How can noise emissions during material handling be reduced?
mo explains: methods for quiet conveying
The noise levels during plastic processing are caused by many different sources. In regards to material handling there are two main sources of noise: the vacuum generator and the material feed lines. The sound pressure levels often measured in at 80 dB(A). Particularly unpleasant are the high frequencies produced by the granules being transported through the material feed lines.
The noise levels produced by the vacuum generators depends mainly on their design and performance. There are two simple methods to reduce the noise they produce – encapsulate the pumps under a noise protection hood or install them outside of the production area in a separate room. The separate installation of the pumps tends to be preferred in praxis, as maintenance work can be easily carried out.
It is much more difficult to encapsulate the pipes for material transport. To half the perceived noise, the sound levels must be reduced by 10 dB, which is easier said than done. Light materials such as foam casing are unsuitable as sound insulation. Heavy materials such as rock wool is difficult to wrap around the comparably narrow pipes (diameters of 45, 50, 65, and 76mm are standard). In addition, insulating the bends, which are particularly liable to wear, is risky, as leaks are then not easily visible.
One possible solution is double-walled pipes. The inner pipe is used as the material feed line in the “pipe within a pipe system”. The air-filled space in-between the pipes insulated in two ways: on the one hand, it reduces noise emissions, on the other hand the insulating layer prevents pre-warmed, dried material from cooling. Tests show noise reductions of 12 dB(A).
In order to identify leaks in a “pipe within a pipe system”, it can be fitted with pressure sensors or visual leak indicators. If a leak is present, the pipe will take in “false air” through the leak, which is displayed by a spinning indicator wheel.