Hydraulic fluid
A hydraulic fluid is a fluid that is required to transfer energy (flow, pressure) in hydraulic systems in fluid technology. The total market of hydraulic oils prepared in accordance with engine oils is the second largest area of lubricant dar. In Germany annually consumes about 150,000 tonnes, of which about 60,000 t in mobile applications.
Properties
Hydraulic fluids must have good lubricating properties, high resistance to aging and a high wetting and adhesion. They also require a high flash point and low pour point. For use in hydraulic systems, compatibility with seals and a resin - and acid freedom is important. Other features include a low influence of temperature on the viscosity ( both dynamic and kinematic viscosity), low compressibility and shear stability and low foaming.
The tasks of the hydraulic fluids heard above all the loss-free transmission of the hydraulic performance of the pump to the motor or cylinder. In addition to this main task of the hydraulic fluid meets the lubrication and corrosion protection for the moving parts (piston, shift slider surfaces, storage, switching elements ) and the metal surfaces of the hydraulic system. It also leads impurities ( for example, by abrasion ), water and air as well as heat loss from.
Types of hydraulic fluids
Exist, depending on the intended use and required property hydraulic fluids of different types of liquids on different material base.
Hydraulic oils based on mineral oil
The hydraulic fluids most commonly used are made based on mineral oil with appropriate additives. They are also referred to as hydraulic oil. The requirements for these hydraulic oils are specified in ISO 6743/4 with the names HL, HM, HV. In Germany, the designations H, HL, HLP, HVLP to DIN 51 524 are common.
H: without additive, corresponding to the lubricating oils according to DIN 51 517 These hydraulic oils are today hardly use.
HL: with additives to increase corrosion protection and aging resistance (also HL according to DIN 51 524, part 1). They are used at pressures up to 200 and satisfy the usual thermal loads.
HM: with additives to increase corrosion protection, resistance to aging and to reduce scoring in the mixed friction area (also HLP to DIN 51 524, part 2)
HV: with active ingredients to increase corrosion resistance, aging resistance, reduce scoring wear in mixed -friction areas and to improve the viscosity-temperature behavior ( also HVLP to DIN 51 524, part 3)
HLPD: with active ingredients to increase corrosion resistance, aging resistance and -detergent additives ( German name, not standardized)
In addition to these standard hydraulic oils, engines and gear oils for mobile hydraulic applications can be used. Above all, the ATF oils (Automatic Transmission Fluid ) are used in hydrodynamic converters.
Fire resistant fluids
A second group are the fire-resistant fluids that are primarily used where mineral oils are not usable because of high fire risk. Particularly for use in coal mines and in civil aviation, the use of fire-resistant fluids is required. Other major applications are systems in which the hydraulic fluid can result in a leakage with glowing or hot metal or open flame in contact ( pressure foundries, forging presses, power plant turbines, metallurgical plants and rolling mills ).
The fire-resistant fluids are divided into the following groups:
HFA: oil-in -water emulsions or solvent products with a water content of more than 80% concentrate and mineral oil-based or based on soluble polyglycols. In concentrate on mineral oil base is a risk of segregation and microbial growth. The liquid is flame retardant and can be used for temperatures between 5 ° C to 55 ° C, due to the very low viscosity results in high leakage losses.
HFB: water-in -oil emulsions with a water content of more than 40% and mineral oil. The liquid is flame retardant and can be used for temperatures between 5 ° C to 60 ° C. In Germany it is not allowed due to inadequate fire behavior and is rarely used.
HFC: water glycols having a water content of about 35% and polyglycol solution. The liquid is flame retardant and can be used for temperatures between -20 ° C to 60 ° C and pressures up to 250 bar. It is the most common hydraulic fluid under the flame-resistant fluids. In case of contact with zinc in the piping system leads to the formation of zinc soaps, which, for example Pressure filter may be added.
HFD: Anhydrous Synthetic liquids with a higher density than oil or water ( not HFD -U) can cause problems with suction pumps and access to many seal materials, since the compatibility with plastics is problematic. The liquid is flame retardant and can be used for temperatures between -20 ° C to 150 ° C. This is depending on the main component of the following types:
- HFD -R: phosphoric ester
- HFD -S: anhydrous chlorinated hydrocarbons
- HFD -T: mixture of HFD -R and HFD -S
- HFD -U: anhydrous different composition ( consisting of fatty acid esters )
Environmentally friendly hydraulic fluids
For use in biologically critical ( Construction in water protection areas, forest machinery in the forest, snowcats in the mountains, etc. ) hydraulic fluids have been developed that are biodegradable. These fluids can be produced from petroleum, but they are often based on renewable resources, such as produced, for example vegetable oils. Biodegradable fluids from renewable raw materials are also referred to as biohydraulic fluids. Environmentally friendly hydraulic fluids are harmful pollutant class I, the labeling is HE (Hydraulic Environmental ).
The environmentally friendly hydraulic fluids of the following types:
- HETG (base = triglycerides vegetable oils ): These fluids are highly biodegradable and usually not hazardous for water. Compared to mineral oils they have a lower resistance to aging and may be used only restricted under temperature stress.
- HEPG (based on polyglycols ) polyglycols are made from petroleum, they are highly biodegradable and non- hazardous for water. Their properties are comparable to those of mineral oils, they are soluble in water and not miscible with mineral oils or vegetable oils.
- HEES ( synthetic ester base ): Synthetic esters can be produced both on the basis of renewable raw materials and on the basis of mineral oil. They are highly biodegradable and non- hazardous for water or meet the water hazard class 1 have a high resistance to aging and are insensitive to extreme operating temperatures.
- HEPR ( other base fluids, primarily in the poly -alpha-olefins ).
The proportion of Biohydraulikölen increased massively in recent years in Germany; he was in 2000, only about 3 %, rising to 2005 especially in mobile hydraulics to 19% of the total market. One of the main reasons for this represents the market introduction program biolubricants the Federal Ministry of Food, Agriculture and Consumer Protection, by the shift to bio-lubricants in the years 2000, was promoted to 2008.
Water
Water is safe as a hydraulic fluid in all respects. Pure water is not used in the hydraulic performance, instead, it is mixed with oil to form an emulsion, similar to cooling lubricants in metal cutting machines. The first technical use of hydraulic performed with water as the fluid. Water has a practically constant low viscosity., The compression factor is about 60 % of the hydraulic oil.
Classification:
- Tap water (filtered)
- Technical water (water -oil emulsion )
- Sea or salt water (filtered, not suitable because of the aggressiveness )