‘ELMECH’ E.O.T Cranes are manufactured keeping in mind the following basic objectives.
High quality : Minimum maintenance : Aesthetic Appearance.
The above objective is achieved incorporating certain advanced technical feature described in the following pages.
ELMECH cranes are designed keeping in mind Indian Standard Specification applicable to the crane, viz.
IS:807-2006
Code of practice for design manufacture, erection and testing (structural position) of cranes and hoists.
IS: 3177-1999.
Code of practice for design of overhead travelling cranes and gantry cranes other than steel mill cranes.
IS: 4137-1985.
Code of practice of design of steel mill duty cranes.
ELMECH double girder cranes are classified as class I, II, III & IV. These cranes are available in capacities ranging from 1 ton to 100 tons.
STRUCTURAL ASSEMBLY:
This basically comprises of two bridges girder fixed on two end carriages carried on forged steel wheels. In case of gantry cranes the two bridge girders are fixed on top of four gantry legs which in turn are carried on two under carriage provided with forged steel wheels.
The bridge girders are fabricated from high quality steel plates forming a rectangular box section. Stiffening diaphragms are filled at regular intervals for the design to confirm to IS-807 and IS-800. The girders are so built that they have the required camber in the unloaded as required under Indian standard specifications.
The Internal surface is adequately sealed from the atmosphere by welding thus preventing internal corrosion.
The box type of girder construction has the following definite advantage over lattice and other type of construction:
More Torsion Rigidity: Box type of girders has much more torsion rigidity than any other type of girder construction. Heavy torsion movement due to starting, stopping and plugging of long travel mechanism and also eccentrically placed masses like long travel machinery, calls for torsion ally rigid girders.
Streamlined and aesthetically pleasing appearance. Ease of maintenance and cleaning.
Limited chances of damage to structure during transportation: A suitable track is provided on top of the girders for the travel of the trolley (crab).
The end carriages are fabricated from M.S. plates and provided with necessary diaphragm members. These are connected to the girders using only machined bolts.
A tapered plate design is incorporated for joining the end carriages to the girders thereby ensuring smooth flow of stresses. This design is ideally suited for cranes which are consistently subjected to dynamically loading.
The end carriages are provided with forged steel wheels carriage on specially designed bearing support blocks of ‘L’ type design (commonly known as ‘L’ type bearing housings).
This method of providing wheels on ‘L’ type of blocks with antifriction bearing has the following advantage:
It provides two load bearing surfaces at right angles to each other as against simple Plummer blocks which provide a single bearing surface only. Wheel load due to skewing of the crane as well as crab is transferred to the structure through machined grooves, the bearing housing and the machined pad welded to the structure, hence no undue stress is developed due to bending and shears on the holding bolts. Wheels are press fitted on axle supported on spherical roller bearing which can withstand more axel thrust, bending and linear expansion due to temperature rise. Complete wheel assembly can be changed within no time, it is supported on only four bolts which otherwise can hold the crane in breakdown condition for quite some time. The end carriages are provided at four corners with rubber buffers. At the end of the trolley track, M.S. curved end stoppers are provided which act as trolley buffers. The trolley frame is fabricated from M.S. plates. Rolled sections welded together to from robust construction to carry the hoisting and traversing machineries. The trolley frame is also carried on four gorged steel wheels provided in ‘L’ type on other bearing support blocks, the advantage of which have already been enumerated above. One full length platform of chequred M.S. antiskid plates is provided on the drive end side of the bridge girders. Platform on other side can be provided at optional extra cost.
For easy assembly erection at site all parts of crane structure is match marked.
Cabin: In case of cabin operated cranes the driver’s cabin is provided on one end of the bridge girder. The joint of the driver’s cabin to the bridge girder is so designed that the cabin becomes integral with the girder. A step ladder is provided from the cabin to the crane bridge platform. The drivers cabin open/close type depending upon indoor/outdoor operations.
The crab frame is fabricated from steel sections and carries the hoisting and cross travel machinery.
HOIST MOTION: This comprises of a motor of sufficient power, a totally enclosed helical gear box, a rope from coupled to the gear box by specially designed flexible coupling. The motor is directly coupled to the gear box and on the coupling an electro magnetic/electro hydraulic thruster brake is provided which comes into operation as soon as the power is switched off. The gearbox is fabricated is from M.S. incorporating all machine cut helical gear trains and is oil splash lubricated. The use of totally enclosed helical gear boxes though rather expensive more than justified the extra price in view of the advantage of high transmission efficiency, less meshing noise and longer life. The gear box is coupled to an M.S. fabricated/seamless pipe rope drum. The rope drum is finally, machined to have right and left hand spiral grooves to take the hoisting rope. It is of such a size that there will not be more than one layer of rope on the drum when the rope is fully wound. Also the length of the drum will be such that each lead of rope will have minimum two full turns on the drum when the hook is at the lowest position and one spare groove for each rope lead when the hook is at the highest position.
A specially designed geared flexible coupling flexible coupling is provided to connect rope drum and the hoist gear box. The main advantages of these systems are:
It eliminates any alignment problem thereby avoiding strain due to basic misalignment in the output shaft hence preventing fatigue failure. Vertical load is taken by a spherical roller bearing and the torque is transmitted separately through a geared coupling and shear pins. Hence there is no bolt to develop compound stresses due to shear and bending in each cycle of rotation of the drum. This avoids fatigue failure in bolts joining drum and gear box. Dismantling and reassembling of hoist gear box and rope drum for maintenance becomes very easy there by considerable reducing the downtime of the crane.
A steel snatch block, complete with forged steel hook carried on ball thrust bearings is provided with cast iron or fabricated M.S pulleys and is fitted with guards to prevent the rope from leaving the pulleys. Lifting g\hook is tested as per IS: 3815 and IDLR test is issued for each hook. Each lifting hook is provided with spring latch. The hoisting wire rope provided is of 6 x 36 x 37 construction of best plough steel having a breaking strength of 160/175kg/mm². The wire rope has factor of safely as stipulated in IS 3177-1999.
A spindle limit switch driven by hoisting drum shaft is provided to give protection against the extreme positions of hook travel.
In case an auxiliary hoist is provided in addition to the main hoist, the principle and the construction of the auxiliary hoist will be similar to the main hoist.
MICRO-SPEED: in case of MICRO-SPEED arraignment required, any one of the following systems can be offered:
Through additional unit, comprising of Gear box, Magnetic Clutch and Squirrel Cage Pony Motor arrangement. The shaft of the main hoisting motor will have double extension shaft. An electro-magnetic clutch will be fitted between the main motor and the out put shaft of the micro-speed gear box. The input shaft of the micro-speed gear box is connected with the micro speed motor through flexible coupling. When the micro-speed motion is put on, the main brake opens while the main hoist motor is not energized. The magnetic clutches energies along with the main brake and drive are obtained through the micro-speed motor, the slow speed obtain due to the additional micro-speed gear box.
Through additional unit comprising of Planetary Gear Box, Squirrel Cage Pony Motor and Reverse Thruster Brake arrangement. As there is no magnetic Clutch, this arrangement is fall-safe as well as long lasting.
Through Variable Voltage and Variable Frequency Drive (VVVF). This is a latest technology arrangement due to which steeples pre-determent speed variation is achievable from “0” o full speed in all motion.
TRAVERSE MOTION: The traverse motion involves power transmission from the motor to the trolley wheels though a totally enclosed vertically mounted spur gear box having an output shaft extending on both sides and driving the trolley wheels through semi-geared coupling on the principle of floating shaft. The motor is directly coupled to the gear box and on the coupling an electro magnetic/electro-hydraulic thruster brake is provided. The brake applies automatically when the current supply is switched off.
A two-way lever type limit switch is provided for protection against the extreme traverse of the trolley (crab)
TRAVEL MOTION: There are two ways in which this motion could be provided on cranes.
SINGLE DRIVE ARRANGMENT: In this case the power is transmitted from the motor through a centrally located horizontally mounted totally enclosed. Helical gear box having an output shaft extended on both sides which drives the bridge wheels one on each end carriage on the principle of floating shafts through semi-geared couplings.
The motor is coupled to the gear box having all stage helical reductions and on the coupling is provided an electro magnetic/electro-hydraulic thruster brake which applies automatically when the power is switched off.
THE SYSTEM of providing a semi-geared and semi-rigid coupling in the traverse and travel transmission shafting is known as the floating shaft system. This system has the following advantage.
It prevents misalignment of the line shaft due to basic misalignment and improper maintenance.
It prevents misalignment arising out of differential of crane girder and shafts.
It prevents development of any unique strain in the platform support which otherwise may give way due to excessive alternate stresses developed in the line shaft with rigid couplings.
For both singles drive arrangement OR twin drive arrangement L.T. end carriages will carry 4 Nos. double flanged wheels supported on ball/spherical roller bearings running in ‘L’ type housing.
Two-way lever types limit switch is provided for protection against extreme travel of crane.
The entire transmission system on the output shafts of traverse ad travel motions is designed with the use of geared coupling which has the following advantages:
· Simple in design and composed of few parts.
· No springs to crystallize or brake.
· No rubber business to require frequent replacement.
· It is self-aligning with no binding action at any point of its revolution.
· Crowned teeth are free to along themselves as in ball and socket joints.
· Can be used on reversing service without any notice or vibration.
· Exceptionally long life.
· Simple to align, install and easy to maintain.
· In capacity of transmitting torque it is the smallest in size and weight in comparison with any other flexible couplings.
ELECTRICALS: The electrical equipment comprises basically of members, their controls and wiring. Etc.
The controls for the crane are of two types:
A) For cabin operated cranes.
B) For floor operated cranes incase of cabin operated in cranes, there are two types of controls available.
By master controllers
By drum/cam type controllers
MOTORS: All motors will be totally enclosed 25% CDF / 40% CDF high torque crane duty squirrel cage / slip ring type, preferably in IEC frame size. Motors will have generally class B insulation suitable for tropical climate and high humidity. All motors will confirm to IS: 325. The motors will confirm to details as given in quotation.
CONTROLLING EQUIPMENT: The floor controlled crane will be controlled by means of pendant push button controller from floor. The cabin controlled crane will be controlled by means of master controllers of Drum/Cam type controller.
RESISTORS: Resistors when provided are designed as per BSS-587-1997 and are made of unbreakable grids formed from stainless steel or a similar or an alloy housed in a ventilated steel housing. These are suitable for intermittent duty having 5/10 minutes rating.
CONTROL PANEL: An electrical protective a panel of sheet metal is provided, housing within it the following:
· Isolating switch.
· Push button for stopping all the motions. This also acts as an emergency stop.
· Triple pole thermal overload relays for individual motors.
· One contractor type circuit breaker.
· One set of fuses for each motor.
· One transformer for low voltage supply.
· One set of switch fuses for transformer protection.
· Plug and socket for connection to the hand lamp.
· One indicating lamp.
WIRING: All wiring between individual motors, controllers, current collectors and resistance is with PVC armored cables, control wiring is done with PVC armored cables having copper conductors.
For the collection of current from the drive’s cabin to the crab (trolley), the most modern and safest arrangement of COBURN TROLLEYS with flexible trailing cables is provided.
For the collection of current to the crane from the down shop leads four numbers of current collectors are provided.
GENERAL:
Testing: The ELMECH cranes are fully assembled and tested to our workshop before dispatch as per ISS-3177. In the testing, all the motions are tried out in our works at load conditions. Cranes up to tones capacity only can be tested at our works at Pune, for full load and overload as per IS: 3177 prior to dispatch.
Load test and 25% overload test for the cranes are performed at site if erection and commissioning of the cranes are ordered on us. Arrangements for test loads for testing of the cranes are purchaser’s responsibility.
PAINTING: Before dispatch from our works, the structure is thoroughly scraped, cleaned and one coat of red lead paint applied. Machinery parts are finished with enamel paint. Exposed machined parts are coated with anti-corrosive varnish.
OUTDOOR DUTY CRANES: In case the ELMECH cranes quoted are for outdoor operation, in addition to the normal features as referred in the specifications, following points are care of:
The structure of the crane is made heavier to take into account wind pressure when the crane is moving against it, as also the long travel machinery in general is made heavier.
The horse power of the long travel motor is increased to account for the wind pressure when the crane is moving against it, as also the long travel machinery in general is made heavier.
Suitable canopies are provided in all exposed parts to protect them against rain, etc.
The driver’s cabin I totally enclosed weather proof type.
FLAME PROOF CRANES: In case of flame proof cranes, following electrical items will have flame proof enclosures.
· MOTORS
· BRAKES
· LIMIT SWITCHES
· PENDANT PUSH BUTTON STATION
· CONTROL PANEL
· Wheels shall have phosphor, horse, and lining to avoid sparking
Questionair For :- Double Girder EOT Crane
1. Capacity in Tonnes.
2. Height of Lift.
3. lenght of Travel
4. exact Span
5. Desired speeds in all motio, i.e. Hoisting, Aux, Hoisting C.T. and L.T.
6. Duty as per IS/BSS (eg, Class I,II,III and IV).
7. Location of the Crane-whether Indoor or Ourdoor.
8. Floor Operated or Cabin Operated. If Cabin operated type of Cabin open type or close type.
9. Type of material to be handled.
10. Any other relevant informations if any, to suit your requirement.
11. Please send shop layout drawing including clearances available. |
