Sprocket technics

Noise reduction in chains and sprockets

Prevention is the best cure

Chains and sprockets can be a source of (excessive) noise. Over the past few years various developments have led to a number of solutions to this problem. Not least of these incidentally is the emphasis that the occupational health and safety law has placed on noise and the (permanent) hearing damage that long-term exposure to high noise levels may cause. In this article we cover the causes of and solutions for this specific noise problem.

On 25 January 2006 the commission resolved to amend the Labour Conditions Act. This resolution relates to the rules with respect to the exposure of workers to the risks arising from noise. On 15 February 2006 the directive will be implemented in the Dutch legislation. The new rules in the Labour Conditions Act will be recorded in the Dutch Official Gazette 2006/56 and consist of some 25 pages. Thus it’s too much to cover here, but it’s enough to know that intensive attention is paid to the occurrence of noise in the workplace and the negative effects that a high noise level over a certain amount of time can have on the human ear.

In the framework it is extensively explained what the occupational health and safety law says about acceptable noise levels. In summary, it can be said that an employee may be exposed for a maximum of 8 hours per day to a noise level of up to 80 dB(A); each 3 decibel increase reduces the allowable time duration by half. If the level or the length of time is exceeded, there is a risk of permanent hearing damage.

Addressing the root problem

The most effective solution to hearing damage is to reduce the noise level to an acceptable and legally authorised level. Prevention is still the best cure. This was also the idea of a customer of K&W Transmissies, supplier of chains and sprockets, as well as producer of special sprockets, based in Lelystad. The customer in question produces sorting installations which are produced in large halls in which many people are employed. Because the manufacturer of the equipment wanted to reduce the noise level as much as possible, he consulted a number of component suppliers to find if an opportunity existed to realize this noise reduction. In this context K&W Transmissies started developing its own low-noise sprocket.

A significant amount of the sound produced by the conveyor chain and sprocket comes from the ‘clapping’ of the rollers of the chain into the tooth cavities of the sprocket. In mechanical terms, this process is as follows: the chain roller collides with the bottom of the tooth cavity, this produces a sound. Moreover, because there is a certain amount of space between the bushing and the roller, the roller also makes a sound as a result of elastic vibration. Furthermore, the sprocket also to some extent will vibrate. The degree of noise production is mainly a result of the following parameters: the chain weight, roller diameter, chain speed, tooth and the pitch of the chain.

To address this problem, a manufacturer of chains has already thought of a solution in the form of the fitting of plastic balls in the tooth cavities. Jan Hoeven, sales manager at K&W Transmissies explains: “Although this solution is effective, the design of K&W Transmissies has the advantage that the power transfer remains at its maximum. It is also simple to replace the plastic ring after a period of time, to ensure optimal sound dampening is again reached. .

Low-noise sprocket

The solution that K&W Transmissies eventually developed consists of installing a special plastic ring on both sides of the teeth of the sprocket. The company makes the ring itself simply by cutting off a bar of special plastic and placing this around the tooth. Then the plastic ring is attached and secured using a metal ring on the chain wheel. The first contact between chain and sprocket is thus not metal on metal, but metal on plastic. The technique reduces the noise by reducing the speed at which the chain meets the sprocket. Because the chain is picked up by the plastic ring, the roller of the chain is slowed in the tooth cavity of the sprocket. This ensures, so to speak, a “soft landing” for the roller. The metal consists of the linking plates of the chain, which are supported on the plastic ring, so that there is less contact between the rollers of the chain and the tooth cavities of the sprocket. By applying this special low-noise sprocket, noise reductions of 7-8 dB are obtainable. These sprockets can only be applied to conveyor chains. From a cost point of view, sprockets are usually the cheaper components and therefore it is more interesting to make the noise-reducing changes to the sprockets instead of to the relatively expensive chain.

Other noise-reducing measures

Besides the application of noise-reducing components, there are also other areas in which noise reductions can be realised. For example, the sound level is also determined by the tolerances of the chain and sprockets. Additionally, the proper alignment of the sprockets in relation to each other is an important noise-reducing factor. This is an important task of both the manufacturer as well as the final machine builder.

Buffering the impact energy

Regarding the buffering of the effects of the impacting parts, the topic of ‘lubrication’ is relevant. Applying lubricants to the bottom of the gear teeth and in the space between the bushing and the roller can do a lot to reduce the energy of the impact. In addition, it extends the life of the chain and protects it against corrosion. A disadvantage of lubrication is of course that this is not desirable in some industries (e.g. in the food industry) and that there are more and more chains come onto the market that no longer need to be lubricated. It is therefore questionable whether clients are interested in the lubrication of chains to achieve noise reduction.

Finally, the impact energy can also be buffered by for example producing the chain rollers themselves with special plastic. There are different versions of these chains but they have disadvantage of increased wear and a higher price. Thus here also one must find the right balance between the limitations of a possible solution and the desire to reduce noise through chains and/or sprockets. Moreover, Hoeven points out: “When you really get into the production of plastic sprockets or parts, then you will immediately encounter a maze of plastic suppliers. You must then be really sure that you actually want to continue in that direction. However, we often make sprockets and gears in which steel and plastic parts are applied next to each other, such as plastic sprockets with a steel core. Usually this has to do with the required power transfer.”

Conclusion

The user can make a valuable contribution by taking the maintenance of his chains and sprockets seriously. When lubrication is required, he will have to stay on top of this. When a chain needs to be replaced, in many cases the sprocket must also be replaced.

Finally, enclosing an entire machine is especially useful when employees only occasionally need to come by the machine. With an enclosure the noise level can actually increase due to reflection or the like. Of course, this is not the case when special insulating walls or cabinets are used.