CNC Machined Stainless Steel Seal Ring
Seal rings machined from 316L stainless, with the sealing face lapped flat to 0.005 mm and finished at Ra 0.4 µm, square to the bore within 0.01 mm, a radial section held to ±0.03 mm and a bore at H7 and round to 0.01 mm. Each face is checked on an optical flat before packing.
- Lapped Face Flat to 0.005 mm
- Face Finish Ra 0.4 µm
- Radial Section ±0.03 mm
- Stress Relieved Before Lapping
*Send the mating ring drawing and the spring load. Face width and radial section set the balance ratio of the seal, and 0.05 mm on the width changes the pressure the faces see.
Stainless Seal Ring Overview
A mechanical seal ring is a flat face running against a carbon or silicon carbide mating ring. Its flatness is measured in optical fringes: one fringe across the face is about 0.0003 mm, and two fringes of waviness is enough to weep.
The ring is turned, bored and faced with stock left on the seal face, stress relieved, then lapped on a cast iron plate and checked on an optical flat before the drive slots are cut.
316L Stainless
316L is used because a seal ring sits in the process fluid and cannot corrode at the face. Its low carbon content also stops sensitisation if the ring is welded into a housing.
Silicon Carbide or 17-4PH
Silicon carbide is used for abrasive or high-duty seals where the face must not wear. 17-4PH is chosen where the ring also carries torque through drive slots and needs to be harder than 316L.
A seal face cannot be repaired once it is scored: 0.002 mm of wear is normal after a season, 0.02 mm means the faces ran dry and the ring is scrap.
Stainless Seal Ring Specifications
Turning and lapping data for seal seats, with the face, squareness and section values that decide whether a seal runs dry.
| Specification | Machining Data | Specification | Machining Data |
|---|---|---|---|
| Product | Seal Ring / Mechanical Seal Seat | Machining Process | CNC Turning, Lapping, Fine Boring |
| Material | 316L Stainless, Silicon Carbide on Request | Envelope | Ø 20 – 200 mm, Section 3 – 25 mm |
| Seal Face | Lapped Flat to 0.005 mm | Face Finish | Ra 0.4 µm, Ra 0.2 µm on Request |
| Face Squareness | 0.01 mm to the Bore | Radial Section | ±0.03 mm |
| Bore | H7, Roundness 0.01 mm | Outside Diameter | ±0.05 mm |
| Face Width | ±0.05 mm | Edge Break | 0.2 mm, Not on the Seal Face |
| Flatness Check | Optical Flat, One Fringe | Pressure Rating | 2.5 MPa Static |
| Customization | Drive Slots, Anti-Rotation Pin, Spring Seat, Groove | Lead Time | 6 – 9 Days Sample, 14 – 20 Days Batch |
| Inspection | Optical Flat, Surface Profilometer, CMM Squareness | Packing | Face Up, Foam Ring, Individually Boxed |
Key Features of Our Seal Rings
Lapped after stress relief, checked on an optical flat, serialised.
Lapped After Stress Relief
The ring is relieved between turning and lapping, so the face does not move after it has been made flat — the usual cause of a seal that weeps after a week in service.
Optical Flat Inspection
Every face is checked against an optical flat and released at one fringe, which is the only way to see waviness that a profilometer trace misses.
Face Square to the Bore
The seal face and the bore are machined from the same datum and checked at 0.01 mm, so the ring does not run at an angle and load one side of the mating face.
Drive Slots Cut Last
Slots and pin holes are cut after lapping, with the face protected, so no burr is raised on the sealing surface during the operation.
Seal that has to run without weeping?
Surface Finishes for Seal Rings
The seal face is the product and must stay bare; everything else can be cleaned or marked.
| Finish | Main Purpose | Finish | Main Purpose |
|---|---|---|---|
| Lapped Face | Sealing surface, no coating | Passivation | Clean 316L before assembly |
| Electropolishing | Removes lapping burr at the edge | Masked Face | No Coating on the Seal Face |
| Bead Blasting | Matte on the outside only | Laser Marking | Serial and face width |
| Coating Build | None on sealing faces | Ultrasonic Clean | Before Packing |
| Face Protection | Tape During Handling | Flatness Re-check | After Any Coating |
| Salt Spray | 720 h on 316L | Serial Marking | Traceable to Heat Number |
*No coating may touch the lapped face: 2 µm of plating changes the flatness by several fringes. Faces are taped through every subsequent operation and re-checked before packing.
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Machining Process for Seal Rings
The face is lapped after the ring is stress relieved, so it holds one optical fringe instead of relieving into a saddle a week later.
01. Seal and Spring Review
Check the mating ring, the spring load and the pressure, then set the face width and radial section from the seal design.
02. Turn and Bore
Turn the outside, bore to H7 and face with 0.15 mm left on the seal face, keeping the ring in soft jaws to avoid distortion.
03. Stress Relief
Relieve the ring and let it cool fully before lapping, so the face does not move after it is flat.
04. Lap the Face
Lap on a cast iron plate with graded abrasive, checking flatness on an optical flat between passes until one fringe is reached.
05. Cut Slots and Pack
Cut drive slots with the face protected, passivate, ultrasonically clean and pack face up in a foam ring.
Send the mating ring and the seal drawing, and we will quote a seat lapped to one fringe and serialised.
Stainless Seal Ring FAQs
One optical fringe, about 0.0003 mm, measured against an optical flat. Two fringes of waviness is enough for a seal to weep at low pressure.
Ra 0.4 µm as standard and Ra 0.2 µm on request. Below Ra 0.1 µm the face holds no fluid film and the seal runs dry and chatters.
Because turning leaves residual stress that moves the face after machining. A ring lapped straight off the lathe can go 0.01 mm out of flat within a week.
Yes, in carbon, silicon carbide or stainless, lapped to the same flatness and matched to the seal ring so the pair is supplied as a set.
They do on a large ring, so slots are cut symmetrically and the ring is checked for balance above 3,000 rpm. A single slot on a 150 mm ring shows as vibration.
Face up in a foam ring, individually boxed, with the face taped. A ring that slides face down in a box arrives with a scratched seal face and cannot be recovered.
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