Acoustics – Sound-modifying means – Mechanical vibration attenuator
Patent
1989-04-04
1990-10-16
Fuller, Benjamin R.
Acoustics
Sound-modifying means
Mechanical vibration attenuator
181208, 181296, 60322, F16F 1500
Patent
active
049628267
DESCRIPTION:
BRIEF SUMMARY
The invention relates to vibration damping, particularly, but not exclusively, to the damping of high temperature pipes and bodies.
Vibrations in pipes, machines and other bodies cause movement and noise which it is often desirable to reduce or eliminate by damping of the vibrations.
Many damping techniques are known, but the need for a lightweight, effective means for damping bodies becomes more difficult to achieve as the temperature of the body increases.
Free layer damping, in which a layer of visco-elastic material is applied to the substrate (pipe or body surface), or stave/constrained layer damping, in which the visco-elastic layer has a stiff outer layer, cannot be used if the temperature of the body rises above about 150.degree. C. as both these techniques require the application of the viscoelastic polymer to the substrate. Polymer properties vary with temperature and/or frequency. Generally, at low temperatures or high frequencies a polymer will appear brittle or glassy wwith little visco-elastic loss. At high temperatures or low frequencies it will appear rubbery and elastic. Between these two extremes the polymer is visco-elastic and able to absorb energy. A polymer for noise reduction purposes is, therefore, selected or designed to have its visco-elastic properties in the particular frequency and temperature range of interest. However, it is difficult to obtain polymers capable of withstanding temperatures of above about 140.degree.-150.degree. C. for long periods of time. Vibration is imparted to the walls of a pipe or other body as radial or lateral motion and this has been damped in some applications where high temperatures are not experienced by using auxiliary mass type dampers. There are many situations, however, where temperatures of 500.degree.-600.degree. C. may be experienced and a means to damp bodies at these high temperatures is required.
The object of the invention is to provide a means for damping and a method of applying such means for the treatment forr pipes and other bodies which can be used even where the temperature of the body may rise above 150.degree. C.
It is a further object of the invention to provide such a means which is lightweight and can easily be applied to a pipe or body in situ.
In one aspect the invention provides a means for damping pipes and other bodies comprising one or more stand-off cantilever, sandwich-type dampers adapted to be attached to the body and wherein the dampers are thermally isolated from the body.
A cantilever damper is a damper in which the mode of vibration of the damper is a cantilever type ie a bar allowed to bend either side of a central support. A cantilever, sandwich-type damper is an auxiliary mass type damper which comprises a layer of visco-elastic material sandwiched between two rigid plates, with one plate being adapted for attachment to a body. Other cantilever dampers have no visco-elastic component and work by phase interaction with the structure. Resonant peaks of vibration are set up and the dampers are tuned to work at one frequency only. The construction of a damper having a visco-elastic polymer in a sandwhich of rigid plates allows a broader band performance and energy is actually absorbed by the damper.
Preferably the dampers are attached to a support which is then attached to the surface of the pipe or body to be damped, the support being thermally insulated from the body by a layer of insulating material. This configuration facilitates the incorporation of a thermal barrier for application to high temperature bodies.
The thickness of the insulating layer determines the temperature gradient between the body and the damper. The higher the temperature of the body, the thicker the insulation layer must be to avoid the damper being raised to a temperature which will damage the viso-elastic material. Any suitable insulating material can be used. Advantageously the insulation is rigid or nearly rigid to ensure efficient coupling between the vibrating body and the dampers.
Preferably each cantilever damper support is atta
REFERENCES:
patent: 1063385 (1913-06-01), Reed
patent: 3314503 (1967-04-01), Neubert
patent: 3640833 (1972-02-01), Oberst et al.
patent: 4096307 (1978-06-01), Lagowski
Fuller Benjamin R.
The Secretary of State for Defence in Her Britannic Majesty's Go
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