What Is Welding?

The processes and technology of this manufacturing cornerstone explained Welding is a process in which metals and thermoplastics are joined together to produce an object or structure. These materials are commonly joined by the melting of a filler material, such as steel, at their boundary points, fusing them together. There are three main techniques: gas welding, arc welding and laser welding. Gas, or oxy-fuel, welding, is the most common type and also the oldest. This process works through the combustion of acetylene in an oxygen stream, with the gas funnelled to a point of focus (ie the welding stick – this can be a handheld or stationary robotic applicator), where it is ignited to produce a high-temperature fl ame. Gas welding produces a welding f l ame of 3,100°C (5,612°F) and, as such, is typically used to weld high-alloy steels. However, the f l ame produced in a gas-based system is typically less concentrated than other methods, leading to greater weld distortion. Arc welding differs to gas welding signifi cantly. This technique involves melting the work materials through an electrical arc. This is generated by attaching a grounding wire to the welding material and then placing another electrode lead against it, itself attached to an AC/DC power supply. When the electrode lead is drawn away from the materials it generates an electrical arc (an ongoing plasma discharge caused by the electrical breakdown of gas), which through its expelled heat, fuses the materials. Unlike gas welding, arc welding produces a more concentrated weld point. Finally, laser welding – which is one of the newest forms of welding – uses a high-energy beam to meld materials. As the laser has a high- energy density, this technique can achieve a deep penetration and incredibly focused weld, with little surrounding distortion. Due to this, laser welding is commonly used in large industrial applications, where speed and finesse are of great importance.

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Welding at process

THE ELEMENTS OF LIFE

Of the 92 natural elements, about 20–25% are essential elementsthat an organism needs to live a healthy life and reproduce. The essential elements are similar among organisms, but there is some variation—for example, humans need 25 elements, but plants need only 17. Just four elements—oxygen (O), carbon (C), hydrogen (H), and nitrogen (N)—make up 96% of living matter. Calcium (Ca), phosphorus (P), potassium (K), sulfur (S), and a few other elements account for most of the remaining 4% of an organism’s mass. Trace elementsare required by an organism in only minute quantities. Some trace elements, such as iron (Fe), are needed by all forms of life; others are required only by certain species. For example, in vertebrates (animals with backbones), the element iodine (I) is an essential ingredient of a hormone produced by the thyroid gland. A daily intake of only 0.15 milligram (mg) of iodine is adequate for normal activity of the human thyroid. An iodine deficiency in the diet causes the thyroid gland to grow to abnormal size, a condition called goiter. Where it is available, eating seafood or iodized salt reduces the incidence of goiter. Some naturally occurring elements are toxic to organisms. In humans, for instance, the element arsenic has been linked to numerous diseases and can be lethal. In some areas of the world, arsenic occurs naturally and can make its way into the groundwater. As a result of using water from drilled wells in southern Asia, millions of people have been inadvertently exposed to arsenic-laden water. Efforts are under way to reduce arsenic levels in their water supply


Elements in the Human Body  

Percentage of Body Mass (including water)
Element

Oxygen 65.0%

Carbon 18.5%

Hydrogen 9.5%

Nitrogen 3.3%

Calcium 1.5%

Phosphorus 1.0%

Potassium 0.4%

Sulfur 0.3%

Sodium 0.2%

Chlorine 0.2%

Magnesium 0.1%

 Trace elements (less than 0.01% of mass): Boron (B), chromium (Cr), cobalt (Co), copper (Cu), fluorine (F), iodine (I), iron (Fe), manganese (Mn), molybdenum (Mo), selenium (Se), silicon (Si), tin(Sn), vanadium (V), zinc

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