Martin Williamson of KEW Engineering, a speaker at Reliability UK 26 September, Old Trafford, will focus on best practice in lubrication, contamination control and oil analysis for machine reliability.
In his guest blog here, Martin highlights the continuous, insidious destruction that can be wrought on a machine’s surface by solid particle contamination of the lubricant and he explains why simply using a filter is not enough to prevent this.
Solid particle contamination of the lubricant is considered to be the worst case scenario of all the various contaminant forms. A continuous, insidious destruction of the machines’ component surfaces via the mechanisms of abrasive, erosive and fatigue wear.
Solid particles are difficult to define, though, as they come in a variety of shapes and sizes. The most destructive, logically, have to be the hard, jagged, angular material of roughly the same size as the oil film. That means sizes in the order of 10µm and smaller, typically. Invisible to the human eye. The hidden enemy, to borrow a phrase.
At any given time the amount of solid material in the system could be defined as:
P(Total) = P(Built-in) + P(Ingested) + P(Generated)
Built-in – debris from the manufacturing and repair or service work.
Ingested – drawn in from outside the machine such as dust, or soot.
Generated – metal wear particles generated through wear.
So we might define the total number of solids as BIG!
However, it stands to reason that the number of particles generated is a function of a number of root causes, or put mathematically:
P(Generated) = f( P(B) + P(I) + Balance + Alignment + Frame Looseness + other root causes)
P(Generated) = Wear or if looking at this against time, the wear rate. Consequently our objective must be to reduce P(Generated) in order to reduce the Wear Rate and maximise the machine life.
Inevitably with rotating equipment, balance and alignment are in control, and to an extent so is frame looseness or the integrity of the fasteners, whilst other minor but possible risk root causes are also under control.
However, flushing procedures during build and post-repair work normally also take care of built-in debris on more complex or critical systems so this too is under control, but on smaller systems, there often remains a large degree of solid contaminant resulting from the manufacturing assembly, such as casting sand, machining swarf, weld spatter and other assembly induced debris. Welcome to pre-filtering the new oil and flushing these smaller systems during commissioning and post repair work can significantly improve the machine life potential.
Of course, the issue of the ingested contaminants must be addressed. Most maintenance personnel think that this is adequately covered by the OEM or supplier. The truth is, it isn’t.
The average umbrella handle style tube breather might stop a pigeon defecating in your tank, the average hole in a bolt breather might stop a large grain of sand, but these won’t protect your machine from AIDs (Agents of Invisible Destruction). Welcome to the high performance desiccant breather, a must fit upgrade on all machines.
The average lip seal sucks, if you will excuse the pun, as much as it dribbles. On worn lip seals, as they inevitably become in relatively short order, then as the machine warms up, it dribbles oil. As it cools down, it sucks in air and the associated crud around the seal. Whilst a breather is supposed to prevent this often the breather is clogged with debris, thus exacerbating the problem. Welcome to high performance mechanical seals.
The average oil level check involves opening a plug or pulling a dip-stick, both allowing the ingestion of solids, more so if wiping the stick with a dirty rag or shoving a dirty finger in the plug hole. Welcome to more efficient, time saving sight gauges.
The process of filling a machine typically involves an open jug that was exposed to atmospheric contamination, and pouring the oil in through a funnel, also covered in dust. Remember the hidden enemy? We can’t see these particles. We think our dispensing tools are clean, that is what our eyes tell us. Welcome to snap-on connectors and hoses and pumping the oil in from a sealed container.
If you have read this far, you may be thinking I have forgotten the basic fact that a machine has a filter and therefore all this is of little consequence?
Not all machines are fitted with a filter. Add to which, a filter should not be a means of cleaning up one’s bad practices like some mother following her messy son around the house. Machine filters are designed to withstand a number of factors such as pressure, flow and vibration as experienced on industrial machinery. As a consequence, these cost a lot of money, typically twenty times as much as what you might pay for your passenger car oil filter. So surely it makes sense to extend their potential service life by not exposing them to easily avoidable solids, but rather to let these high cost, high performance filters focus on the generated material? Furthermore, ingested contaminant is not instantly removed from the oil, it may circulate up to ten times before being trapped (especially if the purchasing department have been buying cheap filters again), in which time a reasonable amount of surface damage is caused with a resulting additional number of wear metal solids created in the process adding to the load on the filter and reducing the potential service life of the machine.
The fact is contamination control is a cradle-to-grave process, not just for the machine, but also for the lubricant. Controlling at source is always more cost effective than controlling through removal within the machine.