Electroslag welding

Electroslag welding (ESW) is a highly productive, single pass welding process for thick (greater than 25mm up to about 300mm) materials in a vertical or close to vertical position. (ESW) is similar to electrogas welding, but the main difference is the arc starts in a different location. An electric arc is initially struck by wire that is fed into the desired weld location and then flux is added. Additional flux is added until the molten slag, reaching the tip of the electrode, extinguishes the arc. The wire is then continually fed through a consumable guide tube (can oscillate if desired) into the surfaces of the metal workpieces and the filler metal are then melted using the electrical resistance of the molten slag to cause coalescence. The wire and tube then move up along the workpiece while a copper retaining shoe that was put into place before starting (can be water cooled if desired) is used to keep the weld between the plates that are being welded. Electroslag welding is used mainly to join low carbon steel plates and/or sections that are very thick. It can also be used on structural steel if certain precautions are observed. This process uses a direct current (DC) voltage usually ranging from about 600A and 40-50V, higher currents are needed for thicker materials. Because the arc is extinguished, this is not an arc process.

Benefits

Benefits of the process include its high metal deposition rates — it can lay metal at a rate between 15 and 20 kg per hour (35 and 45 lb/h) per electrode — and its ability to weld thick materials. Many welding processes require more than one pass for welding thick workpieces, but often a single pass is sufficient for electroslag welding. The process is also very efficient, since joint preparation and materials handling are minimized while filler metal utilization is high. The process is also safe .and clean, with no arc flash and low weld splatter or distortion. Electroslag welding easily lends itself to mechanization, thus reducing the requirement for skilled manual welders.

Заведующий кафедрой

общеобразовательных дисциплин

____________ В.П. Павлов

Уфимский государственный Кафедра общеобразовательных

авиационный технический дисциплин

университет

ЭКЗАМЕНАЦИОННЫЙ БИЛЕТ № 14

Факультет: АТС (СП) Вопрос: 1

Short-circuiting

Further developments in welding steel with GMAW led to a variation known as short-circuiting or short-arc GMAW, in which carbon dioxide shields the weld, the electrode wire is smaller, and the current is lower than for the globular method. As a result of the lower current, the heat input for the short-arc variation is reduced, making it possible to weld thinner materials while decreasing the amount of distortion and residual stress in the weld area. As in globular welding, molten droplets form on the tip of the electrode, but instead of dropping to the weld pool, they bridge the gap between the electrode and the weld pool as a result of the lower wire feed rate. This causes a short circuit and extinguishes the arc, but it is quickly reignited after the surface tension of the weld pool pulls the molten metal bead off the electrode tip. This process is repeated about 100 times per second, making the arc appear constant to the human eye. This type of metal transfer provides better weld quality and fewer spatters than the globular variation, and allows for welding in all positions, albeit with slower deposition of weld material. Setting the weld process parameters (volts, amps and wire feed rate) within a relatively narrow band is critical to maintaining a stable arc: generally between 100 to 200 amps at 17 to 22 volts for most applications. Like the globular variation, it can only be used on ferrous metals.