Here i described how do calculate mill setting for sugar mills.

1. J E G A D E E S H . M
E N G I N E E R
I N D I A N C A N E P O W E R L I M I T E D
MILL SETTING

2. DEFINITIONS :
Mean effective diameter of Top Roller D
= (Outside diameter of roller - Depth of grooving)
Work Opening : Actual opening between any two points on the
surface of the two rollers in their common
axial plane when the mills are in operation.
Mill Setting opening : Actual opening between PCD to PCD of concerned
opening rollers, when mills are at rest and empty.

3. DATA REQUIRED FOR MILL SETTING
C = Crush rate desired in tons (Metric)/hr.
f = fibre % cane
D = Mean effective diameter of Top Roller (mm)
L = Length of the roller (mm)
n = Speed of rotation (rpm) {To be determined based on
No. of rollers in mill tandem, crush rate, preparatory
index, specific fibre loading, power availability at setting
speed etc.}

4. PROCEDURE FOR CALCULATION OF MILL SETTING
V = Mill Roller surface speed
 x D x n
V = ------------- m/min.
1000
Calculate fibre rate 'F' as per formula given below:
F = C x f x 0.166 Kg / min.

5. Calculate the discharge work opening as
per formula given below:
F x 63429.6
Discharge work opening = ---------------------- mm.
S x V x L
Where ‘S’ denotes the Fibre Index to be read from Table – 1.
Actual Discharge Work Opening = (Discharge work opening – Roller
Rise) mm.
The 'Roller Rise' considered for the mills shall be taken as per Table 2.

6. Mills 12 Roller Tandem 15 Roller Tandem
2nd of `B’ Tandem 38 40
3rd of `B’ Tandem 45 46
4th of `I’ Tandem 52 52
TABLE – 1
Values of Fibre Index ‘S’
Mill No. 12 Roller Tandem 15 Roller Tandem
Roller Trash Roller Trash
2nd of `B’
Tandem
7 8 7 8
3rd of `B’ Tandem 6 7 6 7
4th of `I’ Tandem 5 6 6 6
TABLE – 2
ROLLER RISE

7. Calculate the Feed work opening as per formula given below:
Feed work opening = Discharge work opening X (Ratio of feed
to discharge opening) mm.
The Ratio of Feed to Discharge opening for the mills shall be taken as per
Table 3.
Actual Feed Work Opening = (Feed work opening – Roller Rise) mm.
Mills 12 Roller Tandem 15 Roller Tandem
2nd of `B’Tandem 2.00 2.05
3rd of `B’Tandem 2.15 2.10
4th of `I’Tandem 2.20 2.15
TABLE – 3
Ratio of Feed to Discharge Opening presumed for calculations

8. Calculate the Trash plate work opening as per formula given
below:
Trash Plate work opening = Feed work opening X (Ratio of trash
plate to
feed opening ) mm.
The Ratio of Trash Plate to Feed opening for the mills shall be taken as
per
Table 4.
Actual Trash Plate Work Opening = (Trash Plate work opening – Roller
Rise)mm.

9. Mill No. 12 Roller Tandem 15 Roller Tandem
2nd of `B’Tandem 1.70 1.75
3rd of `B’ Tandem 1.80 1.80
4th of `I’Tandem 1.80 1.85
TABLE – 4
Ratios of trash plate to feed opening presumed for calculations

10. SPECIMEN CALCULATIONS

 DATA

 Crushing Rate (c) : 250 Tons (Metric) of Cane per hour (TCH)

 Fibre % Cane (f) : 13%

 Roller Length (L) : 78 1/8 inches

 Mill Size (D x L) : 39 inches O.D. x 78 1/8 inches

 Speed selected (n): 5.5 r.p.m.

 Now calculate the factor 'F' for the above conditions
  x D x n 3.1416 x 915 x 5.5
 V = --------------- m/min. = ------------------------
 1000 1000
 = 15.81 m / min.

11. Calculate factor 'F' as per formula given below:

 F = C x f x 0.3733 lb / min.

 = 250 x 13 x 0.166
 = 539.5 Kg / min.

12. Calculation of Discharge work opening
 F x 63429.6
 Discharge work opening = -----------------mm.
 S x V xL
 For value of ‘S’ see table - 1
 539.5 x 63429.6
 = ------------------------
40 x 15.81 x 1980

 = 27.3 mm


13. Calculation of Feed work opening
 Feed work opening = Discharge work opening X
 (Ratio of feed to discharge
Opening)
 For value of ‘Ratio’ see TABLE-3

 = 27.32 x 2.05

 = 56 mm

14. Calculation of Trash plate work opening
 Trash Plate work opening= Feed work opening X
(Ratio of trash plate
to Feed Opening)
 For value of ‘Ratio’ see TABLE-3

 = 56 x 1.75

 = 98 mm.

15. Mill No. Feed Side Opening
(mm)
Discharge Side Opening
(mm)
Trash Plate
Opening
(mm)
2nd of `B’
Tandem
56 27.3 98
3rd of `B’ Tandem 50 23.8 89.8
4th of `I’ Tandem 45 21 83.7
The discharge, feed and trash plate openings for all the four mills are
tabulated below.

16. Mill No. Feed Setting =
Actual opening- roller
rise
Discharge Opening =
Actual opening- roller
rise
Trash Plate Setting =
Actual opening- roller
rise
2nd of
`B’
Tandem
56 – 7 = 49 27.3 – 7 = 20.3 98 – 8 = 90
3rd of `B’
Tandem
50 – 6 = 44 23.8 – 6 = 17.8 89.8 – 7 = 82.8
4th of `I’
Tandem
45 – 6 = 39 21 – 6 = 15 83.7 – 6 = 77.7
The ‘Mill Settings’ for all four mills can be calculated as given
below:
Mill Settings in mm
The mill settings calculated should be rounded off for practical adjustment
purpose.