January 9, 2007
Autodarkening technology has established a firm place in the welding industry not only as a piece of equipment that provides excellent protection, but also as a means to improve welding performance.
In 1981 Hrnell, now part of 3M, commercialized its first autodarkening filter for a welding helment. Twenty-five years later autodarkening technology has established a firm place in the welding industry not only as a piece of equipment that provides excellent protection, but also as a means to improve welding performance.
In the beginning autodarkening welding filters enabled welders to see their work at comfortable light levels with constant eye and face protection. Today autodarkening filters turn dark the instant an arc is struck and become semitransparent again when welding stops. This semitransparency should work while also providing full ultraviolet (UV) and infrared (IR) protection at all times, which is in accordance with ANSI standard Z87.1-2003 and comparable Canadian regulations for welding safety standards.
Autodarkening technology also reduces the neck strain associated with "helmet nodding." In theory, this should help to increase the accuracy of electrode placement because the welder does not have to raise the helmet to get a closer look at the weld in progress. This, in turn, possibly reduces the need for grinding and rework.
Without helmet nodding, the welder also can get into tighter, cramped spaces with full protection and a clear view, making awkward welds significantly easier.
To understand how autodarkening technology makes these benefits possible, let's look at the pieces of an autodarkening filter. One filter from a leading welding safety product manufacturer is a laminate of nine layers—two replaceable protective plates, a UV/IR filter, three polarizers, two liquid crystal display (LCD) elements, and a cover glass. The UV/IR filter continually blocks harmful radiation whether the filter is on, off, or in "light" or "dark" mode (see Figure 1).
The first layer after the replaceable protection plate is the UV/IR filter. This filter effectively blocks all but the specified visible light. UV and IR wavelengths on either side of the visible spectrum are blocked at all times.
Aided by surface-mounted electronics, the liquid crystal elements in this proprietary lens detect and orient light from the welding arc by twisting it to facilitate filtering by the three polarizing layers. In this case and in the case of about 80 percent of all autodarkening filters, twisted nematic LCDs assist in the filtering.
The discovery of the twisted nematic effect was a breakthrough in the field of liquid crystals in the early 1970s. Researchers discovered that, during their nematic phase, the liquid crystals' molecules, which are shaped like sausages, tend to line up in a specific orientation without any sort of corresponding specific positional movement taking place. Researchers then found that the positional order could be influenced by the application of a weak energy field.
So when voltage is applied to the twisted nematic layers in the LCDs, the necessary alignment with polarizers takes place. The amount of voltage applied determines the shade level.
The polarizers are oriented to block the light based on the orientation achieved by the LCD layers. Most autodarkening filter units use two sets of polarizers. Some autodarkening filters incorporate three for increased effectiveness. Darkening in those types of helmets takes place in about 0.15 millisecond.
An unenergized filter is almost always in an intermediate dark shade and must be turned on to activate the light state. If anything catastrophic should happen to the filter while in use, it typically defaults to the darker intermediate off shade (Shade 6). As mentioned, UV/IR protection is always present in helmets that meet the ANSI standard.
How does all of this translate into a better welding helmet? From a safety standpoint, these types of helmets provide constant UV and IR protection and come with a heat-reflecting front panel. From a welding perspective, the narrow helmets can fit into tight spaces and don't require the extra room needed to flip them up to check welds. In addition, some autodarkening helmets have side windows to increase the viewing area. Regarding comfort, the helmets are lightweight, and one major manufacturer even includes exhaust vents to help reduce heat and humidity inside the helmet. For an evolution of autodarkening helmets, seeFigure 2.
To get the most out of your autodarkening filter unit, here are some final tips:
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