Ball Mill Shell Drilling Pattern

Lafarge Mill Grinding Reference, Edition 2

Addendum                                                                                                                    

Ball Mill Shell Drilling Pattern

There are two main types of drilling patterns employed in the majority of ball mills used in the United States and Canada.  They are the American Lorrain and DIN patterns, (DIN is the German/European equivalent to ASTM).  The drilling and bolting pattern essential fixes the dimensions of the liner to be used.  Thus it can affect the design of the liner.  If the bolting pattern is not properly taken into account then the liner design may not work.

The differences can best be explained by examples.

American Lorrain                                         DIN                                                                Example 1: 9.5′ (or 3 m) Ø Ball Mill

# of bolt holes/ring =                                 # of bolt holes/ring =

9.5 X 2  = 19                                                   3 X 10  =  30

liner width =                                                 liner width =

6 π  = 18.8 inches                                          100 π  =  314.16 mm

Example 2: 13′ (or 4 m) Ø Ball Mill

American Lorrain                                         DIN                                                                

# of bolt holes/ring =                                 # of bolt holes/ring =

13 X 2  = 26                                                    4 X 10  =  40

liner width =                                                 liner width =

6 π  = 18.8 inches                                          100 π  =  314.16 mm

In each case, the liner width is standard which has been done for manufacturing convenience only.  However it is important to realize that a DIN drilled mill always more liners per row or ring than one drilled for Lorrain liners.  Not appreciating this has led to problems when trying a different liner design.  There are two specific cases experienced by Magotteaux.

Step Liner Case Study

Magotteaux through the engineering firm Slegten introduced the step lifting liner, (sometimes called shiplap, wedge or continuous lifting).  Designed and first introduced in Europe they experienced excellent results.  However when later introduced to North America, customers experienced very mixed results.

The step liner was designed for a DIN drilled mill.  However on an American drilled mill, there are far fewer liner plates per row or ring.  As a result such mills were equipped with fewer liner plates giving fewer lifts per rotation.  In addition early installations employed either a lower lift angle (since the widths are much greater) or to maintain the same angle used a thicker plate which reduced the available room for grinding media.

For step liners to work in a mill drilled differently from DIN, one must use either a boltless or semi boltless design to ensure that the number of lifts is comparable to a DIN configuration.

Duolift Liner Case Study

More recently, Magotteaux developed the Duolift liner which is intended to be a more aggressive lifting liner but such that the lift characteristics can be maintained as the liner wears down.  It was developed in the United States for mills drilled for a lorrain liner.  It was met with very good results in North America, but in Europe, mills experienced a loss in production, (there are Lafarge examples).  Duolift liners will only work in mills drilled with other than an American Lorrain liner drilling, if a semi-bolted or boltless design is used.  In this case we would need fewer liner plates.

BEWARE

Unfortunately, within Lafarge, there are many instances where mills have been specified with an unconventional drilling pattern (by either the supplier or original customer).  Usually the number is somewhere in-between the number required by the Lorrain design or the DIN design.  Consult with the liner supplier carefully to determine if this will be a problem.