ISO 7745:2010 pdf free download – Hydraulic fluid power一Fire-resistant (FR) fluids一Requirements and guidelines for use.
The optimum concentration shall be decided after tests with the fluid and the diluting water, and discussion with the fluid supplier. When prepared manually, it is usual to add the concentrate gradually, with continued stirring, to the required volume of water. For large volumes, automatic mixers are available. The concentrate typically consists of a combination of water-soluble corrosion inhibitors, pH buffers, and anti-wear additives; anti-foam agents, bactericides, and fungicides may also be incorporated. For the thickened fluids in this category, the additive package and thickener are up to 25 % of the total volume; these fluids are normally supplied ready mixed, rather than as concentrates.
The mixed fluid is usually alkaline, with a pH typically in the region of 9,0 to 9,5.
6.2.2.2 Viscosity
Due to the very high content of water in unthickened fluids, their viscosities are close to that of pure water (approximately 0,8 mm2/s at 40 °C). Accordingly, hydraulic components designed specifically for use with low viscosity fluids are normally used in hydraulic systems filled with unthickened HFAS fluids. Thickened HFAS fluids have viscosities comparable to mineral oil (e.g. ISO VG 32 and ISO VG 46), allowing more conventional hydraulic components to be used; however, the components are still required to operate reliably with the reduced lubricating properties of these fluids.
6.2.2.3 Lubrication properties
Although the lubrication properties of HFAS fluids are generally poor, additives can be incorporated to raise the lubrication performance to a level beyond that typically achieved by HFAE fluids. Specially designed hydraulic components are usually required for use with these fluids. The lives of rolling element bearings within components tend to be short.
6.2.2.4 Corrosion protection
In order to ensure adequate corrosion protection, it is important that at all times the recommended proportion
of the concentrate in the finished fluid be maintained.
6.2.2.5 Compatibility
a) With seals, gaskets, hoses etc.
Acrylonitrile-butadiene rubber with high nitrile content (NBR) and fluorinated (FKM) rubbers are the preferred elastomeric sealing materials for HFAS fluids. Due to the absence of oil from the formulation, other elastomers such as ethylene propylene diene terpolymer (EPDM) and silicone rubber may be suitable, but their compatibility shall be confirmed by the fluid and seal suppliers. Some polyurethane seals (AU and EU) can be damaged by hydrolysis. Absorbent materials such as leather, paper, and cork should be avoided.
NOTE See ISO 1629 for rubber nomenclature.
b) With paints and coatings
HFAS fluids are generally not compatible with conventional paints. Reservoir interiors should either be left unpainted or covered with two-component epoxy coatings. Where corrosion in the non-wetted areas of a reservoir is likely to be a problem, stainless steel can be considered for the reservoir and its cover.
With metals
The majority of metals used in the construction of hydraulic systems designed for use with mineral hydraulic oils are also compatible with HFAS fluids. However, cadmium, lead, and magnesium alloys should not be used. Aluminium can be suitable if anodized and zinc-plated components are compatible with some fluids provided the surfaces are passivated. Where uncertainty exists, the fluid supplier shall be consulted.
6.2.2.6 Working temperature
The reservoir temperature of an HFAS system should not normally exceed 50 °C to avoid excessive loss of water. Lower working temperatures are preferred. The minimum working temperature is 5 °C to obviate the risk of freezing.
6.2.2.7 Fluid maintenance
Dilution of an HFAS concentrate should normally be with potable mains water unless the chemical hardness is particularly high, in which case softened or demineralized water should be used. Ideally, the properties of the finished product should be assessed by the supplier, with the water to be used by the customer for dilution, to ensure that the mixed fluid meets all the technical requirements.