[RASMB] "Sticky" fit of cells in AN-60Ti rotor

[mmorris]

Dear Jim,

Do you load the cell into the rotor when it is warm (e.g., room temperature) and then
do the run cold? If so, that could explain what you get because the housing shrinks a
little.

You can:
(i) Cool the cell before you put it into the rotor.
(ii) Make sure the brass screws are not overtightened. They just have to be snug to
help seal the gasket into place properly, provided the gasket is properly seated and
has a clean edge. Any more than snug and you will distort the housing enough to make
the fit difficult. With overtightening you also run the considerable risk of stripping
the very soft thread on the screw and then having to drill it out. Not pretty.

Yours, Michael

jim.bloom.b at bayer.com wrote:

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> Hi everyone,
>      This is my first question for "Rasmbers" so please have pity on me!!
>      I am routinely using a AN-60 Ti rotor in an XLA at 60,000 rpm.  I use the
> Beckman Coulter part no. 334606 Cell Housing and Window Assembly (quartz
> windows) with the part no. 306493 12 mm centerpiece, epon charcoal filled.  My
> problem is that I have found that the cells fit sometimes very very tightly into
> hole #3 (ie. it goes in easily about half way and then I really have to force it
> the rest of the way),  moderately tightly into #2 and loosely into #1.  I
> usually use the same cell in the same hole.  The cell fit has been so tight at
> times that I have not been able to get it in and have been afraid that it was
> permanently in there....this is on loading the cell into the rotor.  After the
> spin it is no problem getting the cells out....ie. problem is before the run.  I
> have thought that the cell was getting distorted so I made up a complete new
> assembly and it was also tight.  Switching cells around and playing with the
> same cell in twice etc. gives varying results.  I thought maybe I was tightening
> the brass cell plug screws too tight and thus distorting the aluminum cell
> housing but I'm not convinced of that either.  What is going on?  Has a rotor
> hole become distorted?
>      Anyway, the real problem is that I am afraid of getting a cell stuck inside
> the hole and having no means of getting it out .  Can I lubricate outside of the
> cell housing or rotor hole with say the spinkote Beckman supplies to seal the
> screw ring for the cell housing?
>      Jim Bloom
>      Bayer Corp
>      Berkeley, CA
>      510-705-7760
>
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