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Twiflex TLB Turning, Locking & Braking System for Variable Pitch Axial Fans
A leading global manufacturer was looking for ways to improve the safety on its axial fans
used at coal-fired power plants. The large electric motor-driven forced draft, induced draft, and
primary air type fans are critical to boiler air and flue gas flows in the steam generating process.
Safety concerns arise when the large fan blades need to be replaced per standard maintenance
schedules. The blades are accessible through a hatch in the horizontal fan duct. As blades
are removed the assembly becomes out of balance causing it to rotate. There is a very small
clearance between blade tip and duct, and the inertia of the assembly makes it difficult to stop
by hand once it starts to rotate. This condition presented a safety issue as workers hands could
easily get trapped within the tight space during the uncontrolled rotation.
Upon hearing about Twiflex’s new TLB (turning, locking, and braking) system, the OEM, a
longtime Twiflex customer, recognized it could be a solution to their current maintenance
challenge. The built-in flexibility of the TLB system allowed Twiflex engineers to design a custom
configuration as they worked closely with the customer to meet the specific fan application
requirements. The complete delivered system included turning control (at a very low speed of
0.05 rpm), a manual locking device and hydraulically applied brakes. The high temperature
operating environment, required some modifications to both the brakes and turning drives.
The new TLB system allows workers to inch the unbalanced assembly, in either direction,
to align a blade with the access hatch, stop and lock the shaft in position, and carry out the
necessary maintenance. The TLB features a split disc assembly, allowing it to be easily retrofitted
to the fan drive coupling without disassembling the shaft line. This was important since
the new system needed to be installed on existing fans in the field. The cost of the new system
was in line with simpler, competitor “indexing” type solutions that do not offer the same infinitely
variable positioning of the disc.
Highlights
- Custom direct hydraulic
applied, spring released
caliper brakes
- Integrated motor-driven
geared pinion
- 20 kNm continuous turning
torque at 0.23 rpm nominal
speed
- Variable speed turning
down to 0.05 rpm
- Static locking torque up to
190 kNm
- Braking torque rated at
21 kNm
- Remote or local control
- Split disc assembly allows
for easy retrofitting
- Custom hydraulic power
pack and control panel