SAND CASTING EQUIPMENT.

1、the main factors affecting the mechanical properties of gray cast iron
xinyuanzhu group in the process of casting combined with process, metallurgical factors: mainly cooling rate, overheating of ferrofluid, breeding treatment, furnace characteristics, etc., are the main factors that determine the defects generated by gray cast iron
1.1 On the effect of cooling rate
Cast iron is a material sensitive to the cooling rate, the same casting of thick-walled and thin-walled parts, the internal and external surfaces may obtain a disparity in organization, commonly known as the organization of the inhomogeneity. This is because the graphitization process depends to a large extent on the cooling rate. There are more factors affecting the cooling rate of the casting: the wall thickness and weight of the casting, the type of casting material, the gate and the weight, etc. As the wall thickness, weight and structure of the casting depends on the working conditions, can not be changed at will, so in the selection of chemical composition should take into account their impact on the organization.
1.2 About the influence of ferrofluid breeding treatment
Fertilization treatment is in the molten iron into the cavity before the casting, the fertilizer attached to the molten iron to change the metallurgical state of the molten iron, so as to improve the microstructure and properties of cast iron. For gray cast iron, the inoculation treatment is to obtain A-type graphite, pearlite matrix, fine eutectic group organization, as well as to reduce the tendency of white mouth at the thin wall or corner of the casting and sensitivity to the wall thickness of the casting; for malleable cast iron, in order to shorten the short annealing cycle, increase the allowable wall thickness of the casting and improve the structure of the organization; for ductile iron, in order to reduce the tendency of white mouth of the casting, increase the spheroidization rate and improve the roundness of graphite.
1.3 The effect of superheat treatment on the molten iron.
Increasing the superheating temperature of the molten iron can.
1.31 increase the chemistry carbon content and correspondingly reduce the graphite carbon content
1.32 Refine graphite and enable the formation of dendritic graphite
1.33 Eliminate the "heritability" of cast iron
1.34 improve the uniformity of the organization of the casting in section
1.35 facilitate the casting of the complementary shrinkage. Similarly, the iron insulation also has a similar effect of iron superheating.
1.4 About the influence of the furnace charge characteristics
In practice, it is often found that changing the metal charge (such as the use of pig iron of different origins or change the ratio of the charge, etc.) and the chemical composition seems to have no change in the case of cast iron has a different organization and performance, which indicates that the nature of the raw material directly affects the nature of the cast iron melted with it, known as cast iron: "hereditary" For this reason, the The use of increased iron temperature and the use of a variety of iron ingredients can eliminate this "hereditary", and improve the organization and properties of cast iron.
In summary, the process factors and metallurgical factors of cast iron have a great influence on the mechanical properties of cast iron, therefore, the control of these influencing factors should not be neglected.

2、Grey cast iron cannot be heat treated to achieve the grade requirements
Generally speaking, heat treatment can improve the organization and performance of casting alloys to a large extent, but in gray cast iron conditions, the role of heat treatment is relatively small. In gray cast iron, graphite has a great influence on cast iron properties, and any heat treatment method cannot change the form and distribution of graphite, so it is not possible to effectively improve the performance of gray cast iron through heat treatment to meet the grade requirements.
However, there are many ways to improve the mechanical properties of gray cast iron, such as reasonable matching of chemical composition, change the composition of the furnace charge, over heat treatment of ferrofluid, breeding treatment, micro or low alloying, etc., can achieve very good results.

3、 the production of high-grade gray cast iron (breeding cast iron) considerations
Production of high-grade gray cast iron (generally refers to HT200 above), in order to obtain high mechanical properties, the number of graphite must be reduced as much as possible, reduce the length of graphite. The traditional method is to reduce the carbon and silicon content of the molten iron and increase the condensation rate of the molten iron, but when the magnitude is slightly larger, there will be D-type supercooled graphite and white mouth, but reduce the mechanical properties of gray cast iron.
Before the furnace or in the pouring to the molten iron to add the right amount of ferroalloy particles, mainly ferrosilicon, is called breeding treatment. Fertilization provides a large amount of nucleation mass in the molten iron for graphite to nucleate. Effective inoculation will promote the precipitation of graphite, thus eliminating the white mouth, refining flake graphite and transforming the supercooled graphite into non-directional homogeneous graphite (A-type graphite), which not only can significantly improve the overall mechanical properties, but also improve the uniformity of the casting organization and reduce the difference in mechanical properties caused by the uneven wall thickness and the different cooling speed between the corners and the heart of the casting. Therefore, the inoculation treatment of iron is an essential technology for the production of high-grade gray cast iron (inoculated cast iron).
In order to make the breeding effective, the requirements of the original ferrofluid need to be met, that is, the original ferrofluid should have a low carbon and silicon content, or the original ferrofluid should have a low carbon equivalent, the lower the carbon equivalent, the better the breeding effect, the higher the strength of gray cast iron parts; on the contrary, the high carbon equivalent, poor breeding effect. As silicon can be adjusted by adding the method of breeding agent, so consider the carbon equivalent of the original molten iron always maintain the carbon at 2.8% to 3.2%, maintain the silicon at a slightly lower than the critical value that can significantly promote graphitization, and then add the breeding agent so that the amount of silicon exceeds the critical value to obtain the effect of breeding treatment. In addition, the casting wall thickness and cooling rate also affects the organization of pregnant cast iron parts, in the selection of chemical composition should also be taken into account, generally thick parts of carbon, silicon amount to take the lower limit, thin parts to take the upper limit.
Manganese in high grade gray cast iron (breeding cast iron), in addition to the effect of neutralizing sulfur, there is a special requirement, that is, with the help of it so that gray cast iron can get pearlite organization, so high grade gray cast iron (breeding cast iron) of manganese content is generally higher. Sulfur can weaken the graphitizing effect of the inoculant, so often limit the sulfur to 0.12% or less. In recent years, it is also believed that in order to get a good breeding effect, the amount of sulfur in the original iron solution can not be too low. Therefore, in the future, the sulfur content of the iron liquid gradually reduced, for the amount of sulfur in pregnant cast iron should be determined, it seems to be a noteworthy problem.
Phosphorus content in general from the mechanical properties of the requirements, often limited to 0.15% or less, but some machine tools gray cast iron parts (often manufactured by breeding cast iron) need to wear, phosphorus content can be increased to 0.3% to 0.5% or higher.

Xinyuanzhu Group specializes in the production of Ductile iron castings, Pig iron gray iron casting, Steel casting, Brass Casting, Malleable Iron Casting, and undertakes batch casting processing of castings. Welcome guests to cooperate with pictures or samples.