Research on a Pipe Conveyor with a Completely New Belt Guidance

S. Hinterholzer, F. Kessler and K. Grabner, Austria

1. Introduction

Nowadays, the diversity of the various processes of mining, transportation, loading and unloading, and storage continually increases the requirements of the conveying technology. The continuous efforts of the facility designers, to make transport procedures more economical through organised operating guidelines, opened up new fields of operation with higher requirements and a stronger specialisation to the conveying technology.

The bulk material conveying technology, a powerful and highly specialised field of the conveying technology, is characterised by its distinctive technical variety. At the present time, the development of conveyors for bulk materials concentrates on reaching - as well as a higher operational reliability and economic efficiency - environmental requirements.

1.1 General Mechanism of Pipe Conveyors

In contrast to the common troughed belt conveyor, which just arches the belt on its sides up to a certain trough angle, in the pipe conveyor - as the name implies - the belt totally encompasses the bulk material. Thus, the cross-section can be designed either round or oval. To achieve those cross-sectional shapes, the idler assembly is - apart from some exceptions - arranged hexagonally. Fig. 1 shows a schematic comparison of the cross-sections of the troughed belt conveyor and the pipe conveyor (also 'closed belt conveyor').

Fig. 1: Schematic comparison of the troughed-belt conveyor and the pipe conveyor

Most pipe conveyors use flatly-manufactured belts. Conventionally, they are trough-shaped in the roll-in section of the conveyor, then closed to a pipe by the ring-shaped idler assembly and is held in this shape over the whole distance by the idler stations. In the rolling-out section of the conveyor, the belt automatically opens back to the flat belt shape due to the inner forces. The return travel of the belt beneath the charging section is performed in the same way. Fig. 2 shows the general mechanism of a conventional pipe conveyor.

Fig. 2: General mechanism of conventional pipe conveyors

1.2 Advantages and Disadvantages of Pipe Conveyors

The advantages of the pipe conveyor in comparison to the troughed belt conveyor are:

The disadvantages of the pipe conveyor in comparison to the troughed belt conveyor are:

The enumeration of advantages and disadvantages shows that - in comparison to the troughed-belt conveyor - the pipe conveyor is superior in many ways. This is especially true for the transport of difficult materials and the protection of these materials during the transport from A to B. A further benefit of the pipe conveyor is the capability of managing transport routing under tricky topographical conditions. This is possible due to the ability to cope with essentially smaller curve radii and steeper slopes.

2. Newly-Developed Pipe Conveyor

2.1 Presentation of the New System

Due to the great number of idlers required for creating the pipe in conventional belt conveyors (12 idlers per idler station), the sum of the kinetic resistances increases along the transport route and results in a large amount of power needed for the drive motor(s). Furthermore, the large number of idlers causes excessive noise, which can exceed the permissible limits - especially in the neighborhood of villages or cities - and, often necessitates acoustically absorbing housing of the entire conveying path.

Starting with the initial intention of reducing the number of idlers as well as the noise along the travel path, a new kind of belt guidance was developed at the Department for Conveying Technology and Design Methods, Mining University of Leoben, and subsequently patented (Austrian patent registration No. 1126/99) [1, 2]. Hereby the returning belt is not - as usual - executed as closed belt but is turned round by additional idlers on both ends of the travel path, so that the return strand rests on the already existing idlers of the carrying strand. They support and guide the belt - as illustrated in Fig. 3.

Fig. 3: Newly-developed belt guidance for the pipe conveyor

In comparison to the conventional pipe-conveyors, the two upper idlers on each side are longer to support the belt over its entire width. The finger idlers (the blue ones in Fig. 3), which are situated in certain distances near the extended upper idlers, are necessary to guarantee a steady belt run in curves. They support the belt and prevent it from slipping off. To allow this new kind of system to operate properly, the return stations had to be completely redesigned. Especially the assembly of the deflection idlers and the design of the charging and discharging station had to be changed. In Fig. 4 and Fig. 5, the suitable constructive measures for this new type of pipe conveyor at the return stations are displayed.

Fig. 4:  The new pipe conveyor charging station

Fig. 5:  The new pipe conveyor discharging station

These figures illustrate that the return station - at the charging station as well as at the discharging station - has to be more complex than for conventional pipe conveyors. Consequently, the use of this new system only becomes more economical than the conventional one above a certain transport length. 

2.2 Comparison of the Newly- Developed System with Conventional System

Advantages of the newly-developed system:

Disadvantages:

Discussion of the described advantages and disadvantages:

The advantages of this newly-developed system listed exceed the originally expected disadvantages by far. This is also the reason why the development of this new system is pushed with top priority. The return of the belt (especially the design of the idler assembly is a challenge, which has yet to be met.

3. Test Facility

3.1 Planning of the Test Facility

The goal was to plan, execute, and put on line a test facility, which would make it possible to fulfill the requirements of Binder,& Co - to generate a prototype of the newly-developed pipe conveyor and its subsequent introduction to the market. The test facility should be capable of determining the kinetic resistance of the closed belt and its return strand for a wide range of belt widths.

Check list of all targets for the planning and development of the test facility:

On one hand, the test facility should deliver results close to reality and, on the other, it should be cheap and require little space. Consequently, the test facility had to be designed in a compact way, considering for the high and varying demands, which must be met to achieve the required results. The concept of the test facility is designed to simulate the movement of the closed belt by simply moving the idler assemblies, which are mounted on a trolley.

Fig. 6 shows the schematic design of the test facility.

Fig. 6: The schematic design of the test facility

The dark gray colored surfaces in Fig. 7 symbolise the closed belt and the belt return. The belt return is sketched as a thick black line, although it actually covers almost all of the upper two idlers.

We have to keep in mind, that for test facilities of this kind that just one of the belts can be fixed and measured or otherwise the idler stations wouldn't be able to move. Another criterion for the design of this test facility was that it should not only be able to measure the movement of the belt and the return belt during straight  distances but also simulate curves.

3.2 Suitable Idler Layout

The idler assembly had to be designed to reach the following objectives:

A system had to be developed, which allows varying cross-sections of the closed belt, simply by mechanical adjustment of the idlers, while, at the same time insuring the return belt to fully rest on the upper lateral idlers. 

In the finished system, the idlers were bolted onto a plate by support angles. The slots in the plate permit new positions for the assembly, and thus different cross-section shapes. The slewing capacity of the idlers is illustrated in Fig. 7.

Fig. 7 illustrates the layout of each idler in its most extreme position. The idler positioning used permitted a large variety of conveying cross-sections - from a round one to a strongly compressed one. At the same time a practical possibility for adjusting the idlers for the belt return was achieved.

Fig. 7:  Suitable layout of the idlers

3.3 Measuring Idler Station

The measuring idler station had to be designed to allow the measuring of the occurring kinetic resistance during the moving of the measuring slide and the value of the lateral force during the simulation of a run through a curve without any influence of external friction. Fig. 8 shows the measuring idler station, which is positioned according to the directions in between the other two idler stations on the measuring slide.

Fig. 8: The measuring idler station on the measuring slide

A column saddle was developed to provide free running of the measuring idler station. It guarantees a very small influence of the own friction as well as absorbing developing static torque without any problems. The column saddle has to permit travel in both directions up to reaching the load sensors.

3.4 Measuring Slide

The function of the measuring slide is to provide the motion of three idler stations in longitudinal direction of the belt. The measuring slide has to be accelerated steadily up to the measuring speed, travel with it over the whole measuring distance, and then be slowed down again until standstill. A rack-and-pinion gear was selected for the transmission of power. The steering rack is mounted on the measuring slide. This permits the back-and-forth movement of the slide, produced by the drive motor and the pinion (Fig. 9).

Fig. 9: The measuring slide with drive motor and steering rack

3.5 Cross Slide for Curve Simulation

The function of the cross slide is to displace the belt and the belt return laterally on a straight travel path to permit simulation of curves. The cross slide travels time-locked to the measuring slide. The cross slide design is illustrated in Fig. 10.

Fig. 10: Design of the cross slide station

3.6 Power System

The criterion for the driving motor and control system selection was the required identical same dip angle of the measuring slide and cross slide. For the driving sys tem a complete package from Siemens was selected. It consists of two servo-motors and two frequency converters for the drivers, combined with an internal control system, which allows any required same dip angle of the motors at a certain stress cycle. The decision for this system was based on the following requirements:

3.7. Back-up Station

The back-up station serves the purpose of applying the tensile force for the closed belt  and for the belt return. It is equipped with a back-up weight to keep the belt tension force constant during the measuring of kinetic resistance (Fig. 11). In addition, the back-up station provides the following features:

Fig. 11: Back-up station design

4. Measuring

4.1 Belt Data

For the test series, a belt with the following data was used:

Manufacturer:  Semperit
Type: PIPETRANS
Belt width: 800 mm
Total belt thickness: 8.8 mm
Thickness of the carrying surface: 4 mm
Thickness of the running surface: 2 mm
Rupture resistance: 250 N/mm

4.2 Belt Return

In the initial test series (Figs. 12 and 13) various idler arrangements were tested to determine the optimum idler assembly geometry. This optimum is reached at an angle of 50 between the two upper lateral idlers. In Figs. 14a and 14b the optimum idler layout is shown. Starting at this angle, the entire belt width rests on the lateral idlers.

Fig. 12: Belt return with back-up station in the background

Fig. 13: Belt return with measuring slide

14a: Idler position for an optimum belt return
(dimensions)

Fig. 14b: idler position for an optimum belt return (photo of the test facility)

The variations in kinetic resistance of the belt return were measured under the following variable conditions:

4.3 Belt

The test series for the belt were per formed with the optimum idler arrangement for belt return, which had been determined in the previous test series for belt return. The idler arrangement results in the following belt shape geometries (Figs. 15, 16, and 17):

Fig. 15: Belt shape for 0 % load

Fig. 16: Belt shape for 60 % load

Fig. 17: Closed belt on the measuring slide

With the idler settings described in section 4.2 the kinetic resistance of the closed belt was measured under the following varying conditions:

5. Results

5.1 Belt

The test series of the closed belt resulted in kinetic resistances between min. 10 N and max. 70 N. The kinetic resistance increased with variation of the following parameters:

5.2 Belt Return

The series of measurements resulted in kinetic resistances from a minimum of 4 N to a maximum of 10 N for each idler station. In comparison to conventional closed belt conveyors, the largest differences occurred during the belt return.

The test series of the unloaded belt:

This means that use of the new belt return system - when compared to a conventional pipe conveyor - results in a reduction of the kinetic forces by a factor 2.5 to 5.

6. Conclusion

Currently, facilities with pipe conveyors run the charged belt as well as the belt return in a pipe shape produced by 6 idlers as circular arrangement.

The newly-developed belt return, however, is not as customary with the belt closed. Here, the belt is permitted to resume its original flat shape during the return path traveling on top of the already existing idlers for the loaded strand.

In comparison with conventional pipe conveyors, the charging and discharging stations require a more complex design. On the other hand, there are the various advantages, resulting from the transport path. Because of these advantages, it can be assumed that this new development will be applied in the near future - especially, since these advantages are combined with substantial cost reductions (station design, idlers, belt, noise reduction, and power) when compared to conventional pipe conveyors.

Targets for further research:

  1. Development of a computer-sup ported layout program - based on the test results.

  2. Comparison of kinetic resistances between new and conventional pipe conveyors.

  3. Construction of a prototype in the Conveyor Park of Binder + Co. AG., Gleisdorf.

  4. Development of guides to stabilise belt travel in the return strand in horizontal or vertical curves.

  5. Economical design of the idler stations to achieve a series status.

7. References

  1. HINTERHOLZER, S. and KESSLER, F.: Rohrgurtfrderer (Closed belt con veyor); Austrian patent office, AZ. 1126/99, Application June the 29, 1999 (the company BINDER & Co. took out the patent in 20 further industrial countries).

  2. HINTERHOLZER, S., KESSLER, F. and GRABNER, K.: Patentierte Entwicklung einer neuartigen Streckenfhrung von Schlauchgurtfrderern; Re search information from the Mining University of Leoben, 3rd year, No. 2, April to June 2000

Dipl.-Ing. Dr.mont. Stefan Hinterholzer and
Univ.-Prof. Dipl.-Ing. Dr. mont. Franz Kessler,
Montanuniversitt Leoben,
Institut fr Frdertechnik und Konstruktionslehre,
Franz-Josef-Str. 18, A-8700
Leoben, Austria
Tel.: +43 3842 402 250
Fax: +43 3842 402 254
E-mail: stefan.hinterholzer@sgpvt.at and
kessler@unileoben.ac.at

Dr. mont. Karl Grabner, Binder & Co. AG,
Grazer Straβe 19-25, A8200 Gleisdorf, Austria
Tel.: +43 31 12 800 363
Fax: +43 31 12 800 300
E-mail karl.grabner@binder-co.at