Welding safety goggles are worn to protect the welder from shrapnel, ultraviolet, infrared light and bright light that can cause temporal or permanent blindness. The lens used in these safety goggles have to be hard coated and anti scratch. Anti-fog goggles would also be useful so that the wearer can have a clear view of the welding operation.
Many wonder how safety goggles differ from regular eye wear. The difference is that safety goggles have to conform to a standard, this standard is tabulated in the OSHA (occupational safety and health administration) 29CFR1910.133 (a)(5) eye and face protection. Also listed is the appropriate lens to go with specific welding operations.
The modern material of choice in protective lens manufacture is the polycarbonate lens. These lenses are tougher, thinner and lighter than regular plastic lenses. It is important that welding goggles be comfortable for the wearer and not too heavy so that the wearer is not blinded by excess sweat. The lightness and thinness of polycarbonate lenses provide this convenience without compromising on protection. They offer one hundred times more protection from the suns UV rays and are ten times more impact resistant than ordinary glasses.
Polycarbonate lenses were developed in the 1970’s for use in space related programs like visors on space suites and shuttle wind shields. In the early 80’s goggle lenses made of polycarbonate got introduced due to a demand for tougher and lighter lenses.
The primary properties of polycarbonate lenses are high impact resistance; a refractive index of 1.586 astm d 542; a haze of 1.0 astm d 1003; a light transmission 88% astm d 1003; and the ability to filter 99.9% of harmful radiation.
For the polycarbonate lenses to be used efficiently in welding goggles, they have to be hard coated to increase its impact resistance and treated to the appropriate shade to cope with the bright lights that emanates from and electric arc weld.
Glass protective lenses where the first to be used before the advent of the polycarbonate lens. The first glass lens goggles where those employed in a blast furnace, while this goggles provided protection from shrapnel is failed to give adequate protection from harmful radiation produce during welding. After a series of modification lenses were developed specifically for welding and these offered the desired protection needed.
Glass lenses have their limitations; some of the limitations are listed below.
- They are heavy and thick
- They are expensive in comparison to the polycarbonate lenses
- Scratch proofing the lenses are expensive
- Have lower impact strength than polycarbonate lenses.
Nylon is a tough material used in lens manufacture. It is characterised by its ability to absorb moisture which gives it a very high impact resistance. Nylon lenses also have a high thermal resistance and are scratch resistant.
All materials used in protective welding goggle lenses must be subject to rigorous tests. The OSHA (occupational safety and health administration) and the ANSI (American national standards institute) offer a standard for testing and grading of the lenses.