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The coating on welding rod is called flux. It acts as a catalyst for the surface of material to be welded is to melt easily as well as acts as cleaning agent to that area so as to generate a firm bonding between the metal to be welded and molten welding rod metal. It also acts as a coating to the welded portion which prevents from atmosphere would result a sudden cooling hence brittle. Rusting of surface also will be protected for a long time if not removed before painting or proper coating.
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Direct contamination is a result of touching someone who is infected or through sexual intercourse. Indirect can be through water, soil, food, etc..
There are several gunpowder contaminants such as the fertilizer, detergent, match head, even soil and cigarettes. They contain nitrates which gives similar result to gunpowder residues when treated with Diphenylamine (DPA) Reagent.However, their reaction differ from gunpowder nitrates from the characteristics of the specks as well as the distribution of the specks. Usually a gunpowder contaminants will show a smear of blue color .
Yes. Not only can it be painful it can result in blindness.
The crackelure (craquelure) on an oil painting are the small cracks that appear as a result of the paint and/or varnish shrinking.
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result depends on the user it can be best if user is good in that work and it can also be worst
MIG welding works only with reversed polarity, DC+, + at the torch. The reason is mostly the stability of the arc. Using DC- will result in a very unstable arc with lots of spatter.
In arc welding the electrode (welding rod) is held just a little space away from the workpiece and electric current jumps from the electrode to the work piece carrying material from the rod with it. This material is deposited at the weld site mixed with molten metal from the workpiece. The jumping current is referred to as the arc. You can see it if you are wearing welding glasses with the proper dark lens. Looking at the arc without eye protection will often result in a splitting headache later and, if done recklessly and too long, permanent eye damage can result---in other words, blindness.
Practice makes perfect. Sorta like painting a line. You have to watch the result and react accordingly. Too slow and the weld widens out and gets too thick (tall), too fast and it narrows down and gets thinner. Also if you travel too slow the edges roll and trap slag. Travel too fast and you get less penetration and the weld is too thin and can crack or cause undercut. As you weld observe the whole picture, where you are going and where you have been (the weld). This applies to all welding processes.