Surface quality of extruded aluminum

Surface quality - this is the aspect of design aluminum profiles, which receive less attention, than it deserves. This question often arises only after, as a prototype for the new profile has been pressed. Usually it is too late, that something could be done.

This happens because, that the design stage is the period, when it is possible to influence the surface quality of the future of the aluminum profile.

Proper alloy

Good surface quality starts with the right choice of aluminum alloy. From the choice of the aluminum alloy layer depends on the quality requirements of the aluminum profile surface. surface quality requirements may differ depending on the destination profile, for example, Fine for decorative items or for building structures, which should look good from afar.

for instance, for decorative articles, which will be anodized, the obvious choice is the alloy 6060. This alloy has a relatively low silicon content, what it is important to obtain a smooth surface. If the profile also has load-bearing functions, is more likely to choose an alloy 6063, which has better mechanical properties. In such cases do not apply 6005A and alloys 6082, since the increased silicon content in them gives a dull and streaky surface [1].

Profile design

When aluminum profiles out of the extrusion press, they lie on the output table some of his party. Profile at this time is still very soft. therefore, when it comes into contact with the table, the latter may inevitably generated traces, for example, in the form of small dents. That is why it is very important to agree with the customer and indicate on the drawing the visible (significant) profile surfaces.

The cross-sectional profile may also have an impact on the quality of its surface. The large difference in thickness of the walls or the joints of the walls and shelves can lead to an inhomogeneous structure of the metal surface, that gives the visible band, as in anodizing, and powder coating [1, 3].

This problem is solved or soften, for example, by applying some large fillet radiuses between elements of the cross-sectional. This causes the aluminum to flow through the die more evenly, what, in turn, It reduces the heterogeneity of the metal structure at the profile surface.

Other measures include the application of decorative ornamental ribs or corrugations, such strips to mask. If there are differences in structure of the metal left, but we will not see them anymore (figure 1).

Figure 1 - Figure - Application of decorative corrugations
to prevent surface defects:
a - profile with surface defects of the "strip";
b - an improved profile with decorative corrugation

The ribs on the surface can also help prevent extensive damage of the surface profiles. Scratches on the general profile of the surface is always evident, and the same scratch on the edges is almost not noticeable.

Treatment, Packaging and transport of profiles

Developer profile should not forget, what profile do you need

not only press,

but also:

handle,
pack and
to transport.

Treatment of the profiles during their processing is another threat to their surface, as the manufacturer, and the customer.

At the manufacturer profiles, which must be subjected to one or another surface treatment, may become dirty before this treatment. This pollution can take the form not only of oils or greases, but also ordinary fingerprints (drawing 2). sweat allocation on hand are acidic and they cause acid corrosion of the surface profile. These fingerprints are still visible after anodizing. The occurrence of this defect in the surface of the profiles is prevented by the use of clean gloves during all manual work with the profiles [1].

Figure 2 - Corrosion of fingerprints

Too long storage profiles in stacks and stacks can also impair the quality of their surface. This is due to the natural corrosion processes.

For each profile must be defined method of packing. You need to think through in advance not only a way of packaging, but also materials, which in this case will be applied. for instance, some cardboard and paper materials have acidic properties and, when wet, can leave noticeable traces of acid corrosion on the profiles (picture 3).

Figure 3 - acid corrosion of paper packaging

Surface quality control at SAPA

World leader in the production of extruded aluminum profiles, SAPA company, has a well thought out system of quality control of their surface [2].

Factors surface quality

Company SAPA applies when dealing with customers six classes of quality aluminum profiles surface. When assigning profiles to a particular class, the following factors are taken into account:

profile assignment;
used aluminum alloy;
the presence and location of visible surfaces;
presence and type of protective and decorative coating.

As a result, considering all these factors, the profiles are one of the six classes of quality surface. The degree of reduced surface quality of the class 1 to class 6.

For each class,, except for class 6, defined distance, from which the assessment of surface quality for obvious defects. This distance varies from 0,6 m for class 1 to 5 m for class 5. To the class of surface 6 surface quality requirements are not made.

An interesting point is the time, during which the controller - the manufacturer or the customer - is able to detect surface defects. This time is only 5-10 seconds. This is - a very important condition, because usually this time is not specified, and the controller may "pick" surface defects indefinitely.

An important condition for the customer is, that with increasing degree of surface profiles quality value increases. This ensures, the customer makes demands on the quality of surface profiles, that really fit their purpose.

class quality surface profiles agreed between the manufacturer and the customer, and entered in the order or the contract documentation.

Classes of surface quality

class 1 - Highest requirements

It applies to items of household appliances, lighting devices, decorative items, etc.. P.
Maximum delivery length: 2,4 m, if not agreed other lengths.
class 1 It can be achieved only with a special profiles anodised pretreatment – chemical or mechanical. By such a mechanical surface treatment typically includes grinding, Processing of metal brushes and polishing.
profiles, in which the surface on all sides is visible, can be handled by this class only, if the profile is subjected to grinding on all sides.
During transport, each profile must be separately protected from damage.
Each profile requires individual handling and visual inspection, which entails an increase in labor costs.
alloys only 6060, 6063 and 6463.
Evaluation of surface quality is produced at a distance 0,6 m for 5-10 seconds.

class 2 - Very high demands

It applies to items of furniture, parts of household appliances, picture frame, etc.. P.
Maximum delivery length: 2,4 m, if not agreed other lengths.
The highest class for brilliant anodizing, including, with additional machining. Brilliant anodizing manifests and amplifies all surface defects.
profiles, in which all sides are visible, usually are not produced on the surface quality of this class.
this class, usually, applied to the anodised profiles.
During transport, each profile must be separately protected from damage.
Each profile requires individual handling and visual inspection, which entails an increase in labor costs.
alloys only 6060, 6063 and 6463.
Evaluation of surface quality is produced at a distance 1 m for 5-10 seconds.

class 3 - High requirements

It applies to furniture parts, lighting equipment, refrigerators, shower cabin, Decorative Items interior.
Usually applied to the anodised profiles.
profiles, in which all sides are visible, usually are not produced on the surface quality of this class.
alloys only 6060, 6063 and 6463.
Evaluation of surface quality is produced at a distance 2 m for 5-10 seconds.

class 4 - The normal requirements

It applied to building systems, facade, windows, doors and handrails, as well as products for public buildings, for example, furniture, exhibition stands, shower cabin.
It is applied to the painted and anodized profiles.
alloys only 6060, 6063 and 6463.
Evaluation of surface quality is produced at a distance 3 m for 5-10 seconds.

class 5 - Low requirements

It is used for building systems, balconies, roof, window, doors, openings, railing, sailing masts, stairways, football goal, skladnыh walls.
standard profiles, for example, angles and channels.
alloys 6060, 6063, 6463, 6005A, 6082, 6101.
Evaluation of surface quality is produced at a distance 5 m for 5-10 seconds.

class 6 - No requirement

It is used for carrying constructional profiles, Railings, forests, falsework, sliding partitions.
standard profiles, including alloys of sredneprochnyh, such as 6082. construction profiles, for example, truck bodies.
profiles, which are not specified visible surfaces.
Profiles of aluminum brand 1050A can be pressed only on the surface quality class.

The visible surface and semi-visible

In addition to the company SAPA visible surfaces are distinguished more poluvidimye surface. Poluvidimye surface - these are the surface, which are usually not visible in the finished product, for example, seams of window frames. Visible surface profile indicated in the figure by dashed lines, poluvidimye - two solid lines.

Quality class surface profile is set for the visible surfaces. Poluvidimye surface automatically receive a quality class one unit below. for instance, if the visible surfaces assigned class 4, poluvidimye the surface will have a class 5.

profiles, which are not specified visible surfaces, refer to the lowest, sixth, class. For these control profiles only tolerances in size and shape, as well as mechanical properties.

Sources:

How design can influence surface quality, SAPA-HYDRO, 2020
Design manual. Success with Aluminium Profiles – SAPA, 2014.
Smart design can reduce risk of surface flaws, HYDRO, 2020