Aluminum is a light metal that has a strong tendency to smear during grinding, so open abrasive coatings or special coatings are used to prevent clogging. The machining behavior varies depending on the alloy, for example duralumin, as the material can be tougher or harder and more brittle depending on the application. The grinding pressure applied must be adjusted according to the hardness of the material. As a non-ferrous metal, aluminum has four times the thermal conductivity of iron-based metals, which means that the heat generated during grinding is dissipated more effectively.

For belt grinding applications on aluminum, the cutting speed should be set at 35 to 40 m/s higher than for ferrous metals, which in turn affects the stock removal rates and the service life of the tool used. High-performance sanding belts with precision-formed Cubitron II ceramic grain with grit sizes 36+, 60+, 80+ offer optimum sanding quality for heavy-duty stock removal and chamfering. Areas of use for mostly stationary sanding belt applications can be found, for example, in container construction or in aluminum foundries.

Rough cleaning wheels based on Scotch-Brite technology from 3M, for example, are suitable for removing corrosion, layers of paint or other adhesions on aluminum surfaces. The aim of the treatment is to remove the relevant layer with little pressure and at the same time minimize the risk of under-sanding, as deep sanding grooves would then have to be sanded out manually with great effort.

Any weld seams can be removed using an angle grinder with a fine 120+ grit fiber disc, for example. Cubitron II 787C fiber discs, available in grit sizes 36+ to 120+, are ideal for this. Fiber discs enable fast sanding processes with a high removal rate combined with a fast working speed and long service life.

Quick-change hook-and-loop discs such as the Cubitron II 947A Hookit (grit 40+ to 120+) for quick and easy replacement of the abrasive offer further advantages in terms of work efficiency.

Tip: Test a new sanding and polishing process on a sample part in advance.

Grinding aluminum - how it works

In principle, aluminum can be sanded in the same way as other metals. For larger, easily accessible surfaces on transportable workpieces, for example, processing on a long belt sander is ideal. Alternatively, angle and random orbital sanders are used for manual sanding. However, a few basic rules must be observed to ensure good sanding results on aluminum parts. The following section provides information on an exemplary manual machining process for aluminum sheets. Ultimately, the customer's requirements determine the sanding pattern to which the process is carried out.

• For a high removal rate, the sanding process is initially carried out with an 80 grit, which is refined in the subsequent work steps to remove the sanding marks from the previous pass. Unevenness can be avoided by switching to a random orbital sander using the cross sanding method at an early stage. To remove deep scratches, it may be necessary to work with slightly increased sanding pressure at the beginning.
• After each processing step, the surface should be cleaned of sanding particles using a cleaner and cloth.
• Hookit film wheels such as the 775L (grit 80+ to 400+) can be used for finer surfaces, while the 375L product range, for example, also offers the option of going up to 1500 grit.
• Polishing steps are possible from 800 grit. Depending on requirements, the polishing process can be continued in further steps up to a high-gloss finish.

Tip: When sanding aluminum workpieces, do not use tools that have previously been used for sanding other metals, especially iron and steel materials. Such grinding residues, which are worked into the aluminum in this way, can lead to corrosion later on.

Aluminium is normally matted to achieve a special visual effect. The aim is to retain the structure created during grinding, but to smooth the surface, as it is still relatively rough after processing with the abrasive grain. The peaks in the roughness profile in the form of surface burrs must therefore be removed by subsequent operations in the direction of the sanding stroke. Synthetic fiber nonwovens or nonwoven belts from the Scotch-Brite series, such as the SC-BL nonwoven belt, are primarily used for this purpose. In general, there are usually design or functional roughness depths (_Ra, _Rz, _Rmaxinμm) that must be adhered to during surface treatment. This applies, for example, to hygiene requirements in the food industry.

Tip: When working with the angle grinder over several grit sizes, it is advisable to always maintain the same sanding direction within a sanding pass with the same grit size. Cross-sanding with the same grit should be avoided, as otherwise it is not possible to tell whether the next sanding pass, which is to be offset by 90°, has completely blended the previous sanding.

This visual inspection can only be used to a limited extent for eccentric sanding due to the irregular sanding pattern. In this case, it is recommended to measure the surface roughness to ensure that the grinding grooves from the pre-grinding have been successfully removed.