Objective
The principal noise emitting surfaces during sawing of hot rails were shown to be the unshielded area of the saw blade with a sound power of 125 dB(A) and the saw blade cover (sound power 120.5 db(A)). The noise emission from the red hot rails being cut was by contrast comparatively low (107-92 dB(A)). During the sawing of cold sections the principal noise emissions were from the uncovered section of the blade, the saw cover and the section being cut. The sound intensity from the section being cut depended on its length, shape and cross section and equalled or sometimes exceeded that from the saw unit.
Trials were conducted on the two saws using blades where surface vibration was constrained layer damped using an adhesive mastic damping material and either 1200 mm diameter discs of 0.9 mm or 2 mm thick Zintec or 1.1 mm thick sound deadened steel (SDS) discs attached to earth side of the blades. The constrained layer damped blades produced 5.5 to 6 dB(A) less noise than undamped blades when cutting hot rails and 4 to 4.5 dB(A) less noise as a whole in the area around the saw unit. Although constrained layer damped blades on the saw cutting cold steel sections produced 6.5 dB(A) less noise with SDS disc faced blades and 9 dB(A) less noise with Zintec faced blades that the undamped blades produced, the noise around the saw units as a whole, was not measurably reduced because of the noise radiated from the sections being cut. Trials with a modified saw clamp designed to introduce pressure on the web of beam and channel sections and so damp the vibration and noise emissions from the sections also produced little noise reduction and it was concluded that greater pressure and clamping at more than one point would be necessary to achieve a measurable noise reduction. Modifications to achieve this were not possible on the trial saw before the end of the project, and further work on clamping or other means of damping work place vibration is necessary to obtain benefit from the reduction achieved in noise emissions from the saw blade.
After consideration of various alternative methods for measuring the noise emission from working steel bladed saws a portable sound intensity measuring system has been used to measure the sound emission from various surfaces on two production saws - one cutting cold beam and angle sections and the other hot rail sections. The measurements were made in order to identify the principal noise emitting surfaces on the saws and to target appropriate measures for limiting the noise emission from sawing.
The sound intensities from the surfaces on the saw units and work pieces were able to be measured with a standard deviation of 1.2 dB(A). The total sound power of the hot rail saw unit derived by summing the individual surfaces where sound intensities had been measured enabled the sound pressure at 5 metres from the saw to be calculated with a difference of 0.5 dB(A) from the mean measured value. The sound pressure levels calculated from sound power values of the saw unit cutting various cold sections agreed only within + 5 - 2 dB(A) of measured values, but this poorer agreement reflected the variability of the noise emission from the sections being cut rather than from the saw surfaces.
Topic(s)
Call for proposal
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S60 3AR ROTHERHAM
United Kingdom