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NORGLIDE® PTFE Bearings for seat frames
As automotive vehicles have developed, so have seat structures. The interior design of a car plays an important role for driver and passenger comfort and the design is an important buying factor.
Material choices are changing and this is impacting the overall style, for example, different metals and structural plastics now used in seat structures has resulted in them becoming thinner and lighter, yet the load requirements are increasing. These are important factors for car manufacturers as the seat is the closest the user will get to the car and where they spend the most time. The comfort of the seat can impact the user’s overall perception of the vehicle and so performance of the seat frame and all adjustment mechanisms need to operate smoothly and with minimal NVH concerns.
Another area for consideration is the progress to reduce emissions and hit sustainability targets. This desire has resulted in a greater focus on the vehicle’s engine and output. Modern vehicle engines and the increase of electric vehicles has led to vehicles becoming quieter. The knock-on impact is that the interior of a car also needs to be quieter; previous component rattle and system noise that was masked by the internal combustion engine needs to be eliminated.
Design quality of the internal sub-systems and structures will improve many aspects of the seat frame and its performance. Issues such NVH, tolerance, fit and conductivity can be addressed with better design, resulting in better, easy assembly, reduction in costs and a better overall comfort and quality feel for the user.
Seat adjustment
The frequency of seat adjustment is increasing; shared vehicles with multiple drivers, more vehicle versatility and a future focused on autonomous driving all means seat repositioning is another area that should be paid attention. Drivers and passengers are expecting a smooth operation and feel when adjusting seats, whether it be manually or by power and the feel needs to be consistent over the lifetime of the vehicle.
Comfort is another aspect and should be a prime design factor of the seat frame and the adjustment mechanisms. The seat should minimise vibration transmission from the vehicle to the passengers or driver: a bad fitting joint is one factor that can significantly reduce the level of comfort and also reduce the overall perceived quality of the vehicle.
Across the seat fame and the adjustment mechanisms within it, misalignment and tolerance plays an important role; if it is too tight the assembly will bind and increase operating forces, too loose and the assembly will rattle, therefore having the right components in your seat frame configuration that address these problems and offer solutions to prevent wear and improve NVH will be vital.
PTFE Bearings from NORGLIDE®
NORGLIDE® PTFE Bearings have been widely used in seat adjustment applications since 1992.
The thick layer of PTFE that is exhibited by the unique NORGLIDE® materials offers superb noise and vibration dampening properties. NORGLIDE® Bearings act as a buffer between the mating materials with the unique thick layer of PTFE allowing seat designers to design torsion-resistant seat frames that are easily adjustable at stable low forces over their lifetime and also can compensate misalignment.
Saint-Gobain have developed materials to keep pace with the new developments. By using our building block designed materials, we are able to overcome all development/assembly issues that seat manufactures may have and working with our engineers we’ll make sure the right material is selected for your application.
Load transfer
The metal reinforcement of our low friction NORGLIDE® materials is able to transfer unbalanced load to an equally supported load on the thick layer of PTFE. Finite element analysis shows that NORGLIDE® PTFE Bearings can be used to spread uneven loads much better than can be achieved with an injection-moulded plastic bearing as shown in Figure 1.
Figure 1: FEA showing the distribution of uneven load between a NORGLIDE® Bearing and plastic bearing
Easy to install
NORGLIDE® PTFE Bearings fit between the housing and the shaft (tube, screw, bolt), see figure 2, and are easy to install.
Figure 2: Shows a NORGLIDE® PTFE Bearing inserted in the housing prior to the installation of the bolt.
Coefficient of friction
PTFE, compared to other materials, has one of the lowest coefficient of friction. PTFE particles are designed to migrate onto the shaft and allow a smooth as well as consistent feel of the joint over the lifetime of the assembly.
Figure 3: The relation between the coefficient of friction and radial wear depth of the bearing material for a sintered bronze and PTFE competitor bearing and a NORGLIDE® PTFE Bearing. This highlights that the CoF of NORGLIDE® is less dependent from the wear than competing materials.
Tolerance compensation
There can be a trade-off between having a low-effort seat height adjustment mechanism that rattles due to free play and a quiet mechanism that requires high forces to adjust due to interference. However, the thick PTFE layer provided by NORGLIDE® Bearings allows for interference fit and tolerance compensation through-out; our seat bearing solutions perform under lower force when compared to competing options.
Figure 4: The unique NORGLIDE® PTFE Bearings perform consistently over a wide range of dimensions when compared to competing solutions. The thick layer of PTFE can compensate for manufacturing tolerances of the mating components, ensuring a consistently smooth adjustment feel.
Calibration, sizing and tolerance compensation
Engineering tolerances, or variations, are an everyday occurrence when manufacturing assemblies. The worst case scenario of tolerance stack-ups occur when a housing has the smallest inner diameter and a shaft the largest outer diameter, and opposite extremes of their tolerance ranges. This can lead to excessive torque for a particular assembly whilst the other extreme, large housing diameter and small shaft diameter can lead to free play and rattling.
Using NORGLIDE® PTFE Bearings, in combination with a sizing procedure, can help to eliminate the issues that you may have with tolerance. Sizing, as shown in Figure 5, is a calibration of the inner diameter of the mounted bearing using a sizing pin with a controlled outer diameter to plastically deform the bearing material into a specific and significantly more consistent value. This leads to a more consistent inner diameter than even the housing alone. Completing a sizing operation will allow the operator to control the amount of torque that is required. The benefit of better controlled torque and a reduction in the operating torque range is the possibility for the motor to be downsized saving weight, space and power consumption and giving a consistent feel throughout the lifetime of the operation.
Figure 5: The sizing pin features an “olive” which has a larger outer diameter than the required inner diameter due to the elastic behaviour of the bearing's sliding layer. The pin is inserted into the bearing to plastically deform the NORGLIDE® material into the targeted thickness. The design and dimensions of these can be calibrated by the Saint-Gobain engineering team ensuring that an effective sizing procedure is implemented.
This process can be effective using NORGLIDE® materials that have a stretched metal or metallic fabric layer such as our NORGLIDE® SM, SALC, M and MP materials.
Figure 6: The unique NORGLIDE® laminate is made up of a structural base layer, optional an intermediate metallic layer and a PTFE compound sliding layer.
These flexible intermediate metallic layers facilitate the sizing process by allowing plastic deformation of the bearing material. Figure 8 shows the possible control of the inner diameter using increasing sizing pin diameters with NORGLIDE® SM Bearings. The level of sizing that is achievable depends on the total stiffness of the bearing material. It should be noted that due to the thickness of the deformable layer there is a limit to the highest wall thickness reduction possible. For this reason, our engineers will work closely with you to ensure the initial problems are understood resulting in an effective custom-made solution.
Figure 7: An example case using NORGLIDE® SM Bearings of dimensions: thickness = 1 mm, length = 17 mm. Inner diameter = 12 mm. The sizing steps were performed at 50 µm intervals. The width of the shaded area indicates the range in standard deviation from the average values.
For axial/linear tolerances many people have the dilemma of having axial play or additional costs for precision manufacturing components. The NORGLIDE® step flange bearing offers a solution to this dilemma, without compromise. The elegant solution has a step flange that is capable of absorbing linear tolerances, which means manufacturing costs can be reduced. In addition to the cost reduction, it can improve the NVH properties of the assembly.
For further information on assembly and sizing click here.
Figure 8: This shows the innovative step flange within the bush that allows for compromise on linear adjustment.
Conductivity
Even if most of a seat structure is not visible for the end user, some parts are and it's the reason why many seat frames are coated (painted) – for optical reasons but also for corrosion protection – sometimes the full structure, sometimes only partially. To paint the full structure, the coating process is normally applied after the assembly, if only segments of the structure are painted this usually happens before the final assembly. Using e-painting requires good conductivity of all assembled components to ensure that you have electrical flow through the structures. If bearings are already installed, it’s very likely that paint will cover their sliding layer. This would negatively impact the performance of the bearing. With Saint-Gobain Bearings we are able to supply both Non-Conductive and Conductive bearing materials.
NORGLIDE® LR or the MF materials comprise of a non-conductive PTFE compound that does not attract paint, preventing it from adhering to the sliding surface of the bush during the e-painting process. Using the NORGLIDE® materials and adding conductivity notches to the bearings permits conductivity through the bearing joints. These notches are installed when the bush is manufactured as the picture below displays. Indents are placed from the steel side in and the PTFE is skived off the inside diameter. This leaves a steel surface allowing for conductivity through the housing, bushing and shaft. These conductivity notches allow for electrostatic discharge or to use the metal structure for transferring electric signals – even if using a non-conductive sliding layer. This prevents the build-up of paint (paint bridges) and reduces paint defects in the final, finished layer.
Figure 9:
- LR & MF material gives high resistance to paint sticking during e-painting and does not give any conductivity
- CG material gives conductivity for e-painting
- Any material with notches gives high conductivity but no paint sticking on the functional layer
Noise, Vibration & Harshness (NVH)
Noise can be irritating and unpleasant for the end user, yet for applications with a number of small moving parts, this can be unavoidable. The other consideration is the move to electric cars. Vehicles are becoming quieter and with better sound insulation between the cockpit and the engine bay, any small noises may be heard. The challenge is to design assemblies that provide minimal or no noise over their lifetime.
At Saint-Gobain we have recognised the importance of this. Any pivot on the seat frame comprises of three parts: the housing, the shaft and the bearing. Each part will be manufactured to individual tolerances. When combined, the tolerance stack-up could be different every time, meaning significant potential variation in fit and clearance. Too much clearance in the joint can lead to instability, rattle and vibration. This not only has a negative impact on the user experience when driving the vehicle, but also risks excess wear and damage to the joint which reduces the lifetime of the assembly over time. Interference and misalignments may cause high torque and higher adjustment forces. The elasticity of the PTFE layer and the correct design can relieve you of the burden of any tight manufacturing tolerances, saving costs and producing a smooth, constant friction, eliminating metal-to-metal contact noise and vibration in the joint plus minimising wear over time so that the joint is as good at the end of life as at the beginning.
At Saint-Gobain our testing facilities support product design and development. In our Bristol, UK site we have a 7m x 7m NVH semi-anechoic noise chamber in which we can mimic customer testing conditions for complete seats or individual components.
Figure 10: This shows a full seat having NVH tests within our Semi-Anechoic chamber.
Misalignment
When making seat assemblies, there is always a potential for misalignment between the left and right sides of the seats. Misalignment can also occur between seating components that can create differing high level torque which results in inconsistent adjustment efforts.
The material properties of NORGLIDE® PTFE Bearings, especially the flexible thick PTFE layer, allows for easy alignment of mating components without using extra tools or causing off-line rework and additional costs. Components can be intentionally manipulated or bent to align them and overcome tolerances by creating a certain pretension to the full seat structure. This creates significant additional torque to the joint when using stiff materials. The thick PTFE layer is able to handle this issue much better compared to competing solutions.
SPRINGLIDE® Spring Energised Bearings
Using a spring preload combined with PTFE to address issues such as dampening, misalignment and tolerance compensation, SPRINGLIDE® Spring Energised Bearings uses spring elements like waves, ribs or fingers and the low friction properties of a polymer layer, mainly PTFE-Compound, to solve a number of manufacturing headaches at the same time.
The unique properties of SPRINGLIDE® allows engineers to overcome the combined issue of needing smooth, linear movement in environments with high misalignment. Like all of our components, each SPRINGLIDE® is custom-made to your requirements and the application, so they can be adapted to solve the problems you face. With this combined solution, offering consistent sliding force with misalignment or tolerance compensation, this one solution can reduce total cost, system weight and improve ease of assembly.
As with NORGLIDE®, SPRINGLIDE® can be used in both linear and rotational directional moments.
Finding the solution – speak to the experts at Saint-Gobain
Our engineering team can help you create a customized component to overcome your automotive challenges. Fill out our online form or email us at makingabigdifference@saint-gobain.com for more information about our components for seat frame and seat frame adjustment.