Shutdown tylan6 SNF 2010-09-01 07:40:02: Problems with thermal plug at door end ...

shott at snf.stanford.edu shott at snf.stanford.edu
Wed Sep 1 07:40:03 PDT 2010


I retracted the cantilever a certain distance to see if I could learn more about why we are having unusual smoking problems on the POCl3 tube.
While I can't guarantee that what I found is necessarily the cause of these problems, they are clearly not correct and need to be addressed:
1. The back end of the big thermal plug closest to the door is raised up about 1 cm because it is sitting on a big "wad" of P2O5.  It is sitting sufficiently high that the thermal is scraping against the top of the tube when it is inserted/retracted.  Moreover, this must be greatly altering the flow of gas around the thermal plug so that is is not uniform.
2. The big thermal plug is too close to the door .... it is sitting so that the body of the plug is largely blocking the exhaust hole in the side of the tube.  It needs to be pushed further toward the source end so that there is a largely unobstructed cavity between the door and the plug that extends at least as deep as the exhaust hole.  If I look at tylan 5, I can see that is has one of the little baffle sections between the plug and the door ... but that the big plug there is pushed far enough in along the cantileverer that there is a largely open cavity between the plug and the exhaust port.  Having the big thermal plug sitting in front of the exhaust hold cannot be correct and must be influencing the way that the gas from the tube is getting scavenged.
Here is what I believe needs to happen.
1. Turn off tylan6 and determine whether we only need to pull and clean the cantilevers or whether we want to clean the entire tube.
2. Check any assembly drawings that show the position of the plug relative to the end of the door and, in particular, relative to the exhaust hole.
3. Reassemble the system to ensure that the plug is deeper than the exhaust hole when it is inserted in the tube.
4. Make sure that the cantilver is nicely centered and that there is largely  uniform spacing around the plug so that there is no scraping.
5. Run test runs at both 850C and 1000C (or whatever is the maximum allowed predep temperature) to look for evidence of smoking.
Thanks,
John




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