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Noise Control Product Spotlight

Shock Absorbing Casters


By David S. Cmar

March 2005


Manufacturing facilities that are looking for ways to reduce ambient noise levels may want to look at the contribution from their in-plant material and scrap trailers and containers.  Lowering the ambient sound levels caused by these transient noise sources can reduce employee exposure levels as well as improve communication on the plant floor.  In the past, unless the source in question was in direct and continuous contact with employees, many companies struggled to justify the costs and results of attenuating the noise.  Over the decade, effective noise control strategies and equipment upgrades in some companies have lowered employee exposures to the point where sources such as intermittent carryover noise from passing carts and dollies are now the significant stumbling blocks to further noise level reductions.


Facilities that use carts, dollies, gondolas and other types of wheeled containers to move parts, scrap, trash, etc., will invariably have considerable noise generated by their use.  The use of shock absorbing casters can be a tremendously effective way of reducing the high level noise levels inherent to these devices.


Typically, the number one cause of noise related to the use of wheeled carts and dollies in a facility is the impact created when traversing uneven or different types of floor surfaces.  In a fixed wheel application, any time the wheel strikes an uneven surface the energy from this ‘shock’ is transmitted back through the wheel and dissipated through the container system.  The energy from the shock is dissipated either in the form of noise (where there is slack in the system), is absorbed by the system components (which leads to premature wear and failure), or transmitted to the load which may be sensitive and expensive parts that are susceptible to damage.


In selecting a product to achieve a specific goal such as noise or vibration reduction, it is important to understand that you are not simply buying a ‘commodity’ or an ‘off-the-shelf’ product.  You are in fact purchasing a product engineered for a specific design criteria that may include factors such as load weight, floor surface, load sensitivity, and travel speed.  Bill Chamberlain, Sales Manager at R.T. Laird states, “We strongly recommend that you consult with our engineering staff to specify shock absorbing casters for your application.  Selecting the proper caster for maximum shock absorption demands that certain design elements must be reviewed and discussed”. 


R.T. Laird, Inc., based in Plymouth, Michigan, is the premier supplier of suspension casters to industry, and the leading experts in providing engineered solutions to companies seeking a shock absorbing caster system.  R.T. Laird, Inc. has supplied shock absorbing casters for the aerospace, automotive, medical and semiconductor industries since 1975.


Due to their inherently high initial and final spring rates, conventionally sprung casters with limited spring deflection develop load acceleration so great that the net result is the generation of destructive shock to vehicle and payload.  When payloads and travel surface conditions vary, the risk of serious damage is even greater.  It is not uncommon for casters with conventional suspension systems and limited deflection to cause more severe shock damage than comparable casters under identical conditions.


The key to the R.T. Laird product lies in the spring configuration in the caster.  The wide deflection range engineered into the casters is vitally important to the overall efficiency of the suspension system itself.  Because of its exceptionally wide deflection range, the initial and final spring rates are extremely low and gradual.  As a result, effective shock mitigation is available to a greater range of payloads and at varying speeds.


R.T. Laird has had their products subjected to field evaluations by customers at several automotive plants to determine the noise reduction potential under different types of conditions.  The results are impressive.  Although it is difficult to predict the exact benefit for each particular application, sound level reductions of between 10 and 20 dBA have been achieved for part racks and trash gondolas fitted with R.T. Laird casters.  The racks and dollies with R.T. Laird casters were optimized for load, wheel and tension characteristics and contrasted to versions with fixed casters of various wheel types.


Selecting Casters

The most important aspect of maximizing the noise attenuation is proper caster selection for the intended application.  In selecting caster configurations many options are available including: Spring stiffness, Caster weight/durability (steel vs. aluminum), Wheel Type (Rubber, polyurethane, phenolic resin).  In order to ensure that you obtain the caster that is going to maximize the noise reduction for a particular application, several questions will need to be answered, including:


  • What is the loaded and unloaded weight of the trailer/container?

  • What type of environment will the caster be exposed to? Oily surfaces?  Uneven floors?  Debris?  Indoors or outdoors?

  • How sensitive are the parts being conveyed?

  • What speeds will the cart be traveling?

  • Is the cart being moved manually or mechanically?


All of these factors may influence caster selection, not only to achieve noise reductions but also to allow the trailers or containers to function as designed.



In addition to the noise reduction capabilities, shock absorbing casters provide additional benefits that are equally important to consider when selecting casters.


Increased Lifespan - The most obvious benefit is a significantly increased lifespan when compared to fixed casters.  R.T. Laird conservatively estimates that their casters last 4 – 5 times longer than conventional casters.  Even in harsh industrial settings such as the automotive industry, some R.T. Laird casters are still in service 20 years after installation.  This can be largely attributed to the reduced wear and tear caused by impacts.  It is estimated that as much as 80% of the shock and vibration is dissipated by the springs in the caster.


Maintenance - Because the wheel is no longer the primary recipient of the initial shock wave at impact, wheel wear is also substantially reduced.  This has the added benefit of far less frequent wheel changes.  This provides a substantial cost savings in both labor and materials over the life of the trailer/container.  There are no additional maintenance requirements associated with the shock absorbing caster.  In fact, the R.T. Laird products can be said to be virtually ‘maintenance free’ as they are pre-lubed with sealed bearings that do not require periodic lubrication to operate.


Shock & Vibration Reduction - In addition to the reducing the noise, the shock absorbing casters are also used to protect sensitive equipment and products during transport.  The casters are used in the aircraft industry for aircraft engine and maintenance stands, the semi-conductor industry and in medical applications.


The decision to purchase new or replacement casters for trailers and containers can be big investment for any sized business.  The impact of that decision may affect noise levels in your facility for many years before there is another opportunity to reevaluate your caster strategy.  It is worth investing your time now to consider whether shock absorbing casters can be part of a complete noise solution at your facility.


For questions or information on shock absorbing casters you can contact Bill Chamberlain Sales Manager at R.T. Laird, Inc. (800) 231-7983 bchamberlain@rtlairdcasters.com or visit their website www.rtlairdcasters.com.



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 davecmar@phasteo.com


Phase To, Inc. (PTI) does not represent, sell, or market any noise control materials or hearing conservation products.  References to any specific products in this or any other PTI article does not express explicit endorsement by Phase To, Inc.  PTI focuses specific attention on innovative items or products that we find to be superior in the noise control or hearing conservation marketplace.


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