Technical insight
Aluminum Rotor Anodizing: Approve Masking and Finished Dimensions
If the released rotor design calls for anodizing, settle which surfaces receive it and when each dimensional requirement applies before machining starts. Ask the design authority to approve the coating definition and mask map, the machinist and anodizer to review the proposed allowance, and the designated quality reviewer to confirm the final evidence.
By Geetai Precision
- Published
- Updated
Start with an approved finishing definition
ASTM B580-25 covers electrolytically formed porous oxide coatings on aluminum and aluminum-alloy parts. Its public scope says particular purchaser-desired properties for modified coatings should be agreed between purchaser and manufacturer. That public description does not select the finish for a particular rotor. [3]
ISO 10074:2021 addresses hard anodic oxidation coatings and test methods; its public abstract also identifies information that the customer supplies to the anodizer. Neither a standard number nor a supplier acknowledgment completes the project definition. Obtain the contractually invoked document and edition. [5]
Request the approved alloy and condition, finish specification, coating thickness, sealing requirement, significant surfaces, masking and permitted rack-contact locations. Anoplate lists material, coating, dimensions, masking, racking and function-critical coverage among its requested part information. Use that as an input checklist, with unresolved choices returned to the design authority. [4]
Separate oxide thickness from dimensional allowance
Anoplate explains that anodizing converts aluminum into oxide, with both outward buildup and penetration into the original surface. The full oxide thickness therefore differs from outward dimensional growth. Its guidance also notes that pretreatment can remove aluminum before anodizing. [1]
Ask the machinist and anodizer to review the required finished size against the actual alloy, pretreatment and specified coating. Do not copy a general buildup ratio into the rotor drawing as an approved allowance. Identify the before-treatment manufacturing targets separately from the final acceptance dimensions. [1]
Make one decision for each surface
Anoplate describes selective masking to keep areas anodize-free, including areas requiring electrical contact or close dimensional control. Masking is a surface-definition decision to approve, rather than an automatic fix for every fit. [2]
| Drawing area | Route to review | Approval to record |
|---|---|---|
| Coated functional surface | Keep the required coating and review a machining allowance. | Design authority approves final limits; machinist and anodizer agree the proposed route. |
| Bore, locating face or contact area proposed for masking | Identify exactly where anodizing is prohibited and where coverage must resume. | Design authority approves the uncoated area and transition; anodizer confirms the proposed masking arrangement. |
| Datum target or inspection reference | Record whether the reference is coated or masked and at which stage it is used. | Design and inspection reviewers reconcile the reference condition with the final drawing. |
| Proposed cutting after treatment | Refer the affected surface and remaining coating requirement for review before alteration. | Design authority issues a disposition; quality reviewer defines the subsequent checks. |
This table is an editorial approval aid. Mark boundaries on controlled geometry, identify permitted transition regions and settle any conflict between coating coverage and mating requirements before releasing the affected operation. Do not infer those decisions from a colored screenshot alone.
Connect machining, treatment and final inspection
- Before cutting: reconcile drawing, model, finish note and mask-map revision; name the technical approver for unresolved surfaces.
- Before treatment: check the agreed manufacturing targets, part identity and mask instructions; obtain acknowledgment of coating and rack-contact requirements.
- After the specified treatment and sealing: check finished dimensions, required coverage and mask transitions using the agreed inspection plan. Link the treatment and dimensional records to the same identified parts.
- Before release: refer any dimensional or coverage discrepancy to the named reviewer. Retain the approved disposition and any required repeated checks with the delivery records.
For example, if a coated bore misses its final drawing limits and the proposed remedy is reaming, keep that proposal on hold. Ask the design authority to decide whether local coating removal is permitted and what must be checked afterward. Treat stripping and another anodizing cycle as a separate proposed route requiring review, rather than an automatic retry. This is a hypothetical purchasing decision, not a repair instruction.
Bring the open decisions to drawing review
Use this guide only where anodizing is already required by the approved design. Do not use it to select anodizing for a turbopump, establish vacuum suitability or authorize rotor operation. The cited finishing references do not qualify a particular rotating component for service.
For an authorized replacement inquiry, provide the released drawing and model, finish specification, proposed mask map, final-dimension stage and unresolved rework questions. Use the replacement-parts review route for the ordered component and discuss the required documentation through the inspection route.
Related review paths
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References
- The Impact of Anodize on Dimensions — Anoplate Corporation. Accessed 2026-10-26T05:11:31.501Z.
- Hardcoat Anodize — Anoplate Corporation. Accessed 2026-10-26T05:11:31.501Z.
- ASTM B580-25: Standard Specification for Anodic Oxide Coatings on Aluminum — public abstract and scope — ASTM International. Accessed 2026-10-26T05:11:31.501Z.
- Part Information Requirements — Anoplate Corporation. Accessed 2026-10-26T05:11:31.501Z.
- ISO 10074:2021 — Specification for hard anodic oxidation coatings on aluminium and its alloys — public abstract — International Organization for Standardization. Accessed 2026-10-26T05:11:31.501Z.