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Tips for vibration isolation

clock 3.5 minutes | 24 May 2018

Water showing the impact of vibrations

One of any engineer’s concerns is to ensure their machine or appliance runs efficiently. To that end, vibration isolation is top of mind.

All machines, from the smoothest laptop, to a bandsaw vibrate. The amplitude of these vibrations obviously varies significantly. Vibrations can create imbalances, friction, excessive noise and failure in mechanical devices. In heavy industrial applications, it can present a significant risk to safety and productivity.

In consumer appliance design, it can cause irreparable damage to your reputation for quality products. It’s worth noting that a well-designed machine will have fewer vibration problems than a product whose design is not thought through. Put some time into it. It will save you time in the long run.

What are the causes of abnormal vibrations?

Before you can minimise vibrations, you need to know the causes. It varies, and can result from combined factors. Generally, these factors are:

Imbalance

With components that rotate, the machine’s axis must be balanced. Think of a washing machine when the weight of laundry is not evened out. An imbalanced axis creates a centrifugal force, causing the machine to vibrate. As machine speed increases, so does the impact of the imbalance. In some applications, the imbalance can be caused by manufacturing defects such as machining errors, or maintenance issues such as dirty fan blades. In addition to machine vibrations, imbalance can significantly reduce bearing life.

Loose connections

Bolts and screws can loosen over time. Bearings can loosen after severe wear, or if they’re not tightened to their mounts, causing vibrations to damage components. Other causes can be cracked welds, piping or ductwork problems – the list is long.

Most often, loose connections happen when rotating components have not been fitted correctly.

Misalignment

When rotating shafts are out of line, vibrations can result. When a shaft and motor are not parallel, angular misalignment occurs. Minor vibrations can result, but large angular differences are another matter and can cause significant damage to the machine. Misalignment can happen during assembly or over time because of thermal expansion.

Wear

A roller bearing can become pitted, gears can chip or a drive belt can break down. The result is a machine that vibrates. Vibrations caused by other factors can also cause wear and premature failure. For example, excessive operational stresses can develop that changes the balance condition, or thermal expansion can cause misalignment, which in turn causes wear.

Consumer appliances: controlling vibrations

When designing consumer appliances, you should maximise the balance of the oscillating mechanism. You can also isolate the vibrating component with a sub-frame or springs to reduce the energy of vibration from being transferred to the rest of system. Use a tuned mass damper if you’re concerned about mechanical resonance.

The role of polymers in controlling vibrations

Insulating barriers can prevent the resonance of vibration energy in your consumer appliance. To deaden sound, consider mass-loaded, flexible polymer sheets. Polymers with open cells and polymer composites with fibrous structures -- such as fibreglass – are excellent at absorbing vibrations.

Appliance housings or other components constructed from polymers can absorb vibration energy into the polymer molecule. Consider thermoplastic elastomers (TPEs). These are one of the most effective polymers for this purpose, as they offer both hard and soft segments in the polymer chain.

Appliance designers are already big fans of thermoplastics due to the design freedom they offer. They’re not only lightweight and strong, they can be easily melted and formed into complex shapes using injection moulding and thermoforming.

Vibration-damping TPEs go one step further. These offer all the benefits you expect from thermoplastics, but can absorb significantly more vibration. Don’t confuse these with thermoset polymers used for vibration damping, which don’t offer design freedoms and can not be formed using injection moulding.

Industrial machines and isolating vibrations

The most cost-effective solution for controlling vibrations in machines or equipment is a vibration isolator, specifically, special mounts designed to absorb the vibrations.

What should you consider?

Think about the weight, size, and centre of gravity of the machine or equipment you want to isolate. Size – or shape—dictates the type of attachment and space available for the vibration isolator. Centre of gravity matters, because isolators of different load capacities might be required at different points on the machine, depending on weight distribution.

You should also determine what types of dynamic disturbances need to be isolated. For instance, random vibration tests are common for automotive and transport applications. Shipping containers, too, may need a good deal of vibration testing. Shock tests are important, depending on the equipment. They’re especially beneficial in helping to determine if a product can survive a crash or is dropped to the ground.

Environment matters, as well. If the isolator will be subjected to grease or UV light, then you need material that can stand up to these factors. Temperature is extremely important, and can change the performance of the isolator.

Different isolators used in various applications tend to fall into these categories:

Spring mounts

Vibrations are absorbed by the spring and released in another direction.

Advantages:

  • Very high vibration and shock isolation
  • No foundation is required for small and medium weight machines and reduced depth of foundation for very heavy machines
  • Simple to install and reliable

Typical applications: Heavy industrial machinery, such as boilers, fans, pumps, compressors

Rubber mounts

Provides vibration and shock protection in three different directions.

Advantages:

  • Resists grease and oil,
  • Reasonable degree of isolation efficiency.
  • Efficient, low-cost option

Typical applications: Engines and generators

Oil

Although oil can’t isolate vibration, it can absorb some of the energy, making it a damper.

Advantages:

  • Easy to use
  • Good for limited applications, when friction is a problem

Typical applications: Engines, hydraulic systems

Foam and Polyurethane

Foam breaks down easily and polyurethane has limited flexibility. Still, they have their uses.

Advantages:

  • Both isolates and dampens vibrations
  • Resistance to oil, grease, ozone, and ultraviolet (UV) light

Typical applications: Building and construction, elevators/lifts, automotive. But, it’s worth noting that isolators can always be custom made to give you the exact qualities you need.