THE COBWEB BEARING
THE MOST PRECISE FUNCTIONING HIGH-SPEED BEARING IN THE WORLD
Solving the Cage Instability problem was just a beginning in our innovation path. Based on our unique ability to model and compute the kinematics of the balls, we have also engineered the COBWEB Bearing.
A NEW PREMIUM TYPE OF HIGH-SPEED BEARING
Initially designed for high speed ball bearings applications, the COBWEB bearing is an innovation that offers the most accurate and precise functioning in the world so far. A real breakthrough in the bearings world.
The COBWEB BEARING is particularly suitable for high speed applications, or those that require a more precise and smooth functioning, even in extreme conditions of combination of loads and/or speed.
For decades, designers of mechanisms were forced to accept unsatisfactory compromises to deal with hard conditions of operations, with consequences in terms of noise, vibrations, excessive heat, cage breaking or bearing malfunctioning.
The COBWEB BEARING improves bearing performance in any condition with the most precise, harmonious and smoothest functioning ever.
The COBWEB BEARING is designed to support the highest speeds while ensuring optimum operation at all intermediate speeds.
This definitely opens up the perspectives of designers of mechanical applications such as:
spatial mechanisms (RWA, turbopumps, …)
medical systems & dental milling machines
As incredible as it may seem, the COBWEB BEARING constitutes a new premium category in the types of bearings by improving the bearing performances in any condition. Yes, we have engineered the bearing that has the most accurate, harmonious and smoothest functioning ever.
The COBWEB BEARING is available for licensing.
ELEMENTS OF HIGH SPEED BALL BEARING PHYSICS
WHAT CAUSES BEARING DEFECT?
The commonly used approach, which consists in selecting a bearing from a catalog based on the sizing on the one hand, and on the maximum load at high speed on the other, clearly has its limits. Because this “off-the-shelf” approach is essentially focused on fatigue in connection with the lifespan of the bearing.
However, fatigue and lifespan are not always the determining factors in the choice of high speed bearings like those used in a cryo-turbopump for example. Neither were any satellite bearing broken due to spalling damage or fatigue. It is the very functioning of the bearing that is the cause of failure. And the « catalog » approach will not provide information on the behavior of the bearing itself.
The proper functioning of a bearing does not only depend on its ability to withstand fatigue (which is directly linked to the maximum contact pressure), it also depends on its ability to limit heat dissipation, to prevent thermal instability, and to ensure a proper behavior of its cage.
Bearing failure depends on:
the pressure of the balls on the rings
the heat dissipation (which may lead to race overheating or bearing seizure)
the possible cage rupture (due to high-speed centrifugal forces, cage instability and Ball Speed Variation phenomenon).
A high-speed bearing must therefore be able to take up heavy loads, but it also has to dissipate heat optimally and preserve the durability of the cage.
WHAT REALLY HAPPENS IN A BEARING SUBJECTED TO HIGH SPEED
The radial clearance, essential for the operation of the bearing, induces a ball/ring contact angle. This contact angle is chosen according to the axial load to be taken into account.
Even at low speeds, the contact angle involves also a pivoting component at each ball/race contact, (in addition to the rolling component) which induces a friction torque and thus heat dissipation. When the speed increases in a conventional bearing, even if the inner ball/ring contact pressure is lower than the outer ball/ring contact pressure, the inner ball/ring contact produces more heat (up to 10 times!) due to the increased contact angle.
As stated here above, the operation of a bearing not only depends on its ability to support high contact pressure, it also depends on its ability to limit heat dissipation.
Therefore, when the speed increases:
it is the outer ring that suffers more and more, under the effect of inertia
the inner ring will be less charged but will tend to dissipate more.
And the situation becomes even worse when the rings get misaligned (due to a parasitic torque and/or a combination of axial and radial loads). In that case, balls are put in an asymmetric configuration around the bearing axis : the contact angles vary from ball to ball. This leads to a great amount of Ball Speed Variation, which is responsible of cage failure and high vibration level.
AVOIDING UNSATISFACTORY COMPROMISE
Engineers have three options to improve the performance of the high-speed bearing
Using a lower density ball material
Decreasing the size of the balls, but this will definitely limit the acceptable loads
Improving the design
It is precisely on the optimization of the design that the COBWEB BEARING stands out.
It allows a natural adaptation of the contacts to the operating conditions and an optimal balance between the effects of pressure and heat losses. It thus preserves service life while increasing energy efficiency, without having to make difficult compromises.
IMPROVING BEARING PERFORMANCE IN ANY CONDITION
The COBWEB innovation/breakthrough makes it possible to smooth the movement of the balls (and thus the bearing), resulting in less friction, less heat dissipation, less vibrations, for better operation and lifespan. The best functioning bearing ever.
Above all, using a COBWEB BEARING avoids choosing an optimal operating point. The COBWEB BEARING is indeed designed to support the highest speeds while ensuring optimum operation at all intermediates speeds.
The cage of the COBWEB BEARING is moreover perfectly preserved.
Compared to a conventional bearing, axially loaded, and when the speed increases:
Between 20% and 40% reduction in dissipated power by friction
Drastic reduction of the gap between internal and external contact angles
Smoothing of contact angles -> less power dissipation, less friction, less vibration
Smaller difference between power dissipated at internal and external contacts -> lower thermal gradient between rings -> reduced risk of bearing seizure
Natural balancing of internal and external contact pressures -> lifespan preservation while increasing energy efficiency
Decrease of several hundred % in the Ball Speed Variation phenomenon, balls acceleration and deceleration movement divided by 3 -> cage preservation and less vibration
PERFORMANCE COMPARISON FOR A BEARING ROTATING AT HIGH SPEED
with misalignment (19 balls bearing here)
LOW SPEED HIGH SPEED
HOW WE CREATED IT
In the same way we developed the BUTTERFLY CAGE, which solves the cage instability problem, we used an approach based on our deep understanding of the kinematics of balls to develop the COBWEB BEARING.
More particularly, we used the innovative characterization method based on a power criterion, and our original related computational tool, Rose, to achieve the bearing equilibrium (no matter the working conditions the bearing endures), and then confidently model the COBWEB BEARING.
We did not use common finite element design methods, or other existing tools relying on Newtonian formalism based on the equilibrium of forces and moments.
Our unique ability to understand the kinematics and to model was key.
HOW TO DESIGN A COBWEB BEARING?
The COBWEB BEARING has a very particular and unique internal geometry, whose parameters are calculated with a dedicated computational tool developed by APO-GEE, depending on the operating conditions.
When faced with a complex or very demanding application, a custom approach will be often preferred, on a case-by case basis. The key questions are to determine what is tolerable and what is not, as well as defining the bearing functionings we want to favor.
The combination of understanding of bearing physics, knowledge of the key geometry, and original parameterization tool, allows us to define the best COBWEB BEARING whatever the application.