A turbine starter company came to GMN Bearing USA looking to increase the torque capacity and life of the sprag clutch (also referred to as cam clutches, freewheel clutches, overrunning clutches, and one-way bearings) that they were using in their starters.
GMN offered a direct drop-in replacement to their existing sprag clutch that improved the overall performance of the turbine starter system in the following ways:
- Minimized system redesign
- Increased torque capacity
- Increased sprag life
- Increased system reliability
- Over torque protection
Challenges of Working With A Turbine Starter
Sprag clutches in turbine starters are relied upon to provide high torque to initiate the rotation and firing of the turbine. At times, the torque can be so high that it can cause the sprags to exceed their maximum capacity and fail.
This becomes a challenging application for the sprag clutches and can often result in sprags not living up to their required life expectancy.
Another factor to consider for the sprag clutches is the amount of time the sprags are engaged versus when the part is freewheeling. In turbine starters, the sprags spend a small fraction of their time engaged.
Once the turbines are running on their own power, the starter stops but the sprag clutches are directly connected to the turbine through the gearbox. That means that one of the surfaces the sprags are operating against is still rotating.
So, most of the time the sprag clutches are in a freewheel state experiencing wear between the sprag and the rotating surface. This can also be an issue that decreases the sprag life.
How GMN Bearing USA’s Engineers and Quality Clutches Helped
GMN recommended an FE 8000 series sprag clutch that was a drop-in replacement for what the company was using, but with several distinct features and upgrades:
Minimized System Redesign
Because it was a drop-in replacement, nothing had to be changed from the existing design to incorporate the GMN FE 8000 series sprag clutch.
Increased Torque Capacity
GMN’s FE 8000 series sprag clutches typically have more sprags than the competitors and a more complex engagement curve. Even when the same number of sprags is used, the torque capacity for GMN clutches is much higher.
On average, GMN sprag clutches have close to double the torque capacity compared to other brands. This was the case with the turbine starter company that came to GMN; our team was able to ensure a high torque capacity to increase the performance of the turbine starter application.
Increased Sprag Life
Many of the other sprag clutch brands have drag clips that keep the clutch from floating. However, these clips increase the wear against the sprag and the rotating surface.
GMN sprag clutches are designed to spin in the clutch compartment, which spreads out the wear more evenly between the outer and inner sprag surfaces, extending the sprag service life.
Increased System Reliability
For most sprag clutch brands, if the sprags don’t engage at the same point on the sprag, they don’t share the torque equally. However, due to runouts and imperfect concentricity, it is impossible for every sprag to engage at the same point.
Because of the complex engagement curve in GMN FE 8000 series sprags, they all transfer the same torque regardless of where they are on the engagement curve, improving the overall system reliability.
Over Torque Protection
As the torque applied to the sprag clutches increases, the sprags engage higher on the engagement curve. If the torque exceeds the sprag capacity, it will cause the sprag to roll over and fail, causing potential catastrophic damage to the turbine starter.
GMN sprag clutches are designed to slip under proper conditions if the torque exceeds the maximum torque capacity of the sprag. This protects the clutch and turbine starter from significant damage.
Results of our Turbine Starter Project
This company came to GMN Bearing USA in need of a solution to improve their turbine starter design.
GMN was able to use the technical expertise from their in-house engineers to provide a solution with minimal effect on the customer’s existing design.
The GMN clutches were tested and exceeded the customer’s expectations. The seamless switch to a more artfully designed GMN sprag clutch was the natural choice.
Would GMN Bearing USA’s FE 8000 sprag clutch be right for your needs? Our engineers are standing by to review your specific requirements and conduct an application evaluation.
Contact us today!