Vanadium trioxide is a crystalline powder with a grayish black color and metallic luster, consisting of hexagonal crystals with a corundum structure. Its melting point is> 2000 ℃ When smelting vanadium iron alloy and vanadium aluminum alloy using aluminum thermite and electric aluminum thermite methodsFirst, part of itVanadium trioxideA mixture of aluminum powder is placed in the furnace, and after ignition, furnace materials composed of vanadium trioxide, aluminum particles, and iron filings are added in batches from above the smelting furnace. During the smelting process, the reaction temperature accessible arrive2 000～3 000℃ Under high temperature conditions, a strong chemical reaction occurs and a large amount of rising furnace gas is formed. If low-density powdered vanadium oxide is used as raw material, it will inevitably lead to severe gas and material flying, and the entrainment of overflowing furnace gas will cause expensive vanadium oxide smelting losses. It is extremely necessary to increase the density of vanadium oxide raw material in order to achieve high vanadium recovery rate in vanadium alloy smelting process.

be directed against V2O3Characteristics, using dry methodroll-inGranulation is alreadypowderVanadium trioxide eliminates fine powder and forms larger particlesdensityThe only economically effective method for particles.Raw material powder V2O3The bulk density is0． 6 ～1．2 g/cm3，granularityd(0． 5)= 30． 176 μm. Jingdry processroll-inGranulationafterFinished product granularity 0． 5 ～6 cm, bulk density2 ～2 ．1 g / cm3.

The characteristics of dry granulation are:

The material is forcibly compressed and formed without any additives, ensuring the purity of the product;Direct granulation of dry powder without subsequent drying process, which is more conducive to the connection and transformation of existing production processes;The particle strength is high, and the increase in bulk density is more significant than other granulation methods;Suitable for a wide range of raw materials, particle strength can be freely adjusted according to different materials;Can control environmental pollution, reduce powder waste and packaging costs, and improve product transportation capacity.

The working principle of the roller press machine is shown in the figure,

The powder is continuously fed into the roller press from the hopper, and the hydraulic system applies pressure to the moving roller. The powder begins to come into contact with the rollerA1A2:On the horizontal plane, at this point the powder begins to be driven by the frictional force of the grinding roller surface. The single particle crushed material moves rapidly downwards, and the powder is accelerated in the vertical direction. When the material reaches the planeB1B2At this point, the gap between the rollers becomes smaller and the pressure increases. The crushing stage of the material layer begins, where the vertical velocity of the material is equal to the vertical component of the surface velocity of the rollers. When the material is compressed by the rollers untilC1C2At the plane, the gap is the smallest and the density of the compact reaches its maximum value. The compressed compact passes through at the circumferential speed of the rolling millC1C2Flat, due to the compression rebound characteristics of the billet, the billet will rebound in the horizontal direction, and finally the material will pass throughD1D2The plane is discharged outside the machine as a dense plate at a speed close to the circumferential velocity of the roller surface.

The material in the roller press generally undergoes three interactive processes: sliding, layer crushing, and agglomeration. Based on this process, the entire chamber is divided into three zones:The first area is the slip zone;The second area is the pressure zone;The third area is the rebound zone. Further divide the pressure zone into two stages:The first stage is the crushing stage of the material layer;The second stage is the team formation stage.

1Slip zone analysis

As shown in the pictureA1A2B2B1Area, pre pressing above the feeder, roller squeezing force, and surface friction between the two rollers

Under the joint action, the material continuously enters the crushing chamber and fills above the two extrusion rollers, forming a layer of materialIt is a loose aggregate composed of many irregular mineral particles with high porosity. When starting to load, the load is usually.0~30MPaDue to external forces, particles of various sizes constantly change their state and position with increasing pressure. The displacement methods include the mutual approach, separation, sliding, or transfer between particles. After the particles are displaced, they fill the gaps and rearrange with each other, increasing the contact area of the material layer and improving its density. At this stage, the pressure generated by the material on the roller is relatively small. Due to the difference in linear velocity between the material and the extrusion roller surface, as well as changes in the extrusion space, the material will experience relative sliding along the roller surface, resulting in a certain degree of wear on the roller surface. The main form of wear is the plow wear caused by the relative sliding between the material and the roller surface.

IIStress zone analysis

1. Deformation and crushing stage of material layer

As shown in the pictureB1B2E2E1After the material layer in the area is compacted, the material particles become smaller and the density increases. The material particles also interact with each other, and particle breakage events continue to occur. Line contact between the material and the roller surface begins to occur. The pressure at this stage is roughly30MPaarrive50MPaMoreover, the rate of load increase accelerates, while the displacement increases relatively slowly. The magnitude of load increase is greater than that of displacement deformation. This is because the pressure has exceeded the particle strength of the compacted mineral particles, and the mineral particles begin to fracture. Crushed particles produce fine particles or powders that fill the gaps near them, increasing the contact area between particles and between the material layer and the pressure roller, accelerating pressure transmission, and forming microcracks inside mineral particles at this stage.

At this stage, the difference in linear velocity between the material and the roller surface gradually decreases. It is believed that the vertical velocity of the material is equal to the vertical component of the roller linear velocity, and the mass of the material is equal in any horizontal planeof Assuming there is no relative sliding between the material and the roller surface in this area, the material only undergoes horizontal deformation, and the wear of the grinding roller groove plow is reduced. Under the action of high extrusion pressure, the wear form of the material on the extrusion roller surface is transformed into plastic deformation or peeling wear. Compressive and tensile stresses are generated on the roller surface and at a certain depth inside. When the stress exceeds the fatigue strength of the roller surface material, cracks are formed on the roller surface.

2. Unity stage

As shown in the pictureE1E2C2C1In the region, as the compressive stress continues to increase, the deformation of the material is very small and eventually approaches zero. Pressure begins to transfer to the interior of the material bed, causing particle crushing and microcracks. The material layer is tightly compacted under high pressure stress to form plates. The pressure at this stage is roughly50MPaarrive230MPabetween. The maximum density and maximum pressure of the material occur at the line connecting the centers of the two rollers, which is called the "agglomeration stage".

3Analysis of rebound zone

As shown in the pictureC1C2D2D1Region, i.e. minimum gap between rollersSIn the following section, there is no force acting on the roller surface, and the material begins to recover and expand. The size of the rebound zone is determined by the recovery expansion angle/The size of this area depends on the magnitude of the elastic stress stored during the compression process. In the rebound zone, the vertical velocity at any level is equal to the velocity at the end boundary of the pressure zone. Recovery angle of rebound zoneYGenerally, it is3°~9°.

After being rolled, the relative density of the powder increases significantly, and the volume of powder per unit mass decreases significantly, indicating that the powder is compressed during the rolling processAfter experiencing a series of processes such as particle convergence and rearrangement, reduction of inter particle gaps accompanied by gas escape, and particle deformation leading to an increase in contact area, the particles eventually bite and bond with each other due to deformation or even rupture under roller pressure,Form a compacted mass with a certain strength.

In order to obtain granular materials with high bulk density and high compressive strength V2O3，roll-inAdopting during the process Low speed, narrow width The process of pre degassing large feed.After moldingsector V2O3warpAfter crushing the whole particle, it enters the vibrating screen for screening and grading. The particles on the screen are the finished high-density vanadium oxide, while the powder under the screen is sent back to the silo by the conveying equipment for further granulation.The density of vanadium oxide on the sieve can reach 2 ～2 ．1 g / cm3Significant increase in bulk density;

conclusion

1、Powdered vanadium trioxide is processed by dry methodroll-inGranulationworkmanship, can obtainpile upHigh densityproduct.

2、In order to obtain granular materials with high bulk density and high compressive strength V2O3During the granulation processLow speed, narrow width The process of pre degassing large feedAnd apply6MPaofhydro-cylinderPressure, powderyV2O3The bulk density is determined by 0． 6 ～ 1．2 g /cm3Raise to 2～ 2．1 g /cm3The density has increased significantly.

3、When using powder vanadium trioxide, the yield of vanadium alloy product is89%～92% ;After granulation, high-density vanadium oxide has good resistance to air flow and good contact reaction performance with furnace materials, which can increase the yield of vanadium alloy products94%～97%Moreover, using high-density vanadium oxide for smelting vanadium iron is beneficial for improving the quality of vanadium iron crystals