Casting process for high quality castings

Foundry production is an old and emerging industry and an important basic parts industry for the machinery industry. Determine the service life and reliability of the equipment. Through thousands of years of production practice accumulation, scientific research, from macroscopic understanding to microscopic theory, there has been tremendous development, constantly revealing the control of the technical parameters in the casting production process, and ensuring the use performance of the castings, thus ensuring The service life of the mechanical equipment and the reliability of its use. To produce high-quality castings, we first need to study the factors affecting the performance of cast iron, that is, how to improve the purity of molten iron: how to obtain a good graphite shape; control the fluctuation range of chemical composition, etc., to study the technical control parameters to solve the above problems. And study what smelting method is used to achieve the goal. Now to express it.

 

Quality control of molten iron smelting

 

        Control of the purity of molten iron:

 

        1. Oxide inclusions produced by oxidative burning of elements;

 

        2. Melting the smelting pores generated by oxygen;

 

        3. Control of sulfur content to prevent the formation of sulfur eutectic;

 

        4. Control of phosphorus content to prevent the generation of phosphorus eutectic;

 

        5. Limit the trace element content below the interference amount.

 

        Hot metal smelting process control:

 

        1. Control of molten iron oxidation;

 

        2. Eliminate the heritability of graphite and obtain a good graphite morphology;

 

        3. Control the fluctuation range of chemical composition to obtain accurate chemical composition;

 

        4. Control of molten iron smelting temperature;

 

        5. Selection of the best smelting method and corresponding equipment system.

(1) Control of molten iron

 

1. Generation and control of molten iron oxide holes

 

        The molten oxygen in the cupola molten iron, as described above, reacts with silicon and manganese in the molten iron to form oxide inclusions.

 

        a. A part of dissolved oxygen is adsorbed on the surface of graphite, and graphite oxide forms carbon monoxide gas. Namely: (C) graphite + [O] = {CO} ↑

 

        b. When the produced ferrous oxide is contacted with carbon in the molten iron, the carbon reduces the ferrous oxide and also forms carbon monoxide pores. (FeO)+(C)={CO}↑+(Fe) High-temperature hot metal facilitates the removal of bubbles. The pores formed by the oxidation of molten iron in this smelting process are called smelting pores, and their characteristics are finely and evenly distributed in the section of the casting.

 

2. Element burning and oxide inclusions

 

        Oxidation loss of silicon and manganese in molten iron is absorbed into the molten iron by adsorbing oxygen and carbon dioxide in the furnace gas to the surface of the iron droplet. At this point, the oxygen is dissolved to an atomic state. First, it reacts with iron atoms to form ferrous oxide. Since silicon, manganese and oxygen have higher affinity than iron atoms, silicon and manganese atoms reduce the pig iron atoms from ferrous ferrous oxide, and are oxidized to form silicon and manganese oxide inclusions. It is well known that the oxidation of molten iron is produced as long as it is produced in the melting zone. Since the oxygen in the air has substantially burned light in the oxidized zone. Carbon dioxide is formed; therefore, the oxygen atoms in which the molten iron is oxidized in the melting zone are mainly supplied by carbon dioxide, and the amount of carbon dioxide in the melting zone is reduced to control the oxidation of the molten iron in the melting zone. Since carbon dioxide is reduced by red hot coke, it is an endothermic reaction, so it is improved. The temperature of the furnace gas in the reduction zone can reduce the content of carbon dioxide in the furnace gas and reduce the burning loss of silicon and manganese. Therefore, the hot air cupola can effectively control the elemental oxidation loss.

3. Control of sulfur content in molten iron

 

        During the cupola smelting process, 60% of the sulfur in the coke will enter the molten iron. How to control the entry of sulfur into molten iron is one of the important tasks of cupola melting quality control. First, we must understand the process of sulfur entering the molten iron, in order to find a way to control the increase of sulfur in molten iron. When the coke is burned in the tuyere to reach a high temperature, the sulfur in the coke escapes in a gaseous state, and reacts with oxygen in the tuyere region to form sulfur dioxide (SO2) gas. As the furnace gas rises, there are two ways to increase sulfur with iron:

 

        a. When sulfur dioxide is adsorbed on the surface of the clean metal charge or the surface of the iron droplet which has not been oxidized, a sulfurization reaction occurs: 3[Fe+SO2]=(FeS)+2(FeO)+△F2......(1)

 

        b. For the surface of the oxidized metal charge, the following reaction is carried out: 10(FeO)+SO2=(FeS)+3Fe3O4+?F (2) The ferrous oxide in the formula includes the slag formed by the above reaction and in the slag.

 

        The above two exothermic reactions can be carried out under cupola conditions, but the reaction formula (2) has a higher directionality than (1), so when the metal surface is severely oxidized, the sulfur is severely increased. The test shows that the sulphur penetration depth of the metal charge can reach 1~3mm. When the original sulphur content of the iron material is 0.082%, the sulphur content in the buildup layer can reach as much as 0.45%. It can be seen that the removal of the rust of the metal charge can reduce the sulfur increase. Can we create conditional desulfurization in the cupola smelting process? According to the three conditions of desulfurization, namely high temperature, high alkalinity and low oxidation. This can not be satisfied in the general cupola, and the above conditions can only be met under the conditions of advanced hot air water-cooled cupola melting. In the process of smelting hot air water-cooled cupola, due to high temperature, low oxidation of molten iron, no lining, it can make alkaline slag. When the molten iron is at 1500 ~ 1550oC, the average is 1530 oC, and the alkalinity of slag is controlled at 1.7 ~ 2.3, it can be stably The sulfur content of molten iron is reduced to 0.04%. In the package, the desulfurization measures or the continuous desulfurization before the furnace can be used to control the sulfur to 0.02-0.03%, which fully meets the needs of ductile iron production and converter high-grade steel.

 

4. Trace interference elements

 

       During the smelting process, the high temperature is favorable for the oxidation and burning of the low melting point interference elements. Its content is correspondingly reduced. But control is primarily one of the solutions from the choice of metal charge. In the cupola furnace smelting process.

 

 

5. Control of phosphorus in molten iron

 

        Generally, there is substantially no significant change in phosphorus during the scouring of the cupola. The control of the amount of phosphorus is mainly controlled from the metal charge.