Application Examples

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Abrasion by powders during powder processing

WHY ?  : One issue in the pharmaceutical industry, is the abrasion of processing components for pressing the powders. The intensity of the abrasion phenomena strongly depends on the composition and size of the processed powders. Up to date there is no fixed procedure on how to evaluate such abrasion phenomena, in conditions that simulate the realistic process.

HOW ?  : A modification on the Falex Multispecimen machine was prepared to simulate powder pushing over a pressing disk. In the updated setup a knife - similar to the actual application - was attached to the machine. Powder is supplied and continuously refreshed from the center of the contact. This refreshment and distribution is essential to avoid attrition or poor repeatability.  After completion of a test, the wear mechanisms on both knife and disk are investigated by optical microscopy. Changes in the cutting tip were evaluated by comparing the tip angle before and after the tests with a confocal microscope. The wear damage was assessed by measuring the width of the scar of the knife before and after testing.

 

b2ap3_thumbnail_Falex-Multispecimen Applications - new methods 

 

RESULT :

- A methodology was developed to evaluate the abrasion of components used for powder processing in the pharmaceutical industry.

- The wear mechanisms were assessed and correlated to the one met in the actual application.

- The use of coatings to improve the abrasion resistance and lifetime such components was considered.

 b2ap3_thumbnail_wear-on-knife Applications - new methods

b2ap3_thumbnail_58HRC-beforetest-200-a Applications - new methods b2ap3_thumbnail_HSS_50_2 Applications - new methods

 

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Composite polymers: How do they perform in water “tribocorrosion”

WHY ?  : Polymer based composites are considered as one of the most important engineering materials for naval applications. They can be used in the superstructures, decks, bulkheads, advanced mast systems, propellers, propulsion shafts, rudders, pipes, pumps, valves, machinery and other equipment on large ships. In the majority of these applications these composites are subjected to mechanical loading in a corrosive environment. Thus their performance and/or lifetime is strongly dependent on both of these factors. In this application a methodology was developed to evaluate the effect of the corrosive environment (seawater) on the tribological performance of composite polymers is sliding contacts.  

HOW ?  : A Basalt-S2 was used to measure the friction between polymer composite blocks, having different compositions and a metallic countermaterial (toll steel bearing). The aim is to evaluate how the degradation (corrosion and wear) of both the composite and the metal influences the tribo-systems properties. The influence of chloride ions, which are known to accelerate corrosion, were investigated by comparing the friction of the tribosystem when sliding in distilled water and in seawater. A µSurf confocal microscope was used to measure the wear damage on both the ring and blocks.               

 

b2ap3_thumbnail_S2-machine Applications - new methods b2ap3_thumbnail_nanofocus_usurf_explorer Applications - new methods

RESULT :

- The friction of polymer composites in distilled and seawater were measured.

- The effect of the corrosive environment on friction can be recorded.

- Changes in the evolution of the friction can be linked to the formation of corrosive products on the contacting interface.

- Comparison between different materials, motions (unidirectional or reciprocating), speeds, and geometries is possible with the Basalt-S2.

b2ap3_thumbnail_COF_seawater-vs-distilled Applications - new methods

b2ap3_thumbnail_Surace-morphology_confocal Applications - new methods

 

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Compressor fluids under pressure : unexpected effects

WHY ? : Air conditioner compressor fluids have to prevent friction and wear under elevated gas pressure.  Standard Pin&Vee Block tests with gas 'bubbling' through the lubricant do not correlate with field behaviour, especially with CO2 as the cooling medium.  Another simulation with pressurized gas is needed.  We selected the Falex Block on Ring configuration, as it also recreates the line contacts and is able to work at higher speed than the Pin&Vee block machine.

HOW ? : Our Falex Block on Ring machine allows pressurizing the lubricant chamber with a gas, up to 10 bar.  Standard block-on-ring tests are done with and without pressure on the dissolved gas.  Tests with increasing contact loads (EP) and tests with constant load (Anti-wear) are done.

 b2ap3_small_BlockOnRing Applications  b2ap3_small_BlockOnRingConfigs Applications

 

RESULT :

- A sudden loss of lubricity in the CO2 pressurized oil bath can be measured.  Block temperature increases suddenly at 70°C, while lubricant temperature decreases, which indicates that CO2 bubbles are forming in the interface between block and ring. This phenomenon is only seen when the gas is dissolved under pressure in the lubricant.

b2ap3_thumbnail_Divergence Applications

 

- This leads to poor lubrication and increased wear.  Thanks to right additives, this bifurcation can be eliminated and wear prevention can be significantly improved under pressurized conditions.

b2ap3_thumbnail_Results Applications

 

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Cost efficient data collection for statistical analysis of wear - TRL 6

WHY ?  : One of the most difficult industrial issues related to tribology is the prediction of long term wear or material durability.  In many components and products, materials with or without lubrication are used to reduce wear and maintain functionality of the component.  Required ‘wear life’ may be thousands of hours.  Contrary to the determination of a ‘coefficient of friction’ – which can be done in a few hours, the determination of wear and wear rate under realistic conditions is a long term test. The challenge is twofold : perform low wear rate experiments with many repeats at an economically acceptable cost.  The only way to do this is by a multistation approach (performing many wear experiments simultaneously). 

HOW ?  : Parallel tests were performed in our TRL6 prototype 10-station cross-cylinder block-on-cylinder tester. With this method, we test parallel and simultaneously different bulk or coated materials (metals, alloys, polymers, ceramics and composites), at moderate contact pressures and for a prolonged period of time. Adhesive or mild abrasive wear mechanisms are representative for the “actual” applications.

  • Up to 9 kilometers of sliding distance can be realised in a single day, on 10 wear contacts simultaneously.
  • To measure the wear damage, we use weight loss measurements, optical and/or confocal microscopy.  10 data points collected efficiently

 

b2ap3_thumbnail_10-station Applications   

 

RESULT :

  • The wear of various materials can be measured in a time efficient and economical way, realistic wear rates simulate actual applications.
  • Statistical analysis of the wear data provides a higher confidence level and allows outlier analysis.
  • Reliability testing of materials becomes economically possible.

b2ap3_thumbnail_10-station_ranking-polymers Applications

 

 

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Falex Miller abrasivity tests in clay slurries

WHY

In the brick production industry, components used for the processing equipment (mixing, molding, extrusion) suffer from abrasive wear by the clay slurries. Since this clay differs from site to site, the abrasion damage can differ also.  With this method, we evaluate not only material wear resistance, but can also define the abrasivity of the clay.

HOW

Miller slurry abrasivity tests are performed according to ASTM G75, comparing the slurry abrasion-corrosion damage to materials from the production environment, where a clay slurry causes progressive wear.

The Miller test is appropriate to perform a repeatable and realistic wear process, consisting of the combination of abrasive particle wear and corrosive interactions in the presence of some water.  The test method has been traditionally used to evaluate both slurry abrasivity (Miller Number) or material resistance against slurry abrasivity (SAR number) for applications such as pumps, materials in dredging, mining, etc.

Thanks to its specific design, the test machine creates a repeatable environment between the materials and the slurry, resulting in highly repeatable wear tests.  The evolution of wear, and a convenient comparison of wear resistance of materials AND abrasivity of a slurry, can be measured in one series of experiments.

Clays are mixed with water and some additional ingredients to obtain a 'flowing' slurry, so that the contact is refreshed on each stroke.  The metal parts are cut directly from the processing equipment, to use the as-produced hardmetal coating as the test piece. 

 

 

b2ap3_large_MillerPicture_nobackground Applications

RESULT 

  • Adapted Miller slurry tests are used to compare the abrasiveness of clay slurry with sand slurry or other clays.
  • There is some more variation in the wear results in clay, due to greater inhomogeneity of clay as a slurry.
  • Baseline information when changing the tool materials : will other materials resist the clay wear better ?
b2ap3_thumbnail_weight-loss-evolution_clay Applications b2ap3_thumbnail_SAR_clay-vs-sand Applications
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Fast screening polymer coatings on cables

WHY

Various types of polymers can be used on steel cables, to provide a controlled-friction and noise-reducing coating when used on pulleys.  An efficient way to prescreen the behaviour of different types of polymers, in terms of frictional stability and durability, is needed.

Samples

HOW

Typical loading stresses in the application are estimated and recalculated to a cylinder-on-cylinder contact situation.  In this way, cylindrical test samples can be used.  The coated steel wire is used as one of the two parts of the friction test.  The countermaterial is a hard steel pin, representing steel pulleys that the coated wire is running over.

To simulate the most severe conditions in the pulley-cable contact, pure sliding is used in the lab test.  A reciprocating motion is selected, to allow testing on a short piece of coated cable  (for the prescreening stage, no long coils of coated material can be used).

The Basalt-N2 is used to rub a steel pin over the coated cables and compare the friction coefficient and relative durability of the coatings with one another

 

RESULTS 

  • Direct comparison of frictional behaviour of different polymer coatings measured immediately on the coated cable : production influences are included in the test.
  • Ranking of friction for different materials

b2ap3_large_FrictionResult Applications

  • Ranking of durability of different materials

b2ap3_large_WearDepth Applications

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Friction and wear of thin layers for MEMS

WHY ?  : Evaluating frictional and wear characteristics of very thin nanostructured layers with macro scale tribometers, in the Newton load range, can create unrealistic conditions.  Wear phenomena are highly dependent on the contact conditions: such high loads are not relevant in the case of MEMS. The adhesive and capillary components that contribute to friction, in a micro-contact, can not be simulated with high load devices.  Therefore, there is an increasing need to use new tribological testers and procedures to obtain a better understanding of surface interactions on an appropriate scale.

HOW ? : The Basalt-N2 tribometer can bridge the gap between the macro-load (conventional pin-on-disk) and nano-load (atomic force microscopes AFM) tribometers. Its versatile loading system, and by selecting cantilevers or strain gauges a load range of 0.2 mN up to 100 N is possible. In the case, loads between 500 mN and 2 N were investigated. Different contact geometries (point, line, area contacts) and sliding velocities can also be used. Due to the high sensitivity of this tester the transition between different phases can be successfully recorded (e.g. sliding between coated and uncoated components).  

b2ap3_thumbnail_PICTURE Applications - new methods

 

RESULT :

- Conventional macro-load scale wear testers are not suitable for studying the wear behavior of thin layers, because the high initial contact pressure results in severe deformation and/or fracturing of the coating.

- Meso-load testing was useful as it allowed to record accurately the frictional behavior of the coating without damaging it, and with a minimum substrate effect.

- Thanks to the high sensitivity of this meso-load tester, surface phenomena such as oxidation and/or debris formation can be easily detected by monitoring the evolution of the coefficient of friction of the tribosystem. 

b2ap3_thumbnail_Load-scales Applications - new methods

b2ap3_thumbnail_load-scale_COF_cracks Applications - new methods

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Friction measurements on complex shapes

WHY ?  : One challenge in tribology is to measure friction and wear on complex shapes, such as gears, with precision. Most of the existing setup try to simulate this complicated contact with a simplified ball-on-flat configuration. However, the more you simplify, the more you deviate from the actual application. In this application study we present an approach to evaluate the sliding contacts on complex gears.

HOW ?  : A Basalt-S2 was modified to perform reciprocating sliding tests on bare and coated gears. Holders for the gears were designed and 3D printed, a standardized steel cylinder was used as the countermaterial to create a line contact. The load and contact pressures were calculated by Hertzwin software to be in accordance with the in-field conditions. To ensure the same contacting surface between gears and countermaterial, a self-aligning holder was manufactured to hold the cylinder in contact with one of the spirals of the gear. The evolution of the coefficient of friction was continuously monitored, whereas the wear damage on both the spirals of the gear was measured by confocal microscopy.

b2ap3_thumbnail_S2-machine Applications - new methods

               

RESULT :

- The Basalt-S2 was modified to measure the tribological behavior of gears.

- Differences in the friction between bare and coated gears can be recorded.

- Coatings can improve the wear resistance of gears.

b2ap3_thumbnail_COF_coated-vs-uncoated Applications - new methods

b2ap3_thumbnail_wear-on-gear Applications - new methods

 

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Friction modifiers put to the test. Can we influence friction?

WHY ?  : In the effort to reduce CO2 exhaust, an important approach is to reduce friction in the engine.  One part of the mix of options are ‘friction modifying additives’, such as the well-known GMO, which are known to reduce friction by 5, 10 or 20%. However, the difficult task is to prove the effect of friction modifiers in the engine, since existing engine tests measure the interaction of all sliding and moving components, as well as lubricant viscosity and other effects. In order to isolate and evaluate the efficiency of friction modifiers, a precision frictional approach is required. 

HOW ?  : The high precision tribometer Basalt-S2 was used. Applied loads and friction are measured with mN precision, using a ball-on-flat contact geometry. This creates realistic contact pressures.  Due to the high sensitivity of this tester, differences between the base oils and friction modifiers were successfully recorded.  

b2ap3_thumbnail_S2-machine Applications - new methods 

 

RESULT :

- The effect of different modifiers can be separated by the precision microtribometer.

- Measurements are repeatable enough to draw significant conclusions.

- A ranking of base oils and oils containing friction modifiers is reached.

- A friction reduction of 10 to 18% in the moving contact is possible with the use of the right friction modifier.

b2ap3_thumbnail_Modifiers_COF-evolution Applications - new methods

b2ap3_thumbnail_Modifiers_COF-comparison Applications - new methods

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Hairstyling from a tribology point of view…

WHY ?  : In everyday life people use hairstyling products such as waxes or gels, to improve the holding of hair and improve/change its appearance. However, in the market there are many products available, claiming to have different characteristics (e.g. strong hold, silky/smooth touch…). To define the performance of such products, tribology comes into play. In particular two parameters are important. The friction determines how easy a wax or gel can be applied, whereas the stickiness and tackiness determine their holding ability.    

HOW ?  : For this application case the updated Basalt-N2 was used, operated at the mN range. In particular, two different test procedures are developed to evaluate the friction and stickiness/tackiness of commercial waxes and gels. To investigate the frictional behavior, a scratch test was performed on a thin film of wax or gel on a metallic substrate. The counter material was a silicone disk that simulates the area contact between the finger skin and the hairstyling media. Different sliding speeds, applied loads and sliding distances can be used to evaluate and compare different contact conditions. The stickiness/tackiness of waxes or gels was measured based on approach-retraction curves. In this procedure a silicone counter body gradually approaches the thin film of wax or gel, until a pre-set contact load is reached. Then, the silicone moves away from the greased substrate under well controlled conditions, until complete physical separation is achieved.  During this approach-retraction cycle, the force on the load sensor is measured as a function of time and distance moved. 

 

 b2ap3_large_PICTURE Applications

 

RESULT  :

- Both the friction and stickiness of gels and waxes can be measured by the Basalt-N2. This dual approach can be used to provide a ranking on the stickiness behaviour of commercial hairstyling products.

- Wax appears to stick more than gel : higher pull-off force. But its stickiness decreases sharply after the first cycle.

- Gels have a lower friction than waxes. The coefficient increase during sliding as the gel piles around the silicone counter material.

b2ap3_large_Gel-vs-wax_pull-off-force Applications

b2ap3_large_Gel-vs-wax_COF Applications

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