C-Flex Bearings FAQ's | C-Flex Bearing Co., Inc.
What is a pivot bearing?
C-Flex bearings have a special internal structure of flat springs that allows them to pivot about their center axis a limited amount in each direction, as opposed to say, a ball bearing, which can rotate full revolutions.
What is the difference between the double and single end bearings?
The main differences are mounting preference, load capacity, and stiffness. Single end (cantilever) bearings are generally simpler to install but double end bearings of the same size have higher load capacities and are stiffer.
What makes it move?
The bearing itself does not add any energy into a mechanical system, it must be driven by an external force such as an electronic actuator. However, because the bearing’s internal structure is spring based, it can store energy in the form of being twisted, and then release the energy when allowed to rotate freely. When a torsional load is applied and released in a free system the free end of the bearing will oscillate about its neutral position.
How are the bearings frictionless?
In a normal bearing such as a ball bearing there are components that rub or roll against each other while being covered with a lubricant. This surface contact and fluid displacement creates resistance that drains energy from a system and generates waste heat. Since the C-Flex bearing has no contacting parts and no lubrication there is no energy loss due to friction. This allows for an extremely predictable rotation movement in response to the external force. They do require continuous energy to rotate to a certain position and hold it because of their natural self centering ability.
Why are there three series bearings (10, 20, 30)?
The 10 series bearings have the thinnest flexures, which allow the greatest angle of rotation (+/-15 degrees), however are restricted to relatively light loads. The 20 series has heavier flexures and can support heavier loads, however at smaller angles of rotation (+/- 7.5 degrees). The 30 series has the heaviest standard flexures and can support the largest loads, however at the smallest rotation angles (+/-3.7 degrees). Your particular application will determine which series is best to use.
Can I get a bearing which has a greater angular rotation (>15 degrees)?
Large loads and high angles of rotation are mutually exclusive properties, however in some cases C-Flex can provide bearings which will operate at greater than +/- 15 degrees for applications with very light loads. All C-Flex bearings are also capable of rotating up to twice of their rated rotation without damage but with larger hysteresis and reductions in life expectancy.
Do the bearings have a maximum pivoting speed?
In a free oscillation system the pivoting frequency will be a function of the torsional spring rate and the mass/geometry of the system. In a driven system, the bearing will move at whatever speed it is driven. Every bearing has in inherent natural frequency and driving the bearing faster than this frequency can cause waves to form in the springs which can adversely affect performance. The natural frequency for most bearings is extremely high so this is rarely an issue.
Can the bearing be used to conduct electricity?
In limited cases, yes. The bearings, being all stainless steel, do conduct electricity with a fairly low resistance making them useful for flexible connections or grounding. However, they should not be used to conduct large amounts of power and C-Flex makes no assurance of their use as a conductor.
What types of customization can C-Flex provide?
The bearings can be customized by C-Flex in almost any way. In addition to greater stiffness or higher angles of rotation, C-Flex can provide extended length or shorter bearings, special diameters, custom TSR, and very large capacity (5000 lbs plus).
What do the bearings weigh?
Please see the C-Flex Bearing Weight Chart.
Do you have a price list?
Please contact us for pricing at 315-895-7454 or cflex@c-flex.com
What can cause a bearing to fail?
Basically the only way to destroy a C-Flex bearing is to operate it beyond its specified limits. Excessive loading can cause flexures to buckle when placed in compression, or braze joints to fail if in tension. Flexures can fracture if placed under excessive loads during constant rotation. Flexures can also fatigue and fail if operated at angles higher than recommended for extended cycles.
What is the operating temperature of the bearing?
Between -100 deg. F to 375 deg. F for continuous operation using standard bearings. The bearing can be held or thermally cycled up to 450 deg. however for no more than 8 cumulative hours otherwise damage may occur. Custom bearings made out of titanium or inconel have a wider temperature range which depends on their assembly method.
How does the bearing react to temperature changes?
Uniform expansion and contraction will occur without a change in rotational axis or position. Changes to other specifications such as load capacity and stiffness are negligible over the stated operating range.
How resistant to corrosion is the bearing?
The high strength stainless steel is 400 series stainless and will corrode under certain conditions. 400 series stainless steel corrodes easier than the 300 series people generally think of when hearing “stainless steel” but is still much more corrosion resistant than normal steel. Short term exposure to moisture will leave a harmless tarnish. Long term exposure to moisture or continuous submersion is not recommended. We try to protect against this in storage and shipping using rust preventative and desiccants to provide the best overall quality part that will ultimately arrive at our customers’ facility. For applications that don’t involve extreme precision, a rust preventing oil can be applied to the bearing with no noticeable effect on performance. If a corrosive environment is expected then other materials such as titanium or inconel can potentially be used.
Can the bearing be used in a vacuum?
Yes, the bearing itself is not effected in any way by being in a vacuum. If outgassing is a concern then alternative braze materials can be used that will not contaminate a clean vacuum.
What is the load rating?
The load rating is the maximum load Lc or Lt which is recommended for extended cycle life. Lc is the direction of radial load which places the flexures in compression and Lt places them in tension.
Why are Lc and Lt different?
Thinner flexures (10 and 20 series) can experience buckling under large compressive loads, however they do not experience this problem in tension. Thicker flexures (30 series) are not prone to buckling and so Lc equals Lt for them.
Is load capacity the same for single and double end?
No, because cantilever bearings are inherently supporting the load from only one end they experience more internal stress for a given load than double ended bearings which support the load more evenly.
What is the Yield Load?
Yield strength is the stress at which the spring material stretches to the point of permanent deformation but without breaking. At zero degrees rotation, the Yield Load for both Lt and Lc can be considered to be 1.5 times the load capacities listed in the catalog. A bearing that experiences a force larger than the yield load should be replaced.
What is the Ultimate Load?
The ultimate load is the force required to actually cause a material failure. The Ultimate Load for Lt and Lc can be considered to be 2 times the catalog listed values.
What is the shock load capacity?
The load ratings published for the bearing are operating loads needed to determine life expectancy. Shock loads of 1.5 times the published load ratings can be experienced by the bearings without damage, as long as the bearing is in the undeflected (null) position.
What is a moment load?
When a load is applied in an offset manner, it creates a moment load or rotational force through the bearing center determined by the force and the distance from the center of the bearing where it is being applied. This moment load multiplies the stress that the bearing experiences. A simple example is to imagine a bucket of water, which can easily be carried when your arm is hanging straight down. However if that same bucket was at one end of a level broomstick, and you held the other end with one hand, it would take superhuman strength to carry the bucket. The longer the stick (moment) the more strength is required.
Can the C-Flex bearing support a moment load?
The C-Flex specifications are for loads applied at the OD of the bearing, directly through the center-line of the bearing. Because moment loading multiplies the stress on the bearing, the load capacities must be de-rated when the load is offset from the bearing center, often severely. To compensate for this situation, the customer has 4 options:
- Choose a larger bearing with heavier load capacity.
- Reduce the load.
- Reduce the moment load through better alignment or reduced offset from center.
- Use two bearings to support the load from either side.
How do I determine how much moment loading a bearing can handle?
Moment loading creates strong and complex stresses within the bearing which are difficult to express as load diagrams. If the force and offset distance are known C-Flex can provide a recommendation for which bearing to use.
Does the bearing dampen vibration?
The bearing does NOT stop vibration transfer.
Why is determining Load important?
Loads on the bearing creates stress in the flexures, which along with the bending stress created during rotation, must be considered in determining the life expectancy of the bearing. As the load increases, the angle of rotation must be decreased to maintain indefinite cycle life. Please consult the life cycle curves for each series bearing (10, 20, 30) to determine allowed angle of rotation with expected load values.
Will vibrations damage the bearing?
Vibrations in the general sense do not damage the bearing, however care must be taken that momentum/inertia effects from vibration combined with other loads do not exceed the load capacity of the bearing.
How does the torsional spring rate (TSR) value work?
The torsional spring rate (TSR) is the amount of torque required to twist the bearing 1 degree. For example, a force moment of 0.9486 lb-in applied to one end of a J-20 bearing will cause it to rotate 1 degree about its axis of rotation.
Is the TSR the same for both single and double end bearings?
Yes
Can I get a bearing which has greater radial or torsional stiffness than the standard parts listed?
C-Flex can usually satisfy customer requirements by utilizing heavier flexures, heavier core structure, or even paired flexures for larger sizes.
How accurately can you specify torsional spring rates?
Due to manufacturing and material variables, our flexure bearings are produced with an advertised TSR range of +/- 10%. We can however measure the exact TSR (within < +/-1%) of each bearing. There is a slight cost added for this service.
Is the torque required to cause rotation linear?
The bearing is linear on an x- y chart where y = torque and x = angle of deflection. The torsional spring rate in either direction over the range of travel is a constant.
Spring rate when zero load is applied - is this represented by the torsional spring rate in the catalog?
The catalog value of TSR is determined at zero load.
Is there a graph showing spring return rate, natural frequency, or delay in acceleration/deceleration?
TSR is how the bearing acts with zero load. As mass increases, so does the moment of inertia and relative energy needed to accelerate it. This effect would have to be determined by calculation, FEA analysis, or experimentation.
Understanding radial and axial stiffness note in brochure... the note indicates that the radial stiffness (Lc,Lt) in in/lb for single pivots are to be divided by 2 (this double the stiffness) for the double ended bearings. Is this true? Assuming that the axial stiffness is the same for both single and double end?
The double end pivots have a greater radial stiffness due to their typical mounting where each end is rigidly fixed, thereby avoiding the cantilevered load and moment load affects seen by the single end bearing. The axial stiffness for both single and double is the same.
What is geometric centershift?
When the C-Flex bearings are rotated, they exhibit geometric centershift. It is a radial movement of the bearing segments relative to each other as they rotate. Assuming one end is restrained and the other is rotated, the axis of the rotated member moves radially although remains parallel to the original axis. This is predictable and is dependent upon the diameter of the bearing and amount of rotation. See chart on performance characteristics.
Is geometric centershift the same for double end and single end bearings?
Yes, Geometric centershift is the same for both single and double end.
Does the bearing series (10, 20, 30) affect centershift?
No, Centershift is a property of the bearing diameter and rotation angle only. A G-10 and a G-30 each rotated 2 degrees will have the same centershift.
How large is the centershift?
The centershift is basically an exponential relationship which is largely unmeasureable at small angles and diameters, yet progresses to relatively large proportions at large angles of deflection of large bearings.
How is centershift calculated?
Calculate centershift using the downloadable chart from our .pdf Technical Brochure.
Example 1: A J bearing (1.0″ diameter) rotated 5 degrees. From the chart on the x-axis a 5 degree deflection results in a geometric centershift of 0.08 (as a % of bearing diameter). Therefore, centershift would be 0.08/100 x 1.0″ = 0.0008″
Example 2: For a 3/8 diameter bearing, rotated +3degrees, using the chart at 3 degrees the geometric movement of center is 0.035% of bearing diameter. 0.375 x .00035 = 0.00013″.
Is there a difference in life expectancy for single vs. double end bearings?
No, they have the same life expectancy when operating at the same % of max load and angle.
How long is indefinite life?
Indefinite life is defined as the point where the flexure material’s S-N curve levels out. Minimum life expectancy is 30 million cycles when the load and angle point is below the indefinite life curve on the life expectancy curves.
If rotated greater than the max angle, say 25 degrees for a 10-series, but only in one direction from zero deflection, and the radial loads are low, what would be the cycle life?
Since the bending stress is non-reversing (0-25 deg.), a modified version of the life expectancy charts is used. The life expectancy in this case should be 500,000 to 1 million cycles.
Is there any life test data to determine the statistical distribution of the infinite fatigue line?
After life testing many single and double end bearings, we have never had a failure at the bearings rated angle (e.g 20 series = +/- 7.5 deg) of rotation when tested to ten million +/- oscillations. Also, we have never had a failure below 220,000 cycles when testing to 150% of the rated angle, nor below 35,000 cycles when tested to 200% of the rated angle. This is a result of a 25% de-rating from their actual max. to provide an adequate margin of safety. We can provide a quotation for life cycle testing to specific rotation angles if necessary. (Standard bearings).
What is the best way of mounting the bearings?
The preferred method is by set screw making sure the load is centered between two springs and NOT bearing down through one spring.
Can locator flats be added to the bearing?
C-Flex will put locator flats on the bearings at a small additional charge for sizes B and larger. It is not absolutely necessary to utilize bearings with flats, as the set screw can impinge directly on the OD, as long as it is in the heavy or solid section of the outer sleeve.
What is the recommended tightening torque?
See page: Set-Screw Size & Tightening Torques.
What size set screw should I use?
See page: Set-Screw Size & Tightening Torques.
Can I use adhesive/epoxy?
If using EPOXY, apply through a perpendicular hole, taking care not to allow the adhesive to migrate into the bearing structure where it will impede performance. Some customers utilize low viscosity adhesives which can wick into the bearing/linkage interface before setting.
Can I press fit the bearing?
Press fitting is NOT recommended (ESPECIALLY FOR THE -10 series BEARING) although feasible as long as the maximum axial load rating is not exceeded during the pressing process (see chart for bearing properties). Consider SHRINK FIT as an alternative: cool the bearing to -100 deg. F (liquid nitrogen or dry ice) and heat the mating part to allow the shrink fit upon temperature normalization.
When using a double end bearing, should the mid section be supported?
The normal method for utilizing the double end bearing is either to mount the two ends rigidly, and allow the center section to rotate, or vice verse. The two ends are rigidly connected to each other, and rotate independently of the center section. The bearing cannot rotate if any portion of the center section is rigidly clamped ALONG WITH the outer section.
