In precision casting, graphite sheet in gray iron casting has the function of cutting non-metallic matrix, destroying its continuity and increasing its strength.From the strength of thought, should prevent the production of long and thin graphite sheets and small graphite sheets, graphite sheets with obvious location of the greater reaction.To master the distribution of graphite sheet is a guarantee.

The key of gray iron casting function.

Type A graphite is formed under conditions of low carbonization yield and low freezing rate.Because of the large primary austenite dendritic crystal, eutectic, no big change supercooling degree, graphite centers do not have much, eutectic group is bigger, consisting of the d-type graphite graphite pieces more than. Because of the fast freezing compared, austenitic, crystal, the onset of eutectic change liquid secondary was between primary austenite dendritic crystal, composed of graphite piece along the position of the dendritic crystal growth, deposit is must

In order to prevent it from happening, the mechanical function of pig iron is affected greatly.

Type B graphite is in the shape of a yellow flower under an optical wind microscope. The graphite flake at the core of the eutectic cluster is larger than that at the core, while the graphite flake at the core is smaller.In practice, the core position is d-type graphite and the core is a-type graphite.The nucleation environment of type B graphite is worse than that of type A graphite, and the supercooling degree of the eutectic change is also greater than that of the formation of type A graphite. At the time of crystallization, the supercooled graphite (type D) is occurring at the core of the eutectic cluster, and the latent heat of crystallization released increases the supercooling degree of the periphery, forming type A graphite.If the amount of type B graphite is not much, for the function of iron reaction is not large, under normal conditions can allow it to have.

Type C graphite is a kind of cast iron with low carbonation equivalent, high freezing rate and high undercooling degree. Under the circumstance of flourishing of primary austenite dendrites, it is composed of austenite dendrites, and the graphite sheet is thick and directional.D - type graphite is rare in thin - walled gray iron castings with low carbonation equivalent.In the absence of alloying elements, type D graphite is often accompanied by a lasso.If the matrix mechanism is pearlite, then pig iron

Good wear resistance, and the machine can lose the finer nominal roughness after processing.

Type D graphite is mainly found in highly eutectic (hypereutectic) carbonic equivalent. In the rapidly frozen pig iron, there are small sheets of primary graphite, small sheets of graphite, and sometimes all graphite sheets have sharp angular blocks.When supereutectic ferric liquid freezes, after passing through the liquid phase line, primary graphite is precipitated at a certain degree of supercooling and gradually grows in the liquid phase.Because the crystallization of higher concentration, into a short time longer, constitute fewer branches of the small sheet.When the measurement is elevated to eutectic, malformed eutectic changes occur. The graphite that occurs is malformed eutectic inks (type A graphite). The ultimate result is the dispersion of malformed eutectic inks between tiny graphite sheets.Thus, type C graphite is formed from fine, blocky graphite and type A graphite.Type C graphite can improve the thermal conductivity of pig iron and improve its power of tax resistance. However, the mechanical function of pig iron is highly reactive, and such graphite should not be found in normal structural castings.Type E graphite is formed when eutectic changes occur in the environment with low degree of supercooling due to its high nucleation power and low freezing rate.

When inspected under an optical wind microscope, graphite was found to be of uniform distribution in A serpentine sheet and directional, but its length was not due to the nucleation environment and freezing rate of the pig iron. Similarly, high quality structural castings are expected to have medium length type A graphite.

The consumption of fine grey mouth precision casting, should make its matrix body for pearlite, graphite for A type, and graphite sheets should be evenly distributed in the non-metallic matrix, pearlite should also be large and symmetrical.Type B graphite and type D graphite in the mechanism should be reduced to a minimum to the extent possible without the presence of type C graphite and type E graphite.Therefore, it is necessary to stop ineffective inoculation and control the freezing rate of the casting.The pig iron that can give rise to e-type graphite, such as higher freezing rate, also forms d-type graphite.Therefore, d-type graphite and e-type graphite are commonly seen in high-strength thin-wall cast iron.

The mechanical function of gray iron casting in precision casting is mainly derived from its matrix mechanism. In order to lose high strength, it is expected that the matrix mechanism is dominated by pearlite and excessively reduces ferrite content.If ferrite body amount is overmuch, the intensity that does not invite cast iron only is low, and machining day can make machine tool overheat, raise the longevity of machine tool apparently.Unlike nodular pig iron, there is no requirement for ductility and toughness of gray iron castings, only its strength is required, because normally high pearlite content is preferred.Such graphite can be occasionally found in subeutectic pig iron.Such as: induction furnace smelting and burden in the amount of iron too much, because the original cast iron genetic reaction, can emerge with sharp Angle of block graphite;This graphite also occurs when the amount of inoculant is too large and all the silicon elements are enriched.The mechanical properties of gray iron castings in precision casting depend on the matrix structure and the distribution of flake graphite.The mechanical properties of gray iron castings depend on the matrix structure and the distribution of flake graphite.The mechanical function of gray iron casting is secondary to its matrix mechanism. In order to lose high strength, it is expected that the matrix mechanism is dominated by pearlite and excessively reduces ferrite content, if ferrite