Conveyor Profile Design

Nicholas Russell and John Thomason Sinclair Knight Merz

Brisbane, QLD. Australia

Summary Site layout design requires conveyor belt profiles early in the project development. This paper looks at the bottlenecks in the current design method for conveyor belt profiles and the effects this has on the overall site design. The new design method reduces lead times by integrating & simplifying belt-profile development and calculation.

1 INTRODUCTION Layout work is required very early in the engineering design phase. Amongst other factors, the belt profile of the individual conveyors influences the layout and dictates the minimum site plan footprint. After lift heights for each conveyor are determined, the minimum concave curve radius that ensures the belt does not lift out during starting or operations, drives the belt profile. Determining the vertical curve radii requires a significant amount of conveyor analysis to accurately predict the results. There are major bottlenecks in the current design process for conveyor belt profiles. The new design process mitigates these bottlenecks. An overview of the software package produced from the analysis is also presented including the methods it employees to improves the design of conveyor belt profiles.

2 DESIGN PROBLEM The current methods used to design conveyors are exceedingly time-consuming and thus the iterative optimisation process cannot be performed due to project time constraints. This is compounded by the fact that proper conveyor belt calculations cannot be performed early in the site development since many of the variables required are unknown early in feasibility. Additionally, since the design of a single conveyor is a lengthy process that can only be performed late in the design stage, site changes, investigation of alternative configurations and optimisation of site layout’s footprint is difficult to manage due to time once again. The new design method reduces the time to design a conveyor belt profile and perform the necessary calculations.

3 CURRENT DESIGN METHOD Conveyor belt-profile design is based on three primary variables taken from the site layout. These variables are the transfer height of the material, the length of the conveyor and the ground profile along the conveyor’s length. Since the minimum length of the conveyor is essentially dependent on the other two variables, a guess is initially made on length of the conveyor based on experience. Figure 1 shows the engineering design process for conveyor belt-profiles. The start of the process shows the three fore-mentioned variables coming from the site layout. Following this is the development of the belt profile. Belt profiles are currently designed in the CAD software Autodesk AutoCAD. Once the profile has been drafted, the profile is manually typed using measured point data into a belt analysis software such as Conveyor-Dynamics Inc BeltStat. This stage is the largest time-wasting activity in the belt-profile design cycle. Using the entered profile, a full static analysis is performed and the minimum vertical curve radii are calculated. If the minimum radii are all satisfied then the process ceases and the mechanical and structural drafting of the belt-profile commences. If the current radii are less than their calculated minimum, changes are made so that the conveyor profile is acceptable. The first question asked is “Can the Radii be changed to meet their required minimum?” If the radii can be made larger with the original profile, the radii are altered in AutoCAD and the data is re-entered into the belt analysis software to confirm the profile meets all calculation requirements. On the other hand, due to geometric constraints, it may not be possible to fit the minimum radius in the available space. If this is the case, the entire profile must be altered to fit the minimum radii in. The re-drafting of only the radii

or of the entire profile in AutoCAD is a time consuming process. This drafting time, in addition to the large amount of wasted time in manually re-entering the profile data into the belt analysis software, makes the re-iteration process unacceptably slow and extends lead times. This is one of the major flaws in the current design process for conveyor belt-profiles.

Site Layout

Conveyor Length

Transfer Heights

Ground Profile

Develop Belt Profile in CAD

Calculate Minimum Curves

Output Belt Profile for Drafting

Can Radii be changed to meet

Minimum?

All Minimum Radii Satisfied?

Can Profile be changed to meet

Minimum?

Yes

No

Yes

Yes

No

No

Legend

Process Data Decision Finish

Input Profile Data to Belt Analysis

Software

Manual Input

Figure 1 – Current Conveyor Profile Design Process

Finally, if the conveyor’s profile cannot be altered to fit the minimum radii, changes must be made to the site layout in order to change either the transfer height, conveyor length or the ground profile. This entails redesigning this conveyor and potentially other conveyors that were previously complete. Consequently, multiple conveyors will need to undergo the unacceptably slow design iteration again. This is major rework for the whole site and in some cases, it may mean discarding much of the work done and starting from scratch. This situation has traditionally been avoided by grossly overestimating conveyor lengths at the start of site layout. In addition to the problems discussed above, the current design process places two more fundamental restrictions on the project. Due to the long lead-times in the drafting of the profile and in the manual entry of profile data, often designs of individual conveyors, let alone the site layout are not fully optimised due to project time limitations. The second restriction is since the only available tool to calculate the minimum radii is a full static analysis, these calculations cannot be performed earlier in project design phase. Thus, the time consuming processes in the design of conveyor belt profiles significantly extend lead-times and limits the amount of optimisation.

4 PROPOSED METHOD The new conveyor design method improves the current design method and significantly reduces the design time. The dashed box in Figure 2 shows how the new software fits into the design process and the areas where the current design method has been altered.

Site Layout

Conveyor Length

Transfer Heights

Ground Profile

Develop Belt Profile in 3D CAD

Calculate Minimum Curves

Output Belt Profile for Drafting

Can Radii be changed to meet

Minimum?

All Minimum Radii Satisfied?

Can Profile be changed to meet

Minimum?

Yes

No

Yes

Yes

No

No

Legend

Process Data Decision Finish

Automatically Export Profile Data to Belt Analysis Software

Software Package

Preliminary Minimum Curve

Calculation

Figure 2 - New Conveyor Profile Design Process

The first noticeable difference is conveyor belt profiles are no longer drafted in 2D CAD software. The change to 3D CAD was essential in reducing the time to create and modify belt profiles. Unlike 2D CAD where everything drawn is essentially stand-alone and does not constrain itself to surrounding geometry, 3D CAD offers dimensional and geometric constraints. Therefore, to change a radius in a conveyor profile, only a dimension has to be changed and the profile will update automatically. If the minimum radius does not fit with how the current profile is structured, this becomes quickly apparent. Since the belt profile can be changed dimensionally, adjusting the profile to fit the radius is no longer a major drafting exercise. The disadvantage to using the 3D CAD system is designers involved need training in two different systems.

The next major change to the design process is the change from manually entering profile data into the belt analysis software to the automatic exporting of the belt line. Since the program inside the 3D CAD software keeps track of all of the parts of the conveyor around the belt line, it creates the structured files used by the belt analysis software automatically. The inclusion of this facility in the project creates the biggest reduction in profile design time. The final change to the design process is a new design loop with calculation internal to the software. The preliminary minimum curve calculations have be written to use less information and produce conservative minimum radii. Early in the design process, many details of the conveyor such a roller diameters and belt cover thicknesses are unknown, though are essential to run the full analysis. Including a conservative calculation for the tensions and radii, the design process utilises the software earlier and the design of superior layout is achievable at the beginning of the project. Once conveyor details are confirmed, the full static analysis is run and the profile adjusted accordingly.

5 SOFTWARE The SKM Conveyor Profile Design Tool was created to perform the functionality discussed in the previous section. The program is Visual Basic for Applications (VBA) add-on in the 3D CAD software, Autodesk Inventor. The software package is split into three sections: site layout, profile design and preliminary profile calculations. Although the software does not assist in the design of the site layout, it is an imperative inclusion in the package. The inclusion is important for several different reasons. The first and most beneficial reason is by building the conveyors of the site layout, changes to the site will dynamically reverberate through to the belt profiles of the individual conveyors. This works in both directions in that if conveyor lengths are too short, the effects this has on the site is obvious and if further site changes occur then the changes in length of the conveyors can be updated quickly. The second advantage is that all conveyor profiles are stored in a single file. This is a quality control advantage where the person in control of the conveyor profiles is the only individual who can alter them. This also assists in maintaining strict control of revisions. The final advantage of including the layout is that the entire 3D layout can be exported for drafting as shown in figure 3.

Figure 3 – Layout Conveyors

The second section is the profile design section and includes not only standard conveyor profiles but also the necessary tools to create unique conveyors. Standard conveyors are pre-dimensioned so all that is required is the changing of dimensions to suit the situation. Presently, a limitation of the software is the inability to create horizontal curves. Figure 4 below is one of the standard conveyors that has been dimensioned for that application. The line along the bottom of the profile is the reference geometry for the conveyor from the layout sketch. It is due to dimensioning the conveyor to that line, the conveyor profile dynamically updates when the layout changes.

Figure 4 - 2D Conveyor Belt Profile

When a conveyor has a moveable tripper, several profiles with the tripper in various positions are required for the belt analysis. Figure 5 highlights the ease in which trippers can be moved in the 3D CAD environment. Coupled with automatic profile exportation to the belt analysis software, this programming advantage dramatically improves the design times of similar conveyors.

Figure 5 – Moving Tripper Location

Since the program stores all transition details and the profile is design using 3D CAD, the software automatically generates the 3D belt line with all transitions and trough sections. Figure 6 shows the generated 3D version of the conveyor profile in figure 4. It can be seen on the right hand side of Figure 6 how the belt transitions from the three-roll idler cross section to horizontal as it comes around the pulley. The belt then travels through the take up before going to the two-roll cross section on the return strand.

Figure 6 - 3D Conveyor Belt Profile

The final section of the software is the preliminary belt calculations based on various handbook and design manuals (Beckley 1982; DIN22101 1982; ISO5048 1989; CEMA 2005). Similar to other belt analysis software, the profile is broken into a series of flights and the sum of their individual resistive tensions is equal to the drive tension required. Minimum Take-up tension is then calculated to meet belt sag and minimum low-side tension on the drives. Finally, using the minimum take-up and a user-defined take-up, the transitions optimum heights, minimum lengths, and the minimum vertical curve radii are calculated. The conveyor’s minimum curve radii and transition lengths are then fed back to the profile which is changed if necessary to satisfy all minimum criteria.

6 CONCLUSIONS The design of conveyor profiles is a complex process that is necessary early in the layout of site footprints. In order to optimise the conveyor profiles and the site in general, an analysis of the current design method was performed and the bottleneck processes were identified for improvement. A new method to design conveyors is now employed and details of the software package created were presented. The advantages of integrating the site layout with the design of conveyor profiles and the availability of preliminary belt calculations are a quicker belt-profile design cycle, earlier in the design process that facilitates the optimisation of site footprints and conveyor design.

7 ACKNOWLEDGEMENTS The authors gratefully acknowledge Sinclair Knight Merz (SKM) for their financial support of the project described in this paper. Additionally, we would like to thank David Morrison, SKM and Prasad Gudimetla, Queensland University of Technology, Australia for their kind assistance.

8 REFERENCES Beckley, D. E. (1982). "Belt Conveyor Transition Geometry." Bulk Solids Handling 2. CEMA (2005). Belt Conveyors for Bulk Materials. DIN22101 (1982). "Belt Conveyors for Bulk Material." German Standards. ISO5048 (1989). "Continuous Mechanical Handling Equipment - Belt Conveyors with Carry Idlers - Calculation of Operating Power and Tensile Forces." International Standard.