Question

e. Quenching and Tempering as heat treatment processes f. Normalization and Annealing processes Question (3) For the shown bearing assembly submit the following - Specify certain type of fit between the shaft and bearing 2 degrees] - Specify certain type of fit between the bearing and housing 2 degrees

Answer 1

e) Quenching and tempering are processes that strengthen and harden materials like steel and other iron-based alloys. The process of quenching or quench hardening involves heating the material and then rapidly cooling it to set the components into place as quickly as possible. The process is tightly controlled, with the heating temperature, cooling method, cooling substance and cooling speed all dependent upon the type of material being quenched and the desired hardness. A typical heating range is between 815 and 900 degrees celcius, with extra care being taken to keeping the temperature as stable as possible. Variances in the degree of heat being applied during the process can result in distortion in the resultant metal.

After the material has been quenched to its hardest state, the process of tempering is used to achieve greater toughness and ductility by decreasing hardness. Tempering is achieved by heating the quenched material to below the critical point for a set period of time, then allowing it to cool in still air. Both the temperature and heating time depend on the composition of the material and will determine the amount of hardness removed.

Benifit of Quenching and tempering:-

By tempering quenched steel, it becomes less brittle and more ductile without sacrificing too much hardness. It is the combination of these two processes that produces a harder, tougher steel that’s more weldable and ductile than ordinary carbon steel. While it takes longer to manufacturer, the increased strength makes up for the delay. If the steel becomes too hard after quenching, it can be tempered. This involves heating the element again, but to a point far below the temperature reached in the quenching stage – usually around 540 degrees Celsius. The amount of time the quenched metal is tempered is the determining factor to how much hardness is removed.

The toughness-factor means greater resistance to wear and abrasion. That is why quenched and tempered steel is particularly useful in machinery and structures where greater abrasion resistance and higher yield strength are necessary, such as mining, quarrying, earth moving and construction.

f) Normalizing process is a heat treatment process for making material softer but does not produce the uniform material properties as produced with an annealing process. The most common reason for the normalizing process is to adjust mechanical properties to suit the service conditions.

During the annealing process, the metal is heated to a specific temperature where recrystallization can occur. ... The metal is held at that temperature for a fixed period, then cooled down to room temperature. The cooling process must be done very slowly to produce a refined microstructure, thus maximizing softness.