The main reason for the poor mechanical properties and corrosion resistance of castings is the existence of gas inclusions and oxide inclusions in castings. The content of various inclusions in castings is closely related to the purity of molten steel melted by medium frequency melting furnace. For a large number of small and medium-sized foundries in China, due to high investment and operation costs, AOD (argon oxygen decarburization refining furnace), VOD (vacuum oxygen decarburization refining furnace) and other refining equipment are obviously not suitable.

At present, remelting process is the most common process used in the production of castings in medium frequency electric furnace, but the defect of remelting process is that it has no refining function, can not remove all kinds of inclusions in the remelting process, and the quality of molten steel can not be guaranteed, resulting in low yield and low grade of castings. How to reduce the inclusion content of stainless steel castings in the remelting process with high efficiency and low cost has become an urgent problem for the medium frequency furnace casting enterprises.

The argon blowing porous brick used in medium frequency furnace can reduce the content of various inclusions in the medium frequency furnace melting process with low cost and high efficiency, improve the casting grade, and make the casting production enterprises obtain good economic benefits. Argon blowing refining can degass, decarbonize and remove oxide inclusion from molten steel. What's more, blowing argon into the liquid steel containing chromium will not change the chromium content of the liquid steel while decarbonizing.

(1) Installation of permeable brick. The installation of the permeable brick in the intermediate frequency furnace is very simple. It does not need to carry out large-scale transformation of the structure of the intermediate frequency furnace. It only needs to chisel a round hole with a diameter of 40 mm ~ 60 mm on the asbestos board or prefabricated block at the bottom of the furnace to guide the argon blowing pipe of the permeable brick, and then match it with bottled industrial argon as the argon source. The construction process of medium frequency furnace with permeable brick is the same as that of common medium frequency furnace.

(2) Application of common ladle permeable brick in medium frequency furnace. Air leakage will occur after using the common ladle permeable brick in 750 kg medium frequency furnace for 10-15 times. The results showed that the leakage mainly occurred in the welding between the bottom plate of the permeable brick and the iron sheet, and a small amount occurred in the welding between the bottom plate of the permeable brick and the metal tube. Through analysis, it is considered that the common ladle gas permeable brick is made of iron sheet and carbon steel bottom plate. When the gas permeable brick is working in the medium frequency furnace, the iron sheet and carbon steel bottom plate are cut by the magnetic line of force, and then heated by induction. The temperature can reach about 800 ℃, and it is cooled to room temperature when tapping in the medium frequency furnace. After repeated high temperature and cooling stage, high temperature oxidation and stress concentration lead to cracking and air leakage at the welding seam. At the same time, the thickness of iron sheet is only 1 mm ~ 2 mm, so it is easy to crack at the welding place of carbon steel bottom plate and iron sheet. Based on the above application results and cause analysis, it is considered that the service life of common ladle perforated brick in intermediate frequency furnace is difficult to match the service life of intermediate frequency furnace lining, and it needs to be improved.

(3) Application of new type permeable brick in medium frequency furnace. According to the application results of common ladle gas permeable brick in medium frequency furnace, a new type of gas permeable brick was successfully developed. This new type of permeable brick abandons the design idea of using metal materials to make gas chamber and gas supply pipeline, and uses non-metal materials to make gas chamber and ceramic pipe as gas supply pipeline.

The new type of permeable brick is tested in 250 kg, 500 kg and 750 kg medium frequency induction furnace respectively. Its performance can fully meet the smelting needs of medium frequency induction furnace, and its service life will not become a constraint factor of the overall service life of induction furnace. At the same time, in the process of test, it is found that the erosion of the upper part of the furnace lining or the crucible is accelerated due to the scouring effect of air flow after the bottom blowing measure is applied, which leads to the decrease of the lining life.

The test report of molten steel shows that the content of [O], [n] and [H] in molten steel is significantly reduced by argon blowing process compared with that without argon blowing. At the same time, the test report also points out that the content of non spherical inclusions in molten steel is lower than the forging standard, and the content of spherical oxide inclusions reaches 0.5A standard. The results show that the quality of molten steel can be effectively improved and the casting grade can be improved by using argon blowing process with porous brick in medium frequency induction furnace.

It can be seen that the new type of permeable brick process can well achieve the medium frequency furnace to remove inclusions.

Yiphee Electric Furnace Co.,Ltd specializes in producing induction furnace.Tel(WhatsApp):+ 86-13450756789, yiphee@yiphee.cn