Fasteners Lubrication Alignment Balance

Products
Contamination Control
Reliability Software
Services
Training

Lubrication

oil
Lubrication is the lifeblood of the machine.

The lubricant represents the sole impeding force to prevent that from occurring. Sometimes called the “life blood” of the machine, the lubricant must provide the dynamic separation of machine surfaces – the blood cell-sized film - to protect your machines against the normal dynamic forces of operation. And when vibration is allowed to get out of hand due to poor management of fasteners, alignment and balance, the warrior is overwhelmed and failure ensues.  Here are some common problems seen on the plant floor.

  1. Wrong viscosity or viscosity index.  
    1. If the viscosity is too low, the lubricant can’t develop sufficient film thickness to separate component surfaces.  If the viscosity is too high, it may not flow into the clearance areas easily enough or be sufficiently splashed or slung to the points where it is required.  One can’t determine the required viscosity without considering the operating temperature, since temperature has such a great influence on viscosity.  When temperature fluctuates significantly, the application requires a high viscosity index fluid.  Viscosity index is a dimensionless number that indicates how much viscosity changes for a given change in temperature.  A high viscosity index increases the temperature range in which the lubricant is suitable.  A common mistake in the plant is to overlook the viscosity of the base oil in grease.  Viscosity is the most important property of the lubricant, make sure you get it right for both oil and grease lubricated applications.
  2. Wrong additive package.  
    1. Ideally, the machine develops a full-film separation between moving surfaces – hydrodynamic for sliding contacts and elasto-hydrodynamic for rolling contacts.  However, in some instances due to high loads, frequent starts and stops, load and speed variations, etc., full-film lubrication can’t be achieved.  In these instances, the lubricant must be formulated with an anti-wear (AW) or extreme pressure (EP) additive to protect the machine under boundary contact conditions.  These additives don’t eliminate wear, but rather reduce it through a mild chemical corrosion intervention.  Other operational and/or environmental conditions may warrant other additives to modify the performance properties of the lubricant.  These might include detergents, dispersants, viscosity index improvers, pour point depressants, tackifiers, etc.
  3. Wrong lubrication interval.  
    1. Too many plants just guess at the right interval for greasing or performing oil changes.  An oil change is a downtime task that introduces a lot of risk to the system.  We may not use the right lubricant.  We may not reestablish the correct level.  Valves may be left open and breather and fill caps may be left off.  We may introduce contamination during the process.  The list goes on.  Employ oil analysis to either change the oil on condition or to establish and appropriate change interval through experimentation.  Sometimes, oil is changed with the intent of decontaminating.  Usually, the machine is shut down for some period of time prior to draining, which allows the dirt, water, sludge and other debris to settle to the bottom – rendering the oil change futile as a decontamination tool.  Instead of changing the oil, consider offline filtration when the machine is running where appropriate or while it’s shut down in other cases.  If the goal is to decontaminate, then make sure your PMs are effective.  Greasing is another area where entirely too much guesswork is applied.  Fortunately, formulas exist for estimating the appropriate greasing interval, which consider the machine, the application and the environment.  For some applications, ultrasonic instruments can add an extra degree of precision.
  4. Wrong lubrication volume.  
    1. Occasionally, oil lubricated systems lack a level indicator.  This is really an unacceptable oversight.  We must be able to check the level of all lubricated machines.  Ideally, the mechanism is non-invasive (e.g. no dipsticks) and indicates the acceptable level when the machine is running and when it’s down.  Much more common is lack of detail in PMs to instruct lubrication techs how much grease to apply.  Over and under greasing are primary root causes of electric motor failure. PMs sometimes “grease the motor” without clearly stating what kind of grease and how much to apply to the drive and non-drive ends (yes, it’s commonly different).  We must clearly define the volume of grease to be applied to each lubricant point in our lube routes – the formulas area easy, but it takes some work to gather the input information.  As is the case with precision fastening, alignment and balance, precision lubrication requires a clear definition of the quantity and quality details.
  5. Insufficient contamination control.  
    1. Rivaling lack of precision in quantifying how much grease to apply to each point is a lack of precision on controlling contamination, which prohibits thee lubricant from doing its job.  A contaminant is anything that’s in the lubricant but shouldn’t be.  Water and particles are the most common, so we’ll look at them and their effects in more detail.
      1. Water contamination.  
        1. An obvious risk of water contamination is rust and corrosion on metal surfaces.  Less obvious is hydrolysis.  Water contamination reacts with many lubricant additives, reducing their effectiveness and, in some cases, producing hydrogen sulfide and sulfuric acid.  Water also reacts with metals to produce oxidizing agents that attack the base oil.  Even less obvious, and potentially more deleterious, is how water affects the lubricant’s film strength.  As previously discussed, viscosity is the lubricants most important property because it determines film thickness.  Oil possesses a physical property whereby viscosity increases as a function of pressure.  The higher the load, the higher the viscosity and the film thickness.  Water does not possess this same physical property, so when it’s present, the viscosity-pressure relationship in the oil is compromised, which decreases film strength and increases the likelihood of surface to surface contact. Water is particularly damaging in rolling contacts, where the load forces are very high – in the hundreds of thousands of pounds per square inch.  Rolling element bearings, for example, depend on the viscosity-pressure relationship in oil to protect components.  Water contamination can increase wear rates by as much as 40 times.  Target levels for moisture should range between 100 and 300 ppm or better for most applications. Except for rare cases, water contamination should never be allowed to exceed 500 ppm.
      2. Particle contamination.  
        1. The lubricant provides a blood cell-sized separation between moving surfaces. If it’s not present in contacts that are in relative sliding motion, surface to surface contact and abrasion (two-body) occur.  In rolling contacts, the lack of a lubrication film results in surface fatigue.  When clearance-sized and larger particles are present in sliding contacts, abrasion (three-body) occurs even when there is film separation.  The particles in oil and grease act like the bits of grit on sandpaper to wear away surfaces.  In rolling contacts, the process is somewhat more complex.  Rolling contacts (e.g. rolling element bearings) transfer load via very small point or line contacts.  The momentary load is extremely concentrated – in the hundreds of thousands of pounds per square inch – and the lubricant film - is very small – rarely exceeding half the diameter of a red blood cell.  A hard particle can bridge the gap provided by the lubricant film and transfer the load to the component surfaces, often concentrating it further.  If a 250,000 psi normal load is transferred via a particle to an area one-tenth the normal area, the resulting load is 2.5 Million psi.  This extreme load typically exceeds the fatigue limit of the metal and produces subsurface cracking.  Over time, the cracks propagate (grow) to the surface and the damage material is released.  This is called pitting wear.  The surrounding material is damaged and dented and overtime may lift away from the surface – a wear mechanism called spalling.  Particles are involved in an estimated 80-90% of all wear, though other forcing functions like vibration, water contamination and insufficient lubrication contribute and influence the rate at which this occurs. For most applications, cleanliness should be maintained to ISO 4406 15/12/9 to 19/16/13, depending upon the criticality of the application and the machine’s sensitivity to particle contamination.  Contamination should never be allowed to exceed ISO 4406 21/18/15.
  6. Incompatible grease thickeners. 
    1. Unique to grease is the thickener.  These thickeners are frequently incompatible with one another.  A very common problem is the failure to define the grease used in the initial charge at the motor factory or rebuild shop.  If the factory or rebuild shop employ a polyurea thickened grease, for example, and the plant uses lithium complex thickened grease for routine lubrication PMs, you have a probable compatibility issue on your hand.  The incompatible thickeners will react, soften and separate, causing the grease to leak out and/or for thickener, which provides no lubrication in the component contact zones, to cake up and harden, which prevents new grease from making its way into the components.

 

For more information, call (662) 890-9392 or send us an inquiry.