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Cleaning
Special care must be exercised to keep the return rolls and
snub pulleys clean. Buildup of material on this equipment has
a destructive effect upon training, with the result being that
the belt may run against the structure and damage itself. It is
advisable wherever possible that return idlers be suspended
far enough below the structure so that any misalignment or
dirty idlers can be easily seen. Keeping the return rolls and
snubs clean requires that the belt be clean when it enters the
return run. Scraping is the most common method of ensuring
cleanliness.
Rubber scrapers can be made by clamping rubber slabs 1/2”
to 1” thick (not old belting) between two metal or wooden
bars.
Extend the rubber about twice its thickness beyond the
bars and suspend the mechanism with a counter-weight to
provide the pressure against the belt (Fig. 15).
Replace the
rubber when it wears down near the bars. Two or three such
scrapers can be used in succession. The most common steel
scraper is a series of diagonally set blades mounted on the end
of a leaf spring to maintain pressure against the belt.
These will
scrape sticky materials that rubber scrapers may ride over
(Fig. 16).
Washing the belt with a water spray before wiping with a rubber
scraper will do a good cleaning job on almost any material,
including iron ores and mixed concrete.
Dry materials can be cleaned off the belt with rotating bristle
or rubber vane brushes, driven at fairly high surface speed,
usually three to five times the belt speed (Fig. 17).
They wear
rapidly, require considerable maintenance and are likely to fill
up solid if used with wet and sticky materials. It is preferable
to clean just after the head pulley and before the snub. An
exception to this is that sticky material often requires scraping
on the head pulley. This is because a large part of the fine
material sticks to the belt and must be scraped into the chute.
In some cases, the best possible cleaning is insufficient and
steps must be taken to compensate for the effect of a dirty belt.
Snub pulleys can be kept from building up by using soft rubber
lagging or by scraping directly against the pulley. Diagonal
grooving will distort and discharge accumulations on these
pulleys.
Rubber disc or spiral type return rolls prevent buildup
on themselves and thus save a training problem (Figs. 18 & 19).
The only cleaning required on the pulley side is removal of
material, principally lumps, which may fall or bounce onto
the return run and be carried between the belt and tail pulley
if not removed (Fig. 22). Rubber-faced plows immediately in
front of the tail pulley are used for this purpose (Figs. 20 & 21)
.
They are usually held against the belt by gravity and set at an
angle to the direction of belt travel.
15
Installation, Maintenance & Troubleshooting Guide
Installation