April 14th, 2022
The SALC material’s specific combination of a self-lubricated, low-friction PTFE and embedded metal reinforcement has been developed primarily for this rotational sliding bearing (bushing) application. Building on over 40 years of experience and innovation in vehicle door hinge bearing design, Saint-Gobain has answered every need. For the end user, this means easy opening and closing, with a quality feel, every day of the vehicle’s life, with no deterioration due to corrosion or mechanical degradation. For the automotive manufacturer, it means simple, economical manufacturing and assembly processes, and customer satisfaction.
A corrosion-resistant specification, designed to protect both the bearing itself and the hinge assembly around it, has been one of the highest development priorities. Another function of this material is the ability to set and maintain the required level of torque, for door hinges this is a critical function. In simple terms, too little torque can allow free play, leading to a rattling, with doors tilting or door drop. Too much torque can negatively impact the effort required by the end user to open or close the door.
Managing torque is addressed largely through the NORGLIDE® SALC material’s premium facility to size the material. This property, together with the PTFE layer’s excellent plasticity and elasticity, also enables a high degree of compensation for shaft size variation and misalignment. Meanwhile, PTFE filler choice, together with special bearing design features, addresses the risk of paint defects arising from electrophoretic coating (e-painting).
In addition to these benefits, SALC bearings – or bushings, as they are sometimes known – enjoy other NORGLIDE® advantages which are recognised and applied by all major automotive manufacturers, such as no need for lubrication or maintenance. Furthermore, the specifications and properties of NORGLIDE® can be fine-tuned to meet individual customers’ specialised application needs.
|NORGLIDE® SALC GG Bearing||NORGLIDE® SALC GS Bearing|
NORGLIDE® SALC is aimed mainly at side door hinges. Side door hinges can be placed into two major categories; profile and stamped.
Profile hinges are created from a metal profile, cut to shape and drilled to accommodate a shaft, with a rotational sliding bearing inserted to line the bore.
Stamped hinges are formed by stamping and bending sheet metal into the required shape.
NORGLIDE® SALC is perfect for profile side door hinge applications, where corrosion resistance, perfect fit for stable torque and sizeability (calibration) is paramount, but NORGLIDE® SALC can also be considered for a much wider range of applications where high corrosion protection and/or sizeability is required.
A profile hinge usually contains just one bearing, which is flanged at both ends. The first flange is created during the bearing’s manufacture and the other is formed after the bearing has been assembled. A stamped hinge normally has two bearings, for two pivot points, and normally only one flange per bearing.
Saint-Gobain offers a number of other bearing material options for both hinge types. Our engineers will advise on their suitability each case.
NORGLIDE® SALC products are part of a wide range of Saint-Gobain sliding bearings, or bushings – otherwise known as plain, journal or sleeve bearings. The term ‘plain bearing’ means there are no rolling elements or moving parts. Essential to all NORGLIDE® Bearings is the thick layer of PTFE-compound, with a low coefficient of friction and an ability to self-lubricate. As the pin of a hinge rotates on the bearing the PTFE is transferred to the shaft to form a lubricating layer.
Different fillers for the PTFE compound and metal reinforcing layers can be added to match the bearing to its specific application. A stretched metal layer enhances sizeability as well as increases load capability. Sizing is a way of calibrating the bearing, through plastic deformation, to achieve the required fit with the shaft – and hence the ideal level of torque for a hinge. Plastic and also elastic deformation allows a NORGLIDE® Bearing to compensate for manufacturing tolerances and misalignments.
The name SALC is derived from ‘stretched metal aluminium-cladded’. The stretched aluminium-cladded metal was chosen to match different requirements of door hinges – in particular, for profile hinges; easy to form, good sizeability, high load capability and excellent corrosion resistance (including mating components) are some of them. The solution is a stretched metal (easy to form and to size) with steel as base material (for high load capability) and an aluminium-cladded surface (for high corrosion resistance). Although some of the other NORGLIDE® materials have a higher load capability, SALC is more than strong enough for use in a typical vehicle profile hinge. Car doors normally weigh around 25 to 35 kg, and even with an abusive overload of around 100 kg – equivalent to someone standing on the door – the SALC bearing does not permanently deform. Load capacity is high enough (in combination with a press fit in the pivot) to maintain typical door drop specifications.
NORGLIDE® SALC Bearings are available in a range of specifications and properties. To identify the different compounds, descriptive naming has been used for example, NORGLIDE® SALC GG has glass and graphite (hence GG) fillers in its PTFE compound. NORGLIDE® SALC GS has glass and silicate (hence GS) fillers. For easy identification on production lines, GS is coloured blue while GG is black.
Our Saint-Gobain engineers can advise on the most suitable material for your application and ensure appropriate choices.
NORGLIDE® Bearings can be designed as highly resistant to corrosion. Today’s lightweighting trend, in particular, has led to a variety of material mixtures. So, designers must consider the potential for corrosive interactions between a bearing and the other materials in a hinge assembly.
By choosing bearing metals which are relatively close to those of the hinge assembly on a scale of reactivity, the problem is greatly reduced. In NORGLIDE® SALC, the stretched metal layer is made from steel for strength – cladded with aluminium for extra corrosion resistance. This combination works extremely well with profile hinge assembly metals (e. g. zinc-coated steel) in minimising corrosive effects. The performance of NORGLIDE® SALC corrosion-resistant bushings is even greater when graphite, which is to some extent conductive, is replaced by a non-conductive material such as silicate in the PTFE filler compound.
Extensive and rigorous salt spray tests have proved the effectiveness of NORGLIDE® SALC, in producing corrosion-resistant bearings and hinges. Figures 2 a & b show the typical appearance of a corroded hinge – in this case using a standard bushing whose material is based on bronze mesh. In addition to white rust, the more serious problem of red rust is appearing. Out of the eight hinges in this test, six showed red rust after 336 hours.
|Figure 2a (upper door hinge)||Figure 2b (lower door hinge)|
Salt spray testing – standard bushing with bronze mesh.
This can be compared with the performance of NORGLIDE® SALC GG (see Figures 3 a & b). After hundreds of hours in the salt spray chamber, which creates a much harsher corrosive environment than a hinge would face in real life, the SALC bearings outperformed alternative materials with considerably lower red rust. The newest material, NORGLIDE® SALC GS takes it one step further to provide significantly better results in the same test conditions.
|Figure 3a (upper door hinge)||Figure 3b (lower door hinge)|
Salt spray testing – NORGLIDE® SALC GG corrosion-resistant bushings.
The newest material, NORGLIDE® SALC GS takes it one step further to provide significantly better results in the same test conditions.
Sizing of NORGLIDE® door hinge bearings is the key to an optimal fit of all hinge components. To avoid any free play over lifetime (e. g. by wear) the pin is normally designed with a certain interference to the ID of the bearing. The unavoidably created torque should be within an acceptable range, not to affect the opening or closing of the door too much, but also not allow the door to drop.
Typical door hinge torque targeted by automotive OEMs today are ranging from close to zero up to somewhere below 4-5 Nm. This is due to the fact that smallest variations in size have a significant influence on torque. Without any process to compensate this it’s quite likely to manufacture hinges with torque out of spec causing re-work up to a line stoppage. New and upcoming side doors are targeting torque levels at the lower end of the range, so the impact of the hinge to open or close the door is minimized.
Although sizing works for both profile and stamped hinges, the scope for torque adjustment is greater in profile hinges because the bearings for these have a much larger contact surface area.
To adjust the bearing’s inner diameter to a size which will create the required torque, engineers must take into account elastic and plastic deformation. In other words, with a certain load the bearing shows some permanent deformation (sizing), but a certain amount of shape will recover elastically once the load is removed. This elastic effect mainly creates the torque. With NORGLIDE® SALC, which has a high plasticity, between 60 and 80% of the deformation is plastic and the rest is elastic. Its combination of soft PTFE-compound with a stretched metal reinforcement layer maximises sizeability.
How much the wall thickness can be sized without damaging the bearing varies between materials. NORGLIDE® SALC is exceptionally versatile in this respect, as it can lose as much as 20% of its thickness without ill effect.
Increasing the shaft interference fit typically increases torque significantly. With NORGLIDE® SALC, torque increases gradually with increased interference but remains in the low range. With conventional steel back bearings, torque increases exponentially with increased interference as shown in Figure 4.
Figure 4. Effect of interference on torque, compared between NORGLIDE® SALC Bearings and standard steel backed bearing types.
One further consideration in designing pivot points to achieve the targeted performance is that high temperatures can reduce torque. This is particularly true for PTFE-based bearings. Oven baking of vehicles after e-coating often results in a torque reduction, the scatter of torque reduction can be high for NORGLIDE® SALC, depending on the temperatures involved. Provided that this has been considered in the calculation, the lower torque observed after painting is welcome – as soon there is still some. It should also be noted that NORGLIDE® SALC is temperature-resistant up to 260⁰C, unlike plastic bearings which can be damaged by such conditions.
Importantly, in mass production of hinge components there must be allowance for variation e. g. in shaft diameter. The thickness, plasticity and elasticity of a NORGLIDE® Bearing’s material, combined with appropriate sizing, compensates for manufacturers’ engineering tolerances in this respect. This allows production to less demanding and expensive levels of precision, with few or no rejected shafts.
Electrophoretic coating, otherwise known as e-coating or e-painting, is used to give vehicles their initial protective coating. As long as electric current can flow to all parts requiring paint coverage, this method will give a complete and even coat. NORGLIDE® SALC Bearings are designed to support and enhance the e-coating process, as they provide the needed conductivity to let the current flow through the bearing.
In some applications it is useful for all parts of a bearing – including its PTFE layer – to be conductive, but this is not true for vehicle side door hinges, hoods and tailgate/trunk hinges. As Figure 5 illustrates, when the PTFE-compound is fully conductive paint is deposited on the sliding layer as well as the neighbouring metal hinge components. This creates a paint bridge between the mating structures, which breaks as soon as the door is moved. As the paint chips off, adjacent metal may become exposed and weakens its corrosive protection. In addition, the paint debris resulting from chipping and flaking can interfere with the quality and effectiveness of subsequent paint layers.
|Figure 5. E-coating problem caused by conductive PTFE layer on bearing.|
To avoid deposition of paint on the PTFE-compound, non-conductive fillers can be specified in its formulation. The challenge then is to establish conductivity between all hinge parts. Gaps can lead to electrical arcing between separated elements, which may result in burns, while some parts may simply remain unpainted. In NORGLIDE® SALC Bearings, connection between the shaft and other metal components in the hinge can be achieved through conductive notches. The creation of this modification is explained here briefly:
a. A notching pin pushes in the bearing material at several points.
b. This forms protrusions of material into the bore.
c. At the raised parts the PTFE compound is sliced off.
d. Stretched metall in direct contact to the mating components provides sufficient conductivity.
The principle of the conductive notches in e-painting is illustrated in Figure 6. Provided that the shaft and bearing fit is not too loose, effective conductivity connection will be maintained. Our white paper on the subject contains further information on how this solution avoids paint defects.
Figure 6. E-coating problem solved by combining non-conductive PTFE-compound with conductive notches in bearing.
Like all Saint-Gobain bearing products, NORGLIDE® SALC vehicle side door hinge bearings are custom-designed, configured and manufactured according to the requirements of each individual application and order. Our engineers work closely with you at all stages to understand and meet your needs precisely.