2. Generally, basic magnesia or neutral alumina dry vibration materials should be selected for furnace lining. Japanese magnesium powder is the best magnesium oxide, and imported tabular corundum is the best neutral material. The unit price of high aluminum neutral material is at least 7000 yuan, and lower quality is also guaranteed. If domestic magnesia is selected, large crystal or 97.5 fused magnesium can be selected. Low-grade magnesia is easy to crack and has a short service life, which is unfavorable to the quality of molten steel.
3. It is best to pour directly to prevent secondary oxidation. If pouring ladle is needed, teapot pouring ladle or baffle crucible can be used to prevent slag from entering the mould shell and avoid using quartz sand pouring ladle or improper baking pouring ladle.
4. The baking of shell must be guaranteed by temperature and time. Taiwan-funded factories often use ceramic sheets to correct the temperature difference at various positions in high-temperature furnaces.
This paragraph is the key. Generally speaking, molten steel is deoxidized, refined and purified in this way. Manganese is added first, then silicon is added, and finally calcium silicate is used for deoxidation, but calcium silicomanganese is much better than calcium silicomanganese, especially for black spot defects. (I won't go into details after a lot of practice. Hua Gang brand silicomanganese calcium is solemnly recommended here, with high quality, slightly higher flame and more steel flowers. In the South and North precision foundries, Hua Gang brand has made great achievements. Thanks to the know-how of alloy production used by engineers from Ekeng, I would also like to remind you that although there are many such products on the market, after repeated comparative tests, the composition of some companies' products seriously deviates from the original Japanese formula, mainly because of the cost and production technology. Some of them are suitable for large furnaces in steel mills, but not for precision casting small intermediate frequency furnaces, with obvious differences in appearance. Stop and digress! ), for intermediate frequency furnaces with different capacities and products with different particle sizes, the contrast effect can be affected to some extent, which also depends on the addition time, dosage and static time. 304 and 3 16(L) generally do not recommend deoxidation with aluminum wire to prevent the formation of alumina refractory slag inclusion.
6. Some factories, especially those with Taiwan investment background, such as golf club head factory (such as Dachuan Ming 'an Guangsheng Shunlong, etc.). ) are used to adding this small monosodium glutamate as a purifying agent for molten steel. From the results of our investigation in many factories, 50-60% of factory site engineers said it was useful, some put the bottom on it at the initial stage of smelting, and some threw it directly at the later stage of smelting, because there was no obvious increase in cost to affect the temperature of molten steel, so it is suggested that it can be added if there are mature processes and traditions.
7. Regarding the use of filter screen, if stainless steel, alloy steel and general cast steel are technically decided, zirconia filter screen should be used, and zirconia corundum filter screen can be used if the temperature is not high. One is that the temperature of silicon carbide is not enough, and the other is carburizing. However, if the carbon steel casting is not feasible and the temperature exceeds 1600 degrees, zirconia foam ceramic filter should be used (Zuke brand is a first-class product, and small-size filter manufacturers can produce it. For the large size or high requirements above D70, it is recommended to choose brands such as Zucker, because the castings that generally use filters have higher requirements. If the casting is scrapped due to the quality problem of the filter element, the cost is too high, and all the saved expenses will be recovered).
It is very troublesome to place filters in investment casting. First of all, it should be placed at the bottom of the sprue cup, and it can't be caught by the slag, so it is easier to produce secondary oxidation inclusions due to straight rushing. In addition, because of the filter, the feeding channel of molten metal is not smooth, and the effective area of feeding is reduced. The process of adding filter should be improved, such as slightly increasing the temperature of 10-20 degrees and increasing the gate area by 20% to achieve the same pouring speed. There is a misunderstanding that the larger PPI, the smaller porosity and the better filtration effect. There are several mechanisms of filtration, including rectification, suspension, adsorption and blockage. The probability of slow oxidation with small pore flow rate is high, which does not necessarily depend on the field situation. The filter screen has an effect on the black spots and ash spots of partial oxidation slag inclusion, which obviously improves the overall internal and external quality of the casting.