Testing...
Dear Mr. Qaredaqi,
your supplier did not advance "nonsense", but solid technical facts which might lead to damages, for at least two reasons:
a) overloading: increases the bending of the drum body and the axial load on the drum bearings
b) coarser and more solid input increases the amplitude of the impact load from the milling process
These two factors contribute to the fatigue loading of the machine. But there might be other core causes for the cracks.
By giving crack samples to a knowledgeable engineering body & testing laboratory, the nature of the failure will be / would have been established. This is / would be your responsibility.
As an engineer with a bulk handling plant OEM i however would most strongly reject any claim of an operator, if that operator did run the plant / system outside agreed limits. I do most sincerely hope you were as honest to your supplier as you present this issue here.
From the context given the failure is a fatigue issue, so there might be interest to adapt the design lest you intend to continue running the machine outside the permitted throughput / material parameters. But you rather decided to change suppliers... meaning you are testing the market, .. perhaps we hear from you sometime again?
Regards ■
Thank You For Your Answer
Thank you for your answer and sorry for my bad English, I have a question about overloading issue in a ball mill, in spite of overflowing mechanism in mentioned ball mill, I think it's not possible for this ball mill to overload, I mean discharge hole would not let load level in ball mill go high, because materials will overflow. I appreciate if you correct me if I am wrong. ■
Feedback
Dear Mr. Qaredaqi,
i took it from you, quote "
1. You have fed ball mills with 33% higher than nominal feed over a period of time ( they are right we had to do this for 1 month)
2. You feed the ball mill with higher solid content; yes, we had used 80% instead of 75%.
3. You have fed the ball mill with coarser feed (like two time coarser), yes we had.
"unquote,
so nothing is unclear, to my understanding. Coarser feed shall impact on flowability and throughput, and w/o deeper knowledge about the overflow protection feature its impossible to comment on this issue.
Imo the supplier of the shells as well as of the mill itself should get to one table with you in order to find a techn. solution. Anything else is fishing for a mermaid.
Regards ■
A New Saying.. For Me Anyway.
I like the phrase "fishing for a mermaid".
The cracking is not adequately explained. If the trunnion welds are failing I would expect full circumferential separation. It is a rotating loading which is fairly uniform so the fatigue loading is consistent. Also if you decrease the amount of grinding media and use coarser feed (x 2) you must expect to increase the circulating load, which you did. The larger circulating load hardly affects the fatigue issue and therefore it seems that your trunnions are too small for the duty. I also notice that you claim to be working the mills longer than in other plants. Sorry, but any mill worth its salt should be running all year long minus 2 relining periods! Have you checked the linings are correct? ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Cracks in shell
hello
I am a mineral processing engineer at a mining company in. Recently we have faced a problem with our ball mills in a new built plant; we have a Iron ore concentration plant, which two ball mills have been used. These lines started to work About 2 years ago. Last year both of our ball mill shells cracked where they sit on shoe bearings. This happened to almost all of shells, which have been used by our contactors in Iran with the same sub supplier (like seven shells!) after a while new shells with same supplier were replaced (no difference but just a biggest welding fillet where the shell mounts). Ball mill size is 5.5*11, shell mounted and with a overloading discharge mechanism ( it’s closed with hydro cyclones). After a while (like 6000 hours later) same cracks were appeared.
Our contractor tried to claim with very nonsense reason to justify this failure, after replacing the very first shells in this area, our shells were the first shells, which started to crack (I need to say our working hours and production is higher than other plants).
Our contractor has claimed with these reasons:
1.You have fed ball mills with 33% higher than nominal feed over a period of time ( they are right we had to do this for 1 month)
2.You feed the ball mill with higher solid content; yes, we had used 80% instead of 75%.
3.You have fed the ball mill with coarser feed (like two time coarser), yes we had.
Our company has ordered new shells from a different company, but I need to know if these items really leads a shell to crack? ■