Pivot Ring & Bar Bell Stir Bars

[Hogan]

I have a standard 6cm stir bar that works great in my erlinmeyer when making a starter but I also have two five lt. vessels that have a slight dome on the base. Whilst I can get the standard bar to spin in these, if it is properly balanced, it can also easily drop off, so I am looking for a better alternative. I have seen the bar with a centre pivot ring in the Crown and Livingston web sites but a US forum talks of one that is shaped like a bar bell.

Anyone used either of these on domed bottomed flasks and do they work. Any idea where you can purchase the bar bell variety in Oz.


Cheers, Hoges.

 

[MitchDudarko]

My wife is a lab supervisor on a gold mine over here in WA. She says the bars with the center pivot rings are the ducks nuts. Something about a small surface area.

 

[Wolfy]

Those who have used them (check the epic tight-ass-stir-plate-thread) say the bars with the pivots are very noisy, so not so good if you keep the starter in your living quarters.

 

[Andyd]

The center rings work great in a flat bottomed vessel(i.e. a beaker) but are next to useless if the bottoms not flat (and they are a bit noisy).

I've been meaning to try to source some barbell shaped ones for a while now on the assumption they'd be better than the flat ones...

Andy

 

[Hogan]

It would seem that a convex (or is it concave) surface that bulges upwards would make the pivot ring type of stir bar ineffective. The bar bell or dumb bell (as I have seen it referred to) would sit across the bulge and would be apt to remain in position more than the straight bar. The bar bell type of bar is apparently quite common in the US and I have found sites in India that manufacture them but only in bulk. I have found a US based supplier whose site quotes $30 US for a pack of three bars. I have emailed them to ask if they ship internationally and to get a postage cost.

Cheers, Hoges.

 

[Hogan]

The star shape is worth considering Wally. One would assume with the larger surface area that it would balance on a dome better than a straight bar. I know that Crown and Livingston do stock these types.


Cheers, Hoges.

 

[Hogan]

Thanks Wally. Hopefully I'll get a response from the US on the dumb bell type.

Cheers, Hoges.

 

[GTS350]

Mick,

Cant comment on the "bar-bell" type, but...
I bought my "pivot-ring" bars from proscitech in townsville, a 2pack of 50mm (octagonal profile) and 4pack of 35mm (hexagonal profile)..
Compared to the standard bar, they're definately noisier, yet I think they spin harder than a standard bar.
The 50mm pivot-ring bars are great for a 2l or 5l flask in the shed, they seem to whirlpool the whole starter more easily..
But the little peanut 35mm pivot-rings i got are fine in a smaller flask in the shed, terrible in the laundry- they seem to always "tinkle" every 5mins. Whereas the standard bar can go all night in the laundry and not make a sound.
I think a mix of various types would be handy, Im very tempted by the "star" type, but then I'm also jealous of Franko's 7cm "Excalibur" :lol:
Ultimately, I don't think it matters very much anyway, I doubt there is little difference in the yeast count of either weapon. No matter how they are wielded, both sit in the centre of an almost flat bottomed erlenmeyer flask.
So in hindsight I could've stayed with the standard bar.

Cheers,
Richie

 

[Hogan]

Richie.. I have no probs with the standard bar but I am trying to find one that will sit well on a slightly domed base. I am now sure now that the pivot would be the least appropriate as it needs a bar with either a large flat surface area (as in the star) or one which has contact ends that will span the dome, (as with the bar / dumb bell type).

Cheers, Hoges.