Surface Finishing Lightweight Materials Need New Blasting Methods
Lightweight components require adequate surface finishing for subsequent processing steps. However, since these components are more sensitive, the machining methods must be adapted. One trend is ferrite-free blasting.
More and more components made of stainless steel, aluminium, brass as well as aluminium and zinc die casting require treatment with ferrite-free abrasives, observes KST Kugel-Strahltechnik. The blasting contractor says that they increasingly use stainless steel grit and stainless-steel shot in their bulk or rack processes.
Blasting with Stainless Steel Is Suitable for Many Materials
Stainless steel blasting has a wide range of applications. The blasting contractor removes traces of machining, burrs in connection parts, flash burrs in zinc die casting, welding marks and tarnishes colors. Delicate work is often required: even with metric fasteners can be machined below M6. Stainless steel grit or -shot allows to equalize bar drawings on aluminium profiles or to pre-treat aluminium components for anodizing.
Manufacturers of blasting machines are also observing a trend towards ferrite-free blasting. “For some time now, the demand for blast wheel machines for ferrite-free blasting has been increasing. Users are also considering converting blasting machines designed for ferritic abrasives to ferrite-free abrasives," Ulf Kapitza, Head of Sales and Marketing at Agtos, told MM MaschinenMarkt.
Gently Blasted Aluminium Die Casting
Daniel Schippel, team leader of Foundries and Forges in the sales department of Rösler Oberflächentechnik, sees the growth in lightweight components such as aluminium, zinc or magnesium die casting as the reason for this trend. On the one hand, lightweight components need to be blasted more gently, and on the other hand, ferrite deposits must on the surface must be avoided because they could lead to corrosion," he says in the interview with our editors. The choice between aluminium or stainless steel as the blasting medium depends on the material of the workpiece and the individual blasting task.
For aluminium abrasives, however, the equipment must be overhauled in any case, explains Schippel: "Aluminium has a lower specific weight, which requires a higher discharge rate and quantity of the abrasive material". The larger volume also requires a larger feedback system. According to Kapitza, Agtos has adapted their processes to aluminium abrasives by using special turbines, which avoid increased heat generation that would otherwise destroy the abrasive material: "Agtos makes sure that the abrasive material is treated gently during the process and that it is not wasted."
However, further processing is also a reason for Kapitza to increasingly rely on aluminium as a blasting material. “If hard abrasives, such as stainless-steel, remain on the workpiece in hard-to-reach places, this can damage the tools of subsequent processing stets. This is another reason why aluminium abrasives are often chosen for the non-ferritic blasting process," he explains.
Blasting Machines for Lighter Workpieces
However, it is not only the different blasting media that must be considered. The weight of the workpieces is also constantly decreasing. “This has an impact on the transport of the piece through the blasting machine. Some aluminium workpieces have to be fixed or are processed on completely different machines than previously planned," says Kapitza. According to him, the wire belt blasting machine is a very practical system. It enables high-quality machining of mass-produced parts in continuous operation.
The manufacturer Walther Trowal has also adapted its blasting machines to meet the requirements of aluminium abrasives. For this purpose, the company has developed curved throwing vanes that generate a higher ejection rate. In addition, the blast wheel is located in the continuous trough units close to the workpiece. As the systems also convey a larger volume of abrasive, machining periods are shorter despite the low specific weight of the aluminium. At the same time gentle treatment of the workpiece surface is ensured, the system manufacturer claims. Aluminium as an abrasive also has the advantage that the operating costs are lower compared to stainless steel, because the wear of the blast wheels and the plant is reduced.
Trowal has also adapted other details of the blasting machines to aluminium blasting. Since, for example, rough throwing vanes would shred the aluminium particles very quickly, the manufacturer polishes the surface of the vanes by means of vibratory finishing. This results in lower abrasive consumption, less dust emissions and a longer service life of the blast wheels.
This article was first published by MaschinenMarkt.