Thanks for your reesponse on our cracking problems. We have ordered a new cone and in the mean time we have welded the effected part and have used dye penetration test for finding the magnitude of crack. But what in I am interested is the reasons;thats why such cracks develop, either due to misappropriate operating, startup /shutdown procedures. improper jackingup the mill at the startup time, overdue servicing of trunion etc. Or only due to matelurgical/ casting failure. Furthermore please let me have the diagnoses procedure/test for the above.

The main reasons why these cracks occur are due to the high stresses that the mill end castings are subjected to and therefore metal fatigue. Most suppliers have taken steps to reduce metallurgical or casting failures as much as possible, but pre-delivery inspection and testing would be one step. Many problems are caused insufficient care by the maintenance department when welding, grinding the mill shell, or cutting bolts/drilling holes for fixing bolts. Of course there are steps you can take to during operation to mitigate against these cracks developing, (i) broken wear protection plates must be replaced immediately, (ii) temperature monitoring. Ultimately there is no alternative to frequent and rigorous inspection.

Could you please advise us with optimum length for preheater cyclones inner pipes for increasing cyclones separation efficiency and increasing decarbonation degree. Because we have kiln capacity 5000tpd, kiln length 100m, kiln diameter 5.0m, preheater two-string, four stage cyclones, calciner system and bypass system.

Varying the length of the dip tube in a preheater cyclone will have two effects: (i) the cyclone collection efficiency will be improved which is a good thing, however (ii) the pressure drop across the cyclone and the whole preheater will be increased. If your kiln runs with the induced draft fan close to maximum speed then the increased pressure drop will create a restriction on the process. Because of these conflicting effects it is not possible for me to tell you an "optimum" length for the dip tube in a cyclone. This depends on other factors in the process and the kiln, and also whether you want to push the kiln to the highest output possible.