SPI surface finish standard were defined by the society of plastics industry INC( now it is changed to plastics industry association), which helps part engineers, mold designers, and mold manufacturers have the same understanding of the surface finish.
| Finish | SPI standard | Finish method | Surface finish roughness(Ra um) | Surface finish roughness (Ra micro inches) |
|---|---|---|---|---|
| Super High Glossy finish | A-1 | Grade #3, 6000 Grit Diamond Buff | 0.012- 0.025 | 0-1 |
| High Glossy finish | A-2 | Grade #6, 3000 Grit Diamond Buff | 0.025 to 0.05 | 1-1 |
| Normal Glossy finish | A-3 | Grade #15, 1200 Grit Diamond Buff | 0.05-0.1 | 2-3 |
| Fine Semi-glossy finish | B-1 | 600 Grit Paper | 0.05 to 0.10 | 2-3 |
| Medium Semi-glossy finish | B-2 | 400 Grit Paper | 0.10 to 0.15 | 4-5 |
| Normal Semi-glossy finish | B-3 | 320 Grit Paper | 0.28 to 0.32 | 9-10 |
| Fine Matte finish | C-1 | 600 Grit Stone | 0.35 to 0.40 | 10-12 |
| Medium Matte finish | C-2 | 400 Grit Stone | 0.45 to 0.55 | 25-28 |
| Normal Matte finish | C-3 | 320 Grit Stone | 0.63 to 0.70 | 38-42 |
| Satin Textured finish | D-1 | 600 Stone prior to Dry Blast Glass Bead #11; 8" Distance at 100 psi; 5 secs | 0.80 to 1.00 | 10-12 |
| Dull Textured finish | D-2 | 400 Stone Prior to Dry Blast #240 Oxide | 1.00 to 2.80 | 26-32 |
| Rough Textured finish | D-3 | 320 Stone Prior to Dry Blast #24 Oxide | 3.20 to 18.0 | 190-230 |
Not every mold finish produces the same results with every material. Material properties also have impact on the injection molding surface finish that you can achive on a plastic part. The below table can give you recommendations about SPI surface finish for given plastic material.
Remark: A=Average G=Good E=Excellent N=Not recommended
| Material | A-1 | A-2 | A-3 | B-1 | B-2 | B-3 | C-1 | C-2 | C-3 | D-1 | D-2 | D-3 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ABS | A | A | G | G | G | E | E | E | E | E | E | G |
| PP | N | A | A | G | G | E | E | E | E | E | E | E |
| PS | A | A | G | E | E | E | E | E | E | E | E | G |
| HDPE | N | A | A | G | G | E | E | E | E | E | E | E |
| PA | A | A | G | G | E | E | E | E | E | E | E | G |
| PC | A | G | E | G | G | A | A | N | N | E | N | N |
| TPU | N | N | N | N | A | A | G | G | G | E | E | G |
| PMMA | E | E | E | G | G | G | G | G | G | A | A | A |
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