The high noise emissions of circular saws severely burden users and neighbouring workplaces. The noise level is particularly critical in areas where circular saws are used professionally, i.e. at workplaces in wood- and metal-working and plastics-processing firms. The institution for statutory accident insurance and prevention (BG) in the woodworking industry alone currently has over 53,000 member firms in which - with a few exceptions - it can be assumed that circular saws are used. At the same time, about 6,000 new cases of noise-induced partial deafness are reported in Germany each year.
On circular saws, it is usually the saw blades that cause the high sound pressure level. With conventional saw blades, this level is always within the auditorily damaging range of 85 dB(A) and higher. The highest level of over 95 dB(A) is achieved when sawing plastics and metal, while the sawing of wood yields levels of 85 to 90 dB(A). From a sound pressure level of 85 dB(A) plus, experts reckon with auditory damage. This is why the new German Noise and Vibration Protection Ordinance obligates noise protection measures to be taken and users to wear hearing protectors from this value. Noise-reduced circular saw blades help in most cases to significantly reduce the sound pressure level.
Causes of the high level of noise from circular saws
During sawing, the saw blade and the workpiece are caused to vibrate. This vibration generates sound waves that propagate through the air and are perceived as noise. The saw blade's excitation of vibration is particularly strong because the blade is made of steel, which has practically no damping effect. With damped, noise-reduced saw blades, it is possible to effectively reduce the excitation and hence the propagation of sound. Other factors that have an effect on the saw blade's excitation of vibration (e.g. hardness of the material or saw tooth geometry) can only be modified to a limited extent.
Examination of commercially available saw blades
Although low-noise saw blades have been available for years, they have so far been rarely used in practice. To objectively investigate the effectiveness of such saw blades and enhance user acceptance, the IFA tested commercially available noise-reduced saw blades and compared them with conventional saw blades.
17 commercially available hard-metal circular saw blades with noise-reducing characteristics were investigated in the laboratory and 12 more in practical use. Their propagation of sound was compared to those of conventional saw blades. All these blades were used for sawing different materials. These were wood (wood panels and wooden profiles), plastics (panels and profiles), aluminium (profiles). Also investigated were the effect of blade size, feed rate and height adjustment of the saw blade. The list of manufacturers of noise- reduced saw blades comprises 16 manufacturers at present. The list is the outcome of an extensive market analysis, though the list makes no claim to be complete.
Effectiveness of noise-reduced saw blades
With noise-reduced saw blades, high sound level reductions can be achieved:
Up to approx. 6 dB(A) with the saw idling
Up to approx. 6 dB(A) when sawing aluminium
Up to approx. 7 dB(A) when sawing wood panels
Up to approx. 11 dB(A) when sawing plastic profiles
Up to approx. 12 dB(A) when sawing hardwood edge-banding.
Just how effective these blades are becomes clearer when one considers that a reduction of 3 dB is equivalent to a 50% drop in sound energy and thus to a major reduction in the risk of damage. With a drop of 10 dB, the perceived noise is only half as loud.
An additional advantage of these saw blades is that their higher quality and the low-vibration operation result in an increased capacity and precision and hence better results. These two points compensate for the on average 30% higher cost of purchasing these products. Low-noise saw blades are thus a highly cost-effective way of reducing noise from the use of circular saws - in many cases even to below the threshold of auditory damage.
Low-noise saw blades: Working principle
There are two types of noise-reduced saw blades.
- Saw blades that have a "sandwich design", i.e. consisting of two sheets of metal and a damping film in between.
- Saw blades incorporating laser incisions that inhibit the generation of natural vibration and, thanks to the friction in the incisions, achieve better damping.
For plastics we recommend sandwich-type saw blades, and for aluminium only sandwich-type saw blades should be used. For wood, both types are equally suited.
source : http://www.dguv.de
