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Know-how
Contamination in Hydraulic and Lubricating Oils
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The contamination in hydraulic and lubricating oil systems can be divided in primary and secondary contamination:
Primary contamination (basic contamination):
The primary contamination is the summary of the pollution which is already present in a hydraulic or lubricating system prior to their start up process. Following are typical types of primary contaminations.
Contamination from the component's manufacturing process e.g.:
- Welding deposits
- Welding pearls
- Scales
- Metallic swarfs
- Sand from casting forms
- Residues from painting
Contamination caused by the assembly of the components e.g.:
- Broken and cut off angles (burr formation )
- Released particles by pressed connections
- Residues of sealing materials
- Natural and synthetic fibres of cleaning materials
- Anti-corrosion residues containing partially components in solid form
- Lubricating means present in solid, paste-like form (filter blockage)
Contamination by filled in "fresh oil" in form of:
- Residues from the manufacturing, mixing and filling of operating fluids
Secondary contamination
This is contamination which is caused during and after the start up procedure of a system. To this type of contamination belong:
Mechanical degradation of surfaces through direct friction contact of components (abrasion)
- By wear processes
- By particles which are present in the clearance of components
Mechanical degradation through too high flow speeds in the components (erosion) caused by too high pressure drop in sealing and restrictor areas
- By particles present in the flow
- Degradation of particles by cavitation caused by sudden enlargement of cross sections
Chemical corrosion und coating formation at the component's surface
- Caused by chemical change of the operating fluid
- By too high water concentration
- By excessive oil oxidation in form of lacquer - and resin-like residues
Ingressing contamination from the machine surrounding in form of dust and airborne particles in the surrounding air.
- By damaged sealing in hydraulic cylinders
- By damaged or less effective air filters
- By leaky suction lines
Contamination by mixing with other materials:
- Water ingression by condensation, damaged oil coolers or damaged sealing systems
- Rinsing of lubricants, lubricating greases and anti-corrosion materials.
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