BE electric butterfly valve
The main performance test items of electric butterfly valve are stiffness and damping. In terms of stiffness, it can be divided into static stiffness, dynamic stiffness and impact stiffness according to different load speeds.
Here is a brief introduction to the commonly used test methods for static stiffness, dynamic stiffness and damping.
（1） Static stiffness test
It is generally carried out on the universal material testing machine. The sample shall be prepressed for three times, and then its value shall be measured. Load slowly and evenly. The loading speed of shock absorber with high rigidity can be appropriately accelerated; The shock absorber with small stiffness should be loaded slowly so that the deformation speed of the shock absorber is roughly the same. The load and deformation curve obtained by the shock absorber during loading and unloading are not coincident, forming a hysteresis loop, as shown in Figure 2-1-8. This makes it difficult to calculate the stiffness. We can use the average curve of loading and unloading to calculate the static stiffness of the shock absorber. The calculation formula is as follows: Ks=2 (P2-P1) δ 2,- δ 1,+ δ 2- δ 1 In the formula, P1 and P2 should roughly maintain the following relationship with the rated load P of the shock absorber; P1=(0.5~0.75)P P2=(1.25~1.5)P δ 1 and δ 1, is the deformation of shock absorber during loading and unloading under load P1; δ 2 and δ 2. It is the deformation of shock absorber during loading and unloading under load P2.
Generally speaking, the static stiffness of the shock absorber is only used to determine the static balance position of the machinery and equipment installed with the shock absorber, or to calculate whether the space left around the machinery and equipment is enough when the ship and vehicle tilt and sway. In fact, unloading is of little significance. Therefore, only the loading stiffness curve of the shock absorber can be made and used to calculate the static stiffness of the shock absorber. This not only simplifies the test, but also gives more accurate data in some cases. At this time, the Ks formula can be simplified as: Ks=P2-P1 δ 2- δ one
（2） Test of dynamic stiffness and damping coefficient
1. The vibration damper and the object with mass M are installed on the vibration table as a single degree of freedom vibration system by resonance method. Start the vibration table, adjust the frequency of the vibration table for continuous scanning, find out the resonance point of the system, and measure the amplitude of the object at resonance x0, the amplitude of the table of the vibration table x0s, and the resonance frequency wn. According to the vibration theory, the dynamic stiffness can be obtained as Kd=wn2. In the formula M, wn is the angular frequency (rad/s), and the relationship with the vibration frequency f is wn=2 π f. Attention to damping ratio:
① The above formula can only be true in resonance state;
② Adjust the excitation force of the vibration table to make the amplitude of the vibration table approximately within the range of 0.2~0.5mm, so that the resonance amplitude of the mass M object and the total deformation of the shock absorber under the static load do not exceed 15 ± 5% of the original height;
③ The measurement should be rapid and accurate in the resonance area to avoid the shock absorber's temperature rise, stiffness reduction or even damage caused by the shock generated heat inside the shock absorber.
2. Half power point width method
Install the shock absorber on or below the single degree of freedom elastic system composed of the shock absorber with mass M1, stiffness Kd and damping C, as shown in Figure 2-1-10. M2 is the mass participating in vibration with M1 in the shock absorber. The total mass of the system participating in vibration is M=M1+M2. According to the vibration reduction principle, as long as the system resonance frequency wn, the resonance amplitude x0 with mass M and the two frequencies w1 and w2 to which the resonance amplitude drops can be measured, the dynamic stiffness and damping ratio can be calculated. The calculation formula is as follows: dynamic stiffness Kd=wn2. M damping ratio w1-w1 is called the half power point bandwidth. The time-domain signal attenuation method makes the mass installed on the shock absorber resonate (such as knocking the mass or exciting the mass). After the disturbance stops, it will produce a free vibration with attenuation. Use a recorder and a vibration meter to record the attenuation wave, as shown in Figure 2-1-13. Optical oscilloscopes are often used to record such signals, as well as signal waves of known frequencies, as standard time markers (such as 50Hz city telecommunication signals). By comparing the vibration signal with the standard time mark, the natural frequency wn of the system can be obtained, and then the dynamic stiffness can be calculated. According to the logarithmic attenuation relationship of amplitude, the damping ratio can be obtained: where xk and xk+1 are two adjacent amplitudes on the attenuation wave.
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