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What is wheel blasting?
Wheel blasting, wheel blast cleaning, or centrifugal wheel blasting is a mode of surface preparation that does not require compressed air.
These systems can be standalone batch cabinets or fitted with a monorail/conveyor to be a part of a larger production line. It is a highly efficient form of processing that uses recyclable media for prolonged operation. However, this blasting lends itself to repeated shapes/products and is not as versatile as a blast room.
So, how do they work?
Instead of compressed air, wheel blast cleaning systems utilise a rotating wheel to propel abrasive. The wheel sits inside a wheel housing, and abrasive is fed into the wheel’s centre called the “control cage”. Inside the wheel, there are several blades, abrasive travels along with these blades from the control cage. Abrasive is then propelled in an arc at the product in a “blast pattern”.
The size of the blast pattern is typically more than a few centimetres wide and around a metre long. When impacting the product’s surface media concentration per square inch depends on the type of the machine and how far away the wheel is from the part you are trying to clean. Moreover, in one wheel blasting machine, there can be many wheels propelling abrasive.
Media, mix, and how they affect finish
The product’s finish requirements and its gauge dictate abrasive selection before coating. Abrasive variables that affect surface finish are size, shape, mineral composition, and friability.
Once an abrasive is selected, the media mix inside the machine must be monitored. When blasting with recyclable abrasives, they gradually decrease in mesh size once they strike the product’s surface. Once media reaches a specific size, it is filtered out of the machine; however, when this abrasive is expended, the same volume of new abrasive must be fed into the machine. Therefore, if there is a media mix imbalance of small and large abrasive particles, it can drastically affect the surface profile and impact paint adhesion. Although many systems on the market are automated to account for this, some require manual refilling and monitoring.
Warping
It is also important to add that compressive stress builds in the metal you are processing. Therefore, once the component can no longer tolerate these stresses, it will warp and bend. Before blasting, product gauge, abrasive mesh size, and the speed at which abrasive is thrown must be considered to reduce this risk.
For instance, blasting light gauge workpieces requires a smaller mesh size abrasive to reduce the risk of warping from compressive stresses.
Setup and blast pattern
When setting up a new machine, it is important to read and adjust the blast pattern before processing. Personnel will carry out this by blasting a painted test piece for half a minute, revealing the pattern.
The control cage’s opening position determines where the abrasive’s arc will start. The cage’s positions are analogous with a clock face, and it takes 180o to come off the blades. If the cage opening is aimed directly at the workpiece, abrasive will miss it completely and blast up right into the wheel housing. To avoid damage to the machine, consider the cage opening position, wheel RPM, diameter, and other variables before processing.
