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Rolling Margin:
Rolling Margin:
Rolling margin is
percentage of diviation in Sectional weight of Reinforcement steel allowable as
per
IS codes. Reinforcement steel is extruded from a mould which is made for a
particular size e.g. 8mm Dia.When the mould is brand new, the sectional weight
of 8mm steel extruded through mould would exact as per IS standard of lower
than that.i.e. 0.395Kg per Metre or lessor.
Mould gets little bigger after
certain period of time or after certain quantity of production is taken from a
particular mould. Now same 8mm dia bars extruded from the same mould will have
more weight per Metre say 0.400Kg per Metre insted of 0.395 as per IS. That is
more mass per Metre/Length is required for same length.
This diviation in weight is defined in IS code-1786 for different
dia which is as under:-
8mm to
10mm +_ 7%
12mm to
16mm+- 5%.
20mm and
above+ -3%.
Rolling
Margin is calculated as under:-
Total
Weight of Bars (Dia wise) / Total Running Metre of Bars = Actual Sectional
Weight of bars.
Compare
sectional weight with Standard IS Weight.
Weight as per IS Standard.= Dia X Dia / 162.
Rolling margin is the difference between the
theoretical and actual weight of steel. This is because of the die which is
used for casting of rebars. Over a period of time the shape of die changes and
as a result the diameter of the steel bar also changes which results in
difference in unit weight of steel.
The size of the die is kept small and as a
result rolling margin is negative in the initial stage of production, there
after it is more of less close to theoretical weight and then the size of die
increases which results in rolling margin on positive side.
If you purchase steel from same supplier over
a period of time the rolling margin would be adjusted and you are not at a
loss.
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