Dr Chris Carmody looks at how bearing protection technology has advanced and how operators can take advantage of it to deliver improved productivity in their plants
Plant downtime, lost production, increased plant maintenance and refurbishment costs are real concerns for reliability engineers around the world, and in today’s highly competitive environment there are huge pressures to keep equipment running.
A crucial part of preventing equipment failure is understanding why it fails and, with machinery, issues often stem from the smaller mechanical parts. A huge percentage of breakdowns are caused by bearing failure, so how can manufacturers and asset managers extend the life of their bearings to improve the reliability and lifespan of their equipment?
|Labtecta seal on a steam turbine
The reliability of most rotating equipment is almost inevitably linked directly to bearing life, and according to research, it’s estimated that bearing failure is responsible for almost 21 per cent of all equipment breakdowns. Of this number, just over half of failures can be attributed to contaminated bearing oil.
To optimize bearing life, reducing or eliminating the contamination of the bearing lubricant is a crucial first step in improving equipment reliability (MTBF) and plant efficiency. However, eliminating contamination is easier said than done, as it often stems from the enclosure breathing process – a cycle which is required by all rotating equipment.
When equipment rotates, the bearing housing heats up, expanding the oil and air mixture inside the pump, which is then forced through the seal. However, problems occur when the equipment cools, causing the oil and air mixture to suck air from the external atmosphere through the bearing seal and back into the housing, which results in moisture entering the system.
Moisture in the system leads to water contamination, which proves hugely detrimental to bearing protectors. Moisture is able to penetrate the bearing housing, destroying the bearings and causing inefficiencies. Even miniscule amounts water can significantly reduce the life span of a bearing, with research showing that water contamination as low as 0.002 per cent (20 ppm) in some oils can reduce bearing life by 48 per cent.
As well as reducing contamination, properly aligned bearings are critical to the life and health of machinery. However, misalignment is still a regular cause of bearing failure, and stems from bent shafts, out-of-square shaft shoulders and spacers. Alongside these factors, improper installation is also problematic for alignment, as it can result in loosely fitted parts, which will cause the machine to overheat, and result in unplanned plant downtime.
The challenge facing maintenance and engineering professionals is to reduce these causes of bearing failure, while providing an effective method of sealing the space between the bearing house and the drive shaft.
Historically, bearings were protected through the use of a lip seal – a design which relies on surface contact between the seal lip and the shaft to create a seal. However, with advancements being made to enhance the seal process, it has since been generally accepted that lip seals have limitations when compared to more modern technology – but sadly, they are still widely specified because they represent an inexpensive option.
The main limitation of a lip seal is the damage it causes to the shaft itself. Due to surface contact being made, the use of lip seals often results in costly damage to the shaft, which in turn, causes further downtime, expenditure and loss of productivity. A further downside to lip seals is the lack of protection given to the bearings in regards to moisture and particle ingress, which also contribute to bearing failures.
Plant managers often agree that lip seals have a relatively short service life when compared to more modern technology. Similarly, they can not be used in API applications and they don’t prevent the loss of bearing oil, which causes a gradual loss of lubrication – a problem which results in premature equipment failure.
A common alternative to lip seals are bearing protector seals (sometimes called bearing isolators), but the designs often vary significantly. Typically, some of these bridge the gap between rotating and stationary components with an O-ring or wedge ring. These components often wear or don’t effectively seal the bearing housing, and as a result, are viewed as outdated and ineffective.
Fortunately, industry recognition of the shortcomings of the available solutions has driven significant innovation. One such development is the creation of more advanced Labyrinth bearing seals. Labyrinth seals provide a winding and convoluted path to help prevent leakage of the oil which is lubricating the bearing, and can offer protection against ingress of both solids and liquids that are also non-contacting in operation. The seals are therefore capable of increasing equipment reliability in a number of systems, including pumps, electric motors and steam turbines.
An extension to the labyrinth design is the LabTecta from AESSEAL, which incorporates patented dynamic lift technology to protect against the ‘breathing’ issues that contribute to 52 per cent of all bearing failures.
This dynamic lift technology uses the centrifugal force of rotating equipment to open a temporary micro gap allowing expansion of the oil and air mixture in the bearing housing, which consequently allows the equipment to breathe. When the equipment stops rotating, the micro gap instantly closes, again forming the perfect seal. This prevents dust and moisture being sucked back in to the bearing housing, and eliminates bearing oil contamination.
The LabTecta also offers increased life span, while providing the machinery with improved efficiency. Within the first seven and a half years of the product being on sale, AESSEAL sold more than 120,000 of the range, with just 52 returns – all of which were due to issues during the installation process.
Lost production, unfulfilled customer orders and overtime are just a few of the tangible costs associated with equipment downtime. Issues with bearing seals can easily be prevented, and yet are often overlooked until it’s too late, resulting in a high equipment failure rate.
Today, the bearing technology exists to allow engineers to select the right product for the right application to improve operational efficiency and reduce downtime.
Dr Chris Carmody is Special Products Manager at AESSEAL