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Repair and Welding of Diesel Generator Set Spare Accessory

Dec. 26, 2018

Welding repair of aluminum and aluminum alloy


Aluminum and aluminum alloy aluminum oxide is easier to oxidize than copper. It forms a dense and refractory alumina film with high melting point. It is difficult to melt during welding, hindering the fusion of matrix metal, easily causing weld metal slag, reducing mechanical properties and resistance. Corrosive; aluminum has a large gas absorption, liquid aluminum can dissolve a large amount of hydrogen, when it is rapidly cooled and solidified, hydrogen can not be precipitated, and pores are easily generated; aluminum has good thermal conductivity and requires high and concentrated heat source; thermal expansion and contraction is serious, easy Deformation; because aluminum has no obvious color change during solid-liquid transition, it is not easy to judge the temperature of the molten pool according to the color change during welding; the strength of aluminum alloy is very low at high temperature, and it is easy to cause collapse and weld penetration during welding. . The above are the characteristics of the welding repair of aluminum and aluminum alloy parts of diesel generator sets, which are determined by some of their own characteristics.



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When welding aluminum and aluminum alloys, the standard grade welding wire similar to the base metal composition is generally used. Commonly used are: wire 30l, welding pure aluminum and low-demand aluminum alloy; wire 311 universal welding wire, welding aluminum alloy other than aluminum alloy; wire 321, used for welding aluminum-manganese alloy and other aluminum alloys; wire 331, welding aluminum-magnesium alloy and other aluminum alloys.

 

In order to make the welding repair smoothly, ensure the quality of the weld, add welding powder during gas welding and eliminate the gasification film and other impurities, such as gas 401 (CJ401).

 

Aluminum and aluminum alloy welding repair, the most used gas welding applications. Because the gas welding equipment is simple and easy to operate, the quality is poor, the deformation is large, the production efficiency is low, and it is difficult to grasp. It is mainly used for the welding repair of small aluminum alloy workpieces with low corrosion resistance and small wall thickness. The gas welding process is: pre-weld cleaning, chemically or mechanically cleaning the oil on the workpiece weld and the surface of the wire; opening a V-shaped, X-shaped or U-shaped groove; welding the crack of the larger part at the two ends The crack hole is blocked; the north side is covered with asbestos board or copper plate pad, and the edge closer to the weld fill is fixed by the metal plate to prevent metal overflow. Preheating when welding: use small nozzle; neutral flame or slightly carbonized flame, avoid using oxidizing flame or carbonized flame, avoid oxidation and bring hydrogen into the bath, produce pores; pay attention to the inclination of the tip and wire; The left or right weld is determined according to the thickness of the weld; the entire weld may be welded one time later, and should not be interrupted; pay special attention to the heating temperature. After the workpiece is welded, it should be slowly cooled. After it is completely cooled, brush the weld near the weld and rinse the residual solder powder.

 

For welding of large aluminum and aluminum alloy parts, arc welding is recommended. Prepare the same gas welding process before welding. Commonly used welding rods are L109, welding pure aluminum and general joints are not required aluminum alloy; L209, welding aluminum plate, aluminum silicon castings, general aluminum alloy and hard aluminum: L309, used for pure aluminum, aluminum manganese alloy and other aluminum Welding repair of alloy workpieces. In the arc welding process, it is mainly to preheat and dry the coating; to select the diameter of the welding rod and the welding current; in operation, under the premise of maintaining stable combustion of the arc, try to use short arc welding and rapid welding to prevent metal vaporization and reduce Splash to increase the depth of penetration. Arc welding is highly demanding for welders due to the difficulty in thermal regulation and operation of the arc.

 

Soldering of copper and copper alloy

 

Non-ferrous metals commonly used in diesel generator sets are copper and copper alloys, aluminum and aluminum alloys. Because of their high thermal conductivity, large coefficient of linear expansion, low melting point, high brittleness at high temperatures, low strength, and easy oxidation, the weldability is poor and the weld repair is complicated and difficult. The following is a brief introduction to the welding repair methods and precautions for copper and copper alloys in generator parts.

 

The characteristics of copper and copper alloy are: in the process of welding repair, copper is easy to oxidize, and cuprous oxide is formed, which reduces the plasticity of the weld and promotes cracking; the thermal conductivity is strong, 5~8 times larger than steel, and must be repaired. Use high and concentrated heat source; large amount of thermal expansion and contraction, weldment is easy to deform, and its internal stress increases; oxidation, evaporation and burning of alloying elements cause it to change the composition of the alloy, causing the mechanical properties of the weld to decrease and generate heat. Cracks, pores, slag inclusions; copper can dissolve a large amount of hydrogen in liquid state, too much hydrogen can not be precipitated during cooling, and pores are formed in the weld fusion zone, which is one of the common defects after copper and alloy welding repair. In view of the above characteristics, to ensure the quality of the weld repair, the following issues must be emphasized.

 

1. Supplementary materials and their choice


At present, the main types of domestic welding electrodes are: TCu (T107) for welding copper structural parts; TCuSi (T207) for welding silicon bronze; TCuSnA or TCuSnB (T227) for welding phosphor bronze, copper and Brass; TCuAI or TCuMnAI (T237) for welding aluminum bronze and other copper alloys. Welding wire for gas welding and argon arc welding, commonly used: SCu-l or SCu-2 (wire 201 or wire 202), suitable for welding copper; SCuZn-3 (wire 221), suitable for welding brass . Solder powder can also be used when welding copper and brass alloys with gas welding.

 

2. Rework process

 

Pre-weld preparation must be made during welding, and the surface of the welding wire and the weldment should be cleaned to open a V-shaped groove of 60 degrees to 90 degrees. Pay attention to preheating when welding. The general temperature is 300 - 700 °C, pay attention to the welding speed, follow the welding repair specification, hammer the weld; select the appropriate flame during gas welding, generally neutral flame; the arc welding should consider welding law. Pretreatment is required after welding.

 


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