Tools of a Metallurgist

How to Size & Design a Regrind Ball Mill

Regrind Ball Mill

F = 210 micrometers.
P = 45 micrometers.
Wi = 14.0
W = 10 x 14.0/√45 – 10 x 14.0/√210 = 11.21 kwh/s. ton

Efficiency Factors:

EF1 does not apply.

EF2 Many regrind operations are closed circuit, but assume this one is open circuit and 80 percent passing grind will be the controlling point. Refer to Table VIII. The EF2 factor is 1.2.

EF3 Because balls will be smaller than 40 mm (1.5″) and other minor factors neglect EF3 unless mill diameter is less than 2.44 meter (8.0′) diameter inside liners.

EF4 does not apply.

EF5 Grind is 80 percent passing 45 micrometers.

45 + 10.3/1.145 x 45 = 1.07

EF6 does not apply.

EF7 Rr = 210 ÷ 45 = 4.67 which is less than 6.

2.0 (4.67 – 1.35) + 0.26/2.0 (4.67 – 1.35) = 1.04

EF8 does not apply.

Referring to Table VI ….Read more

Pebble Mill Design Calculations – HOW TO

Pebble Mill: Rod Mill Pebble Mill Circuit

The calculation for determining grinding power for Pebble milling (secondary autogenous) can be the same as for ball milling from rod mill product size to the desired specified size, neglecting the diameter efficiency factor if less than 1.0.

5.47 x 1.102 x 1.341 x 500 = 4039 HP

To this add the power required to wear the pebbles down to rod mill product size (pebble mill feed size).

F = 70,000 micrometers.

P = 1,200 micrometers.

Wi = 13.2

W = 10 x 13.2/√1,200 – 10 x 13.2/√70,000 = 3.31 kwh/s. ton

The inefficiency factor to allow for the inefficient use of power in wearing down from pebble size to rod mill product size is 2.0.

3.31 x 2.0 x 1.102 x 1.341 x 30/500 x 500 = 294 HP

4039 + 294 = 4333 HP

Select two 2200 HP pebble mills. For specific sizing refer to mill manufacturers for recommendations as they have proprietary equations for calculating mill power draw taking into account the various ore media and pulp factors involved.

Rod Mill Design Calculations

EF1 – Dry Grinding – for the same range of work, dry grinding requires 1.3 times as much power as wet grinding.

EF2 – Open Circuit Grinding – when grinding in open circuit ball mills, the amount of extra power required, compared to closed circuit ball milling, is a function of the degree of control required on the product produced. The inefficiency factors for open circuit grinding are given in Table VIII.

EF3 – Diameter Efficiency Factor – using the base mill diameter of 2.44 meters (8′) inside liners, the diameter efficiency factor can be calculated from the following:

Table IX gives a tabulation of the EF3, factors for some of the more common mill diameters in both the imperial and metric measuring systems.

Note: In selecting mills for new operations, where this factor is less than 1.0 it is sometimes neglected and ….Read more

Mill Operator Training Program

Few people would dispute the necessity of transmitting literally thousands of pieces of information about the new plant to the operator. In fact, there is really only one way to actually do it We have found that writing a series of custom plant operating manuals, specifically designed for an education level of the average high school graduate, is the correct approach. These manuals are then used in a formal classroom training program, complete with graphic support, work books, and tests. The training must occur prior to mechanical completion. Ideally, the trained operators complete the class work and then assist with the final stages of preoperational testing. Only then are they ready to introduce feed and perform their normal operating functions.

The operating manuals that we have used over the years for this purpose have evolved based on our direct experience. We have found that the following contents work well, both for training, and as a continuing reference.

Operating Manuals Contents

Introduction: This section describes the purpose of the manuals and identifies those volumes in the set. It also illustrates the scope of the particular manual volume.

Use of the Manual: This ….Read more

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