WEAR .. Understand this and you’ll add life to your all your engines, machines and equipment.
The following article is reproduced by kind permission of the author, Brid Walker, from his book “Discover the Secrets of .. Adding Amazingly Long Life to YOUR Vehicles & Equipment” © 2001. Brid, who lives in Queensland, is an authority on vehicle and machinery maintenance.
Wear: The simple reason why machines don’t last forever. Wear is more than just two parts rubbing together. There are seven important types of wear that occur in all machinery. Wear is one of the most costly factors in operating machinery, causing direct cost, inconvenience and lost production.
• Adhesive wear occurs when similar materials in sliding contact weld together, because of the frictional heat generated. This type of wear follows a “weld and tear” pattern and can produce wear debris.
How to minimize the adhesive wear. The aim must be to maintain a lubricating film at all times, so viscosity selection is important. Selection of lubricants with a higher viscosity index will provide a more constant film thickness across a wider range of temperatures at the point of lubrication. As a general rule, I prefer to recommend individual lubricants at the higher end of the viscosity range that is nominated for that type of equipment/operation. Boundary lubricants are important to provide temporary lubrication when the oil is not present, such as at start up and during severe load, which ruptures the oil film. A good boundary lubricant (anti-wear additive) will produce noticeable improvements to most commercially available oils when the going gets tough, or importantly in highly stressed components. An example of the latter is modern 5 speed manual transmission, drive trains of modern aerodynamic line-haul trucks where the aerodymanics reduce cooling air that passes over gearboxes.
We recommend SupaSLIP anti-friction/anti-wear/anti-seize additive for oils and hydraulic fluids to combat adhesive wear.
• Abrasive wear is due to gouging by debris trapped between two rubbing surfaces, or by microscopic protrusions on one surface gouging into the other. It is a ploughing action. Debris may be wear metal fragments, dirt, or even combustion bi-products .. especially soot in diesel engines.
How to minimize abrasive wear. Once again, the aim must be to separate the sliding surfaces by a strong lubricating film. Remove wear debris. Thorough cleaning or flushing of the component is sometimes necessary to remove as much wear debris as possible in a contaminated component. Reduce the amount of wear-causing debris entering the system. Change to an oil of higher anti-wear or higher viscosity, to reduce the wear rate. Be careful to ensure that the higher viscosity does not produce excessive churning and heat generation. The oil must be fluid enough to be easily pumped to all components that require lubrication.
For diesel engines, reduce the size and amount of oil soot (produced by combustion) by improving engine efficiency. Keep it in tune. Use an oil of higher dispersancy, to keep the soot finely dispersed. Prevent dust entry. Ensure all seals, joints, breathers and filtration equipment are working efficiently.
• Fretting wear often occurs during transport of equipment. Small oscillating movements, due to vibration, can cause wear due to a combination of abrasive and adhesive wear.
How to reduce fretting wear: Reduce vibration to equipment. This may mean changing to more suitable mounts, or better couplings.
• Fatigue wear. Repeated load cycles placed on a part will eventually cause small cracks and eventual failure of that part. For example, rollers in a bearing concentrate stresses in front of the contact zone and slightly beneath the surface. After a number of cycles, failure occurs and is evident as pitting.
How to reduce fatigue wear: Ensure the viscosity of the lubricant is as high as possible without compromising its pumpability, or producing excessive fluid friction causing heat build up. This allows the load to be spread further, rather than concentrated on a smaller area, which localizes the stresses.
• Corrosive wear. Any chemical reaction that removes material from the surface (eg rusting) is a form of corrosive wear. Sulfur in diesel fuel forms a corrosive acid during combustion and this can damage engine parts. Lubricating oils contain additives that combat this effect.
How to reduce corrosive wear: For lubricated parts, the main method of control is chemical, through lubricant additive packages. For engines, be sure to match the oil TBN (acid neutralizing power) and the oil change interval with the level of sulfur in the fuel. For differentials, transmissions, hubs and final drives, ensure water contamination is avoided, (or managed properly after water crossings). Where the risk of damage from high sulfur fuel is high, engines can be treated with an impervious inert barrier, that is totally resistant to chemical corrosion. One product that provides this is called Petro Tech 2000. It is also a dry film lubricant, offering boundary protection. FTC catalytic decarbonizer will also reduce oil sulfur levels .. oil analysis consistently shows that it has quite a marked effect. It is believed, that this is related to improved combustion and better sealing against “blow-by”, due to cleaner piston rings/grooves. Condensation and the growth of “bugs” is prevalent in diesel fuel and can cause corrosion to fuel injection parts. You need to control this, by draining off sediments from stored diesel fuel and where necessary, use a biocide to kill these organisms.
• Erosive wear. This is due to the impact of particles that strike a surface at speed, cutting into that surface. Carbon deposits formed in exhaust parts from inefficient combustion tend to break away and this is an example of erosive wear as they strike turbocharger blades.
We recommend FTC catalytic decarbonizer is added to diesel fuel to combat erosive wear, especially in turbochargers.
• Cavitation wear. This occurs when bubbles in a liquid collapse against a surface, eg in water pumps. The sudden change in pressure causes pitting on the component surface. Keeping cooling systems topped up to the correct level will reduce bubble formation.
Types of lubrication related to wear .. there are two main types of lubrication:
• Fluid Film Lubrication occurs when contacting parts are separated by a film of lubricating fluid (grease, oil or even air). As the relative speed between the parts increases, the motion of the lubricant provides an increased film thickness. This is termed hydrodynamic lubrication. A higher lubricant viscosity will also increases the film thickness, but heavy loads and higher temperatures decrease it. Higher speeds also create greater fluid friction within the lubricant. It becomes obvious that correct viscosity selection requires a consideration of operating speed, amount of stop/start operation, duty cycle, component loading, operating temperature, variation in ambient temperature and more.
We recommend SupaSLIP anti-friction/anti-wear/anti-seize additive for oils and hydraulic fluids to assist Fluid Film Lubrication.
• Boundary Lubrication occurs when the lubricant film no longer separates the moving parts. For example, the oil film may have ruptured due to a high loading, or the oil viscosity may be too light for the application. Some oil types provide inherently better boundary lubrication, but most commonly, the additive package contains some form of boundary lubricant. Anti-wear oil additives, EP (extreme pressure) additives for gear oils, molybdenum disulfide, PTFE (teflon) and graphite are some of the more common additives providing boundary lubrication.
We recommend SupaSLIP anti-friction/anti-wear/anti-seize additive for oils and hydraulic fluids to provide boundary lubrication.
• Beyond boundary lubrication, rapid wear takes place. At worst component seizure!