Choose the finish by what it is for
Specify surface finishing by the protection, appearance and interface requirements of the finished part, then agree treatment, thickness, masking and inspection condition before production. A finish chosen for corrosion protection will not necessarily give the appearance a product needs, and the reverse.
| Finish | What it gives | Watch on a casting |
|---|---|---|
| Anodising | Hard, corrosion-resistant conversion layer, clear or dyed | Result depends on alloy chemistry; high-silicon die casting alloys anodise grey and uneven; cosmetic parts need surface preparation |
| Powder coating | Durable colour and weather resistance | Forgiving on surface variation; curing heat can raise blisters on gas-bearing castings; agree film thickness and edge and hole coverage |
| Wet painting | Colour match, texture, thin coating | Adhesion depends on preparation |
| Blasting | Uniform matte texture | Usually a preparation step; mask sealing faces and threads |
| Chrome or nickel plating | Bright, hard surface | A plated casting shows every surface defect underneath |
| Machined finish only | Controlled surface on machined faces | As-cast surfaces left unfinished or sealed |
What the drawing should state
| Specification | Define |
|---|---|
| Appearance | Colour reference, gloss, permitted cosmetic variation, surfaces evaluated, viewing distance |
| Protection | Service environment; corrosion test method, exposure and pass/fail |
| Functional areas | Masking of sealing lands, electrical contact, threads, fitted bores |
| Dimensions | Coating allowance; which dimensions apply after finishing |
| Roughness | Ra on machined faces where sealing or fit needs it |
A finishing requirement without an acceptance standard leaves the result open. Use a coating specification and an approved sample when appearance matters, and draw the masking boundaries instead of a general note.
Sequence with machining, impregnation and leak test
Finish after the operations that change the surface: machining, impregnation if permitted, and the leak test that counts. Blasting and coating can close a fine leak path temporarily, so a leak test on a coated part answers a different question than one before coating. Agree which test is the release test.
Finishing in our plant
Blasting (tumbling and hanging shot blast, handheld sandblasting), vibration tumbling, grinding, polishing and ultrasonic cleaning are done in-house. Our published parts include powder-coated components.
