Thursday, 11 February 2010

Eye Protection for Welding

At Granite we have recently introduced a range of welding helmets and masks from Bolle for protection of the eyes when carrying out welding of all types. We also have Welding Safety glasses suitable for people who are walking through areas where welding is being carried out and for the welders when carrying out tasks when they are not using the masks, these offer protection against flying objects, see Bolle Univis 1011 Welding Safety Glasses on our website.

Risk of Injury

While most welding-related eye injuries are reversible, more than half of injured workers return to work in less than two days and 95 percent in less than seven days, some eye injuries are irreversible and permanent visual impairment occurs. This is especially true with infrared and visible spectrum (bright light) radiation. Both can penetrate through to the retina and can cause permanent retinal damage, including cataracts, diminished visual acuity, and higher sensitivity to light and glare.

Welders are not the only workers at risk. While the welding arc is the principal source of ultraviolet radiation, other workers in the area can sustain eye damage from the radiation as far as 50 feet away with the radiation reflecting off shiny surfaces, concrete, or unpainted metals. To counteract this reflection, you should install shielding curtains where practical or require that all workers in the area wear appropriate eye protection.

Selecting the right helmet

To make the right choice in selecting a helmet, it is important to understand the meaning of arc flash and what types of emissions radiate from the welding arc. Arc flash is simply the unexpected exposure of the eyes to the welding arc. The welding arc emits several forms of light including ultraviolet, infrared radiation and high-intensity visible light. Both infrared and ultraviolet radiation can cause permanent damage to the eyes, such as retinal burns. While high-intensity visible light may not cause permanent eye damage, it may leave the operator with temporary discomfort, similar to being exposed to the flash of a camera bulb.

Many people mistakenly think that the lens shade number corresponds to the amount of protection that is provided to the eyes and hence the higher the number, the better the protection. In reality, all properly constructed quality welding lenses, have a screen that filters out 100 percent of the harmful ultraviolet (and infrared) wavelengths and provides protection to the eyes. The number just denotes the amount of darkness provided by that particular lens and should be used by operators as a guide to select the one that is most comfortable but still provides good visibility for carrying out the operation.

High quality auto-darkening helmets provide UV and IR protection even when the helmet is not activated, you are always protected. However, for maximum comfort, look for a high quality helmet that has a response darkening time of 0.4 of a millisecond or less. Less than a millisecond is not perceivable by the human eye and will provide the most comfort. The auto-darkening helmets in the Bolle range work between 0.2 and 0.25 milliseconds.

Helmets come with either battery power or solar power as is the case with the Bolle range. In most cases, it simply is a choice of personal preference and what is most convenient to the operator. With a battery powered helmet there is a chance however of being flashed. These helmets offer a feature that will automatically turn off the battery after the helmet has been sitting idle, or the batteries may have lost their charge. If the welder isn't careful, he could get arc flash thinking that his helmet is still dark. Solar powered helmets do not suffer from this and also eliminate the time and cost of recharging.

Fixed or variable shade

If you are always using the same arc welding process on the same material, a fixed shade is sufficient. But if you, like most welders, are using a variety of materials and welding a number of different applications, your best bet is a variable shade, which will adjust to the correct darkness for your particular process. As an example, when you are TIG welding at lower amperages, you may need to lighten up the lens to see what you are doing, a variable shade will allow this while a fixed shade will not.
Types of Welding

MIG is short for Metal Inert Gas welding. The system uses a metal wire fed through the gun surrounded by an inert gas such as Argon, because the cost of inert gases are high this system is not generally used for welding steel, but is more used for aluminium.

MAG is short for Metal Active Gas welding. The system here also uses a metal wire but in this case is surrounded by an active gas such as carbon dioxide. The lower cost has widened the use of this system to include steel welding.

TIG is where an arc is formed between a non-consumable tungsten electrode and the metal being welded. Gas which can be Argon, Argon and Hydrogen, or Argon and Helium, is fed through the torch to shield the electrode and the molten weld pool. If there is a need for filler wire then this is added to the pool separately.

The benefits of this type of welding are: superior quality welds, the welds can be made with or without filler metal, there is fine control of heat and there is no splatter and low distortion.

Plasma welding is very similar to TIG as the arc is formed between a pointed tungsten electrode and the work piece. However, the electrode is positioned within the body of the torch allowing the plasma arc to be separated from the shielding gas envelope. Plasma is then forced through a fine-bore copper nozzle which constricts the arc. By increasing welding current and plasma gas flow, a very powerful plasma beam is created which can achieve full penetration in a material, as in laser or electron beam welding. During welding, the hole progressively cuts through the metal with the molten weld pool flowing behind to form the weld bead under surface tension forces. This process can be used to weld thicker material (up to 10mm of stainless steel) in a single pass.

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