Slamming nylon fine screen (3)
Substituting X=ad i /2 Y i =d i /2 into equation (3) to solve d i , that is, to obtain the theoretical formula for separating the particle size of the fine sieve portion at the initial stage of use.
From the condition d i /a ≤ 1, solve 45 ° ≤ a ≤ 90 °.
Therefore, the applicable range of the formula (4) is 45° ≤ a ≤ 90°; V i ≥ 0, a > 0.
In the same way, considering the late use of the fine sieve, its edge of the sieve strip is seriously worn, so X i = dd i / 2, y i = d i is substituted into the formula (3), and the partial separation granularity after the fine sieve is obtained. The theoretical formula is
The applicable range of formula (5) is 26.565 · ≤ a ≤ 90 °; u i ≥ 0; a > 0. It can be seen from equations (4) and (5):
(1) When the screen inclination angle a is increased, the separation particle size d i is decreased, and when a = π/2, d i =0;
(2) Other conditions are certain, when the ore movement speed υ i increases, the separation granularity decreases, and when υ i → ,, d i → 0;
(3) Other conditions are certain. When the mesh width a is increased, the separation particle size d i is increased.
Equations (4) and (5) are derived from two specific points. Considering that the wear of the screen strip is continuous throughout the use of the fine screen, the separation particle size d i should also be continuously changed correspondingly, so it is necessary to establish a general formula to solve this problem.
When V i =0, it is derived from d i /a ≤ 1: arctgl / K ≤ a "π / 2. When K = 1, when the formula (4) K = 2, that is, the formula (5). Therefore, taking a different K value, a partial sieve particle size formula using a different period of time can be obtained. Since K is continuous between 1 and 2, there is a continuous value of d i corresponding to any degree of wear during use of the fine screen. [next]
The theoretical value of d i /a i calculated according to equations (4) and (5) at different inclination angles, speeds, and screen widths.
The calculated data illustrates the above three-point analysis. At the same time, it is also qualitatively stated that the reason for the lower screening efficiency of fine screening is that under the conditions of Ï… i and a-, the value of d i /a i decreases due to the serious wear of the sieve strip, so that the same sieve The d i is reduced. Figure 11 is a graph drawn from partial data in the table.
The data at a=55° is taken in the curve. The data calculated by equation (4) for the curves 1 and 2; the data calculated by equation (5) for the curves of 3 and 4 are the broken lines with the mesh width a 2 = 0.2 mm; A curve with a width of a 1 = 0.1 mm.
Equation (6) establishes a quantitative functional relationship between the separation particle size and the movement speed of the fine-grained layer, the screen inclination and the mesh width, ie d=f(a, V i , a). This effectively guides us. The production of fine sieves makes sense:
(1) It is possible to determine any one variable and determine another variable by measuring two variables; it is also possible to conditionally determine two variables and determine another variable by measuring one variable (because there is a relationship between V i and X) The function relationship is treated as an independent variable. In addition, two (or one) variables can be arbitrarily determined to derive the relationship that the other two (or three) variables must maintain. For example, if a and a are determined, the velocity of the thin layer V i close to the sieve surface can be determined by measuring the value of d i of each sieve surface, thereby understanding the velocity distribution of the thin layer of the fine sieve layer, and vice versa. Of course. [next]
(2) When the variable changes, the result can be predicted qualitatively or quantitatively. For example, when a changes, the magnitude of the change in d i can be quantitatively known.
The theoretical formula of the separation particle size of the whole fine sieve can be used to replace the V i in the formula (6) by measuring the velocity of the thin layer of the fine layer near the appropriate part of the fine sieve to the ore end, thereby obtaining the theoretical formula of the total separation particle size. . The specific deduction is as follows:
Set the length of the fine sieve to L, the width to B, the inclination angle to a, the thickness of the thin layer of fine particles to a (equal to the width of the sieve hole); the thickness of the upper and middle part of the ore supply end is R, the initial velocity V 0 , and assume (1) The grain size of the ore in the ore slurry process is evenly distributed along the thickness direction, and the volume of the upper layer of the slurry is dv=BRdx. When moving from the ore end to the discharge end, the diameter of the uppermost layer is d. Separation of the size of the ore particles just falls on the screen surface. (2) The middle and upper layer micro-element volume slurry is only subjected to gravity, and the thin layer of fine particles does not count the viscous resistance therein. Take the coordinate system as shown in Figure 12.
Then the equation of motion along the x-axis of dv (the volume is gradually decreasing during motion) is X=V 0 t+1/2gsinat 2 (7)
When x=L
According to the assumption 1), it can be considered that when the dV motion is T/2, the number of ore particles having a diameter d in dv has fallen to 50% on the sieve surface. At this time, the position where dv is located is x=x v , and the separation granularity of the corresponding sieve hole is d.
X=v 0 T/2+1/8gsina · T 2 (9)
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