SAND CASTING EQUIPMENT.

4、The 4 prohibited when using inoculants for gray cast iron inoculation treatment
The inoculant used in gray cast iron can be classified by function, main elements, shape, etc. Four rules should be prohibited when using inoculant for inoculation treatment of gray cast iron.
4.1, the inoculant must be dried before use.
4.2, the use of pure silicon or pure ferrosilicon as inoculant is prohibited
4.3, the breeding agent should not be added hastily, to be careful about the method.
4.4, the particle size of the inoculant

5、 gray cast iron parts may appear defects
In the production of gray cast iron parts, common casting defects are: porosity, inappropriate composition and performance, hot and cold cracking, shrinkage and shrinkage, slag eyes and iron beans, cold isolation and under-pouring, sand eye and sand trapping, succulent and wrong box, deformation, etc.. Usually, the cause of these defects is not only molding core problems, sometimes there are melting and pouring, sand quality, sand cleaning and many other production process problems. Therefore, specific analysis must be made in order to take appropriate and reasonable measures to solve.
Gray cast iron parts due to melting and pouring the main defects and their causes and prevention and prevention analysis are as follows.
5.1 Pore
5.11 characteristics and discovery methods:
Sieve-like pores: more uniformly distributed throughout the casting or most of the cross-section.
Subcutaneous pores: 1 ~ 3mm from the casting surface, the appearance of dense small pores, with the appearance of inspection, machining, blast cleaning or magnetic flaw detection can be found.
5.12 Cause analysis:
When the ferrofluid, gas content is high, and the pouring temperature is too low, the precipitation of gas is too late to float and overflow castings when produced.
The furnace material itself has high gas content, or rust is serious, and there are many greasy substances on the surface.
Subcutaneous pinholes are mainly caused by hydrogen. Silicon can reduce the content of oxygen in cast iron, but can increase the content of hydrogen, so high silicon cast iron is prone to hydrogen gas holes. When the furnace charge can contain aluminum or alumina, it is also easy to produce pinholes.
The ferrofluid pack does not dry.
The inoculant does not dry.
5.13 Prevention methods:
Furnace material should be properly managed. The furnace material with serious rust or surface grease material should be cleaned or treated before use.
For its own high gas content of the furnace material, should be remelted and regenerated before use.
Before the furnace can add the right amount of rare earth in order to de-gas.
Control the appropriate temperature of iron out of the furnace and pouring temperature.
The furnace cylinder, pre-furnace and molten iron package should be dried.
When pouring, avoid breaking the flow.
The inoculant should be fully preheated.
When pouring, it must be ignited to induce gas.
5.2 Composition, organization and performance failures
5.21 Characteristics and discovery method:
Material is too hard or too soft.
The macrostructure and microstructure of the casting section do not meet the standard or technical conditions.
Section observation, chemical analysis, metallographic examination, hardness test, etc. can be found.
5.22 Cause analysis:
When the carbon and silicon equivalent is low, it makes the material hard, and when the carbon and silicon equivalent is high, it is soft.
Improper superheating of the iron solution.
Insufficient breeding treatment.
5.23 Prevention method:
Proper batching and prevention of tampering during operation.
Control the proper superheating temperature.
Observe the operating procedures and handle the pre-furnace breeding correctly.
5.3 Shrinkage
5.31 Characteristics and detection methods
There are many scattered small shrinkage holes inside the casting with rough surface and water seepage during hydraulic test.
Can be found with mechanical processing or magnetic flaw detection.
5.32 Cause analysis:
When the phosphorus content is high, so that the solidification interval is expanded; at the same time, the low melting point phosphorus co-crystal in the final solidification, not complemented, resulting in microscopic shrinkage. Especially for high grade cast iron (lower carbon content), the body shrinkage rate is larger, more attention should be paid. Pouring speed is too fast, so that the parts that need to fill the shrinkage is too late to replenish enough ferric liquid.
5.33 Generally control below 0.15% and control the stable chemical composition of the molten iron.
When pouring, pour slowly as appropriate to facilitate sufficient shrinkage.
5.4 Shrinkage
5.41 Characteristics and discovery method :
Concentrated holes with irregular shape and rough surface are produced at the hot section of the casting.
With the appearance of inspection, mechanical processing or magnetic flaw detection can be found.
5.42 Cause analysis:
Due to the large shrinkage of the body, the chemical composition of the molten iron does not meet the technical requirements, especially the high grade low carbon cast iron.
The pouring temperature is too high, which increases the liquid shrinkage value.
5.43 Prevention method:
Correctly control the chemical composition of the molten iron. Try to make Ws low, generally below 0.12%.
Control the suitable pouring temperature.
For large pieces, make up the iron liquid at the riser.
Properly increase the breeding volume.
5.5 Thermal cracking
5.51 Characteristics and discovery method:
Crack with dark or almost black oxidized surface.
It is found by appearance inspection, light transmission method, magnetic flaw detection, pressure test, kerosene penetration and other methods.
5.52 Cause Analysis:
The chemical composition of the molten iron does not meet the requirements, so that the solid shrinkage value is large, such as low carbon and high sulfur.
Castings containing low melting point slag, reducing the high-temperature strength (because the thermal cracking generated in the solidification is nearly over, mainly in the castings at the thermal joints shrinkage by mechanical obstruction and produce).
5.53 Prevention methods:
Control a reasonable chemical composition, try to make the original ferrofluid in the sulfur content is low.
When pouring, avoid slag into the cavity.
5.6 Cold cracking
5.61 Characteristics and methods of detection:
At the crack, a cleaner or slightly dark red slightly oxidized surface.
The method of detection is the same as for hot cracks.
5.62 Cause Analysis:
The chemical composition of the iron liquid does not meet the requirements, so that the solid shrinkage value is large
High phosphorus content in the molten iron increases the brittleness, thus reducing the tensile strength of cast iron (because cold cracking occurs after the casting cools, mainly at the stress concentration of the thick and thin junction of the casting, due to thermal stress).
5.63 Prevention methods:
Control the reasonable chemical composition.
Generally Wp in the ferrofluid should be below 0.15%.
5.7 Slag Eye
5.71 Characteristics and detection methods :
There is slag in the hole outside or inside the casting
With the appearance of inspection, mechanical processing or magnetic flaw detection can be found
5.72 Cause analysis:
More molten slag in the molten iron or slag in the molten iron ladle is not removed, and when pouring, no attention is paid to blocking slag.
Pouring, due to the broken flow and brought in the molten slag.
5.73 Prevention method:
Properly increase the temperature of the molten iron and add a small amount of dry sand in the molten iron package to facilitate the gathering of slag skimming. To avoid sulfur re-transfer into the ferrofluid
Pre-clean the residual slag in the molten iron package.
When pouring, pay attention to slag blocking and not to break the flow.
5.8 Iron beans
5.81 Characteristics and discovery method :
There are small iron beads in the air holes.
Check with casting section, mechanical processing can be found.
5.82 Cause analysis:
Due to the iron casting temperature is too low, when the iron splash generated by the iron beans, can not be melted by the iron again, the result with the external gas into the casting a piece of package; or this iron beans by FeO + C Fe + CO generated by CO and iron beans into the casting a piece of package.
5.83 Prevention methods:
Suitable pouring temperature.
When pouring, do not break the flow.
5.9 Cold isolation and under-pouring
5.91 Characteristics and detection method :
Castings with incompletely fused gaps or localized missing flesh with rounded edges around them.
Can be found with the appearance of inspection.
5.92 Cause analysis:
The temperature of the iron liquid is too low, which reduces the fluidity of the iron liquid.
In the molten iron, the carbon and silicon content is low, and the sulfur content is high, which also reduces the fluidity of the molten iron.
When pouring, there is a break in the flow or the amount of primary iron is not enough, and when the second pouring is done, it is easy to produce cold compartment.
5.93 Prevention method:
Properly increase the pouring temperature of the molten iron.
Control the proper chemical composition of the molten iron and reduce the sulfur content as much as possible.
Pour the full amount at one time, and avoid the replenishment. and when pouring, do not break the flow.
5.10 Over-hardness
5.101 Characteristics and discovery method
White mouth iron tissue appears at the edge of casting and thin wall.
Cross-sectional observation, hardness test, machining can be found.
5.102 Cause analysis:
Low carbon and silicon equivalents.
Insufficient breeding treatment.
5.103 Prevention method:
Correct ingredients.
Increase the breeding amount appropriately.

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