This article will answer the following questions:
- Why and how do lubricants fail?
- Why do I need to change my oil?
- Do I have to use the recommended oil for my machine?
Lubricant failure means the basic lubricant functions have become overwhelmed, which ultimately can lead to wear and machine failure. This article will discuss some of the ways lubricants can fail.
Under / insufficient lubrication
This can be thought of as anything preventing lube oil getting to the right places at the right time within the machinery. The two common sources of under or insufficient lubrication are not maintaining sufficiently high enough oil levels or poor lubricant delivery systems.
In terms of oil level this can usually be addressed by simple sight glass checks or regular dipstick measurements to maintain the oil levels. In many vehicles there are also automatic sensors to detect low fluid levels and warn drivers too on the dashboard. The solution is usually a top-up and some machines need more top-ups than others with some machines seeming to guzzle oil. The reason for the top-up requirement can only really be identified through a thorough inspection or better still an oil analysis as this can help rule out mechanical failure mechanism causes such as worn rings vs a leak in the sump. Moreover, a sufficiently high fluid level does not necessarily mean the system is being well lubricated as in an engine for instance, fuel and coolant leaks will increase the volume but not be healthy for the lubricant or engine. Hence, regular oil analysis will help identify causes of rising fluid levels as well as oil levels that are satisfactory but the oil is contaminated with a foreign fluid.
The second most common under lubrication cause is from lube delivery systems, which are commonly seen with automated greasers which deliver a set volume of new grease at set time intervals. The problem can be if the nozzles on these delivery systems block then no grease reaches the bearing and metal to metal contact can occur. Therefore such procedures on site should include regular checks of automatic lubricators to confirm they are operating as they should be. Regular grease microscopic analysis has proved very beneficial in analysing the wear particles such as sliding wear to confirm if the system is being sufficiently lubricated and is becoming common place on key greased systems. Even when microscopic analysis is not possible as only small volumes of greases can be obtained then elemental analysis using the LubeWear technique is a great way to identify abnormal wear early and far superior to traditional grease analysis wear element techniques.
Even when the oil in use is perfect for your machine and the machinery is in good working order, lubricants will still degrade over time. This can be in two ways i.e. degradation of the base oil and degradation of the oil additives.
Let’s start with additives. Additives are compunds added to oils to enhance desirable or remove undesirable properties of an oil. This becomes more significant when a lower quality base oil is used with higher additivisation compared to higher quality base oils with lower additivisation. For example common additives added to enhance the viscosity index of an oil so it remains more constant with temperature changes are called VI improvers and they are found in almost all multi-grade oils on the market. They have a great property in uncoiling during hot temperatures to give an appearance of thicker viscosity at high temperatures and are very effective. However, over time these additives going through the hostile conditions of an engine get mechanically broken apart over time. This process is called polymer shear and means that the oil will over time get worse at staying thick at high temperatures. This can mean that metal to metal contact can occur in the worst scenario, but depends on the quality of the additives and base oil used to start with. Measuring the VI of an oil regularly with oil analysis can help identify when the VI improvers are starting to be spent before the lubricating properties of an oil begin to be impaired.
In terms of the base oil, oxidation, which is accelerated by high temperatures leads to sludging of an oil and also varnish production which can coat components, sieze valves and prevent heat loss leading to overheating. Regular monitoring of properties such as acid number, base number and oxidation in an oil can identify when the oil is coming to the end of its life and allow lube oil changes to be done at the correct times.
Contaminated lubricants account for approximately half of all lubricant related failures and as high as 80% of all hydraulic failures. This can be from either solid or fluid contaminants. Solid contaminants such as dirt or grit are abrasive causing cutting or three body wear to components. When under high pressure they can also bombard surfaces similar to sand blasting and lead to damage. Solid contamination can also block filters and small orifices restricting the flow of lubricant and lead to lubricant starvation and wear. Fluid contaminants such as water will alter the load handing ability of an oil and catalyse lubricant degradation. The lubricant degradation point is explained above, but the load handling can be be because of multiple mechanisms. For instance, antiwear additive depletion termed additive wash out. However more importantly is the fact oil is denser than mineral oils and hence will collect at the bottom of all lubricant pathways. This is usually the load carrying point such as a the bottom of a bearing. Water is a much poorer lubricant than oil, but it is when under high load it boils and turns to water vapour that the most damage is done. Firstly the gas has negligible lubrcating properties compared to the oil leading to metal to metal contact. Secondly the act of the water boiling will collect at certain points repeatedly on the loaded surfaces meaning the small bubbles as they form and collapse cause very small impacts repeatedly on the loaded surfaces to lead to fatigue cracks and pinhole corrosion within the machine.
Water has the added problem in that it can also cause corrosion / rusting. Naturally a cleaner oil is a healthier oil and so appropriate lubricant handling and preventative measures can be adopted such as breathers, and bottom of storage tank run-off. However it often comes that post contamination entry solutions are required such as filtration. Thankfully lube anlaysis is the most effective way to monitor your machinery cleanliness and is the best way to detect early water and dirt contaminants.
Incorrect Lubricant Selection
Unlike the other methods of lubricant failure discussed above that generally happen over time causing the lubricant to not function as well as it previously had, incorrect lubricant selection is a problem from the moment you make the purchase as a wrong oil can potentially cause serious wear and damage to the machinery.
Most important is to ensure the oil is of the correct viscosity grade for your application. The additive package will also have approvals depending on the manufacturer of the equipment, so it is worthwhile confirming the additive package meets the requirements for your machinery too. Additional characteristics depend on what your key criteria for the lubricant actually are. So in large volume systems exposed to water that you want to drain off regularly, then good water shedding properties are desirable. If looking for a longer life or varnish handling properties the base oil selection becomes more important. If your lubricant needs to handle temperature extremes then the pour point and oxidation resistance properties become more important for low and high extremes respectively.
The great thing with all these failure modes is with correct lubricant management training and an established lubricant analysis programme, these failures are all avoidable or manageable to a point where the impact on your business is minimal. If you would like to find out more about lube analysis training and testing options you need for your business then press the contact button on the bottom right of this screen.