Method and technique of welding the cast iron

Method and technique of welding the cast iron

Date 06/05/2019
How to overcome the appearance of organizations I and white cast organization
One note during welding is the need to create a process that slows down solder and heat affected areas by methods such as preheating, which slows down the cooling process after welding.
These measures relate to the high thermal factor of the welding process. If it is not possible to use a large-capacity heat source, it is possible to use a small-capacity, fast-welded heat source to transmit a minimum amount of heat to the weld to avoid the occurrence of whitish areas and to organize me. . This method is also called cold solder without preheating. In addition, for the cast iron, a soldering method is used.

 

 
How to overcome the problems related to the mechanical of cast iron:
 
The mechanical characteristics of cast iron is low plasticity, easy to crack when stress exceeds durability. A pre-welding rule needs to create a preliminary deformation so that when the weld cools, the weld is free to coil.
 
The easiest way to do this is to preheat the entire weld. It is also possible to heat locally if the weld is relatively simple. In the absence of reverse deformation, it is possible to produce a minimum power heat source combined with a good plasticity welding material.
 
Method and technique of welding the cast iron
 
In the iron welding process there are two basic steps: determination of basic metals and selection of appropriate welding methods.
 
How to determine the base metal:
 
In practice, cast irons are often parts that need to be repaired. It is important to determine what type of welding material to use for the method and select the appropriate welding mode.
 
Often cast iron parts are made of cast iron. The simplest way to distinguish cast iron and steel is to chisel the material for testing. For steel, after blanking the workpiece and bright surface. In contrast, cast iron, when rendered, will crumble, its surface rough and dark in color. It is also possible to determine the type of cast iron due to the hardness of the material. The ductile cast iron also has an instant cast when opaque, but its hardness is not that of cast steel. Shape of steel castings are generally simple structure and fairly uniform thickness. In contrast, casts of cast iron often have more complex structures and different thicknesses.
 
Molded castings can also be identified as cast irons: Cast iron with a strength of 120 MPa and HB 140 ÷ 180 (equivalent to GX 12-28) is used to cast thin walled articles. Gang GX 21-40 is used to make cutting parts, motor cylinders, and mechanical parts. For large engine cylinders, gears, machine parts with high loading are often used GX 24-44.
 
Another way is to try on a grinder. When grinding, if the sparks emit red or yellow straw, short of 500 ÷ 600mm and broad branches, it is cast iron. If carbon steel is low, when sharpening, the sparks fired relatively long, interrupted and not spread.
 
The broken of the cast iron is not as glistening as steel and opaque, if the hands rub up can see lead - graphite. The most accurate way to determine is to determine the chemical composition and the needle analysis. This measure is only used when it is necessary because it is very expensive.
 
How to choose the appropriate welding method:
 
The most important thing in repairing a new weld is that the color of the weld must be the same as the color of the base metal. With the repair of solder or used parts, the color of the weld is not as important as the quality of the weld. Water tightness and air tightness are also important requirements. If only water tightness is required, cold welding can be used.
 
1. Method of welding hot cast iron
 
Hot soldering is a preheating method of welding to about 600 - 650 degrees Celsius with a heating rate of 120 degrees Celsius / hour. That temperature is maintained during welding. This helps to avoid the appearance of pig iron and my organization in the heat affected area. After welding, the weld should be cooled slowly at a rate of 120 ° C / h for welding objects with an average thickness of 25 mm. Welds can be cooled in the oven or in the insulation. Graphite molds can be used to shape the weld due to the difficult handling of cast iron during welding.
 
For welding rods with cast iron rods, the rod diameter is relatively large (14-16mm). Coil sheaths have a thickness of at least 2mm and must ensure a uniform burning of the arc, sufficient to compensate for the metal loss caused by oxidation during welding.
 
Before welding, the welding rod is dried at 200 - 250 degrees C. The welding current is about 60-100. The heat capacity of the welding is very large so it is necessary to ensure the heat resistance for welding and welding. Although for molten solder welding, the quality of welds is almost the same as that of base metals, the welds are easy to weld after machining but are less applicable due to certain constraints on working conditions. Of the welders as well as the preparation of welding.
 
2. Method of cold solder
 
Cold welding requires the use of a minimum of heat source to limit the appearance of the weld
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