ConFlat is the only flange family that reaches true UHV, and it does so with a copper gasket crushed by a knife edge. That puts the whole burden on two machined features: the knife edge angle and the bolt-hole pattern. Get either wrong and the flange leaks at a rate no gasket will compensate for.
How a ConFlat seal actually works
A soft OFHC copper gasket sits between two flanges. Each flange has a raised knife edge at 70° included angle. When the bolts are torqued the knife edge cuts into the copper, cold-welding locally and producing a metal-to-metal seal with no elastomer in the gas path. Because there is no polymer, the joint can be baked to 450 °C and the chamber can reach pressures an O-ring cannot survive.
The dimensions that decide whether it seals
Knife-edge included angle and edge radius; the flatness and surface finish of the gasket seating face; the bolt circle diameter and hole count; and the depth of the gasket recess. On a large flange the bolt pattern also has to be uniform, because uneven bolt loading tilts the knife edge and the leak appears on the opposite side.
Standard sizes and what we machine
CF flanges run from the small CF16 and CF35 used on gauge ports up to CF250 and beyond on large chamber doors. We machine standard sizes to the published dimensions and also produce non-standard sizes and port geometries where the chamber design demands them, including tubulated, rotatable and blank variants.
Materials
304L is the general-purpose choice and machines cleanly. 316L is used for corrosive process environments. 316LN is specified where magnetic permeability must stay low. The gasket is always copper for UHV — Viton and aluminium options exist for lower-temperature service but give up the bake-out capability.
ConFlat sealing characteristics
| Property | ConFlat (CF) | KF (NW) | ISO-K / ISO-F |
|---|---|---|---|
| Seal type | Copper gasket, knife edge | Elastomer O-ring | Elastomer O-ring |
| Typical pressure range | UHV, to ~1 × 10⁻¹³ Torr | Rough to high vacuum | Rough to high vacuum |
| Bake-out temperature | Up to 450 °C | ~150 °C (Viton) | ~150–200 °C (Viton) |
| Reusable | Gasket replaced each time | O-ring reusable if undamaged | O-ring reusable if undamaged |
| Assembly | Bolted, high torque | Clamp or claw | Bolted or clamp |
| Typical use | UHV chambers, beam lines, SEM | Foreline, roughing, service ports | Larger HV ports, pumps |
What we control in-house
- 304 / 316L stainless steel and 6061 / 5083 aluminium fabrication
- Clean-environment TIG welding with full penetration and no micro-porosity
- Helium mass-spectrometer leak testing to 1 × 10⁻⁹ mbar·l/s
- In-house electropolishing and passivation — not subcontracted
- Chamber bake-out to 150–400 °C for UHV outgassing control
- Precision-machined ISO-KF, ISO-K and CF (ConFlat) flanges
- Zeiss CMM verification to ±0.02 mm across large work envelopes
- 12 m gantry CNC machining — 12 m × 4 m × 2 m envelope
- SEMI-referenced documentation and inspection protocols
Frequently asked questions
What pressure can a ConFlat flange hold?
ConFlat joints are rated into the ultra-high vacuum range, commonly quoted as better than 1 × 10⁻¹³ Torr with a copper gasket. The limit in practice is the rest of the chamber, not the flange.
How much torque do ConFlat bolts need?
Enough to fully seat the knife edge in the copper, applied evenly and in a cross pattern. The exact figure depends on bolt size and gasket material — under-torquing leaves the knife edge partly embedded and produces a leak that appears only after bake-out.
Can a ConFlat gasket be reused?
No. The knife edge cold-works the copper, so a used gasket has the impression already formed and will not seal reliably a second time. Reusing one to save a few dollars is a false economy on a chamber that has to reach UHV.
How do I choose between CF and KF?
Use CF wherever the joint will be baked or must hold UHV. Use KF for roughing lines, gauge ports and anywhere the joint will be opened often — KF is far quicker to assemble and the O-ring can be reused, but it cannot be baked to UHV temperatures.
Do you machine non-standard CF sizes?
Yes. We machine standard sizes to published dimensions and also produce custom diameters, tubulated ports and non-standard bolt patterns where the chamber geometry requires it.
Related capabilities
Need this made to spec?
Send the drawing or the specification and we will come back with a DDP price, lead time and inspection plan.