What are Free Cutting Steels ?

Free cutting steels (also free machining Steels) are extensively applied for machining parts subject to comparatively light loads (bolts, nuts, screws, etc.) and produced on automatic screw machines or multiple spindle automatics. These steels are intended for uses where easy machining is the primary equipment.

The distinguishing features of free cutting steels i.e., high machinability and high quality surface finish after machining., are due to the higher Sulphur and Phosphorous content.

Sulphur exists in the free cutting steel in the form of manganese sulphide which forms inclusions stretched out in the direction of rolling. These inclusions promote the formation of short brittle chips, reduce the friction on the surface being machined, and enable a satisfactory surface finish to be obtained at high cutting speed. Phosphorus dissolves in the ferrite (pure iron) and increases its brittleness. This also makes the chip more brittle and enables a smooth bright surface to be obtained in cutting. The addition of 0.15 to 0.35 per cent phosphorus considerably improves the machinability without reducing the physical and mechanical properties of the steel.

The tool life achieved in machining free cutting steels is from 2 to 2.5 times higher than when carbon steels of the same carbon content are machined. It must be noted., however, that free cutting steels have lower dynamic strength characteristics and are more susceptible to corrosion.

Free cutting steels are frequently supplied in the cold drawn (work - hardened) form. These cold drawn steels have a high tensile strength and hardness but less ductile when compared to ordinary carbon steels.

Comments

THROTTLE GOVERNING OF STEAM TURBINES

Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the turbine constant at part load and hence this method of governing is called "Throttle Governing". Construction : Throttle governing system consists of a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber. Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movement of the

ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a roll. The object to be checked is place

Advantages And Disadvantages Of Air Refrigeration System :

Advantages Of Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content.

Mechinopedia For Mechanical Engineers

Search This Blog