mechanical engineering

Thermodynamic Air Standard Cycles The working fluid of  heat engines  is subjected to a series of changes (in temperature, volume, pressure, etc.), known as thermodynamic air standard cycles, through which the energy absorbed as heat is converted into mechanical work. Internal combustion engines do not operate on a thermodynamic cycle as it involves an open system. However, it is often possible to analyze the open cycle by imagining one or more processes that would bring the working fluid at the exit conditions back to the condition of the starting point. The actual gas power cycles are rather complex. To reduce the analysis to a manageable level, the following approximations, commonly known as  air standard assumptions , are made: The working medium is a perfect gas. There is no change in the mass of the working medium. All the processes that constitute the cycle are reversible. Heat is supplied from a constant high-temperature source. Some heat is as...

Drill Presses Figure 1. Upright drill machine The standard machine tool used for drilling is the  drill press . There are various types of the drill press, the most basic of which is the upright drill, Figure 1. The upright drill stands on the floor and consists of a table for holding the workpart, a drilling head with a powered spindle for the drill bit, and a base and column for support. A similar drill press, but smaller, is the bench drill, which is mounted on a table or bench rather than the floor. The radial drill machine shown in figure 2, is a large drill press designed to make holes in large parts. Radial drill machine has a radial arm along which the drilling head can be moved and clamped. The head, therefore, can be positioned along the arm at locations that are a significant distance from the column to accommodate large work. The radial arm can also be swiveled about the column to drill parts on either side of the worktable. The g...

Belt Drives: Types, Advantages, Disadvantages A belt is a looped strip of flexible material used to mechanically link two or more rotating shafts. A belt drive offers smooth transmission of power between shafts at a considerable distance.  Belt drives  are used as the source of motion to transfer to efficiently transmit power or to track relative movement. Types of Belt Drives: In a two pulley system, depending upon the direction the belt drives the pulley, the belt drives are divided into two types. They are open belt drive and crossed belt drive. The two types of belt drives are discussed below in brief. Open belt drives: An open belt drive is used to rotate the driven pulley in the same direction of driving pulley. In the motion of belt drive, power transmission results make one side of pulley more tightened compared to the other side. In horizontal drives, tightened side is always kept on the lower side of two pulleys because the sag of the upper side...

Classification of Gears Classification of gears can be done according to the relative position of the axes of revolution into three types. They are: Gears for Parallel shafts 1.1 Spur Gears 1.2 Helical Gears 1.3 Herringbone Gears 1.4 Rack and Pinion Gears for Intersecting Shafts 2.1 Straight Bevel Gears 2.2 Spiral Bevel Gears Gears for Skew Shafts 3.1 Hypoid Gears 3.2 Worm Gears Classification about these  types of gears  discussed below. 1. Gears for Parallel Shafts: The motion between parallel shafts is same as to the rolling of two cylinders. Gears under this category are the following: 1.1 Spur Gears: Straight Spur gears are the simplest form of gears having teeth parallel to the gear axis. The contact of two teeth takes place over the entire width along a line parallel to the axes of rotation. As gear rotate , the line of contact goes on shifting parallel to the shaft. 1.2 Helical Gears: In helical gear teeth are part of helix ...

Distinguish between Crater Wear and Flank Wear of a Single Point Cutting Tool Crater Wear: The wear taking place on the rake face of a  single point cutting tool  like crater is called  crater wear . The crater wear is mainly caused due to The presence of friction between the chip-tool interface, The abrasion action of microchips present at the chip-tool interface. The abrasive action of fragments of  Built Up Edge  (BUE) at the chip-tool interface and diffusion wear. The diffusion wears, due to the atomic attraction between the tool and work the atoms of the tool material will get diffused and deposited over the workpiece called diffusion wear. Diagram of worn cutting tool, showing the principal locations where crater wear and flank wear occur Flank Wear: The wear taking place on the flank face of a single point cutting tool is called  flank wear . The reasons for flank wear are: The presence of friction at ...

Why Apply Lubrication to Engine Parts ? The lubrication is the supply of oil between two surfaces having relative movement. While applying lubrication to engine parts one should choose good lubricant  to make the engine run efficiently. The objective of applying lubrication to engine parts are: To reduce the frictional forces between the parts having a relative motion by minimizing the force of friction and ensures the smooth running of the engine. To reduce the wear and tear of moving parts. To cool the surfaces by carrying away the heat generated due to  friction . To seal a space adjoining the surfaces such as piston rings and cylinder linear. To absorb the shocks between bearings and other parts and consequently, reduce noise. To act as a cleaning agent and removing dirt, grit and any deposits that might be present between the moving parts of an automobile. To help the piston rings to seal the gases inside the piston cylinder. Parts of Engi...

Plasma-arc Welding (PAW) In  Plasma-arc Welding  (PAW) is an arc welding process, a concentrated plasma arc is produced and directed towards the weld area. The arc is stable and reaches temperatures as high as 33,000°C. A plasma is an ionized very hot gas composed of nearly same numbers of electrons and ions. The plasma starts between the tungsten electrode and the orifice by a low current pilot arc. What makes plasma-arc welding unlike other processes is that the plasma arc is concentrated because it is forced through a relatively small orifice. Operating currents usually are less than 100 A. When a filler metal is used it is fed into the arc as is done in Gas Tungsten-arc Welding. Arc and weld-zone shielding are supplied by means of an outer shielding ring and the use of inert gases like argon, helium or mixtures. There are two methods of plasma-arc welding: In the transferred-arc method of plasma-arc welding(in pic left side), the  workpiece  being...

Bernoulli’s Principle and Equation During 17 th  century, Daniel Bernoulli investigated the forces present in a moving fluid, derived an equation and named it as an Bernoulli’s equation. Below image shows one of many forms of Bernoulli’s equation. The Bernoulli equation gives an approximate equation that is valid only in inviscid regions of flow where net viscous forces are negligibly small compared to inertial,  gravitational  or pressure forces. Such regions occur outside of boundary layers and waves. Bernoulli’s Principle Image Source:  Hyperphysics Despite its simplicity,  Bernoulli’s Principle  has proven to be a very powerful tool in  fluid mechanics . Care must be taken when applying the Bernoulli equation since it is an approximation that applies only to inviscid regions of flow. In general, frictional effects are always important very close to solid walls and directly downstream of bodies. The motion of a particle and t...

Electro Chemical Machining (ECM) Electrochemical machining (ECM) is a  non-traditional machining process  uses the principle of Faraday to remove metal from the workpiece. Electrolysis is based on Faraday laws of electrolysis which is stated as weight of substance produced during electrolysis is proportional to current passing, length of time the process used and the equivalent weight of material which is deposited. Michael Faraday discovered that if two electrodes are placed in a bath containing liquid and when a direct potential is applied across electrodes, The metal can be depleted from the anode and plated on the cathode. This process is universally used in electroplating by making the workpiece the cathode. Electrochemical Machining (ECM) is performed by reversing the process of electroplating, ECM utilizes the principle of electrolysis for metal removal. The high rate of electrolyte movement in the tool-workpiece gap washes metal ions away by an...

Gruebler’s Equation Degrees of freedom for planar linkages joined with common joints can be calculated through Gruebler’s equation. Gruebler’s equation is given by the formula: where, n = total number of links in the mechanism j p  = total number of primary joints (pins or sliding joints) j h  = total number of higher-order joints (cam or gear joints) Mechanisms and structures with varying mobility for Figure (a), (b) and (c) Most linkages used in machines have a single degree of freedom. An example of single degree-of-freedom linkage is shown in figure (a). Linkages with zero or negative degrees of freedom are termed locked mechanisms. Locked mechanisms are unable to move and form a structure. A truss is a structure composed of simple links and connected with pin joints and zero degrees of freedom. An example of locked mechanism is shown in figure (b). Linkages with multiple degrees of freedom need more than one dri...

Grashof’s Law The Grashof’s law states that for a four-bar linkage system, the sum of the shortest and longest link of a planar quadrilateral linkage is less than or equal to the sum of the remaining two links, then the shortest link can rotate fully with respect to a neighboring link. Consider a four-bar-linkage. Denote the smallest link by S, the longest link by L and the & other two links by P and Q. If the Grashof’s Law condition is satisfied i.e S+L ≤ P+Q, then depending on whether shortest link ‘S’ is connected to the ground by one end, two ends, or no end there are 3 possible mechanisms. They are: Double crank mechanism Double-rocker mechanism  and Crank and Rocker Mechanism 1. Double crank mechanism In double crank mechanism, the shortest link ‘S’ is a ground link. Both input crank and output crank rotate at 360°. Grashof’s condition for double crank mechanism: s+l > p+ q Let:  ‘s’  = length of shortest link, ‘l’  = length...