9/9/97

Someone recently commented about having a glassblower grind down a bell jar

that has a chipped rim. We have had this done a number of times with good

success. It is indeed a feasible solution, provided you can find a

glassblower willing to undertake the task. On the other hand, you could

probably do it yourself, if you are willing to devote the time and energy

required, because all one glassblower I observed did was to spread a slurry

of silicon carbide abrasive on a piece of window glass, and sit and rub the

bell jar around over it.



Alternatively, we have been successful in some instances in 'patching' the

chips in bell jars using a stiff epoxy (e.g. Torr Seal). Clean all grease

and oil off the bell jar (try using Tilex Soap Scum Remover), then fill the

chipped hole with the epoxy, and set the bell jar on a flat, smooth surface

covered with waxed paper (so that the surface comes out flat and smooth)

while the epoxy cures.

Good luck,



Wilbur C. Bigelow, Prof. Emeritus

Materials Sci. & Engr., University of Michigan

Ann Arbor, MI 48109-2136 e-mail: bigelow@umich.edu;

Fx:313-763-4788; Ph:313-764-3321

I consider a bell jar with any defect to be a considerable risk for an

implosion.If your users don't use a implosion gaurd with 100% consistency then

replace the

bell jar ...





cheerios, shAf

--

<\/>/\<\/>/\<\/>/\<\/> cogito, ergo zZOooOM <\/>/\<\/>/\<\/>/\<\/>

Michael Shaffer, R.A. - University of Oregon Electron Probe Facility

mshaf@oregon.uoregon.edu -or- mshaf@darkwing.uoregon.edu

http://darkwing.uoregon.edu/~mshaf/

Allow me to second this repair method. I used it to repair a seriously

chipped Denton 502A bell jar (it would work on any), and after overnight

curing (room temperature), the unit pulled as good a vacuum as quickly as

it did before the chip.



Phil

Philip Oshel

Station A

PO Box 5037

Champaign, IL 61825-5037

(217) 355-1143

oshel@ux1.cso.uiuc.edu

We have repaired our Bell Jars 10-15 times using Vacuum epoxy, such as

Bell Torr or Torr Seal. We do it a bit different than above. We actually

file and sand the surface smooth. Basically, I have come to the

conclusion that for the level of vacuum that Denton Coaters use, the only

time a new bell needs to be bought is if it cracks. Chipping is easy to

take care of.



oh...The reason I replied to the above is that if you use the wax paper

technique, make sure you get the epoxy thick enough in the chip (ie. as

thick as the glass)



Christopher Adcock

yoyodine@UNM.EDU

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