Читать книгу Hydraulic Fluid Power - Andrea Vacca - Страница 22

The most common hydraulic fluids in hydraulic systems for off‐road (agricultural vehicles, construction, and mining machines) and industrial applications are mineral‐based oils. These fluids have good operating features (according to the parameters described in the previous paragraphs) and are particularly economical in comparison with the other categories of hydraulic fluids. A good subclassification of the mineral oils can be represented by the schematic of Figure 2.2. From a base oil (HH), several other hydraulic fluids can be derived by using additives: HL implies an HH oil with anti‐oxidation and anti‐rust additives. From an HL oil, the use of additives that reduce the dependency of viscosity with temperature (VI improvers) leads to HR oils. If anti‐wear additives are added to an HL oil, the fluid is then indicated with the letters HM (or HLP). HM oils are probably the most common fluids in today's hydraulic systems. More variants can be derived from the HM oils by adding VI improvers (HV oils) or with the use of additives that reduce the stick‐slip effect that can occur inside hydraulic control valves.

The International Organization for Standardization (ISO) classification of Figure 2.2 is similar to the alternative DIN standard, which is still in use, especially in European countries. Table 2.1 shows the designations of the two standards for the most common oils.

Figure 2.2 Classification of mineral oils according to ISO 6473‐4.

Source: Adapted from Zarotti [8].

Table 2.1 Correspondence between the DIN and the ISO standard for mineral oils.

Source: Adapted from Assofluid [11].

DIN (code)	Additives	ISO
H	None	HH
HL	Anti‐rust + antioxidant + antifoam	HL
HLP	Anti‐rust + antioxidant + antifoam + anti‐wear	HM
HLP‐D	HLP + detergent + dispersant	Not envisaged
Not envisaged	HM + additives to improve viscosity index	HV