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Furnace of choose
Reference of furnace lining
Reference of furnace lining

Choice and lining sintering technology of MF lining materials.
1. Lining refractory clay
Refractory clay is cement that is refractory and insulation. A kind of materials of 1.5-2.5cm thickness that protects induction coils and improves the machinery intensity of coils is coated in the inner wall of induction coil, meanwhile, which can make lining swell when hot and shrink when cold in the direction of uprightness. At present, domestic refractory clay can endure the high temperature of 1800℃ for half an hour and can prevent earth leakage effectively.
2. Choice of lining materials( crucible)
① Lining materials
There are 3 kinds of MF crucible furnace: alkaline, acidic and neutral crucible. Alkaline crucible is mainly made from magnesia; acidic crucible only from SiO2, neutral crucible only from Al2O3 and MgO•Al2O3 compound oxide and graphite and so on.
Induction furnace crucible has the following features:
(1) Higher refractory function. Requirement for melting steel crucible is 1700oC and melting iron is 1500oC-1600oC;
(2) Steady chemical quality. Crucible product endure melted slag and steel liquid corrosion;
(3) A fine shockproof and high temperature intensity. 
(4) With insulation function;
(5) Weaker heat conduction;
(6)smaller cost and no pollution
The common-used refractory materials that crucible is made from has 3 kinds: magnesium sand, magnalium spinel and quartz sand and now the introduction is as follows:
magnalium spinel is a kind of manual synthetically refractory, theory component isω(Al2O3)=71.5%,ω(MgO2)=28.5%;melting point is 2135℃,refractory degree is 1900℃,with fine shockproof and can be used as various kinds of induction furnace crucible materials. The way is that mix Al2O3and MgO2and then sinter, compose or electric arc, electric slag compose. Quartz sand is acidic refractory used for making acidic crucible. Raw quartz sand is carefully refined, higher purity quartz sand can be obtained. Harmful impurity of quartz sand is alkaline oxide. The refractory temperature of quartz sand is 1650℃,and working temperature of crucible is 1550℃。This kind of crucible has good quality of shockproof and heatproof with long life expectation working under the temperature of 1500℃.
The materials that crucible is made from except for refractory, small amount of additive, such as boric acid(H3BO3)whose main function is to lower sintering temperature of sand and promote the formation of magnalium spinel and alter the change rate of crucible volume that can be adjusted as putting different quantity of boric acid which has a different influence on the change rate of quartz volume. Boric acid as additive, whose grain is smaller than 0.5mm,is ok to reach the industrial purity. The amount of adding boric acid is related to the working temperature and using condition of crucible, and crucible working temperature will lower when adding boric acid. When melting in the vacuum induction furnace, boric acid added in the crucible will make metal liquid increase its amount of boric acid to which more attention should be paid when melting super alloy. 
② Molding of induction furnace crucible
Before induction furnace crucible moulds, the first thing is to match charge, mainly grain proportion. Reasonable grain proportion good quality crucible of small air hole rate, fine sintering, high intensity, enduring urgent hot and cold. Sand materials of building crucible can be divided into 3 grain degree: namely thick grain(2~6mm)、middling grain (0.5~2.0mm)and thin grain(≤0.5mm). Sand materials of thick grain play a main part in the crucible, which offers certain intensity to crucible. Grain gap is filled with middling grain sand materials by which stack density is increased; intensity and sintering quality of crucible is improved. The function of sand materials of thin grain guarantees the sintering capability, quality of crucible and continuity of sintering network, which makes crucible compact and close. Crucible with less than 500Kg capacity generally uses 0~4mm grain sandy materials and crucible with large capacity uses 0~6mm sandy materials.
Ramming formation in the furnace: According to this way, the first step is to confect sandy material as stipulated grain and mixed with additive equally and If hydro-sintering way is taken, 1%~2% moisture should be added, it can be ok after mixed 1-2 hours. The second step is to put asbestos cloth in the inner side of inductor. More layers of asbestos should be put as for acidic crucible. The third step is to ramming completely. Sandy material is put in batches and tamp it repeatedly with steel awl of 12~14mm diameter, which repeats for 4~5 times and tamping time lasts at least 10 min。The thickness of furnace bottom should be rammed up to the stipulated height. The fourth step is to put crucible core, namely the model that controls crucible shape and capacity. Type core is generally made from steel plate when sintered at lower temperature. Crucible core should be put pointing to the centre of furnace.
3. Choice of crucible materials 
① Alkaline crucible material is used for melting special steel, alloy steel such as
stainless steel and so on.
②Acidic crucible material is used for carbon alloy steel and low alloy steel and unsuitable for melting steel containing alive element such as Al、Ti、B and so on.
Special attention should be paid to crucible maintenance, timely repair for the inner walls of crucible and prolong the life of crucible to the most extent.

 
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