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       Brandon Acker, president of Titan Abrasive Systems, talks about how sandblasting can play a huge role in bringing aging aircraft back to life.
       The impact of Covid-19 on the financial health of the airline industry is evident in the numbers. The staggering losses caused were the main catalyst behind major airlines’ decision to renew their existing fleets rather than acquire new aircraft.
       The process of repairing old aircraft falls under MRO and lasts for decades. With Covid-19 severely hampering revenue streams and eroding profitability, more and more airlines are turning to MRO to maintain fleet efficiency.
       There are many methods for repairing an aircraft; Perhaps the most important of these is sandblasting. Many parts can be made practically new by sandblasting. Sandblasting alters the surface of a part or structure in a variety of ways, depending on the type of material and sandblasting parameters.
       In aircraft repair, the sandblasting process typically has two purposes: 1) Clean and sand the surface not only to remove all dirt, grime, oil, etc. from the surface, but also to roughen the surface to provide improved adhesion. new surface finish, whether paint, powder coating or polyurethane. Gliders provide the best example of this type of application. 2) Cleans the surface and removes burrs without creating any “outline” or removing any material from the surface of the product. For example, this process can be used for jet turbine parts, where removing even the smallest amount of metal can affect engine performance and safety.
       Simply put, softer materials at lower pressure can gently remove coatings, while very hard abrasives applied at high pressure can add texture to surfaces that require finishing.
       There are several parts or systems on commercial aircraft that cannot be retrofitted. However, the most important components are the engine components. Sandblasting these valuable items may require only minor dirt removal or major repairs (although complete overhauls are not performed as often as repairs).
       In an engine, the most expensive components are the turbine blades, bearings and engine control systems. These issues must be carefully addressed during the repair process to not only avoid huge financial losses, but also to ensure the overall safety of the engine itself. Typically these parts are repaired using a process called microblasting. It is used for extremely localized tasks and can be done manually or by machine.
       Microblasting involves mixing air and abrasive into a highly concentrated stream. The “laser” focus of microblasting is ideal for removing coatings from recessed and protected areas of engine blades, as well as the inside of small air passages. Microblasting precision is achieved by using a small nozzle and fine, sharp abrasives such as aluminum oxide. If more complex coatings are used, silicon carbide can be used as an alternative material.
       Vacuum, centrifugal, soda blasting, steel chips, bristles, dry ice, bead blasting and bead blasting are other sandblasting procedures. Abrasive particles can be organic, metal, silicate, plastic or stone. The most widely used include glass beads, aluminum oxide, plastics, steel granules, silicon carbide, cinders and even corn cobs. The question is, which media is best for aircraft repair? How do you know which media to use for each part?
       First, the reason there are so many media is because each one does a different job well. The performance of each material depends on several key grinding characteristics: shape, size, hardness and density. Typically, for anything made of steel, a material is used to create a profile on which the coating can be placed. In contrast, engine parts do not require roughing; as mentioned earlier, the desired result is a smooth surface without actually removing material from the part. Airplanes are primarily made of aluminum, so they are usually sandblasted using some kind of plastic. It cleans aluminum without roughening it or removing material.
       Sandblasting is performed by companies that specialize in the process, rather than by the airlines themselves (although some airlines actually own companies or have separate departments doing this work). Regardless of the process or medium used, the process takes place in a sandblasting chamber or sandblasting cabinet, depending on the size of the part. As the name suggests, the only difference between the two is size: both have the same basic components, namely the blast cleaning system, dust collector and media recovery system.
       Sandblasting booths can be large and are used to blast fuselages, landing gear, landing gear and other large items. Larger sandblasting booths are usually made to measure; size is determined by many factors, including the size and weight of the largest part to be sandblasted. A sandblasting room is a place where you can go in and work inside a structure.
       In contrast, many jet engine components fit nicely into a sandblasting cabinet. In sandblasting rooms, work is carried out from the outside wearing protective gloves.
       The method of application of the material is also a key part of the sandblasting process. There is a report on the Aerossurance website called “Aggressive Sandblasting Leads to Engine Fire and IFSD.” Apparently, during maintenance on one of the aircraft, the plasma spray on the bases of the blades was removed and replaced. Before applying the plasma coating, the surface of the blade is sandblasted with aluminum oxide.
       The problem was that the operator performing the procedure was holding the sandblasting gun about 2 inches from the surface instead of the intended 4 to 6 inches. According to the post-mortem audit, shortened spacing and “incomplete closure of the blade root collar, resulting in exposure of uncleaned areas during blade overhaul” were the root causes of fatigue cracks due to “incorporation of the sandblasting media into the blade.” Fatigue cracks continue to grow until the blades would not separate, resulting in a complete loss of engine power. “Although the plane landed safely and no one was injured, the damage was significant – not to mention the frayed nerves of the pilot and crew.
       When done correctly and using the right materials, an aircraft in need of repair can be given new life through sandblasting. With the cost of new aircraft prohibitive due to the financial impact of Covid-19, every airline should seriously consider refurbishment and sandblasting.
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