SAND CASTING EQUIPMENT.

1、Shrinkage shrinkage
1.1 Influencing factors
1.11 carbon equivalent: increase the amount of carbon, increase the graphitization expansion, can reduce the shrinkage shrinkage. In addition, increasing the carbon equivalent can also improve the mobility of ductile iron, which is conducive to complementary shrinkage. The empirical formula for the production of high-quality castings is C% + 1/7Si% > 3 9%. However, when increasing the carbon equivalent, should not make the casting produce other defects such as graphite floating.
1.12 phosphorus: high phosphorus content in the molten iron, so that the solidification range is expanded, while the low melting point phosphorus eutectic in the final solidification is not replenished, as well as making the casting shell weaker, so there is an increase in shrinkage, shrinkage loose tendency to produce. General factory control of phosphorus content of less than 0 08%.
1.13 rare earths and magnesium: rare earth residue is too high will deteriorate the graphite shape, reduce the spheroidization rate, so the rare earth content should not be too high. and magnesium is a strong stabilization of carbide elements, hinder graphitization. It can be seen that the amount of residual magnesium and the amount of residual rare earth will increase the tendency of white mouth of ductile iron, so that the graphite expansion is reduced, so when their content is high, will also increase the shrinkage, shrinkage tendency.
1.14 wall thickness: when the casting surface to form a hard shell, the higher the temperature of the internal metal liquid, the greater the liquid shrinkage, the shrinkage, shrinkage of the volume of not only the absolute value of the increase, its relative value also increased. In addition, if the wall thickness changes too abruptly, isolated thick sections do not get complementary shrinkage, so that the tendency to produce shrinkage holes shrinkage pine increased.
1.15 temperature: high pouring temperature, conducive to shrinkage, but too high will increase the amount of liquid shrinkage, the elimination of shrinkage, shrinkage is not conducive, so the pouring temperature should be reasonably selected according to the specific situation, generally 1300 ~ 1350 ℃ is appropriate.
1.16 sand compactness: If the compactness of the sand is too low or uneven, so that after pouring under the action of metal static pressure or expansion force, the cavity expansion phenomenon, resulting in the original metal is not enough to fill the shrinkage and lead to shrinkage of the casting shrinkage loosening.
1.17 pouring and cold iron: if the pouring system, the mouth and cold iron set improperly, can not ensure that the metal liquid order solidification; In addition, the number of the mouth, the size and the connection with the casting when or not, will affect the shrinkage effect of the mouth.

1.2 Preventive measures
1.21 control the composition of the ferrofluid: maintain a high carbon equivalent (3.9%); minimize the phosphorus content (0.08%); reduce the amount of residual magnesium (0.07%); the use of rare earth magnesium alloy to deal with the rare earth oxide residue control at 0.02% to 0.04%.
1.22 Process design to ensure that the casting in solidification can be constantly supplemented by high-temperature metal liquid from the riser, the size and number of risers should be appropriate, and strive to achieve sequential solidification.
1.23 If necessary, use cold iron and subsidies to change the temperature distribution of the casting to facilitate sequential solidification.
1.24 The pouring temperature should be 1300-1350℃, and the pouring time of a pack of ferrofluid should not exceed 25min to avoid spheroidization recession.
1.25 Improve the compactness of the sand, generally not less than 90; bump sand evenly, water content should not be too high, to ensure that the casting has sufficient rigidity.

2、Clagging
2.1 Influencing factors
2.11 silicon: silicon oxide is also the main component of the slag, so as far as possible to reduce the amount of silicon content.
2.12 sulfur: sulfide in the ferrofluid is one of the main reasons for the formation of ductile iron parts with slag defects. The melting point of sulfide is lower than the melting point of the iron liquid, in the process of solidification of the iron liquid, sulfide will precipitate from the iron liquid, increasing the viscosity of the iron liquid, so that the molten slag or metal oxides in the iron liquid is not easy to float. Thus, when the sulfur content of the molten iron is too high, the casting is prone to slagging. Ductile iron original molten iron sulfur content should be controlled at 0 06% or less, when it is 0 09% to 0 135%, cast iron slag defects will increase sharply.
2.13 rare earths and magnesium: in recent years, the study that the slag is mainly due to oxidation of magnesium, rare earths and other elements, so the residual magnesium and rare earths should not be too high.
2.14 pouring temperature: pouring temperature is too low, metal oxides in the metal liquid because the viscosity of the metal liquid is too high, it is not easy to float to the surface and remain in the metal liquid; temperature is too high, the surface of the metal liquid slag becomes too thin, not easy to remove from the surface of the liquid, often with the metal liquid into the type. In actual production, the pouring temperature is too low is one of the main reasons for slagging. In addition, the pouring temperature should also consider the relationship between carbon and silicon content.
2.15 pouring system: pouring system design should be reasonable, with slag blocking function, so that the metal liquid can be filled smoothly casting, and strive to avoid splashing and turbulent flow.
2.16 sand: if the surface of the sand adheres to the excess sand or paint, they can be synthesized with the metal liquid oxide slag, resulting in slagging; uneven compactness of the sand, the surface of the low compactness of the type wall is easy to be eroded by the metal liquid and the formation of low melting point compounds, resulting in the casting slag.

2.2 Prevention measures
2.21 control the composition of the molten iron: try to reduce the amount of sulfur in the molten iron (0.06%), the appropriate amount of rare earth alloy (0.1% to 0.2%) to purify the molten iron, as far as possible to reduce the amount of silicon and residual magnesium.
2.22 melting process: to try to improve the metal liquid furnace temperature, suitable sedation, in order to facilitate the floating of non-metallic inclusions, aggregation. Pick clean the slag on the surface of the iron liquid, the surface of the iron liquid should be put covering agent (perlite, grass wood ash, etc.) to prevent the iron liquid from oxidation. Choose a suitable pouring temperature, preferably not less than 1350℃.
2.23 The pouring system should make the flow of molten iron smooth, and should have slag collection bag and slag blocking device (such as slag filter, etc.) to avoid sand flushing from the straight pouring channel.
2.24 Casting compactness should be even and strong enough; blowing the sand in the casting when closing the box.

3. Graphite floating
3. 1 Influencing factors
3.11 carbon equivalent: the carbon equivalent is too high, so that the ferrofluid precipitates a large amount of graphite at high temperatures. Because the density of graphite is smaller than the iron liquid, driven by magnesium vapor, so that graphite floating to the upper part of the casting. The higher the carbon equivalent, the more serious graphite floating phenomenon. It should be noted that the carbon equivalent is too high is the main reason for graphite floating, but not the only reason, the size of the casting, wall thickness is also an important factor affecting the graphite floating.
3.12 Silicon: Under the condition of constant carbon equivalent, the appropriate reduction of silicon content can help reduce the tendency to produce graphite floating.
3.13 Rare earth: when the content of rare earth is too little, the solubility of carbon in the ferrofluid will be reduced, and the ferrofluid will precipitate a large amount of graphite, which aggravates the graphite floating.
3.14 spheroidization temperature and incubation temperature: in order to improve the absorption rate of magnesium and rare earth elements, domestic experimental research shows that the most appropriate spheroidization treatment of the ferrofluid temperature is 1380 ~ 1450 ℃. In this temperature range, as the temperature increases, the absorption rate of magnesium and rare earths increases.
3.15 Pouring temperature: In general, the higher the pouring temperature, the greater the tendency of graphite floating, this is because the casting is in the liquid state for a long time is conducive to the precipitation of graphite. If the solidification time is shortened, as the pouring temperature increases, the tendency of graphite floating decreases.
3.16 retention time: the retention time between the conception treatment and the pouring is too long, which provides the conditions for graphite precipitation, generally this time should be controlled within 10 minutes.

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