Many companies operating high-capacity production plants utilize cooling towers with large heat-rejection capacities, such as those in the power and chemical sectors. The respective plants typically use cooling towers to keep on top of the heat load, which can be extreme.
Given the intense temperatures, these cooling towers have large fans and motors – but those components can lead to worksite challenges, from excessive sound and vibration to continuous maintenance and difficult repairs.
That’s where cooling tower gearboxes come in; these critical pieces address several challenges within the towers. An AC motor powers the gearbox, driving the huge rotating fan blades that cool the industrial plant’s water. Essentially, these cooling tower gearboxes serve as speed reducers, slowing the rotational speed from the incoming motor to the outgoing cooling tower’s outgoing fan.
However, gearbox maintenance is almost a full-time job; these elements work under immense pressure and variable load conditions, subjecting them to excessive, prolonged stress that can lead to degradation. Of course, problems arising from wear and tear result in poor performance and, eventually, system failure.
What does a failed system do? Impact productivity, budget, and, more seriously, safety. As such, preventative measures to minimize gearbox degradation and mitigate the risk of failure are vital. With that in mind, it is paramount to look into the causes of gearbox degradation and failure – and how to prevent them.
What are the main causes of cooling tower gearbox failure?
Many factors can lead to vibration: misaligned drive shafts, wear or excessive loading, and imbalance. In time, too much vibration can lead to plastic yielding, shaft deflection, falling and scaling, and tooth fracture.
High operating temperatures and humidity
Extreme temperature and humidity inside the cooling tower can degrade mechanical systems, impacting sound levels as well as reducing gear set life spans.
Further issues include shorter cycles of operation and even premature cooling tower gearbox failure and unplanned downtime.
Improper cooling tower inspection and maintenance
Regular, scheduled inspection and maintenance of cooling towers are essential. Without proper inspection and maintenance, system failures can happen – not to mention the incubation and spread of infectious diseases, such as Legionella.
Lack of gearbox options
In some parts of the world, a lack of gearbox options and availability for professional maintenance and replacement of parts and components poses a problem, leading some plant owners to “make do” – much to their peril.
However, custom gear manufacturing is an excellent solution – both for companies with limited options and those located in regions where gearbox ranges and components are aplenty.
Improper lubrication and insufficient lubrication schedules are common reasons for cooling tower gearbox failure. Lack of or irregular lubrication may lead to oil film breakdown and shaft seal leaks, as can the presence of foreign materials in the lubricant – another frequent issue.
An inadequately lubricated gearbox can suffer from scaling and galling failures and extremely high temperatures, potentially resulting in tooth surface damage, excessive wearing of the pinion shaft, gear and bearing losses, and compressor drive failures.
The elements can also lead to bearing corrosion and gear tooth fracture, dramatically reducing the effectiveness and lifespan of gearboxes. In particular, humidity, dust, and dirt are major players, throwing spanners into the mix.
Cooling towers and gearboxes are overly vulnerable to environmental damage, as they’re difficult to reach, frequently resulting in inadequate inspection and maintenance.
How to prevent cooling tower gearbox failure
Although cooling tower gearboxes are meticulous components with a track record of vulnerability and an easily worn-down nature, it’s possible to reduce the likelihood of problems, boost their lifespan, and enhance their effectiveness.
Thankfully, due to innovations and product development, engineers have devised solutions to address some of the most common gearbox operational issues that plant managers and maintenance engineers often face.
Of course, routine inspection and maintenance are a given (and remote monitoring can help keep systems in check and spot issues from afar) – but what other, more specific aspects need addressing when it comes to gearboxes?
Conduct vibration analyses
Undertaking a periodically scheduled vibration analysis can predict and diagnose potential problems. This type of assessment utilizes a low-frequency accelerometer and two monitors that can detect gear mesh frequencies, bearing defect frequencies, and blade passage.
A professional analyst then evaluates the data to identify any undesirable mechanical forces stirring up issues in the cooling tower gearbox – problems that might turn into a system failure.
Control high operating temperatures and humidity
Choosing a gear drive with integral cooling fans designed into the housing can help control excessive temperatures. Instead of a conventional smooth casting, cooling fins increase surface area, thus amping up heat rejection as the cooling tower fan pulls air over the gearbox.
In addition, steel shims at case-connection points can help reduce the heat and humidity to which cooling towers are subjected. Plastic shims can creep over time when exposed to the tower’s high temperature and humidity conditions, leading to tolerance changes that can impact the sound and lifespan of the gear sets. In contrast, steel shims are much better at maintaining gear settings and controlling gear sound – even under the stresses of cooling tower operating conditions.
Furthermore, selecting a gearbox with large internal oil ports is ideal since it assists oil circulation, improving overall operating temperatures. Oil also lasts longer, meaning oil changes are less frequently required, and gears and bearings remain well-lubricated, which boosts performance and gearbox life.
Schedule period lubrication and oil analyses
Leading on from lubrication and oil, periodically scheduled lubrication and oil analysis is crucial to maintain gearboxes and towers. Lubrication also requires the right lubricant for the job, as well as the ideal method of application.
Ideally, a cooling tower maintenance specialist is the best person for the task; they can determine the exact lubricant and method best for the equipment and setup in question. A professional technician can also conduct an oil analysis, revealing any concentrations of particulate matter that could pose problems down the line.
Dampen sound levels
It’s impossible to eliminate vibration and sound levels coming from gearboxes. However, dampening them is a possibility. In particular, metal castings are excellent for reducing noise levels, as can thicker castings. Selecting a gearbox specifically engineered to reduce the case deflection associated with the torque and thrust loads of cooling tower operation is best advised.
Ultimately, such gearboxes with thicker castings that have been created for cooling tower service can lead to reduced metal wear-and-tear, a longer service life, and a quieter and safer work environment.
Prevent premature bearing failures
Heavy-duty, double-row interstage bearings can help ward off premature bearing failure and excessive wearing of the pinion shaft.
Opting for a premium-grade isolator-type bearing oil seal equipped with a fixed stator sealing surface for shaft wear prevention is also advised – instead of a lip-type seal that wears against the pinion shaft. Inpro seal-bearing isolators may also prolong seal life without causing excessive shaft wear.
Repair issues quickly
Never ignore a problem – and never “just” patch it up. Putting off repairs and masking problems is extremely unsafe and can result in a costly total system failure, leading to lost productivity and high costs for more extensive repairs, expedited part orders, and expensive emergency service procedures.
There’s no way around it; all mechanical equipment demands repair – it’s only a matter of time. However, planning repairs and fixing issues quickly saves time, money, and hassle and keeps productivity – and business – constant with minimal loss and disruption, the latter for which your customers will be grateful, too.
Industrial plant operators and engineers must manage various cooling tower issues – via scheduled and unplanned maintenance, monitoring, inspection, and repairs. Long-term solutions to common pain-points facilities and simplifies routine maintenance and repairs, as well as uphold safety and a minimally disrupted service, boosting productivity as a knock-on effect.
As cooling tower gearboxes are an important cog in the works, ensuring they’re properly cared for, inspected, maintained, and acquired from reliable suppliers is crucial. Quality, properly serviced gearboxes help ensure consistent plant operation and productivity and a methodical approach to solving problems that may arise.