In order to scientifically document the industrial benefits of some wear treatment of metals, Louisiana Tech University, Division of Engineering Research, conducted a series of studies to determine what happens to materials when they are exposed to wear treatment. Of primary interest were the effects of such treatment on the wear resistance of tool steels. The fundamentals of wear and the factors controlling wear are explained in order to identify the mechanisms by how different wear treatments influence the wear resistance of different materials.
Wear, a complicated but familiar process, is described as a loss of material from a surface when it slides, rolls or impacts with another surface. Wear occurs in almost every system. In most industries the cost of replacing worn-out items such as gears, bearings, cutting knives, and machine tools is a major expense.
Wear is often the major factor that limits the life of tools and parts even though gross damage does not occur. A completely worn-out five-ton truck, for example, may weigh only 5 pounds less than it did when new. Wear is not a simple process. It may involve mechanical action, some chemical action, or a combination of both.
There are many terms used to describe wear (fretting, pitting, spalling, scuffing, scoring, abrasion, and many others). This suggests that several physical phenomena are involved. There are essentially four main types of wear: adhesive, abrasive, surface fatigue and corrosive-wear.
The complexity of the wear process is compounded by a number of influential factors, including a) Metallurgy Variables (i.e. hardness, toughness, microstructure, chemical composition), and b) Service Variables (i.e. contacting material, pressure between contacting parts, relative speed of the parts, temperature of the parts, surface finish of the parts, atmosphere) and others such as c) Lubrication and d) Corrosion.
Adhesive Wear (sometimes called scuffing or galling) involves several steps. When two surfaces press together, the microscopic bumps on the surfaces squeeze together and form a solid junction when the atoms of the two surfaces bond. When one surface moves relative to the other the weaker material breaks at some distance from the junction and forms a lump of wear material.
Abrasive Wear occurs when a hard particle digs into a softer surface and plows out material. This is called two-body abrasion. Three body abrasion may happen when free particles are trapped between the two surfaces. As the surfaces move relative to each other, the hard foreign particles plow out material from the softer surface areas.
Metal Fatigue is the third mechanism of wear. It occurs when continuous sliding, rolling, or impacting motions subject a surface to repeated stress cycling. The stress cycle starts with very small cracks on or near the surface. These cracks spread and eventually link up to form a free wear particle. Surface fatigue is also involved in spalling and pitting wear. Surface fatigue wear depends strongly on the stress at the surface and the roughness of the surface.
Corrosive Wear involves both chemical activity and mechanical action. It is a modifier of adhesion, abrasion or fatigue wear. The presence or the rate of formation of an oxide film can greatly alter the wear characteristics of a material. The oxide usually has properties quite different from the base metal, therefore, the wear rate is affected by the oxide layer. Failure may occur at the oxide-metal interface.
As we understand these differences and realize that any product can be subject to different applications and working environments, Cryotron’s team of experts will provide your business with the right solution for your application. Your business will gain a reduction in tool consumption, as well as decreases in downtime and change out time.
Info at cryotron.com or phone us (Edmonton, AB) 1-780-405-2515 or (Houston, TX) 1-832-690-2717.