Most finishing problems are not finishing problems. An enclosure that rusts at the weld, a black panel that is a different black from the extrusion bolted beside it, a brushed door that looks right on its own and wrong next to its frame — all three are decided upstream, at the point where the finish is written on the drawing, or not written at all.
This page is a selection guide for the two materials most of our work is made in, stainless steel and aluminum. It is organised by what goes wrong in service rather than by what each process is, because that is the order the decision actually happens in. If you are specifying brushed stainless on its own, that has its own page: brushed stainless steel finishing.
Choose the finish by what will kill the enclosure, not by the swatch
A finish is a response to an environment. Name the environment and the finish usually follows, which is why the first question we ask is not “what finish do you want” but “where does this live and what touches it”.
| Where the enclosure lives | What fails first | Finish we would specify | What we would steer you away from |
|---|---|---|---|
| Indoor, dry, handled daily — control cabinets, instrument housings | Fingerprints, scuffs, cleaning marks | Brushed stainless in No. 4, or brushed aluminum with a clear anodize | Mirror polish. It shows every hand mark and there is no way to pack it that guarantees otherwise |
| Indoor, wiped down with disinfectant — medical and food equipment | Cleaning chemicals and crevices that stay wet | 316 brushed and passivated, or sealed anodize on aluminum | Unsealed anodize, and any finish that needs a coating to survive being wiped |
| Outdoor, no direct sun — kiosks, EV charger housings, traffic and telecom cabinets | Water sitting in joints, and UV on organic dye | Anodize in an integral or inorganic colour, or 316 brushed and passivated | Bright organic dyes in a sun-facing position |
| Outdoor, coastal or exposed to road salt | Chloride pitting | 316, brushed and passivated; on aluminum a thicker anodize, sealed | 430 stainless, and a thin anodize left unsealed |
| Wear and sliding contact — guides, latches, drawer runners | Abrasion of the finish itself | Type III hardcoat on aluminum | Decorative Type II on a surface that rubs. And on stainless, understand that brushing is cosmetic: it adds no wear life |
| Parts with an electrical or EMC bonding path | An anodic film is an insulator | Masked or machined-after-anodize contact lands, or a plated contact face | Anodizing a face and then bolting an earth terminal through it |
| Visible panels sitting next to extrusions or castings | Colour mismatch between alloys and between processes | One alloy and one anodize class across every visible part, approved on a single sample panel | Mixing 6061 and 5052 in one dyed colour and expecting them to match |
What each finish actually does on stainless
Stainless already protects itself with a chromium-oxide film. Every finish below either changes the appearance, or restores that film after we have disturbed it, or both. None of them is a coating you can add on top and forget about.
| Finish | Where it runs | What it solves | What it does not do |
|---|---|---|---|
| Brushed — coarse, No. 4, fine, or non-directional satin | Our own workshop | Hides handling marks, gives a low-glare surface that reads as industrial. The cheapest of the four on a sheet metal part | Protect. Brushing cuts away the passive layer, so the part is passivated afterwards, not before |
| Mirror polish | Our own workshop | A reflective decorative surface that wipes clean | Hide anything. It amplifies every handling and packing mark, so it needs protective film and packing designed for it |
| Passivation | Audited partner line | Removes free iron picked up from cutting, forming and handling, and rebuilds the chromium-oxide layer | Remove weld heat tint or mill scale. Those have to come off first, mechanically or chemically |
| Electropolishing | Audited partner line | Smooths and deburrs surfaces an abrasive cannot reach, and improves cleanability. This is the finish for parts that are sterilised or wiped constantly | Fill scratches. It removes metal from every surface, so holes grow and edges round |
The order matters more than the choice. A brushed panel is passivated after brushing. On a welded assembly, the heat tint has to come off before passivation, because passivation will not touch it — and that is the single most common reason a stainless enclosure stains in service and nobody can say why. If you want the appearance of a weld and the corrosion resistance of the parent metal, the weld has to be dressed and the tint removed, then the whole assembly passivated as one piece. Which specification the passivation is performed to, and whether a passivation record travels with the batch, are confirmed with the applicator at quotation stage: if your incoming inspection needs the record, ask for it then rather than after delivery.
Aluminum: anodizing is grown, not applied
Anodizing is the one aluminum finish that is not a layer sitting on the metal. The part is made the anode in an acid bath and the surface is converted into aluminum oxide: it grows out of the base metal and into it at the same time. Three practical consequences follow, and they decide whether a batch is right.
- It cannot flake or peel, because there is no interface for it to fail at. This is the real advantage over anything deposited.
- It is an electrical insulator. Any face that must conduct or bond has to be masked before the bath, or machined after it. There is no third option, and it is the one thing that most often gets missed on a drawing.
- It changes the size of the part. Roughly half the coating thickness builds outwards and half grows inwards, so a hole or an internal thread closes by about the total coating thickness on diameter, and a shaft or an external thread grows by the same. On a clearance hole it is easy to ignore. On a reamed hole, a pressed-in PEM fastener or a sliding fit it is not.
| Type II — conventional | Type III — hardcoat | |
|---|---|---|
| Typical thickness | 5–18 µm for decorative and dyed work | 25–50 µm |
| What it is for | Appearance, light corrosion protection, colour | Wear and abrasion resistance, and heavier corrosion duty |
| Colour | Takes dyes across a wide range, including bright colours | The natural colour darkens as thickness rises; dyed colours are more limited and read duller |
| Effect on dimensions | Small enough to ignore on most sheet metal | Has to be allowed for on holes, threads and fits |
| Cost and lead time | Lower. The standard choice for enclosures | Higher. The bath run is longer and it is a separate line |
| Where we would push back | If the part rubs against something — you will wear through it | If it is only for looks. You are paying for thickness you do not need, and the colour will be darker than you expect |
The specification is a number, not a word. “Anodize” on a drawing tells the applicator nothing he can be held to. “Anodize to MIL-A-8625, Type II, 10–12 µm, black, sealed” does. The thickness ranges in the table above are the industry-typical ones for each class. What a specific bath can actually hold is narrower than that, so where the thickness is load-bearing we confirm the achievable range and the colour and seal options with the applicator before we quote, and we tell you which line the work will run on. If you do not have a class in mind, tell us what the part has to survive and we will write the number into the drawing note before the batch is released.
Five things that go wrong on anodized aluminum, and how each one is headed off
1. Alloy-to-alloy colour mismatch. Alloys do not anodize the same colour. 6061 gives the cleanest clear finish and the most predictable dyed colours. 5052 and 5754 clear-anodize slightly duller and a shade greyer; they are perfectly good for a natural finish and are the wrong choice when two parts have to match a dyed colour. 3003 takes a clear anodize well and is often the better call for a visible panel in a natural finish. So: every visible part of an assembly gets one alloy, and it is written on the drawing.
2. The weld line. Anodize amplifies the difference between filler and parent metal. A 4043 filler, which is the general-purpose choice for welding aluminum, goes grey to near-black under anodize and draws a visible band across the panel. A 5356 filler stays close to the base metal. It costs the same at the welding stage and it saves the batch, so for any part that will be anodized we specify 5356 unless you tell us otherwise. That decision belongs to the welding stage, not the finishing stage — it is the same discipline we apply on every weldment that leaves the shop, described under sheet metal welding.
3. Rack marks. The part has to be electrically connected to be anodized at all, and the contact point comes out unanodized. That is unavoidable, not a defect — but its position is a choice. Put it on a hidden face, under a hem, or under a fastener head, and it never gets seen. Leave it to the applicator and it can land in the middle of a fascia. We mark the allowed contact area on the drawing.
4. Holes, threads and fits. Hardcoat on a reamed hole closes it; a sliding fit sized without the coating will bind. These are caught in the DFM review before anything is cut, not discovered at assembly — which is the practical argument for having the fabricator route the finishing rather than sending parts out yourself.
5. Fading and chalking. Organic dyes vary enormously in light fastness. Blacks and bronzes hold up outdoors; bright reds and blues are the first to chalk. Sealing is part of the specification, not an extra, because an unsealed or badly sealed dye bleeds and the corrosion protection drops with it. For a part that will sit in sun, say so on the drawing and the colour and the seal are chosen for it.
Brushed, anodized or as-cut on aluminum
| Finish | Appearance | Handling marks | Relative cost | Where it suits | Where it does not |
|---|---|---|---|---|---|
| As-cut / mill finish | Inconsistent sheen; the laser edge and every handling scratch shows | Shows everything | Lowest | Hidden brackets, internal plates, anything nobody sees | Anything visible |
| Brushed | Directional grain, satin | Hides them well | Low to moderate | Internal panels, chassis, parts that get handled | Outdoor use on its own. Brushed aluminum still oxidizes and dulls, unevenly |
| Clear anodized | Even, slightly metallic | Hides them well | Moderate | Visible enclosures, outdoor housings, food and medical equipment | A face that has to conduct — it insulates |
| Dyed or black anodized | Uniform colour | Hides them very well | Moderate to high | Consumer-facing panels, bezels, fascias | Sun-facing parts in bright colours |
| Type III hardcoat | Dark natural grey, matte | Hides them very well | Highest | Slides, wear surfaces, heavy-duty housings | Decorative panels. It is too dark and too dull to be a look |
Where plating fits, and where it does not
Plating deposits a different metal onto the surface. On stainless and aluminum it is usually the wrong tool for corrosion, for a simple reason: both metals already protect themselves with their own oxide, and a deposited layer adds an interface that can lift, chip or blister. That is why it is the finish we quote least often for these two materials.
We do quote it for the two jobs it is genuinely good at. The first is contact faces that must stay conductive — an anodic film is an insulator, which is exactly what you do not want on an earth path or an EMC joint, and a plated land solves it without masking. The second is parts that will be soldered. Both are routed to the audited plating line, and the drawing states which faces are plated and which are masked, because a plating line that has not been told will plate the whole part.
If you are considering plating an aluminum part for wear resistance, ask us about hardcoat first. In most cases it is the cheaper and more durable answer, and it is part of the same metal rather than a layer on it.
What finishing changes on the drawing
- Masking and contact faces. Anything that must stay bare for bonding, earthing, adhesive or welding is marked on the drawing, not left to be discovered.
- Dimensional allowance. Coating thickness on holes, threads and sliding fits; metal removal if the part is electropolished. Both are applied to the drawing dimensions before cutting, not corrected afterwards.
- The appearance standard. An approved sample panel, agreed lighting and an agreed viewing distance. A written description of a finish is not a standard that two people will read the same way.
- The sequence. Brush, then passivate. Weld, remove the heat tint, then passivate. Anodize, then seal. Getting the order wrong is how a part passes incoming inspection and fails in the field six months later.
- The packing. Mirror-polished and anodized parts need protection designed for them. We pack to the finish, and export packing is quoted as its own line when the surface is cosmetic.
What to put on the drawing
- Material and grade or alloy, and the same alloy across every visible part of an assembly
- Finish as a name and a number: grit sequence for brushing, class and micrometres for anodize, Type II or Type III
- Grain direction, and the datum it is measured from, for brushed work
- Cosmetic faces and non-cosmetic faces — and where rack or handling marks are allowed to fall
- Faces that must stay conductive, and faces that must be masked
- Holes, threads and fits that carry a tolerance, and whether the coating is allowed for
- Where the enclosure lives: indoor, outdoor, coastal, disinfectant, sunlight, or wear
- Your appearance acceptance standard, if your incoming inspection grades finish
Lead time and what we need to quote
- Simple samples: 3–7 days. Complex first article: 15–20 days. Production batch: 25–35 days.
- Finishing that runs outside our building is quoted into the route, not added afterwards. The applicator’s queue is part of the date we give you, and we would rather say so than promise a date that depends on somebody else.
- Tooling, where the finish follows a formed part, is quoted separately: 7–15 days simple, 30–45 days complex.
Send 2D drawings (PDF, DWG or DXF) and 3D models (STEP, IGES or SolidWorks) with material, finish, the environment the part lives in, and quantity. We will confirm the finish we can hold, flag anything the drawing does not say, and quote it with the parts.
Questions buyers ask before they send the drawing
Can you match a panel we already have?
Send a sample, or a photograph with the alloy and finish if you know them. We match against a physical panel, because a photograph hides both the grain direction and the gloss level, and those are most of what you see. If the existing part is an extrusion or a casting rather than sheet, tell us — its alloy will anodize a different colour from the sheet we would use to replace it.
Does anodizing make the part electrically insulating?
Yes, and it is a property rather than a defect, which is why it catches people out. Any face on an anodized enclosure that has to bond to earth or carry a shielding path is either masked before the bath or machined clean afterwards. Say which faces they are on the drawing and they are designed in from the start.
Do you anodize in-house?
No, and we say so rather than implying it. Brushing and mirror polishing run in our own workshop. Anodizing, passivation, electropolishing and plating run on audited partner lines that we specify and inspect: the process parameters go on the drawing, and the result is checked on receipt against them. What we hold in-house is the work that has to be right before the part leaves the building — the forming, the weld quality, the grain direction and the surface preparation.
Will the finish hold up outdoors?
On aluminum, a sealed anodize in a light-fast colour will. On stainless, choose 316 and passivate it: 304 will tea-stain in a coastal atmosphere and 430 will rust. The thing that usually fails outdoors is not the finish but the joint — a lap that holds water, or a crevice that never dries. That is a design question and it is cheaper to fix on the drawing.
Can you hold a colour across two batches?
We hold it against an approved sample panel, the same alloy and the same anodize class. Batch-to-batch variation inside a class is real, so where appearance matters, an assembly is finished as one batch rather than panel by panel. If you need two batches to match each other and not a sample, say it at quotation stage — it changes how the job is routed.
Related reading: aluminum sheet metal fabrication · stainless steel sheet metal fabrication · brushed stainless steel finishing · metal surface finishing · enclosure assembly · anodized aluminum enclosures · transport and rail enclosures
What stands behind this quotation
- Manufacturing since 20162,500 m² Ningbo plant — 3 laser cutting machines (including newer TRUMPF), 4 CNC press brakes and 10 welding stations.
- Shipped to more than 30 export marketsEnclosures, cabinets and formed parts supplied to OEM buyers across Europe, North America and Asia.
- 123 documented product casesMedical device housings, HVAC and heat pump enclosures, agricultural and livestock equipment, industrial hydraulics, material handling trolleys and EV charging cabinets.
- Factory evidence you can checkTUV Rheinland audit reference MIC-ASI243729 and Bureau Veritas reference MIC-ASR263630 available for buyer review under NDA.
Before you send drawings: an NDA is signed on request · first-article inspection is carried out before a batch continues · pricing is staged from prototype quantity to repeat volume · pre-shipment photos and packing records are prepared when the project needs them.