Banana screen, also known as equal-thickness screen, is named for its shape similar to that of a banana. Currently, it is mainly applied in various technological links such as classification, desliming, medium removal and dewatering in mineral processing plants. Due to its advantages such as large processing capacity, high screening and medium removal efficiency, and stable and reliable performance, it is increasingly favored by a wide range of users. In recent years, with the promotion of heavy medium beneficiation technology, the construction of large-scale beneficiation plants and the increasing simplification of beneficiation technology, the large-scale of banana screen has gradually become the development direction. One of the key issues in developing large banana screens and improving screening efficiency and processing capacity is to enhance the structural strength of large banana screens. For this reason, the majority of scientific researchers have made unremitting efforts, which can be summarized as mainly divided into theoretical research, simulation analysis and field experiments, etc. Among these works, a very important aspect is to study the vibration characteristics of the main modes of banana screen at each order within the frequency range through the experimental modal analysis method, and to investigate the actual vibration response of banana screen under the action of various internal and external or internal vibration sources in this frequency band.
Take a certain large banana screen as an example. In addition, according to its structural characteristics, a reasonable vibration signal acquisition method is adopted. The dynamic performance of the screen machine is studied through the results of experimental analysis, providing guidance for the structural design of this large banana screen in the future, and also providing reference for the modal analysis, structural design and optimization of other similar equipment. The large banana screen in the project adopts a frame structure made of steel. It is a continuous elastic body. The elasticity and mass parameters have the characteristics of continuous distribution, and its vibration meets the conditions of linearity, steadiness and stability. After discretization processing, it is simplified into a multi-free system with a finite number of discrete centralized parameters. It is analyzed by using the vibration model simplified to a finite degree of freedom. The system dynamics equation is established by using the lagrange equation, and the following formula is obtained: M,[p]+c,[9]+k,=f(1) where: P, p, p are respectively the matrices of acceleration, velocity and displacement response quantities at each point of the structure; m, c, k, and f are respectively the structural mass matrix, the structural damping matrix, the structural stiffness matrix, and the structural load vector. When a unit force is applied at point j, the response formula at point i is: H=x:/f(2), where h is the frequency response function at point i; x: Represents the displacement variable at point i; e is the force variable at point i. Equation (2) is equivalent to the mechanical admittance of the system and is also known as the transfer function in the frequency domain. Due to the reciprocity of linear systems, there should be: H.=h(3) when this multi-free system is subjected to any excitation f, the system starts to move from the static equilibrium position. The response of the forced vibration of the multi-free vibration system is obtained from equation (1) : [h]= ee(4) k,-0'm,+jwc, where: {p is the eigenvector; {, "Is the transpose of {p,}. (1) any row in the frequency response function matrix (such as the i-th row) is: [hah2... Hx]=[h]=∑ee' \ n (4) k-0'm,+jwc, where: O is the eigenvector; {9,} "Is the transpose of {p,}. (1) the frequency response function matrix of ren yixing (such as the first line) i to: [hah2... Hx] = [p] pp2... (5), k - w 'm + jwc,
The modal analysis of this experiment adopts the 4261 large banana screen with a width of 4.2m. This is one of the banana screens with a larger width in the current domestic market. It is mainly used for operations such as classification, dewatering, desliming and desliming of materials. It is mainly composed of components such as the screen box, screen surface, vibrator, transmission device and support device.
During the modal analysis of this experiment, a large-scale comprehensive system for vibration testing and modal analysis was adopted to conduct vibration testing and modal analysis on banana screen. The test method of its vibration signal acquisition and analysis system is shown in figure 2. The vibration of the force hammer hammering is collected by using an acceleration sensor. The collected vibration analog signal is converted into a digital signal by a multi-channel charge amplifier, and the unwanted frequency band signals or noise signals are filtered out to make the collected signal purer. Then, the data acquisition instrument collects digital signals, which are synchronously sampled by the computer for digital-to-analog conversion and recorded.
At present, there are mainly two ways to collect data using the comprehensive system of large-scale vibration testing and modal analysis (single-point excitation with multi-point vibration pickup and multi-point excitation with single-point vibration pickup). When a force hammer strikes the banana screen, the excitation signal is obvious at any point of the banana screen when collecting the signal. In order to facilitate the conduct of the experiment and data collection, a multi-point excitation and single-point vibration pickup method is adopted here. When collecting data, a total of 88 positions were arranged respectively on the two side panels and each crossbeam of the large banana screen as excitation points, and a powerful transmission rake gangue machine linkage spray system was installed at one end.
After the comprehensive system for large-scale vibration testing and modal analysis completed the data collection, on the system platform, the 264 collected data groups were successively conducted for "Transmission calculation", "Spectral array analysis" And "Modal parameter identification", and the dynamic characteristics of the first four orders of the banana screen were identified.