Ship Maintenance
Shipboard corrosion control and preparation of surfaces for recoating are two of the most expensive maintenance challenges facing both military and civilian ship operators. For example, the US Navy estimates that fighting corrosion absorbs 25 cents of every maintenance dollar; the annual corrosion cost for Navy ships in 2007 was estimated at $3.2 billion. Ever-increasing operations tempo, as well as business economics, manning reductions, training cutbacks, shortened shipyard availabilities, and diminished waterfront/intermediate maintenance capacity all contribute to a growing need for new and better maintenance approaches.
Lasertronics’ laser ablation technology is a game-changer in this demanding environment.
Corrosion Removal
The Lasertronics system removes rust and mill scale from steel materials like no other method. The laser excites the oxygen in the corrosion layer, popping the oxide off the native metal.
Laser cleaning with color pulse control is highly selective, removing only metal oxides, and leaving the parent metal substrate intact.
The physics of the laser process make it exceptionally effective in removing corrosion products from weldments and complex details in ships’ structures. The laser can efficiently remove corrosion products from any textured surfaces or notch details that the laser can “see”.
The images below depict the before and after removal of paint and corrosion from a complex fixture. No other technique can deliver this degree of cleanliness on complex surfaces.
Before laser cleaning
After laser cleaning
Coating Removal
Concentrated laser energy “ablates” coatings cleanly by quickly heating the coating material to the point of chemical dissociation. The coating breaks down into its chemical constituents and falls away from the surface. If the laser can “see” a coated surface, it can strip the coating, regardless of the complexity of the surface. Lasertronics’ unique color-sensing workhead selectively ablates only a particular color of coating. This unique color-selective workhead forms the core of Lasertronics’ product line.
The unique optical detector in our workhead interrogates the surface before each laser pulse. It allows the pulse to proceed only if the color to be stripped is still present. When the sensor no longer detects that color, the laser is instantly suppressed. When the moving workhead once again finds that specific color, the laser is re-enabled.
In addition to permitting selective stripping of a particular coating, this unique Lasertronics feature completely prevents damage to any substrate: When a coating has been stripped, the sensor detects its absence, and supresses the laser. This feature allows use of the Lasertronics system on delicate materials such as aircraft skins, and on metals where surface hardening is unacceptable, such as warship hulls.
In addition to paints, our system quickly strips sealants, anti-corrosion coatings, and anti-fouling coatings. These coatings can be particularly troublesome to remove by conventional means.
The simplest version of our technology consists of a single color-selective workhead with air purge system, designed to be used by a human operator. More complex installations involve multi-laser, robotically controlled systems that automatically strip complex surfaces such as helicopter rotor blades. One of these systems is in use at the US Navy’s Fleet Readiness Center – East in Cherry Point, NC.
Top Coat Selective Removal
The Lasertronics closed-loop color-sensitive controls enable selective coating removal. The operator can set the controls to strip one color, and leave others untouched. One example would be stripping top coats, but leaving primer intact. The image below shows both X-Y raster and rotary laser scan patterns on the green “Marine One” finish coating where the laser selectively removed only the finish coating, leaving the zinc chromate primer in place.
Example of the laser selectively removed only the green finish coating for the “Marine One” rotor, leaving the zinc chromate primer in place. Both X-Y raster and rotary laser scan patterns are shown..
For ship hull applications, this allows removal and renewal of discrete layers in contemporary anti-corrosion (AC) and anti-fouling (AF) coating systems. In many situations, this capability allows refurbishment of hull coatings without needing to remove all coating materials and recoat the hull surfaces from bare metal. For instance, depleted AF coatings can be selectively removed from large areas of the hull where the AC coatings are still serviceable. This approach provides significant benefits for hull overhaul cost and schedule, as well as significant reduction in the total waste stream generated.
Closed-loop controls, unique to Lasertronics systems, enable safe stripping of coatings or corrosion to any level, including bare metal, while preventing any damage or melting of the surfaces. Critical metallurgical parameters such as ductility, hardness, and surface profile are preserved by the Lasertronics process. By contrast, open-loop laser processes that lack Lasertronics’ controls incur risk of damaging metal surfaces by overheating. When working on surfaces with low reflectivity, such as steel, this overheating danger is heightened.
Waste Stream Management
The Lasertronics laser ablation system dramatically reduces and simplifies management of the waste products generated by stripping. It does this in two ways:
- Laser ablation produces significantly less waste than do other stripping processes. The laser “photoablation” (vaporization) process converts a significant mass fraction of the target coating materials into benign gases, which vent to the atmosphere. The remaining particulate coating and corrosion products, typically polyaromatic hydrocarbons (PAHs) and fine particulate, are a small mass fraction of the total coating compound.
- The GLC laser system accommodates an integral waste handling system that captures and sequesters effluent particulate materials in standard HEPA and carbon filter media. Controlling and disposing of these filters is far easier and cheaper than comparative disposal of contaminated solvent or blast media.
In comparison to current shipyard coating removal methods such as grit blast, needle guns, and solvents, the laser achieves ten-fold to one hundred-fold reductions in waste stream (see Figure 3 for comparison of resultant waste streams). The exceptionally clean environmental footprint of the laser decoating process simplifies non-recurring job-site pollution mitigation measures and significantly reduces waste management costs.
Toxic waste generation: Stripping one pound of paint generates very different volumes of waste, depending on the stripping method chosen
Versatility
The Lasertronics system can be configured for both manual and robotic tool positioning. The photo, below left, shows a standard Lasertronics 400W laser system installed in a maintenance hangar at U.S. Naval Air Station, Patuxent River, MD. The gray laser cabinet connects to the hand-held laser tool via a 50-meter, orange-colored fiber optic umbilical cable.
This 400-watt manual Lasertronics system was delivered to the Pax River Presidential Helicopter Base. From left: chiller, laser, umbilical cable, workhead.
Lasertronics laser system in use by the US Naval Undersea Warfare Center, Keyport, WA, for cleaning test torpedoes.
Heads-up display for confined space access
The manual tool with extended fiber optic umbilical can easily reach surfaces difficult or impossible for human access. An optional video camera in the tool and heads-up operator’s display enables stripping of surfaces in confined spaces, e.g., voids and tanks, or in difficult to reach spaces such as beneath or behind equipment.