VACUUM · 316L · SEALING FACE
A chamber flange that stayed flat through passivation.
A Ø260 sealing face that has to stay flat through passivation. The classic failure is not the machining — it is the distortion nobody took out before the finish cut.
- Material
- 316L forged ring
- Size
- Ø260 × 32 mm
- Flatness
- 0.01 mm
- Finish
- Passivated, Ra 0.4
- Process
- Turn-mill + surface grind
- Inspection
- CMM + flatness report
- Typical lead time
- 10–15 working days
- Typical quantity
- 1–20 pcs
Representative program — figures are typical for this part class, not a specific customer record. Machined at a partner shop we manage; we don't own the machines.
THE PROBLEM
Within tolerance, and still leaking.
The incoming batch met its dimensional drawing. It still failed the leak test, because the flange had been machined from plate in two setups and sent straight to passivation — with no stress relief and no grinding operation.
- Face was 0.03 mm out of flat by the time it reached the seal
- Bolt circle torque pulled the part into a different shape
- Plate stock carried residual stress the drawing never mentioned
| Flatness | 0.01 mm |
|---|---|
| Surface finish | Ra 0.8 µm |
| Bolt circle | 12 × Ø9, position Ø0.05 |
| Material | 316L, mill cert required |
| Finish | Passivation, no coating |
WHAT WE DID
Five operations, one of them the whole job.
The fix wasn't tighter tolerances — it was moving the distortion upstream of the finish cut and keeping one datum from start to seal.
- 1
Forged stock, not plate
316L ring blank with mill certificate, chosen for lower residual stress than plate.
- 2
Rough + stress relief
1.5 mm of stock left on every face, then a stress-relief cycle before finishing.
- 3
Finish from one datum
OD, bore and bolt circle machined in one setup so the seal face and bolt pattern share a datum.
- 4
Grind the seal face
Surface ground after machining — the only way to hold a sealing face at this level once the part is released.
- 5
Passivate, then measure
Nitric passivation with no material removal, then CMM and flatness check on the finished part.
INSPECTION & DOCUMENTATION
The report is part of the part.
A flatness number with no measurement method is a rumour. Every batch ships with the method, the instrument and the datum stated.
- Flatness checked on a granite plate, reported per part
- CMM report with datum scheme on the drawing
- Ra measured on the sealing face, not the OD
- 316L mill certificate traced to heat number
- Passivation certificate with bath and batch reference
WHAT THIS ROUTE GIVES YOU
Flatness that survives the last operation.
On this route we'd quote 10–15 working days for a batch of six, against OEM lead times usually measured in months. The rough–relieve–finish–grind sequence applies to every stainless sealing face we quote — the drawing rarely needs to change.
- Flatness measured on a granite plate before shipment
- Distortion removed before the finish cut, not after
- Bolt circle and seal face share one datum
Have a sealing face that keeps moving?
Send the drawing and tell us how it failed last time. That's usually the most useful line in the RFQ.