Sandblasting in the Aerospace Industry
Corrosion on aircraft is the same as rust of the metal parts, although aluminum corrosion doesn’t produce the reddish color most people think of as rust. Rather, it usually first shows as a whitish or grey “dulling” of the aluminum surface, then progresses to more and more severe pitting and eventual destruction of the metal. Left untreated, corrosion can make an aircraft unairworthy in just a few years.
The main types of corrosion in the aerospace industry are:
- Uniform surface attack by exposure to oxygen
- Stress corrosion in highly stressed parts such as landing gear or engine crankshafts
- Crevice corrosion in joints where moisture is trapped
- Filiform corrosion through poor surface preparation
The problems caused by the corrosion in the aircraft industry are:
- Risk to safety – cost to human life
- High cost of maintenance
- Hard to detect
- Reduction in life of asset through fatigue cracks
The only sure fix to corrosion is to remove it once it has been detected. Light surface corrosion can be removed with abrasion (the specifics of which depend on the metallurgy of the corroded part), then application of a corrosion inhibitor, primer and paint.
Dry Blasting or Brushing
Traditionally, aviation manufacturers and MRO providers have relied on manual steel brushes or dry abrasive blasting processes for surface finishing and cleaning. The problems associated with these processes are:
- Removing corrosion with stainless brushes or brushes that have been used on steel or rust result in working steel into the aluminum where it will ruin the paint job
- The dust resulting from dry blasting poses health problems to employees
- Dry blasting also creates safety hazards due to static electricity, which can lead to explosions and fires.
- These traditional abrasive blasting methods also require costly post-cleaning processing, amounting to more time, labor and floor space needed.
- In addition, all of these issues combined increase the potential for premature, possibly catastrophic structural failure in the field.
Wet Abrasive Blasting
Aerospace is one of the many industries that now uses wet blasting in various manufacturing processes.
In wet vapour abrasive blasting, the abrasive is moistened in a buffer of water prior to impacting the surface. The process involves mixing water and abrasive inside a pressurised blast tank and the mixture of air, water and abrasive is propelled onto the surface being blasted. When wet abrasive impacts a surface, fine particles are sequestered in water droplets. The additional water weighs the particles down, preventing dust getting airborne.
The main advantage of vapour abrasive blasting over dry blasting is that it reduces dust, allowing operators to work in a wide range of environments with minimal setup and clean-up costs. By suppressing the ambient dust, it causes minimal disruption to the surroundings. The abrasive media is encapsulated in water, which immediately falls to the ground, and up to 95% of the airborne dust is eliminated.
Wet abrasive blasting processes are being increasingly used in the aviation industry from bonding and etching newly formed components, making, landing gear or radial engine parts. It is also used in preparing surfaces for non-destructive testing to expose stress cracks. The applications in the aerospace industry include:
- Etching and bonding;
- Degreasing, de-rusting,
- Descaling, general cleaning;
- Stripping paints from composites; stripping coatings;
- Smoothening. degreasing,
- Testing during overhaul for crack detection.
Wet abrasive blasting can offer several benefits over other forms of cleaning using chemicals or dry blasting
- Improved Process Control
In high precision applications such as the aerospace industry, wet blasting offers the operator to precisely control the blasting process and adjust the parameters to produce an impact that ranges from minimal to aggressive. The use of water in the process provides a cushioning effect and feathered finish that minimizes the risk of damage to these parts.
- Scalability
Unlike dry blasting, wet blasting does not require encapsulation and the use of blast booths as it is virtually dust free. Large parts such as the fuselage, wings and the rudder do not need to be dismantled for blasting.
- Quality Control
The aerospace industry follows strict performance and quality standards. The ability to repeat the wet blasting procedure from one application to the next ensures the consistent, uniform results that meet these stringent specifications.
- Environment protection
The increasingly stringent environmental standards make wet blasting an effective substitute for metal finishing processes that use harsh chemicals to achieve the desired result.
- Speed and efficiency
Not only is wet abrasive blasting effective, but it is very efficient when compared to processes that use chemicals or rely on manual finishing.
- Economy and time saving
Ultimately, all the above factors result in greater economy, reduced costs, and savings in time.
Different abrasive media can be used for different aerospace applications and surfaces such as:
- Removal of carbon deposits from turbine blades using natural sources with a non-aggressive blast media such as corn cob.
- Aggressive blasting for casting investment removal using aluminium oxide
- Paint stripping with plastic blast media
- Cleaning delicate aerospace components from landing gear to engines using soda bicarbonate
