What Blast Media Should I Use In A Wet Blast Cabinet?
Introduction
Choosing the correct abrasive media for wet blasting is very important because an inappropriate media choice will not provide the desired finish. It can not only cause a rework but in some cases may cause damage to the blasted surface.
This article guides you in choosing the appropriate media for a wet blasting cabinet.
Different abrasive media that can be used in a wet blast cabinet
The different abrasive media that you normally use in a wet blast cabinet are garnet, glass bead, aluminum oxide, crushed glass, and soda bi-carbonate
Garnet (Almandine and Alluvial) : Garnet is a type of gemstone and has good natural abrasive properties. Garnet has a sub-angular shape, Mohs hardness number 7 to 7.5, comes in different grit sizes and it can remove coatings, old paint, rust, and mill scale from metal surfaces and can work on hard metals also. The coarser grit is suitable for working on aluminum, steel, stainless steel, and other metals and finer grit is suitable for materials like fiberglass. Garnet can quickly work through coatings and contaminants.
Crushed glass: Crushed glass has Mohs number of 5.5 to 7 and is good for wet blasting aluminum and steel. The crushed glass has an angular shape and forms a sharp anchor profile; however, selecting a proper grit size and blasting velocity can give you the required anchor profile/finish. The advantage of crushed glass is it is a recycled material (environmentally friendly), cheap, and effective for many works. Crushed glass can be an economical media for the wet blasting of components like alloy wheels.
Glass beads: A glass bead media consists of spherical glass particles and leaves a fine and polished finish on the blasted surface. The Mohs hardness of glass beads ranges from 5.5 to 6 and the particle size can be coarse to fine.The glass beads have a smooth surface all over and are safe for blasting soft and delicate materials. Glass beads are very popular for wet blast cabinets and by varying the blasting velocity a smooth anchored profile or a fine finish can be achieved.
Aluminum oxide: The aluminum oxide has angular shaped particles; a Mohs hardness of 8 to 9 and the grit size of this media can be coarse to fine depending on the need. By varying the grit size and blasting velocity, aluminum oxide can be used for wet blasting hard metals (even with thin sections) and this is a good media for tough cleaning, extracting paint, coating, and rust. This is useful for finishing and edge rounding of surfaces. The high recyclability of aluminum oxide makes it an affordable media.
Soda bi-carbonate: The soda bi-carbonate used for wet blasting is not the baking soda used in our kitchen. There are companies like Armex and Natrium that manufacture a variety of soda bi-carbonates specifically for the soda blasting process. The size of soda bi-carbonate particles may vary from 70 to 270 microns. Soda bi-carbonate is not an abrasive material and hence it cannot be used for surface profiling. Soda bi-carbonate is used as a media when the surface needs a smooth finish without any profile.
Factors to be considered for selecting the right abrasive media for wet blasting
The factors you have to consider when selecting an abrasive media for wet blasting are the grit size, shape, hardness, and density of the media, and blasting velocity. Factors like friability (tendency to break into smaller particles under force), recyclability, and cost are also important.
Size: The blast media comes in different grit sizes. Larger media particles will make deeper depressions but lesser depressions per unit area resulting in a rough surface finish. Smaller abrasive particles make shallow depressions but more depressions per unit area result in a finer surface finish.
