What is segregated production – and why does it matter?
Stainless steel is widely used because it resists corrosion, allows high-grade surfaces and suits hygienically demanding applications. Those properties, though, do not depend on the material alone.
The surface can be contaminated or damaged while the part is being worked on. Contact with ordinary steel and with iron-bearing particles is the critical case.
This is exactly where segregated production comes in: a way of working in which stainless steel – and often aluminium too – is kept as strictly as possible apart from carbon steel and the residues of working it.
What does “segregated production” mean?
The term does not denote a single method. It is about a controlled environment for sensitive materials and surfaces, which can include:
separate material storage
defined working areas
suitable tools
separate abrasives
clean transport and support surfaces
controlled processes
protection of high-grade surfaces
The aim is to keep foreign material out throughout production. Segregated production is therefore less a room than a discipline.
Why is ordinary steel a problem for stainless steel?
Stainless steel owes its corrosion resistance partly to its protective passive layer. If particles of unalloyed steel reach the surface, those particles can corrode themselves.
Visible rust spots then appear even though the stainless steel beneath may be perfectly sound. This is known as rust marking, or foreign rust. Avoiding rust marks on stainless steel
Where do iron particles come from?
The causes can be remarkably inconspicuous. Typical sources are:
Tools – a tool was previously used on carbon steel and carries metallic residue.
Abrasives – grinding discs or brushes have been used on different materials.
Work surfaces – stainless steel is laid on surfaces where steel was worked before.
Transport – forks, chains, racks or other aids carry particles across.
Grinding and machining dust – in a mixed shop, iron-bearing particles settle on neighbouring parts.
Storage – different metals lie directly on one another or are stored together.
Rust marks therefore often come not from the stainless steel itself but from its surroundings while it is being worked.
Can stainless steel really rust?
Yes – “stainless steel does not rust” is too sweeping in any case. Corrosion resistance depends on, among other things:
the grade of stainless steel
the alloying elements
the medium
temperature
surface condition
design conditions
chlorides and other chemical loads
Rust marking is a separate matter: there it is foreign iron-bearing particles on the surface that corrode first. To the user, at first sight, the two look much the same.
Why is cleaning at the end not enough?
If the surface is cleaned or ground at the end anyway, surely keeping the materials apart beforehand is unnecessary.
It is not quite that simple. Contamination can:
be worked into the surface
be spread around by grinding
reach areas that are hard to get at
remain under parts fitted later
be removable, once production is over, only with extra effort
It is usually better, then, to avoid contamination from the start rather than have to correct it later.
The surface begins with the first operation
That applies to more than rust marks. A high-grade stainless steel surface can be damaged in storage, in transport, in laser cutting, bending, welding or assembly.
Scratches, pressure marks and foreign material cannot always be removed later without leaving a trace. A good stainless steel surface is not produced at the end – it is protected throughout the process.
Which parts of a shop are affected?
Ideally, segregated production concerns not just welding or grinding but the whole chain:
Goods inwards and storage – materials have to be clearly identified and stored suitably.
Cutting – supports and the machine’s surroundings govern what the material touches.
Forming – tools and machines can transfer foreign material.
Welding – material, filler metal, preparation and dressing all have to match.
Grinding and finishing – abrasives should suit the material.
Assembly – surfaces can be contaminated or damaged at this last stage too.
In critical applications it makes sense to keep certain tools apart – wire brushes, abrasives, files, hand tools that touch the surface directly, and clamping and support elements above all. A brush that has worked carbon steel should not then be used on a high-grade stainless steel surface.
What has segregated production to do with welding?
In welding, too, a clean material environment matters. Besides foreign material, other factors play a part:
joint preparation
heat input
filler metal
shielding gas
root protection, or back purging
heat tint
dressing of the weld
Segregated production is therefore no substitute for sound welding – it creates the conditions for it. Welding stainless steel
Segregated production does not automatically mean “hygienic”
This distinction matters. A segregated stainless steel shop can be a prerequisite for high-grade hygienic components. It does not automatically mean a part meets every requirement of, say, food or pharmaceutical processes. In addition, the following may be necessary:
a defined roughness
particular material grades
hygienic design
freedom from dead spaces
complete drainability
special weld execution
pickling or passivation
defined cleaning procedures
documentation requirements
Segregated production protects the material. It is no substitute for a product specification.
Is “segregated production” a certification?
No. The term describes a way of organising production, a process philosophy, not a product or quality certification in its own right. When choosing a manufacturing partner it is therefore worth asking more precisely:
Which materials are worked in that area?
Are steel and stainless steel kept apart, physically or organisationally?
How are tools and abrasives handled?
How is material stored?
How are parts moved between operations?
How are delicate surfaces protected?
The term on its own says less than the process actually lived day to day.
When does segregated production matter most?
Food processing technology
Where stainless steel surfaces are cleaned regularly and corrosion spots are unwelcome.
Where scratches, rust marks and rework would also be a problem to look at.
Does segregated production apply to aluminium too?
The basic principle of keeping materials apart can make sense for aluminium as well. There, though, rust marking is not the main concern. What matters is, for instance:
protecting delicate surfaces
keeping foreign material out
clean joint preparation
separate tools and abrasives
protecting surfaces that will later be visible or anodised
Stainless steel and aluminium thus both benefit from a similarly controlled environment – for partly different reasons. Working aluminium
What should an enquiry state?
Where surface and material cleanliness matter for a part, that should not simply be assumed. Specific details help:
is no substitute for a material, hygiene or product specification
is not a certification in itself
How does stainlesstec put segregated production into practice?
stainlesstec works stainless steel and aluminium in an environment set up for the purpose, bringing several operations together there within one controlled chain.
How that segregation is organised, and which processes are available there, is set out on our capability page. Segregated production at stainlesstec
Let’s talk about your project.
Send us your drawing or CAD data by email – together with material, batch size and your requirements. We will come back to you with a sound assessment.
