The raw materials of the grate of cermetall composite sintering machine include 25 ~ 50wt % heat-resistant steel fiber, 75 ~ 50wt % Al2O3-SiO2 mullite ceramic powder. Among them, the chemical composition of heat-resistant steel fiber is as follows: C≤ 0.25%, Si≤ 2.0%, Mn≤ 2.0%, Ni8 ~ 37%, Cr14 ~ 26%, the rest is Fe, and the chemical composition of Al2O3-SiO2 mullite ceramic powder is as follows: Al2O365 ~ 75%, SiO218 ~ 26%, CaO1.0 ~ 4.0%, TiO21.0 ~ 3.0%, Fe2O30.5 ~ 2.0%, P2O51 ~ 0.5%, alkali metal oxides 1.0 ~ 1.5%.
The grate has the advantages of abrasion resistance, corrosion resistance, oxidation resistance and high temperature resistance of ceramic material and good toughness of metal material. In addition, it has the characteristics of low thermal conductivity and light weight compared with metal grate. It can also make the sintering trolley as a whole more energy saving, environmental protection, lightweight and longevity, reduce the consumption of sintering energy, improve the site operating environment, and generate more economic benefits.
The four classifications of the grate are as follows:
I. High chromium cast iron grate
Due to the large amount of chromium in high temperature, Cr203 film structure is formed on the surface of high chromium alloy cast iron strips, which delays the process of alloy from external oxidation to internal oxidation. Therefore, high chromium alloy cast iron strips have good heat resistance and oxidation resistance. Due to the high stress, cracks are easy to occur on the surface of the oxide film, and the high chromium content in the matrix and the decomposition of (Fe, Cr) 23C6 carbides provide a large amount of Cr, so the high chromium alloy cast iron itself can have a good maintenance effect on the cracks of the oxide film.
Two, ordinary cast iron basket bar
Before 1980, due to the small capacity of the sintering equipment, the equipment is relatively old, the use of pen strips mainly gray cast iron, this kind of pen strips short service life, large consumption. When gray cast iron is oxidized, a layer of iron oxide film is formed on the surface, which is Fe203, Fe304 and FeO from outside to inside. There are a large number of holes in the FeO layer, and metal and oxygen ions are easily diffused through FeO. In addition, the outer layer of oxide film Fe203 is loose and cracked, which is easy to flake off. Therefore, the surface oxide film of non-alloy cast iron has no protective effect, and the service performance is very poor. Later, si was added to gray cast iron, which changed the oxide film structure of iron, and formed dense compounds rich in alloying elements in the original FeO layer, which can effectively prevent oxidation. The oxidation resistance of silicon-containing cast iron increases with the increase of Si content, but with the increase of silicon content, the strength of cast iron decreases. Heat resistant cast iron rods in middle silicon based on gray cast iron are developed in our country, w (Si) is in 4.5%-5.5%. Because the graphite in this cast iron is basically joined together, it acts as a channel for oxygen to enter the metal, which speeds up the oxidation rate. Ordinary cast iron labyrinth strips are rarely used and are largely obsolete.
Three, multiple alloying high chromium alloy basket bar
Although the high chromium alloy cast iron strip has good oxidation resistance, it has some shortcomings such as low strength, poor toughness and easy fracture. And because of poor nickel metal, the cost of heat-resisting steel bar containing nickel used abroad is too high. The content of Cr on ZG9511 steel grate used by Shougang Machinery factory in 1995 is on the basis of foreign RTCr25Ni steel, the carbon content is reduced, the nickel content is removed, and an appropriate amount of Ti, B, A1, RE and other elements are added. The content of Cr203 in the oxidizing layer is much higher than that of RTCr25Ni, and RE oxide is also included. Compact structure, no cracks and holes, good combination with the collective, dense organization. The basic organization of RTCr25Ni is &gamma+α +P, and the matrix structure of ZG9511 is &alpha. +p, no α & rarr; & gamma; The matrix is more stable during the phase transition.
Four, heat-resistant ductile iron grate
Because the graphite inside nodular iron is isolated distribution, there is no channel for oxygen to enter the metal, so the oxidation rate and growth rate is lower than gray cast iron, the use effect is better than gray cast iron. There is still a big gap between the high chromium alloy cast iron rods developed in recent years, but because of the simple production process, no need for heat treatment, low production cost and easy promotion, it is still used in small and medium-sized sinter trucks.
