Different manufacturers of welded stainless steel products use different techniques in the production process. As a result, the quality of the finished products is varies highly.
Stainless steel welding
Welding of all stainless steel products on PMP Ventilacia factory is performed with an argon-arc technique with protection of the back side of the weld. The explanation of the method is displayed below.
The photo above displays the front side of the weld. We welded two sheets of stainless steel with the thickness of 1.5 mm with the argon-arc technique. The temperature in the welding area reaches up to 2000°C, which causes a rapid oxidation of heated and melted metal during its interaction with oxygen. To prevent this process from happening, the welding area is submerged in an inert gas (argon is used in this case). Argon displaces air and oxidation does not occur. In the picture, it can be easily seen that steel does not oxidize in the argon medium, the weld looks even.
In the photo above, the same weld is shown, but after chemical cleaning (chemical etching) in an acid solution. During the chemical cleaning process, iron oxides formed during welding are removed. The surface of the product is also cleaned from any iron and organic compounds polluting it during production.
In the photo above, the reverse side of the weld is displayed. Usually the front side of the weld is placed in an inert gas medium, while the other side of the welds remains exposed to oxygen. Oxygen quickly starts a chemical reaction with the highly heated metal, forming an uneven porous and severely oxidized weld.
The picture above shows the same weld, but after it was chemically cleaned. It is easy to see that even long chemical etching can not remove all of the oxides from the porous structure and clean the weld completely. As a result, this connection point has reduced strength and is prone to corrosion. In addition, it is absolutely unacceptable to allow such blemish in certain highly technological processes that require the use of clean stainless steel ducts and other elements.
We have to note that some manufacturers avoid this problem by welding the metal only half way deep. The weld is usually 0.5 - 1mm thick. The main and crucial flaw of that technique is the weld's low strength and durability under impact.
The photo above displays the back side of the weld. We used the same argon-arc technique, but with the back side of the weld submerged in argon this time (the metal sheet is 1.5 mm thick here). As a result, we produced two metal sheets fully welded through without any oxygen-caused deformations on the back side.
The photo above displays the same back side of the weld, but after chemical cleaning now. The weld is clean and has no protuberances, while the sheets are welded throughout the entire thickness of the metal. Such surface allows to be easily be coated with Teflon or similar coatings.
Carbon steel welding
Most of the time, carbon steel is welded semi-automatically with a stainless steel additive and submersion in argon and carbon dioxide. This technique works best for large products with metal thickness of 3.0mm or more. The back side of the weld is left exposed to oxygen, because the metal is not welded throughout the whole thickness. Moreover, splashes of molten metal severely ruin the appearance of the product. To prevent that from happening, the surface of the metal in the welding area is coated with a special liquid beforehand.
The two pictures above show semi-automatic welding. The surface of the metal is painted after deep mechanical cleaning. The welds noticeably stick out even after being well cleaned and painted.
The picture above displays an inner corner weld performed with an argon-arc technique. The surface is painted and the weld is almost unnoticeable.
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