Surface Preparation Techniques for Large Parts
There are many applications for abrasive blasting; however, when you have gargantuan parts your choices are more limited…
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Cleaning parts using spray washers or immersion systems is sometimes prohibitive due to the size of the parts. Ships, airplanes and rail cars are a few of the items that require a different approach to surface preparation.
One method of surface preparation is dry blasting of which there are two common types: air blasting and airless turbine wheel type blasting systems.
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Air blasting uses compressed air to propel media against the workpiece. Centrifugal (wheel) types use centrifugal force to propel the media. The two types of compressed air blasting systems are suction and pressure blast processes.
Suction type blasting systems use blast guns with two hoses. One hose handles incoming compressed air and the other handles media. A vacuum is created when the compressed air passes through the suction gun. The vacuum pulls the media through a hose, and air and media are propelled toward the workpiece. The vacuum created, the lift required and the type of abrasive control the amount of abrasive.
Direct pressure systems propel media using direct pressure from a pressurized media storage bin. This creates a higher velocity. Direct pressure units are used for processing large components, such as aircraft and ships, since they can be used in either cabinets or portable equipment.
In an airless turbine wheel unit, a high-speed rotating paddle wheel propels the media randomly toward the component. The blast stream is larger because of this. It is used for light burr removal, cosmetic finishing and surface preparation. Less abrasive and heavy media must be used with these systems so that the media will reach the workpiece.
Alabama Shipyard
Alabama Shipyard (Mobile, AL) was looking for a way to improve maintenance and construction applications. Because complete hulls, sections and components had to be blasted and protected for marine vessels, the sheer size of the work was a challenge.
One of its largest projects was a three-story BCPR blast room that doubled as a paint facility. Because of EPA and OSHA concerns, as well as the need for improved productivity, open blasting was replaced with an enclosed blast cleaning process. The blasting room, supplied by USF Surface Preparation Group, recovers spent media, using the room's floor recovery system and Schmidt vacuums. Recovered steel shot is placed back into a storage hopper. From there it goes to a wash system and back into a double chamber blast pot.
After blast cleaning, the plenum doors in the room are repositioned, converting the room into a paint spray facility.
McEntire Air National Guard Base
As one of only a handful of "stand alone" National Guard bases in the country and the home of South Carolina Army and Air National Guard, McEntire Air National Guard Base in Eastover, SC, required numerous maintenance services.
McEntire was looking for a number of maintenance and facility solutions, including upgrading facilities and replacing equipment. After a productivity audit that focused on the paint and blast facility, engine and transmission rebuild bay, radiator cleaning and equipment wash down bays, detailed surveys and equipment were evaluated for solutions to maintenance productivity.
The Base converted the blast room operation from garnet to aluminum oxide, upgraded all ducting through the blast and paint facility and replaced outdated equipment and hand tools with Graco applicators, Dynabrade tools and Accustrip equipment.
The Base also completed a major aircraft hangar floor restoration, replacing an existing and ongoing sand blast operating that was contaminating aircraft maintenance operations.
Ministry of Railways of Russia
After more than a year of detailed analysis and study, the Ministry of Railways of Russia (MPS) ordered three blasting systems for its facility in Burlington, Ontario, Canada. The MPS employs 1.3 million and has more than 140,000 kilometers of rail track. All Class One railways of North America combined would equate to one third of the rolling stock used by the entire railway system of Russia. The Wheelabrator blast wheels throw steel abrasive using centrifugal force.
This order was the largest of its kind in the surface preparation blast industry in Russia. The Russian market has much potential and the company has made a long-term commitment to allocate resources and people to continue to develop the trust and confidence of the Russian business community.
