- ▸Seal face flatness is typically 0.0009 mm (within 3 light bands under He-Ne monochromatic light) — about two orders of magnitude finer than a rough-lapped blank
- ▸The chain has three stages: rough lapping sets geometry (removing 0.1-0.5 mm), fine lapping achieves flatness, polishing brings roughness to the Ra 0.1-0.2 μm class
- ▸Cast iron lapping plates dominate for graphite fine lapping; grooved plates distribute slurry and clear swarf
- ▸Slurry and abrasive (SiC or diamond micro powder) are refined stage by stage, ending at W1-W3 grades
- ▸Flatness is checked with an optical flat under monochromatic light by counting bands, and band distortion must be read as convex or concave
- ▸The environment makes the data trustworthy: temperature control and cleanliness discipline are prerequisites for 0.0009 mm
The seal face is the highest-precision surface in the whole sealing system: 0.0009 mm flatness means holding surface deviation to a small fraction of a human hair. No single operation gets there — a process chain does.
I. Why 0.0009 mm
The faces seal by conformal contact with a sub-micron liquid film between them. Beyond the light-band requirement the contact zone breaks up, the film cannot hold, and leakage rises. Engineering metrology uses interference fringes: one light band corresponds to half the light wavelength, about 0.0003 mm, so 3 bands means within 0.0009 mm.
II. The Three-Stage Chain
Rough Lapping: Set Geometry
Blanks after impregnation and curing carry 0.1-0.5 mm of face allowance. Coarse abrasives here target geometry, not precision — parallelism and thickness brought into fine-lap allowance quickly.
Fine Lapping: Achieve Flatness
1.Equipment: flat lapping machines, rings in carriers moving in planetary motion
2.Plate: cast iron, grooved — grooves spread slurry and evacuate swarf, preventing local heat
3.Abrasive: SiC or diamond micro powder, grade refined step by step
4.Parameters: pressure and speed matched to plate and ring size; excessive pressure rounds the edges
Polishing: Bring Roughness Down
The final stage uses W1-W3 micro powder for a soft polish to Ra 0.1-0.2 μm, removing micro-scratches left by fine lapping — micro-scratches are early leakage paths.
III. Slurry and Plate Management
1.Slurries are typically water-based with rust inhibitors; viscosity and concentration control abrasive distribution
2.Plates are reconditioned regularly — plate flatness is copied directly onto the workpiece; a non-flat plate cannot make flat rings
3.Incomplete swarf cleaning lets coarse particles scratch faces in the next, finer stage
IV. Flatness Inspection: Monochromatic Light and Optical Flat
1.Press the optical flat onto the face, illuminate with monochromatic light, count the fringes
2.Straight bands under 3: pass; bent bands: height deviation — determine concave or convex and re-lap
3.The interface must be dust-free; a single dust particle produces a false band
Huahao Sealing completes the full lapping and polishing chain at its Lu'an, Anhui plant, inspecting every ring under monochromatic light and recording band counts. 0.0009 mm is not a machine setting — it is process discipline: plate reconditioning, abrasive changes, cleanliness. Miss any link and the precision never lands.