RWF Draft Metallurgy Lab Procedures PDF

64 M Lab M lab also known as Metallurgy lab is an integral part of the RWF. The main objective is to test the consumables and the specimens in order to ensure safety, quality and confirm that they meet the specifications. The M lab is divided into various...

64 M Lab M lab also known as Metallurgy lab is an integral part of the RWF. The main objective is to test the consumables and the specimens in order to ensure safety, quality and confirm that they meet the specifications. The M lab is divided into various sections:  Machine shop  Physical testing  Chemical lab  Refractory lab Tests can be carried out in two ways:  Destructive tests  Non-destructive tests DESTRUCTIVE TESTS Physical section will carry out various metallurgical tests on wheels and axles. After being destructively tested, the component of the specimen either breaks or remains no longer useful for further use. Ex. Tensile tests, Impact tests, etc. NON-DESTRUCTIVE TESTS  65 A component does not break in non-destructive testing and after testing it can be used for the purpose for which it is made. Ex. Magnetic particle inspection, Ultrasonic testing, etc. MACHINE SHOP Machine shop is generally used for preparation of specimens. Since destructive testing is done, wheel and axle has to be sectioned correctly to accommodate all tests. The machine shop contains a lathe machine, grinding machine and a drilling machine. Tasks that are performed by the operator in the machine shop are:  Axle specimen is prepared.  Cross section of the wheel is obtained from EMMS (Electrical Mechanical Machine Shop).  Specimen for the Charpy test is prepared. The specimens from machine shop further go to physical testing to check for their physical parameters. PHYSICAL TESTING All tests in the physical testing are of destructive type. Since the wheels are produced by casting process, there is lot of stress induced during solidification of the molten metal. These are not good for working of wheels, hence to check the limiting stress, tests are carried out.  66 The axles undergo forging in the axle shop. Due to changing temperatures, stresses are developed. To test their limiting stress and grain structure, physical testing is necessary. Tests carried out are:  Closure test Radial saw cut analysis technique is used to measure the bulk circumferential residual stress levels in rail road cast steel wheel. With this technique the opening or closure of the saw cut, at the flange tip is monitored as a function of the radial cut depth.  Hardness test To a metallurgist, hardness is a material’s resistance to penetration. In general, an indenter is pressed into the surface of the material to be tested under a specific load for a definite time interval, and a measurement is made of the size or depth of the indentation. The greater the hardness of the metal, the greater resistance it has to deformation. In metallurgy hardness is defined as the ability of a material to resist plastic deformation. Hardness tests can be performed with the help of instruments such as :  Brinell Hardness tester : This test is a type of indentation test. J.A. Brinell introduced the first standardized indentation- hardness test in 1900. The Brinell hardness test consists in indenting the metal surface with a 10-mm diameter  67 steel ball at a load range of 500-3000 kg, depending of hardness of particular materials. The Brinell hardness tester uses a steel ball for indentation. The hardness number is determined by its characteristics such as applied load, diameter of indenter, diameter of indentation, depth of the impression.  Rockwell Hardness Tester : Rockwell hardness test is most preferably used and is generally accepted due to the speed, small size of indentation and ability to distinguish small hardness difference. The hardness is measured according to the depth of indentation under a constant load. The type of indenter used here is a diamond indenter. The acceptable HRC (Rockwell Hardness) are as follows: Wagon : 277 to 341  68 Coach : 255 to 321  Portable Hardness Tester: Conventional hardness testers, like Rockwell, Brinell or Vickers machines, require the test piece be brought to the testing device; but this is not always possible. Portable testing devices have been developed that permit in-situ hardness measurements thus offering quick and economical supplements to conventional, stationary testing machines. An ideal solution for metallic hardness measurements with conversions to HLD, HRC, HRB, HB, HV, and HS are available. There is no indentation in this hardness tester.  Micro Hardness tester : Determination of hardness over very small areas for example individual constituents, phases, requires hardness testing machines in micro or sub-micro scales. Vickers hardness can also be measured in a micro scale, which is based on the same fundamental method as in a macro scale. The micro indenter (diamond-shape) is used for measuring in a small area, such as at the cross section of the heat-treated metal surface.  69 The micro hardness test is mainly for testing hardness of steel shots. Steel shots are used for finishing purposes. The acceptable hardness value is in the range of 375 to 550 HV.  Tensile test In tensile testing, the ratio of maximum load to original cross sectional area is also called ultimate strength. This test gives an idea of material strength obtained by proper process adopted of steel making and its effective heat treatment done. Tests will be carried out by turning to the standard test method and breaking by using tensile testing machine. There are two tensile test machines - one of a 100 ton capacity and another of a 20 ton capacity. The important parameters that are considered are – Peak load Breaking load Maximum displacement Area Ultimate stress Elongation Reduction in area Yield stress  Grain structure A very important feature of a metal is the average size of the grain. The size of the grain determines the properties of the metal. For example, smaller grain size increases tensile strength and tends to increase ductility. A larger grain size is preferred for improved high-temperature creep properties. Creep is the permanent deformation that increases with time under constant  70 load or stress. Creep becomes progressively easier with increasing temperature. Grain size are reported in terms of grains per unit are or volume average diameter or as grain size number derived from area measurements. This will be done by a metallurgical microscope with an image analyzer. This indicates the type of structure having the material and it reveals defects of the material like porosity, shrinkage etc. There are 8 different grain size distributions of Iron Carbon. The required range is 6 to 8. This is evaluated by measuring the grains per unit volume. 71  72  Charpy Impact test It is a test to determine the behavior of the material when subjected to higher rates of loading, usually in bending, tension or torsion. The loads that are suddenly applied to a structure are known as shock or impact load. These loads build up rapid stress and affect the resisting properties of material. The property of a material is associated with work required to cause rupture. In charpy test, the specimen is place d as ‘cantilever beam’. The specimens have U-shaped notch of 45°. The notch is located on tension side of specimen during impact loading. Depth of notch is generally taken as t.5 to t/3 where ‘t’ is thickness of the specimen. Specimen Charpy Impact test  73 Charpy Impact testing equipment  74 CHEMICAL LAB Chemical lab consists of analysis of various consumables to check for their parameters and compositions. Two types of analysis are conducted. They are:  Wet analysis  Instrumental analysis In Wet analysis, individual analysis of consumables is made by dissolving them either in water/acid or any liquid medium. It is a classical method which involves observation to analyze materials. Most of the analyzing is done in the liquid phase. Wet techniques often depend on the formation of a product of the chemical reaction that is easily detected and measured. Some tests are conducted by using certain reagents to indicate the presence of a specific chemical in an  75 unknown solution. Few tests are based on volumetric analysis for volume measurements. In Instrumental analysis, the consumables and specimens are tested using scientific instruments. It is used to measure the property of the analyte (material). The various types of instruments used in M-lab are:  LECO Analyzer: It is an elemental carbon and sulfur analyzer that has a variable power combustion furnace, and has an enhanced IR cell design. It has available automation that makes it a valuable resource for any industrial environment requiring accurate analysis of carbon and/or sulfur. The unit gives fast analysis in less than a minute.  Particle size analyzer: A particle size analyzer is used to test the size of the fused silica that is used in spraying the cope and drag. The particle size is important because if it does not conform to the required size, the silica might clog at the tip of the nozzle, hence making it difficult for spraying. A laser beam is used to count the particles and the size is measured.  76  XRF: Wavelength dispersive X-Ray fluorescence spectrometer is an instrument used for rapid quantitative elemental analysis of major and minor atomic elements, from beryllium (Be) through uranium (U), in a wide variety of sample types with minimal standards. It is a Micro analysis technique to analyze samples as small as 500 µm. The principle of working is based on Brooks’ law. It is the latest instrument, eliminating the necessity of chemical analysis, thus saving time.  Mono quartz distillation unit  Kinematic viscometer  77  Flame photometer  Flash point apparatus  Melting point apparatus  Electro chemical Analyzer  Flow length apparatus  Viscometer  Electrolytic Analyzer  Centrifugal apparatus  Muffle furnace REFRACTORY LAB Refractory means difficult to melt or work (resistant to heat). A refractory material is one that retains its strength at high temperatures. Refractories can be defined as "non-metallic materials having those chemical and physical properties that make them applicable for structures or as components of systems that are exposed to environments above 1,000 °F (811 K; 538 °C)”. Refractory materials are used in linings for furnaces, kilns, incinerators and reactors. They are also used to make crucibles and moulds for casting glass and metals. Refractory lab is an important part of the RWf since they use refractory consumables such as refractory castables and Alumina bricks. To ensure that they are heat resistant, tests are conducted in the Refractory lab. Refractory lab consists of Flue gas analyzer, permeter (Atomic clock permeability), muffle furnace, RVL machine.  Flue gas analyzer: Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. A device that monitors the composition of the flue gas of a boiler heating unit to  78 determine if the mixture of air and fuel is at the proper ratio for maximum heat output.  Atomic clock permeability: Permeability is a property of foundry sand with respect to how well the sand can vent, i.e. how well gases pass through the sand. And in other words, permeability is the property by which we can know the ability of material to transmit fluid/gases. The permeability is commonly tested to see if it is correct for the casting conditions to find Permeability number permeter is used.  Muffle furnace: A muffle furnace is front-loading box-type oven or kiln for high temperature. It is used in many research facilities to determine what proportion of a sample is non-combustible and non- volatile.