Abrasion is when a material's surface is degraded (worn out) due to direct frictional contact with other materials.
The ability of a material to resist abrasion is called abrasive resistance.
Abrasion resistance is the property of materials to resist wear and tear caused by scraping. As the abrasion resistance increases, the material will become more durable. Different materials show varying levels of resistance toward abrasion because of their varying properties.
But can you improve the abrasive resistance of a material?
This article explains abrasion resistance in detail by discussing its fundamentals, types, techniques, and standards adopted to test and improve abrasive resistance.
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What is Abrasion Resistance?
In short, abrasion resistance is the property of a material that helps it resist scratches on its surface.
Material wear occurs due to the relative motion between rough or irregular surfaces. The micro-debris that get locked between the surfaces can further aggravate the wearing of parts.
Coating the surface with abrasion-resistant paints, using lubricants, and filtering the abrasive particles are some techniques used to prevent abrasion and increase the durability of metallic parts.
Hard materials with a good surface finish can better resist damage from abrasion.
Some of the common worn-out parts include blades, impellers, rotors, pipings, automobile or aircraft frames, and chute liners.
As the abrasion impact on each part differs based on their working conditions, the design requirements of these parts are also different.
The machining of these parts needs to be precise and tolerable as they are exposed to harsh working conditions.
For example, crude oil is known to have debris or abrasive particles in them. When they are carried over a long distance through pipes, the floating particles cause internal abrasion to the pipe, resulting in leakages over time. Hence these pipes are designed to be abrasive resistant.
Types of Abrasion
Abrasion is classified into two types: two-body abrasion and three-body abrasion.
In two-body abrasion (low-stress abrasion), the hard surface particles embedded in a material rub against a soft material in contact.
It is well observed in alloys having carbides. The more the fraction of carbide present in the material's microstructure, the more its abrasion. The debris can also sometimes penetrate soft materials.
The following image gives a visual idea of the process. The area marked with purple color is the abraded area.
One example of the two-body abrasion process is sanding.
When the sandpaper is rubbed over another surface, the silica particles ingrained in the paper remove the material from its peripheral surface.
You can lower the impact of two-body abrasion on a material by improving its surface finish. The smoother the surface, the lower will be the abrasion.
For example, a journal bearing or a sleeve bearing is made of materials having a superior surface finish to allow the sleeve or the shaft to smoothly slide over it without causing abrasion.
Usually, materials of lower hardness and good surface finish are chosen to manufacture these bearings.
A characteristic feature of two-body abrasion is long parallel lines running along the direction of the sliding/reciprocating motion.
In industrial settings, two-body abrasions occur primarily in impellers of sewage handling pumps and blades of agricultural and earth-moving machines.
An abrasion is called three-body abrasion or high-stress abrasion when abrasive particles get trapped between two sliding or rolling surfaces.
The movement of abrasive particles creates numerous indents on both surfaces, which can initiate and propagate cracks.
Here, both the materials and the trapped particles (three bodies) are involved in the abrasion process. The diagram below gives a visual image of the process.
When materials with rough surfaces are in contact, it increases friction forcing the micro peaks on the material surface to break.
These broken pieces can get trapped between moving parts, promoting abrasion.
The characteristic feature of a three-body abrasion is the dents formed on the surface of the soft material.
Spring bushes and marine steam bearings are a few examples where three-body abrasion occurs.
How to Improve Abrasion Resistance?
The abrasion resistance of materials can be improved in many ways. Some of them include using lubricants, coating with abrasive-resistant materials, etc.
Following are some techniques used to improve abrasion resistance on different materials.
|Coating||Pipes, springs, valves|
|Electroplating||Imitation jewelry, dentures, aerospace|
|Anodizing||Space satellites, architectural frames, mechanical components|
The primary method used to improve the abrasion resistance of a material is by applying a surface coating.
|Type of coating||Application|
|Polymer coating||Automobiles, aircraft, pipes, springs, and valves|
|Protective paint coating||Ferrous materials, offshore oil and gas pipelines|
Polymer coatings like silicones, polyurethanes, epoxies, PVC resins, etc. are generally applied on materials with high elastic deformability as they can withstand high tensile strains.
The protective paint coating is good when the material surfaces are not exposed to mechanical stresses. For example, air-dried epoxy, ceramic epoxy, and phosphate.
Some of the other advantages of coatings include
- Heat resistance
- Increased hardness
- Water resistance
- Electrical insulation
- Fire resistance
The abrasion resistance of coatings depends on the thickness, cohesiveness, and elasticity of the coating material.
You can electroplate metals to the exposed surfaces of high-performance parts. It offers better abrasion and corrosion resistance than regular coatings.
Anodizing is the process of developing an oxide layer over the base metal. This layer protects the material from abrasion and corrosion.
You can use the hard anodizing process to provide good abrasion resistance to the material, as it provides a thick oxide layer.
Anodized aluminum parts have widespread applications in various industries, from architectural panels to extrusions used in satellites.
Importance of Abrasion Resistance in Machining
The abrasion resistance of a material minimizes the material wear due to friction or the presence of abrasive particles.
Materials with high abrasion resistance are preferred in manufacturing as they maintain the component's original structure and improve its lifespan.
Thus, such materials have found a place in many applications. However, they are difficult to machine.
Some factors affecting the abrasion resistance of material are
- Fracture toughness
- Elastic modulus
Polymers generally have low hardness, meaning they have poor abrasion resistance.
But in the case of ceramics, as their hardness increases, the abrasive resistance also increases.
Interestingly, materials with a high carbon content also have a high abrasion resistance.
To better understand the importance of abrasion resistance in machining, evaluate the following case.
The table below shows different materials, their corresponding abrasion resistance value, and the tool used to machine them.
|Material||Abrasion resistance||Tool used|
|Mild Steel||120 BHN||High-speed steel|
|Cast Iron||415 BHN||Cemented carbide|
Here, cast iron has the highest abrasion resistance value. Hence, it is machined with a tool made of cemented carbide, a hard material.
On the other hand, aluminum, a soft metal, has a low resistance to abrasion. Here, considering the toughness property, a carbide tool is used.
Abrasion Resistance Standards
The American Society for Testing and Materials (ASTM) provides a set of tests or procedures to effectively measure the abrasive resistance properties of different materials through different techniques.
Below given table lists a few tests for finding out abrasion resistance and its respective codes.
|G81-97a(2018)||Standard test method for jaw crusher gouging abrasion test|
|G171-03(2017)||Standard test method for the scratch hardness of materials using a diamond stylus|
|G75-15(2021)||Standard test method for determination of slurry abrasive (Miller Number) and slurry abrasion response of materials (SAR Number)|
|B611-21||Standard test method for determining the high-stress abrasion resistance of hard materials|
|G174-04(2017)||Standard test method for measuring abrasion resistance of materials by abrasive loop contact|
It is vital to conduct abrasion tests on different materials to identify the quality of the product, performance consistency, and durability.
The most commonly used abrasion testing method is the Taber test. It is performed on a rotary abraser platform that rotates at a constant speed on the vertical axis.
Two abrasive wheels on the table apply a specific pressure onto the specimen placed on the platform.
As the table rotates, the abrasive wheels abrade some material from the test specimen's surface by rotation and sliding.
The flexibility to use different types of abrasive wheels and loads makes the Taber test a widely used abrasion test.
Abrasion resistance is one of many determining factors in choosing a material for manufacturing and other applications.
Though the abrasive property changes with materials, you can enhance it by adopting different techniques like coating, electroplating, anodizing, etc.
Abrasion resistance has applications in polymer science, concrete technology, the textile industry, machining, etc.
Frequently Asked Questions
Does abrasion affect fits and tolerances?
Yes, abrasion affects fits and tolerances as it involves the removal of material which in turn alters the dimension of the component, leading to a loose fit.
Can I improve the abrasion resistance of a weld?
Yes, you can improve the abrasive resistance of a weld by flux-cored arc welding (FCAW), which adds a high alloying element to the weld.
Does the cost of the abrasion resistance method come down with batch production?
Yes, the cost of the abrasion resistance method comes down with batch production. Anodizing and electroplating are amenable to batch production. Here, you can reduce the cost significantly. Coating, however, is not a cost saver for batch production.