Key Technology of Cold Briquetting Production
In order to make the large and medium-sized reduction electric furnaces of ferroalloy run better, it is required that the burden has proper fragmentation and ensures good air permeability. At present, the supply of high-quality lump burden which can be directly fed into the furnace is becoming increasingly tight. In order to adapt to this situation, some manufacturers at home and abroad have adopted various lump technologies to effectively utilize fine ore and concentrate and obtained better smelting indexes. Among them, the cold-pressed pelletizing method has become a new development direction of ferroalloy lumping technology in recent years because of its simple process, fuel-saving, and wide range of fine ore aggregates.
Principle of Cold Briquetting
The main equipment of cold briquetting method is the briquette machine, and its working principle is to press powdery materials into briquettes of the corresponding size by using a pair of forming rollers rotating in opposite directions.
The linear velocity of the Press Roller
In order to improve the productivity of the briquette machine, the faster the rotation speed of the two rollers, the better. However, as the raw materials are squeezed by the press roller, the internal air between the loose raw materials will gradually be discharged. When the rotating speed of the press roller is too fast, cracks will be left on the surface of the briquettes because the gas between the raw materials is too late to be discharged, resulting in the strength of the briquettes being reduced or even unable to form briquettes.
Because the internal air volume of various raw materials is different and the characteristics of materials are different when they are loose, it is required that the linear velocity on the surface of the pressing roller is different when briquetting. The pressing of different raw materials requires many tests to find the appropriate linear velocity.
Roller Line Pressure
In order to improve the strength of pellets, there is a misunderstanding in production, that the greater the pressure between the two pressure rollers, the higher the strength of pellets. However, in fact, the pressure between the molecules of the material has a certain limit. When the pressure exceeds this limit, the molecules of the material will slip, causing the material to be crushed. At this time, a large number of hemispheres will appear, thus greatly reducing the pelletizing rate and reducing the strength of the briquettes.
Binder Selection
When mixing and grinding, a certain amount of binder is generally added to the raw materials, mainly to increase the cohesion, adsorption, and dispersibility between the raw materials. Binders are mainly divided into inorganic binders and organic binders. Organic binders with good performance shall have the following conditions:
(1) The molecular structure has multiple polar groups and can undergo strong chemical adsorption with the concentrated surface.
(2) It has hydrophilic genes that enhance the hydrophilicity of the mineral surface.
(3) It has enough relative molecular mass and viscosity, and its chain frame is not easy to break.
(4) The molecular chain is longer and the branched-chain is more.
(5) Aromatic structure is better than fatty structure.
Moisture content of Briquette Machine
Except for a few raw materials such as limestone and dolomite, which are pressed by dry powder, most materials are pressed by wet materials. Moisture change affects the particle size and quality of green balls. Usually, if the moisture content of raw materials is too high, the initial ball formation will be faster, but it is easy to cause the phenomenon that green balls are bonded and deformed with each other and are not easy to demould. As a result, the particle size distribution of green balls is uneven, the strength is poor, and it is difficult to dry. However, when the moisture content of the raw material is too low, the gap between the two hemispheres is easy to increase, resulting in poor bonding strength of powder, too many hemispheres, low pelletizing rate, and even no pelletizing.
The proper moisture content of raw materials is the key to pelletizing. The physical properties of the material with the best moisture content of the ball, such as particle size, hydrophilicity, density and particle void ratio, mixture composition, and the productivity of the ball press are related to the pelletizing conditions.
