Viewpoint: finding the right fit for anti-vibration mounts

With such a wide variety of anti-vibration products on the market – mounts, buffers and pads to name a few – specification can feel like a minefield.

However, by working through the best practice guidelines described below, engineers can ensure their mount is correctly installed and delivers the right performance characteristics over a long and arduous life cycle.

To help determine the most suitable solution, operating conditions, such as the temperature and environment of the application, must be monitored, but other factors must also be assessed to enable informed specification.

These areas include: deflection, centre of gravity, equipment configuration, disturbing frequency, mass moment of inertia, static loading, shock/thrust loading, alignment and natural frequency.

By working through the best practice guidelines engineers can ensure the mounts are correctly installed and deliver the right performance characteristics over a long and arduous life cycle

Assessed alone, none of the above will provide a complete picture of the system performance, and if any of the input data is inaccurate, then the mount may not perform effectively.

For example, understanding the centre of gravity helps to determine the loading at each mounting position, and as this may vary, it’s often necessary to select different products across the mounting system.

Calculations also help ensure that mounts are not overloaded – either statically or dynamically – which will affect performance.

All calculations should be balanced with other aspects of system design, such as gross motion and dynamic conditions, to achieve optimal isolation of vibration once installed.

The composition of a mount is also important and rubber-to-metal bonded solutions offer the greatest benefits for several reasons:

• The high load bearing capacity of rubber, plus its low modulus of elasticity, allows the natural frequency of the mount to be tuned.

• Natural rubber can be chemically manipulated through additives to achieve different hardness grades or damping capabilities according to the application.

• When bonded to metal, the inherent strength of rubber dramatically increases to further enhance load capacity.

While mounts can be specified at any stage of a project, there are typically fewer restrictions if considered at the outset. If factored in too late, it may prove prohibitively costly to retrofit and, if equipment is damaged as a result, expensive maintenance may be required.

Early involvement from anti-vibration specialists allows six degree of freedom calculations to be carried out that will ensure the optimum mounting system is selected, followed by testing to validate the mount.

Once installed, simple checks can be made to assess success before the equipment is ready for use. A straightforward visual inspection can flag misalignment, missed fasteners, fixings or any damage that may have been caused during installation.

As incorrect usage can lead to excessive noise, vibration and harshness (NVH) and decreased vibration isolation, ongoing monitoring is recommended

Following this, it’s a case of taking a series of measurements and comparing them to the original calculations – deflection under static load should be checked, as well as measuring vibration velocity and frequency through the use of a fast Fourier transform (FFT) spectrum analyser.

As incorrect usage can lead to excessive noise, vibration and harshness (NVH) and decreased vibration isolation, ongoing monitoring is recommended. Typically, such issues would manifest themselves in terms of higher levels of noise or harsh movement.

However, these may not be the first indication of damage. Periodic inspection through visual checks will reveal loosening of bolts, while the rubber and metal parts should be examined for any signs of damage such as rust, wear or dents.

If there are signs of excessive deflection, at any mounting position, inspection should be handed over to the mount’s manufacturer who can advise on remedial action.

Machinery and components that are properly protected through the use of anti-vibration mounts will last longer and operate more efficiently – but only if these mounts are specified correctly using in-depth calculations; installed with care and checked against those calculations; and periodically monitored to flag any issues before they become critical.

• Geert Keustermans manages general industry and distribution markets at Trelleborg