This specification details the drawing notes to be used on PEP-II
vacuum drawings for parts and assemblies which are exposed to
the ultra-high vacuum of the PEP-II storage rings. These notes
are intended to replace references to SLAC FP-202-631-14-R4: "Fabrication
of UHV Components." They are intended to be used as needed,
following the guidelines given, and modified when necessary. This
will ensure that they are not just boilerplate verbage with limited
utility, but are actually useful notes which guide the fabrication.
In the bottom right corner of each drawing, above the bill of materials, show this UHV Part label. This will easily identify the part as an ultra-high vacuum part, and will mimic the label used by other groups which still use the FP-14 call-out.
Materials should be called out in the bill of materials, with
a reference to these material notes. Each of the notes below reference
an ASTM Specification for fabricating a type of material, and
contain the minimum information required by the Specification.
Typically, what is called-for is "industry standard,"
but the chemical analysis and mill certificates ensure that the
quality is good.
Copper: C10100-H02, Class 1 or 2 O.F.E.; made to ASTM F68-93 and B152-88. Mill source certificates, including heat number and chemical analysis must accompany part.
Stainless Steel Tubing: TP304 or TP316, seamless; made to ASTM A269-90. Mill source certificates required, including heat number and chemical analysis.
Stainless Steel Rect Tubing: MT304 or MT316, seamless; made to ASTM A511-90. Mill source certificates required, including heat number and chemical analysis.
Stainless Steel Pipe: TP304 or TP316, seamless or welded; made to ASTM A312-89. Mill source certificates required, including heat number and chemical analysis.
Stainless Steel Plate: 304 or 316, hot-rolled, annealed, and pickled; made to ASTM A480-90 or A240-90. Mill source certificates required, including heat number and chemical analysis.
Stainless Steel Sheet: 304 or 316, 2B finish, annealed; made to ASTM A480-90 or A240-90. Mill source certificates required, including heat number and chemical analysis.
Stainless Steel Rounds, Bar, Extrusions, and Struc Shapes: 304 or 316, annealed; argon-oxygen decarburized and electro-slag remelted, vacuum arc remelted, or vacuum-induction melted; made to ASTM A276-90. Mill source certificates required, including heat number and chemical analysis.
Stainless Steel-to-Aluminum Transition Material: Roll-bonded
3003 aluminum (0.5" thick), to 304 stainless steel (0.37"
thick). Mill sources certificates for both materials required.
These apply for general machining processes. Special notes may
be needed for special processes such as for EDM'ing or forming.
Knife-Edge Flanges: See SLAC Spec PS-341-475-04 for material requirements. Knife-edge must be free of all nicks and defects; protect at all times.
Machining: The use of polishing, sanding disks, abrasive paper, or grinding wheels is prohibited without prior approval.
Lubricants: Refer to SLAC Spec SC-700-866-47 for a list of
approved lubricants and coolants. Lubricants not on this list
must be approved by the SLAC engineer.
Any process involving heating the part or assembly should include instructions as to how the part can be heated. Welding and brazing processes should reference the appropriate note, and include the welding/brazing alloy, size of joint, and type of joint. Since these processes can be very specific for the parts to be joined, the notes should be modified to fit the appropriate application.
The idea is to specify as many of the important parameters as possible on the drawing, so there is less guess-work needed at assembly.
"High-Temperature Processing" may include baking, annealing,
or heat-treating. For the latter two, the specific thermal process
should also be noted, including temperature, times, and cooling
method.
Brazing: Braze in a dry hydrogen furnace. Cool to room temp in the furnace atmosphere.
Braze Alloy: Braze Temp: °C
Gas Tungsten Arc Welding: Weld preparation and cleaning with metal tools only (no abrasive grinding). Clean filler metals with alcohol. Use 99.95% pure, dry shield gases.
Filler Metal:
High-Temp Processing: Parts requiring heat treating above 300°C
must be processed in a dry hydrogen or inert atmosphere, or in
a clean oil-free vacuum furnace. Cool to room temp in the furnace
atmosphere.
During and after clean assembly of a non-recleanable assembly,
parts must be handled and stored in a clean environment. Use these
notes to call this out. These should be included for use at SLAC,
since they are not well-defined enough for use by an outside vendor.
If more detail is needed, there are SLAC Specifications for the
types of gloves, lint-free tissue, aluminum foil, and tote boxes
to be used.
UHV Handling: Handle UHV-clean parts with clean polyethylene and nylon gloves, in/on a clean room and surface. For storage or shipping, wrap parts in lint-free tissue and food-grade aluminum foil; store in clean tote boxes.
Leak Testing: Use a helium mass-spectrometer leak detector,
calibrated to 2 x 10-10 std cc/sec. Probe with helium
for 1 min and reject any part with a leak rate of 2 x 10-10
std cc/sec above background. Use of silicone grease is prohibited.
Notes should only be used if applicable. The idea is to use notes that are actually important, and leave out unimportant or inapplicable ones. This will minimize the verbage on the face of drawings, and give more weight to what is actually there.
Below is a list of typical drawing types, and the UHV notes which should be used on the drawing. Once again, notes may be omitted, or the content of the note may be altered to better match the particular drawing. However, these notes reflect good practice for UHV fabrication, so modifying them should be done with caution, by an engineer familiar with UHV design.
The notes called out refer to the notes described above.
Parts fabricated in-house or outside, which are re-cleanable.
Assemblies fabricated in-house or outside, which are re-cleanable, using a combination of fabricated parts or standard materials. These may include standard assembly methods such as brazing and welding, but should be designed so that they can be re-cleaned before use in its next assembly.
Assemblies fabricated in-house which cannot be re-cleaned. These must be assembled with clean parts, in a clean environment.
Notes used:
Assemblies which are fabricated and assembled clean by an outside vendor or collaborator and will be brought in and used as-is, should receive careful attention. Depending on the part, a special specification should be written, and the vendor inspected and qualified for UHV-clean work.
Clearly, some notes, such as material and machining call-outs,
still apply, but others, such as the UHV Handling notes, are not
defined enough to be used by a vender not familiar with SLAC's
UHV practices. This is why an additional specification may be
needed.