Roll-and-disc screen

Contents

Contents

Introduction

1. Informational overview

2. Development of technical product proposal

2.1. Description of the design and operation of the product

2.2. Calculations

3. Use of the product in production conditions

Conclusion

Literature

on the topic :

Roll-and-disk screen

"

Introduction

Most briquette plants typically use a high degree of decomposition of low-lying peat produced in stubble-free deposits and having a bulk density of more than 300 kg/m3 for processing. However, the remaining massifs of lowland peat have already been developed by briquette factories or are involved in agricultural production, and reserved deposits will be used in the coming years. For these reasons, many plants are already forced to develop existing peat reserves of low bulk density with a high stump of the deposit. Briquetting of such peat is not widespread due to the unsatisfactory quality of the briquettes produced, low productivity and low reliability of existing equipment, especially preparatory compartments, where, moreover, the required preparation of raw materials is not provided.

The preparation of peat for drying and briquetting in the preparatory sections of existing and designed briquette plants processing peat of low bulk density with fibrous and wood inclusions will increase the raw resources for the production of household fuel and increase the efficiency of peat briquette production. To classify the material in the peat industry, vibration screens of GIL, HDG, GVR, PMT and others are used. Drum screens of the GB design of Belniitopproekt and the Kalinin branch of VNIITP were also widely used.

The preparation of peat plays a primary role in the formation of qualitative indicators of raw materials supplied for drying, which include the required size and ratio of fractions by size classes, as well as the average particle diameter. Existing low bulk density peat screening equipment is not working well due to a number of reasons. As a result of the presence of a large number of large wood inclusions, SM431 crushers are clogged with chips and garlic, DMT crushers do not crush large stump at all, but only grind it, despite repeated return to repeated crushing. Drum and vibration screens have low screening efficiency when preparing peat of low bulk density or high humidity. Which forces the use of sieves on screens with cells 13x13, 15x15 mm or more, and this causes an unsatisfactory preparation of raw materials for briquetting.

In this course design, a shaft screen with a capacity of 30 t/h will be developed.

Informational overview

Classification - the process of separating loose materials by the size of pieces or particles. There are three types of classification: mechanical (screening), pneumatic (separation) and hydraulic. Peat processing plants use the first two types of classification, with pneumatic classification mainly combined with the drying process, for example, in dryers with a mine mill. The most common is mechanical classification in the preparation of peat for various technological processes: drying - at briquette plants, mixing with other components - at factories for the production of pressed soil "Violka" and nutrient briquettes, etc. Devices designed for mechanical classification are called screens.

In mechanical classification (screening), it is necessary to distinguish a particular type of this process - separation, by which we will mean the separation of pieces from the material with dimensions that are sharply different from the dimensions of the main mass of the material. For example, separation of pieces of shrinking peat or large wood inclusions, for which mechanical separators are used.

The classification process is evaluated using the following values: qualitatively - screening efficiency, quantitatively - screen productivity and energetically - energy consumption per material classification.

Screening efficiency is the ratio of the mass of material passed through the screening surface of the screen to the amount that could pass, expressed in percent.

Efficiency E (%) is determined by the formula

,

where and is the content of the lower class, respectively, in the starting and oversize material,%.

The capacity and energy costs of material classification depend on the type and design of the screens.

Peat processing plants use classifiers that, depending on the type of work surface, can be divided into flat, drum and roll-toothed screens.

It is advisable to classify screens with a flat working body according to individual characteristics characteristic of them.

By the position of the working surface, the screens can be divided into fixed and movable. According to the type of drive mechanism, screens are divided into mechanical (eccentric or V-belt) and electromagnetic drives. Peat processing plants use screens with a movable working surface and V-belt transmission to the drive shaft. When using the V-belt transmission from the electric motor to the driving shaft of the screen, the shaft pulley can have a fixed axis in space - gyratory screens (Fig.1) or the pulley axis describes a circle with a certain radius of swinging screens (Fig.2). Gyratory screens are distinguished by the fact that the shaft of 4 screens is closed

Vibration screens. At plants for the mechanical processing of peat from screens with a flat working surface, vibration screens of GVR and GVP, borrowed from the coal industry, became most widespread.

GVR1 screen box 1 is fixed by means of two sets of flat springs 2 on frame 3, which can be supported on the foundation or suspended on flexible rods

Shaft-vibrator of screen 5 rotating from electric motor 6 by means of V-belt transmission is installed on two roller bearings, bodies of which are fixed on side walls of box. Screen box represents welded metal structure consisting of rear and two side walls rigidly connected by two rows of pipes. A wire screen is laid on the upper row of pipes, which is gripped to the cross-piece in the front part of the screen and pulled by bolts to the rear wall of the box.

The screen oscillates due to centrifugal force caused by unbalance of the vibrator shaft, since in the middle part the shaft has a recess and the drive pulley on the shaft is fitted with a slight eccentricity. Due to the different stiffness of the supports along the springs and in the direction perpendicular to them, the conduit moves along an elliptical path. Motor of drive is installed so that axis of V-belt transmission is close to direction of springs.

In this case, the tension of the drive belts caused by the fluctuations of the box will be minimal.

Screen of RTG 1 operates in zabonance mode. During start-up and stop, when the screen oscillation frequency is reached equal to resonant, the amplitude increases sharply and accordingly the load on the screen springs increases.

To reduce overloads on springs, automatic unbalance is used (Fig. 4). The stiffness of the springs 2 of the unbalance 1 is selected so that during normal operation the screen is compressed under the action of the centrifugal force of the springs. The distance g from the center of gravity of the unbalance to the axis of rotation is maximum. When the screen stops, the centrifugal force decreases, the springs push out the weight, and the eccentricity of the unbalanced weight decreases. This causes the disturbance force to decrease and the screen springs to load accordingly. Unlike GVR1 screen in GVP1 screen, the box is suspended from the building floor on spring suspensions (Fig. 5). With this attachment, it makes circular oscillations. The structure of the box and the shaft-vibrator is similar to the design of the screen GVR1. Vibration screens have a number of drawbacks: they are not sealed, are a source of increased noise and vibrations, require the attention of maintenance personnel. Several screens are installed in the plants to ensure the necessary performance with high efficiency of the classification process, and therefore the number of equipment increases. These drawbacks of vibration screens were the reason that at some torphobricket factories (TBZ) of the RSFSR, and in the BSSR everywhere, they are replaced by drum or roll-and-roll. However, vibration screens have an important advantage: they can provide a sufficiently high efficiency of the classification process.

This advantage of vibration screens is especially evident in the processing of light (p < < 200 kg/m3) peat of high humidity (w50%). It is thanks to this advantage of screens with a flat working surface that they almost completely supplanted drum screens in the chemical industry and in coal-rich and budget factories.

Drum screens. At peat processing plants, drum screens were most widespread at TBZ. For the first time in torphobricket production, drum screens were used at the Olain TBZ (Latvia), where they showed satisfactory work results. After the successful use of drum screens at TBZ Usyazh of the BSSR and the development of working drawings of the screen GB1A BelNIItopproek-tom, the replacement of vibration screens with drum screens began. Over the past years, in the BSSR, drum screens have completely supplanted vibration. This is explained by a number of advantages of drum screens: simplicity of design and maintenance, tightness, quiet operation. In addition, when using drum screens, the number of equipment of the preparatory compartment of the TBZ is reduced. Drum screens are installed directly under hammer crushers. Therefore, there is no need for a screw distribution conveyor above the screens and in the blade feeders, the number of screens is reduced, the length of the large and fine-fraction conveyors is reduced, and, as a result, the power consumption for peat preparation is reduced. The reduced efficiency of drum screens compared to vibration screens does not significantly affect the performance of TBZ processing peat with a density of 250400 kg/m3. In this case, all screening is sent to the boiler room and, thus, its re-processing is not carried out. On TBZ plants that do not have their own boiler houses, as well as for peat processing plants in which screening is not used and is exported from the territory of the enterprise, drum screens have not been widely used.

In drum screen GB1A (Figure 6), mesh 1 with 6x6 mm cells of wire with a diameter of 2 mm is used as a screening surface, which is pulled over cylindrical frame 2 and fixed to it by strips 5.

Adjustment of drum axis inclination angle is provided in screen depending on density of processed peat. The angle of inclination of the drum is changed by the screw gear 6. Lower end of drum shaft is fixed on crossbeam 7 connected with screw. Guides moving in sleeves of crossbar of strut 1 of screen frame 8 are also fixed on it. Drum shaft rests on spherical roller bearings that do not prevent displacement of inner ring of bearing relative to outer ring at change of drum inclination angle

To intensify screening, the screen of the drum is cleaned with an air jet. Air is blown by fan into pipe 3 located along upper generatrix of drum cylinder and through holes in it blows reel net. The pneumatic system operates in a closed cycle: fan - diffuser - screen drum - dusting system of the preparatory compartment of TBZ - fan.

Screen drum is closed by casing 4. Tightness of rotating deposit in end walls of casing is provided by means of multilayer packing of seal. The seal body is connected to the casing wall through a canvas fabric, which does not constrain the vertical movement of the shaft when adjusting the inclination of the drum axis.

Rotation of drum is performed from electric motor through worm reduction gear. Note here that drum shaft is fitted in said shaft instead of worm wheel shaft. Screen drive (electric motor and worm reduction gear) is attached to frame connected to screen frame by tie-rod 9.

Roll-disc screens. The simplicity of the design and operation of drum screens contributed to their introduction in many briquette factories in the country. However, the long-term use of these screens revealed a number of serious shortcomings in their design. When processing raw materials with a low degree of decomposition and high humidity, clogging of mesh cells is observed, the wires of the drums are wrapped, the screening efficiency is sharply reduced and, as a result, the raw materials are transported to the screening. Therefore, at briquette plants processing peat of low bulk density, the problem of classifying raw materials arose. Trying to solve it, at a number of factories, they began to use valovodisk screens (GVD).

The roll-disc screen consists of a frame made of two metal plates 7, the lower parts of which are connected by channels 2 (Fig. 7). Upper parts of plates are detachable and attached to lower parts by means of studs. Housing of bearings 3 of screen shafts is inserted into holes of plates. Disks 4 are installed on shafts. Disks of one shaft are arranged with entry between disks of adjacent shafts. Thus, there are slightly larger gaps between the disks of one shaft than their thickness. Torque is transmitted sequentially from shaft to shaft. To do this, on each shaft (except for the extreme ones) two sprockets are fitted, on the extreme ones - one. Roll-and-roll screens are simple in design, have high productivity, are stable in operation. These virtues of valovodisk screens contributed to their widespread distribution for preliminary screening in the chemical industry, as well as in brown-coal briquette factories. For the same purpose, such a roar is used on the Sangla TBZ (Estonia).

In the roller screen screens used in brown-coal briquette factories and the chemical industry, the disks are either round in shape and are installed in this case with a slight eccentricity (the eccentricities of the disks of neighboring shafts are shifted by 90 °), or triangular - from the side of the triangle in the form of an arc.

To ensure fault-free operation and self-cleaning of discs, when classifying peat in the screen GVD0.6, an increase in the rotation speed of each subsequent shaft in the direction of material movement is provided compared to the previous one by 1.061.1 times. The screen discs each have 12 teeth, the rear face of the tooth is directed radially, and the front face is at an angle of 5560 ° to the rear. Due to this shape of the teeth, large peat particles are transferred from one disk to another and are not pushed between the disks into the sub-lattice product.

Development of technical product proposal

2.1. Description of product design and operation

Roll-and-disc screen consists of frame 1 (welded structure), on which roll-and-disk screen is mounted. Screen drive is also installed on frame 1.

The first roller of the roller guide screen is rotated by means of a reduction motor 2 by means of a sleeve-flange coupling 3, pulleys and a gear-belt transmission 4. For subsequent rolls in order to increase their rotation speed by 1.07 times, gear-belt gears 6 are used.

The working tool of the roller screen is rollers with disks 7 installed on them, which are installed so that there is a gap (cell) between the hub of the disks and the disks of adjacent rollers. To reduce the load on the bearing supports of the roll, supports 5 are welded into the screen body, which support the rolls along the entire length of the screening surface.

A protective housing 8 is installed above the screen, which serves to reduce dust during loading of the unit.

The operation of the unit is carried out as follows: the material through the loading window 9 is evenly distributed along the screening surface of the screen, on which its classification takes place, then the sub-grating product enters the transporting conveyor, and the over-grating product through the unloading window 10 enters the transporting conveyor into the crushing compartment for grinding.

2.2. Calculations

2.2.1. General calculation of the article

Screen performance (t/h) per sieve product

2.2.2. Calculation of gear-belt transmission.

The shaft is driven by the ZMP - 40 reduction motor, power N = 3 kW, and rotation frequency n = 112 rpm (n1 = 1.87 s-1).

Hooking module

2.2.3. Kinematic calculation

The rotation speed of the first screen roll = 1.10 s taking into account the subsequent increase in the frequency of adjacent rolls within 1.07 times, we calculate the rotation speed and the main parameters of the remaining 6 rolls:

Use of the product in production conditions

3.1. Description of the article operation in production conditions.

Raw materials (milling peat) are delivered from production fields to the plant using narrow gauge cars 3. Which are unloaded with the help of a car puller to the receiving hopper 2. Further, from the receiving bin, peat enters the plate feeder 11, which supplies raw materials to the belt conveyor 7. The belt conveyor (above the conveyor there is a suspended magnetic separator 12 to exclude metal inclusions accidentally falling into the peat) feeds peat to the preparatory compartment on the roll screen 4, where the raw materials are classified. The sublet product enters the belt conveyor 8, which transports peat to a further technological operation (drying) using the elevator 16, and the oversize product enters the hammer crusher 6, in which it is crushed, and then supplied by the elevator for re-screening.

3.2.Material balance of the preparatory department.

The material balance of the preparatory department is drawn up according to individual processing operations, taking into account the losses for each operation in the following sequence.

Productivity of peat preparation department.

Set in the course design and equal to, t/h.

Performance of the preparation department taking into account losses during transportation.

3.3. Selection of process equipment.

Based on the assignment of the exchange rate project, the output of the water screen is 30 tons/h, the bulk density of the material is 340 kg/m3, the number of presses in line 2, knowing this we will pick up the technological equipment of the preparatory department.

Calculation of the receiving bunker.

We calculate the receiving hopper for two hours of continuous operation of the compartment [8]:

Calculation of plate feeder.

Peat is discharged from receiving bin onto belt conveyor by plate feeder. Since the performance of the preparatory Q = 30.24 t/h, we accept one feeder and calculate its width from the performance [4]:

Calculation of belt conveyor for raw material supply to the unit.

By the specified capacity of the belt conveyor we will find the width of the belt [4]:

We take b = 125 mm, and recalculate the speed of the tape:

Conclusion

In this course project, a roll screen (with a capacity of 30 t/h) was developed - designed to classify milling peat for its subsequent briquetting.

Elements of novelty and practical significance are:

installation of rubber discs on the screen shafts, which facilitates the design of the screen and improves the quality of the processed material;

The field of possible practical application is torphobricket plants and construction materials plants.

The calculation and analytical material presented in the course design objectively reflects the state of the studied process, all theoretical and methodological provisions and concepts borrowed from literary and other sources are accompanied by references to their authors.

Literature

1. Gorfin O. S. Peat processing machines and equipment: Study for universities. - M.: Nedra, 1990. - 318 p.: il.

2. Peat Handbook. ed. Lazoreva A.V. and Korchunov S. S. - M.: Nedra, 1982.

3. Calculation and design of machine parts. Ed. Prof. Stolbina G. B. and Zhukov K. P.: Higher School, 1978.

4. Kuzmin A.V., Maron F.L. "Handbook on the calculations of lifting vehicles." - Mn.: Higher School, 1983.

5. Kurmaz L.V., Skoibeda A.T. "Machine details. Design. " - Mn.: UP "Technoprint," 2001

6. Kuzmin A.V. Calculations of machine parts.: Right. Accessory. -3rd ed., Conversion. and additional - Mn.: Vysh. shk., 1986400s.: il.

7. Ivanchenko F.K. Bogdarev V.S. Calculations of lifting and transporting machines.: Training for universities. - Kiev, 1975.

8. Naumovich V.M, "Peat drying in drying units of briquette plants." - M.: Nedra, 1973