Rice Lake BCi Belt Scale - Maintenance & Troubleshooting Manual - Manual (Page 7)

Belt Scale Maintenance Instructions - Maintenance Checkpoints 3
2.0 Maintenance Checkpoints
The scale should be checked frequently to determine when calibration is required. It is recommended that zero
calibration be checked every other day and that calibration be checked every week for several months after
installation. Observe the results and lengthen the period between calibration checks, depending upon the
accuracy desired. More information is available in “Parts Breakdown List” on page 8.
Establish a routine inspection procedure including not only the belt conveyor scale itself but the entire material
handling system. Note any changes in the scale function and report them to the individual or department that is
responsible for the scales’ performance.
2.1 Housekeeping Tips
There are several maintenance issues that need attention to maintain the general well being of the belt scale. They
are listed below.
Cleaning
Keep the scale area clean of rocks, dust and material build-up.
Lubrication
The weigh idlers should be greased one to two times yearly. Overloading the weigh idlers with grease can change
the tare weight and place the scale out of calibration. A zero calibration is necessary after greasing.
Idler Alignment
The alignment of the scale service idlers to close tolerance is the single most important step in the installation of
a belt weighing system. In order to minimize the dynamic effects of the moving belt and to provide a straight belt
path through the scale, the weigh area idlers must be aligned to close tolerance.
Belt Training
The belt must be trained to run true to the center line of the idlers in the area of the scale while running empty, as
well as under loaded conditions. Where this cannot be accomplished due to off-center loading, the loading should
be modified. Where a belt does not train while empty but does train while loaded, it will be necessary to train the
belt over the scale area at least during the calibration checks.
Because of lateral forces and changes to belt tension produced within their area of influence will degrade scale
accuracy, training idlers should not be located closer than 12 meters from any scale mounted idler.
Belt Tension
It is important that the conveyor conditions remain constant at all times. Therefore, gravity-type take-ups are
recommended on all conveyors where belt scales are installed. Conveyors which do not have a constant tension
device will require calibration whenever the belt tension changes and the take-up is readjusted.
A gravity take-up weight that is fully supported by accumulated spillage can no longer be effective at
maintaining the correct tension of the conveyor belting. The take-up carriage should move freely in its guides
when the belt is operating.
Belt Loading
Extreme loading conditions which cause flow rate of material to be above 125% of the instrument range must be
avoided. Any load capacity above this amount can’t be measured. Belt loading should be adjusted to stay within
the instrument range. On the other hand, very low flow rates, with respect to full scale range, can produce low
accuracy.
Material Sticking to the Belt
Material can form a film on the belt which is carried continually around the belt and is never discharged. This
condition is often true when handling wet, fine material. Belt scrapers may correct this condition. If the film can’t
be removed, the zero will have to be adjusted. Any change in the build-up of the film adhering to the belt will
require further adjustment.
Skirtboards and Covers
Skirtboards should not be placed closer to the weigh idlers than the +3 or -3 idler. If skirts or covers are necessary
in the weighing area, they must not place any external forces on the scale. Even though the skirts are clear of the
belt under “no load” conditions, material will jam or slide between the boards and the belt when the conveyor is
operating. Errors of several percent can be expected where such conditions exist.