CLUTCHES, BRAKES & COUPLINGS FEATURE THE IMPORTANCE OF ALIGNMENT
For drive couplings to be fully effective, it is essential that the right type of coupling is specified for the application, and that it is correctly installed and aligned. With a
widely accepted figure of 50% of rotating equipment failures attributed to misalignment, David Proud of Reich Drive Systems UK discusses the importance of not only selecting the right coupling but also adhering to the manufacturer’s specifications
W
hile certain coupling types are designed to accommodate some shaft misalignment or
displacement in service, they do have limitations. Failing to ensure that a coupling is properly aligned, or if it has levels of misalignment outside of the manufacturer’s specifications, will result in premature failure of the coupling and, potentially, other drive train components. The term coupling
alignment is best described as ensuring, as far as possible, a finely toleranced and common rotational centreline between the shafts that are to be coupled together. Achieving this will allow them to transmit power efficiently and operate reliably over extended periods. Misalignment – including axial, radial or, in
extreme cases, a combination of one or more alignment issues – can result in drive train problems. The reasons for this misalignment
can, however, be varied, ranging from gradual movement of machinery over time to the simple fact that the drive train was not properly aligned at the time of installation.
ALIGNING COUPLINGS Drive couplings should be installed and maintained in line with the original manufacturer’s recommendations; and a drive coupling that has been correctly fitted and aligned will pay dividends in the form of long and reliable service. Not only will
misalignment outside of the coupling’s specification cause it to wear at an accelerated rate, but there is the
potential for a negative impact on
other components such bearings which could cause them to fail prematurely. There are of course a number of different
methods of aligning a drive coupling, ranging from the use of straight edges and feeler
YAW BRAKE LIFTING TOOL HELPS TO REDUCE WIND
TURBINE MAINTENANCE TIME Maintenance of the yaw brakes used on some large wind turbines is critical to minimise operational downtime. On the average offshore wind turbine, however, a brake change results in up to three days of downtime – with five or more calipers being changed. During the process, all the calipers are removed and then winched to the yaw section floor for assessment. Pads are changed and each completed caliper, which weighs around 200kg, is then winched back to the top of the turbine for reinstallation. To minimise downtime and protect crew against fatigue, service providers
are developing new methods to improve the efficiency of yaw brake maintenance. One method is to carry out the maintenance process in-situ using Svendborg Brakes’ LBS Yaw Brake Lifting Tool. This attaches to the brake disc, allowing the brake to be slid out of its mounting position and winched to the yaw section floor, out and away from the disc, with minimal effort by a two person service team. Once the brake pads have been replaced and the caliper assessed on-site, it can then be winched back into place and reinstalled via the tool. The system has been tested
iStock – ssuaphoto Image Source:
in both onshore and offshore windfarms. In one case an operator required yaw brake
gauges right through to sophisticated laser alignment systems. Many laser shaft alignment systems utilise software that can calculate accurate values for any adjustments that need to be carried out to achieve perfect alignment.
THE BENEFITS OF FLEXIBLE COUPLINGS In some cases, however, it is not possible to achieve perfect shaft alignment, so the choice may be to select a flexible coupling such as Reich’s MULTI MONT SELLA (pictured). With the capability to compensate for axial, radial and angular misalignments, as well as absorb shocks and vibrations, these couplings can help to mitigate the effects of alignment errors and vibration. These pluggable claw couplings have been field proven over a number of decades. Of further benefit, the couplings offer ease
of assembly and alignment, maintenance free design, and the capability to change the flexible elements radially, without the need to de-couple the drive train elements.
Reich Drive Systems UK
www.reich-uk.com
replacement across hundreds of offshore turbines but wanted to minimise the effects of downtime across the site. Using the LBS Yaw Brake Lifting Tool, downtime was cut by 50% and maintenance work was carried out with increased efficiency. Beyond brake pad
replacement, damage to the actual brake disc is another issue which can lead to significant expense and long periods of downtime. Typically, the average turbine brake disc could measure 2.5m wide and 40mm thick. Consequently, the nacelle and blades must be removed completely to replace the disc, a process that could cost up to €800,000 depending on the location. One operator required brake resurfacing, but wanted the reinstallation
Svendborg Brakes’ LBS Yaw Brake Lifting tool
of all brake components on turbines at the end of each day. So, the LBS Yaw Brake Lifting Tool was used, first to remove two brakes, then a CNC controlled Disc Resurfacing Tool designed and built by Svendborg Brakes was winched into place and attached to the bedframe. With the brakes removed, the resurfacing tool machined the disc back to the optimum condition without nacelle removal. Brake resurfacing was finished in a day at less than 50% of the usual costs. Furthermore, the process was efficient enough to have all brake components reinstalled for the evening, allowing power generation at night.
Altra Industrial Motion
www.altramotion.com
DESIGN SOLUTIONS | OCTOBER 2019 49
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