15 major questions about grading during the beneficiation process

1. What is the role of grading?

Answer: In the closed-circuit grinding process, the function of the grading equipment is to separate the qualified products in time to avoid over-grinding, and at the same time, it can separate unqualified coarse sand and return to grinding. This is of great significance for ensuring better sorting effect and improving grinding efficiency.

2. What are the classification machines used in the closed-circuit grinding process?

A: Mainly: spiral classifier, hydrocyclone, rake classifier, floating classifier, sieve, etc.

3. What are the components of the spiral classifier?

A: It is mainly composed of U-shaped water tank, screw device, transmission device, lifting mechanism and support bearing.

4. What is the working principle of the spiral classifier?

A: The working principle is: after the grinding of the slurry, it is fed into the inclined U-shaped water tank from the feeding port of the classifier. With the low-speed rotation of the spiral and the continuous mixing of the pulp, most of them are light and thin. The particles are suspended on top, overflowing from the overflow weir, and become an overflow product. The coarse and heavy particles will settle on the bottom of the altar and become a grit, which is sent by the screw to the discharge port of the classifier, and returned to the grinding and regrind.

5. What are the classifications and characteristics of spiral classifiers?

A: According to the number of spiral axes, it can be divided into single spiral and double spiral classifiers. According to the overflow weir height of the spiral classifier, it can be divided into low-lying, high-slung and sunken spiral classifiers.

The sorghum type spiral classifier has a position higher than the center of the bearing at the lower end of the spiral main shaft but lower than the outer edge of the spiral of the overflow end, and is suitable for the classification of coarse grain size (overflow particle size equal to or greater than 0.15 mm).

The low-lying overflow weir is lower than the center of the lower bearing, and the classification area is small and rarely used.

The sinking type of the spiral at the overflow end is completely immersed under the overflow surface of the slurry, and is suitable for the classification of fine-grained grades, generally obtaining -0.074 mm (200 mesh), and the overflow fineness of the fractional content of more than 65%.

6. What is the role of the spiral classifier lifting mechanism?

A: Its function is to lift the screw when it stops, so as to avoid overloading the machine due to backlog of sand when the machine is restarted. In the grading process, the lifting mechanism can be used to raise or lower the spiral to adjust the load of the spiral.

7. What is grading?

A: The process of dividing a mixture of different particle sizes into two or more narrow levels of similar particle size in the medium according to its sedimentation rate is called classification.

8. Describe the tasks and functions of pre-grading, checking and controlling grading?

A: The pre-graded task is to separate the qualified products in the raw ore beforehand, so that it can propose grinding efficiency.

The task of checking the grading is to separate the unqualified products in the mill discharge and return to the mill for re-grinding. At the same time, it can control the maximum particle size in qualified products, reduce over-grinding and improve grinding efficiency.

The task of controlling grading is to control the overflow of the classifier (such as inspection grading), and to separate the substandard products that are mixed into it so that it meets the granularity requirements of the next operation.

9. What kinds of process organizations are there?

Answer: The process structure of grinding classification can be roughly divided into two types: one-stage closed-circuit grinding classification process and two-stage closed-circuit grinding classification process.

10. What is the impact of the classification rate and the sand return ratio on the grinding-grading?

A: The higher the classification efficiency, the less the qualified grain size in the sand returning, and the lighter the overgrinding phenomenon. Therefore, the grinding efficiency is higher, and the increase of the sand returning ratio is beneficial to the increase of the mill output. However, the grinding machine and the grading overload are caused by the assembly, which destroys the normal operation. Actually, the sand return ratio is increased from 100% to 400. From % to 500%, the mill production capacity can be increased by 20% to 30%.

11. What is the effect of grinding concentration on grinding grading?

Answer: When the grinding concentration is too low, the solids in the mill are reduced, which reduces the effective grinding effect of the grinding medium. If the concentration is properly increased, the grinding efficiency may increase, but the coarse particles are easily discharged from the mill to make the product The coarseness of the particle size and the high concentration may reduce the productivity of the mill and reduce the grinding efficiency, and even the phenomenon of "increased belly" due to too small discharge.

12. What is the level of grading efficiency? What is the condition?

Answer: The higher the classification efficiency, the less the qualified product with particle size in the sand returning. The lighter the grinding process in the grinding process, the higher the grinding efficiency, and vice versa.

The classification efficiency is related to the nature of the ore, the type of classification equipment, and the impact of operating conditions. At present, the classification efficiency of the classifier used in production is not high, generally 40-60%. Therefore, improving the grading equipment and improving the grading efficiency is one of the important directions for strengthening the grinding operation.

13. What is the structure, performance, working principle and maintenance method of the motor?

Answer: 1. The structure of the motor: The motor consists of a stator, a rotor and a winding.

2. Performance: Convert electrical energy into mechanical energy. There are different power speeds, which can drive various sizes of loads and have different directions of rotation.

3. Working principle: After the motor is energized, a rotating magnetic field is generated in the air gap between the rotor and the stator, the rotor winding induces a current, and the current rotates around the rotating magnetic field force, and the rotor rotates.

4. Maintenance method:

a: Prevent the motor from getting wet.

b: Prevent motor overload.

c : The motor surface temperature should not exceed 75 °C.

c: The motor running temperature is normal and the bearing temperature is normal.

e: The motor vibration is normal.

14. What is the basis for choosing the type of mill?

Answer: The choice of mill type is mainly determined by the quality requirements of the grinding products, the degree of mud of the ore, the performance of the mill and the production capacity of the grinding workshop.

Due to its characteristics, the rod mill is generally used for the grinding of tungsten, tin and other brittle brittle ore. It can be used as the last stage of crushing, or it can be used as the first stage of grinding. It can be used for the sorting operation with uniform particle size and thicker requirements. mill.

For the sorting operation with a finer granularity, the ball mill is generally used.

15. What is the technological development of grinding grades at home and abroad?

Answer: Grinding and grading as preparation for ore dressing are generally considered in combination with crushing. Its development direction has the following three aspects: firstly reducing energy consumption; second reducing steel consumption; thirdly, improving grinding grading efficiency as much as possible Overgrinding. The measures taken to achieve these three aspects: 1. Multiple crushing and grinding only reduce the ore size of the grinding, and improve on the crushing equipment; 2. Use high-efficiency grinding equipment , such as high-pressure roller mill, tower type Grinding machine, etc.; 3, using high-efficiency wear-resistant grinding medium; 4, improved lining material, such as the use of rubber lining; 5, the use of grinding aid; 6, using new grading equipment and grinding machine.

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