The Issue on
Rotation and Safety of the Balancing Drum of movable beam lifting system of the
Gantry-type Bucket Wheel Stacker & Reclaimer
(Abstract)
(Classic)
Yimin Li Bulk-Onweb March 30, 2017
Keywords:
Gantry-type bucket wheel stacker reclaimer; lifting system; wire rope reel;
balance; balance wheel balance wheel to rotate;Balance
drum; Gantry; Bucket wheel stacker & reclaimer;
Overview
The gantry-type bucket wheel stacker & reclaimer have been used in domestic
nearly half a century. It is estimated that nearly a hundred of gantry-type
bucket wheel stacker & reclaimer and similar equipments have been designed and
manufactured in China. Which are mainly used in thermal power plants, and most
of them are still in service. The key feature of gantry-bucket wheel stacker and
reclaimer is its lower part contains a movable beam which consists of bucket
wheel, bucket wheel trolley and belt conveyors. The beam is driven up and down
using pulley blocks by hoist. The basic design method of the movable beam hoist
system for equipments of this kind are the same. It appeared that many serious
accidents happened domestically caused by movable fallen down due to steel wire
rope worn and broken. The accidents affect the users’ production schedule, and
lead to significant economic loss.
gantry-type
bucket wheel stacker reclaimer
1. Movable beam
and the lifting mechanism
The movable beam of gantry-type bucket wheel stacker & reclaimer acts as the
important steel structure which supports the conveyor, bucket wheel device and
bucket wheel trolley. The movable beam consists of two pieces of I-shaped beams.
There are angle steels and channel steels connect between the two. Usually,
there are three belt conveyors installed in the middle of movable beam. Tracks
for bucket wheel trolley travelling lay on the upper part of the two I-shaped
beams. Fixed pulleys used to drive and adjust the lifting height of movable beam
are arranged on both ends of the beam.
lifting mechanism
The lifting mechanism of movable beam for gantry-type bucket wheel stacker &
reclaimer are mostly driven using pulley blocks by steel wire rope hoisting
mechanism. So far, the principles of wind the wire rope of pulley blocks for
most equipment domestically are almost in the same. The differences between them
in detail are the ratio of pulley blocks. The ratio of pulley blocks for lifting
mechanism is designed in 8 times or 6 times as usual.
The lifting system of movable beam for gantry-type bucket wheel stacker &
reclaimer is the four ropes system which driven by dual drums. Each sheave is
pull by two wire ropes wound on drive pulley respectively between the lifting
side and opposite side of the movable beam. These steel ropes are finally
gathering and fixed on the balance drum (the balance wheel). Steel rope end
fixed on the drum should be wound at least 3 safety cycles, which ensure that
there is enough friction that the rope cannot be drawn from the rope clamp. The
four-rope lifting system of movable includes 8 ropes. Four ropes of which are
fixed on the drum, and the other fixed on the balancing drum. There are two
purposes of the original design for the lifting system. One purpose is that
protect the equipment as dual fail-safe, which means if one rope broken the
other can protect the movable beam not to fall down. The dual fail-safe make
sense at the precondition of rotational angle of balance drum is not too big and
there is enough braking power if one rope broken. The other purpose is that
ensure that both ends of movable beam keep horizontal and synchronically during
lifting.
At present, the basic principle of wire rope hoist lifting system for movable
beam of gantry-type bucket wheel stacker & reclaimer in domestic is almost the
same. The differences of lifting system for movable beam as following: the power
of driving motor on hoist, the ratio of pulley block of lifting system and the
form of balancing devices using to balance the forces between the two ropes(most
of devices use balance drum, and the others adopt balance beam).
2. Reasons of big rotational angle of balance drum for movable beam lifting
system
Balance drum on movable beam system (balance wheel) is used to balance the
forces between the two ropes, and automatically adjust the small difference of
ropes length on two sides. The balance drum act as protection device is designed
to dual ropes system. If one side of balance drum’ steel rope is broken, the
balance drum will be blocked after rotating a small angle. Which means if one of
the steel ropes was broken and fall, the other will still been wound on the
balance drum and pull the movable beam. But too big rotational angle of balance
drum is not acceptable for the equipment in normal working condition. The
reasons of big rotational angle of balance drum are:
The value of forces at lifting points on the two sides of movable beam are
inequality(F1≠F2), including the frictional resistance forces of pulley and
elasticity factors of ropes, will cause the small difference of the forces on
the two drive drums. And it will lead to the difference of rotational angles of
drive drums, so as to cause the balance drum rotation.
2) Difference of the frictional resistances, different performances of motors
and different braking moments of brake will cause the difference of rotating
speeds of start-up and braking, which result in the balance drum rotate at a
certain angle.
3) When the bottom of movable beam or bucket wheel fall on stockpile or ground,
the force at the support position will cause the changes of tensile forces on
both ends of movable beam. The movable beam will be held in this situation that
cannot be lay down. It is possible that hoist wire ropes at one or both side are
relaxation or even accumulated at the drum, which is commonly known as ’wire
ropes disorder’. At that time, the balance drum will inevitably rotate. This
phenomenon will lead to grave consequences, especially when the movable beam
touch to the ground or lay onto stockpile for a long time. As the movable beam
has been move up and down, more ropes will accumulate on the drum, the steel
rope will easily to wear or even break. At this situation, it will be cause the
serious accident.
To sum up three points above, the no synchronous speed of the driving drum for
movable drum is the main reason of balance drum rotation. The secondary reason
is the different pull forces of lifting points on the two sides of movable beam
(which will make the balance drum to rotate a small angle). The movable beam
bottom or bucket wheel lay on the stockpile or ground will cause
In fact, the balance beam moves up and down several times there will be problem
that balance drum rotate at big angle. The gantry-type bucket wheel stacker &
reclaimer system is that balance drum of the movable beam runs permanently. If
the balance drum is not been adjusted immediately, the consequences will be
unthinkable.
3. The consequences of too big rotational angle of the balance drum of
movable beam for gantry-type bucket wheel stacker & reclaimer.
Too big rotational angle of balance drum (balance wheel) of movable beam for
gantry-type bucket wheel stacker & reclaimer will cause very serious
consequences, which are:
If the balance drum (or balance wheel) does not install the stop block, the
rotational angle of it would have not any limit. And the balance drum may turn
several laps.
If the balance drum to be installed with angle limiting block, suppose that the
limit is ± 45 degrees, it will hit the limit block after the movable beam being
lifted in several times. In some situation, a stop pin was designed on the
circular arc groove and to limit the balance drum rotation angle. If two balance
drums hit angle limiting block together, the tension forces of four ropes will
be not equal. Besides, due to the forces are uncertain, there are potential
security liabilities. The function of block or stop pin act as protection device
in case of the wire rope was broken.
If the rotational angle of the balance drum in one side is too big, even reach
to safety 3 laps, wire rope may been pulled out from the clamp, and the movable
beam will fall off. At the time, even if the rope was not been pulled out of
from the clamp, due to the rope been wound on drum reversely, the wire rope
maybe damaged and broken. In addition, due to the balance drum rotational angle
is too big, the ropes will been hurt by the steel structure. And steel ropes may
be broken leading to significant accidents.
4. To avoid the accidents of lifting system gantry of movable beam for
gantry-type bucket wheel stacker & reclaimer
We suggest, in the future, that design of lifting system of movable beam for
gantry-type bucket wheel stacker & reclaimer should adopt the automatic cable
balance system and the synchronization drive on drums. The balance drum that the
rotational angle can be cumulative should not been used.
The equipments has been designed and manufactured in the past should be equipped
with encoder, limit switch and other detection devices to monitor the balance
drum angle. The movable beam lifting system should adopt variable frequency
motor, and the driving motor can separately controlled when been lifting in one
side, in order to control the balance drum at a reasonable angle. In this case,
balance drum might rotate to a big angle position easily due to forces on the
two cables are unequally, operators and maintenance personnel should keep an eye
on the angle of balance drum.
Safety operating procedures should be obeyed strictly. The bottom of beam or
bucket wheel touched by the stockpile or ground is prohibited when lifting
movable beam the up and down.
In normal operation condition, the block of balance drum should not block the
rotation of drum unless the rope was broken. Otherwise, the balance drum will
not work due to steel ropes forces are not equal at the two sides.
It needs to have a comprehensive understanding of the principle of the movable
beam lifting system and the reasons of balance drum (balance wheel) rotation so
as to avoid the accidents during operation.
The design of movable beam lifting system exist a potential safety hazard when
the balance drums rotating at a big angle.
It needs to detect and adjust the rotational angle of balance drum immediately
when using the movable beam lifting system.
Excerpted from <Heavy Industrial & Hoisting Machinery>2017,first
About The Author
Li Yimin ;
Professor Engineer ;
Sex : Male ;
Graduated : DUT ->. Jan .1982;
Major : HOISTING AND CONVEYING MACHINERY ;
Metier: Designer For Bulk Machinery;
Main contribute for bulk machinery: He has embarked on design and
researsh Bulk Machinery for 34 years. Main contect include stacker
,reclaimer ,stacker / reclaimer , bridge type reclaimer , Blending
stacker ,Blending Reclaimer , gantry type reclaimer . He research the
main date for the bulk machinery especially.
He wrote many piece for the bulk machinery . some piece had released on
the journals in P . R . China , and had invented four item patents.
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