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The design of all commercial cranes and hoists shall comply with the requirements of

ASME/ANSI B30 standards and Crane Manufacturer’s Association of America standards

(CMAA-70 and CMAA-74).

There are two major considerations that are taken into account in the design of cranes

1. The crane must be able to lift a load of a specified weight2. The crane must remain stable and not topple over when the load is lifted and moved to

another location. (Lifting capacity)

Cranes illustrate the use of one or more simple machines to create mechanical advantage.

THE LEVER: A balance crane contains a horizontal beam (the lever) pivoted about a pointcalled the fulcrum. The principle of the lever allows a heavy load attached to the shorter end of

the beam to be lifted by a smaller force applied in the opposite direction to the longer end of the

beam. The ratio of the load‟s weight to the applied force is equal to the ratio of the lengths of the

longer arm and the shorter arm, and is called the mechanical advantage.

THE PULLEY: A jib crane contains a tilted strut (the jib) that supports a fixed pulley block.Cables are wrapped multiple times round the fixed block and round another block attached to the

load. When the free end of the cable is pulled by hand or by a winding machine, the pulley

system delivers a force to the load that is equal to the applied force multiplied by the number of

lengths of cable passing between the two blocks. This number is the mechanical advantage.

THE HYDRAULIC CYLINDER: This can be used directly to lift the load (as with a HIAB), orindirectly to move the jib or beam that carries another lifting device. Cranes, like all machines,

obey the principle of conservation of energy. This means that the energy delivered to the load

cannot exceed the energy put into the machine. For eg: if a pulley system multiplies the appliedforce by ten, then the load moves only one tenth as far as the applied force. Since energy is

proportional to force multiplied by distance, the output energy is kept roughly equal to the inputenergy (in practice slightly less, because some energy is lost to friction and other inefficiencies).

In order for a crane to be stable, the sum of all moments about any point such as the base of thecrane must equate to zero. In practice, the magnitude of load that is permitted to be lifted (called

the “rated load” in the US) is some value less than the load that will cause the crane to tip. UnderUS standards for mobile cranes, the stability-limited rated load for a crawler crane is 75% of the

tipping load. The stability-limited rated load for a mobile crane supported on outriggers is 85%

of the tipping load.

An overhead crane typically consists of three important parts: The hoist providing up/down

motion of the load item. The trolley, providing left or right for the hoist and the load. The bridge providing the back or forward motion of the hoist, trolley and the load. A EOT crane is

permanently installed in a factory, shop or ware house to move the items which cannot be moved

by human beings.

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SOME RELATED TERMS WITH CRANES:-

HOIST: A hoist is a device used for lifting or lowering a load by means of a drum or lift-wheelaround which rope or chain wraps. It may be manually operated, electrically or pneumatically

driven and may use chain, fiber or wire rope as its lifting medium. The load is attached to the

hoist by means of a lifting hook.

SIMPLE MACHINE: In physics, a simple machine is any device that only requires the

application of a single force to work. Work is done when a force is applied and results inmovement over a set distance. The work done is the product of the force and the distance. The

amount of work required to achieve a set objective is constant; however the force required can be

reduced provided the lesser force is applied over a longer distance. The ratio between the twoforces is the mechanical advantage.

MECHANICAL ADVANTAGES: In physics and engineering, mechanical advantage (MA) isthe factor by which a mechanism multiplies the force put into it. The ratio A:B is called

mechanical advantage.

HYDRAULICS: Hydraulics is a topic of science and engineering dealing with the mechanical

properties of liquids. Hydraulics is part of the more general discipline of fluid power. Fluid

mechanics provides the theoretical foundation for hydraulics, which focuses on the engineeringuses of fluid properties. Hydraulic topics range through most science and engineering disciplines,and cover concepts such as pipe flow, dam design, fluid control circuitry, pumps, turbines,

hydropower, computational fluid dynamics, flow measurement, river channel behavior and

erosion.

LIFTING HOOK: A lifting hook is a device for grabbing and lifting loads by means of a device

such as a hoist or crane. Lifting hooks are usually equipped with a safety latch to prevent thedisengagement of the lifting wire rope sling, chain or rope to which the load is attached. Hook

may have one or more built – in pulleys to amplify the lifting force.

WIRE ROPE: Wire rope consists of several strands laid (or „twisted‟) together like a helix.

Each strand is likewise made of metal wires laid together like a helix. Initially wrought iron

wires were used, but today steel is the main material used for wire ropes.

Design & Constructional Features of “LIFT UP” Electric Wire Rope Hoists:-

DESIGN: Hoists are designed as per standards (IS 3938 Class II) duty operations and repetitive

use under most severe operating conditions. Hoists specially designed for higher lifts, fasterhoisting & cross travel speeds & moveable on curved.

MOTORS: Hoist & crane duty hour rated squirrel cage induction motors, confirming to IS 325

with comparatively higher H.P. and higher starting torque to reduce handling time. It is flange

mounted to suit the design and provided with suitable insulation

ROPE DRUM: The rope drum should be made of seamless pipe machined & grooved

accurately, to ensure proper seating of wire rope in a proper layer. The drum should be fitted

with two heavy duty Ball / Roller bearings of reputed make for smooth operation & longer life.

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ROPE GUIDE: Rope guide should be made of special close grain castings & is specially

designed and accurately machined to suit the grooves of the rope drum & prevents the rope from

overriding & loosening. It also operates the limit switches provided as a safety feature to limitthe over hoisting & over lowering of the hook. The guide is designed to ensure proper tensioning

of rope.

GEAR BOX: Totally enclosed oil splash lubricated & dust free gear box should be provided forsmooth, trouble free & longer life. All gears are helical type and cut from alloy steel / low carbonsteel on hobbing machines for achieving higher precision & a special process of gear toughening

ensures smooth, silent, trouble free running of drive system. The pinions and gears are supported

on anti-friction bearings on both ends.

MODULAR : Design is of modular construction and its maintenance is easy as each component

CONSTRUCTION: Brake, motors, gear box & Control panel are independent units and are

accessible easily. The complete hoist can be easily maintained by keeping it in its installed

position, thus saving on precious labour as well as down time maintenance time.

BEARINGS: Heavy duty deep groove ball / roller bearings of reputed make i.e. FAG / NACHI

or equivalent make are used on all rotating parts and are grease packed for longer bearing life.

TROLLEY : Push-pull, Hand Geared or Motorized Trolleys are of adjustable type and fitted with ball bearings to suit recommended size of I-Beams.

HOOKS: Heavy duty high tensile steel forged hooks are used & fitted in such a manner that

they rotate and swivel freely.

BRAKES: Heavy duty 3 phase AC fail safe electromagnetic disc type brakes are provided on

hoisting motion held closely to sustain the full load when current supply is switched off either

accidentally or intentionally. It is mounted on the rear end of the motor for easy maintenance.

TESTING: The hoist components should be subjected to strict quality control procedures. And

the hoist should be finally tested to 25% overload to prevent any accidents.

SIMPLER HOIST DESIGN REDUCES COSTS

In brief, the hoist has a drive that is formed with an integral decelerator and brake flanged on one

side of the main frame. The drive decelerator and brake are formed as a single body and thetraveler can be detached from its mounting simply. This is said to make installation and

exchange easy, reducing maintenance costs. This is operated together with the wire-rope drum

by a drive motor mounted on the opposite side of the flange. A traveler unit connected below themain frame has wheels coupled to bearings on both sides of the unit through a bored space. Each

wheel has an involutes spine gear groove on its centre bore matching a groove gear on the drive

shaft. This design reduces the weight and volume of the main frame compared to previous

designs, thereby making production costs lower. Other claims include reduced transports costsand simpler installation. Existing art problems According to the earlier laws, one type of

conventional electric hoist has an intermediate shaft, connected to the traction motor, and

extending through the inside of the wire-rope drum to a decelerator and electromagnetic brake.

This makes it comparatively long, causing a loss in power. Any widening of the wire-rope drumalso means that the intermediate shaft has to be lengthened, but the wire-rope drum cannot be

increased over a predetermined width. The conventional design also means that the extended

intermediate shaft rotates with the lifting operation of the hoist. It is claimed that a high speed inthe intermediate shaft causes vibration, which can damage the object being lifted. Avoiding this

problem by rotating the intermediate shaft at a predetermined speed limits the speed and capacity

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of the traction motor, and thus limits the weight of the object that can be conveyed by the hoist.

An existing design of hoist, adapted to carry heavier objects, uses a motor rotating at high speed.

In this a decelerator, hoisting traction motor and brake are mounted at one side of the drum witha horizontal arrangement on the upper portion of a main frame, also carrying the wire-rope drum.

Four wheels on the corners of the frame each have a travelling decelerator, travelling motor and

brake formed at one side of each to operate in cooperation. This arrangement of horizontal fixingmeans that each part occupies a relatively large space, resulting in a bulky structure. The largeweight increases installation and production costs.

LOAD HOIST ARRANGEMENTThere are load hoist arrangements that enable a manually-guided load moving in three

dimensions to be driven by sensing the lateral movement of a lifting cable. These designs often

have a problem with self-induced vibrations or excessive swinging. The changes in acceleration

and direction, induced manually by the operator to the load-carrying device often make it start toswing. Once it has started to swing, it is difficult to stop, especially if the load is heavy,

decreasing the system‟s maneuverability and increasing the risk of accidents.

A load hoist arrangement consists of a traversing device with traveling bridge and carriage. Twomotors on the support structure drive cables that pull the traveling bridge in either direction.

But the design has some drawbacks. There is a need for a load hoist arrangement that supports

motions in both lateral directions and not only along a line. By positioning the motors on the

support structure, the design makes a relatively stable working environment. However, there area lot of cables connecting static components with moving parts. These cables often connect to

sensitive connections and couplings that will be prone to wear in this dynamic environment,

risking less accurate motion control and increasing the need for maintenance. There is also aneed for a load hoist arrangement that is easy and quick to install. The invention is designed to

overcome these issues and be capable of handling manually-induced accelerations, maintaining

stability in the load hoist arrangement even when handling heavy goods. A control device is

arranged along a lifting cable between a traverse device and load-carrying device. This load-carrying device is manually guidable in a three-dimensional space. A driving device controls the

lateral movement of the load carrying device. The vertical motion is not part of this patent. An

industry-standard electronically-controlled balancer controls the vertical motion of the load-carrying device. The transmitter is a control device that tells the hoist to compensate for any

load, so that an operator guiding the crane manually will experience a fraction of the total

resistance of the load. The driving device comprises two motors secured to carriage. The ends oftwo drag cables and are secured to opposite ends of the supporting rails and cross at traveling

bridge. The drag cables cross each other at the carriage so that a driving wheel unit of one motor

works in contact with one drags element.

The axle unit has two separate grooves, one for each drag cable. The combination of the twodrag cable paths, each working in a different direction, locks the axle unit, providing the driving

device with increased stability. The drag elements are arranged to turn in a 90 degree angle

around a pulley from their anchor point to the carriage. With this arrangement, possible

imperfections will be almost automatically corrected because the two drag cables working inopposition to each other. The friction between the drag element and possible guide wheels axle

units and driving wheel units together with the drag cable path will prevent the drag cable from

sliding when the driving device is in operation. The carriage is moved by actuation of the twomotors and hence the load carrying device will follow. The motors are capable of clockwise and

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counter-clockwise motion. The motors are actuated by the movement of the load. The angle of a

load-carrying element is used as reference of force impact for guiding and controlling the driving

device, and thus the load carrying device in a lateral direction. The traverse device moves in proportion to the force manually applied by the operator. This allows a controlled movement of

the load carrying device relieving the operator from bearing the actual weight of the load while

still being able to lift and move them. The invented driving device is easy to manufacture andinstall since the carriage can be made in a standardized manner and the support structure togetherwith the drag elements are simple to adapt to suit the location in question. Furthermore, the need

for control data transmission cables is limited to a zone near the carriage. This design reduces the

need for cable racks interconnecting motors and sensors. Since it is a dynamic system, oftencovering a large working area, and frequently used, the risk for play in the interconnections of

the control system, e.g. motors, transmitters and recording sensors, may lead to downtime and

reduced productivity.

THE DESIGN: We are concerned with the design of the hoisting arrangement of 2 tonne

capacity of EOT crane, which will lift the load up to a distance of 8 meters.

Selection of section: The section is trapezoidal

Selection of material: Mild steel

Load to lift : 2 tonne

Considering 50 % over loading.

So the design load = 2 tonne+50% of 2 tonne = 3tonne

Taking the help of (IS 3815-1969) for selection of material for 8 dimensions of crane hook.

In IS 3815-1969 the nearest selection for 3.3 tonne is 3.2 tonne.

For load 3.2, proof load (P) is 6.4 tonne.

So C = 26.73√P = 26.73 x √6.4= 67.62≈ 68 mm

A = 2.75 C = 2.75 x 68 ≈ 187 mm B = 1.31 C = 1.31 x 68 ≈ 89mm

D = 1.44 x C = 1.44 x 68 ≈ 98mm

E = 1.25C = 1.25 x 68 ≈ 85mm

F = C = 68mm

G = 35mm

G1 = M33, Pitch = 6mm (Coarse series)

H = 0.93 x C = 0.93 x 68 ≈ 63mm

J = 0.75 x C = 0.75 x 68 ≈ 51mm

K = 0.92 x C = 63mmL = 0.7 x C = 0.7 x 68 ≈ 48mm

M = 0.6 x C = 0.6 x 68 ≈ 41mm

N = 1.2 x C = 82mm

P = 0.5 x C = 34mm ≈ 34mm

R = 0.5 x C = 0.5 x 68 ≈

U = 0.33 x C = 0.3 x 68≈20 mm

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Checking for strength Area of the section = ½ x 63 x (41+8) = 1543.5 mm2

Centroid from ‘a’= (.05 x 8 x 65) 63/3+(.5 x 41 x 63) x (2 x 63)/3

½ x 68 x (41+8)

= 38.571mm

So centroid from b = 63-38.6=24.4mm =h10 = 34 +24.4 = 58.4mm

r0 = A/(dA/u)

dA/u = [b2+r2/h (b1-b2)] ln r2/r1 – (b1-b2)=28.65mm

r0 = A/(dA/u) = 1543.5 =53.87 53.9 mm

28.65

e=0-r0 = 58.4 – 53.9 = 4.5mm

Moment:-

M = -P x 0= -3 x 58.4= – 175.2 (tonne x mm)

Stress due to bending is given by

b = M X 4

Ae r0-y

For point a

Y = -(e+h2)= -(4.5+38.6)= – 43.1 mm

For point b

Y = r0-r1= 53.9 – 3.4= 19.9 mm

Stress due to direct loading = P/A= 3/1543.5= 1.9436 x 10-3 Tonne/mm3

Stress due to curvature of „a‟

ba = – (-175.2) x -43.11543.5 x 4.5 {53.99 – (-43.1)}= 0.0112

So total stress at a= – 0.0112 + 1.9436 x 10-3 = – 9.2642 x 10-3 Tonne/mm2

-90.85 Mp= – 9.2642 kg/mm2

Stress due to curvature at b

bb = -(-175.2) x .19.991543.5x 4.5 (53.9 – 19.9) = 0.014763

So total stress at b= bb + 1.9436 x10-3=0.014763 + 1.9436 x 10-3

=0.0167 tonne/mm2 = 16.7 Kg/mm2 163.84 MPaLet the material be class 4 carbon steel ( 55C 8)

Ultimate tensile strength I 710MPa

Design strength = Ultimate tensile strengthFactor of safety

= 710/4

= 177.5 MPa

163.84 > 177.5

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So design is safe

Determination of length of threaded portion

Pitch = 6mm Nominal dia of thread = 33 mm (G1) = d

Considering the screw and thread are of single safest & square mean diameter of screw =

dm = d- (p/2)= 33 – (6/2)= 30

tan= 1/dm = 6/( x 30)

tan= tan-1{6/( x 30)} = 3.640

Let the co-efficient of fraction be 0.15

So = tan = tan 0.15= 8.530

Torque required to resist the load

T =W x dm* tan ( + )/2Where w is the weight of load is 3 tonne and the load of the hook itself.

The maximum weight of the hook is 50kg (from the use of the soft ware „Pro-Engineer‟)

So T = 3050x 30 x tan (3.61+ 8.53)/2 =9866.42 Kg-mm

Stress induced in the screw Direct tensile stress (allowable or design)

=4w/ d02 d0 = core diameter of the screw.

dc = d-p = 33-6 = 27 mm

1 = 4x 3050272

= 5.326 kg/mm2 52.24 MR

Torsional shear stress

= 16T = 16×9866.42

de3 x 273= 2.5529 Kg/mm2 = 25MP

Maximum shear stress in the screw

max = ½ 2)2 + 4 (

= ½ √ (52.242 + 4 x 252) max = 36.15Mpa=

Height of the nut a) Considering bearing action between the thread in engagement.Let „n‟ is no of thread in engagement with screw.

Considering bearing action between nut & screw

Let the permissible bearing pressure =pi= 6 MR.We know

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Pi = 4W

(d2-dc2) x n

So 6 = 4×3050 x 9.8

(332-272) x n N = 4 x 3050 x 9.8

(332-272) x 6 1.27 x 9.8 12.5 So the height of the nut is = 2 x 12.5 = 25mm

b) Considering shear failure of thread across root Shear stress induced

= W

dc (0.5xP) x n = . 3050 x 9.8

x 27 x (0.5 x 6) x n = 117.46

n

= 0.5 x 177.5 = 117.46n n

= 117.46

177.5 x0.5

= 1.32 = 2So height is n x p = 2 x 6 =12mm

Taking the highest value 25mm

Design of pin which will carry the dead load & the load of hook: We have to determine the dimension of „t‟.

n = M x Y

I

= M x (24)

I 2Where “I” is moment of inertial about bh3 t x 243 x 2

12 12Maximum bending moment for = M = ¼ x W x LLet L = 70 mm

So M = ¼ x 3050 x 70 = 2 x 26687.5 Kg-mm

= 2 x 261.715 x 103 N-mm

= 2x 261.715 x 103 x 241 t x 243 2

177.5 = 1363 x 2

t

t = 1363 x 2 = 15.2 MM7.8 x 2

177.5

16 mmTaking 20 m for additional safety

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