stainlesstec carries out the surface finishing of stainless steel and aluminium as part of complete part and assembly manufacturing. Depending on the application, we dress welds and surfaces, produce defined surface patterns or prepare parts for subsequent surface processes.
For us the surface is not simply a question of looks: depending on material and application it affects the corrosion resistance, cleanability, hygiene, function and appearance of the finished part. We therefore consider the surface wanted as early as the production planning stage.
A stainless steel cover with a high-grade visible surface makes different demands from a welded assembly for a machine. A part for a hygienically sensitive area, in turn, needs a different surface from an aluminium cladding panel. Surface finishing therefore starts with the question of what properties the finished surface has to meet. The decisive criteria may include:
the appearance wanted
roughness
corrosion resistance
cleanability
hygiene requirements
removal of heat tint
blending worked and unworked areas
preparation for subsequent coatings
requirements for visible surfaces
technical or functional surfaces
Only from these does the appropriate process follow.
Grinding stainless steel
Grinding stainless steel can serve both technical and visual purposes: welds can be smoothed, transitions blended and defined grinding patterns produced. On visible parts, what matters is not only the one area worked on but the appearance of the surface as a whole.
With pre-ground sheet in particular, the grinding direction and the existing surface structure therefore have to be taken into account during production. Typical applications are:
ground stainless steel enclosures
cladding
visible parts
machine components
vessels and troughs
dressed welded structures
Dressing welds
A technically sound weld does not necessarily have to stay visible in the finished part. Depending on design and requirement, welds can be ground back, smoothed or blended into the adjoining surface.
This takes experience: remove too much material and geometry and wall thickness change; work unevenly and the transitions stay visible. On high-grade parts, welding process and later surface finishing therefore have to be matched to one another before welding begins.
Pickling stainless steel
Welding stainless steel can produce heat tint and oxide layers through the thermal load. Pickling removes such oxidised areas chemically and produces a metallically clean surface.
This is not only a visual matter: in corrosion-critical applications especially, treating the weld area properly can be decisive in restoring the surface properties wanted. Which treatment is required depends on the material, the welding process and the eventual service conditions.
Passivating stainless steel
Stainless steel owes its corrosion resistance to a very thin, chromium-rich passive layer. After manufacturing and welding, demanding applications may call for the surface to be cleaned accordingly and for conditions that allow it to passivate evenly.
Pickling and passivation are not the same thing: pickling removes oxides and near-surface contamination chemically, whereas passivation aims at a suitable passive condition of the stainless steel surface. Which treatment is needed depends on the material and the service conditions.
Polishing stainless steel
Where particularly smooth or high-grade surfaces are specified, stainless steel can be worked further. Polishing serves both visual and functional requirements. Depending on the application, smoother surfaces can for instance:
be easier to clean
allow less soiling to adhere
create high-grade visible surfaces
support defined surface roughness requirements
In technically or hygienically relevant applications, though, the surface should not be described merely as “shiny”. What counts is the specific surface quality required.
A defined roughness, not just “nice and smooth”
In pharmaceutical, hygiene and process applications the surface roughness may be a technical specification. A note such as “ground” or “polished” is then not enough.
A defined Ra value, for example, can be decisive: it describes the average roughness of a surface and so allows a measurable specification. Which roughness is required depends on the part, the medium, the cleaning method and the project’s own requirements.
Where defined roughness values are specified, the process and the quality control have to be matched to them.
Surface finishing of aluminium
With aluminium, too, the surface affects both appearance and technical properties. Depending on the part, surfaces can be:
ground
worked mechanically
prepared for subsequent coatings
or sent out for external surface treatment
With visible aluminium parts in particular, it is important to protect the surface during cutting, forming and welding. Damage, scratches or pressure marks on the finished part can usually only be put right with extra effort. A high-grade aluminium surface therefore begins not at the final operation but with how the material is handled throughout.
Anodising aluminium
One important surface treatment for aluminium is anodising, in which the metal’s natural oxide layer is strengthened electrochemically. Among other things, that can influence wear and corrosion properties as well as the appearance of the surface.
For a good result, the later treatment has to be taken into account in design and production: welds, different alloys and local material conditions can all affect the appearance of an anodised surface. If an aluminium part is to be anodised later, that should therefore be known before welding and machining begin.
Glass-bead blasting and other surface finishes
Depending on the appearance wanted, stainless steel surfaces can also be worked by blasting. Glass-bead blasting, for instance, can produce an even matt surface and even out the look of machining marks.
Blasting medium, process and material have to be properly matched. With stainless steel especially, care is needed that no unwanted foreign particles are driven into the surface. The process suits, for example:
enclosures
machine components
cladding
visible parts
complex welded assemblies
Avoiding rust marks on stainless steel
A stainless steel surface can only show its corrosion resistance reliably if it is treated in a way the material calls for. Iron-bearing particles introduced through tools, abrasives or contact surfaces, for example, can lead to rust marks later.
Consistently avoiding such contamination is therefore part of high-grade stainless steel work. On demanding applications in particular we look not only at the final grinding or pickling operation but at the whole process chain.
Protecting visible surfaces from the start
A high-grade surface cannot simply be “produced” at the end. On parts with defined visible surfaces, those surfaces have to be considered throughout production:
Cutting → bending → welding → assembly → transport
Otherwise tool marks, scratches, weld spatter or unsuitable handling can make extra work necessary – or put the surface wanted out of reach altogether. We therefore define demanding visible surfaces before production starts wherever possible.
Surface and manufacturing from one source
One substantial advantage of stainlesstec is that we can build the surface requirement into the whole production plan.
At the welding stage, for instance, we can already allow for whether a seam will stay visible, be ground flush or be dressed for a particular surface quality. That cuts later corrections and improves the quality of the finished part.
Surfaces for demanding applications
Surface quality matters most where it takes on a technical function.
Pharmaceuticals and hygienic applications
Cleanability, defined surfaces and material-appropriate processing can be essential requirements.
Machinery and plant engineering
Here function, corrosion resistance and a robust technical surface usually come first.
Aerospace and high technology
Defined surface conditions, repeatable manufacturing and documentation can all be part of the part specification.
Defence technology
Depending on the application, functional surfaces, corrosion protection and defined manufacturing processes may be required.
Which surface quality is actually required is set by the drawing, the specification and the eventual service conditions.
The right surface begins with the specification
Terms such as “ground”, “matt”, “clean” or “high-grade” leave a great deal of room for interpretation. On demanding parts we therefore recommend defining the surface wanted as unambiguously as possible – through the grinding pattern, roughness, a reference sample or specific technical requirements.
That way design, production and quality control all know from the outset what result is to be achieved.
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.
