Suitability For A Hlt / Mash Stirrer

[ant]

So, I was searching through posts past, looking for some good ideas wrt mixing an HLT (for proper temp distribution) and/or the mash (for temp distribution and avoidance of doughballs in an automated system). I was staggered at the abilities of some of the AHB folk who come up with beautiful designs and systems, not to mention the quality of welding involved. Now, I also fall into the "tool tard" category, so ready made is the way to go to me. I looked at industrial paint stirrers and the like, but they're only going up to about a 25cm diameter, and my mash tun is 50cm diameter, and at this size, a couple of $100.

So, a quick search on ebay, and it seems to me that an outboard blade would fit the bill - they're generally stainless, they're pitched, they have a standard fitting and they're cheap as chips (don't need no racing prop at the speeds it will be going!). Has anyone else thought about going down this road but decided against it? If so, why? What am I missing??? :blink:

 

[mika]

I don't know Ant, the ones I've seen have a lot of casting webbing which could make it a bugger to clean. A 250mm dia mixer in a 500mm tun is maybe not soo bad, as you will get the contents being agitated in the centre, tending to drag the outer grains as well, though certainly if you can get more diameter cheaply it's the way to go. I know industrial mixing tanks have baffles to break the vortex action, otherwise it's possible for the contents of the tank to rotate with the mixer and result in inefficient mixing. If you're planning on intermittent shaft reversal, that will allieviate a lot of the problems, but leads to my next thought.
You may need to have a close look at the shaft size being used in the industrial mixers against what you can get thru the prop. These shafts have a long un-supported length, with signifcant forces being generated at the end. It may well be fine, but I know it's something the mixer people put a lot of engineering thought into. Obviously this strength carries on to the gearmotor driving the whole lot. If you've got examples of similar setups you've probably already got idea. But I'd suggest what will work for the HLT will probably not work for the MLT due to the increased viscosity/density of the mash mix.
So not so much an answer, but a few more thoughts on evaluating it thoroughly.

 

[Tony M]

Most of those props are aluminium and as your mash is acidic things might get buggared up ---the beer more than the prop.
If you want to direct heat, the blades should be shaped to scrape the bottom so you dont burn the mash.

 

[mika]

People use Aluminium Kettles Tony ? Didn't think it 'd be any worse in the mash ?
As the prop will have a pitch its likely to circulate the mash from bottom to top (or vice versa) as well, rather than just stirring it around.
The more I think about this idea the more I like about it.
Ant will probably come back at 3am in the morning and tell me I've got it completely wrong.

 

[ant]

Good thoughts gents. On further thought - what I'm ideally looking for is an inboard motor (like below) - that way I can just tig a rod (probably search for a damaged prop shaft as they are sized for it, are s/s and if completely stuffed, should be cheap as) into it without having to worry about the crevices etc. Biggest hassle with these is that most of them are Nickel/Brass/Ali combos - not s/s. Perfect shape though - a 16" prop will only leave a 50 mm gap around the blade. Might just have to keep an eye out andrign around a few places for damaged bits and pieces.


Alternatively - might track down one of these "mudbuddy" units... need a threaded fitting and are more common in s/s


Tony - not looking to direct fire the tun - this "stirrer" is going to be lid mounted and sit a couple of cm above the false bottom. It's sole job will be to stir the mash for the first 10 minutes to get rid of doughballs and circulate the mash while the HERMS is getting it up to speed.

 

[MHB]

I dont think it would matter that much what you used. A shaft with a couple of bits of bent flat bar welded/bolted on will work fine.

The major design requirements are to: -
Keep the tip velocity below 3.8m/s
Conform closely to the bottom of the vessel
Cause the grain to rise (flow up) so that the whole mash is mixed

Large low speed blades are best, mounting them off centre is a benefit, as is making sure they dont "Walk" (torque can make the shaft flex) and bang around inside the Tun.

It is easy to underestimate the amount of power required for effective mixing, especially when restarting after a rest, a good gear box or reduction pulley system is a must, a large load start capacitor is going to increase the motor life.

MHB

 

[Tony M]

People use Aluminium Kettles Tony ? Didn't think it 'd be any worse in the mash ?

Yeah Mika, I didnt think it out. That protective film of aluminium oxide is a good barrier to weak acids. It was 11.30pm and it was Friday nite so I was very tired from holding up a glass for seven hours!

 

[mika]

Yeah, know what you mean Tony...that glass starts getting heavy towards the end of the night, best solution is to :chug: