Saint-Gobain testing capabilities

NORGLIDE^® sliding bearings (rotating and linear), whose layer of self-lubricated, low-friction PTFE enables smooth interaction with contact surfaces. Their layered structure can be reinforced by selecting metals and PTFE filler materials in application-tailored configurations.

RENCOL^® Tolerance Rings, used primarily for effective frictional fastening of cylindrical mating components. In addition to firm mounting of bearing and other assemblies, their functions can include torque transfer in pulley or gear mounts for example. They can also act as slip clutches, disengaging components in the event of a potentially damaging overload. 

SPRINGLIDE™ Spring Energised Bearings, which combine steel spring elements with a soft, low-friction polymer layer. They eliminate the need for clearance and address issues like rattle noise dampening, misalignment and tolerance compensation. In effect, they roll NORGLIDE^® and RENCOL^® technology into one simple solution.

Our linear friction testing (LFT) machines measure friction and wear resulting from linear movement relating to bearings. They include ‘yoke testers’ (Figure 2), uniquely built for Saint-Gobain for the initial purpose of testing automotive steering yokes. The same machines can be used for brake systems, head restraints and many other applications in the automotive industry and beyond. Wherever different materials slide against each other in a linear motion, our LFT machines can determine their friction levels and durability. Tests can be carried out under varying conditions, including load, sliding speed, stroke, lubrication and temperature, to reflect real-life application circumstances.

Figure 2. ‘Yoke tester’ (for linear friction and wear testing)

Figure 3. Torque tester (for rotational friction and hysteresis measurement)

Torque testers (Figure 3) look instead at rotational (or torsional) friction. In addition to overall torsional friction, they can measure hysteresis (deformation) in materials as they move against each other, change direction, for example turning clockwise or anti clockwise or between loading and unloading. Examples of applications in the automotive sector include hinges, sensor assemblies in steering systems and input pinion assemblies in head-up displays, but there are uses in many other systems and industries. Again, factors such as input torque, rotation speed and temperature can be varied.

Figure 4. M15 torque tester

Figure 5. Mcmesin torque tester

Figure 6. TL500 Torque tester

Our flexible test beds (Figure 7) measure friction and efficiency for whole systems, which they can subject to a complex combination of simultaneous linear, rotating and oscillating forces. Movements are typically applied in two linear axes and one rotational. They may involve, for example, a repeated pattern of rotating several times in one direction, stopping, and then doing the same in reverse. Aside from automotive door, seat and steering mechanisms, flexible test beds are used for applications including bicycle steering set-ups and solar power equipment. Along with their almost infinite variety of movement combinations, they can be used to test the effects of changing factors like input torque and load, sliding and rotating speeds, and stroke. 

Figure 7. Flexible test bed (for multi-factor friction and efficiency testing)

Figure 8. Pneumatic pulser (for lifetime testing)

A further application testing option involves use of a pneumatic pulser (Figure 8). Our Pneumatic Pulser test machines allow oscillating linear motion test up to 35Hz. These testers are used for both fundamental and application related testing. Fundamental tests such as three-point bending are conducted to identify material properties related to fatigue. On application level the PP tester is used for tests on finished products for fatigue testing and to validate required endurance strength.

Using high-precision microscopes, we can closely examine surfaces before and after application tests to see what has changed. For example, we might find areas of scouring damage, or transfer of material from one surface to another. Our equipment includes scanning electron microscopes (SEMs) with energy-dispersive X-ray spectroscopy (EDS) – see Figure 9. This not only gives extremely detailed images but enables analysis of the chemical make-up of transferred material, so we can determine its origin in a system.

Figure 9. Scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS) uses focused beams of electrons to identify surface topography and composition

Figure 10. Digital 3D microscope

Figure 11. 3D laser scanning confocal microscope

Another aspect of our analytical work is quality control. For example, we need to be certain that all dimensions of a product are exactly as they should be – before and after application, and throughout production runs. We can use a three-dimensional co-ordinate measuring machine (CMM) – see Figure 12 – to measure anything from a single point location to the whole 3D shape of a product.

Figure 12. 3D co-ordinate measuring machine (CMM)

When physical probes are not an option to measure features, an optical measurement system can be used. On our site in Bristol we have a OGP CNC 670 (Figure 14). It features a bed and programming function where geometric characteristics can be measured and checked against drawings. It is used to measure tolerance rings, jigs, customer components and assemblies.

Figure 14. OGP CNC 670 optical measurement tester

We test bearings, tolerance rings (if required), assemblies and other components for corrosion resistance using salt spray chambers (Figure 16). These accelerated tests normally involve a 5% sodium chloride solution, with a pH between 6.5 and 7.2, at 35⁰C, according to DIN EN ISO 9227. A check for rust is made once every 24 hours, and between checks the specimen is sprayed constantly. Most commonly, testers are looking for the number of hours taken for red rust to appear. Results may be stated as 24, 48, 72, 96, 120, 240, 480 or 960 hours without red rust.

In addition to red rust, there are more than 50 different classes of corrosion – named according to their appearance or their cause. The main categories affecting bearings are surface, galvanic and crevice corrosion.

To reflect the changeability of real-life conditions, we can make the ‘climate’ in the chamber vary over a cycle of several days – with periods of salt spraying (rain), dryness (sun) and high humidity (fog), for instance according to OEM specs. This testing typically lasts 6 or 12 weeks. We can also combine it with factors such as mud and mechanical stress to test the overall effect.

For more detailed corrosion test and to characterize the electrochemical systems - with less complexity - we also have the possibility to use potentiostat in combination with electrochemical impedance spectroscopy (EIS). This allows us as well to change the electrolytes easily, that specific investigation can be conducted with acids, bases or alkalines.

Figure 16. Salt spray chamber.

At Saint-Gobain, Finite Element Analysis (FEA) is used to support the design and development of our products, considering the processing, assembly and performance in representative sub-assemblies across a range of tolerance and operating conditions.

FEA complements testing by virtualising physical processes, providing a predictive capability to understand a much wider range of parameters than would otherwise be possible. It can also reveal hidden behaviours and mechanisms that allow insights to be drawn which may not be possible from physical tests alone. 

Figure 18 shows a visualisation of a RENCOL^® Tolerance Ring assembly, with a precise representation of a tolerance ring assembled into the mating components. This type of analysis can help predict the impact of the assembly process on the final performance before any parts are made and can be routinely undertaken by our tolerance ring Application Engineers utilising a unique democratised FEA tool based upon ABAQUS. 

As well as the FEA embedded in the design process, a specialist in-house team is constantly developing new, bespoke methods to help our customers with specific project requirements as well as supporting the development of new products including SPRINGLIDE™ and certain NORGLIDE^® developments.

A simple example of the kind of prediction made possible by FEA for some rotating bearings which have been used in a press-fit assembly. The NORGLIDE^® Bearing, in this test, has a layer of PTFE backed by a layer of steel. Its competitor has an all-plastic construction. Pressure from the metal link into which the bearing is inserted is transmitted right through the plastic product, producing broad line contact stress on both its inner and its outer surfaces. In the NORGLIDE^® product, PTFE spreads the pressure out evenly. The result is line contact stress on the steel outside surface but none on the PTFE inner surface.

Figure 18. FEA of a Tolerance Ring assembly showing Von-Mises Stresses

Our advanced testing, as summarised in the sections above, builds on the essential knowledge gained through fundamental test processes. Moving into material testing and characterisation we have a number of universal tensile / compression test machines available that are used (Figure 20) to determine stiffness and strength characteristics of our materials. We also have equipment for determining material density, hardness and surface roughness. 

Figure 20. Tensile tester

Alongside tribometer testing fundamental investigations are done using our journal bearing tester (JBT) (Figure 22). These tests are used to determine coefficient of friction (COF) and wear performance of our sliding bearings. Tests are carried-out at different loading conditions representing the wide range of the operating conditions of our different markets.

Figure 22. Journal bearing tester (JBT)