Cast iron is a rather difficult material to process. It contains graphite in its structure, which makes it difficult to wet the surface with solder. Cast iron needs sand blasting.
Soldering iron is quite time-consuming process, since graphite in its composition prevents wetting the surface with solder.
Welding and brazing is then much easier, due to the fact that sandblasting with further electrochemical removal of graphite or burning it out with an oxidized gas makes the metal more susceptible to soldering.
Low temperature soldering
Diagram of the process of low-temperature brazing of cast iron with cast-iron filler material to correct defects: a - with longitudinal groove; b - with defect of shell type.
For low-temperature soldering, you can prepare the metal by fluxing. The electrochemical method using salt baths can also be applied. After this treatment, the surface is required to be processed. To do this, you can use acetone, gasoline or alkali solutions.
The soldering of cast iron is done with a soldering iron, and the welding with a gas torch. For this purpose, fluxes made of zinc chloride can be used if chloride salts of tin and copper are added to the solder. To alleviate the soldering can be, if you apply the method of contact copper in the solution of copper sulfate, you can also apply the method of electroplating.Back to table of contents
High temperature soldering
Brass or other copper-based alloys are usually used for high-temperature soldering. Less commonly, high-temperature brazing is performed using filler alloys based on silver containing nickel. This solder forms a strong compound, while its melting point is relatively low.
The scheme of high-temperature soldering of cast iron: 1 - movement of the burner; 2 - bar movement; 3 - movement of the burner and rod.
To dissolve graphite on the metal surface for welding or soldering, it is most efficient to use the active fluxes P209 and PV285X. These materials reliably wet the joined areas. In this case, there is no need to pre-remove graphite. In addition, when processing at a temperature of 900 degrees, the cast iron does not overheat.
Overheating of the metal leads to its structural changes. As a result, after treatment, it cools, and fragile cement is released from it. Therefore, it is recommended to avoid using copper-based materials that have a higher melting point. It is strictly forbidden to use phosphorus-based solders, since this leads to the fact that phosphorus and iron compounds are formed in the seams, which are quite fragile.
You can heat parts made of cast iron for welding and soldering using a blowtorch or a gas torch. In this case, only a neutral flame is used. You can make joints more durable by performing annealing for 20 minutes at a temperature of 700 to 750 degrees. If the seams are soldered in a furnace with a controlled atmosphere, then flux is used, thanks to which the solder flows into the gap more easily and freely and wets the main surfaces well.Back to table of contents
Features of processing defective areas
If it is necessary to connect parts of defective areas, it is best to use an alloy of lead and tin as a solder.
As a rule, POSZO is used to connect porous areas, cracks and shrink holes. In this case, a solution of zinc chloride in water should be used as a flux. Chloride salts of tin and copper are also added to the solution.
It is possible to join parts only after preliminary processing. Details on the defective areas are cleaned and they are tinned. For tinning it is necessary to clean the casting crust from the surface of the parts. For this suitable wire brush. Next, the surface must be degreased. Gasoline or alkaline solution can be used for this. After that the flux is applied. The place of soldering is heated by a gas burner. It is required to reach the melting temperature of the filler metal. After that, you can solder all defects using a soldering iron or torch. After that, the surface must be washed with water. It can be both hot and cold.
Thus, brazing or welding of cast iron can be performed using various solders. Different metals used for this purpose have different characteristics. They are distinguished by the melting point and strength of the connecting joints formed. The complexity of metal processing due to the fact that it contains graphite.