Safety And Health – In Operations of Cutting And Welding Of Metals
Welding can be considered a process with heat input, by means of which two metal pieces are joined, and may or may not intervene another substance or material foreign to the pieces or of its very nature.
This form of operation is usually popular in a wide range of activities, particularly in workshops, and despite its apparent simplicity, it should never be forgotten that energy sources are capable of being used at 3000 ºC or higher are manipulated, Constituting sources of ignition that may trigger fires, explosions, burns, and injuries on a variety of grounds, as well as the generation of vapors of a diverse nature, the inhalation of which may affect the health of exposed persons.
Such potential risks include a thorough understanding on the part of the users, as well as the good functioning of the equipment, as for the circumstances of the environment, which may cause more or less serious accidents.
Depending on the heat source, the welding may be electrical by using this form of energy or autogenous when the heat comes from the combustion of the gas.
The operations similar to those of welding are those of metal cutting, and the flame from the combustion of a gas or an electrical arc may also be used, so that, in order to achieve greater efficiency in the creation of this manual, they will be studied together.
Electric welding and plasma arc cutting
There are two types of electric welding:
This method of welding is based on the JOULE effect, where the heat needed to melt the metals involved in the operation (usually tin) originates from the heat generated by heating the electrode, which acts as an electrical resistance when passing a certain current intensity:
Q = I 2 . A. t. 0.24
This form of welding poses few risks (mainly thermal and electrical contacts) even though it is convenient to take into account some general guidelines, namely:
Before starting work, verify that electrical equipment and tools are in perfect condition of use. When finished, do not remove the plug from the socket by pulling the cable, but from the plug itself.
Place the resistance welder on the correct support, orient the electrode in the opposite direction of where the operator is located and, although it is hot, it should not be left on the work stable.
Don't store the soldering iron until the electrode is at room temperature.
Evite inhalation of the fumes produced in the weld, especially when flow resins are used.
In this method of welding, the heat source comes from the electrical arc created when two metallic elements are joined together in stress, reaching temperatures of the order of 3000 oC.
The most common risks resulting from this method of welding are essential:
Inhalation of smoke
There are two main types of electric arc welding:
MIG (Metal Inert Gas) welding: is an arc welding in which the electrode, usually a copper wire wound on a coil, is consumed as the process progresses. This is achieved in an inert gas atmosphere (carbon dioxide, argon, or mixtures of such gasses) in order to prevent oxidation and the creation of so-called "welding beads" and therefore to obtain a better finish. Figure 1 displays the MIG welding tools, in which a gas bottle can be seen.
TIG (Tungsten Inert Gas) welding: it is similar to the previous method of welding, except that in this one, the electrode is not a continuous wire, but a thin metal bar that is mounted in a welding device, which must be adjusted every time it is used, so that the process is discontinuous. As in the previous case, the procedure is conducted in an inert gas atmosphere.
The following are the precautions to be taken into account in order to avoid the risks arising from these types of welding:
Personal protection equipment
For arc welding, personal protective equipment shall consist of the following elements:
The screen of the face and eye protection. ( welding helmet with proper lens)
Long gloves of leather.
The apron and shoes.
Quick-open leggings over them with pants.
Isolating health socks.
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Equipment handling and transportation
All conductors, both those for group power supply and those for welding, must be secured during transport or use against potential mechanical damage.
Mains cables, as well as welding cables, must be wound up for transport and never pulled to move the unit.
If any damaged cable or element has been detected, it must be notified and repaired immediately and should not be used under any circumstances.
Secure connection of the equipment to be welded.
The power circuit terminals must be separated and secured. Furthermore, in the field of contact with the eye, the outer surface of the electrode holders must be removed.
The mass or return clamp must be rigidly attached to the component to be welded, the distance between the point to be welded and the clamp to be welded must be reduced.
Never use metal structures in buildings, pipes, etc. as return conductors if they are not part to be welded.
Welding in locked spaces
When operating in tight spaces or small areas, fresh air, never oxygen, must be constantly pumped in to extract contaminants, vapors and fumes.
In the case that adequate ventilation is not possible, air-supply respiratory safety devices should be used.
Using indoor and outdoor clothing that is not extremely flammable.
If welding works are carried out in highly conductive locations (boilers, metal plates, tunnels, etc.), no voltages greater than 50 v shall be used and the welding equipment shall remain outside the enclosure in which the people work.
Evite welding in areas where flammable materials are processed. If necessary, the room will be ventilated until there are no remnants of substances in the indoor atmosphere that could create a risk of fire or explosion.
As very high temperatures are reached in electrical arc welding, a large amount of smoke is often generated, which should be avoided as much as possible. Such measures should be severe when welding operations are carried out on parts galvanized or painted with lead chromate or coated with antioxidant minium primers. When this form of general protection can not be used, the use of personal respiratory protection shall be used.