NOISE CONTROL IN THE WOODWORKING INDUSTRY
By David S. Cmar
In the metal products manufacturing world, factory automation and manufacturing technology have been installed and replaced at a dizzying pace. In recent years, most noise control efforts have shifted from retrofitting existing noisy equipment to integrating controls as part of the design and build process. Does this mean the need for retrofit noise control expertise is fading away? Obviously not. The focus for noise control experts, regulatory agencies, and health and safety awareness in general, has shifted to the so-called ‘1st Tier Suppliers’ and other manufacturing industries such as manufactured wood products.
Historically, the woodworking industry has had difficulty with the implementation of planned and retrofit noise control because of the difficulties in overcoming three main challenges that help define feasibility:
Challenges for Woodworking Noise Control
Material - There are thousands of varieties of materials used in woodworking throughout the world. Unfortunately, this creates challenges in attempting to design quieter equipment that can be applied universally. Characteristics such as hardness, moisture content, size and thickness all impact the cutting process and should be considered when selecting tooling or designing work fixtures.
Tooling - Many of the tools required to cut and shape wood have inherently high noise levels, generally in excess of 95 dBA at the operator location.
Typical Woodworking Tool Noise Exposures
In the case of woodworking cutting tools, many manufacturers and end-users are reluctant to experiment with existing technology, i.e. ‘If it’s not broken, don’t’ fix it!’ Some of this can be overcome by adopting simple, and proven techniques for minimizing tooling noise that have been utilized in woodworking as well as metal cutting applications. Best of all, the impetus behind many of these tooling techniques is tied to improved performance! (You may find that there is a direct correlation between improved performance and source sound level reductions – which makes sense as noise is an unwanted by-product stemming from system inefficiencies.)
Dust Control - The control of dust and wood chips created during the cutting and shaping process makes the use of dust collectors in the workspace a necessity in today’s workplaces. This may also have the unintended effect of creating additional noise exposure for machine operators. Poor dust collector design and positioning can cause employee exposures to exceed 85 dBA due to the dust collector alone. This could severely limit the potential benefits from tooling noise control efforts.
The economics of every business is different and it can be difficult to judge the threshold that companies are willing to spend in order to achieve desired sound level reductions. A reasonable and justifiable control at one company can bring a quick rejection from management at another. Ultimately, the decision to implement a control is seldom made by the people directly involved in the selection process. This is why it is vital to provide as much information to allow someone that may not have the background to fully understand the technical or health and safety aspects of the project to arrive at a decision that is balanced and informed. Some things to consider include:
1) Life expectancy of the control
2) Maintenance/upkeep and replacement costs
3) Cost reductions for Hearing Conservation Program implementation
4) Affect on the life expectancy and upkeep of the tooling/equipment being controlled
5) Cost of retrofit vs. purchase of newer quieter equipment with integrated noise controls
Many of the noise control solutions implemented for woodworking tools involve the use of some type of enclosure or barrier between the noise source and the operator. While this may be excellent from a noise control standpoint, this also highlights a couple issues that raise the howls of protest from machine operators and maintenance workers – access and maintainability.
“Striking a balancing between operators needs for access versus delivering on noise reduction requirements is usually the hardest part of designing enclosures for woodworking machines”, states Tom Kaffenbarger, President of IES 2000. IES 2000 is one of the premier designer and installation experts in North America, and is a world-wide supplier of noise control enclosures for the woodworking machines. Tom says, “The key to a successful enclosure application is your ability to work with the customer, including the people using the equipment, to find out how they interact with the machine and then figure out how to design and install an enclosure that provides a quieter working environment, without making their jobs more difficult.”
Noise Control Solutions
The challenges may seem daunting, but they are hardly insurmountable. There are several options available for companies to reduce harmful noise levels without impeding production efficiency. The most effective controls are categorized below:
Tooling and associated wood-cutting and shaping actions are the primary source of noise for wood-working machines and equipment. Generally, reducing noise directly at its source is the most effective way of controlling noise emissions. Several methods exist for minimizing the noise created by tooling.
Saws - Investing in quality saw blades can have a significant effect on lowering noise levels as well as extending the life of the blade and providing more precise cutting. Selecting the proper saw blade for the type of cut, wood type and thickness, and rotation speed are common sense solutions for improving the noise level. Several options are available and utilizing improper blades increase the noise level while also shortening the life of the tooling and possible affecting the quality of the finished material. One aspect to consider is the blade tooth construction.
The use of Carbon composite cutting tips provide a much more durable tool that can last up to 10 times the life span of comparable steel tips. Sharper tooling reduces heat and friction that builds up during the cutting process. This makes it harder for the tools to cut and increases noise levels.
Rotational saw blades with equally spaced teeth can produce resonance during cutting when the rotational speed matches the natural frequency at which the blade material vibrates. Sometimes this is also noticeable when the saw is not under load. This can produce a distinct tone in a particular frequency band that is present during cutting. This condition can be alleviated by using saw blades with teeth staggered at irregular intervals along the saw plate. The varying intervals does not allow the blade pass frequency to match the material's natural frequency, therefore producing a more uniform noise across all frequency ranges.
Damped Saw Plate
Some premium saw plates incorporate damping materials into the saw plate. This involves constructing saw plates with recessed areas to attach stiffening composites similar to those used on automotive and aerospace body panels to reduce torque and vibration in the steel plate. This can have a considerable reduction on noise, as it prevents the blade from deforming (wobbling) as it cuts through the wood. This has an added benefit of more precise cuts, increased plate and tip life, as well as potentially allowing for use of a thinner kerf and plate thickness which can save in material costs for high volume producers.
Planers & Molders - Planers and molders generate significant noise both at idle and while cutting wood. The cause of both noises is related to the cutter head/block configuration and design. The most common type of cutter head for planers and molders incorporates straight blades mounted perpendicular to the rotating block at various cutting angles. At idle this configuration creates sound similar to rotating helicopter blades as the blades ‘cut’ through air trapped at the work surface as the blades pass by. During cutting, the straight blade configuration requires additional energy to cut the material, also creating more noise. Noise reducing cutter/block configurations include:
Low profile blades and blocks provide a better aerodynamic profile during idle rotation, therefore reducing the ‘air thump’ that occurs during rotation. These blades also allow for smoother finishes and less wear and tear on the tooling.
Helical cutters distribute the cutting surface to minimize the surface contact between the blade and the material at any one time. This provides significant noise reduction (5 dB or more) when compared to straight cutters. This also requires less feeding force and produces smoother finishes.
When it is not possible to treat sources directly it sometimes becomes necessary to use enclosures and barriers to block the transmission path to the receiver. In order to design effective and assessable enclosures it is important to properly consider the critical parts of enclosure.
The most effective enclosures, from both a noise reduction capability and a durability standpoint, are made from acoustical panels.
An alternative to acoustical panels involves the uses of mass loaded vinyl barrier/quilted blanket absorbers commonly referred to as ‘acoustical curtains’. Enclosures such as the IES 2000 curtain enclosure picture below may not have the robust look and feel of a steel panel enclosure but can be a cost-effective and easy-to-install alternative to acoustical panels. “Many of our customers have opted for acoustical curtains for cost reasons. For applications where durability and substantial noise reductions are not an issue, curtain enclosures can more than meet their needs”, states Kaffenbarger. Typically, mass loaded vinyl barrier/absorber composites can be expected to provide 5-7 dB of reduction when installed with proper attention paid to sealing openings and blocking flanking and direct transmission paths.
One consideration in comparing the cost of panels to curtains is the life-expectancy for the application. In abusive environments, curtain materials will need to be replaced at regular intervals. This may make the overall cost comparable or even more costly then acoustical panels over the life of the machine.
Feed and Exit Tunnels
The use of Feed and Exit Tunnels can vastly improve the performance of an enclosure by addressing one of the difficulties of enclosing equipment that requires product in-feed and out-feeds. The In-feed and Out-feed for wood shaping and cutting tools have the potential to severely degrade the performance of an enclosure. For example a 4” thick acoustical panel enclosure can provide up 10 – 20 dB reduction in typical field installations. This reduction is decreased by 10% for every 1% opening in surface area. A 2’ x 2’ opening on a 40 ft2 panel correlates to a 5 – 10 dB reduction in performance. Contrastingly, an acoustical entry or exit tunnel may actually increase the performance by 3 – 5 dB due to blocking direct noise paths and increasing the surface area for the absorption of mid to high frequency noise. Additionally, vinyl and rubber curtains at entrances and exits can help block high frequency noise from exiting the tunnel when lumber is being fed in/out of the machine.
The location and installation of access doors is one of the most contested issues of enclosure design. Tom Kaffenbarger of IES says “One of the hardest things for customers is to try and visualize the enclosure and how they will be able to interact with it”. A noise control expert looks at an enclosure without openings or access points as the ‘perfect design’, acoustically. This is in direct conflict with end-users who see barriers between them and the machine as potential impediments to their jobs. It is imperative that engineers, enclosure providers, and employees have an opportunity to give input into the design and review prior to construction to ensure that a) the enclosure meets the intended noise control design goal and b) that it can be implemented as designed. Without this, much time and money can be lost trying to modify the enclosure during installation.
A portion of the noise generated by woodworking machines is radiated through the machine structure. This can be transmitted through both the floor and the other structural elements attached to the machine such as the enclosure frame. Isolation mountings or materials should be installed between the machine and floor or the surfaces that may transmit radiated noise.
Traditionally the people employed in the woodworking industry have accepted higher noise levels as the trade-off for the increased productivity that cutting and shaping machines bring. A recurring theme in this article shows that control measures that reduce sound levels do not have to penalize productivity, and in many cases can actually lead to improved quality and longer tooling life. As industry changes to accommodate the need for increasingly safer and healthier work environments, an opportunity exists for the woodworking industry to take a fresh look at the issue of noisy equipment in the workplace. The methods, materials and expertise exist to implement cost effective solutions that can benefit workers and employers from both health and competitiveness standpoints.
Mr. Cmar is President/CEO of Phase To of Canada, Inc. and also in charge of Business Development for Phase To, Inc. Mr. Cmar has over 15 years of experience in noise engineering. He can be reached at (519) 734-7001 or email firstname.lastname@example.org
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Phase To, Inc.