Technical
side of these for short periods are not immediately detrimental to the performance of the biofluid.
However, at longer lasting or continuous high working temperatures, the molecular structure of vegetable oil will be damaged and deterioration or ageing of the fluid is drastically accelerated.
If an environmentally friendly product is required outside the common temperature range mentioned above, a biodegradable synthetic fluid would be required. These synthetically manufactured products still offer all the biodegradability of vegetable oils, but they can operate at temperatures in excess of +200°C and still retain a long fluid service life. The only caveat is that they tend to have a significantly higher price.
If a biodegradable fluid is not agitated for a considerable period of time, the surface in contact with air and/or moisture may start to biodegrade, which is what it is designed to do. This can have an impact on the way the fluid is stored; for example, in a used container or if a machine is stored and not used during the quieter winter period. To prevent this natural occurrence, it is suggested that the machinery stored during prolonged inactive periods is started and run for a few minutes once a month. Also, half-full containers should be given a vigorous shake at the same interval.
Ageing of Biofluids
Various possible causes can lead to irreversible and irreparable damage to hydraulic fluids in general, which can be regarded as ageing of the fluid. This deterioration occurs not only during use of the fluid, but also during storage. It may be accelerated by particulate and water contamination, as well as direct contact with metals.
It is widespread, but mistakenly, believed that mineral based hydraulic fluid does not age. There are chemical reactions in every type of oil, which change the properties of the base fluid, as well as the additive package. If a hydraulic fluid (or lubricant) cannot perform to its technical requirements, it has to be changed.
There are four dominant mechanisms contributing to the ageing of oils:
Polymerisation, Oxidation, Hydrolyses and Thermal Cracking.
Polymerisation: This leads initially to an increase in viscosity and, eventually, to the formation of silt and sediment. This reaction is dependent on temperature, moisture, light and metallic catalysts. The result is an hydraulic system reacting and performing much slower than normal.
Oxidation: Oxidation is the loss of electrons or an increase in oxidation state of a molecule. If the oil comes into contact with oxygen, e.g. through the air breather of the reservoir, the oxygen will react primarily with the molecular double bonds of the oil. The more double bonds are present in the molecules, the faster the oil will oxidise. The final reaction products are often very corrosive, which can cause damage to machine components, especially to the seals, as well as silting of the oil.
Hydrolysis: The chemical reaction between an ester molecule (found in oils and
132 PC FEBRUARY/MARCH 2014
Types of Biofluids and their Applications
Due to mineral-based hydraulic oil’s slow and long biodegradability, the use of vegetable-based hydraulic oil could be an excellent environmentally friendly alternative for the fine turf manager. Readily biodegradable hydraulic fluids are classified in the following four main groups, as dictated by DIN ISO 15280:
Conventional Vegetable-based Fluids - HETG (Hydraulic Oil Environmental Triglyceride): At the start of biofluid development, the focus was on lubricants made from vegetable oils, typically from rape or sunflower seeds. Vegetable-based fluids are readily biodegradable.
Hanfried Sievers
“If a biodegradable fluid is not agitated for a considerable period of time, the surface in contact with air and/or moisture may start to biodegrade”
lubricants) and a molecule of water or metal compound is described as hydrolysis or saponification (formation of soap), causing the cleavage of chemical bonds of the ester molecule into alcohol and acids. The acid products especially can lead to damage of the hydraulic system and its components.
Thermal Cracking: When the molecules of the oil are split by high temperatures it is called thermal cracking. The temperature spikes may be caused by cavitation, too small diameters of the hydraulic pipes or hoses, lubrication grooves, etc. Some of the reaction products are very flammable gasses, which will cause further temperature spikes during oxidisation, so that a chain reaction could be started.
To counteract this ageing process of oil, it is important to look after and maintain the oil. Research has proven that optimal filtration can extend the life of oil. Removal of metal particulates and oil ageing products will slow down the chain reactions and lengthen the intervals between necessary oil changes.
Unfortunately, multiple unsaturated fatty acids in the vegetable-base stock leads to oxidation and hydrolysis, especially at elevated temperatures. In general, these vegetable-based fluids can only withstand operating temperatures not exceeding 80°C. A further drawback is that they become unstable when exposed to wet environments or are contaminated with water.
Therefore, their performance is most suited to cool and dry operating conditions and equipment operators must take care to ensure that these limitations are not exceeded. These fluids are typically used in land-based and forestry machines, which are subjected to low peak performance only.
Synthetic Esters - HEES (Hydraulic Oil Environmental Ester Synthetic): The second phase of biofluid development focused on synthetic esters. Synthetic esters are readily biodegradable and only very slight water pollutant. Full-synthetic saturated esters exceed in oxidation tests, compatibility and lubricating properties in comparison to most mineral oils.
Esters are synthesised by the reaction of vegetable oil with fatty acid and alcohol, with water and heat as by-products. At elevated temperature, and in the presence of water, this reaction is reversible, which is known as hydrolysis. This reforms the alcohols, acids and original triglycerides. which can cause rust and wear, seal degradation and corrosion to yellow metals. Consequently, ester-based fluids must be maintained in a cool, dry state to obtain maximum performance. They are used where higher working temperature of the fluid cannot be avoided; such as construction machines (excavators).
PAO-based Fluids - HEPR (Hydraulic Oil Environmental Polyalphaolefine and Related Hydrocarbons): This classification embodies fluids blended from Polyalphaolefine (PAO) basestock and related hydrocarbons, such as bio- polyolefin. These are made by hydro cracking of the paraffins resulting from mineral oil distillation.
One distinct advantage of PAO- based fluids is that they can be tailor-made to fit specific requirements. These fluids do not hydrolyse and, as such, are much more stable in hot, wet conditions. Bio-olefins are typically compatible with Buna N, Viton and all common elastomers, as well as adhesives used in filters. One drawback is its high price and another is that it is only inherently biodegradable.
PAG-based Fluids - HEPG (Hydraulic Oil Environmental Polyglycole): PAGs can be either
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156