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Energy Absorption
Experimentation has shown that the use of
injection molding to encapsulate motors and transformers provides significant
advantages in attenuation of noise and vibration and an ability to shift
the frequencies of peak amplitude. The demonstrated ability to influence
system noise and vibration opens up a new capability to modify the thermoplastic
encapsulating materials in order to account for the harmonics of a specific
motor. It is important to carefully match both the design of the system
geometry and the critical material characteristics in order to maximize
dampening and avoid harmonic reactions. Testing has shown that ceramic
filled resins have higher loss factors than other filler systems, such
as glass, and that LCP tends to provide a higher loss factor than other
base resins.
Thermoplastic resins using various base resins
and filler levels have been evaluated by Encap to provide dampening of specific
harmonic ranges. The chart below shows cumulative sound power of a specific
high speed spindle motor when the stator is encapsulated with different
thermoplastic resins. In this particular case, the softer resins are seen
to wash all high frequency energy. However, with these same resins in this
structure, it can be seen that points of resonance occurred at 2k and 7.5k
Hz, respectively. Other samples are more effective at suppressing lower
frequency energy.
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