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THE GEOMETRY OF CONVEYOR SET-OUT POINTS
It is becoming more common nowadays, for conveyor designers to
be presented with aconveyor layout that gives the vertical
dimension of the conveyor with respect to theterminal pulley
centre-lines. This, of course, presents the designer with an
extremelyfrustrating problem, because the geometry of the system
cannot be correctly defined
until the set-out points are finalised. While the horizontal
dimensions to the terminalsare given to the centre-line of the
pulleys that is simply because the set-out points passthrough the
centre-line of the pulley, when horizontal dimensions are
considered.However, the vertical set-out points at the terminal
pulleys will never pass through thecentre-line of the pulleys and
the set-out points are some theoretical point, which isdetermined
as a function of the belt inclination at the terminals.
It is obvious that the pulley diameters in any conveyor system
are unknown until thetensions in the conveyor have been designed
(even on a preliminary basis). Theultimate selection of the pulley
diameters is a result of iterations, based on the tensionsderived
for the system. The exception, of course, is when the pulley
diameters are
nominated as a result of rationalisation. However, even in the
case of rationalisedpulleys, the overall geometry of the system
must be determined about the set-outpoints.
The basic system tensions are designed on the basis of the
horizontal terminal pulleycentres, with the overall lift measured
between the set-out pointsat the head and tail(the terminals) of
the conveyor. Since the pulley diameters at neither the head nor
thetail are known at the initial design stage, it is substantially
incorrect to dimension thevertical lift to the centre-line of the
terminal pulleys. Thus, the layout as shown
is incorrect and can lead to a great deal of confusion and
unhappiness.
In order to alleviate the apparent confusion surrounding the
correct setting out of
conveyors and their internals, the following procedure should
apply:
At the tail end
Horizontal
Vertical
Set-out point
level +0,0
Belt slo e
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It is noted that the set-out point, which is given the value
+0,0 at the tail pulley, is not atthe pulley centre-line, nor at
the top of the pulley. The set-out point at the tail is
thetheoretical point, as shown. Only when the belt line is
horizontal, will the set out pointbe at the top of the pulley. If
it is required, the level at the centre-line of the pulley will
be determined from
cos
R-0 ., where refers to the belt inclination at the tail and R
is
the pulley radius.
At the head end
Again, it is noted that the set-out point, which is at the level
as determined from theproject requirements, is given with respect
to the level at the tail pulley. Again, the levelis not at the
pulley centre-line, nor at the top of the pulley. Only when the
belt line ishorizontal, will the set out point be at the top of the
pulley.
From this, the level to the centre-line of the pulley is
determined simply by the
following, cos
R
.P.O.SatLevel
The level at all the other pulley locations, such as internal
drive pulleys, bend pulleys,take-up pulleys and so on are given to
the centre-line of the particular pulley, sincethese do not affect
the overall system tensions but, indeed, are determined by them.
Inkeeping with the convention, the level at these pulleys will
always be given with respectto the level at the tail SOP. Thus, the
profile that the designer would prefer would be asfollows.
Armed with such a profile, the design has a much greater chance
of being right firsttime.
Graham Shortt
[email protected]
A
Pulley radius R
Belt slope
Overall lift is determined at S.O.P level andis determined with
respect to the set-outpoint at the tail pulley
Horizontal
Vertic
al
Slope Slo e
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