Oil and elements

[kritter]

What benefits do these additives add to a hydraulic oil?

phosphourus
zinc
calcium
silicon


I assume it helps seals and o-rings but I dont know that for a fact.

Thanks,

Kris

 

[patprimmer]

This is not my strongest area, but I think the metals are not added as elements, but are contained in compounds. The compounds are extreme pressure additives. They may also serve other functions like detergency, especially the calcium compounds

The silicon, I don't know why, maybe anti foam?

Regards
pat pprimmer@acay.com.au
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[kritter]

I ask becuase I sent out a few oil samples for analysis and they came back with varying amounts of those elements and I havent been able to get an explanation as to what those elements do or how those elements improve the oil.

 

[aviat]

The zinc and phosphorous are anti wear agents, and the magnesium, calcium and boron are anti corrosive agents. The silicon is usually from dirt entering engine though air intake system or oil.

 

[25362]

To kritter. A few lines concerning Si.

Hydraulic oils, or fluids, have all the characteristics of lubricants: viscosity, VI, oxidation resistance, tribological and anti-corrosion properties, most of those achieved by the additives already mentioned by patprimmer and aviat.

Apart from those characteristics, the specific important features of hydraulic fluis are:
incompressibility, to transmit power successfully; compatibility with seals;
air-release;
filterability;
shear stability in the case of non-Newtonian fluids; and
anti-foam properties (to avoid gas (air) entrapment with an increase in compressibility).

The most important antifoam chemicals to deal with non-aqueous foams are polydimethylsiloxanes, and fluorosilicones. These contain Si, and may be the source of the Si found in the samples, in addition to what aviat has said.

As for the compatibility with elastomeric seals and O-rings, since oils have a tendency to shrink and harden elastomers, a careful balance with polar esters, which are known plasticizers, are formulated.

 

[drwebb]

Technically, Zn/P compounds are properly anti-wear additives because they activate at lower surface temperatures than extreme pressure additives. They also impart good anti-oxidancy as well.

All these additives can be found in motor and gear oils, although for hydraulics they're typically at a small fraction of those concentrations.