A NORGLIDE® PTFE Bearing is an integral part of a seat frame joint that gives a robust, smooth, consistent operation over its lifetime. The seat and consequently the seat frame is the closest that any driver or passenger will get to the car and therefore, it is the area that any noises and vibrations will be heard most. With the onset of quieter engines and electric vehicles, the end user’s expectation for a quiet, smooth operation in the interior of the vehicle is more important. Saint-Gobain interior engineers have many years of experience in understanding and designing assembly joints for seat structures. Quality of design is not only important from a manufacturer’s view point for reduction in costs and ease of assembly but also to the end user to minimise noise and vibration to deliver a quality feel within the vehicle.
Figure 1: NORGLIDE® laminates are made up of a building block design allowing for differing layers, a PTFE sliding foil, optional a metallic interlayer and a structural metal backing.
When assembling a seat frame you will always have an issue with tolerance: too tight and the assembly will bind, too loose and the assembly will rattle.
The NORGLIDE® PTFE Slide Bearings act as a buffer between the mating materials. By using the unique thick layer of PTFE, it allows seat designers to design torsion-resistant seat fames that are easily adjustable at stable low forces over their lifetime and also can compensate misalignment with the elimination of any noise or vibration.
With the housing mainly being made by stamping the steel, this often leaves a breakout. The metal reinforcement of the low friction NORGLIDE® materials is able to transfer unbalanced load to an equally supported load on the thick layer of PTFE.
Figure 2: Finite element analysis shows that the NORGLIDE® PTFE Bearing can be used to spread the uneven loads much better than can be achieved with an injection-moulded plastic bearing.
NORGLIDE® PTFE Bearings fit between the housing and the shaft (tube, screw, bolt). They are easy to install. By working with the Saint-Gobain engineers, we’ll make sure the right material is selected for your application. PTFE, compared to other materials, has one of the lowest coefficient of friction. PTFE particles will migrate onto the shaft and allow a smooth as well as consistent feel of the joint over the lifetime of the assembly.
NORGLIDE® PTFE Bearings have been widely used in seat adjustment applications since 1992. We are your glocal 1st choice for automotive seat height adjustment – global engineering, local production and support.
Drivers and passengers are expecting a smooth operation and feel when adjusting seats, whether it be manually or by power, the feel needs to be consistent over the lifetime of the vehicle.
The quality of design is not just felt by end users through performance but also manufacturers through ease of assembly and reduced costs.
As mentioned, the most physical contact that the end user will have in a vehicle is with the seat. For this reason comfort should be a prime factor that is considered during the design phase. 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 can also reduce the overall perceived quality of the vehicle.
The thick layer of PTFE that is exhibited by the unique NORGLIDE® materials offers superb noise and vibration dampening properties. It reduces or eliminates the induced discomfort which comes from high speeds or bumpy roads.
Vehicles that have multiple drivers and with the future focused on autonomous driving, re-positioning the seat is a crucial consideration. The frequency of movement is increasing, therefore the need for a bearing to overcome this greater potential for wear is more important. With NORGLIDE® we have the right material for the required specification.
As automotive vehicles have developed, seat structures have also advanced to keep pace with new designs and requirements. With the use of more advanced materials, seat structures are becoming thinner and lighter, even with the load requirements increasing. Saint-Gobain have developed materials to keep pace with the new developments. By using our building block designed materials, Saint-Gobain are able to overcome all development/assembly issues that seat manufactures may have.
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.
Figure 4: Shows a NORGLIDE® PTFE Bearing inserted in the housing prior to the installation of the bolt.
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 exhibited by the unique NORGLIDE® materials allows for interference fit and tolerance compensation through-out which our seat bearing solutions perform under lower force when compared to competing options.
Figure 5: 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.
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.
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 – simply, the smallest inner diameter of the housing with the largest diameter of the shaft as one example. 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 7, is a calibration of the inner diameter of the mounted bearing using a sizing pin of 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. Controlling torque will allow for any motorised systems to be able to use smaller motors.
Figure 7: 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. 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 which is why it is important we work closely with you to ensure the initial problems are understood. This way an effective custom-made solution can be provided. For further information on assembly and sizing click here.
Figure 8: 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.
Even if most of a seat structure is not visible for the end user, some parts are. That’s the reason why many seat frames are coated – for optical reasons but also for corrosion protection – sometimes the full structure, sometimes only partial. To paint the full structure, the coating process is normally applied after the assembly. Using e-painting requires good conductivity of all assembled components to ensure that you have electrical flow through the structures. If only segments of the structure are painted, this usually happens before the final assembly. If bearings are already installed into these segments, it’s very likely that paint also cover their sliding layer. This would negatively impact the performance of the bearing. With Saint-Gobain 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 joints. These 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 of 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 is using a non-conductive sliding layer.
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. By working with Saint-Gobain’s engineers we can ensure that you have the right material in the right place and the correct tolerances are met to eliminate noise from pivot joints. The elasticity of the PTFE layer and the correct design can relieve you of the burden of any tight manufacturing tolerances. Thus, 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.
In addition to the many years of experience our Saint-Gobain engineers have in designing seat pivot points, 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 11: This shows a full seat having NVH tests within our Semi-Anechoic chamber.
Engineering tolerances, or variations, are an everyday occurrence when manufacturing assemblies. The worst case scenario of tolerance stack-ups occur for these two extremes: “smallest housing / largest shaft” – “largest housing / smallest shaft”. Working with the Saint-Gobain engineers and their vast experience and knowledge ensures that radial and axial/linear tolerances are under control – for both extremes.
In radial tolerances it is possible to overcome these by calibration or sizing the pin (highlighted above) but for axial/linear tolerances many people have the dilemma of having axial play or additional costs for precision manufacturing components.
Figure 12: This shows the innovative step flange within the bush that allows for compromise on linear adjustment.
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.
When making seat assemblies, there is always a potential for misalignment between the left and right sides of the seats. At Saint-Gobain we have materials that can overcome this potential issue. By utilizing 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 – with moderate torque increase only, still providing much lower adjustment forces.