Handles, knobs, hinges and fasteners are processed packed in baskets rather than hung on racks. That removes the part-length driver that sizes every other anodising line, and changes what limits your output.
If you make handles in Aligarh, hinges in Rajkot or fasteners in Ludhiana, the anodising question arrives as a margin problem: the job shop's rate and its queue are eating the difference between your quoted price and your cost. The plant that fixes it is not a small version of the one an extruder builds. It is a different plant.
Parts under roughly 100 mm — rivets, screws, spacers, knobs, small brackets — are processed packed in baskets rather than hung on racks. That single fact removes the part-length driver that sizes every other anodising line. There is no longest part to dip. The tank is sized by how much you can pack per load.
The consequences run right through the capital cost. No long rails. Tanks around 1.2 × 0.9 × 1.0 m instead of six metres. A transporter at roughly half the cost, because it is moving baskets rather than long, heavy, expensive jigs. Commodity baskets instead of designed fixtures. On the same throughput, a basket line is the cheapest of the four archetypes to build.
The word "barrel" is misleading and the industry increasingly avoids it. Parts are not tumbled during anodising. They are packed tightly enough that they cannot move at all.
The full mechanism, the packing-density band, and how to read the defects are in contact marks in bulk anodising.
The reason is electrical. An anodised surface is an insulator. Once a part shifts and breaks contact, the oxide already formed prevents it from re-establishing a current path — so it stops anodising, and you get a part with a partial coating. Packing density is therefore not a productivity setting. It is the process control that decides whether the load is saleable.
On a rack line, throughput is limited by rectifier capacity and cycle time. On a basket line it is usually limited by contact-mark rate — the proportion of parts that come out with a witness mark where a neighbour touched them.
Small parts without long flat faces — rivets, screws, rings, knobs — bulk-process well. Flat plates and anything with a large visible face are poor candidates: the contact marks land where they show.
Hardware is a catalogue product. A customer ordering handles in March and again in September expects them to match, and will return a batch that does not. Colour consistency on a basket line is harder than on a rack line for two reasons: current distribution through a packed mass is less uniform, and the loads are large enough that a small drift in bath chemistry or dye concentration affects thousands of pieces at once.
The controls that matter are bath chemistry discipline, dye bath monitoring, and consistent load weight per basket. See anodizing dyes and bath chemistry.
Worked through with an example in anodising cost per piece for small parts.
Anodising is conventionally quoted per square metre of surface. For high-volume small parts that unit is close to useless for decision-making — you are making a per-piece margin decision on a component that may cost forty rupees. Convert early: total surface area per basket load, divided by piece count, gives you cost per piece, and that is the number to compare against your job shop's invoice.
Set the archetype to Bulk / basket in our plant cost and payback calculator. It will size tanks by pack volume instead of part length, halve the transporter, and price baskets rather than bespoke fixtures.
Most hardware makers should also set the mode to Captive and enter what the job shop charges today. For this archetype the payback case is usually the simplest of the four: you already know your outsourced spend to the rupee, because you pay it every month.
If you know the plant you want and need the numbers before a serious internal conversation, the plant setup snapshot is a ₹2,500 written feasibility note in three working days, credited against Phase 0.
Start with the numbers. If they look close, that is exactly when the plant design decisions matter most.
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