SICK AG WHITEPAPER. 18th Bulk Goods Conveyor Equipment Symposium, Roland Dunker Portfolio Manager for Industrial Instrumentation

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1 SICK AG WHITEPAPER "Meeting Point for Research and Practice" Non-contact Volumetric Flow Measurement on Conveyor Belts in Practice AUTHOR: Portfolio Manager for Industrial Instrumentation Certified electrical engineer Certified business economist SICK Vertriebs-GmbH Willstätterstr Dusseldorf Germany

2 Non-contact Volumetric Flow Measurement on Conveyor Belts in Practice During the operation of bulk materials conveyor processes, problems often arise due to the volume of bulk materials exceeding the capacity of the conveyor belt or subsequent process stages. This results in stoppages and requires the fault to be rectified manually. Current measurement methods do not provide an adequate solution. In order to solve this problem, a new laser measurement process for volumetric flow measurement on conveyor belts has been proposed. Introduction Many factors are taken into consideration in the planning and implementation of conveyor systems. For this reason, a multitude of factors including the slide-angle of the bulk materials are taken into account, the maximum mechanical loading of the conveyor belts is calculated, and the required motor power P M and the maximum belt pulling power P U [N] are computed. It is necessary to determine the volumetric flow for bulk materials filling or for optimum conveyor design system control. In practice, however, the volume of the bulk material is often rarely or insufficiently considered. In day to day operation, this leads to problems in subsequent process stages. 1 Definition of Density and Volume Mass m Density of a body = p = Volume V In simple terms, the volume of bulk materials is derived from mass in relation to density. Dependent upon the material, additional factors, such as granularity, material characteristics, and cavities have an effect. 2 Use of Belt Scales for Indirect Volumetric Flow Measurement In practice, belt scales are frequently used to measure bulk materials. In order to do this, the conveyor belt is divided into sections and the belt scales are integrated into the conveying line. 2.1 Problems during Filling Belt scales only determine the weight of the bulk material. The density is normally assumed to be a fixed value and the volume is calculated. In many applications, the density of the bulk material is not homogeneous, consistent, or cannot be completely determined. Dependent upon the material, the bulk material may also decompress on the conveyor belt and increase in volume (e.g., tobacco). Similarly, the shape of the bulk material and associated cavities influence the determination of the actual volume on the conveyor belt. Further difficulties arise for open-air applications due to factors such as dampness of the bulk material and environmental effects such as rain and foreign material. If these issues arise in cases where belt scales are the only measurement method used, significant conveyor volume discrepancies can arise. Thus when filling loam, for example, dependent upon the season and the dampness of the material, the bulk bags (1.3 t) may either be under filled or overfilled. Where under filling occurs, standard practice is to top up the loam manually to avoid customer complaints. In the case of overfilling, the bulk bags cannot be closed. Along with increased labor and material usage, this procedure can also lead to such issues as the overloading of haulage vehicles, due to bags weighing more than 1.3 t. 2

2.2 Problems with System Control As with any process, it is important to adapt the individual process and handling stages to each other during the system planning stage.

3 2.2 Problems with System Control As with any process, it is important to adapt the individual process and handling stages to each other during the system planning stage. This is the only way to guarantee the optimum utilization of the system. In the bulk materials conveyor process, this means that the system downstream of the conveyor belt is able to accept and handle the amount of bulk material delivered. If the amount of bulk material exceeds the handling capacity of the subsequent stages, there will be over filling and material blockage that will ultimately cause stoppage of the system. Furthermore, machines and conveyor belts may be damaged, further lengthening the stoppage time. Examples of problems from lack of volumetric flow measurement: If the volume of tobacco on the conveyor belt exceeds a defined amount, the down-stream laser sorting machine will become blocked and the production process must be interrupted. If a crusher hopper is filled with an excessive quantity of building rubble, the crusher becomes blocked and the hopper must be manually emptied to release the blockage. If a conveyor belt in the food industry is not properly loaded, the subsequent freezing process takes longer and production costs (for energy) increase significantly. 3 Solution by Direct Measurement of the Volumetric Flow Such cases can be solved by measuring the actual volume on the conveyor belt using a laser scanner. 3.1 The Principle of Direct Volumetric Flow Measurement In direct measurement of the volume, the contour of the conveyor belt is sampled by means of the laser scanner. The volume of the bulk material is calculated using the difference between the contour of the conveyor belt and the contour of the bulk material, combined with the speed of the conveyor belt. The measurement is recorded without contact and the conveyor belt does not need to be divided into sections. Figure 1: Measurement principle 3

4 Figure 2: Difference between the reference surface and the current measurement surface produces the bulk material surface 3.2 Advantages of Direct Volume Measurement The measurement principle of determining volume by means of a laser beam produces a series of practical advantages: The measurement is recorded without contact the conveyor belt does not need to be divided into sections. The process can be optimized according to volume. Overloading the downstream station is prevented. The actual volume on the conveyor belt is measured. In doing so, the influences and changes in the bulk material described above are taken into account during measurement. By direct measurement of the volume, filling processes are optimized. Because the laser beam measures the height profile of the bulk material, the conveying line and system components can be protected by the height and center of gravity monitoring integrated into the measurement system. In particular, the monitoring of the center of gravity increases system throughput. Conclusion/Summary Laser based volume measurement on the conveyor belt with the SICK BULKSCAN is the ideal complement to belt scales. By additional volumetric flow measurement, system throughput can be increased and stoppage times can be minimized. The operator of a conveyor or filling system can thus optimize the conveying and filling processes and hence save time and money. 4

5 Sources flowmeter.aspx SICK AG Waldkirch Germany

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