An abrasive is a material that is used to rub against another material in order to wear it away. This technique can ultimately be used to cut through a material or simply for finishing. Abrasives are usually made of minerals or mineral-like substances. Common uses for abrasives include grinding, buffing, polishing, cutting, drilling, sharpening, honing, lapping and sanding.
In order for the abrasive to wear away the material being worked upon, the abrasive needs to be harder than the material. Abrasion is one of the most commonly occurring processes in nature and day-to-day life. It is inevitable that two materials experiencing repeated friction, will eventually wear each other away. Even in practice, the abrasive will eventually wear away due to this friction. In the industry, common materials that are used as abrasives are either really hard minerals or synthetic rocks.
The process involves bringing an abrasive and the material to be worked into contact and applying force in relative motion to each other. The friction causes fragments of the material to break away, while simultaneously smoothing the abrasive grain or causing the grain to break away from the the abrasive.
There are certain factors that will influence how fast a material is abraded. Difference in hardness between the two materials rubbing against each other determines which one is being abraded, because the harder substance of the two acts as the abrasive - even though it might not be its intended purpose.
Grain size will determine how fast a substance is abraded - the larger the grain, the faster and the deeper it will cut the work piece. The adhesion between these grains and between the grains and the backing will determine how quickly grains are lost from the abrasive.
The force applied will determine the level of abrasion. When more force is applied, the friction between the substances will increase which causes faster abrasion. Loading occurs when the cast off material from the abraded substance fills the spaces between the abrasive grains and reduces the abrasive's cutting efficiency. Using a lubricant or a coolant can prevent loading by carrying away excess material.
Files also act by abrasion, but they are not classified as abrasives due to the fact that they are shaped bars of metal. Certain files are coated with abrasive grains, which will classify them as coated abrasives.