FAIL SAFE VS NON FAIL SAFE ANTI VIBRATION MOUNTS: WHEN TO USE THEM AND ADVANTAGES OF EACH

INTRODUCTION

Noise and vibration isolation is necessary throughout a wide range of applications. These can range from static applications (such as small compressors or refrigeration units) in which the anti-vibration mounts will only have to withstand the loads corresponding to the weight of the system itself, to the suspension of engines or cabins for off-road vehicles in which the anti-vibration mounts must withstand important dynamic loads

Due to this variety of applications several types of anti-vibration mounts are required, each with the aim of adapting to the needs of each case.

Anti-vibration mounts can be classified according to several characteristics (type of anti-vibration mount, union between the rubber and the metal elements, materials ...). This article aims to discuss two ways of classifying these elements, these are fail-safe anti-vibration mounts and non-fail-safe anti-vibration mounts.

NON FAILSAFE ANTI-VIBRATION MOUNT

This type of anti-vibration mount is one that does not maintain its integrity in the unwanted event of failure of the elastic element. The integrity of the mount depends on the adhesion between the rubber and the different metal parts of it.

Some examples of this classification of anti-vibration mount would be for example, cylindrical mounts, VD or DRD/DSD type mounts. Below we will analyze the adhesion zones on which the integrity of each of the mentioned anti-vibration mounts depends.

In the case of large dynamic loads and deflections, if the anti-vibration mount is subjected to these frequently and for long periods of time, it could be the case that this adhesion is compromised. In extreme cases separation from the rubber could occur, at which point the suspended element would no longer be secured in place.

Therefore, this type of mount is not recommended for applications with large dynamic requirements. Its field of applications usually extends to mostly static machines such as compressors, rotary pumps, air conditioning equipment, small groups of motor pumps or fans.

FAILSAFE ANTI-VIBRATION MOUNT

This type of anti-vibration mount has a fail-safe system that guarantees its integrity even if there is a failure in the elastic element, so the integrity does not depend on the adhesion, but on the mechanical resistance of the metal components.

Within this group of anti-vibration mounts would be included a large part of the catalog anti vibration mount of AMC Mecanocaucho®.

As an example we will review the bell type anti vibration mounts, such as the anti-vibration mounts of the BRB, BSB or marine anti-vibration mounts. These would have a structure that would consist, as in the previous case, of a rubber section adhered to the base. Unlike the previous case they also contain a central boss metal with a larger diameter at the bottom than the diameter of the central hole at the base.

In the event that the anti-vibration mount is installed in an application with large dynamic loads that cause the rubber element to fail, the suspended element would still be mechanically captive since the geometry of the metal components prevent it from coming apart.

Another example can be seen in the anti-vibration mounts that are installed with washers, such as cone type anti-vibration mounts or symmetrical anti-vibration mounts (such as CB or TF).

In these anti-vibration mounts the washers act as a fail-safe system, since they cannot move through the outer metal component of the anti-vibration mounts, so the suspended system would not be free due to failure of the elastic element.

In the case of symmetrical mounts, these are installed through a hole in the frame or in the bracket of the suspended element as can be seen below.

A similar type of anti-vibration mount would be the families of the SCB, SCH (and their reinforced versions) and the cabin mounts, which are also installed through a hole and by means of a washer at the top and bottom.

In the case of cone mounts, these are installed through a hole in the chassis and secured via the holes in the flange of the outer metal (either in 2 or in 4 points, depending on the type of cone). After that, the washers are installed at each of the two ends as can be seen below.

This type of mount is typically recommended for applications with dynamic requirements. Its field of application is more diverse, it can be used to isolate almost all types of vehicle elements (engines, cabins, transmissions ... ) as well as generator sets or compressors, both mobile and static.

Below is a summary of the main fail-safe products available within the AMC Mecanocaucho range of anti-vibration mounts.

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CONCLUSIONS

As discussed, each of the two types of anti-vibration mount is designed for a specific field of application. Fail-safe anti-vibration mounts the most recommended for applications with high dynamic demands while the non-fail safe anti-vibration mounts would be considered for applications that are mainly static.

AMC Mecanocaucho® has developed a calculation tool to assist with the selection of anti vibration mounts. This calculation tool is called Vibration Isolator Pro.

This tool has been developed to perform anti-vibration calculations in a simple and effective way using basic input data such as the equipment mass and number of mounts.

It is accessible as a web version on Mecanocaucho.com and also via our mobile app ‘Vibration Isolator Pro’ which is available for Android and IOS environments.

If you are interested in this matter, please do not hesitate to contact our application engineers. They will be able to help you and offer you their point of view.

Contact form for AMC-MECANOCAUCHO application engineers®.