Clean, cool and dry:  Conditions conducive to machine performance

When Ron Dennis and architect Lord Foster designed the new McLaren Technology Centre, it was designed to be technically advanced, light and cool to enhance the work experience and decision making. The result which is said to have cost around £300 million pounds is the ideal environment for man and machine! If you have not seen it have a look into the future on Utube. However there are other engineering companies, who also realise the importance of the working environment on man and machine. The Rotherham based factory of AESSeal producing pump seals is another prime example where the floors and machinery gleam and run with quiet efficiency. The result is minimal down time, high reliability, and impressed customers. This has helped the company to grow regularly at 21% per cent per annum even throughout the recession!

When SKF realised that unplanned downtime in a plant could be up to 7%, it was determined to ensure they minimised this quantifiable drain on funds, and significantly improve the bottom line. They targeted the number of failures of electric motors, with bearing failure high on the list of causes. SKF design bearings to last 50,000 hours.  That is equivalent to equipment running 5.7 years in continuous service 24/7, or with a much less demanding 8 hour day: 24 years of service. If this does not seem realistic, SKF estimate that only 9% of machine bearings achieve their L10 design life.

Not surprisingly all the destructive elements of water, dust, and heat, as well as vibration, load, speed and alignment, cause the much more familiar rapid demise of a bearing. The following data from INA FAG shows the pattern of bearing failures in motor systems in which 80% are lubricant based. The failure of the lubricants properties are primarily caused by dust, water, and heat.

Airborne dirt and hard contaminants are a major problem causing 20% of bearing failures, which is why successful engineering companies like McLaren and AESSeal go to such lengths to ensure a spotless environment. Some degree of protection is given by the lip seal and oil seals, however these only have a limited design life of 3000 hours, well below the bearing life of 50,000 hours, and can in themselves lead other problems such as shaft damage. Contaminants cause very rapid bearing failure, and better protection can be provided by fitting a labyrinth seal.  The first number of the IP rating is included on a motor’s nameplates to indicate the resistance to solids and dust i.e. IP5x is dust protected and IP6x is totally dust protected, the second number relates to protection from water.

Water is the second most destructive lubricant contaminant. At just 0.02% equal to only 200ppm (parts per million) bearing life is reduced by 48% see the graph below. It is difficult to exclude water when machinery may be operating in a naturally humid atmosphere, or wash down procedures are part of the hygiene procedures. On larger motors, pumps, and gearboxes oil analysis forms the basis of predictive and preventative maintenance, particularly as halving the water content in ppm can lead to a 50% increase in bearing life. The 2nd number of the IP rating represents protection against water ingress, as such IPx5 can withstand a water nozzle, and IPx6 water on a ship’s deck, however despite this protection, in a stop start situation the heating and cooling effect of the motor can draw in natural humidity.   

Heat is the third destructive element, lowering the viscosity of the lubricant, which in turn creates more heat, as it loses its ability to support the load. The heat can also lead to a 'varnish' residue and coking which introduces solid particles into the lubricant, and reduces the lubricants effectiveness. SKF claimed that pure uncontaminated grease and oil had a useful life of 30 years at 30°C, however its useful life is reduced by half for each 10°C rise in temperature. This highlights the importance of using the correct and best available grease for each application, with synthetic-based aluminium complex greases often paying for themselves in their longer life and reduced downtime.

Heat also speeds up the ageing of a motors insulation system. It is often quoted that for every 10°C rise in temperature, the life of the insulation is halved, and conversely every10°C drop in temperature can double the life of the insulation.  Motors are typically designed for 20,000 hours of service at an ambient temperature of 40°C, and for normal operation often use a class F varnish, which is rated at up to 155°C. These are hot temperatures, and certainly much too hot to test by touch. 

The older A type varnishes and materials were rated at only 105°C as such the motors were larger and heavier and ran much cooler. Today’s motors take advantage of the improvements in varnishes, to run much hotter in a smaller cheaper frame size for a similar design life. Energy efficient motors tend to have gone up a size using more material, so that less energy is lost in heat, and they run correspondingly cooler. 

Heat is wasted and destructive energy, if it feels much hotter than a 2kW fire then that is probably a guide to the amount of wasted energy. This could be caused by a wrong application, high ambient temperature, poor cooling (often found in thin air above 3300 feet), overloading, or misalignment.  

This is a complex area and worth calling in an expert such as an AEMT member to see whether it is drawing more current than it should, whether it is misaligned, what the resistance of the windings are, etc.  A well specified motor typically runs at 80% of its load capacity, leaving some room for additional protection.

Having stated some of the problems that damage a motor, it is a fact that they are an incredibly reliable machine. The only wearing part is the bearing, and if looked after it is surprising how many motors last 20 to 30 years without any major overhauls. Others can be relied upon to work 24 hours a day every day and when well maintained can outlast the plant they are running, and go on to a second life! As Ron Dennis has found, machines and people work better and are much more reliable and efficient in a clean, cool and dry atmosphere.

AEMT members are the largest group of companies internationally that specialize in the care of motors, pumps, and gearboxes. Most are adept at establishing whether equipment is correctly sized and have an array of condition monitoring and reconditioning skills to be able to carry out well managed equipment maintenance, and prevent unexpected downtime.  In the right environment they can ensure equipment has a long trouble free and energy efficient life. They are available internationally and many are used to working on Hazardous Area Equipment, or in confined areas. You can find the companies closest to you on the member’s maps and the services they offer at  www.aemt.co.uk.