Mill and Trash Plate Setting
Do these mill setting calculations online now
Geometry of Mills
| Top roll mean diameter | MDT = 45 in |
| Discharge roll mean diameter | MDD = 45 in |
| Feed roll mean diameter | MDF = 45 in |
| Tooth Pitch | TP = 2 in |
| Tooth Flat | Tfl = 6 mm |
| Tooth Angle | Tang = 45° |
| Tooth Depth | Tdepth = (TP - Tfl) / (2 · tan(Tang / 2)) |
| Roll Length | lroll = 7 ft |
| Speed of top roll | n = 3 rpm |
| Ratio of feed opening to discharge opening in the working position | millratio = 2 |
Tooth Profile
Mill Operating Parameters
| Cane throughput | tch = 250 ton/hr |
| fibre % cane | f%c = 15% |
| fibre throughput | fibrethput = tch · f%c |
| fibrethput = 567 kg/min | |
| Average peripheral velocity of top/feed rolls | vTF = n / 2 · (MDT + MDF) / 2 |
| vTF = 10.77 m/min | |
| Average peripheral velocity of top/discharge rolls | vTD = n / 2 · (MDT + MDD) / 2 |
| vTD = 10.77 m/min | |
| fibre fill in the discharge opening | ffD = 850 kg/m3 |
| fibre fill in the feed opening | ffF = ffD / millratio |
| escribed volume in the discharge opening | volEscrD = fibrethput / ffD |
| volEscrD = 0.667 m3/min | |
| Discharge Work Opening | woD = volEscrD/ (vTD · lroll) |
| woD = 29 mm | |
| escribed volume in the feed opening | volescrF = fibrethput / ffF |
| volescrF =1.334 m3/min | |
| Feed Work Opening | woF = volEscrF/ (vTF · lroll) |
| woF = 58 mm | |
| Top - Feed roll Centres (Working) | TF = MDT / 2 + MDF / 2 + woF |
| TF = 1201 mm | |
| Top - Discharge roll Centres (Working) | TD = MDT / 2 + MDD / 2 + woD |
| TD = 1172 mm | |
| Vertical distance between top and side roll centres at rest | Vrest = 33.25 in |
| mill lift | l = 15 mm |
| Horizontal distance between top roll and feed roll centres | HF = √(TF2 - (Vrest + l)2) |
| HF = 839 mm | |
| Horizontal distance between top roll and discharge roll centres | HD = √(TD2 - (Vrest + l)2) |
| HD = 797 mm | |
| set feed opening (Tip to Bottom) | soF = √(HF2 + Vrest2) - MDT / 2 + MDF / 2 |
| soF = 47 mm | |
| set discharge opening (Tip to Bottom) | soD = √(HD2 + Vrest2) - MDT / 2 + MDD / 2 |
| soD = 18 mm |
Trash Plate Settings
There are a number of methods of setting out a trashplate for a mill, these are discussed by Hugot, Handbook of Cane Sugar Engineering, Jenkins, Introduction to Cane Sugar Technology, 1966 and Maxwell, Modern Milling of Sugar Cane, 1932. In addition a number of papers discussing this topic have been published among them Ashe, GG, SASTA, 1963 and Van Hengel, A and Douwes Dekker, K, SASTA, 1958.
Each factory that I have knowledge of has their own idiosyncratic method of laying out a trashplate, but when analysed all these methods amount to much the same thing. Hugot notes that the ideal shape of a trashplate is the logarithmic spiral, and points out that the simplest approximation to this is an arc whose center is offset from the centre point (in the working position) of the top roll along a horizontal line towards the discharge roll. The amount of the offset is given below.
The work opening on the vertical plane through the centre of the top roll is 1.75 times the feed work opening.
| Offset Distance from center of top roll to center of radius for trashplate surface | Ow = (MDT / 2 + woF) / 25 |
| Ow = 25.2 mm | |
| Radius of Trash Plate in working position | Rw = MDT / 2 +1.75 · woF |
| Rw = 673.1 mm | |
| Length of vertical line from centre point of top roll (in set position) to top surface of Trash Plate | Rs = MDT / 2 +1.75 · woF - l |
| Rs = 658.1 mm |
The above calculation was done using Mathcad 7. This file is available for downloading. Mathcad takes care of the units so the above equations appear not to take account of conversion factors. The conversion factors are handled internally by Mathcad.
