Oil analysis: Helping boost machine uptime?
23 September 2015
If 80% of all hydraulic failures on machinery can be traced back to contaminated oil, why do maintenance engineers place their faith in component monitoring? Chris Gray, filtration product manager at Bosch Rexroth explains why oil sampling is the key to greater machine uptime
Preventive maintenance and component monitoring are two of the big buzzwords being used more and more across British manufacturing. This puzzles me, particularly in relation to hydraulics because figures suggest that only 20% of unplanned downtime can be identified through component monitoring. In fact, 80% of all hydraulic failures on machinery can be traced back to contaminated oil.
Oil analysis has the capability to prevent expensive repairs, minimise downtime, detect early damage to components, optimise filtration systems and even provide environmental relief through the minimisation of wasted oil.
There are three types of contamination which can be identified by oil analysis. The first is solid particles, such as dirt and dust particles which can cause jamming; influence control behavior, prematurely wear components leading to failure and a reduction in machine availability.
The second type of contamination is liquid contamination which are in the main water and fluid mixtures. This type of contamination can cause corrosion and wear, along with impairment of viscosity and even cause a chemical reaction with the fluid which can impact lubricating properties. In addition, the effectiveness of machine filters can be reduced along with filter service life. Again, all of these issues can lead to reduced machine availability.
Finally, gaseous contamination, such as air, can have a number of serious consequences. Foaming in the oil sequences; inaccurate response of valves; energy loss; damage to pumps; chemical reactions with the fluid and oxidation, can all result in a reduction in machine availability.
Contamination can find its way into a machine’s oil supply in a number of ways. Built-in contamination is a product of the component manufacturing process. Foundry sand or dust and residues from welding, metal chips, shot blasted materials, paint particles, preservatives and cleaning residues can all find their way into the oil and create machine problems.
External contamination occurs from the ambient air once the hydraulics are operational within a manufacturing environment. Ambient air, via piston rods, labyrinth seals and vents, can have an adverse effect on oil and reduce its operational effectiveness.
Lastly, generated contamination will also impact machine oil. Metal wear through abrasion or erosion of components can cause seal abrasion, chemical corrosion and oxidation residues which all occur when mixing oil with insoluble substances.
A typical contaminant would be silica, a hard airborne particulate, which can get between the working surfaces or clearances on machinery components, such as a pump or cylinder. Once contamination has occurred it will circulate between the two components, gradually wearing away the surfaces. As the surface abrasions get bigger, leakage occurs leading to component failure, such as valve stitching.
These hydraulic failures are directly attributable to oil contamination, via components such as cylinder rods. What’s more, once in place, there is often a chain reaction of particles. One particle rubbing against another breaks off and splits into two. Two particles split to become four and four become eight. Often, the solution is simple, such as the installation of offline filter units.
While oil analysis can be incredibly effective as part of a preventive maintenance programme, it does take valuable time which takes engineers away from more critical problems. All-too-often, no oil analysis is undertaken or the schedule falls by the wayside as more critical issues take priority.
Oil analysis, such as the Bosch Rexroth oil analysis service, can identify how much particulate is potentially affecting the smooth running of a machine. What’s more a recognised industry standard is now in place, ISO 4406, which measures 100 millilitres of oil and gives a particulate reading.
Only regular oil analysis can prevent build-up of particulates and ensure the machine stays available 100% of the time. Cleanliness of the oil is crucial and is an efficient method of identifying potential problems. It offers the opportunity to identify appropriate levels of filtration and, if necessary, upgrade.
Ideally, machines should be sampled on at least a quarterly basis and levels of contamination should be plotted on a graph. Only in this way is it possible to identify problems before they become critical.
Oil sampling does come with a small cost, but if a company has 100 machines working intensely, a simple oil analysis, costing as little as £15, has the potential to prevent a costly component fault or stoppage which far outstrips the sampling cost. When you consider that the cost of replacing an average sized pump is approximately £5000 the financial argument really begins to stack up.
Monitoring oil cleanliness is an important factor in preventing failures and should become a must in any modern maintenance and servicing regime.