New Machines / New Challenges

Ronald Bakker, Product Application Specialist at Shell, explains the demands new machinery is placing on hydraulic oils and gives advice on what properties to look for when purchasing an oil to meet the challenge.

With the developments in modern machinery, hydraulic machines are now smaller, more compact and operate at a much faster rate.  This is ideal as engineering and manufacturing companies can now fit more machinery in a factory, substantially increasing productivity. However, these improvements in machines place additional pressure on hydraulic oils.

The simple fact is new machines have a reduced reservoir capacity as large and traditionally older machines have more space for oil and consequently more oil is available to be used during cycles.  In addition, with new, more compact machinery running at a much faster rate, more oil is needed per pump to meet the increase in productivity.  With more power being absorbed by less oil, the hydraulic oil operates at a higher temperature, which can cause the oil to oxidate.

Temperature In our experience, temperature significantly affects hydraulic performance and lifetime.  Our research shows that for every 10°C rise in oil temperature above 70° C, oil lifetime reduces by 50%, which is why the additives used within the oil play a crucial role in determining the quality/performance of the product.  When oil oxidises it creates sludge and clogs filters and valves resulting in the system eventually failing.  In addition, the viscosity (thickness) of the oil becomes thicker which can result in increased pump noise, more system wear, all adding significant maintenance costs.

Speed of the machines

With the oil capacity of machines being reduced and yet the running speed increased, resulting in more oil being pumped to generate the required energy, the oil retention time is significantly reduced, placing further demands on the oil.  For example, an older hydraulic machine has an oil capacity of 600 litres and a pump capacity of 100 litres, giving a six minute oil retention time.  In newer systems, the oil capacity is for example 300 litres with a pump capacity of 150 litres, significantly reducing the oil retention time to two minutes.

Impurities

This puts increased pressure on the oil getting rid of all the impurities, such as air and water, picked up during the cycle.  If the oil fails to get rid of the impurities it will go through to the pump and be sent around the system again.  This process will continue with the oil picking up more and more impurities each time its goes round due to the oil not having enough time to recover.  This obviously has an effect on the quality of the hydraulic oil which will ultimately reduce productivity and cause damage.  Engineering companies need to ensure when buying newer models of the same application that they check the operating manual and the oil requirements.  For example, newer machines might need a higher viscosity of oil due the demanding operational conditions.

The simple fact is new machines have a reduced reservoir capacity as large and traditionally older machines have more space for oil and consequently more oil is available to be used during cycles.  In addition, with new, more compact machinery running at a much faster rate, more oil is needed per pump to meet the increase in productivity.  With more power being absorbed by less oil, the hydraulic oil operates at a higher temperature, which can cause the oil to oxidate.

Oil Sufficiency

If the oil is not of sufficient quality to cope, water, air and other materials will get into the system which can have serious effects on the hydraulic system, application and the actual finished workpiece.  If excessive amounts of water get into the system then several problems occur.  During shutdown time, weekends or annual holidays, water will sink to the bottom of the tank and will cause internal rusting in the reservoir.  This means that on Monday morning, the first shot of oil will carry a significant amount of water causing further problems.  As we all know, water is a poor lubricator and consequently excessive water in hydraulic fluids can cause pump damage, bearing failure and possible filter blocking due to bacterial growth.

Air in hydraulic fluids

Air in hydraulic fluids is another serious issue and if air bubbles caused during the cycle are not given enough time to go to the surface and clear, then just like water, the pump will carry them around the system.  Air in hydraulic fluids can cause a number of problems including cavitation, with air bubbles within the oil causing the temperature to rapidly rise until the air bubble implodes.  This rapid acceleration in temperature causes the oil to carbonate, which results in the oil turning black and carbon deposits damaging pumps.

If cavitation leads to the pump to be replaced, then as well as changing the pump, you need to change the oil and clean the system of all particles.  Our research shows that the lifetime of a pump will continue to decrease if only the pump and oil are changed following the failure.  Other problems caused by air in hydraulic fluids include spongy controls, horsepower loss, foaming, poor temperature control, noise, poor lubrication and oxidation.

With all this pressure on hydraulic oils to perform, an effective oil needs to excel in many different areas; anti-wear, air release, demulsibility, filterability, storage, thermal stability, anti-foam, hydraulic stability and rust.  The DIN (Deutsches Institut für Normung, Germany's National Standards Organisation) standard on hydraulic oils sets out the requirements that hydraulic oils must meet.  Engineering companies should look at this standard as a minimum and should look at specific Original Equipment Manufacturers (OEMs) lubrication guidelines or/and standards which will meet their individual hydraulic system and production requirements.

Hydraulic oil is the lifeblood of any system and you must make sure it can cope with the pressure.