What is Rolling Margin?
The rolling margin is the difference between the actual weight of round bars (Reinforcement) Vs. Theoretical weight of round bars. This theoretical weight of round bars picks in IS Codes.
IS Codes 1786: 2008 ( High Strength Deformed Steel Bars and Wires for Concrete Reinforcement, Fourth Revision), this picks in Table-1 Nominal Cross-Section Area and mass, ( Dia Bars: 4mm, 5mm, 6mm, 8mm, 10mm, 12mm, 16mm, 20mm, 25mm, 28mm, 32mm, 36mm, 40mm).
This is because of the dia, which is used for casting rebars. Over a period of time, the shape of dia changes, and as a result, the diameter of the steel bar also changes, which results in a difference in the unit weight of steel.
The size of the die is kept small, and as a result, the rolling margin is negative in the initial stage of production, thereafter it is more or less close to theoretical weight, and then the size of the die increases, which results in a rolling margin on the positive side.
As per IS code tolerance for reinforcement as below.
As per the above tolerance of reinforcement weight
- Up to and including 10 mins: 4 mm to 10 mm dia of a bar, Individual weight of Up and Down 8%, The Batch weight of Up and Down 7%.
- Over 10 up to and including 16 mins: 12 mm dia bar to 16 mm dia bar reinforcement, individual weight of Up and Down 6%, The Batch weight of Up and Down 5%.
- Over 16 mins: 20 mm dia bar to 40mm dia bar reinforcement, individual weight of Up and Down 4%, The Batch weight of Up and Down 3%.
Procedure of Rolling Margin
Rolling Margin of Steel Format: Download Format
The above format is used in a rolling margin for reinforcement.
- In this method, one dia of bar minimum three sample requirement, Each sample length minimum 1 m. (1000 mm)
- All the above three samples take the induvial weight, Heter correct length because of cutting of reinforcement not perfect length (Example: 990 mm, 995 mm, 996 mm)
- So Convert in 1000mm length in weight Like 10 mm dia bar 990 length steel weight 0.598 kg, After converting 1000mm length steel weight 0.604 kg, all three weight fill in a block No. 8
- And block No. 9 actual weight of IS 1786, page- 5, table-1 consider
- Block No 10 is a difference between block no. 8 and block no. 9
- Here, Block no 11 is a negative all their average sample difference. Same as block no 12 positive blocks, all three different.
Why is Rolling Margin?
The rolling margin differs between “-“and “+” depending on the tolerance as per IS code 1786: 2008. Here rolling margin show round bar is uber the weight or over the weight.