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Why NORGLIDE® Bearings and bushings?
Every bearing comes with intelligence built in.
We scrutinise a product’s end use to create a customized, high performance bearing solution. By working in collaboration with our customers, we can deliver engineered component solutions based on the challenges they face. The result is a tailored bearing solution with exact specification of mating metal backing, PTFE compound, material structure, shape and geometries.
The wide range of different materials and unique combinations is an unbeatable advantage, the thick PTFE sliding layer (~0.25mm) offers a number of benefits such as damping rattle caused by bearing play, should the shaft be pressed lightly into the sliding bearing or in the event of misalignment, the friction coefficient remains low. With the addition of a metal interlayer, the load carrying capacity of NORGLIDE® can be increased. A metal interlayer or a soft metal choice for the metal backing will allow the sliding bearing to be calibrated (plastically deformed) during assembly to compensate for manufacturing tolerances. This represents just some of the reasons why NORGLIDE® offers superior performance. Here we further explore the benefits of the versatile NORGLIDE® Bearing and the key advantages that can be delivered:
- Load capability
- Wear & friction
- Tolerance compensation
- Corrosion resistance
- Noise & Vibration
- Misalignment
Load Capability
Materials such as NORGLIDE® PRO & NORGLIDE® SMTL are designed with a higher load capability than other plain PTFE-Bearings or plastic bushings. This feature enables smaller bearings to be created allowing smaller mating components to be used. The result is an application that takes up less space, weighs less and has reduced overall cost. NORGLIDE® Bearings can also be used as ball bearing replacements, providing a reduction in component weight and space.
Wear & Friction
The coefficient of friction of a composite material is not a constant. It is determined by the materials of the mating contact surfaces and by the roughness.
Friction
With combinations that have very different strength values (such as polymer with steel) the coefficient of friction also depends on the load. In addition, due to the polymer’s strong tendency to change all mechanical properties under temperature, the coefficient of friction is also affected by speed and ambient temperature.
Graphs A-C show the influence in the coefficient of friction (COF) of PTFE on steel (100 Cr6 1.3505).
Graph A demonstrates the influence of temperature in the COF. The COF drops as temperature increases.
Graph B demonstrates the impact of speed in the COF. The COF increases as speed increases.
Graph C demonstrates the influence of load in the COF. The COF drops as load increases.
During the wear-in period, a polymer transfer layer forms on the metal contact surface. After this, a consistent performance range is found which is controlled by the PTFE compound layer.
Constant friction
Generally speaking, the coefficient of friction of NORGLIDE® materials is outstandingly low and consistent in comparison with other plain bearings, due to the use of PTFE as the main component in the bearing surface.
Tolerance Compensation
A mark of quality in any product is the ability to perform consistently from part to part. This is how a company can build a brand by having a consistent and smooth feel when parts are actuated. Often, this can lead to a difficult decision: consistent performance can be guaranteed through precision manufacturing but this comes at a significantly increased cost.
With NORGLIDE® Bearings, Saint-Gobain offers a solution to this dilemma due to the forgiving configuration of the low friction PTFE layer. This layer is able to absorb tolerance stack ups and perform consistently for a wide range of customer part tolerances, resulting in less total cost for our customers without the need to compromise on performance.
Two major considerations of performance throughout a tolerance range are assembly force and torque. If the parts are made with too much interference due to a tolerance stack-up, then both the assembly force of the shaft into the housing-mounted bearing and the torque to turn the shaft within the bearing can become too high. Not only this but the force and torque will be quite different compared to that of the same system but in the opposite tolerance extreme, i.e. very low interference or even clearance.
Figure 1 shows the assembly, or press in, forces of a shaft into a housing-mounted bearing for five different sizes of pin, simulating a tolerance range of 200 µm. As can be seen the NORGLIDE® solutions are significantly superior in maintaining a consistent assembly force for the different pin sizes. Two of the competing PTFE-based solutions failed as the pin (shaft) diameter was increased as the assembly forces became too high.
The torque was also tested for different pin sizes. The torque is generated purely from the radial surface of the bearing. Torque can also be generated by applying an axial force to the flange. The results can be seen in Figure 2. A similar result as the assembly test is obtained, as expected. This shows a consistent performance of the NORGLIDE® Bearings throughout the 200 µm range whilst the alternative PTFE-based solutions increased significantly. Obviously if the pin couldn’t be assembled in the press-in force test for high interference, then they could not be tested for torque either.
Figure 1. failed after 0.10 mm and 0.15 mm interference
The press in forces of pins of varying diameters into the bearing mounted in a housing. NORGLIDE® Bearings perform consistently throughout the pin dimension range whereas the competing solutions press in forces increase significantly for higher diameter pins. Competing solutions 1 and 3 both fractured at 10.10 mm and 10.15 mm respectively. Test conditions: housing and pin are dummy components made out of hardened steel; the assembly speed is 1 mm/s.
Figure 2. failed after 0.10 mm and 0.15 mm interference
The torque generated by the radial surface of the bearings for a range of pin diameters. The NORGLIDE® solutions offer consistently low torque when compared to the competing solutions. Competing solutions 1 and 3 could not be tested at higher pin diameters because they fractured during assembly. The housing and the pin are dummy components made out of hardened steel. Test conditions: housing and pin are dummy components made out of hardened steel; sliding speed = 45°/s; axial load = 0 N; test stroke = 90°; cycles = 5.
Some systems are controlled by electric motors which require software to run. In these applications, consistent performance will decrease the complexity of the software. One input parameter for the software will be the speed of actuation. If the bearing’s torque changes too much for different speeds, then calculating the right amount of input power to the motor can become a difficult task. Therefore, it gives confidence to our customers to know that we test our bearings with such detail that sliding speed is considered, especially as PTFE performance is sensitive to speed and pressure. Figure 3 presents the change in torque for three different angular speeds, 45°/s, 90°/s and 135°/s. The stability of torque over the three speeds is significantly better than all but one of the competing solutions. This allows confidence for our customers that not only will their systems have a consistent feel but also that the software doesn’t have to become needlessly complex.
Figure 3 – left: torque generated by the plain bearings for three different speeds (45°/s, 90°/s and 135°/s). This test highlights the choice in torque level our customers have by choice of bearing. Right: the same test as the left graph but plotted as a change in torque between the 3 data points per material (Δ torque) to highlight the consistency of the bearings when the speed changes. NORGLIDE® Bearings perform consistently when compared with all but one of the alternative PTFE-based bearings. Test conditions: housing and pin are dummy components made out of hardened steel; pin size = 10.05 mm; axial load = 0 N; test stroke = 90°; cycles = 5.
The impressive tolerance compensation qualities exhibited by NORGLIDE® Bearings are achieved due to the unique composition of the products. The PTFE layer seen in Figure 4 has the ability to absorb tolerance stack-ups of mating components. The low friction layer also has the benefit of reducing the impact of wear on the performance throughout the lifetime of the system.
Figure 4– The PTFE layer on the NORGLIDE® solutions has a unique structure which allows greater compensation of tolerance and more consistent performance over time than sintered bronze plain bearings.
Corrosion Resistance
When assemblies, including bearings are exposed to external environmental factors such as dirt, the weather and changes in temperature corrosion resistance becomes a high priority. The materials used in both the assembly and bearing need to work together to help reduce and even prevent galvanic corrosion. NORGLIDE® plain bearings with their modular design allow the metal backing and the PTFE sliding layer to be matched exactly to requirements. As a result, NORGLIDE® Bearings offer premium corrosion protection with over 1000 hours without red rust in the salt spray test.
Noise & Vibration
Our engineers minimize noise by developing solutions that reduce the noise source strength, interrupt the noise path and absorb any noise or vibrating energy. NORGLIDE® Bearings are lined with a PTFE compound. PTFE has viscoelastic properties which absorb energy that would otherwise radiate as noise. Combined with the unique structures in NORGLIDE® Bearings noise is kept to a minimum. It is because NORGLIDE® Bearings can be designed so that the shaft can be press fit into the bearing that rattle noise can be eliminated completely by eliminating clearance.
Anechoic test environment
Using our state-of-the-art anechoic chamber, our engineers are able to perform benchmark testing to fully understand the current problems of the customer. A comparison test with NORGLIDE® Bearings then means that our customers can have confidence that our parts will give superior performance.
The chamber has a 7x7 meter space with a 20 dB noise floor so can be used to test most automotive assemblies, no matter how big or how quiet.
Reducing vibration
Traditional metal-to-metal joints can create vibration. Our solutions have a vibration damping effect due to the viscoelastic nature of PTFE, eliminating excessive vibration creating a smoother performance.
4 x Reduction – up to 15 db(A) – in noise compared to competing solutions under rattle test conditions.
Misalignment
Misalignment of an assembly can cause issues for manufacturers such as; increased assembly forces, excessive torque, and higher wear rates. These issues can diminish the perceived quality of a system.
An example of misalignment is found in the seat track mounting in the automotive industry. The tier 1 seat manufacturer could design a perfectly aligned seat, however the mounting holes in the car body in white can be misaligned which can distort the shape of the seat. Figure 5 shows a mechanism in which the distortion of the seat can produce misalignment between two housings that hold the seat cross-tube. Misalignment in this case can cause excessive torque and wear when the seat is adjusted.
Figure 5: the diagram above shows a mechanism of misalignment where two housings with a shaft running between them are misaligned. When the shaft is rotated within the bearing, torque is produced. Misalignment between the two housings can result in higher torque values.
Saint-Gobain engineers replicated the test as shown in Figure 5. One of the housings was misaligned by varying amounts and the torque to turn the shaft was measured. This was performed on different plain bearing solutions. The resulting torques are shown in Figure 6. The plastic POM bushing showed a significant increase in torque, even at low misalignment values. The NORGLIDE® Bearings show a great improvement in torque consistency throughout the misalignment range. Particularly, the NORGLIDE® MP material shows excellent misalignment compensation properties.
Where plastic bushings have a hard and unforgiving surface, our unique NORGLIDE® Bearings maintain their low friction properties of the PTFE, as shown previously, which helps to minimise issues caused by misalignment in assemblies.
Figure 6: The graphs above show the resulting torque under different values of misalignment between two housings. POM plastic bushings show a significant increase in torque, even at low value of misalignment. NORGLIDE® Bearings show far greater compensation for misalignment with the NORGLIDE® MP material performing best.
Tailored to your needs
Our NORGLIDE® Bearings are not off-the-shelf products. Each one can be supplied in an enormous variety of geometries, materials and other configurations. They are custom-designed to meet the specific requirements of your application. We work engineer to engineer at all stages to understand and meet your needs precisely.
Interested in finding out more? Contact us to speak to an engineer about how you could use NORGLIDE® Bearings to solve your challenges. Use our contact form or email us at: makingabigdifference@saint-gobain.com.