Cast iron welding is an extremely difficult and complex technique, but not impossible. Typically, the welding method is only used for repairing, not to connect the details to each other. Such as fixing molds or fixing products after casting or post-processing because of the brittleness of most cast irons. Cast iron has a carbon content of 2-4% and is 10 times stronger than steel.
Difficulties in welding cast iron
– The plastic deformation capacity of cast iron is very low. In the towing chart of the cast iron there is almost no significant deformation.
– Cast iron is very sensitive to heat, so it is easy to change the organization during the welding and the process of cooling after welding. Due to the large cooling speed of the cast iron, the weld and the adjacent metal are easy for me to organize, and the white cast iron with high brittle strength (up to 800HB) is easy to crack.
– Cast iron products are diverse in terms of chemical composition, organization. It is difficult to accurately determine the welding mode and heat processing mode.
– In cast iron liquids are highly diluted, so the cast iron is difficult to solder in other positions.
In the process of welding the cast iron, note the following issues:
– Types of welding process
Cold process: Sold each short section 2-3 cm then let cool until it touches the weld and then solder. Sequence welding should be applied in reverse-phase or symmetric welding.
Hot process: Heating over a special conversion temperature of 600-650 0C and simultaneous keeping heat during welding. After welding, it is necessary to slow down the solder (120 ° C / s) in the furnace or by insulating cover (difficult to carry with large structures)
Additional tips for hot welding process is to heat the iron to be soldered to see the tomatoes are ripe tomatoes (tips dry pine needle swept on the place where the baked canker saw is flying).
– Welding materials
Choosing the right materials for cast iron: Normally, cast iron requires very high plasticity, so the nickel content in it is very high, up to 90%
Should choose welding rod and welding mode reasonable, common welding rods are copper rod, stainless steel rod. It is best to use copper nickel alloy electrodes and carbonized flames to compensate for the carbon content of the cast iron.
For cracked iron surfaces we can still weld with special welding rods.
Kind of welding rods: Eutectic 240 (Welding rod and filler for cast iron)
Sources of welding: AC / DC +
Ingredients: Ni Fe Mn C
Tensile strength: 55 000 psi (380 MPa)
Some techniques, experience when welding cast iron
Due to the hard and brittle cast iron, the excess residuals in the cast iron are quite large, the cracks will continue to grow during use and especially during welding. Therefore, in order to avoid further rupture break, it is common to block the two ends of the crack before welding. The next step is to use the welding sequence from the start of the crack to the point where they meet. Finally, drill holes.
With the large parts, we can go to brake (ie create the same V-groove steel welding) then machining the threaded hole can be threaded holes 6, 8, 10 … as depending and try as much good order in sequence. Come here and take the bolts in and cut off (remember to excess 5 to 10 mm so that we will welding on it).
Thanks to the addition of bulb tips and knobs to eat in the details of the welding process will be much more favorable and better structure (by this time we will weld both cast iron and steel that will be easy to solder).
When welding the cast iron must be performed in the environment separated from the wind if the process of burning and welding will occur the phenomenon of separation, cracking.
With high rigidity details, it is possible to conduct a local heating (crossed out) instead of heating it completely. The purpose of preliminarily heating is to enable the weld metal and adjacent metal areas to have a uniform heating and cooling rate, avoiding cracks due to heat stress.