Aiming at the problems of easy component loss, low screening efficiency and high energy consumption of the existing compost trommel screen used in the composting industry, a trommel screen, a new transmission mode was designed, and a cleaning screen device was added. The mathematical model of material particle movement of the roller screen machine was established, the structural parameters of the key components were determined, and the main factors affecting the working performance of the screen machine were tested and analyzed. Based on the optimal screening effect, the optimal parameter combination of screening efficiency and power consumption was analyzed by using three factors and five levels test with the feed volume, rotation speed and inclination Angle of the drum screen machine as the test factors. The results show that when the feeding rate is 39.6t/h, the roller speed is 12.4r/min, and the roller Angle is 5.6? When, the roller screen machine screening effect is the best, screening efficiency is 96%, power consumption is 2.55kW. According to the factory test, under the condition of optimal parameter combination, the screening efficiency is 95%, the power consumption is 2.69kW, and the relative error between the model and the predicted result is 1.1% and 5.5%, meeting the quality requirements of material screening.
With the gradual improvement of people's living conditions, according to the Outline of China's Food and Nutrition Development (2014-2020), the nation's meat and eggs
Milk consumption and proportion increased year by year (1-4). At the same time, large-scale breeding industry develops rapidly and large-scale livestock and poultry sites gradually lead to livestock and poultry manure pollution become an important factor threatening factory production and people's health [5-6]. Manure composting is one of the most important methods in livestock manure treatment
Ring. Screening equipment is an important equipment to ensure the smooth composting process of livestock and poultry manure. In the composting process, large equipment such as turning machine and vertical composting bin are needed to turn or stir in the composting materials to provide a good fermentation environment. If there are a large number of stones, plastics, ropes and other debris, long-term collision with the stirring parts in the equipment will reduce the service life of the composting equipment or even directly destroy the composting equipment. At the same time, due to the need to add a large number of carbon containing fillers in the composting process to ensure that the material has the appropriate pH value, water content, carbon nitrogen ratio and particle size of raw materials , after the composting process needs to be cleared out the large unreacted fillers, only the fertilizer is reserved. Therefore, screening equipment can not only remove impurities from materials in the pre-composting stage, reduce the loss of composting equipment, but also ensure the smooth processing of subsequent materials in the post-composting stage, recycling filler to control costs.
For the compost material screening problem, the domestic development of different screening equipment, including compost trommel screen, shaking screen, roller screen, roller screen, etc. 14]
Vibrating screen one-time investment cost is small, but because of its working characteristics, hard objects on the screen surface damage degree is larger, and easy paste screen inconvenience cleaning. Disc screen has strong material turning ability and wear resistance, but its use is limited by the aperture, it is not suitable for the screening of materials after composting stage. As rotary screening equipment, roller screen machine works smoothly and is widely used in grain classification, selection and mineral sorting [15-23], but it is rarely reported in the composting industry. The traditional mechanical transmission mode of roller screen machine used by some enterprises is complicated to install and directly applied in the composting industry. Due to the high processing capacity, broken shaft and other phenomena often occur, and due to the particularity of compost materials (high humidity and strong corrosion), the spoke structure is easy to be damaged. At present, most of the equipment of compost screening is borrowed from other industries, which solves some problems of compost material screening. However, it can not adapt to the characteristics of compost materials well, which is prone to paste screening, easy corrosion damage of components and high power consumption under large processing capacity, which seriously affects the quality of screening operation.
In order to solve the problems such as complex mechanical transmission mode of traditional compost trommel screen, easy paste screen, low screening efficiency and large load applied in composting industry, this paper designs an external transmission type supporting wheel roller screen machine, the center shaft type transmission mode is converted to the transmission mode of roller chain gear, increase the bearing capacity of roller screen, avoid corrosion damage of transmission and supporting parts; At the same time, the screen cleaning device is added. During the operation of the roller screen, the screen is continuously brushed and scraped to ensure that the roller screen is not pasted to a large area, improve the screening efficiency and reduce the load of the roller. Regression analysis and response surface analysis were used to obtain the best working parameter combination, which provided technical and theoretical basis for further improving the screening performance.
The main structure of the roller screen machine is shown in Figure 1, which is suitable for material cleaning and impurity removal. The roller screen machine is mainly composed of inlet and outlet, transmission system, screen cleaning device, frame and outer cover, roller and other key components.
1.2 Working principle The power output of the motor is connected with the power input of the reducer to provide sufficient operating power for the drum screen machine, while the power required for the drum rotation is matched and transmitted through double or single row chain drive. The compost material is transported by the belt conveyor and enters the inner cavity of the roller screen under the action of the aggregate at the human material mouth. The high-speed rotating drum uses the copy plate device on the inner wall to copy the material repeatedly to the highest point of the inner cavity, and then uses gravity to fall, and the material particles pass through the screen repeatedly through this process. And because the drum is placed on the frame with a certain inclination Angle, in each material copying process, the material particles gradually move to the discharge port, through this reciprocating, qualified particles through the screen into the conveyor belt under the equipment, the next step is carried out, unqualified materials by the discharge port collection.
The sieve drum is the core working part of the drum screen. Whether the material can be effectively screened in the screening process depends on the properties of the drum, including the drum diameter, the drum length and the drum screen inclination Angle and other structural parameters, as well as the drum speed and other motion parameters. The movement form of material particles on the screen surface determines the final screening effect of the screening equipment to a certain extent [24]. The motion of particles in the drum is analyzed, and the relationship between the structural parameters and the motion parameters is obtained, which is helpful to determine the basic structural parameters and the basic motion model of the drum, and provides the theoretical basis and design direction for the future design of the drum screen.
2.1 Dynamics Analysis of particles in the screen The motion law of a single particle in the drum is shown in Figure 2. The dotted line is the motion track of particles in a movement cycle. Without considering the collision, the motion track of particles in the drum is composed of the arc along the inner wall of the drum in the front part and the parabola away from the wall of the drum in the back part. Particles into the screen surface, the friction provided by the drum and its own gravity, particles with the drum to do circular motion, in the process of motion, when the resultant force is not enough to provide the centrifugal force required for circular motion, material particles from the drum, at a certain speed, do parabolic motion, and return to the screen surface.
The movement of particles in the actual screening process is shown in Figure 3.
Therefore, the mathematical model is established. Firstly, it is assumed that there is no relative sliding between the particle and the screen surface, and since it is a single particle analysis, it is necessary
Ignore the interactions between particles. The force analysis of particle movement is shown in FIG. 4. In this case, the Angle between particle and horizontal plane is α.
2.3 The transmission device is the excessive contact between the rotating shaft of the traditional central shaft roller screen machine and the compost material, resulting in corrosion damage, and the load at the central shaft leading to broken shaft, as well as the high cost of the outer gear meshing big gear, a gear and chain outer meshing transmission mode is specially designed, as shown in Figure 6. In terms of transmission, the chain adopts the segmented type. As shown in Figure 7, the segmented chain is connected through the supporting lug, and the chain is fixedly connected to the outer wall of the roller by the supporting lug. Different from the traditional integral chain with only one joint, the key is effectively swiped, which can effectively replace the whole chain if it is partially damaged and facilitate maintenance. In terms of the overall support, the original sieve cylinder weight from the shaft and spoke all bear to the four supporting wheel and support side, the key under the high processing capacity, the spindle to bear the rotating transmission torque and bear the overall weight of the sieve cylinder may bring broken shaft, spoke damage, screen damage and other problems. There are no spare parts in the screen, which reduces the contact between the compost material and the equipment parts and reduces the corrosion loss. In terms of load, the transmission mechanism placed outside the drum increases the torque brought by the motor to the drum, and the load that the drum screen can bear increases accordingly.
Through simulation, the maximum torque of the drum in the screening process of the maximum feeding amount was obtained, and the chain position was calculated
For tangential load, chain 28A with A-level joint P=44.45mm is selected, and its tensile load is 200MPa.
The diameter of the ring where the chain is located is 1540mm, the height of the chain limit is 41.5mm, the number of chain links is calculated as z =112.38, and the even number of chain links is taken as 112 after rounding. The output speed of the reducer is 93r/min, and the maximum speed required by the late test is 14r/min, that is, the transmission ratio is 6.64, and the calculation formula of the number of gears z is
2.4 Screening device Because the moisture content of compost materials is higher than that of general screening materials, there is a great loss rate when the material is screened, resulting in the paste screen. To solve this problem, the screening device is added.
As shown in the compost trommel screen cleaning device is composed of screen mesh, screen cleaning brush roller, support frame and spring stabilizing mechanism. Placed on the inclined side of the roller, the use of its own gravity and spring mechanism imposed by the elastic force, the cleaning brush roller and the screen tightly solid, and the two ends of the cleaning brush roller through the bearing and support connected to ensure that the cleaning brush roller can be fixed together with the roller rotation. At the same time, the spring controlled configuration to absorb the cleaning screen brush roller through the support frame to bring the type of vibration, he plus the roller screen to complete its transport only type control.
