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1. The challenge to determine anti-wear and extreme pressure properties of dry lubricants in industrial lubrication applications
Lais Lopes, Dirk Drees, Pedro Baião, Falex Tribology, Rotselaar, Vlaams Brabant, Belgium
Abstract: Dry lubricants are in industrial forming processes, notably wire drawing. Consisting of flakes, pellets or powders, they stick to workpiece and pass through a die or forming tool, where localized high pressure melts them. Characterizing their EP and Anti-wear properties in a lab test is challenging: a constant supply of particles into a standard tribological geometry needs to be achieved. four ball wear/ep tests fall short.
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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.
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Some parts in mechanical high quality watches (like Swiss...) perform a slow motion that consists of an increase of contact pressure during some time (a day, for instance) and then a quick release and impact.
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One of the main issues in the watch industry is reduce the friction and sticking between moving components. To achieve this, a small quantity of lubricant is added in the contact. However, due to the high expectations of the costumers, the increased lifetime of the watch, the size and geometry of components and contact conditions (loads in the mN range), there is a huge need to develop a tool that can evaluate such lubricating tribo-systems. The main challenge is to perform precision frictional measurements, in conditions that simulate the “actual” application.
1. Fast Screening of Wear Regimes in a Four Ball Setup
Lais Lopes, Dirk Drees, Pedro Baião, Falex Tribology, Rotselaar, Vlaams Brabant, Belgium
A fast-screening method is developed in four ball setup, to evaluate wear regimes more efficiently. Current ASTM methods require running multiple short tests over a range of loads. In this presentation, we show an alternative approach by an automated method. How to evaluate the results of this method, how parameters can be fine-tuned to suit ranges of products, and what new insights can be gained, are the results of this research. The level of correlation with other test methods is also examined. The method is initially focused on detecting the seizure regime, because once a lubricant enters this regime, all lubricating functionality is los in a normal application. Some indications to extend the method to the catastrophic failure range, called weld load, are made, but the real discussion is whether this weld load has any practical value. This approach intends to provide the additives and lubricants industry a new method to continually check and improve quality and performance.
WHY
In an industrial forming operation, the friction between tool and workpiece, or workpiece and die, determines the quality and efficiency of forming. Too high friction can cause wrinkles or tears, resulting in scrap. Forming lubricants appear to be sensitive to temperature, so the optimal forming conditions may vary with increasing temperature, as the machines warm up.
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The standard method for evaluating anti-wear of hydraulic fluids in a vane pump, is by the 100 hour ASTM or 250 hour ISO method, using a real Conestoga-built vane pump. This method takes a long time to run, and requires a lot of fluid. This makes it difficult to use the method for development or research.
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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).
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Examples of corrosion are found in many industrial applications ranging from aeronautical, automotive, naval, and the construction industry over home appliances, water systems, pipelines, and ‘bio’ applications. Corrosion phenomena can be significantly accelerated by the simultaneous occurrence of a mechanical load on the surface: the formation of cracks and surface defects, along with surface strain and stress fields lead to faster diffusion of corrosive ions or the destruction of protective layers (depassivation). Thus there is a need to understand the synergy between wear and corrosion.
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Nowadays polymer based coatings are applied in all walks of life, due to their excellent corrosion resistance, low friction and cost, good surface finish, molding ability and low density. However, one of the main issue of these coatings is their relatively poor performance in terms of wear. Especially, when sliding under high speeds, frictional heating can lead to a softening of the coating and accelerate the wearing-off process. Evaluating the high speed sliding performance of polymer coatings is a key issue in many applications.
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High temperature tribological testing often requires the development of complex mechanical setups, that should meet rigorous standards and specific performance metrics. Thus, the development of a state-of-the-art experimental setup to study the reciprocating sliding behaviour of various bulk and coated materials at temperatures that can reach up to 1000 °C is needed, especially for the evaluation of high temperature materials for aeronautical applications.
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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.
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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.
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Wiper blades are of great importance to the safety of the driver. In reality they can operate under different speeds (various scales in the car) or under different lubrication conditions (from dry to wet with thin or thick film of water). To simulate these conditions in lab scale you need to have a versatile apparatus and you will need to use the actual components to be as close to reality as possible.
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A variety of oils for the automotive industry is available in the market. These oils have different composition, additives and can operate under different conditions (motion, load, speed and temperature). A method need to be used to prescreen the performance and endurance of these oils under different conditions, which are relevant to the automotive industry.
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The steering system of cars is based on a rack and pinion system. Over time, the metal on these gears wears out, resulting in a loose fitting. Some other applications also make use of a rack and pinion system to translate a rotary drive motion into a linear displacement. The wear and tear of such systems occurs through a roll-slip mechanism. Therefore a tribological method needs to be developed to simulate such roll-slip contacts and their failure mechanisms.
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Nowadays there is a great demand to use lightweight materials, such as aluminium alloys. One of their application possibilities is in the forming industry. In such demanding applications the use of a cutting fluid is essential to lubricate cutting edge and cool down the workpiece. Until now, to evaluate the efficiency of cutting fluids, ASTM D3233 tests on a Falex Pin-and-Vee Block tester were performed. However, this procedure was developed on hard tool steels and thus it is not appropriate for soft materials, such as aluminum alloys. In this application study and a modification of this procedure is proposed for testing of cutting fluids for soft materials and alloys.
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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.