECT

To make a complete mechanical device: The idea is to make a device which does not use

any electrical power so that it is wholly independent of its own.

To make a device which is suitable economically for small Scale industries: taking in to

consideration the cost factor this device is suitable for small scale as well as big scale

industries.

Taking safety as prime consideration: This device is safer in all respects.

To build a device which cuts the bolt without applying greater force

To develop the abilities such as working in groups, sharing responsibilities, initiative,

perseverance

CHAPTER 3



LITERATURE SURVEY

HYDRAULIC CYLINDERS

Hydraulic actuators, of which cylinders are the most common, are the devices providing

power and movement to automated systems, machines and processes. A hydraulic cylinder is a

simple, low cost, easy to install device that is ideal for producing powerful linear movement over

a wide range of velocities, and can be stalled without causing internal damage. Adverse

conditions can be easily tolerated such as high humidity, dry and dusty environments and

repetitive clean down with high pressure hoses. The diameter or bore of a cylinder determines

the maximum force that it can exert and the stroke determines the maximum linear movement

that it can produce. Cylinders are designed to work at different maximum pressures. The pressure

actually supplied to a cylinder will normally be reduced through a pressure regulator to control

the thrust to a suitable level. As an example of cylinder power, a 40mm bore cylinder working at

6 bars could easily lift an 80kg man. The basic construction of a typical double acting single rod

cylinder is shown in the cut away section (Fig 1), where the component parts can be identified.











Fig 1: Main components of a cylinder

1 Cushion seal 8 Front port

2 Magnet 9 Magnetically operated switch

3 Cushion sleeve 10 Piston rod

4 Barrel 11 Wear ring

5 Nose bearing 12 Piston seal

6 Rod seal and wiper 13 Rear end cover

7 Front end cover 14 Cushion adjustment screw

SINGLE ACTING CYLINDERS

Single acting cylinders use hydraulic oil for a power stroke in one direction only. The

return stroke is affected by a mechanical spring located inside the cylinder. For single acting

cylinders with no spring, some external force acting on the piston rod causes its return. Most

applications require a single acting cylinder with the spring pushing the piston and rod to the in

stroked position. For other applications sprung out stroked versions can be selected. Fig 2 shows

both types of single acting cylinder.



Fig 2: Single acting cylinder

The spring in a single acting cylinder is designed to provide sufficient force to return the

piston and rod only. This allows for the optimum efficiency from the available pressure. Most

single acting cylinders are in the small bore and light duty model ranges and are available in a

fixed range of stroke sizes. It is not practical to have long stroke or large bore single acting

cylinders because of the size and cost of the springs needed. Single acting cylinders with no

spring have the full thrust or pull available for performing work. These are often double acting

cylinders fitted with a breather filter in the port open to atmosphere. The cylinder can be

arranged to have a powered outstroke or a powered in stroke (Fig 3).

Fig3. Single acting cylinder with no spring, push and pull

DOUBLE ACTING CYLINDERS

Double acting cylinders use compressed air to power both the outstroke and in stroke.

This makes them ideal for pushing and pulling within the same application. Superior speed

control is possible with a double acting cylinder, achieved by controlling the exhausting back

pressure. Non cushioned cylinders will make metal to metal contact between the piston and end

covers at the extreme ends of stroke. They are suitable for full stroke working only at slow

speeds which result in gentle contact at the ends of stroke (Fig 4). For faster speed, external stops

with shock absorption are required. These should be positioned to prevent internal contact

between the piston and end covers.

.



Fig 4: Double acting non cushioned cylinder

Cushioned cylinders have a built in method of shock absorption. Small bore light duty

cylinders have fixed cushions which are simply shock absorbing discs fixed to the piston or end

cover (Fig 5).

Fig 5: Fixed cushion cylinder.

Other cylinders have adjustable cushioning. This progressively slows the piston rod down

over the last part of the stroke by controlling the escape of a trapped cushion of air (Fig 6).

Fig 6: Adjustable cushion cylinder

RODLESS CYLINDERS

For some applications it is desirable to contain the movement produced by a cylinder

within the same overall length taken up by the cylinder body. For example, action across a

conveyor belt or for vertical lifting in spaces with confined headroom. The novel design of a rod

less cylinder is ideal in these circumstances. The object to be moved is attached to a carriage

running on the side of the cylinder barrel. A slot, the full length of the barrel, allows the carriage

to be connected to the piston. Long sealing strips on the inside and outside of the cylinder tube

prevent loss of air and ingress of dust. The slot is unsealed only between the lip seals on the

piston as it moves backwards and forwards (Fig7). Direction and speed control is by the same

techniques as applied to conventional cylinders.



Fig 7: Rod less cylinder

CYLINDER SIZING FOR THRUST

CYLINDER The theoretical thrust (outstroke) or pull (in stroke) of a cylinder is calculated by

multiplying the effective area of the piston by the working pressure. The effective area for thrust

is the full area of the cylinder bore. The effective area for pull is reduced by the cross section

area of the piston rod (Fig 8).



Fig 8: Piston and rod diameters

Current practice specifies bore (D) and piston rod diameter (d) in millimeters and working

pressure (P) in bar gauge. In the formula, P is divided by 10 to express pressure in Newton’s per

square millimeter (1 bar = 0.1 N/mm 2)

The theoretical force (F) is given by

F= (p / A)

Where

D = Cylinder bore in millimeters

d = Piston rod diameter in millimeters

P = Pressure in bar

F = Thrust or Pull in Newtons

USABLE THRUST

When selecting a cylinder size and suitable operating pressure, estimation must be made

of the actual thrust required. This is then taken as a percentage of the theoretical thrust of a

suitably sized cylinder. The percentage chosen will depend on whether the thrust is required at

the end of movement as in a clamping application or during movement such as when lifting a

load. 63 48\\

254 46 55.6 (14) (2

1/4) 59588 58049

CLAMPING APPLICATIONS

In a clamping application the force is developed as the cylinder stops. This is when the

pressure differential across the piston reaches a maximum. The only losses from the theoretical

thrust will be those caused by friction. These can be assumed to be acting even after the piston

has stopped. As a general rule, make an allowance of 10% for friction. This may be more for



very small bore cylinders and less for very large ones. If the cylinder is operating vertically up or

down the mass of any clamping plates will diminish or augment the clamping force.

DYNAMIC APPLICATIONS

The actual thrust and speed from a moving cylinder are determined by friction and the

rate at which oil can flow in and out of the cylinder’s ports. The thrust or pull developed is

divided into two components. One for moving the load, the other for creating a back pressure to

help expel the oil on the exhausting side of the piston. For a lightly loaded cylinder, most of the

thrust is used to expel the back pressure and will result in a moderately fast speed. This is self

limiting however as the faster the speed, the less will be the pressure differential across the

piston. This is due to the increasing resistance through the ports, tubing, fittings and valve as the

rate of flow increases. For a heavily loaded cylinder most of the thrust is used to move the load.

The exhausting pressure will fall considerably to give a higher pressure differential before

movement starts. The acceleration and speed will be determined by the inertia of the load and

rate at which the lower back pressure is expelled. A heavy load simply diverts a greater

proportion of the power of the cylinder away from creating a back pressure to moving the load.

Although the speed for a heavily loaded cylinder is going to be slower it is not unreasonably so,

providing the cylinder has been correctly chosen. As a general rule, the estimated thrust

requirement should be between 50% and 75% of the theoretical thrust. This should give

sufficient back pressure for a wide range of adjustable speed control when fitting flow regulators.

SPEED CONTROL

For many applications, cylinders can be allowed to run at their own maximum natural

speed. This results in rapid mechanism movement and quick overall machine cycle times.

However, there will be applications where uncontrolled cylinder speed can give rise to shock

fatigue, noise and extra wear and tear to the machine components. The factors governing natural

piston speed and the techniques for controlling it are covered in this section.

The maximum natural speed of a cylinder is determined by:

• Cylinder size

• Port size



• Inlet and exhaust valve flow

• Oil pressure

• Bore and length of the hoses

• Load against which the cylinder is working.

From this natural speed it is possible to either increase speed or as is more often the

requirement, reduce it. First we will look at how the natural speed for any given load

can be changed by valve selection. Generally, the smaller the selected valve the slower the

cylinder movement. When selecting for a higher speed however, the limiting factor will be the

aperture in the cylinder ports (Fig 9)

Fig 9: Full & restricted port aperture

Valves with flow in excess of this limitation will give little or no improvement in cylinder speed.

The aperture in the cylinder ports is determined by the design. Robustly constructed cylinders

will often be designed full bore ports. This means that the most restrictive part of the flow path

will be the pipe fitting. These cylinders are the type to specify for fast speed applications and

would be used with a valve having at least the same size ports as the cylinder. Lighter duty

designs, particularly small bore sizes, will have the port aperture much smaller than the port’s

nominal thread size. This has the desired effect of limiting the speed of the cylinder to prevent it

from self destructing through repeated high velocity stroking. The maximum natural speed of

these cylinders can often be achieved with a valve that is one or two sizes down from the

cylinder port size. Larger bore cylinders are designed with port sizes large enough to allow fast

maximum speeds.

In many applications however they are required to operate at relatively low speeds. For

an application like this, a cylinder can be driven from a valve with smaller sized ports than those

of the cylinder. Once a cylinder/valve combination has been chosen, and the load is known, the

natural maximum speed will be dependent on pressure. For an installed cylinder and load, an



experiment can be carried out. Connect a control valve that will cause the cylinder to self

reciprocate. Then start the system running at low pressure and gradually increase it. The cylinder

will cycle faster and faster until a limiting speed is reached. This is the optimum pressure for that

application. Increase the pressure further and the cylinder starts to slow down. This is caused by

too much air entering the cylinder on each stroke. More time is therefore taken to exhaust it and

results in a slower cylinder speed With any fixed combination of valve, cylinder, pressure and

load, it is usually necessary to have adjustable control over the cylinder speed. This is affected

with flow regulators, and allows speed to be tuned to the application. For the majority of

applications, best controllability results from uni-directional flow regulators fitted to restrict the

flow out of the cylinder and allow free flow in. The regulator fitted to the front port controls the

outstroke speed and the one fitted to the rear port controls the in stroke speed. Speed is regulated

by controlling the flow of air to exhaust which maintains a higher back pressure. The higher the

back pressure the more constant the velocity against variations in load, friction and driving force.

On the other side of the piston full power driving pressure is quickly reached. Many flow

regulators are designed specifically for this convention.

SEALS

SEALS

There are a variety of seals required within a hydraulic cylinders Single acting non

cushioned cylinders use the least, double acting adjustable cushioned cylinders use the most

Fig 10: Types of seals

Key:

1) Cushion screw seal 4) Piston seal

2) Cushion seal 5) Barrel seal

3) Wear ring 6) Piston rod/wiper seal



A sliding seal such as fitted to a piston, has to push outwards against the sliding surface

with enough force to prevent compressed air from escaping, but keep that force as low as

possible to minimize the frictional resistance. This is a difficult trick to perform, since the seal is

expected to be pressure tight from zero pressure to 10 bar or more. There is a large difference

between static and dynamic friction. Static friction or break-out friction as it is sometimes called

builds up when the piston stops moving. Seals inherently need to exert a force radially outward

to maintain a seal. This force gradually squeezes out any lubricants between the seal and the

barrel wall and allows the seal to settle in to the fine surface texture. After the piston has been

standing for a while, the pressure required to start movement is therefore higher than it would be

if it is moved again immediately after stopping. To minimize this effect, seals should have a low

radial force and high compliance. High compliance allows the seal to accommodate differences

in tolerance of the seal molding and machined parts without affecting the radial force by a great

degree.

HOST PIPE

Hose is flexible pipe used to transmit flow from one point to another it completes. The

hydraulic circuit.

Advantages

allow relative motion between components at either end of the hose assembly

To simplify routing and installation.

easy to route over, under, around, or through a series of obstacles

Replacement is convenient.

HYDRALIC OIL

Hydraulic oil servo 68grade mineral oil is used



Viscosity range = 16 to 32 cst

Temperature range -10 to 80degree Celsius

CHAPTER 4

COMPONENTS OF DEVICE

Hydraulic hand pump

Hydraulic actuators

Hydraulic single acting cylinders

Top base plate

Base – C channel

Host pipe.



FEATURES OF PROJECT

1) It is easily operated

2) It is easily replaceable

3) Easy in construction & dis assembling

CHAPTER 5

WORKING

The principle of hydraulics where in fluid force is applied on the piston to move the load

is applied here .The working of the hydraulic scissor lift is simple in operation. It consists of tank

or reservoir where hydraulic oil is stored which is 13 liters of capacity. Hand pump mounted on

the top of tank is used to displace the oil from tank to the cylinders with the help of hoists pipe.

Due to the pumping action the oil from the tank will move from the tank to the rear end

of the cylinders and applies the oil pressure force on the face of the piston head which moves the

piston rod in the forward direction there by lifting the upper platform as per the requirement

needs of the project. A relief valve which is inbuilt into the pump and oil tank is used for the

purpose of relieving the pressure which helps to bring back the piston in original position due to



gravity. C channels frame are used and circular pin is been used for distributing the pressure as

well as the external load.

CHAPTER 6

DESIGN OF HYDRAULIC SCISSOR LIFT

CYLINDER

Bore = Φ50 & having a pump of 16 HP with the working pressure 315bar

Bore = Φ50



Standards for single acting cylinder

Pressure = 315bar

Material – structure steel st-42 hollow tube

Tensile strength = 42kgf/mm2

= 412.02 N/mm2

FOS = 4

σt = 412.04 / 4

= 103.00 N/mm2

t = di/2 x {√st +(1-2µ)p / st-(1+µ)p -1}

t= 50/2 x {√103 +(1-2x0.3)31.5 / 103- (1+0.3)31.5 -1}

t = 9.120645

t= 10 mm

Outer Diameter = d + 2to

= 50 + 2 x 10

= 70 mm

But the standard size is Φ75

Therefore a cylinder of 75 / 50 is used.

Since the available size is Φ75mm then

t = (D-d) 2

t = (75-50) / 2 = 25/2 =12.5 mm

Hoop stress induced can be found by

t = d/2 { √st + (1-2µ)p / st-(1+µ) P -1}

12.5 = 50 /2 { √ st +(0.4 ) 31.5 / st-(1.3) 31.5 -1}



St + 12.6 = 4 St- 40.95

St + 12.6 = 4 st – 163.8

St = 58.8 N/ mm2

The stress is less than 103.00 N / mm2 and hence the design is safe.

DESIGN OF PISTON ROD

MATERIAL : EN-8

Load F= A x P

= {п / 4 x 50 2} x 31.5

= 61850.10537 N

The internal resistance of piston is given by

Force F= Area x Stress

For piston rod material of mild steel EN – 8 ,σt = 541.9856 N / mm2.

σt = 541.9856 / 4 = 135.5 N / mm2

61850.10537 = {π / 4 d p2 x 135.5}



dp = 24.0176.mm

But the piston rod diameter is rounded off to 32 mm in order to sustain buckling load

dp= 32 mm

DESIGN OF END COVER

Material used Mild steel

Based on strength basis

F = d x tc x σt

σt = 107.5 Mpa for load on cylinder F = 61850.10537 N

61850.10537 = 50 x tc x 107.5

The minimum thickness of end cover is 11.5069 mm but choosen thickness is 16 for the

consideration of seal thickness & the port dimensions.

tc = 16 mm

The thickness is found by industrial formula



tc = d √ ( 3 x σw / 16 x P) where σw = working stress

tc = 50 √ ( 3 x 800 / 16 x 31.5 ) σw = 800 N / mm2

tc = 50 x 0.690065

tc = 34.5032 mm

PISTON HEAD

Piston head diameter is 49.794 – 49.970 mm the clearance is given as the piston is used

to slide forward and backward. The piston head length is choosen based on piston seals to fox

and width also no of seals to fix.

To check the piston rod for column action

When a structure is subjected to compression it undergoes visibly large displacements

transverse to the load then it is said to buckle, for small lengths the process is elastic since the

buckling displacements disappear when the load is removed

For one end fixed and other end free

C = 0.25



Let Fcr = Critical buckling load

E = 207 Gpa σy= yield point

= 280 Mpa

A = π / 4 x d2 = π / 4 x 322 = 804.247 mm2

A = 0.80424 m2

L = length of rod

K = Minimum radius of gyration

K= √ I / A

K = √ { (π / 64) x d4 } { (π / 4) x d2 }

K = d / 4 = 0.032 /4

K = 0.008 m

Slenderness ratio

L / K = 0.590 / 0.008

L / K = 73.75

Critical load using Euler’s Formula

Fcr = C x π2 x E / (L / K) 2

Fcr = π 2 x E I / 4 L2

Fcr = π 2 x 207 x 1000 x 51471.85404

4 x

Fcr = 75522.41833 N



Since the critical load for buckling is more than 61850.10537 N the buckling of rod will not

occur

BASE

The base structure is built up of C – channels & hollow bars are usually used in

engineering applications due to their high rigidity, strength as compared to the other bars

The choosen C channel is ISMC (Indian standard medium Weight channel)

Where

h = height

The dimension are h = 75 mm b = 50 mm t w = 4.4 t f = 7.3

A = 8.72 cm2

The supports and the two cylinders are flexibly coupled to the base there by not

transmitting the full load on to the base

The total load on the platform & load kept on it is taken by the two cylinders &

four supports which are made up of C – Channels

F = P / A

Assuming the total load coming on the upper platform which is being lifted ie more than design

load.

P = 250000.00 N = 250000 N

P = 250 KN

F = 250000 / 872

F = 286.6972 Mpa



Since four supports are used stress on each support is

F = 286.6972 / 4

F = 71.67410 Mpa

Which is less than the yield stress i.e. 280 Mpa

DESIGN OF CENTER PIN

Total load = 61850.10537 x 2

= 123700.2107N

Stress = P / A

Where

A = area

P = Pressure

Assuming bending stress of mild steel as 95Mpa

95Mpa = 123700.2107π /4 x d2

d2 = 123700.2107 x 4 π x 95



d = 39.78mm

d = 40mm

There for the pin dia is 40mm

WHEELS

Wheels are made up of mild steel having diameters of Φ180mm and shaft diameter of

Φ25 mm. the wheels are chosen on the base on the design load criteria which can sustain the

external load and well as the equipment load during transpiration in industrial line. The main

function of using wheels for this equipment is that machine can be moved from corner to the

other corner of the industry premises as per the requirement to lift the load.

CHAPTER 7

FABRICATION

1. Top frame C channel (ISMC)

Material: Mild steel ISMC 75

Operation: Cutting & welding.

2. Bottom frame C channel (ISMC)


Operation: Cutting & welding.

3. Support arms C channel (ISMC)


Operation: Cutting, Drilling & welding.



4. Pin

Material: Mild steel

Operation: Facing, Turning, Stepping & Drilling.

5. L angle (35 x 35 x 5)


Operation: Cutting, welding & Drilling.

6. Piping & flexible piping


Operation: Bending. Fitting.

7. Hydraulic Cylinder


Operation: Facing, Turning, Boring, Threading, Honing.

8. Piston & Piston Rod


Operation: Facing, Turning Stepping, Drilling, Plating, grinding, Threading,

Slotting.

9. Metal plate:


Operation: Gas cutting, welding.

10. Clampers


Operation: Cutting, Drilling, Machining & Welding.

11. Handle




Operation: Cutting & Welding.









COUPLING SELECTION



STRAIGHT LINE MAIL THREAD











HYDRAULIC SCISSOR LIFT



CHAPTER 9

ADVANTAGES OF HYDRAULIC SYSTEM

Transmission of high forces with a small space

High energy density

Energy storage capability

Steeples variation in motive quantities such as speed, forces and torques

Easy monitoring of force

Rapid reversal due to low component masses (low inertia)

Fast operating response

Uniform motion (free from shock)

Wide transmission ratio



Long service life

Design freedom in the arrangement components

Easy usage of standing components and sub –assemblies

Overload protection

DISADVANTAGES OF HYDRAULIC SYSTEM

Pressure and flow losses in pipes and control devices

Fluid viscosity sensitive to temperature and pressure

Leakage problems

Compressibility of the hydraulic fluid

ADVANTAGES

o Easily movable

o Capable of handling greater loads, reducing in labor stress

o Easy in operation.

o Lifting of loads at particular height

o Accuracy of device is higher as it works on hydraulic system.

DISADVANTAGE



1) Initial costs are more.

2) Prone to oil condition.

APPLICATION

1). Used in industrial application.

2). Used in hydraulic pressure system.

3). Used to lift vehicle in garages.

4) Maintenance of huge machines.

5). Used for staking purpose.

CHAPTER 9

COST EXPENDITURE

Materials CostSL No Particulars Rate Quantity Cost in Rs

1 Cylinder 3450/piece 2nos 6900

2 Hand pump 2950/piece 1nos 2950

3 ISMC C channel 45/kg 1nos 11700

4 Base plate 62/kg 1nos 930

5 Wheels 280/piece 4nos 1120

6 Handle Pipe 45/kg 1nos 234

7 Nut, bolt & studs 80/kg - 1120



8 Shaft 45/kg 3nos 833

9 Host pipe - - 450

10 Coupling 65/piece 3nos 195

11 Hydraulic servo Oil 68grade 115 13liters 1495

12

13

14

Process Cost

1 Machining - - 560

2 Drilling - - 600

3 Grinding/Filling - - 850

4 Welding - - 700

5 Greasing - - 50

6 Painting - - 560

1 Project Report - - 850

2 Miscellaneous - - 1800

Total 33,897

CHAPTER 10

FUTURE SCOPE OF THE PROJECT

We feel the project that we have done has a good future scope in any engineering

industry. The main constraint of this device is the high initial cost but has low operating costs.

The shearing tool should be heat treated to have high strength.

Savings resulting from the use of this device will make it pay for itself with in short

period of time & it can be a great companion in any engineering industry dealing with rusted and

unused metals.



The device affords plenty of scope for modifications, further improvements & operational

efficiency, which should make it commercially available & attractive. If taken up for commercial

production and marketed properly, we are sure it will be accepted in the industry. It has plenty of

scope if the device is made larger in size.

CHAPTER 11

CONCLUSION

The project work carrier out is successfully designed meeting the requirement as

constraints. Design and fabrication of hydraulic scissor lift for effort less lifting of load is done

because; it is operated by hydraulic cylinder which is operated by the hand pump. The scissor lift

can be design for high load also if a suitable high capacity hydraulic cylinder is used. The

hydraulic scissor lift is simple in use and does not required routine maintenance. It can also lift

heaver loads. For the present dimension we get a lift of 5ft. the scissor lift can lift a load of 1.5 –

2 ton.



CHAPTER 12

BIBLIOGRAPHY

TEXT BOOKS

1). Machine Design by R.K. Gupta

2). Theory of machines by R.S. Khurmi.

3). Mechanical Engineering science by R. K. Hedge

4). Fluid mechanics by R. K Bansal

5). H G Patil data hand book



WEB SITE

1). www.howstuff.com

2). www.google.com

3). www.hand pumps .com


5

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