In recent years, due to the requirements of environmental protection, most small cupolas have been replaced by small-sized medium-frequency induction furnaces. The use of coke and other fuels in the cupolas causes metallurgical reactions in the smelting process, and electric furnace smelting mainly involves alloy remelting and the metallurgical reaction is not significant.
According to the smelting characteristics of electric furnace cast iron, it is required that the casting workers select components in cast iron, charge ratio, scrap amount, inoculation process, carbon and decarburization, sulfur-enriched desulfurization, spheroidizing process, vermicularization process, temperature control, casting process, etc. Many aspects need to update their concepts and adopt practical measures to ensure and improve product quality.
1
Electric Furnace Cast Iron Furnace Ratio and Synthetic Cast Iron
In the foundry industry, it is often said that the composition of the cast material determines the organization and organization of the left and right properties; this statement is not entirely comprehensive. We found many cast irons in our production practice. However, when the same composition is used, the mechanical properties are quite different. In addition to its quality, the quality of molten iron is closely related to the charge ratio of pig iron (the amount of pig iron used, the amount of scrap steel used, the amount of recycled materials, the amount of alloy added), melting and tapping temperature, and the brewing process. The so-called synthetic cast iron refers to the use of more than 50% of the scrap in the ingredients, and the cast iron material obtained by the method of carbon synthesis is required to be melted in the electric furnace because it needs a higher melting temperature. At present, the synthetic cast iron mainly includes synthetic gray iron and ductile iron.
Through a great deal of practice, for the high-strength gray cast irons such as HT250 and HT300, the scrap left and right strength and pig iron influence the organization.
Ingredient taboo
High proportion of scrap (especially shipbuilding) and high proportion of recycled materials (roughing, waste castings, iron filings) with the amount of synthetic iron scrap addition should not exceed 50% ;
High proportion of scrap (especially shipboards) with high pig iron containing sulfur and phosphorus ;
More than 40% of recycled material (roughing, waste casting, iron filings).
Ingredients optimization combination (%)
Composition of pig iron scrap
The ratio of A403030, the ratio of B304030, the ratio of C204040, the ratio of D205030
Manganese sulfur content
When the hardness needs to be increased, the content of manganese can reach 1.0-1.2%, but it is not required to increase the sulfur content correspondingly (the sulfur content in gray iron is analyzed separately).
In order to save costs, a company uses scrap steel more than necessary. Trial production of high-grade gray cast iron within two months results in the use of 60% of scrap steel. For a period of time, in addition to the addition of scrap steel, additional charge and a small amount of iron scrap are added. After a period of time, it was discovered that the castings had large shrinkage holes, shrinkage and white hard spots, and they continued to become more and more serious.
The cause of this defect is that the preliminary judgment is that the MnS content in molten iron is too high and the castings are micro-shrinkage and shrinkage, and MnS is enriched to form white hard spots. This is because the high-grade gray iron HT300 composition requires a high Mn content (about 1%), and the scrap itself is also high in manganese (16% manganese in the shipboard contains Mn at 1.6%), while the scrap S and the return iron ( The accumulation of MnS produced by the reaction of S and manganese, including iron filings, in the charge reaches a certain level, resulting in an excess, resulting in the above defects.
In order to reduce the content of MnS in hot metal, it is generally adjusted by adding a certain amount of high-quality new iron (low S, low Mn). In addition, the effect of gestation is improved, and MnS can be refined to reduce its adverse effects.
When the amount of scrap added is too large, the melting point of the scrap is about 1530 degrees, and the melting point of the pig iron and the return charge is only about 1230 degrees. The use of scrap steel increases the power consumption, increases the tendency of the hot metal to cool, and also absorbs a large amount of nitrogen. The synthetic cast iron process is not suitable for gray cast iron and is more suitable for ductile iron.
2
About Sulfur Increase of Gray Iron in Electric Furnace
As mentioned above, compared with the cupola smelting in the middle frequency induction electric furnace melting cast iron process, besides having the advantage of high melting temperature, there are many shortcomings. There are mainly three problems:
The tendency of hot metal is too cold, and it is easy to produce D and E graphites that affect the mechanical properties of the material ;
The purity of the molten iron is less and the core of heterogeneous crystals is less, resulting in poor gestation effects. Under the same composition conditions, the casting strength is low and the iron is hard ;
The shrinkage tends to be larger. When the manganese content in the high-grade gray cast iron is high, microscopic shrinkage and shrinkage tend to occur.
In response to the above problems, the measures to be taken are: Â
In the late stage of melting, a high temperature holding time is added to make the iron crystal grains melted by various charge materials as uniform as possible, especially to refine the graphite ;
Increase the amount of foreign exotic cores (such as sulfides), strengthen the inoculation effect, and promote the formation of A-type graphite ;
Control the sulfur and manganese content of high-grade grey cast iron and its proportion, control the proportion of return charge to achieve the appropriate composition.
These measures are different for different structural casting products and need to be mastered in practice.
Cases
On a certain day, a company smelts 6 iron grey iron HT300 molten irons in an electric furnace and casts hydraulic valves G03, G02 and other products. After dissecting internal tissues, large areas of microscopic shrinkage, shrinkage, and shrinkage are found, and a total of 830 are scrapped (see attached Figure). Brinell hardness HBS241, chemical composition C3.27, Si1.78, Mn0.83, S0.087, P0.04 were measured. 98% of pearlite, 80% of E-shaped graphite (20% of type A), and 5th grade of graphite. According to relevant personnel's research and analysis, there should be problems with the hot metal material.
The results of the chemical composition analysis seem to be normal for the general thin-walled HT300 castings, but there is a problem for the hydraulic valve castings (thicker walls). The cause of this defect is that the initial judgment is that the content of S and Mn in the molten iron exceeds the range that the casting can accommodate due to the excessive shrinkage, shrinkage, shrinkage and shrinkage of the casting caused by the high content of MnS in hot metal. There is a difference in the amount of ingredients.)
As a certain amount of S-addition agent is added in the smelting process, the S and Mn contents in the molten iron will accumulate to a certain degree, which will cause the S content in the molten iron to exceed the normal solidification and crystallization requirements of the casting itself, resulting in such defects. Countermeasures: Stop adding S-addition agent, adjust the content of Mn, and ensure the normal content of the five elements of HT300 gray iron. After adjustment, all defects are eliminated.
It is theoretically correct to add a certain amount of MnS by adding an S-addition agent to the molten iron in the electric furnace to increase the gestation effect. However, in recent years, most of the literature says that the electric furnace has a high grade of gray iron. The S content needs to be controlled to be 0.05-0.10%, but many factories have proved that when the content of Mn is about 1%, if the composition analysis contains more than 0.05% of S, the casting will start to have cratering defects. When the content of S exceeds 0.07%, bulk shrinkage occurs. How can this phenomenon be explained?
There are two forms of S in gray cast iron, one is elemental, and the other is MnS in the compound state. Sulfur in the gray iron plays a role in the crystallization of the core, mainly MnS in the combined state. Our current testing methods (whether it is Chemical analysis or spectroscopic analysis can only analyze the S in the state of the elemental state of the casting and molten iron, but the existence of S in the combined state (MnS) is not detectable. When the content of elemental S exceeds 0.05%, the S content in the combined state is relatively high. At this time, the molten iron: MnO+FeS=MnS+FeO, FeO+C=Fe+CO, or 2FeO+C=2Fe+CO2
At this time, during the solidification process, the molten iron is precipitated with CO or CO2, and at the same time, part of the brown MnS powder is generated, and the iron slag reaction gas shrinkage hole is formed. As long as there are certain conditions, this kind of gas shrinkage hole occurs not only in the electric furnace hot metal but also in the cupola hot metal. In fact, we have added some sulfur in the melting process of the electric furnace. These sulfurs come from:
The re-melting pouring system brings the sulfur content in the pouring system to be much higher than that in the casting .
Sulfur in pig iron, the sulfur content in cast iron is not high, and the ordinary pig iron we buy carries different levels of slag (garbage). We will not test it, but these rubbish have a high Sulphur phosphorus will be brought into the furnace ;
The rust and iron oxide content of scrap and pig iron are higher, and the absorption rate of sulfur increases when entering molten iron. In such a situation, if we add iron sulfide to increase S, it will be excessive. In actual production of high-grade grey iron castings, the elemental S in hot metal is controlled to be between 0.03-0.05%.
3
Electric furnace high grade gray iron breeding and modification
Regarding the gestation process of high-grade grey iron (HT300 as an example), the traditional amount of inoculum is 0.3-0.4% of the amount of processed iron (mainly for cupola production). In recent years, with the popularity of electric furnace, the amount of inoculation has gradually increased. The latest information recommended 0.5-0.6%, I through long-term practice, choose the amount of ingestion of about 0.8%, to obtain a comprehensive increase in the intensity of hardness and cutting processing performance, casting internal defects after processing significantly reduced.
Cases
A company producing high-grade solenoid valves, the technical requirements of casting hardness greater than HB200, strength greater than 300N/mm2, the main wall thickness of the product exceeds 50mm, through multiple tests, while increasing the amount of inoculation, take the second inflow Eliminates the thick defects caused by thick walls, improves the casting density, and ensures product quality.
With regard to the secondary incineration of molten iron, a uniform inoculant with a particle size of 0.2-0.7 mm is added before casting, which is more suitable for thick parts, but when used for small parts, it increases the shrinkage of hot metal.
At one stage, after the processing of some products of a company, the surface was bright white with high hardness, and the tool was slippery. After analysis, the original block of inoculant was too large and was not suitable for the capacity of the hot metal package, resulting in inoculant when the molten iron was poured. If it is not completely melted, the local silicon content of the casting is enriched to form a hardened phase; when the temperature of the molten iron is too low to carry out secondary flow inoculation, the same defect will also occur.
There is a factory specializing in the production of HT300 gray iron hydraulic parts, a KP pump body is poured, the wall thickness of the casting is about 30mm, and the ingredients are in accordance with the experience of HT300. The composition of hot metal is: C3.0-3.1%, Si1.7-1.8%, Mn0 .95-1.05%, P0.05%, S0.04%, castings body anatomy up to 300 N/mm2, but successive lots of product collapsing and shrinking near the gate, no matter how the gating system is adjusted, There is no effect. There is no way to increase the carbon equivalent reduction strength. When adjusting to C3.2-3.3%, Si1.8-2.0%, the defect disappears. However, after the product has been processed and tested, most of the expansion leakage occurs. Ontology test is not qualified, resulting in bulk returns from the OEM. Associating a batch of similar pumps in the past, due to listening to other people's suggestions, using S-iron to increase S, when the molten iron contained S at 0.07% or more, the castings shrink in a large area and accumulate large amounts of waste products. In order to dispose of these waste products, according to rare earth desulfurization The principle of adding rare earth magnesium ferrosilicon (about 0.2%) during the incubation process when adding such waste products effectively reduces the sulfur content and solves the shrinkage problem.
In view of the collapse and shrinkage of the KP pump at that time, although the original molten iron contained less sulfur, a small amount of rare-earth-magnesium-ferrosilicon (about 0.2%) was also added during gestation, and the ideal result was achieved. solve. Analysis of the mechanism, the cast iron produces shrinkage, mainly iron gas (including oxygen, nitrogen, hydrogen, etc.) play, these gases in the late solidification precipitation, the molten iron can not be added, resulting in defects, and rare earth magnesium ferrosilicon as a Gray iron modifiers (also a kind of inoculants) are good at removing gas. The amount of gas contained in molten iron is greatly reduced, and defects are eliminated.
Nanjing Kirin Scientific Instrument Group Co., Ltd.
Testing Center
October 20, 2017
Commercial Vehicle Fuel Water Separators
A machine for separating oil and water is usually used by ships to deal with sewage. Because of the requirements of environmental protection, the sewage generated by the ship machine space discharged into rivers, lakes and seas must be treated. The working principle and working process of the oil and water separator system: 1 by AOD (gas) diaphragm pump into the water - > 2 flow control valve into the -- > 3 primary cellular chamber, water washing, because within it there are a lot of close honeycomb interlayer, the water in the process of the tiny particles falling on the water flow in the honeycomb chamber, waste water high into the - > 4 hole mesh cloth (5/32 ") into the - > 5 adsorption chamber and extraction chamber, Water flow into the oil adsorption chamber composed of JT57 liquid filtration medium, in this process, oil and grease are a large number of adsorption and extraction of a large number of complex heavy metals, organic matter, TSS, BTEX, PCB and many water pollutants. Then the water flow in the adsorption chamber turns upward into the -->6 second stage honeycomb chamber, the water flow through the second stage close honeycomb compartment, three times reverse flow up and down, and the residual trace oil will float up and collect in its upper part, the water flow into the -->7 clear water chamber, the final water from the bottom of the clear water chamber discharge. Traces of residual oil on the second stage honeycomb and clean water chamber cloths are removed by skimming the skimmer on top to an external oil storage container.
Commercial Vehicle Fuel Water Separators,Vehicle Fuel Water Separators,Car Fuel Water Separators,Fuel Water Separator
Ruian Guangzhong Auto Parts Co.,Ltd , https://www.greatfil.com