Appendix to OC 690/13 - Safe operation of batch ball mills used in potteries and allied industries

OC 690/13a

APPENDIX 3 Summary of the findings of the SIRIUS research (paragraph 7)

Conclusions

1 Un-cracked Boulton-type mill end plates have a large margin of safety if worked at pressures that are less than 0.5 bar.

2 Any cracks that develop in the end plates have to reach very large sizes before becoming unstable, when mills are worked at pressures below the 0.5 bar limit.

NOTE: Both these conclusions only stand if the mill is operated below 0.5 bar.

3 A mill running at 23 rpm with two adjacent cracked ribs (less than 90⁰included angle) should have nearly three years of safe continuous working life remaining. Once the crack is through seven ribs the continuous working life is less than a day.

4 Operating procedures to ensure pressures do not exceed 0.5 bar are essential.

5 The findings of the report allow a realistic specification of safety procedures for the operation of potentially cracked mills. They identify those flaws which are:

1) not immediately significant;

2) significant but are sufficiently safe to allow the mill to continue running whilst repairs are effected;

3) dangerous and require the mill to be immediately withdrawn from service and repaired or scrapped.

6 The safe working of the mills depends upon inspection being carried out for potential flaws at agreed and regular intervals.