Thread Content
The flat grid belt conveyor is a specialized equipment for transporting food materials; it features high-speed operation, smooth performance, low noise, and the ability to transport materials both upward and downward. The conveyor belt of the grid belt conveyor can be selected according to the different process requirements of the materials, with various control modes such as normal continuous operation, rhythmic operation, and variable-speed operation. The flat-grid belt conveyor also uses straight lines, curves, and slopes, among other line shapes, as appropriate for the specific conditions. The flat grid belt conveyor features strong conveying capacity and long conveying distance, a simple structure that makes it easy to maintain, and it allows for convenient programmatic control and automated operation. For flat belt conveyor motors, three-phase squirrel-cage asynchronous motors or three-phase wound-rotor asynchronous motors are generally used. Three-phase squirrel-cage asynchronous motors are more widely applied, while three-phase wound-rotor asynchronous motors are used less frequently. Since motors for grid belt conveyors are required to have low current at startup, high torque, and strong overload capacity, many motor manufacturers produce specialized three-phase asynchronous motors for such conveyors. For example, coal mine machinery factories produce motors designated for coal mine conveyors, the DSB-55 model, with a rated power of 55 KW and a rated speed of 1470 rpm. The torque multiplier at startup is 2.5 times, the overload capacity is about 2.3 times, the current multiplier at startup is 6.5 times, the efficiency is 91%, and the power factor is 0.87. Although dedicated motors can meet the production needs of coal mining enterprises, they still have some shortcomings. For example: (1) their efficiency is not high enough. According to the latest energy efficiency standards for small and medium-sized motors, an asynchronous motor with a power rating of 55 Kw and 4 poles should have an efficiency of 95% for Class 1 efficiency, 94.2% for Class 2, and 92.5% for Class 3. The efficiency of the 55 Kw DSB-55 motor designed for use in coal mines does not even meet the efficiency standards of motors in Class 3. (2) Low efficiency at light loads: The efficiency of asynchronous motors varies with the load. It reaches its highest level when the load is around 80%, at which point it attains its rated efficiency. If the load is low, the efficiency also decreases. The load on a flat belt conveyor changes depending on the production conditions, and these loads often fluctuate. Therefore, the motor used must be selected based on the maximum load expected. As a result, in most cases, the motor operates under light load conditions, leading to low operational efficiency and power factors, which results in wasted active and reactive power. A high-efficiency motor for grid belt conveyors refers to one whose losses are about 20% lower than those of motors currently in use, while an ultra-high-efficiency motor means one whose losses are about 30% lower than those of motors currently available. China and the EU have classified the efficiency of small and medium-sized three-phase asynchronous motors into three standard efficiency levels: Level 1 efficiency, Level 2 efficiency, and Level 3 efficiency. Mandatory regulations require that motors with an efficiency lower than Level 3 cannot be produced or sold. When these motors leave the factory, they must be fitted with efficiency level labels in a standardized format. The rated power for energy efficiency level 1 ranges from 3 kW to 315 kW, while that for energy efficiency levels 2 and 3 ranges from 0.55 kW to 315 kW. These motors are usually explosion-proof motors with 2 to 6 poles. The production, sales, and use of high-efficiency motors for grid belt conveyors have little impact on increasing the costs of the conveying system’s transmission components. According to studies, over the lifetime of a motor, operating costs account for 92%, the purchase cost constitutes 7%, and maintenance costs are only 1%. If the efficiency of the motor is improved, the savings in electricity costs will far exceed the cost of purchasing a more efficient motor. Although high-efficiency asynchronous motors have a high efficiency at their rated operating points, they operate under relatively light loads, resulting in lower efficiency; they also have certain drawbacks. Rare earth permanent magnet synchronous motors do not suffer from these problems. They can maintain high efficiency across a load range of 20% to 120%. However, they are more expensive and require an inverter for starting control. With the continuous advancement of science, it is expected that rare earth permanent magnet synchronous motors will see wider application in the coming years.