From the day of installation and commission, hydraulic components start to wear out. Obviously, often slowly at first, then quickly. In this blog we aim to reveal how this happens.
The scuffing and scoring of a lubricated surface is known as abrasive wear. It can be further divided into two-body abrasion and three-body abrasion. Two-body abrasion occurs when two lubricated surfaces come into direct contact with each other, usually as a result of loss of the lubricating oil film. Three-body abrasion 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 surfaces.
Adhesive wear is normally a progression of two-body abrasion. If the oil film between two lubricated surfaces moving relative to each other is lost, the two surfaces begin to scuff. This scuffing culminates in friction which creates heat. If the friction and heat is sufficient, the two surfaces can begin to adhere (friction weld) to each other. Although complete seizure is possible, adhesive wear typically 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.
Fatigue wear can occur in heavily loaded lubricated contacts-especially bearings and gears. Point loading can cause elastic deformation of the component’s surface. And the resulting stress concentration causes surface cracking and eventually, spalling 0r break away of the surface material.
When chemical reaction results in loss of surface material, Corrosive wear occurs. Rusting of ferrous metals is an obvious example. But 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 any oil additives – especially if water is present.