When the spindle speed is close to the natural frequency of the spindle’s natural vibration, a resonance phenomenon will occur and a huge amplitude will be generated. The spindle speed at this time is called the critical speed of the spindle. The spindle bar is a continuous polyurethane elastomer material with infinite natural frequencies. The introduction of the braiding machine manufacturer is related to the mass distribution and bending strain of the spindle bar; the mechanical spindle (including spindle bar, spindle disc, and supporting prefabricated (Component) is a complex vibration system, which also has many natural frequencies, so the spindle has multiple critical speeds.
The operating speed of the roving frame is much lower than the first critical speed of the spindle. If the dynamic balance between the spindle and the spindle wing rotor is poor, the vibration will increase significantly as the spindle speed increases. Therefore, in order to increase the spindle speed of the roving frame, the structure of the spindle and spindle flyer should be improved as much as possible to improve the production quality.
The working speed of the spinning spindle is in the middle of the first and second critical speeds. After exceeding the critical speed and then accelerating, the vibration of the spindle will improve. Comparing the vibration characteristics trend charts of the two spindles, it is not difficult to see that the vibration characteristics of the spindle at the plastic support point are better.
The spinning spindle produces longitudinal vibration and transverse vibration when it rotates rapidly. Longitudinal vibration refers to the up-and-down shaking of the spindle and bobbin. The horizontal vibration is also known as the spindle shaking. In the early days, it was detected by feeling the numbness level at the top of the spindle. Nowadays, optical vibrometers are widely used to detect the amplitude of the top of the spindle immediately.
Horizontal vibration is actually a composite of three vibration conditions: ① natural vibration; ② forced vibration; ③ resonant circuit vibration.
The natural vibration of rapid knitting machinery is caused by the action of external forces in a moment, such as the destructiveness of the spindle belt joint, etc. Its vibration range value depends on the starting specification, and the vibration frequency is the natural frequency. This kind of vibration will gradually decrease and dissipate; Forced vibration is the vibration caused when the spindle is continuously subjected to periodic external forces, such as the load or bending of rotating parts such as the spindle rod, disc, bobbin, and the rapid dynamic deformation of the yarn tube. At this time, the vibration frequency is equal to the spindle’s The working speed and vibration range values depend on the mass, load value, and working speed specifications.
Resonant circuit vibration is a vibration excited by the system itself, such as friction caused by abnormal contact between the spindle bottom and the spindle bar, or caused by the rolling friction of raw materials such as the spindle bar, spindle plate, etc. Once this type of vibration is excited, it is very likely that it will continue to exist and is not easy to dissipate. Its vibration frequency is approximately equivalent to the natural frequency of the spindle, and the vibration range value depends on the structural condition of the vibration system.