Corrosion and scale are common issues in many industries, especially in harsh environments with exposure to high temperatures or salt water. Rust forms as a result of chemical reactions when iron and steel is exposed to water or oxygen, signifying the return to its natural state.
If not treated promptly, rust can lead to various problems including pitting, brittleness, stress corrosion, cracking and structural damage, affecting performance and reliability. To prevent rust, methods like painting, oiling, greasing or plating with another metal are used, but these can be costly and impact weldability.
Traditional rust removal methods involve chemicals, acids, electrolysis, mechanical abrasion, or blasting, but they are labour-intensive, time-consuming, generate waste and may produce toxic chemicals and fumes.
Today, a more effective alternative is utilising industrial-grade, precision laser-based systems that remove corrosion and scale with a high-energy laser beam that leaves the substrate unaffected. This has been a technology that until recently was too expensive to justify, but economies of scale are beginning to bring it into use in a multitude of applications.
PRICE DROP
“The cost per watt of laser power has dropped dramatically,” says Dave MacLellan, executive director, the Association of Laser Users (AILU). “It’s a straight line going down, getting cheaper because of new technology, higher volumes in manufacturing, and huge numbers of handheld laser cleaning and welding systems being made in China. I used to sell laser welding systems starting at £15,000; they now start at under £5,000 and the price is dropping still.”
This technology can be used in diverse applications, from cleaning large commercial aircraft parts to microchips. It’s effective for selective cleaning and even de-painting. Minimal preparation and cleanup time are needed, and the equipment is durable, lasting for decades. It’s a ‘low heat-input process,” meaning parts are cold to the touch after laser treatment.
The laser emits pulses, with some energy absorbed by contaminants, causing them to change from a solid to a gas instantly, with the remaining energy heating a specific area in such a way to generate a shock wave that removes surface contaminants without harming the substrate. This method is not limited to rust but addresses oxide buildup on various metals. For instance, automotive companies use it to remove oxide layers from stored aluminium parts before welding to prevent weld porosity.
MacLellan adds: “Some handheld laser welding systems now have a cleaning function so you can pre-clean and/or post-clean.”
Laser cleaning systems also play a significant role in industries utilising moulds, such as tyre manufacturing, to remove accumulated residues from rubber, plastic, grease, oils or fluids.
PPE REQUIREMENTS
Both MacLellan and Tara Murphy, senior laser applications engineer, Woodrow Scientific, warn that the systems are not risk-free, despite the lack of fuss in the supply chain. Murphy says: “If you were to order a laser cleaning system and have it delivered, you might be forgiven for not realising that there are implications and particularly how to insure such a product, in terms of public liability.” It could be easier to use service providers that bring in systems or take away parts and clean them for you for a fee.
MacLellan says: “The two main hazards with laser cleaning are direct or reflected laser light in your eyes and on your skin, and the fumes that come off the process which you could breathe in.”
He adds that responsible users of laser cleaning systems should protect their eyes with goggles and their breathing with a mask as well as using fume extraction, as they would with processes such as welding or soldering for example. Users should be particularly careful in laser cleaning applications because of the variety of materials vapourised in the process.
“You’ve only got one pair of eyes,” he warns. “You wouldn’t stare down the barrel of a laser pointer, it’s the same with laser cleaning except that the wavelength of the laser is outside the visible spectrum of human sight, so you can’t see it. This is why everybody in the vicinity of a laser cleaning system being used should wear eye protection, an invisible reflection off a shiny surface could be almost as damaging as the direct beam itself.”
It’s crucial to provide the right safety equipment, such as goggles designed to protect against the laser’s specific wavelength, typically 1064 nanometres (nm). Traditional green welding curtains are usually transparent to 1064nm wavelengths, but specialised laser-safe curtains and partitions are available from reputable laser safety suppliers.
Hand-held laser cleaning systems using Class 4 lasers at 1060nm wavelength can be purchased directly from suppliers. However, these units may lack safety guidance on proper usage and required protective gear. Therefore, companies acquiring and operating such equipment should appoint a laser safety officer, and anyone using the system must undergo relevant safety training. Training courses are available from various companies, which can be found via, among other places, the AILU website’s ‘Products and Services Directory’ section.
NEW WAVE
Woodrow Scientific is one company, however, that is developing eye-safe laser cleaning systems that operate at 1550nm. This wavelength, rather than being transmitted through and focussed by the lens of the eye and instantly damaging the retina, gets absorbed as heat, giving human reflexes the chance to kick in, prompting the eye to blink and the body to move away.
Murphy says: “We’ve been operating for 18 months, so we’re still very much in our development stage, dabbling in relatively low powers. The state of the art for 1064nm lasers are now in the order of kilowatts; our 1550nm ones are 100W, but we do have plans to increase so that we can be more competitive in terms of power.
The technology for 1064nm lasers has been established and proven for decades, whereas 1550nm lasers are in their infancy. But Woodrow Scientific’s eye-safe laser technology, once at comparable power to the traditional technology, could eventually be used in open spaces in a variety of delivery methods, such as on robots in a factory production line, drones for cleaning larger structures outside or up high.
“We see ourselves as trying to remove some of the barriers that are blocking the adoption of laser technology,” says Murphy. “We don’t want to be negative about 1064nm; it’s a very well-known and reliable wavelength and has an important place in the market, but in offering something that’s safer we hope to make it more accessible.
“I would encourage laser cleaning all round, at whatever wavelength; it’s a technology that needs to grow.”