Blast off that Dirt, Paint, Rust and Debris
by Rebekah Fuller, Editor IQS
When I started thinking of the topic “sandblasting”, I developed a mental image of this Hulk-type man clad in goggles and protective work clothes with a heavy-duty hose in his hands blasting highly pressurized sand at … anything. Maybe he’s removing an old paint job from a car; maybe he’s eradicating barnacles from a ship. He’s the “Sandblaster” – reviving surfaces everywhere! I guess I’m assuming he’s located in a vacuum while doing this; otherwise, bystanders look out! It’s fun imagery but inaccurate as far as the technologically advanced sandblasting that exists in the real world.
From nuts and bolts to engine components to ships, cars, aircrafts and buildings, sandblasting is a way to clean off unwanted paint, dirt, rust, scales, flash and other debris; prepare surfaces for painting, plating and coating; and create texturing, roughening, etching and detailing. Sandblasting is an industrial-strength cleaning method great for eliminating all the caked-on gunk and grime that inevitably builds up on surfaces over years and years. Sandblast cabinets can in minutes get a filthy part down to shiny metal, but more intricate procedures can also be performed. Depending on the amount of pressure and type of media used, sandblasters of various configurations can completely strip parts or just polish and decorate them.
Sand is definitely not the only abrasive medium used in the blasting process; this is why it is often called media blasting. Sand can cause hazardous dust that’s harmful to the eyes and lungs. Less caustic materials include glass, ceramic and aluminum beads. Plastic, wheat starch, corn cob, pumice or walnut shells can be used for softer applications. Aluminum oxide and silicon carbide grit and powder are popular synthetic alternatives to sand because they don’t quickly break down and disperse, thus eliminating dust and making them reusable over and over again. It is very important to select the correct blasting material. You don’t want to damage delicate surfaces, and you want to ensure the desired level of cleaning on those tougher, filthier ones. Each material has certain advantages. For example, aluminum oxide is very light but penetrating and fast-cutting, making it highly versatile, and pumice is among the softest and ideal for tumbling plastics. Corn cob is used to safely blast fragile parts and wood surfaces like log homes. Silicon carbide is the hardest blasting material and very fast-cutting, making it perfect for glass engraving and stone etching.
Steel shot is also a widely used form of blast media, and machines such as shot blasters or shot peening equipment are good examples of how practical and multipurpose sandblasting can be, offering mechanical and cosmetic benefits. Striking the surface of metal parts with metallic, glass or ceramic rounds creates dimples that shape, form and mold to relieve surface strain, protect against cracks, raise fatigue resistance and enhance lifespan and also visual appearance, on top of cleaning. Care must be taken with the more aggressive forms of media blasting. You don’t want to warp something, which could easily happen with sheet metal, and sometimes industrial washing can be a more appropriate cleaning method, like when degreasing, and might prove useful prior to blasting. On the less aggressive side, sandblasting is very similar to deburring or vibratory tumbling/finishing.
No matter what material is used, containment, safety and media reclaiming and recycling are issues that require careful planning before you can start blasting away. That is why someone like my imagined Hulk-man cannot simply go outside blasting in wide-open spaces. Portable sandblast machines exist for proper utilization outside on the surfaces of buildings or objects too big to put in a sandblast cabinet or that cannot be transported to a larger blast room. Stationary sandblast cabinets are similar in size to a clothes washer or dryer. Other sandblast equipment includes complete batch processing systems with stations and mechanisms for loading, blasting, parts drying/blow-off and media recovery and reuse. Sandblast equipment relies on adjustable streams of pressurized air or water, or a combination of the two, to shoot the media out of guns or nozzles either contained inside a blast cabinet or room or attached to a portable pressurized vessel. The water helps to eliminate sand’s dust.
Manufacturers offer a wide variety of manual, remote controlled, automatic or robotic sandblast equipment, plus protective eyewear, clothing and respirators for workers in and around the machines. Please consult a manufacturer or sandblasting professional before undertaking any procedure, from cleaning and polishing small parts to eradicating graffiti from a building to engraving a glass piece or a stone monument. You want to be certain of the appropriate blasting apparatus, media and amount of pressure before commencing.