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Join Date: Sep 2016
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How to Open Manholes on a Ball Mill dia 6m x 9 m length

09/25/2016 12:31 AM

I have to open two manholes on a Ball Mill Shell (6 m dia x 9 m length).

Please, Could you tell me your points of view or opinions how to open it. I think that, before to open the manholes I have to install inside trusses in order to avoid the shell deformation, because it is an old ball mill, and it is possible to find fatigue stress. Other point to take in to account is, If I need to get out the balls charge or it can be avoid putting a pair of supports on the shell.

Thank you for your answers.

Ricardo Pasco

Lima - Peru

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#1

Re: How to open Manholes on a Ball Mill dia 6m x 9 m length

09/25/2016 12:56 AM

How do you plan to get inside to install internal trusses without opening the manhole(s) in the first place?

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#2
In reply to #1

Re: How to open Manholes on a Ball Mill dia 6m x 9 m length

09/25/2016 1:20 AM

I plan to get inside for the trunnion central hole.

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#5
In reply to #2

Re: How to open Manholes on a Ball Mill dia 6m x 9 m length

09/25/2016 8:03 AM

So why do you need to open the portholes at all? I don't get it yet.

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#3

Re: How to open Manholes on a Ball Mill dia 6m x 9 m length

09/25/2016 7:30 AM

I’ve never seen a ball mill without access portholes, how do you change the charge?

If you’ve got to cut your way in weld compensating plates externally around the intended entrance first. Using compensating plates there’s no need to enter the mill before it is made safe.

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#4

Re: How to open Manholes on a Ball Mill dia 6m x 9 m length

09/25/2016 7:33 AM

Are the panels structural?

In a ball mill that size I would have doubts that it would be made of such light steel that it couldn't support itself with the access ports open.

Or if it's worn out and structurally damaged to the point it can't support itself without the ports bolted in place you have far greater issues to deal with than changing the balls.

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#6

Re: How to open Manholes on a Ball Mill dia 6m x 9 m length

09/25/2016 9:41 AM

Has this ball mill been inactive for a long period? I ask that because these mills can sag and this can pinch the bolts to the point they become oblong and break on attempted extraction. In this case they will need drilling with careful concentricity to avoid the thread and re-tapped to a larger round size after corrective work to correct the sag (at time, this damage can ruin a mill left for a decade or so)

If not sagged, you might try repeated thermal cycling with a torch followed by a oil quench (blast off the oil with a pressure washer before the next torch session. This can often degrade the corrosion mediated bond caused by the inexorable expansion of the rust in the threads. Often stainless bolts are used, but the steel shell will rust and the grip is strong enough to exceed the bolt strength.

In any event, call in an experienced ball millwright, they have the tools and experience to deal with this. Once you have observed the process, you will gain some experience and might be able to do it yourself.

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#7

Re: How to Open Manholes on a Ball Mill dia 6m x 9 m length

09/26/2016 11:43 AM

Please Ricardo,

Insert pictures! That will help a lot.

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#8

Re: How to Open Manholes on a Ball Mill dia 6m x 9 m length

09/26/2016 1:24 PM

Ricardo: In America we have the saying: "One picture is worth one thousand words."

Two pictures is worth more than I can say.

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aurizon (1); Crabtree (1); James Stewart (1); Mikerho (1); Ricardo Pasco (1); tcmtech (1); TonyS (1); Tornado (1)

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