A NORGLIDE® PTFE Bearing is an integral part of a seat frame joint that gives a robust smooth, consistent operation over 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 the need of 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 vibration and give a perceived quality of feel within the vehicle.
Figure 1: NORGLIDE® laminates are made up of a building block design allowing for differing layers, a PTFE sliding surface, a metallic interlayer and structural backing
When assembling a shaft through a housing (in this case the seat frame) you will always have an issue with tolerance: too tight and the assembly will bind, too loose and the assembly will rattle. NORGLIDE® Bearings have the right material for a solution whatever the issue.
The NORGLIDE® Bearings act as a buffer between the mating materials, by using the unique thick layer of PTFE it allows for seat designers to design seat fames that can provide a low stable torque over lifetime, which can absorb for misalignment in the X, Y and Z directions with the elimination of any noise or vibration.
With the housing mainly being made by stamping the steel, this often leaves a breakout, the thick layer of PTFE is also able to absorb this. The metal reinforcement is able to transfer the linear load to an equally supported load on the thick layer of PTFE.
Figure 2: Finite element analysis shows that the NORLGLIDE® Bearing can be used to spread the external loads much better than can be achieved with an injection-moulded plastic bearing.
NORGLIDE® PTFE Bearings fit between the housing and the shaft. They are easy to install. By working with the Saint-Gobain engineers, it is ensured that 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® Bearings have been widely used, resulting in the global market leadership within automotive seat height adjustment since 1992.
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.
The most physical contact that the end user will have is within the seat. This is why, comfort as a prime must be a consideration when designing. 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 layer of PTFE-compound tape 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.
Within the use of shared vehicles and the future of autonomous driving, the need to move the seat is becoming more often, now often on a daily basis. 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. Where often with the use of more advanced materials seat structures become thinner and lighter, even with the load requirements increasing. Saint-Gobain have developed materials to keep pace with the new developments. By using our structured 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® seat bearing. This highlights that the wear capabilities are greater than competing materials
Figure 4: Shows a NORGLIDE® Bearing inserted in the housing prior to the installation of the pin
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® Bearing allows for a level of tolerance compensation through-out which our seat bearing solutions perform consistently when compared to competing options.
Figure 5: The unique NORGLIDE® 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, an intermediate metallic layer and a PTFE filled 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 and a shaft are at equal 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 low or no torque.
NORGLIDE® 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. By completing a sizing operation will allow the end user to control the amount of torque that is required. By 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 PTFE sliding layer into the specified 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 materials that have a stretched metal or metallic fabric layer such as our NORGLIDE® SM, SMALC, M and MP materials. This stretched metallic layer within the PTFE compound enables the sizing process by allowing plastic deformation of this layer. 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 to work closely with our customers 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
When assembling interior components for the vehicle most require good conductivity to ensure that you have electrical flow through the structures. But often, this is not required. With Saint-Gobain we are able to supply both Non-Conductive and Conductive fillers.
NORGLIDE® LR or the MF materials comprise of a non-conductive PTFE material that does not allow for paint to adhere to the surface of the bush. Still, you can use these materials and have conductivity through the joints by using conductivity notches. 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 that leaves a steel surface allowing for conductivity through housing, bushing and shaft. These conductivity notches elevate the traditional issues that you have with the paint bridging across the PTFE which can cause paint flake.
1. LR & MF material gives high resistance to paint sticking but does not give any conductivity
2. CG material gives conductivity for painting but allows for paint flakes
3. LR & MF material gives high conductivity and the addition of not omits paint bridges.
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 challenge is to design assemblies that provide minimal or no noise over lifetime.
As the vehicles are becoming quieter with the introduction of electric cars and the better sound insulation between the cockpit and the engine bay, any small noises may be heard.
Within 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. The surface finish and hardness of the mating parts also have an effect on operation of the assembly and its longevity (housing too rough results in bearing damage and the joint will wear quickly; too smooth will create a stick slip scenario). By working with the Saint-Gobain engineers to ensure that you have the right material in the right place and the correct tolerances you are able to elevate any noises from pivot joints. The elasticity of the PTFE and the correct design can relive you of the burden of any tight manufacturing tolerances. Thus, saving costs allows for a smooth, constant friction, eliminating metal-to-metal contact noise and vibration in the joint plus minimising wear over time ensuring that the joint is as good at the end of life as at the beginning.
In addition to the many years that the Saint-Gobain engineers have had in designing seat pivot points, Saint-Gobain are able to support the designs of pivot points with our own in house NVH semi-anechoic noise chamber, based in Bristol UK. Our 7m x 7m chamber is able to 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. Working with the Saint-Gobain engineers with their vast experience and knowledge ensures that radial and axial/linear tolerances are eliminated. The worst case scenario of tolerance stack-ups occur when a housing and a shaft are at equal and opposite extremes of their tolerance ranges. With Saint-Gobain we are able to overcome these issues in both, axial and radial tolerances.
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 flange that is capable of absorbing a wide range of mating component tolerances, which means manufacturing costs can be reduced. In addition to the reduction in cost, 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/vehicle. Within Saint-Gobain we have materials that can overcome this potential issue. By utilising one of the number of differing materials that Saint-Gobain have with calibration of the bearings you are able to remove any potential binding or clearances that may occur.