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Frozen Mill Charge alarm (7 replies and 8 comments)
Are you grinding your ball mill out before you stop it or you just crash stop it?
How long it the mill stopped before you restart, ie: how long do you think it takes for your charge to freeze?
Assuming you are not "doing anything wrong", an inch drive is what you need.
They are expensive however and maybe hard to obtain where you live.
Some less safe alternatives I have seen, is inching the mill using the overhead crane [I AM NOT RECOMMENDING THIS].
If you grind your ball mill out to a low %Solids of say under 30% before you stop it, you should not have the restart issue.
Do you know how to do that?
https://www.youtube.com/watch?v=Ih3TBexFIXM&feature=youtu.be
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Mostly due to the mixture of water and the sedimentation of the fine grind ore on basis of the different density of the charge (density of water 1.0, ore –depending of the ore type2.5-3.0, steel balls 7.8) upon certain time of standing still.
Gradually the charge becomes a sticky and hardening mass – especially when containing clay– unable to slide or cascade while turning the mill.
In our plant the ore is quartz and micro-granite Sp.gravity 2.74
This how we solve the problem in my place I hope it can help you.
- we stop the feed first and we run the ball mill until clear water starts to discharge.
- During restarting also we use inch drive to disintegrate the frozen material , it works we don't have any problem.
Actually we have not had the problem yet, but as i mentioned above we follow the procedure to prevent it from happening.
In your case is it happening after long shutdown ?
A few questions:
- what are conditions of shutdowns prior to freeze? - how long are the shutdowns?
- is this new / getting worse / always this way in your mill
- any details of mill, changes in media, etc.
- any details of ore, grind, change in grind
- any details of operating conditions, changes in operating conditions
Before you shutdown, you need grind your ball mill out to a low %Solids of say under 30% before you stop it.
To do this, you stop the ore feed to the ball mill and let it operate for about 30 minutes with all the normal water on. This will remove the 'cementing load' from the mill and just leave you with mostly balls and very fine particles.
This is called a grind-out after which you should not have the restart issue.
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Hello Hamid72
One of the factors that could contribute to that is the ore characteristics. Normally an ore that has a high quantity of limestone can lead to cementing. Try the following; 1. Do analyse your ore and check if there's more than 40% of limestone and if there is, do blend your ore with the one with less or no limestone, 2. Try to balance your mill-in-L/S ratio. Try to use a mill-in-density of 1.7t/m3 or 1.75t/m3. Do also inform your operators to monitor the mill load. If it increases with the drop in power draw, they must increase the mill inlet water to flush out the mill rather than to wait until the mill is fully cemented. Good luck.
Hello everybody
In our plant sometimes freezing of the charge happens for the ball mill and if we cant solve this issue after three times the ball mill will be stopped for 5 hours. I want to know why this issue (the load cementing) happen? And what parameters cause this issue?