Rust-Free Surfaces: Why Stainless Steel Grit Could Be Your Best Option
PHOTOS: COURTESY OF WINOA
As technology, materials and design trends evolve, more and more products are manufactured with light alloys or corrosion-resistant materials. These surfaces—such as stainless steel, titanium and aluminum—require more specific cleaning and preparation than previously used materials. This is relevant to applications requiring tight specificities on ferrous contamination, including those used to protect water/wastewater, petrochemical, rail and shipyard equipment.
With elevated environmental and health concerns, rising disposal costs and ever-increasing transportation prices, this is a good time to review and, perhaps, reconsider your blasting options.
For surface preparation, the choice of abrasive is determined by:
Before discussing the possible advantages of upgrading to stainless-steel media, let’s look at other available media with non-ferrous contamination properties.
Aluminum oxide (AlOx):
Pros. Aluminum oxide (AlOx) is well known in the world of sandblasting, and it certainly has some advantages: an angular shape, iron-free, very high hardness (9 on the Mohs scale).
A good etch on the blasted surface is obtained mainly through the use of new abrasive product or the regular addition of new media to the operating mix. AlOx is also very effective for light deburring, creating a nice opaque matte surface finish.
Cons. One challenge is its breakdown rate. Being brittle, AIOx creates very fine particles that don't have enough mass to transmit the energy to clean and etch, so it quickly loses efficiency. Media life is approximately 10 to 12 times when used in a typical blast system.
Like many expandable abrasives, it can create a dusty environment for operators, reducing vision and production. A high breakage rate has an impact on the dust collector system, filter cartridge consumption and the disposal cost of all the dust and fines.
Pros. Garnet—primarily alluvial or almandine (crushed) rock—is a natural stone, a hard material that is generally a good choice for many air blasting applications. If properly cleaned, rinsed, screened and handled, the chances of saline and ferrous contamination are low, which also makes it a good choice for stainless steel, brass or aluminum surfaces.
Pros. Glass grit is typically used in shot blasting and surface finishing on surfaces machined to tight tolerances. Glass beads create a glossy matte surface finish without contamination or damage to the ferrous surface.
Cons. As round particles, beads remove paint, rust or scale very slowly and are, therefore, unsuitable for profiles and surface coatings on many substrates. The glass grain is the angular counterpart of the glass beads. The grain of glass is aggressive and suitable for coating preparation. Glass beads are typically blasted at pressures between 40 and 80 psi with a low life (cycles between three and four times).
Advantages of Stainless Steel Grit
Available in both shot and grit, in various specifications (431, 430, 301, 303 alloys), this non-ferrous media is ideal for many applications. It’s not as hard as AlOx, garnet and glass grit, but it’s heavier, durable and almost dust-free. With high energy from its mass, elasticity that makes it durable, and the ability to maintain rust-free and salt-free surfaces, stainless steel shot is also great for deburring and cleaning. To create a better bonding surface and for overlay and coating applications, angular grit is preferable.
Efficiency. Using stainless steel grit will help create a bright surface and reduce media consumption, thanks to its typical 250 life cycles and wear rates that are lower than many other solutions.
Consistency. An important advantage of using a highly recyclable abrasive, such as stainless steel, is the homogeneity and regularity of the surface profile obtained. By adding a small amount of new media daily to replace the volume consumed, the size of the operating mix remains constant, eliminating profile variation.
Remember, though, that the surface profile created by a stainless steel abrasive is greater—due to its higher mass (energy)—than the profile obtained using a lighter media of the same size, like AlOx. It is, therefore, necessary to choose a size adapted to the desired profile.
Stelux CG20 stainless steel grit surface profile on Aluminum
Ra : 9.35 µm / Rz : 70.2 µm [2.7 mils] / Rmax : 78.1 µm [3.1 mils] / Pc: 67/cm
Better ROI. The equipment required for using stainless steel media is similar to that used for an expandable media system—reservoir, blast pots, nozzles, hoses; however, since the recyclability rate is much higher, it is appropriate and recommended to add a cleaning system, such as cyclonic, air curtain or gravity. Most blasting equipment companies have simple and cost-effective solutions. Newer blast rooms and basic recovery systems are inexpensive and within reach for most finishing operations. Building an enclosure to contain and recover the abrasive may seem daunting, but the return on investment will be quick.
Cost savings. With significantly lower consumption rates than expandable media, the total cost of “sandblasting” can reasonably be five times lower using a Stelux Stainless Steel Grit product versus any expandable abrasive, provided a recycling system is used. The main savings come from:
Happier employees: Low to no dust leads to better visibility, better room cleanliness and a better work environment.
Are stainless steel abrasives suitable for all applications? Certainly not. Each of us is familiar with plants that blast in the open air or in environments that cannot physically recycle or recover abrasives, or that do not have adequate ventilation. Stainless steel is not suitable in these cases.
For appropriate applications, however, it is worth testing and evaluation to determine if stainless steel abrasive is a good fit. While the most efficient recovery systems make the use of stainless steel media inexpensive, it’s not necessary to have very sophisticated recycling systems to obtain appreciable savings.
For information about W Abrasives products or to request a visit from one of our specialists, visit wabrasives.com.
Claims or positions expressed by sponsoring authors do not necessarily reflect the views of TPC, PaintSquare, JPCL or its editors.