alt=""/>Glass bead blasting cabinets feature rubber gloves that allow the operator to handle and manipulate parts in the cabinet. These gloves are prone to wear and should be inspected on a routine basis. Gloves are available in various sleeve diameters and lengths to accommodate all blasting cabinet models. A blasting cabinet features a glass viewing window. The inside surface of the glass eventually becomes abraded, making it difficult to see through. Depending on how much use the cabinet sees, plan to replace the glass about once each year.
Blasting cabinet guns feature a ceramic nozzle that provides the appropriate media spray pattern. The ceramic nozzles, although very hard, eventually wear, lowering media blasting efficiency. Nozzles are easily replaced. It’s wise to keep a few new spares handy.
A view of a hopper in a glass bead cabinet. Depending on the cabinet’s hopper design, media may start to build up on the tapered walls. In conjunction with airborne moisture absorption, the media is less able to accumulate over the media feed tube. Keeping the hopper full with the required level of fresh media helps to avoid this.
Maintaining a blast cabinet’s clear viewing glass and adequate dust vacuum improves worker visibility.
If the part to be cleaned features hidden passages that cannot be positively cleaned, avoid blasting with an abrasive media. Also, avoid bead blasting into female threaded holes, since beads can be trapped, and the abrasive action can degrade the thread integrity. After bead blasting, use compressed air to flush all traces of the bead particles. Do not try to initially remove bead particles with a wet rinse, as this can easily cause beads to be stuck to surfaces, possibly in small clumps inside any passages. Also, never use an abrasive media on a part that is wet or features oil or grease. The part must be degreased, rinsed, and dried prior to blasting.
Concerns about potentially contaminating threaded holes with media can be avoided by plugging these holes with temporary bolts. After bead blasting, remove the bolts and manually clean female threaded holes with a chaser tap and solvent. I discuss the use of chaser taps later in this chapter.
Soda (sodium bicarbonate, essentially a form of baking soda) is a nice choice, since it’s water soluble and allows easier removal via rinsing. Soda’s benefits include being able to clean even surfaces that are still contaminated with oil or grease. Soda does a great job of cleaning, but it does not allow you to soften sharp edges because it’s not as aggressive as other media such as glass bead. Although soda might be usable in a conventional blast cabinet, it’s best to use a blast system that is designed for soda for highest efficiency and dust reclamation.
There are distinct advantages to the use of soda, instead of traditional methods using glass bead or plastic. Unlike these other medias, soda easily removes surface grease and oil residue, as well as paint, eliminating the need for a precleaning step. One distinct benefit relates to cleaning an intake manifold (especially a dual-plane-style manifold). The danger when using glass bead (or other abrasive media) lies in the concern for particulates becoming trapped inside hidden/hard-to-reach runner areas, which could lead to disastrous results in a running engine. Because soda is water soluble, entrapment is avoided with a simple water rinse. Any particles that might remain don’t pose an abrasion danger (because they’re not hard abrasive particles) and effectively break down during engine operation.
Benefits of Soda Blasting
• Soda is granular, suitable for use in pressure pots or in cabinet systems.
• Soda crystals are sharp and provide outstanding cleaning/stripping performance when delivered under relatively low pressure but with high velocity.
• Soda is “friable,” meaning that it fractures into smaller particles. This increases cleaning performance while softening blasting impact. Unlike other blast media, soda is relatively soft and doesn’t damage metal surfaces.
• Soda is nontoxic and nonhazardous, with a nearly benign pH of 8.2.
• Soda is water soluble and easy to rinse clean.
• Soda leaves no abrasive “grit” that can damage moving parts.
A wide range of blasting media is available, each with its own characteristics. Depending on the material to be blasted, including cast-iron, cast-aluminum, steel, etc., and type of component including blocks, heads, manifolds, pistons, connecting rods, etc., and the desired surface finish, attention must be paid to selecting the appropriate type of media for the specific application.
Sand
Commonly available silica sand is far too aggressive and should never be used on any engine-related surfaces. This is often used on car components, body panels, frame rails, and suspension parts. But sand is so abrasive that it literally eats away at soft aluminum, pits cast-iron, and does irreparable harm to other steel parts.
Glass Bead
Depending on the specific grade (grit), glass bead media is produced as preformed tiny balls, which, depending on the grade of glass, produce a smoother and “brighter” finish than angular abrasives (results in a matte satin finish). Glass bead, like most blasting media (other than soda), does not act as a desiccant, so the component must be dry and grease-free prior to blasting. Grease, oil, etc., are eventually removed during blasting, but over the long haul, you end up contaminating the glass bead in the hopper. The same applies to layers of paint that flake off easily. Large flakes (larger than, say, your little fingernail) collect in the hopper and eventually clog the feed tube. When/if this occurs, a quick fix is to place the tip of a bolt into the gun nozzle and hit the foot pedal. This causes the bead to “back-flush,” temporarily clearing the system for continued use. Regardless, glass bead or any blast media should be routinely changed to remove foreign contaminants and to renew the capabilities of the media.
What most people don’t realize is that a huge range of glass bead is available, from very, very aggressive down to ultra-fine grades. All glass bead is not created equal, so pay attention to what you’re buying. A fine-grade glass bead produces a matte satin finish.
Crushed Glass Grit
Similar to glass bead in initial appearance, but the particles feature random shapes and sharper edges. This cuts faster and is more aggressive than glass bead, and produces a medium texture.
Soda
Unlike hard and aggressive media such as sand,
