140 replies to this topic

[digger]

I really didn't consider the use of an intrinsically safe motor and am quite sure a household fan motor is not. However, proper housekeeping methods should keep the hazard to a minimum by keep flammables away from the motor and keeping the BP tighly sealed in it's drum. Although I think I will investigate a replacement motor sooner than later.

I agree good housekeeping should minimise the risks, for instance I run my mill on a farm dug into a hole and turned on via a 40m extension lead so if it did go off there would be no problem other than a ruined mill.

I agree with your concern on glass media and am closely inspecting the glass balls after every batch milled for signs of deterioration. I will change at the first sign. I actually have stainless steel 1/2" balls on the way. Perhaps that will add to the media discussion as well; ceramic vs. lead vs. stainless vs. brass vs. glass

Lead would appear to be the media of choice, I believe stainless steel has been discussed on this forum before so it may be worth doing a bit of a search. For instance what type of stainless is it? ferritic stainless steels will still spark and I believe martensitic steels can also still spark with austenitic (316 etc) posing the least sparking risk

[Shake]

I agree good housekeeping should minimise the risks, for instance I run my mill on a farm dug into a hole and turned on via a 40m extension lead so if it did go off there would be no problem other than a ruined mill.




Lead would appear to be the media of choice, I believe stainless steel has been discussed on this forum before so it may be worth doing a bit of a search. For instance what type of stainless is it? ferritic stainless steels will still spark and I believe martensitic steels can also still spark with austenitic (316 etc) posing the least sparking risk

The stainless is 18/10 so it does fit in the 300 category of stainless steel. Thanks for the info though, at this stage any little bit helps.

[Bonny]

The stainless is 18/10 so it does fit in the 300 category of stainless steel. Thanks for the info though, at this stage any little bit helps.

I'd personally go with brass for milling comps as there may (apparently) still be a chance that the SS could spark. Use the SS for milling individual chems.
In any case I'd ditch the marbles ASAP due to glass contamination AND they could also cause a spark from static.

[Shake]

I'd personally go with brass for milling comps as there may (apparently) still be a chance that the SS could spark. Use the SS for milling individual chems.
In any case I'd ditch the marbles ASAP due to glass contamination AND they could also cause a spark from static.

I'm not very concerned with static discharge from glass as it has a neutral charge and the entire mill is grounded, safety first, and I don't think milling introduces enough energy to create a bound charge.

I haven't been able to find any brass milling media, perhaps I need to source ceramic a little more aggresively.

PS What part of Canada are you in?

[Bonny]

I'm not very concerned with static discharge from glass as it has a neutral charge and the entire mill is grounded, safety first, and I don't think milling introduces enough energy to create a bound charge.

I haven't been able to find any brass milling media, perhaps I need to source ceramic a little more aggresively.

PS What part of Canada are you in?

My knowledge of static is not too good, but I'd still avoid the glass. Even though the mill is grounded, the plastic jar is insulated from the ground, and the friction of the marbles may create a charge. Remember it only takes 1 spark, so why risk it at all.
The brass media I use is an ugly mess of cut up rod, balls, melted rifle casings and misc shape chunks chopped in an iron worker from bushings.

PS I'm out in the Prairies.

[Pyrogeorge]

My ball mill rotates 95 rpm..The jar dimension is 7".Is it good speed or i must reduce it?Thanks

[pyrotrev]

My ball mill rotates 95 rpm..The jar dimension is 7".Is it good speed or i must reduce it?Thanks

What size are your media Pipipi?? that has an effect on the optimum rotation speed.

[Arthur Brown]

The challenge with glass media is that microfine flakes of glass will break off in the process and these will sensitise the product significantly to pressure so subsequen pressing or ramming has added risk. Keeping the risk right down is sometimes all we can do to stay alive so we keep it as low as possible, even to the point of keeping on with the old ways because the newer ways are less thoroughly tested.

[BrightStar]

My ball mill rotates 95 rpm..The jar dimension is 7".Is it good speed or i must reduce it?Thanks

That's probably a bit fast if your jar id is 7".

With 20mm media, you should aim for 69 RPM optimal and by 106 RPM critical there will be almost no grinding action.

With 1/2 inch media it's 65 RPM optimal, 100 RPM critical.

Edited by BrightStar, 17 July 2009 - 06:16 PM.

[Pyrogeorge]

I think that my media is .75" to 1/2.so the optimal speed is around 65rpm..thanks

[sir steve]

if you want a really cheap ac motor strip an old tumble dryer. Ignore washing machines they have complicated motors dependant on controller boards. the motor in tumble dryers is a capacitor run motor. it has 2 coils, no slip rings or brushes to create sparks. one coil has mains voltage across its ends the other is connected to the mains with the capacitor in series. The shaft is long with a great big fan for the heater blower rivetted on. just saw it off, its not needed. ive got 3 dryer motors in my junk box at the moment, if anyone is struggling to find one pm me .Also look for old type writers the platten rollers make tumbler rollers as do conveyor rollers .

Dear mr Icarus do you want to sell me a motor? also dead printers. I have some sweety 8mm bearings don' t know if it is ok
to sell on this list a quid each.

Steve.

[cooperman435]

I can also get a number of sealed 240v motors ideal for ball mills. Aluminium bodied with heat fins to dissipate the heat.

Ill try to post a picture if anyone's interested?

[sir steve]

I can also get a number of sealed 240v motors ideal for ball mills. Aluminium bodied with heat fins to dissipate the heat.

Ill try to post a picture if anyone's interested?

I am interested. Has anyone tried a car whipper motor? Q why do a lot of desing i have seen drive both rollers
does that not just add friction? I also just made a 8" rubber roller with a stainless 8 mm rod, cost 4 quid and is easy.

Steve.

[Arthur Brown]

The drum rests on both rollers obviously. If the friction between the driven roller and the drum is poor then the drum will slip, leading to poor or failed milling. SOMETIMES driving both rollers is the answer to keeping the drum turning.

[portfire]

IMO windscreen wiper motors make bad ballmill motors, too slow and get hot QUICK. My first mill had one and was instantly ditched, not too bad for star rollers though. The mill I have now uses a old washing machine motor with a fan over the top. As I only mill in 50g batches, I get pretty fast BP in 30mins

I'll be building a new mill at some point next year, so they maybe a free mill for someone