Engineeringdev

Comparator A comparator works on the relative measurement It gives only dimensional differences in relation to a basic dimension A comparator has to compare the unknown dimensions of a part with some standard (Basic Size) These are commonly used for linear measurement in mass production Classification Depending on the amplification system, Comparators are classified as Mechanical Comparators Electrical Comparators Optical Comparators Pneumatic Comparators

Mechanical Comparators : Mechanical comparator s are extremely convenient to use It does not require any external power for its operation The measuring head consists of the work contact plunger(Stylus) The movement due to size difference between standard and work piece operates a pointer The pointer moves over a dial This movement of the plunger is magnified by means of the gear train or levers The magnification of mechanical comparators is limited to 1000 These are cheap and intended to measure external surfaces However the mechanical devices are subjected to wear Types of Mechanical Comparators Dial indicator Reed type mechanical comparator The Sigma comparator

Comparator A comparator works on the relative measurement It gives only dimensional differences in relation to a basic dimension A comparator has to compare the unknown dimensions of a part with some standard (Basic Size) These are commonly used for linear measurement in mass production Classification Depending on the amplification system, Comparators are classified as Mechanical Comparators Electrical Comparators Optical Comparators Pneumatic Comparators

METROLOGY Metrology is the science of measurements. In manufacturing industry the dimensions are measured to control the shape and sizes of an object Controlled measurements are necessary in the manufacture of interchangeable parts Linear Measuring Instruments Slip gauges Dial indicator Angle Measuring Instruments Bevel Protractor Sine bar Angle gauge Slip gauges Slip gauges are used for precise measurement of parts and for verifying measuring tools such as micrometers,comparators and various limit gauges Slip gauges are rectangular blocks made of alloy steel having a cross-section of about 32mm by 9mm The distance between two opposite faces determines the size of the gauge During use, the required number of gauge blocks are used together to know the required dimension. Dial Indicators Dial indicators are used to test and inspect the size and trueness of a finished work It is measured to an accuracy of 0.01mm They are also used in conjunction with other measuring instruments like

Reed type Mechanical Comparator The instrument used to measure linear displacement of spindle with the help of the reed mechanism is known as reed type Mechanical comparator. It is a device magnifying small motions of spindle. Constructional details : The reed mechanism is frictionless device for magnifying small motions of the spindle It consists of a fixed block `A` which is rigidly fastened to the gauge head case The floating block `B` carries the gauging spindle The floating block is also connected horizontally to the fixed block by reeds `C` A vertical reed is attached to each block with upper ends jointed together These vertical reeds are shown in fig by letter `D` A pointer is attached to this joint Working principle A linear motion of the spindle moves the floating block vertically upwards This vertical movement causing the vertical reed on the floating block to slide past the vertical reed on the fixed block The movement causes both reeds swing through an arc As the point is

BOND ENERGY Definition : ·       The energy required to break a bond between the two bonded atoms is called bond energy. Or ·       The energy required to convert one mole of a diatomic molecular substance in the gaseous state into its free atoms is known as bond energy.  ·       As the bond energy increases, the stability of the bond also increases. ·       sigma - bonds are stronger than pi bonds ·       Number of bonds between atoms increases the overall bond strength increases -C-C- < -C=C- < -CC- BOND LENGTH AND ENGERY BOND LENGTH Definition: The distance between the centres of the nuclei of two covalently bonded atoms is known as bond length. ·       Bond lengths are measured in angstroms or nanometers.   METALLIC BOND ·       Properties of Metals: 1.       Metals are good electrical and thermal conductors 2.       They are opaque and have high refracting power 3.       They have high melting and boiling points 4.       They crystallise with high coordination number

Defects of Lewis electron-dot model : It can not explain a) Stability of molecules which do not obey octet rule b) Shape of molecules c) Bond characters  Valence bond theory (VBT)  1)It (VBT) explains the directional nature and strength of covalent bond. 2)Covalent bond is formed by the overlapping of half filled orbitals of two bonding atoms. 3)The electrons involved in the bond formation must have opposite spin.  4)Strength of covalent bond is directly proportional to the extent of overlapping of orbitals. 5)Covalent bond is formed in the direction in which the bonding orbital is concentrated to a maximum extent. TYPES OF COVALENT BOND ·       Overlapping of orbitals are of two types. a) Sigma bond   ·       A bond formed by the axial or end-on over lapping ·       Electron density of -bond is concentrated along the inter nuclear axis b) Pi-Bond ·       A bond formed by the lateral or side wise overlapping ·       Electron density of pi bond is concentrated above and below the inte

Covalent Bonding  Definition : A chemical bond formed by mutual sharing of electrons between two atoms is called covalent bond Covalent bond formed between two atoms: ·       If the electronegativity value difference is less than 1.7 ·       Each atom contributes electrons equally for sharing. ·       The sharing takes in pairs ·       The shared electron pair belongs to both the bonded atoms. The sharing can involve in 1.     One pair of electrons, Single bond (-) formed 2.     Two pairs of electrons, double bond (=) 3.     Three pairs of electrons, Triple bond (≡)  Lewis dot model or Electron dot model : ·       Electrons present in the outer shell only are used for bonding ·       The sharing of outer electrons results the covalent bond ·       The bonded atoms get octet configuration to get stability ·       Each valence electron of bonded atom is regarded as a point charge indicated as ‘dot’ Example 1: Hydrogen molecule (H2) ·       Hydrogen atom has a single electron in 1st orbi