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What Is Wear
What Is Wear
When two contacting solids move relative to each other, the surface material of the solids gradually decreases, and material loss occurs. This phenomenon is called abrasion, and some people call it wear.
In most mechanical structures, there are parts with relative motion such as sliding or rolling. Since wear can determine the life of the machine, this phenomenon is very important in use.
Examples from life
To remove sediment from a riverbed, a pump is used to extract both sediment and water simultaneously. When the sediment strikes the fan blades or the pump’s outer casing, it causes wear. The relative motion between solids and the impact of hard particles lead to this wear, which is known as erosion.
Sometimes erosion is not caused by the impact of hard particles. For example, when an airplane flies quickly in clouds and rain, rain or cloud droplets impact the plastic structure of the airplane. This is called raindrop erosion, which is also a type of wear.
The Benefits of Wear
From the perspective of material loss, although it is harmful, on the other hand, thanks to the help of wear, many things have been fed back and improved. For example, using a grinder to perform metal surface flattening processing, using hard-grained abrasives to perform metal or silicon semiconductor grinding, and finishing it to a smooth mirror surface.
In addition, writing on paper or blackboard with pencil or chalk belongs to the application of adhesive wear. Moreover, erasing the words written on paper with an eraser causes the pencil abrasive powder to adhere to the eraser, which is also an application of Wear.
Wear Rate
There is no standard formula for wear rate. It varies according to the product properties and inspection methods of each company. Here are the units that may appear. Therefore, the wear volume, weight and size per unit distance, cycle and time are called wear rate. Most people use this as a standard to express wear intensity. The wear rate of the material varies due to different contact loads, time, speed, lubrication, environment and other conditions. I personally prefer to use the wear weight/distance standard. You can know the result by weighing it directly, but you must pay special attention to the Moisture Absorption characteristics of the material, otherwise you will make mistakes when looking at the data.
Wear and distance (time) curve
The amount of wear will vary with time or distance (friction distance), and the curve graph is divided into three types.
Description
Before explaining the curve graph, we need to explain two terms. The initial wear state means that the wear rate gradually changes after the wear begins. The fixed wear state means that the wear rate becomes a constant value (stable value).
The wear rate is larger in the initial wear state, and smaller in the fixed wear state, which can be called the running-in stage. When the two surfaces of two objects are in contact and friction, the raised parts of the surface gradually become blunt and disappear due to continuous wear, resulting in changes in the surface structure and achieving smooth sliding. For example, after the engine is manufactured, the wear rate is larger in the initial operation, and then gradually decreases. This is why the mileage of the first oil change when the engine is just bought is relatively short.
Specific Wear Rate
The degree of wear is mostly expressed as the amount of wear per unit sliding distance. However, to judge the quality of the material, the wear volume V after fixed wear is proportional to the contact load L and the sliding distance D. Therefore, the wear volume V/LD per unit distance and unit load is called specific wear or specific wear rate. The units used are mm3/Nm or mm3/kgf mm, the latter can be written as mm2/kgf.
The reciprocal of the Specific Wear Rate is LD/V, which can be used as a standard for the wear resistance of materials. The larger the number, the more wear-resistant the material is.
