UHV Vacuum Chamber Parts Fabrication and Cleanroom Assembly
For UHV vacuum chamber parts fabrication, Aerospace Sourcing matches your drawings to qualified machine, weld, cleaning and leak test suppliers, flows down materials, venting, cleanliness and packaging rules, and checks the leak test and cleaning records before delivery. Send drawings, material callouts, flange standard, pressure target, cleaning level and bake temperature.
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What UHV vacuum chamber parts fabrication involves
UHV vacuum chamber parts fabrication means vacuum compatible machined parts and weldments: ordinary precision work held to rules that ordinary shops do not follow by default: no zinc bearing alloys, no trapped volumes, no cutting oil left in a thread, welds made from the vacuum side, and parts cleaned, leak tested and bagged before anyone touches them with a bare hand. Most failures in vacuum hardware trace back to one of those rules being left off the drawing or the purchase order.
The buyers who send us this work are research labs, university groups, national facility users and space test facilities building thermal vacuum chambers, beamline components, detector housings, feedthrough plates, cryostat parts and fixtures that go inside a chamber. Some want one weldment, others a cleaned and assembled subassembly.
We are a sourcing service. We do not run machines, cleaning lines or cleanrooms. We place each step with a supplier qualified for it, write the vacuum rules into every purchase order, and check the records before the hardware ships. If the hardware is for a grant funded project, our research labs and universities page covers purchasing thresholds and export questions.
Vacuum compatible materials
Choose materials with a low outgassing rate and no high vapor pressure constituents. Austenitic stainless steel, aluminum alloys such as 6061, oxygen free high conductivity copper and titanium cover most UHV hardware. Zinc, cadmium and lead, and alloys containing them such as brass, are excluded.
The guidelines DESY publishes for UHV components (Vacuum 005/2008, version 1.6) list aluminum, copper, molybdenum, tantalum, titanium and tungsten as compatible pure metals, name preferred stainless types by EN number (1.4429, 1.4435 and 1.4404), and list copper beryllium, Inconel 600 or 718, tin bronze and ceramics such as alumina, Macor and sapphire as acceptable. Zinc, cadmium, lead and alloys containing zinc or lead are listed as incompatible, along with most organic materials. A LIGO design note citing O'Hanlon's vacuum text adds phosphorus, selenium and sulfur to the excluded list, while noting that trace amounts are tolerated, so 6061 with up to 0.25 percent zinc is considered acceptable. That rule is why free machining grades that rely on sulfur, selenium or lead are a poor choice for vacuum parts.
| Material | Where it fits | What to watch |
|---|---|---|
| 304L stainless | Chamber bodies, ports, brackets | Higher hydrogen outgassing than treated alternatives in NIST's comparison |
| 316L and 316LN stainless | Chambers needing vacuum firing or low magnetism | 316LN is the least magnetic of the grades NIST compared; cost |
| 6061 aluminum | Lightweight chambers, plates, fixtures | Aluminum CF flanges need aluminum gaskets |
| OFHC copper | CF gaskets, thermal straps, RF parts | Specify grade and temper |
| Titanium | Low outgassing chambers, non-galling screws | Machining cost, weld shielding |
A NIST study compared seven geometrically similar chambers. Titanium, aluminum and vacuum fired 316L and 316LN chambers all reached specific outgassing rates below 1 x 10^-11 Pa L s^-1 cm^-2, a factor of 100 or better than the 304L chamber, and the authors note 316L is typically chosen for vacuum firing because it resists softening during the cycle. DESY's guidelines call for vacuum firing stainless at 950 °C when hydrogen outgassing must be reduced. If you need that, it changes the material, the flange grade and the routing, so say so at quote.
Polymers, adhesives, potting and lubricants need outgassing data. ASTM E595 holds a sample at 125 °C for 24 hours below 5 x 10^-5 torr and reports total mass loss (TML) and collected volatile condensable materials (CVCM). The standard notes that 1.00 percent TML and 0.10 percent CVCM have been used as screening levels for spacecraft materials, and NASA Goddard's outgassing database reports E595 results by product. Look up the exact grade and color, not the generic polymer. Plastics are covered in more depth on our engineering plastics page.
Have a part like this?Send it in under a minute. A person replies within 1 business day.CF and KF flange standards
Use CF (ConFlat style) metal sealed flanges for UHV and bakeable joints, and KF quick clamp flanges for roughing lines and joints that are opened often. Put the standard and size on the drawing, not just the word flange.
| Family | Standard | Seal | Use |
|---|---|---|---|
| CF | ISO 3669 covers DN 16 to DN 250; ISO/TS 3669-2 extends to DN 10 to DN 400 | Knife edges bite a flat OFHC copper gasket | UHV, bakeable joints |
| KF (ISO-KF) | ISO 2861 and DIN 28403 | Elastomer O-ring on a centering ring with a clamp | Rough and high vacuum, fast assembly |
| ISO-K and ISO-F | ISO large flange families | Elastomer seal, clamped or bolted | Large ports where bakeout is not needed |
Details that trip up fabricators:
- Above DN 250 there is no single CF standard, and manufacturers' large flanges differ. Name the flange maker's drawing or catalog number for large ports.
- Pfeiffer Vacuum cites CF bakeout to about 450 °C, while other makers rate their fittings lower. Elastomer sealed KF and ISO joints cannot follow.
- Silver plated copper gaskets are recommended where bakeouts are frequent. Aluminum CF flanges need aluminum gaskets.
- Rotatable versus fixed flanges, tapped versus through holes, and the clocking of bolt holes relative to other ports all need to be stated. A port welded at the wrong clocking is a scrapped weldment.
- A scratched knife edge will not seal. Ask for protective caps from machining onward.
Vented screws, trapped volumes and welds
Every trapped volume is a virtual leak. Design it out, and where a blind hole cannot be avoided, use a vented screw or a vent path so gas can escape.
- Blind tapped holes trap air under the screw tip. Use vented screws, a cross drilled vent, or a through hole. Commercial vented UHV screws are offered in 18-8 stainless rated to 450 °C by at least one maker. DESY's guidelines ask for venting holes in screws and pins wherever possible.
- Stacked or lapped surfaces, such as a plate bolted flat to a flange, trap gas between faces. Add relief grooves or standoffs.
- Welds belong on the vacuum side only, with full penetration. Where a weld must be made from outside, DESY requires the interior to be purged with inert gas. TIG, MIG, plasma, electron beam and laser welding are listed as acceptable.
- Brazing is done in vacuum or a shielding gas without flux, and the filler metal is approved by the user in advance.
- Water to vacuum boundaries may not be formed by a single brazed or welded joint under DESY's rules.
- Screws inside cleanroom assemblies should be unlubricated and uncoated types that do not cold weld, such as titanium screws in stainless parts, per DESY's particle free guidance.
Machining and surface finish
Machining for vacuum is about what is left on the surface, not just the dimension. Specify how coolant, tooling and surface treatments are controlled.
DESY's guidelines are a good template even outside accelerators. Any machining after cleaning must be approved in advance, uses isopropanol as the only cooling fluid with new cutting tools, and standard cooling lubricants and cutting oils are not allowed. Surface treatments such as glass bead blasting or electropolishing must also be approved before use.
On the drawing, give a surface finish for sealing faces and vacuum side surfaces, call out whether electropolish is required, and forbid anodize and plating inside the vacuum unless engineering has approved a specific coating. DESY's plating guidance, for instance, requires copper plating on stainless to survive ultrasonic cleaning and a one hour, 300 °C vacuum heat test without blistering or peeling.
Precision cleaning, cleanroom class and bagging
Specify a cleaning process, a verification method and the packaging, and specify the cleanroom class separately. A cleanroom class describes the air in the room, not how clean your part is.
A typical UHV cleaning flow, as DESY describes it: high pressure prewash, ultrasonic cleaning in hot deionized water with a detergent matched to the material, thorough hot deionized water rinse, and drying in a low dust, hydrocarbon free gas stream such as dry nitrogen. After cleaning, no oil or grease may touch the part, even for leak tests, flanges are wiped with isopropanol only, and vacuum surfaces are handled with clean lint free gloves.
ISO 14644-1:2015 classifies cleanroom air by particle count. A few reference points from its table, as maximum particles per cubic meter at 0.5 µm and larger:
| ISO class | Particles at 0.5 µm and larger, per m³ |
|---|---|
| ISO 5 | 3,520 |
| ISO 6 | 35,200 |
| ISO 7 | 352,000 |
| ISO 8 | 3,520,000 |
Particle free UHV parts in DESY's scheme are cleaned in an ISO 6 or better room, dried in air better than ISO 5, checked for particles in ISO 5 or better, and assembled in the specified class. Packaging follows the same logic: vessels are back filled with dry nitrogen and closed with blank flanges or polyethylene film, knife edges get covering caps, small parts are sealed in polyethylene, and particle free parts go in two layers of antistatic polyethylene. Aluminum foil is not permitted for particle free packing. Movable parts such as bellows and rotatable flanges are fixed for transport.
Oxygen service and fluid system cleanliness levels are a separate topic, covered on our precision and oxygen cleaning page and the cleaning reference.
Helium leak testing and acceptance records
Every UHV weldment and sealed assembly should be helium leak tested against a stated limit, with the method and detector sensitivity recorded. Without a number on the order, a leak test result has nothing to pass against.
- ASTM E498 covers the mass spectrometer leak detector in tracer probe mode: the part is evacuated and helium is sprayed on the outside. It applies to leaks of 1 x 10^-8 Pa m³/s (1 x 10^-9 std cm³/s) or greater.
- ASTM E499 covers the detector probe or sniffer mode, with the part pressurized with tracer gas. It applies to leaks of 1 x 10^-7 Pa m³/s or greater and is better for finding leaks than for sizing them.
DESY's acceptance limit for UHV components is an integral leak rate of 1 x 10^-10 mbar l/s, with the detector's sensitivity verified against a calibrated test leak first. Its rules also require welds that will be hidden after assembly to be tested before assembly, parts that are vacuum fired or baked to be tested before and after the thermal cycle, and final tests to be made with metal gaskets. For hydrocarbon cleanliness, DESY uses a residual gas analyzer: the part must reach below 10^-7 mbar total pressure, with the sum of partial pressures from mass 45 to at least 100 below 10^-3 of the total. Your lab may set different numbers. The point is to set them.
Ask for a leak test report that names the method, the detector, the calibrated leak used, the background, the limit and the result, tied to the part serial number.
Pressure, cryogenic and safety review
A vacuum chamber is also a pressure boundary when it is vented, backfilled or cooled. Check your institution's rules before you order.
Whether a chamber or dewar has to be designed and stamped to a pressure code depends on its pressure, contents and the authority having jurisdiction, so ask your environmental health and safety office. Viewports, bellows and feedthroughs are usually bought from vacuum component makers and integrated, rather than fabricated. Our research hardware reference covers pressure and cryogenic considerations in more detail.
What drives cost and lead time
Vacuum hardware costs more than the same geometry in air service because of welding, cleaning, testing and handling. We do not publish prices or promise lead times.
- Material availability, especially 316LN, OFHC copper in thick sections and vacuum melted grades
- Weld procedure, weld from the vacuum side, and inert gas purging
- Vacuum firing or bakeout as an added step
- Cleaning and cleanroom assembly class
- Leak test sensitivity and residual gas analysis
- Packaging and transport restraints for large weldments
What to send with your request
Send enough for a supplier to judge the vacuum rules on first read.
- Drawings and models at the current revision
- Material callouts by specification, with any forbidden materials
- Flange standard, size, type and port clocking
- Base pressure target and maximum bakeout temperature
- Venting requirements for screws and blind holes
- Weld and braze requirements, and whether vacuum firing is needed
- Cleaning process, cleanroom class for assembly, and packaging
- Leak rate limit, test method and any residual gas analysis requirement
- Quantity, need date and export control status
Export controlled drawings should not go through the web form. Our confidentiality page explains how to send them, and our aerospace CNC machining and space test lab time pages cover the machining and the thermal vacuum testing that often follow.
How Aerospace Sourcing handles vacuum hardware
We match each step to qualified suppliers and keep the job on one purchase order. That means one quote, one lead time and one point of contact, even when machining, welding, cleaning and leak testing happen at different suppliers. We flow down your material, venting, cleaning, packaging and leak test requirements, check the records against the order, and ship with a certificate of conformance plus the cleaning and leak test records you require. A person replies within one business day.
Request vacuum or cleanroom hardware
Use the cleaning and cleanroom request form. It is preset for cleaning work, so it asks for the cleanliness level, packaging and test requirements that decide which suppliers can take a UHV job.
Send the job. A person replies within 1 business day.
Part, quantity and date are enough to start. Drawings and the mutual NDA follow by reply, and controlled programs never send technical data through this site.
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Questions
Can 304 stainless be used for UHV chambers?
Yes, 304L is common for chamber bodies and ports and reaches UHV with proper cleaning and bakeout. A NIST comparison of seven similar chambers found untreated 304L, 316L and 316LN had higher hydrogen outgassing than titanium, aluminum and vacuum fired 316L or 316LN, which were a factor of 100 or better than 304L. If your target pressure is very low, consider 316L and vacuum firing. Avoid free machining grades that add sulfur or selenium.
What leak rate should I put on a UHV purchase order?
Use the number your system design needs. As a reference, DESY's guidelines for UHV components require an integral leak rate of 1 x 10^-10 mbar l/s, measured with a helium leak detector verified against a test leak, and final tests made with metal gaskets. ASTM E498 covers tracer probe testing for leaks of 1 x 10^-8 Pa m³/s or greater. Put the limit, method and required report contents on the order.
Why do UHV parts need vented screws?
A screw in a blind tapped hole traps a small pocket of air under its tip. That gas leaks out slowly through the threads and looks like a leak that never goes away, called a virtual leak. Vented screws have a hole drilled through their length so the pocket pumps out with the chamber. Where a vented screw is not possible, use a through hole or a cross drilled vent in the part.
Does ISO 5 cleanroom assembly make my part clean?
No. ISO 14644-1 classifies the air in the room by particle count, for example 3,520 particles per cubic meter at 0.5 µm and larger for ISO 5. Part cleanliness depends on the cleaning process, rinse, drying and packaging. Specify both: the cleaning method and verification for the part, and the room class for drying, inspection and assembly. Packaging should keep the part clean until it is opened in your own controlled area.
How do I check whether a plastic or adhesive is vacuum compatible?
Look up the exact product and grade in NASA Goddard's outgassing database, which reports ASTM E595 results. The test holds a sample at 125 °C for 24 hours in vacuum and reports total mass loss and collected volatile condensable materials. ASTM notes that 1.00 percent TML and 0.10 percent CVCM have been used as screening levels for spacecraft materials. Your own system may need tighter limits.
Should I use CF or KF flanges?
Use CF flanges with copper gaskets for UHV and any joint that will be baked, since the metal seal tolerates high bakeout temperatures. Use KF flanges, which seal with an elastomer O-ring on a centering ring and a clamp, for roughing lines, gauges and joints that are opened often. Mixing them on one chamber is common, and adapters between the families are standard catalog items.
Related
Sources
- DESY: Guidelines for UHV-Components, Vacuum 005/2008, version 1.6 (2010)
- NIST study via arXiv: outgassing rate comparison of seven geometrically similar vacuum chambers
- LIGO technical note T080106: vacuum compatible alloy constituents
- Pfeiffer Vacuum know-how book: CF flange and ISO 3669
- Wikipedia: vacuum flange families (KF, ISO-K, ISO-F, CF)
- Accu-Glass Products: vented UHV fasteners
- ASTM E595 outgassing test method
- NASA Goddard outgassing database
- Cleanroom.net: ISO 14644-1:2015 classes of air cleanliness by particle concentration
- Nimonik: ASTM E498/E498M tracer probe mode leak testing
- Nimonik: ASTM E499/E499M detector probe mode leak testing
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