What does an order for fine grain alone produce?

Answer: Most shops run MT-11020 at Ra 2.0–2.6 μm. Ask for MT-11010 to go finer or MT-11030 to go coarser, since adjectives let two lots differ 0.8 μm.

Can blasting and etching share one tool?

Answer: Yes, with a 15 mm transition blended at 240 grit. Direct contact forms a 0.03 mm step, and that step tears first at ejection.

Is deeper grain more wear resistant?

Answer: No. MT-11040 loses 12 mg on Taber against 8 mg for MT-11020, because valleys trap grit. Deeper grain hides scratches rather than resisting them.

How much draft does laser texture need?

Answer: At least 1°, and 1.5° at 0.03 mm depth, since square laser valleys raise release force 8%.

Case Surface Finish Options

Quick answer: Case surface finish runs three roads: MT-11020 texture at Ra 2.0–2.6 μm, 120 grit blasting at Ra 0.8–1.2 μm and laser texture at Ra 0.4–1.0 μm.

Three routes for case surface finish
MT numbers and roughness
Blasting grit and roughness
Etching versus laser
Wear, repair and rework
Visible and structural faces
FAQ

1. Three routes for case surface finish

One 520 mm × 380 mm × 200 mm case was finished three ways: MT-11020 on the lid, MT-11040 on the sides, bare steel inside. After three months the lid measured Ra 2.4 μm with 6% of parts showing scratches, the sides Ra 5.8 μm with 2.5%, and the inside Ra 0.35 μm with 12%.

They are three tools: a film-etched MT grade, grit blasting for a random matte, laser cutting for a fixed pattern, with Ra ranges, drafts and repairs that do not interchange.

Route	Ra (μm)	Depth (mm)	Draft	Repair
MT-11010	1.2–1.6	0.02	≥1.5°	Re-etch
MT-11020	2.0–2.6	0.03	≥2.0°	Re-etch
MT-11040	5.0–6.5	0.08	≥4.0°	Full re-etch
Blast 120	0.8–1.2	0.01	≥1.0°	Local
Blast 80	1.6–2.0	0.02	≥1.5°	Local
Laser	0.4–1.0	0.01–0.03	≥1.0°	Return

Settle visible versus structural faces first: visible faces want evenness, structural faces want hiding power.

2. MT numbers and roughness

The MT number is a texture standard, and higher numbers run deeper. MT-11010 sits at Ra 1.2–1.6 μm and 0.02 mm, MT-11020 at 2.0–2.6 μm and 0.03 mm, MT-11030 at 3.2–4.0 μm and 0.05 mm, MT-11040 at 5.0–6.5 μm and 0.08 mm.

Case surface finish sample shelf with four tiers of olive, black and grey cases, moulded ribs and black latches, one open with cables inside

An order saying fine grain buys whatever the shop stocks: write the number and the depth, since two suppliers reach the same Ra at different depths.

MT	Ra (μm)	Depth (mm)	Use
MT-11010	1.2–1.6	0.02	Instrument lids
MT-11020	2.0–2.6	0.03	General shells
MT-11030	3.2–4.0	0.05	Tool case sides
MT-11040	5.0–6.5	0.08	Grip areas

Draft follows depth: 1° per 0.02 mm of grain, so MT-11020 needs 2° and MT-11040 needs 4°. Short draft pulls texture white, and only polishing fixes it.

Five tools cut from one film stay within 0.3 μm of each other, which is why volume orders accept a 3–5 day etch. Deeper is not better: MT-11040 traps oil on a lid but adds 30% grip friction.

3. Blasting grit and roughness

Grit sets roughness: 80 grit glass bead gives Ra 1.6–2.0 μm, 120 grit 0.8–1.2 μm, 240 grit 0.4–0.6 μm. Halving grit roughly halves Ra, a smoother scale than MT numbers.

Repeatability needs fixed air at 0.4–0.6 MPa, nozzle at 150 mm, 60° incidence, three crossed passes. Skip the grit change and Ra drifts 0.2 μm coarser.

Repair is the real advantage: a bright knock is masked, re-blasted twice and blended with 120 then 240 grit, vanishing at 300 mm, while an etched face needs everything re-etched.

Randomness cuts both ways, with Ra varying 0.4 μm across one cavity, so lids above 1 m are rarely blasted all over.

4. Etching versus laser

In-mould texture means a fixed pattern in the cavity: logos, grids, woven effects. Chemical etching reaches 0.02–0.10 mm in 3–5 days; laser stops at 0.05 mm in 6 h, but rework means recutting the face.

Case surface finish colour sample rack behind a man in a cream shirt, rows of orange, blue, yellow and green small cases under downlights

Laser leaves a 0.02 mm step at each edge that drags material at ejection, marking the wall. Etched valleys end in R0.03 mm, cutting release force 8% at equal depth.

Laser wins on detail: a 0.3 mm line cuts cleanly where etching widens it 0.05 mm. Etching costs about CNY 4000 for MT-11020 on a 520 mm × 380 mm tool; laser runs near CNY 1800 for 6 h.

5. Wear, repair and rework

Taber with a CS-10 wheel at 500 g for 500 cycles gives 12 mg loss on MT-11040, 8 mg on MT-11020 and 5 mg on a polished face. Field use reverses that, because deep valleys hold grit.

Repair follows the route: blasting takes 2 h on site, etching needs a new film and 3–5 days, laser means a week at the shop.

Rework tracks how visible a scratch is. Across three lots of 500 shipped alike, polished shells returned 12%, MT-11020 returned 6% and MT-11040 returned 2.5%.

Mixing grades in one lot is worst: inspectors cannot separate a scratch from a texture step, so they judge by the shallowest face, and the number must be frozen before tooling.

6. Visible and structural faces

Visible faces are the lid top, side walls and latch area: Ra 1.2–2.6 μm from fine etching or 120 grit, draft of 2° or more, grain along release.

Structural faces are inner walls, ribs, base and bosses: no decoration, Ra 0.3–0.6 μm, 1° of draft, and shallow grain releases cleanly.

Area	Ra (μm)	Draft	Route	Test
Lid top	1.2–2.6	≥2°	MT-11020	No seam at 300 mm
Sides	2.0–4.0	≥3°	MT-11030	Grip holds
Inside	0.3–0.6	1°	None	No white marks
Base	3.2–6.5	≥4°	MT-11040	No sliding

Leave 15 mm between zones, blended at 240 grit, or the boundary becomes a 0.03 mm step that tears first. Check visible faces at 300 mm, structural faces for pull marks under 0.05 mm.

Conclusion

Two questions settle case surface finish: will this face be seen, and can a scratch there be repaired. Visible faces are judged at 300 mm and take MT-11020 or 120 grit at Ra 1.2–2.6 μm with 2° or more of draft, while structural faces only need clean release at Ra 0.3–0.6 μm with 1° and no grain. Keep 15 mm of blended transition between them, because skipping it guarantees a torn seam. Write repair rights into the purchase terms: blasting may be touched up on site, etching allows two re-etches, laser returns to the shop. Where grain exceeds 0.05 mm, add 1° of draft per 0.02 mm of depth instead of polishing damage out later, since polished patches show at once at 300 mm. Applied together, these rules hold scratch returns under 3% on a 500 piece lot, half the rate of a polished shell.

This article discusses container-side specifications and design implications only, and does not cover any handling, loading or use of the contents.