Damping compounds on heavy plates
The problem
A common source of high-level, short-duration noise in the warehousing and distribution industries is caused by hard-wheeled pallet trucks passing over decks of dock levelling plates and scissor lifts during the loading and unloading of road vehicles.
These decks are usually manufactured in a heavy gauge undamped material such as steel or aluminium, with chequered or similar top surfaces for slip resistance. Peak A-weighted noise levels of up to 108 dB have been measured, arising from the impact between pallet truck wheels and deck surface ridges.
Noise can be reduced by applying damping materials. However the effectiveness of such treatments is limited because:
- the weight and thickness of typical deck plating requires a heavy application of conventional materials;
- low resistance to damage would mean that the damping material has to be applied to the underside of the deck where it is ineffective in reducing the amount of vibrational energy generated in the plate;
- most damping materials have poor weathering properties, limiting their application to decks.
The solution
Recent advances have included the development of blended resin compounds which effectively overcome all of these drawbacks. In particular, one such compound can be applied to the top surface of the deck to improve its anti-slip qualities. It also provides a measure of impact isolation between the truck wheel and the deck.
The method could equally be applied to other instances of noise generated by impact loads on heavy plate structures.
The cost
The approximate cost for the materials to cover 8 square metres of deck is £500. (1995)
The result
On controlled tests of the compound it was found that peak A-weighted noise levels could be reduced to 97 dB.