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Re: comments to the draft Pb specifications



Sounds good to me.

Just one more fact...

I have measured the BCAL wedge that is here at jlab. It measures approx. 1.21 mm per layer. For the matrix height on the current dwg. (22.18cm) we would have 183 layers.

George, would the 1st layer of lead against the aluminum plate be swaged? It appears the BCAL sample here at JLAB has a swaged piece and the hollows just fill with epoxy. There is 1 fiber used to orient the 1st lead layer. Is that the plan?

Thanks,

       Tim

George Lolos wrote:
Hi Elton:

Your proposal makes a lot of sense.  Zisis will be back at the office on
August 28th and given the amount of work he had put into writing a BCAL
dimensions document and the calculations of radiation length, I suggest
that it's best we wait until he can participate and we do the final
exercise only once but with all the facts in front of us.

Cheers,

George

  
Elton Smith <elton@jlab.org> 08/12/08 11:13 AM >>>
        
HI George,

As we move into construction, we will need to firm up all the numbers
that
define the Bcal geometry, some critical to physics, others simply for
proper integration into the overall detector. But all of these MUST be
incorporated into the drawing package. This will be the definitive
source
for all dimensions. It is the only way we will be able to make sure that
all work, integration, documentation, definitions for interfaces, etc
are
consistent. Therefore, I urge you, Zisis and everyone else to review
what
is presently in the drawings and send me and Tim comments and
corrections.

Again, you can find the drawings at
http://www.jlab.org/Hall-D/reviews/Lehman-2008/Pre-Brief_Material-HallD/CD3_DRAWING_PACKAGE/01.DETECTOR/07.barrel.calorimeter.pdf
These were presented at the Bcal review as well as Lehman, etc. They
repreent the present "nominal" plan, but again updates and changes are
welcome as we add more details to the 3-D model. It is not practical to
keep updating the drawings daily, but they do need to be brought
up-to-date for various milestones, such as the Bcal review. Changes
should
go through both Tim and I with Elke in the loop. I suggest we spend a
little time at the next working group meeting (Monday) to review the
procedure for this.

Once we all agree on the dimensions, we can use the drawings for
reference, without having to rely on our aging gray cells.


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

On Tue, 12 Aug 2008, George Lolos wrote:

  
Hi Tim:

The number of 65 cm to 90 cm was originally meant to accommodate the
matrix only, resulting in the original 25 cm of matrix thickness. 
    
This
  
was later reduced to 23.5 cm plus the 2.54 cm of Al plate bringing the
total thickness to 26 cm.  I never recall a different thickness and
    
all
  
our plans were for the 200 layers, including the construction reports
and calculations for materials.

I have stated in writing that gluing the innermost Al plate on to
    
fibers
  
is not a good idea.  Instead, I insisted that the Al plate should be
glued on the last Pb sheet because the bond with the fibers will not
    
be
  
as strong and shear stresses can shift the fibers.  The innermost Al
plate should be glued with industrial epoxy (the same we use to glue
    
the
  
base Pb sheet on the base Al plate) on the last Pb sheet.

Construction-wise, whether we go for 188 layers or 200 layers has a
minimal effect on construction times so there's no issue on this.  The
difference is approximately one radiation length and we had already
reduced it from the early design of 25 cm of matrix.  Perhaps someone
can simulate the new thickness and if it has no effect on physics,
    
let's
  
go with 188 layers.

George


    
Tim Whitlatch <whitey@jlab.org> 08/12/08 6:33 AM >>>
          
Good morning all,

Here is my take. Addressing the issue of the number of
layers............

We are currently using 22.18 cm of matrix in each wedge. We have an
    
8mm
  
al plate on the inside to take the place of 1 layer of lead (radiation
length)(see drawing D00000-07-1008 from the link Elton supplied) We
    
also
  
have a 1.25" thick aluminum plate on the outside for structural and
mechanical reasons. This increased from 1", but only towards the
    
outside
  
thus not changing the matrix qty. Looking back at documents as far
    
back
  
as 2004, the OD is 90cm and ID is 65cm. Subtracting the 2.54cm for the
outer aluminum plate, we get 22.46 cm of matrix. I do not recall a
    
time
  
since I have been involved that we had 23.5 cm of matrix. Removing 1
layer of lead on the inside for the 8mm aluminum plate gives us 22.41
cm. Another 1.5 mm removed because the outer al plate is flat yields
22.26 (very close to our current 22.18 cm). So 221.8 mm divided by
    
1.18
  
pitch yields 187.9 layers. Let's make it 188.

I am in agreement with George that consistency of the swaging is what
    
is
  
important here. If there is documented problems with the alloyed
versions of the lead, we should go with the 99.98% pure. Does this
increase the cost significantly?

Cheers,

       Tim

George Lolos wrote:
    
Hi Elton:

I will address comments to your comments on my comments, below :-)

On 11-Aug-08, at 3:14 PM, Elton Smith wrote:

      
On Mon, 11 Aug 2008, George Lolos wrote:

        
Hi Elton and Elke:

I went over the draft for the lead and I have some comments:

1.  The purity, as I wrote last Friday, is 99.98% (known as "pure
          
lead"
    
and "non-Cu alloyed")
          
I will add this to the specs.

        
2.  The amount of lead required should be based on 200 layers per
module
NOT 187.  The 200 layers will give us the ~23.5 cm of matrix.
Therefore, the no-waste number is 9600 strips.   This is the "base
number" and the total mass of lead should be based on that number.
Also, the minimum width we start with for the base layers is 13 cm
          
not
    
12cm.  After machining the base width is 11.8 cm.

          
The current drawings for the Bcal call for 187 layers of lead. See
        
p.
  
8 of

        
http://www.jlab.org/Hall-D/reviews/Lehman-2008/Pre-Brief_Material-HallD/CD3_DRAWING_PACKAGE/01.DETECTOR/07.barrel.calorimeter.pdf
  
If this is not correct, we need to update the drawings accordingly.

        
Frankly, why the number of 187 layers has persisted so long, while
      
it
  
is not right for the final module of 23.5 cm, I don't know.  I have
corrected it in the various submissions I have made but it survives
unscathed.  It should be corrected and the rough calculation here
proves I am right :-)

23.5 cm matrix thickness/ 1.18 mm/layer = 199 and with the lead
      
being
  
the topmost sheet makes it 200.   Whether is a little over or under
200, 187 it's not.



      
So, I would have 9600 sheets x 0.05 cm x 13 cm x 400 cm x 11.2
          
gr/cm3 =
    
28 metric tons of lead (no waste).  Please check my calculations
          
again
    
but I believe they are correct.
          
Note that this number needs to be very precise, but for the sake of
consistenty, we should use the same number for the density of Pb.
From the
PDG the density is 11.35 g/cm3. Does the "purity" result in a
        
different
    
number?

        
You're correct.  The density of lead is 11.35 g/cm3, I used the
      
wrong
  
number.  This is the density of lead of purity we want.




      
While the Modules 1 and 2 were built with lead we received in
          
rolls,
  
the
latest shipment of lead was in sheets and Paul See from Vulcan
          
told
  
me
    
that most likely the shipment will also be in sheets, no rolls. 
          
In
  
order to reduce waste as much as possible, we should specify
          
desired
  
width for either rolls or sheets and desired length per sheet for
          
the
    
latter.  So, for length, we require an integer multiple of 400 cm
          
and
    
for width an integer multiple of 13 cm as optimum.
          
The request for rolls comes from your initial "specification"
        
document.
    
Please take a look at the document and make corrections to it so
        
that
  
we
    
put down what we want to request from the vendor. For example, the
original request indicates that standard rolls of 20" would suit
        
our
  
purpose. This seems to be a tad short, so do we ask for 13x4 = 52
        
cm,
  
or
    
how much extra is needed to account for cutting?

        
The reason I was quoting a "standard" roll is because I was led to
believe that that was indeed the case.   Of course, with the huge
amount we're going to order, "standard" is what we define.  One more
variable in the width definition is that with the step pyramid
      
design,
  
we have more flexibility in cutting strips off the roll or sheet.
So, even with 20" (50.8 cm) width, we can use all of it by
combinations of different width strips.  Give me some time to come
      
up
  
with a number and get back to you.

With rolls or sheets, but with rolls more subject to damage, the
      
edges
  
are often damaged in transport and handling and from our experience
that caused the most waste in the cutting operation as strips
sometimes as wide as 3 cm along the edges had to be sacrificed
      
because
  
of damage that could not be repaired.  Cutting by itself does not
really waste any lead and the only waste is due to damage, length
      
and
  
width mismatch.

If we have the luxury of receiving shipments in batches, even though
we place one order for a specific quantity, we can always adjust our
estimates on fraction of waste as we go along quite early in the
operation, once we know for sure how much we waste for one module
given the construction technique and the shipment format.


      
Let me know if this is fine and what further itterations we
          
require,
  
if
    
any.
          
We also need to think about a) what tests we require from the
        
vendor
  
and
    
b) what tests we intend to do ourselves, first for the
        
first-article
  
test
and second for routine acceptance of shipments.

Thoughts?

        
Well, if the vendor can screw up the certification for lead purity,
we're in deeper trouble than we could imagine.  I think too much hey
is being made about the purity of lead here.  A pure lead, according
to the industry standard, is fine.  As long as the lead is not
classified as "alloyed", we're fine.  So, I would say that from the
vendor we should require a certification of purity and we will
      
perform
  
our own tests of swaging and we can also spot check the lead for
softness (Brinnel number) to match that of tables for pure lead (I
think it's 5).

The ultimate judgement is: does the lead swage evenly or not, all
      
else
  
is irrelevant.


My two bits,

George
      
    

  
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tel;work:757-269-5087
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