Due to the different properties of the materials transported by the belt conveyor, the adhesion of the materials on the belt surface and the cleaning difficulty are also different, so the cleaning methods are also different. If the cleaner is not designed and installed in combination with the characteristics of materials, it will not only fail to achieve the expected cleaning effect, but also easily damage the belt surface and shorten the service life of the belt. Since 2019, our company has cooperated with many cleaner manufacturers to carry out trial effect evaluation for the belt material problem of belt conveyor. At the same time, we have also carried out many discussions and adjustment tests in combination with the actual production, and finally solved the problem of incomplete cleaning of belt surface of belt conveyor.
1. Causes of belt surface materials of belt conveyor
Most of the materials conveyed by belt conveyor in cement enterprises are clinker, cement, coal-fired slag powder, coal grinding stone, limestone, coal, clay, desulfurization gypsum and other raw and combustion materials. The reasons why the materials on the belt surface cannot be completely separated: first, the moisture content of coal-fired slag powder, clinker, cement and other materials is low (≤ 0.5%), and the dust particles adsorbed on the belt surface are mainly its fine powder. The dust particles are very small and the surface energy is very large, resulting in electrostatic adsorption; Second, the moisture content of coal, clay, desulfurization gypsum and other materials is between 10% ~ 17%. Due to the surface tension of water, cohesion is generated between particles, so it is easier to adhere to the belt surface; Third, the moisture content of granular materials such as limestone and coal gangue is between 1% ~ 4%. In addition to the absorption of fine powder dust, a small amount of powdery materials adheres to the belt surface due to moisture; Fourth, because the belt surface of the belt conveyor is uneven, powdery materials and particles are mixed between the gaps of the belt surface.
2 Classification and working principle of sweeper
The function of the sweeper is mainly to effectively clean the adhesive or materials on the belt surface of the belt conveyor, prevent the corrosion of the adhesive on the package of the supporting mixture, reduce the environmental pollution caused by the random falling off of the adhesive on the belt surface, and prevent accidents. Common cleaners mainly include the following types. Scraper sweeper: ① polyurethane belt cleaner, automatic tension alloy belt scraper, scraper sweeper, etc.; ② Roller brush sweeper: electric roller brush sweeper, brush sweeper and rotary sweeper; ③ Air swept sweeper: compressed air purging, fan purging, etc.
The working principle of the scraper sweeper is that the action surface of the scraper is close to the load surface of the conveyor belt to clean and unload the materials bonded on the conveyor belt. It has a good cleaning effect on the materials adhered to the belt surface due to high moisture content.
The working principle of the roller brush cleaner is that the brush tip is in slight contact with the belt surface, the rotation direction of the nylon brush is opposite to the running direction of the return conveyor belt, and the fine particle powdery materials adhered to the belt surface are brushed down to achieve the purpose of cleaning. It has good cleaning effect on powdery materials with low moisture content.
The working principle of the air swept sweeper is mainly to purge the belt surface by relying on the gas with a certain wind pressure to achieve the purpose of belt surface cleaning. It has a good cleaning effect on powdery materials or fine powders with serious belt surface damage and low moisture content.
3. Current situation of cleaning effect of belt conveyor during operation
The materials conveyed by our belt conveyor mainly include clinker, limestone, coal grinding stone and coal-fired slag powder. The desulfurized gypsum first falls into the belt and contacts with the belt surface, followed by limestone, coal grinding stone, coal-fired slag mixture and clinker. In other words, materials with different moisture and particle size are in contact with the belt.
In view of the fact that the desulfurized gypsum with high moisture content first contacts the belt and is also the most difficult problem to clean the attachments on the belt surface, the measures we have taken are as follows: in the first stage, polyurethane cleaner and scraper cleaner are used for cleaning, and the cleaning effect can reach 40% ~ 50%, but the expected goal is not achieved. In order to improve the cleaning effect, the contact surface between the cleaner and the belt is increased, the pressure of the cleaner on the belt surface is increased, and the scraping force is improved. However, the wear of the cleaner is significantly accelerated after adjustment, especially the groove is formed on the contact surface, and the cleaning effect begins to decline after only 4 days. Material crusts begin to appear in the center area of the belt surface. In the second stage, aiming at the problems existing in the first stage, the contact pressure between polyurethane cleaner, scraper cleaner and belt surface is reduced, and a roller brush cleaner is added for cleaning, and the cleaning effect can reach 60% ~ 70%. However, there is a common problem in the first and second stages, that is, the angle of the receiving plate is too slow, which is lower than the rest angle of material accumulation, and the receiving plate is made of steel plate, with rough surface and large friction coefficient, resulting in the deposition of materials cleaned by the increased sweeper in area a and area B. after the roller brush sweeper operates for about 8 hours, the cleaned materials can contact the roller brush after deposition in area B, This causes the roller brush to clean the belt and pick up the deposited materials at the same time, which greatly reduces the cleaning effect.
4 Analysis on the causes of poor cleaning effect in the operation of belt conveyor
(1) The polyurethane cleaner can effectively remove the desulfurization gypsum adhered to the belt surface and the material particles mixed in the gap on the belt surface. The greater the contact pressure, the better the cleaning effect, but the greater the pressure, the greater the damage to the belt joint. At the same time, the sliding friction resistance increases after the pressure increases, the wear of the cleaner accelerates, and the cleaning effect deteriorates with the wear degree of the cleaner. Secondly, the cleaning effect of polyurethane cleaner on fine powder dust particles is not obvious.
(2) The working principle and function of scraper cleaner and polyurethane cleaner are basically the same. They have good cleaning effect on high moisture adhesive materials, but they also have no obvious cleaning effect on fine powder dust particles. At the same time, due to the close distance between the scraper sweeper and the receiving plate, the cleaning materials are accumulated. If not cleaned in time, the sweeper will be buried by the materials and the belt surface will contact the materials twice, and the cleaning effect will be greatly reduced.
(3) Due to its relative movement with the belt, the roller brush sweeper rotates to clean the belt surface, and has a good cleaning effect on the dust materials with low moisture adhered to the belt surface. Although the cleaning effect for fine powder dust particles and low moisture dust materials is better than that of the scraper sweeper, its cleaning effect still can not achieve the expected purpose. At the same time, the distance between the roller brush cleaner and the material receiving plate is relatively close. If the materials are not cleaned in time during operation, the deposited materials will directly wrap the roller brush, resulting in the failure of the roller brush and the complete loss of cleaning function.
5 Belt conveyor cleaner combination selection and material receiving plate transformation
In order to fully understand the cleaning effect of the cleaner, taking the batching belt of our company as an example, the following tests and data collection were carried out. The bandwidth of the batching belt conveyor is 800 mm, the effective contact width of materials is about 700 mm, and the belt speed of the belt conveyor is 1.25 m / s. When there is no cleaner to clean, collect the attached materials and dust on the belt surface (s = 0.8m) with a bandwidth of 800 mm and a length of 1000 mm, about 27g.
In view of the current situation of our company’s belt conveyor, if the above cleaners are used alone, the effect is difficult to reach more than 60%. Combined with the existing problems at this stage, after demonstration, it is decided that the combined type selection and application should be carried out in combination with different characteristics of materials, different types, functions, advantages and disadvantages of cleaners. At the same time, the butt plate is reformed to make the inclination angle of the butt plate greater than the rest angle of material accumulation, and then the surface of the butt plate is treated to reduce the friction coefficient.
In view of the above analysis, we have carried out the re selection, design, combination and installation of the sweeper, and transformed the material plate, as shown in Figure 3. The cleaning effect has reached nearly 95%, and cleaner production has been further realized. The self-designed high-pressure air curtain cleaner is added to carry out back blowing and cleaning of fine powder, which avoids the increase of air compressor load and power consumption when some companies use compressed air to clean the belt surface, and has a certain impact on the gas consumption stability of the grinding system.
(1) In view of the use effect and characteristics of polyurethane sweeper and scraper sweeper, we have reduced the contact pressure between polyurethane sweeper and scraper sweeper and belt surface on the original basis: first, to prolong the service life and maintenance time of sweeper; The second is to reduce the damage to the belt joint and belt surface. In order to make up for the poor cleaning effect caused by reducing the pressure, an automatic tensioning alloy cleaner is added between the two. The contact surface of the cleaner is made of alloy, which effectively prolongs the service time, and maintains a certain pressure range and elastic activity space between the contact surface and the belt surface through the pressure spring, so as to effectively avoid and reduce the damage to the belt joint. These three scraper cleaners can effectively remove 65% ~ 70% of the materials adhered to the belt surface.
(2) The original roller brush cleaner is replaced with an electric roller brush cleaner, which improves the rotation speed of the electric roller brush and the cleaning force of the brush on the belt surface. The high-speed moving brush can clean, peel and disperse the fine powder adhered to the belt surface under the pressure of the scraper, so as to reduce the contact energy between the fine powder material and the belt surface, and further improve the cleaning effect to 80% ~ 85%.
(3) After cleaning by the electric roller brush cleaner, the residual fine powder, a small amount of water containing adhesive materials and fine powder mixed in the gap of the belt surface are not completely removed, so as to further remove these materials. Our company has independently designed a high-pressure air curtain cleaner to comprehensively clean the belt surface. The belt surface cleanliness has increased significantly, and the cleaning effect has reached more than 95%.
(4) In order to solve the problem that the material deposition after cleaning affects the use effect of the sweeper, the angle of the material receiving plate is adjusted from 28 ° to 40 ° ~ 45 ° in combination with the site spatial position, so that the angle is close to the natural repose angle of the material. At the same time, a Teflon plate is laid on the surface of the material receiving plate to reduce the friction coefficient of the plate surface, so that the cleaned material can directly slide into the blanking opening.
6 Application effect
For the problem of cleaning the return belt surface of the belt conveyor, the cleaner should be selected in combination with the characteristics of the materials transported by the belt. In production, the most difficult thing to completely remove the attachments on the belt surface of the belt conveyor is the micro powder attachments containing water. After the three-way scraper cleaner cleans a large amount of attached materials and dust on the belt surface, the electric brush and Sabei of the Bureau electric are used together to remove the remaining micro powder attachments on the belt surface: it can greatly improve the cleaning effect, Realize cleaner production. At the same time, reducing the impact of cleared materials and dust deposition on cleaning is also very important, which should be considered and implemented in the process of installation and transformation. Through the above transformation, the cleaning time of employees is reduced from once per shift to once a week.
In order to realize cleaner production and solve the problem of belt surface cleaning on the return of belt conveyor, this paper introduces a series of measures such as the selection and matching use of sweepers and the transformation of supporting blanking port. It basically solves the environmental pollution caused by incomplete cleaning of the return belt surface, and greatly reduces the labor intensity of employees. In the later stage, with the development of society, it is an inevitable trend to realize “zero” residue in the return belt surface cleaning of belt conveyor. The diversification of sweepers and the application of new cleaning technology will be new research directions.
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