Hydraulic machines are machinery and tools that use liquid power to do simple as well as complex tasks. The hydraulic fluid pressure is transmitted throughout the machine to various hydraulic motors & hydraulic cylinders to perform some useful work. The fluid is controlled directly or automatically by the control valves and distributed through hoses and tubes.
The Hydraulic components includes
- Hydraulic pump
- Control valves
- Hydraulic fluid
- Tubes, hoses and pipes
- Seals, fittings and connections etc.
As soon as they are installed and commissioned, the hydraulic components start to wear out. The wear out will be slow in the initial stage, then will increase at a rapid pace.
How can they wear out?
Here is a glance of 6 ways by which the hydraulic components can wear out.
1. Abrasive wear:
- It is the scuffing and scoring of a lubricated surface.
- It can be divided into two:
- Two-body abrasion – As a consequence of loss of the lubricating oil film, two lubricated surfaces come into direct contact with each other.
- Three-body abrasion – It occurs when the clearance between two lubricated surfaces is bridged by one or more hard particles. In this case it’s the clearance-sized hard particles that are responsible for scoring the lubricated surface(s).
2. Adhesive wear:
- This is an advanced level of two-body abrasion.
- Here, the two surfaces begin to scuff when there is a loss of oil film between two lubricated surfaces moving relative to each other.
- Thus, the Scuffing results in friction which produces heat.
- When the friction and heat are sufficient, the two surfaces can begin to adhere (friction weld) to each other and a complete seizure is possible.
- It results in the transfer of metal from one surface to the other, as the asperities (microscopic high points) adhere and are then torn from their parent-metal surface.
3. Fatigue wear:
These generally occur in heavily loaded lubricated contacts – especially bearings and gears. Elastic deformation of the component’s surface is caused by point loading, which as a result causes surface cracking and eventually, spalling (break away) of the surface material due to stress concentration.
4. Erosive wear:
A large amount of silt-sized (< 2-micron) hard particles when contaminates the hydraulic fluid can cause Erosive wear. As the contaminated hydraulic fluid moves past lubricated surfaces at relatively high velocities, it works like an abrasive slurry, polishing (eroding) away these surfaces and eventually, increasing the clearances between them.
5. Cavitation wear:
Any metal surface can incur erosion or metal loss when vapor or air bubbles collapse under pressure in proximity. For example, oil-vapor bubbles (or air bubbles) form-at the pump inlet collapse under pressure at the pump outlet. The microjet formed during bubble collapse is powerful enough to erode case-hardened steel.
6. Corrosive wear:
It is a loss of surface material occurred due to chemical reaction. If the hydraulic oil has been degraded by water or heat, chemical by-products such as acids can chemically attack some metals. In addition, yellow metals (bronzes) can be susceptible to chemical attack by some oil additives – especially if water is present.
Covering all these 6 types of wear, it is essential to test a hydraulic fluid and monitor the trend. Thus Viswa Lab – lubricant condition monitoring program will enable you to monitor the trend and alert when there is a severe wear of components. Viswa Lab tests every hydraulic fluid for its cleanliness and reports the ISO cleanliness code against the target code.
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Source: Hydraulics & Pneumatics