1. Pre-furnace inspection Pre-furnace inspection is an indispensable part of its production process, which is directly related to the quality of ductile iron castings. Judge the spheroidization of molten iron timely and accurately, and you can quickly take measures to control the quality of ductile iron. Misjudgment before the furnace will cause a large number of castings to be scrapped and waste molding time. Therefore, timely and accurate judgment of the spheroidization before the furnace is much more important than the inspection after the furnace. There are several methods for inspecting the molten iron spheroidization before the furnace used in actual production. 1 Surface crust and flame judgment method Rare earth magnesium nodular cast iron has low magnesium content and rare earth elements. The surface of molten iron is different from pure magnesium nodular cast iron. There are not so many scales on the surface, and the flame is not so powerful. However, when supplemented with 1/3 iron liquid, the liquid surface will escape the magnesia and white flames, shaped like candlelight. Judging the spheroidization and the residual amount of magnesium according to the number and height of flames, the higher and more powerful the flames, the better the spheroidization. Especially when pouring, the fire can be seen from the molten iron flow, such as a height of 25~ffice:smarttags"/>50mm, that is, the spheroidization is good; if the flame is less than 15mm, the spheroidization is poor. From the treatment After the surface of the nodular cast iron liquid iron, an oxide film is formed, and there is a bright spot of silver-white rolling, which means that the spheroidization is good. However, if the oxide film is too thick, it means that the temperature of the molten iron is low. 2 Triangular test block method Blocks to determine the spheroidization is a commonly used method. The test blocks used in various factories have many shapes and different sizes. Most factories use triangular test blocks. According to the production characteristics of our factory, the size and thickness of the castings, the triangular test block cross-sectional area is selected. The size is 12.5mm (bottom) × 50mm ((height). Some factories use round test blocks, such as gear shaft Manufacturers Ф15mm, Ф25mm, Ф30mm. After the molten iron is finished, use a sampling spoon to extract the liquid from the 200mm below the surface of the molten iron. It is cast into a test block and cooled to dark red to be water quenched. The outer circle of the good cooling ball is much larger than that of gray cast iron. The appearance is clean and bright and very sandy. The triangular test block usually poured on the sides has a top surface or a sinking block. There are sinking test blocks on both sides. After cooling and breaking, the spheroidization test is good, and the silver-white or silver-gray porcelain-shaped fracture has a clear white tip and a loose in the middle. If the fracture is silver-white and has a radial pattern, the amount of the surface sphere agent added is high. There are many carbides. At this time, the test piece emits a "patting" crackle sound. The test piece is broken and the new mouth has a strong scent of calcium carbide. Therefore, it is best to pour the floating silicon when pouring. If the mouth is silver gray and has If the evenly distributed small black spots are broken into colored crystals, it will be defeated (see table). The two methods for identifying the spheroidizing quality of the triangular sample are as follows: 1) The triangular test block with good spheroidization is interrupted by quenching water The smell of calcium carbide will escape immediately. 2) The white mouth depth is related to the type, type and molten iron composition of the ductile iron, so the data is not given in the table, and the white mouth depth of the rare earth magnesium ductile iron is not very obvious.
