[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Inner plate on bcal
Hi Tim, Elke and Elton:
Well, it seems we all agree that a 8 mm Al plate glued on top of the
last Pb (grooved) sheet is a good idea. We have also agreed that the
base plate will be 1.5" thick instead of the original 1". I hope that
there's sufficient space for these two additions amounting to ~ 20 mm of
extra thickness.
One more revision needed, as a result of the above changes, is the
budget adjustment. The extra thickness of the base plate will need to
be incorporated in the budget and all metals have gone up in prices, so
one has to revisit the costs. The new top plate will also carry extra
costs in addition to the machining costs to trim it to some size just
above the pre-machined top layers of the modules and the machining to
assure some surface roughness to obtain better adherence with he epoxy.
Cheers,
George
whitey@jlab.org wrote:
>This sounds good! We will work out the details for supporting the CDC/FDC
>rails with the plate.
>
>Tim
>
>
>
>>Hi Zisis,
>>
>>Thanks for your response.
>>
>>Tim: I guess we can go forward with refining a design with an 8 mm Al
>>sheet at the inside of the Bcal.
>>
>>Cheers, Elton.
>>
>>On Wed, 6 Feb 2008, Zisis Papandreou wrote:
>>
>>
>>
>>>Hi Elton:
>>>
>>>a few remarks embedded in your text.
>>>
>>>On Feb 5, 2008, at 2:34 PM, Elton Smith wrote:
>>>
>>>
>>>
>>>>Hi George and Zisis,
>>>>
>>>>We had our weekly meeting with the JLab engineering/design team this
>>>>morning and discussed bcal installation (along with other issues).
>>>>There
>>>>are many good reasons to have an inner skin to the bcal which can
>>>>be used
>>>>for mechanical assembly. We have discussed this previously, but
>>>>wanted to
>>>>try to pursue this a little further. We have a slightly different
>>>>proposal
>>>>now and some questions.
>>>>
>>>>The current thinking would be to attach an 8 mm Al skin (equivalent
>>>>to the
>>>>first 0.1 rad length of Pb sheet). This has structural advantages
>>>>over the
>>>>lead, and also would be symmetric to the Al plate on the outer
>>>>layer, so
>>>>you could use the same procedure for attachment.
>>>>
>>>>
>>>Fine, sounds ok.
>>>
>>>
>>>
>>>>Here we have some questions or be reminded of how the first layers are
>>>>constructed: Is the layer of Pb next to the Al base the same
>>>>thickness as
>>>>the other layers? How is that it has a flat surface instead of a
>>>>grooved
>>>>surface? (We assume that the swaging machine groves the top and
>>>>bottom of
>>>>each layer at the same time). Finally, can one put grooves into the
>>>>Al and
>>>>use it instead of a Pb sheet?
>>>>
>>>>
>>>The very first Pb sheet is glued to the aluminum base plate with a
>>>two-compound industrial epoxy. We chose this as something expected
>>>to be stronger than the BC-600 optical epoxy, and since there are no
>>>fibers (actually there is only one, see below) between the Pb and Al;
>>>the extra surface (and porosity?) of the fibers help the BC-600
>>>adhere better and keep everything together. This 1st Pb sheet is
>>>identical in construction to all Pb sheets: it is grooved on both
>>>sides of course, and has the same 0.5mm thickness. The Al base plate
>>>has a single 0.5mm groove (trench) machined along its entire length.
>>>In it we glue a single fiber using BC-600. This acts as a "guide
>>>rail" for the 1st Pb sheet. Once the BC-600 is cured, we then apply
>>>the industrial epoxy and glue the 1st Pb sheet; the single fiber
>>>keeps it from twisting/migrating under pressure when the industrial
>>>epoxy is setting/curing. We haven't seen the need to increase from 1
>>>guide fiber to 3 or 5; 1 seems to do the job.
>>>
>>>Grooving the 8mm Al sheet that you are proposing to use at the other
>>>end (inner side) of the modules, may not be the best way of tackling
>>>this. Reversing the above process would have us installing a single
>>>fiber (or wire of equivalent diameter) in the middle of the topmost
>>>(last) Pb sheet using BC-600, let it cure, and then use industrial
>>>epoxy to glue the 8mm Al plate, once it has been machined with a
>>>single groove for the guide fiber. We should be able to do this easily.
>>>
>>>We have measured module thickness difference of ~1mm from one end of
>>>the module to the other (over its 25cm thickness). This is quite
>>>good, but Tim you have to take into account that the 8mm Al plate
>>>will not be perfectly parallel to the beam axis, and its inclination
>>>will be slightly different from module to module (along all three
>>>axes probably), since no two modules are precisely identical, due to
>>>the nature of the construction process. How is this best handled?
>>>Using varying depths of bolts into threads (we assume you are
>>>thinking of putting threads into the 8mm Al)? What about spring-
>>>loaded mechanisms? Of course all this needs to be accurate and
>>>reproducible for the alignment of the tracking packages.
>>>
>>>
>>>
>>>>These questions arise as we would like to see if an inner skin can be
>>>>added because it increases the mechanical robustness of the
>>>>calorimeter.
>>>>
>>>>Thanks for your patience, Elton.
>>>>
>>>>
>>>So the answer is yes on adding an inner skin. We just have to think
>>>things through. On the BCAL side it is a more straight forward
>>>issue, and we can certainly experiment with some small samples, to
>>>ensure that the reversed process (fiber on lead first, then plate)
>>>works as well as the regular process (fiber on Al first, then Pb
>>>sheet). The rest is up to you Tim! :-)
>>>
>>>Cheers, Zisis...
>>>
>>>
>>>
>>>
>>>>---------- Forwarded message ----------
>>>>Date: Tue, 5 Feb 2008 14:31:49 -0500 (EST)
>>>>From: Elton Smith <elton@jlab.org>
>>>>To: Tim Whitlatch <whitey@jlab.org>
>>>>Cc: Elton Smith <elton@jlab.org>, Elke Aschenauer <elke@jlab.org>
>>>>Subject: Inner plate on bcal
>>>>
>>>>
>>>>Hi Tim,
>>>>
>>>>I checked the radiation lengths of materials to see how much we can
>>>>afford
>>>>to use for the inner plate of the calorimeter:
>>>>
>>>>rad len Al = 8.9 cm
>>>>rad len Fe = 1.76 cm
>>>>rad len Pb = 0.56 cm
>>>>rad len W = 0.35 cm
>>>>
>>>>We are nominally starting out with 0.5 mm Pb (0.09 rad len). So
>>>>adding/replacing with another material of roughly the same
>>>>thickness in
>>>>rad lengths is reasonable. This corresponds to 8 mm of Al and 1.6
>>>>mm of
>>>>Fe (i.e. stainless). This is somewhat thinner than what we were
>>>>considering this morning, but I wanted to get your feedback on how
>>>>useful
>>>>this would be.
>>>>
>>>>If Al is chosen, it was additional advantages. First it will be
>>>>relatively
>>>>thicker, so attachments are easier. Also, it may be possible to
>>>>groove the
>>>>Al sheet, which might allow us to replace the first layer of Pb and
>>>>therefore increase the amount of backing structure. Finally,
>>>>machining Al
>>>>along with the rest of the pyramid should be very straightforward.
>>>>
>>>>Let me know what your thoughts are regarding Al/Fe before I run
>>>>this by
>>>>our Regina friends.
>>>>
>>>>Thanks, Elton.
>>>>
>>>>
>>>>Elton Smith
>>>>Jefferson Lab MS 12H5
>>>>12000 Jefferson Ave
>>>>Suite # 16
>>>>Newport News, VA 23606
>>>>elton@jlab.org
>>>>(757) 269-7625
>>>>(757) 269-6331 fax
>>>>
>>>>
>>>>
>>>---
>>>Dr. Zisis Papandreou | email: zisis@uregina.ca
>>>Department of Physics | tel. : (306) 585-5379
>>>University of Regina | tel. : (306) 585-4149
>>>Regina, SK S4S 0A2 | fax. : (306) 585-5659
>>>World Wide Web: http://www.phys.uregina.ca/sparro/zisis/
>>>
>>>
>>>
>>>
>>>
>
>
>
>