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The overwhelming majority of the time a conveyor is being used, the conveyor will be in a steady state or static conditions (running at full design speed). Therefore, the static design is the starting point for the conveyor design.
One of the first requirements in statically designing overland conveyor flights is to develop and verify design parameters appropriate to the application. These parameters get amplified in importance as the length and capacity of the conveyor increases. For example, the extra drag associated with poorly aligned idler sets is amplified with every idler set added to the conveyor.
For any conveyor, many variables go into estimating the drag, the total power required from the drives and the resulting belt tensions. Some forces such as lift force (simply defined by gravity) are dictated by the route and moving load and, subsequently, these forces are difficult to minimize without altering the conveyor route. Some resistances, such as rubber indentation and idler drag can be minimized by selecting the appropriate components. Others such as misalignment are affected by installation tolerances.
With any new design, many of these variables can only be estimated until components are bought, built, installed and running. To handle this uncertainty during the design phase, possible options can be considered and a range of resistances developed for design purposes.
The high side of the friction range represents the worst case high power possibility which might occur with component selection, the coldest days, unfavorable loading pattern and typical/poor installation tolerances. The low side of the friction range represents the worst case low power possibility which might occur with component selection, the warmest days, favorable loading pattern and good installation tolerances. In short, the highest values dictate some component sizes such as the motors and the lowest values dictate other properties like idler spacing. Some components, like take-ups and curve radii, need to be able to accommodate both extremes. By designing to a friction range, much of the design risk is mitigated.
When considering the probable range of friction the following design parameters are typically considered (in BA):
•Rubber Indentation
•Idler Resistance
•Idler Manufacturing Tolerance
•Installation Tolerance (Idler Alignment)
•Idler Tilt
•Temperature: Cold temperatures affect grease and rubber, resulting in changed (normally higher) frictional resistance.
•Regenerative Conditions
Another major design condition involves possible loading conditions.
The loading patterns that are encountered in normal operations are a primary consideration. The following are typically considered, at a range of drag values.
•Fully loaded at design capacity
•Empty
•The sequence of loading the conveyor going from empty to fully loaded
•The sequence of unloading the conveyor going from fully loaded to empty
Other loading patterns creating different running conditions are possible, although some of them are not probable and often they are very temporary.
•Inclines are all loaded, often the high power requirement
•Declines are loaded, often the low power requirement
•Loaded at greater than design capacity
All the operating cases defined in BA are imported to DA. This allows the DA simulation cases of "Stopping" and "Starting" to be run with each of the BA cases. However, only one stopping and one starting case can be run on each of these BA cases.
The typical dynamic stopping cases are:
•Drift to stop: this case often simulates what happens when power is lost to the conveyor. It may also be the typical stopping mode. If the conveyor is regenerative, this will not stop the conveyor.
•Brake to stop: this case may also simulate what happens when power is lost to the conveyor if the brake operates in a fail-safe manner. It may also be the typical stopping mode.
•Drive controlled stop: using the drives to control the stop is often the normal method of stopping the conveyor.
The typical dynamic starting cases are:
•Drive controlled start: using the drives to start. For a regenerative case, this may be combined with a controlled release of the brakes.
•Aborted start: Using the DA control input tab, power to the conveyor drives can be stopped at any point in the simulation. This allows the user to simulate this possibility.
•Plugged Chute: extra drag in the loading zone is added in BA. DA is used to confirm that installed power is sufficient to start conveyor.
Since the number of DA cases associated with a single file name is limited, if the user wants to run more than one stopping or starting cases a second BA file should be created.
If the BA case being evaluated in DA contains an intermittent loading pattern such as those typical of "Inclines Loaded" and "Declines Loaded" or "Load On" and "Load Off", it should be noted that DA does not move the material mass along the conveyor during the simulation. This results in a somewhat conservative outcome in that the worst case loading being modeled is preserved throughout the simulation rather than changing as time advances.