In various sectors of the national economy and industry, crushing and grinding of raw materials is often required. It can be both food enterprises and heavy industry factories, grinding coal with semi-anthracite and all kinds of waste. In each case, the task is to provide technical support for this operation with a high level of productivity. Such requests are met by a mid-range roller mill, combining optimal power and structural characteristics.
Unit device
Using this equipment you can perform a wide range of diverse tasks, in addition to direct grinding. This determines the complexity of the design of some models. In the basic version, the standard roller mill, the photo of which is presented above, includes the following parts:
- Bearing platform with supporting elements. The metal structure on the frames, which holds the weight of the functional blocks. In this part, there can be both a stationary support and a running gear with wheels for moving.
- Power drive. An electric motor with a gearbox and electric infrastructure for connecting to the network (as a rule, three-phase 380 V sockets are used).
- Mechanical drive part. The force from the engine to the working bodies is transmitted through a system of bearings, buffer springs, belt elements, gears, V-belt drive and pulley.
- Working bodies. Directly rolls with teeth, grinding the raw materials.
The principle of the mill
The engine activates the movement of the rolls, which, depending on the configuration of the teeth, can perform operations of crushing, coarse grinding and fine grinding. The gear drives the shaft and, in accordance with the specified operating mode, rotation begins. Before this, the user performs the loading of raw materials through a special funnel - it is integrated into the housing through a detachable connection or is constantly present in the structure like other working components.
During operation, the output product may be subjected to fractionation. Additional organs of the roll mill are responsible for this. The principle of operation of the unit, for example, allows the grinding, drying and separation processes to be carried out within one technological session. But in this case, the integration of auxiliary force transmitters and even drive mechanisms that are separately connected to power sources may be required. In machines that perform heterogeneous operations from the efforts of one electric motor, as a rule, the dimensions are increased and the mechanical basis is complicated.
Types of Roller Mills
There are modular, dish-shaped and vertical designs of roller mill crushers. The modular device is the most modern and allows you to perform the layout of the gross levers, rolls and shock absorption system in different configurations, changing the overall, molding and functional characteristics of the equipment.
Especially for the chemical industry, plate-roller mills (roller-disk) are produced. They are based on a rotating disk plate, lined with special plates. Through this platform, crushed raw materials are sent through the feed choke. Then the product passes under the rollers, there it is milled and, due to centrifugal force, is discharged to the armor ring, where the separation process begins.
As for the vertical mills, they are considered the least flexible in the capabilities of the construction and installation device, as they are designed for stationary permanent installation within a specific project without the possibility of change. But the vertical form factor itself with functional blocks directed from top to bottom (from the loading funnel to the lower links of the crushers and separator) is characterized by the highest productivity.
Features of flour mill
The principal difference between the units for grinding flour is the reduction in the size of the structure, an increase in the number of roll elements and an optimized system for classifying the product according to the quality of processing. Such machines, in particular, are produced by the German company Nagema, which represents an eight-roll flour mill. A description of laboratory modifications of the equipment with the possibility of obtaining a test granular grinding of grain can be represented through the following structural composition:
- Grinding roll elements performing multifractional grinding.
- Receiving pallets designed to collect and classify bran flour.
- Sieve through which the separation of flour of different quality. Some systems also evaluate grinding using electronic sensors.
- Using a silk net with an aluminum overlay, flour with bran is sifted after crushing wheat. By the way, silk nets can have different parameters with mesh sizes from 150 to 300 microns.
As you can see, the roll units for flour can not only perform mechanical processing operations, but also produce a basic assessment of the quality of the product and, in accordance with this, ensure its separation.
Main characteristics
Due to the variety of structural devices, this equipment can have different technical and operational parameters. And yet, focusing on the average power level of units, the characteristics can be represented as follows:
- The power potential of the electric motor is from 1300 to 5500 kW.
- The diameter of the rolls in industrial models is up to 1500 mm.
- The length of the rolls in industrial models is up to 2000 mm.
- Pressure exerted during crushing of rocks - up to 250 MPa.
- The height of the teeth of vertical roller mills is from 30 mm.
- The diameter of the plate for disk units is from 0.5 to 2 m on average.
- The speed of rotation of the plate is about 3 m / s.
- Productivity - from 10 to 25 t / h.
Control system
In modern models of mills, electronic process control with automation elements is provided. The operator can adjust the speed of the rolls, the feed rate to the feed neck, the rotation parameters of the separator rotor, the grinding characteristics, etc. In automatic mode, air flows are adjusted with the grinding pressure. Having set the initial data, one can expect to obtain the desired particle size distribution at the product output without interfering with the workflow. Since roller mills operate at high capacities with connection to three-phase networks, they are obligatorily provided with protective devices. They also operate automatically in the event of short circuits, overheating of the motor or severe voltage drops in the network.
Unit disadvantages
Almost all roll mechanisms have a common negative factor of action, which consists in close contact with raw materials. Mechanical impact on the material is accompanied by the sticking of crushed particles on the surface of the rolls. Since humidification of the working bodies is supposed in some technological modes of processing, after the completion of the procedure, the surfaces are completely covered with the final product. A relatively modest degree of grinding in roll mills is also noted, which forces designers to experiment with the same increase in the number of crushing aggregates.
In general, this equipment is considered obsolete and does not meet the new requirements for the production of crushed materials. On the other hand, the simplicity of design and the ability to maintain high performance with optimal unit sizes while maintaining the demand for roll machines.
Wear surfaces
Actually, this is one of the main operational factors of the negative spectrum, which is determined by the intensity of the mechanical effect on the loading material. It is obvious that the segments of the rolls, which periodically have to be changed, are primarily exposed to wear. The problem is that the highest coefficients of friction are present when processing solid raw materials, which requires the use of highly abrasive teeth. In such modes of operation, the shortcomings of the mid-range roller mills are manifested, the wear of which imposes considerable costs for maintenance items. On the other hand, manufacturers of rolls do not stand still, offering more and more high-quality abrasive segments for grinding, provided with high-chromium cast-iron surfacing.
Conclusion
Today, roll grinding mechanisms have few direct competitors who could offer the same set of technical and operational qualities. The main advantages of this technique come down to the simplicity of the technical organization of material processing and a simple scheme of integration into the production processes of a wide range of enterprises.
At the same time, roller mills are inferior in market positions to less productive, but more ergonomic and functional roller-ring, vibration and jet units. Factors such as maintainability and energy efficiency of equipment play an increasingly important role. The technological level of roll structures also does not allow for these indicators to come forward in their niche.