Elimination of Possible Chance of Contact Between

Stacked Materials and Boom Structure Conveyor Belt

Assembly during Stacking Operation.

Generally in the operation of Stacker (Wing or Rotary Boom Type), the interlock is provided between the operation of the Boom & Stacker Belt Conveyors. Until the Boom Belt is actuated, the Stacker Belt starting is not possible, and correspondingly with the stoppage of Boom Belt, the Stacker Belt gets automatically stop. This particular interlock is a "must" and well established.

The Stacker is used for stacking one type or various types of bulk materials over a bay. When particular type of material is stacked all along over a bay, the stacking process is carried out at a free height of the Boom Assembly with the long travel motion of the stacker. On reaching one end, the Boom Assembly is lifted to a desired height (considering minimum dust propagation and breakage of particle size with the free fall of materials) and long travel motion is reversed back.

Against stacking of various types of materials at a bay, generally a point discharge with restricted long travel motion within a specific area of the bay to segregate each stacked material from the other. The stacking process needs special attention of blending features, which is built up at the root level during the course of stacking so as to achieve constant homogeneous (as far as possible) property of material being reclaimed for the convenience / optimization of down line end process treatment.

During such normal routine of stacking, there is every possibility of Boom Assembly getting obstructed or come in contact with the higher heap height of the stacked material and at such juncture, it becomes harmful to the Boom Structure conveyor belt Assembly.

At the initial starting operation of the stacker, generally a Hooter signal is ON, thereafter, actuation of all other operational elements is possible. The actuation of the operational elements such as Starting of Boom Belt, lifting/lowering Boom Assembly, long travel motion of the Stacker, lowering of Boom Assembly beyond certain limit and its parking etc, are subjected to the free hand of the operator. At a certain critical juncture of operation such free option of the Operator may land up with following consequences.

i. Boom Assembly may bend or get distorted with its approach forcing against the higher heap height of the existing stacked materials. The life of the several components of the Boom Assembly may get shorten.

ii. Boom Assembly resting over the stacked materials being subject to long travel motion shall damage the structure.

iii. In the above condition with the continuation of the discharged materials through Boom Belt shall build up unwanted accumulation of materials at the long travel platform by the feed back through return belt.

iv. Unrestricted hoist of Boom Assembly at this critical juncture may attend height above critical level where there can be every possibility of retreat of flowing materials over the boom belt, resulting accumulation of the materials at the stackers chute discharging point.

The dangerous repercussions from all angles with multi various unwanted consequences should not be permitted by not allowing any possible chance of Boom Assembly coming in contact with the stacked material. Suitable protection device application is desired against such incidental critical occurrence.

It has been observed; the stacker smooth operation is interrupted due to direct contact between Boom Structure Conveyor Assembly with the stacked materials during the stacking process. This situation is most unwanted but cannot be avoided under the present circumstances. The repercussions are of serious nature and needs special attention to eradicate such possible chance by introducing some suitable external element. The remedial measure is to introduce VERTICAL FLOW LEVEL INDICATOR, mounting its Sensor Unit on both sides at the tip end of the Boom Structure to cater for both forward & reverse long travel motion of the Stacker. The Sensor unit comes in contact with the Stacked height materials before the same can approach the Boom Structure. The Sensor unit coming in contact with the stacked height materials raises immediately the Boom assembly for a predetermined period by activating the existing hoist arrangement of the Stacker.

While the success of objective of application of Sensor Unit is achieved by automatic raising of Boom Assembly to clear away from the stacked materials, it is essential that the Sensor Unit must be in a position to withstand all the adverse effects of confrontation with the stacked materials. Reliability aspects of the Sensor Unit depend upon its own inherent design and the desired operating status of the stacker following to the contact of Sensor Unit with the stacked materials. The inherent design of Sensor Unit is well understood and the matter is manufacturers expertisation. But the desired status of Stacker operating condition at the time of Sensor contact with the Stacked Materials is very much important and essentially calls for some specific automatic actuation within the Stackers operation, which shall be effective by the Sensor pulse for a prefixed period. The Sensor Unit coming in contact with the Stacked height transmits pulse which apart from activating the Boom hoist for a pre-fixed period, shall be effective for following automatic interlock activities in the sphere of Stacker operation.

i. Boom hoist is raised irrespective of the operating status of hoist arrangement.

ii. Long travel motion of the stacker is stopped.

iii. Activation of the existing Hooter Signal.

At present circumstances the above desired operating condition of the Stacker with the contact of Boom structure assembly with the stacked height, is left at the mercy of the stacker operator and such dependence should not be permitted any longer. Sensor detects the unwanted confrontation during the process of stacking and is able to transmit the pulse at the right moment for the required corrective measures to be effective for the operation arrangements of the Stacker for a pre-fixed period without any involvement of the operator of the stacker.

The Vertical Flow Level Indicator is composite of the following units:

i. Sensor Unit.

ii. Control Panel.

The Sensor Unit is placed vertically and mounted suitably at the tip end of the Boom Assembly. The unit is composite of paddle shaft protruding down below being rotated by stalled torque Tacho-Motor assembly. The mounting on the Boom Structure is flexible in nature to swivel sidewise as well as free to move backward and forward. This feature is to avoid intensity of impact load to the sensor when coming in contact with the stacked materials. The location of the Sensor should be as closed as possible to the delivery drum of the Boom assembly but the free fall of materials from the delivery drum, normally should not have the access to the Sensor. Two nos. of Sensor Unit are located on both sides with paddle being partially projected outside the side end of the Boom Structure. Thereby the stacked materials contact with the paddle happened before any contact with the boom structure under all stages of operation of the stacker.

The height of paddle below the boom structure is determined by the following factors:

i. The contour and shape in general of the stacked materials.

ii. Distance of Sensor Unit from the tip end of the delivery Drum of the Boom.

iii. Time period between paddle obstruction and actuation of Boom hoist.

The Sensor unit must be suitable to bear all types of weather condition and dust environment for the minimum attention of maintenance. The objective of sensor unit is to protect the boom structure assembly against the following adverse situation during the operation of the stacker.

i. Not to allow Boom Assembly coming in contact with the build-up stacked material and finally resting over the same with continuous discharge from boom belt.

ii. To avoid boom structure coming against the existing high heap height stacked materials during the course of long travel motion of the stacker.

The sensor unit can be actuated both under Manual or Auto with the corresponding selection, at its control panel. For normal operation, auto-selection is made but during the period of its maintenance manual selection is opted. Under normal operation of the sensor unit along with the stacker operation, the sensor is automatically activated with the power ON to the Stacker and is non-operative with the power OFF. Over and above such interlock in case of Wing Stacker (to enhance the operating life of the Sensor) the operating Boom Belt of one side keeps the sensor on the other side Boom Belt (under parking position) non-operating. Moment the operating Boom Belt is stopped, the sensors of non-operating Boom are automatically activated to ensure effectiveness of sensors prior to lowering of the Boom Assembly from its parking position. The automatic starting of Sensor Unit through interlock with the operation of the stacker cannot be generalized and is set to suit each individual operation condition of type of stacker.

The paddle is normally rotated at low r.p.m under low voltage parameter transmitted from the control panel. With the obstruction to the paddle coming in contact with the stacked height, the motor-tacho assembly is automatically subjected to higher pre-selected voltage to assess the type and kind of obstruction. If the obstruction is not artificial, the paddle comes to stalled condition even under higher voltage parameter. The paddle remains in stalled condition for a prefixed period and thereafter with automatic activation of the contactor/timer raise the Boom and set the requisite condition of the stacker operation for the predetermined period. With the raising of the boom assembly the paddle gets free from the stacked materials and starts rotating under higher voltage. With the attainment of full rotation, the operating high voltage automatically attends its low value to rotate the paddle under low r.p.m. till such time the paddle is not further obstructed. The reason and necessity of low r.p.m. of the paddle under normal operating condition can well be perceived.

In course of failure/breakdown of the Sensor, a simple bypass can be achieved by putting off the power connection to the control panel of the Sensor and resting the Sensor unit in its parking place. Faultfinding and rectification can be carried-out during the idle operating condition of the stacker. During such parking of the Sensor, the stacker can be operated as per normal routine.

Stacker availability and uninterrupted operation during the incoming of materials is similar to a situation of emergency. More so, stacker a capital equipment remaining under breakdown is not at all desirable. The breakdown of Boom Structure Conveyor Belt Assembly is a major failure and the rectification with modification takes appreciable time. Any device fruitful for imparting protection eradicating the possible chance of breakdown of the Boom Structure Conveyor Belt Assembly calls for special attention and need to be incorporated without any second thought. Vertical Flow Level Indicator being incorporated in Stacker-1 of R.M.B.B. plant at its initial trial stage is a positive step in this direction. Need be this unit shall be extended in all other Booms of the existing stackers and shall be part of the specification in future procurement of the stacker.

B. Banerji

Focoss India Corporation

38, Lake Temple Road,

Kolkata - 700 029

India ■