FEATURE PRODUCTION & ASSEMBLY
TAKING THE STRAIN: anti-vibration specification for industry
Optimum performance service life of anti-vibration mounts is only guaranteed if specified and installed correctly. Geert Keustermans of Trelleborg looks at best practice
A
nti-vibration mounts protect both people and assets by isolating and
attenuating vibration and noise, preventing damage to moving machinery and the environment in which it works. Optimum performance service life however, is only guaranteed if the mount is both specified and installed correctly. With such a wide variety of anti-vibration
products on the market including mounts, buffers and pads, specification can feel like a minefield. How can engineers ensure their mount delivers the right performance characteristics and are correctly installed? By working through the following best practice guidelines engineers can rest assured that their mounts will continue to perform over a long and arduous lifecycle. Operating conditions such as the
temperature and environment of the application will help determine the most suitable solution. However, additional factors must be assessed through calculation and analysis to enable informed specification including: deflection, centre of gravity, equipment configuration, disturbing frequency, mass moment of inertia, static loading, shock/thrust loading, alignment and natural frequency. 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 help ensure that mounts are not overloaded either statically or dynamically which will hamper performance. Ideally, all calculations should be balanced with other aspects of a system’s design such as gross motion and dynamic conditions to achieve the best possible isolation of vibration once the mount is installed. The composition of a mount is 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
8 JULY/AUGUST 2016 | FACTORY EQUIPMENT
manipulated through additives to achieve different hardness grades or damping;
capabilities according to the application when bonded to metal the inherent strength of rubber is dramatically increased to give an even higher load capacity.
SELECTING OPTIMUM MOUNTING SYSTEM While mounts can be specified at any stage of a project there are typically fewer restrictions if they are considered at the outset of the design phase. 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 degrees of freedom calculations to be carried out which will ensure the optimum mounting system is selected followed by testing to validate mount design: analysing static and dynamic characteristics and fatigue and the operating environment to justify its use. Even after a robust specification process the performance of an anti-vibration mount can be hindered by incorrect installation. All surfaces must be clean, dry and free from debris before the device can be fitted. The equipment to be mounted must be lifted carefully onto sufficient supports both to maintain correct alignment when lowered on to the mounts and to prevent damage to the asset or to individuals during installation. 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.
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
Anti-vibration mounts must be specified correctly using in-depth calculations
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 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
Component with anti-vibration mount
who can advise on remedial action. Machinery and components which are
properly protected through the use of anti- vibration mounts will last longer and operate more efficiently 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. Trelleborg’s industrial anti-vibration
engineers can assist with every stage of the project from bespoke mount design through to testing, training and aftercare.
Trelleborg
www.trelleborg.com
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