Re-selection of the basic principles (4)
This results in particles of different densities that can become equal drop particles with a suitable difference in particle size. Visible resistance is an unfavorable factor that affects the effective stratification of the population by density. If the resistance action term in the sedimentation process can be reduced and the buoyancy action term is increased accordingly, the influence of the particle size can be reduced, and the effect of layering by density can also be improved. But this can't be done under free settling conditions. υ hs =u vo (1-λ) (26) As can be seen from the comparison of Equation 6, the velocity of the particles relative to the gap medium is significantly lower than the relative velocity υ 0 of the free settling. So what power compensates for this lack of fluid dynamics and maintains the particle balance movement? This is due to the presence of surrounding granules which increases the density of the entire suspension compared to a single medium. The static buoyancy compensates for the dynamic pressure of the fluid. Decompose equation (6) to: υ hs =υ 0 (1-λ) n-1 (1-λ) (27) In the visible expression, υ 0 (1-λ) n-1 is equivalent to u vo in (26). (1-λ) n-1 is considered to be a coefficient that reduces the gap velocity u vo to υ 0 due to an increase in hydrostatic factors, and (1-λ) is a modified interference settling velocity υ hs . A factor that is lower than the gap speed υ vo . Since the value of N is often greater than 2, it can be approximated that the static factor affecting the reduction of the interference settling velocity is even stronger than the dynamic factor. The denser the granules, the more the static factors increase, and the smaller the relative velocity of the fluid required for particle suspension. As a result, the trend of stratification by density is also enhanced. Where R—the hydraulic radius is expressed as the ratio of the cross-sectional area A to the wet perimeter L, ie R=A/L. When the thickness of the water layer is small relative to the groove width, the hydraulic radius is close to the water depth H; Therefore, the average flow velocity of the laminar flow is 2/3 of its maximum flow rate. It has been found that the nature of the shear stress varies with the way the particles are in contact during shearing. When the velocity gradient is high, the upper and lower particles collide directly, and the inertial force of the particles plays a leading role in the formation of the shear stress. This is the inertial shear stress. Bagnold puts the calculation as: [next] Steel U stud machine roll forms steel stud and track members for use in wall, floor and truss framing. The standard machine produces stud & track thickness is 0.3-0.8mm. The sizes is from 28-100mm.U stud machine including the decoiler, the main Roll Forming Machine, the hydraulic cutting system and receiving table. there are normal speed 25-20 meter/min and high speed 60 meters per minute by servo tracking cutting system. C Stud Rollformer,Feeding Through Channel Rollformer,Light Gauge Tee Grid Making Machine,False Ceiling Panel Rollformer WUXI ZHONGTUO ROLL FORMING MACHINERY CO LTD , https://www.rollformertec.com
Interference sedimentation occurs when the particles settle in the suspended particle population. By definition, the Ï… hs in equation (6) is the settling velocity of the particles relative to the wall, and the velocity u vo relative to the internal interstitial medium is greater than Ï… hs . The relationship between the two is:
In extreme cases, when the relative velocity between the fluid and the bed particles is zero, there is only a static interaction between the local suspension of light minerals and the local suspension of heavy minerals. If there is still a possibility of relative transfer between the particles at this time, the stratification is based on the difference in the density of the suspension or the potential energy drop. Such delamination is no longer affected by particle size. But this can only be an ideal, because the bed is not loose, stratification can not be carried out, and in most cases, fluid power is required to participate. Therefore, the respective limit the scope of the mineral crystal size always have. [next]
Layering by heavy medium can be regarded as a special case of the differential layer of the suspension density. When light: the volume of the mineral is large relative to the heavy mineral particles (see Figure 3), the volume of the dispersion medium surrounding the light mineral is relatively small, so the density of the local light mineral suspension will be close to the density of the light mineral itself. , ie Ï su1 ≈δ 1 . Therefore, layering according to the heavy medium relationship can be considered as a natural change of the difference layer of the density of the suspension after the difference in particle size difference between the light and heavy minerals is greatly increased.
This theory is closer to reality because small heavy mineral particles can be loosely suspended by a small valence velocity, and this fluid dynamics has little effect on large granular light minerals, that is, the latter mainly relies on the static force of the suspension. Dominating its movement,
This is the static stratification mechanism exhibited by light minerals.
At this time, although there may be a large difference in particle size between light and heavy minerals, strict requirements are imposed on the density difference between minerals. For example, when the bed is slightly tight and active, λ 2 ≈ 0.5, the density of heavy minerals separated from quartz (δ 1 = 2650 kg / m 3 ) in water can be calculated from formula (14). At 4300 kg / m3 .
In re-selected production, stratification occurs mostly between interference settling and heavy medium action. When the density difference between the sorted minerals is not large or there are more connected organisms, it should be appropriately classified according to the size of the medium flow rate during sorting. When the density difference is large and the boundary is obvious, it can be selected without classification. However, in order to avoid the loss of fine grain heavy minerals, it is better to select the effects after pre-desilting.
It can be seen from the above analysis that the stratified kinetic system theory and the static system theory are actually in the same vein. From free settlement to interference settlement to static stratification, it is a process of weakening dynamic factors and enhancing static factors. Various stratification theory is a rational understanding of different concentration conditions in this chain. The situation is used flexibly.
(III) Theory of slope flow sorting The application of slope water flow for mineral processing is also a long-standing one. In the early years, thick and medium-sized ores were treated in thick tanks in thick tanks, which were called coarse-grain chutes. Water was stronger turbulent flow regime, manual operation, it is still used in sorting gold sand. However, a large number of bevel flow beneficiations are now treated with thin layer water flow to treat fine and fine ore, called flow film beneficiation. The fine-grained flow film has a weak turbulent flow state characteristic, such as a shaker, a cone concentrator, a spiral concentrator, and the like. The flow film of the fine-grained grade is mostly laminar flow state, such as the slime belt chute, and the Batelles-Mozley turn-over bed belongs to this category. The centrifugal concentrator treats the fine-grained ore by centrifugal force, and the weak turbulent flow appears due to the increase of the flow velocity. Judging the flow state of the slope flow is based on the Reynolds number Re: [next] 
u mea — The average flow rate of the beveled water flow.
The Reynolds number indicating the boundary between laminar flow and turbulence is related to the transition condition. The lower limit Reynolds number from turbulent flow to laminar flow is about 300, and the upper limit Reynolds number from laminar flow to turbulent flow is about 1000, but it is very unstable, sometimes reaching 2000.
The sloping flow and water flow of the coarse, medium and fine ore can still maintain independent flow characteristics. At this time, Ï, μ and u mea in the above formula should be calculated by water flow; the fine-grained pulp is treated with uniform flow. Characteristics should be calculated using the slurry value.
The slope flow can be divided into a constant velocity flow or a non-equal velocity flow depending on whether the flow velocity changes along the path, and whether the flow velocity at a certain point along the process changes with time, and is divided into a steady flow and an unstable flow. At present, there are more applications for re-election, such as constant velocity flow dressing, and a few applications for non-equal flow, such as fan-shaped chutes. Unsteady flow is accompanied by acceleration forces and is only used in individual equipment such as the vibrating belt chute.
1. Flow characteristics and loose force of laminar flow The flow velocity of laminar flow along the depth The fluid particles in the laminar flow move along the layer, and the intergranular particles do not exchange. The distribution of water flow (or pulp) velocity along the depth can be derived from the equilibrium relationship between the viscous friction between the layers and the gravitational component. As shown in Fig. 6, the viscous friction between two layers with a basin area of ​​A is calculated according to Newton's internal friction law: [next]
The loose force of the B laminar slurry film—interlayer repulsion [next]
In the laminar flow slurry film, there is no diffusion effect of vortex disturbance, then how is the mineral particle group loose? In 1954, Bagnold discovered in the study that when the solid particles in the suspension are continuously subjected to the shearing motion, a repulsive force (or dispersion pressure) will be generated perpendicular to the shearing direction. The population has a tendency to swell to both sides. This interlayer repulsion increases as the shear velocity gradient increases, and when it is large enough to overcome the weight of the particles in the medium, the population is in a suspended state. As shown in Figure 7.