Specifications for Cast Irons.
Specifications for Materials can be classified into major sections based on the specifying authority and the field for which the specifications are made. To clarify simple table can be created,
International bodies Customer Supplier / Foundry
Chemistry
Manufacturing process
Heat Treatment
Mechanical properties
Microstructure
Major difference between Cast Irons and Steels and other metals
• For steels and other metals the specifications start with chemistry. The manufacturing process and heat treatment govern the mechanical properties and microstructure. There is a definite correlation between chemistry, process, heat treatment and the properties and microstructure.
• International material specifications are prepared without any specific end component in mind. Hence these become generic, one set giving chemistry, other giving heat treatment cycles and corresponding mechanical properties. The customers use these standards to prepare their requirements. The starting point is chemistry.
Cast Iron Specifications : International
Cast irons do not enjoy such straight forward relationships between chemistry and properties. Hence the International standards specify the grades by tensile strength obtained on a test bar of standard size. And these values mainly indicate the melt quality and not the tensile strength of casting.
International standards also define the generic types of graphite forms, size and shape distribution. They do not define acceptance / rejection limits or the microstructural requirements for a casting.
Cast Iron Specifications : Customer
For the customer, the scope or applicability of the specification is much narrowed down for one specific casting, or a set of component families.
• From the requirement of finish, cleaning of the casting, he specifies the casting process – sand casting, shell casting etc.
• As the size and shape of the casting is known, he has a definite relation between the test bar properties and the casting properties. He therefore can specify the hardness range and the location on the casting where it should be tested.
• With fixed size, shape and properties requirements, and after finalisation of the casting process, he can specify the range of chemistry – which will give consistant properties on finished casting. Though there can be some variation from foundry to foundry, an overall guideline can definitely be specified.
• Based on the service conditions, he specifies additional limits on the acceptance of chemical elements – for example phosphorus content for cylinder liner application, manganese content for SG iron etc.
• If any heat treatment or specific stress relieving operation is required, that is specified.
• Then the microstructure definition comes. The microstructure cannot be consistant through out the casting. Hence to avoid any ambiguity, he specifies in detail the microstructure requirements and the location where it should be checked.
• Lastly the component testing procedures are defined like pressure testing for leakages etc.
It should also be appreciated that these specifications are not prepared at the designers table. They are evolved after thorough interactions with foundry, and after testing on a number of samples.
Cast Iron Specifications : Foundry
When the drawings and specifications are received in the foundry, it becomes a foundryman’s responsibility to translate these into unambiguous process sheets. This calls for similar preparation of specifications for raw materials, consumables and working procedures in the foundry. They also get fine tuned over a period. Typically these should cover following areas of foundry operations,
Raw materials :
• Pig iron
• Ferro alloys
• Scrap
• Inoculants
• Raw material sources
• Storage of raw materials and foundry returns
Sand :
• Moulding / Core Sand Quality
• Sand preparation
• Testing of sand quality
Melting :
• Charge calculations
• Molten metal analysis
• Temperature control
• Wedge test
Pouring :
• Pouring time
• Inoculation method
• Pouring temperature
• No of castings per heat
Fettling :
• Cooling duration – when the boxes are broken
• Runner riser removal process
• Shot blasting
• Heat identification
Testing :
• Sample selection
• Tensile testing
• Hardness testing
• Testing procedures and records
• Analysis of records
• Casting defects records and analysis
To ensure that these systems are initiated at the foundries, customers have started taking keen interest in the foundry operations by auditing the quality systems in the foundry.
Thursday, March 17, 2011
Cast Iron Polishing
Cast Irons : Optical Microscopy
Preparation of microscopic specimens
Polishing :
• Obtain a flat, semi polished surface by abrasive cutting
• Grind on suitable belt for reducing surface finish
• Intermediate grind on series of emery papers of decreasing grit size ‘O’, ‘OO’ and ‘OOO’
• Lap on suitable abrasive lapping wheel
Care during grinding
• Apply moderate pressure, to avoid distorsion and to prevent overheating
• Clean specimen thoroughly between changing grades
• Turn specimen at right angles
• Protect Edges
Final aim is to produce a flat, highly polished, scratch free surface.
The polishing process is directional, which results in draging out inclusions, graphite particles and locally abrade away material immediate adjacent to the particles leading to formation of ‘Comet Tails’. Rotating the specimen in counter to the rotation of the lap during final polishing operation effectively changes the direction of polishing and prevents formation of comet tails.
Electrolytic polishing - Not suitable for cast irons
• as specimen gets etched also and an unetched surface is preferred for graphite shape observation.
• complete or partial removal of inclusions / graphite particles and
• non suitability of mounted specimen due to staining.
Special precautions for cast iron specimen preparation
Due to difficulties to retain graphite particles
• Prepare by grinding on usual three papers 0, 00, 000, with prolonged grinding on a well worn sheet of 00 paper. Final grinding on 000 paper glazed with either graphite or soap stone.
• Graphite particles are more prone to dislodge if the polishing cloth is deep piles. Final polishing is best carried out on napless cloth such as fine silk.
• Polishing abrasive should be preferably levigated alumina instead of heavy magnesium oxide.
• The cloth should be kept damp, but not wet.
• Polishing should proceed in one direction only. Rotating specimen will quickly dislodge graphite particles.
• The polished surface should be frequently examined microscopically and excess polishing should be avoided.
Etching
The purpose of metallographis examination is to determine the true structural characteristics of the specimen of interest. It is therefore necessary that the various components of the microstructure be delineated with preciseness and extreme clarity.
This is usually achieved by subjecting the polished surface of the specimen to the chemical action of some reagent under carefully controlled conditions.
Preparation of microscopic specimens
Polishing :
• Obtain a flat, semi polished surface by abrasive cutting
• Grind on suitable belt for reducing surface finish
• Intermediate grind on series of emery papers of decreasing grit size ‘O’, ‘OO’ and ‘OOO’
• Lap on suitable abrasive lapping wheel
Care during grinding
• Apply moderate pressure, to avoid distorsion and to prevent overheating
• Clean specimen thoroughly between changing grades
• Turn specimen at right angles
• Protect Edges
Final aim is to produce a flat, highly polished, scratch free surface.
The polishing process is directional, which results in draging out inclusions, graphite particles and locally abrade away material immediate adjacent to the particles leading to formation of ‘Comet Tails’. Rotating the specimen in counter to the rotation of the lap during final polishing operation effectively changes the direction of polishing and prevents formation of comet tails.
Electrolytic polishing - Not suitable for cast irons
• as specimen gets etched also and an unetched surface is preferred for graphite shape observation.
• complete or partial removal of inclusions / graphite particles and
• non suitability of mounted specimen due to staining.
Special precautions for cast iron specimen preparation
Due to difficulties to retain graphite particles
• Prepare by grinding on usual three papers 0, 00, 000, with prolonged grinding on a well worn sheet of 00 paper. Final grinding on 000 paper glazed with either graphite or soap stone.
• Graphite particles are more prone to dislodge if the polishing cloth is deep piles. Final polishing is best carried out on napless cloth such as fine silk.
• Polishing abrasive should be preferably levigated alumina instead of heavy magnesium oxide.
• The cloth should be kept damp, but not wet.
• Polishing should proceed in one direction only. Rotating specimen will quickly dislodge graphite particles.
• The polished surface should be frequently examined microscopically and excess polishing should be avoided.
Etching
The purpose of metallographis examination is to determine the true structural characteristics of the specimen of interest. It is therefore necessary that the various components of the microstructure be delineated with preciseness and extreme clarity.
This is usually achieved by subjecting the polished surface of the specimen to the chemical action of some reagent under carefully controlled conditions.
Cast Iron Properties
Development of Microstructure in Cast Irons
Main difference between the molten cast irons and steels is that the liquid cast iron is a micro heterogeneous system which is not in equilibrium. It consists of carbon saturated iron and microgroups of carbon. An iron may solidify as grey, white or mottled depending upon the eutectic value and the rate of cooling.
Composition has effect on eutectic value. To simplify the effect of composition, a concept of carbon equivalent value has been developed. (CE). A commonly accepted definition of CE is Total Carbon % + (Si% / 3 + P% / 3). This carbon equivalent value tells whether the iron will be hypo eutectic, or hyper eutectic. In general, the lower the C value, the greater is the tendency for an iron to solidify white or mottled.
• Hypo eutectic irons do not solidify with the formation of graphite. Instead the solidification takes place by formation of austenite dendrites. The interdendritic areas remain high in carbon and solidify as a eutectic of iron carbide and austenite - called as ledeburite.
• Hyper eutectic irons solidify by the direct formation of graphite from the melt in the form of KISH generally appearing as long straight flakes. Graphite phase continues to solidify till the eutectic temperature. The eutectic graphite as a general rule solidifies as flake graphite.
ASTM A247 defines the graphite shape, size and distribution. ISO 945 has also accepted these definitions with extensions of additional graphite forms.
Type C : Kish, straight, thick chunkey flakes.
Type A : Normal Flakes –
Type D/E : Undercooled – is normally associated with rapid cooling, and is particularly common in thin sections. It can also be produced by other means like addition of titanium.
Type B : Rosettes type - is typical of slightly less rapid cooling.
Both Rosette and Under cooled graphites are frequently associated with ferrite, since the larger surface area of graphite flakes reduces the distance required to be traveled by carbon atoms during gamma to alpha cooling.
Other forms of graphite : Trace elements like lead (above 0.0007%) results in Widmannstatten graphite. Tellurium results in Mesh type graphite. Both these types of structures result in drastic reduction in strength of Cast Iron.
Manganese has its chief function to neutralise the sulphur content by formation of Manganese sulphide and to prevent formation of more harmful iron sulphide. This is possible if manganese contents equals 1.7 x sulphur percent + 0.3 %. When sulphur content is not balanced by the manganese content, anomolous inverse chilling effect may occur, indicated by free carbide in the center of an other wise grey section.
Mechanical Properties.
Although the structural constituents of steel can all be present in cast iron, there are two important constituents not normally present in steel which are responsible for major characteristics of cast iron - graphite and phosphorus. Effect of graphite on purely mechanical properties is essentially that of a void. Phosphorus forms a low melting point eutectic forming a brittle network affecting shock resistance and hydraulic soundness.
The structure and strength of grey iron castings are mainly governed by the amount and form of graphite - ie not only on the composition but also on the section thickness of the casting or the rate of cooling. Thus the metal cast from the same ladle may produce -a chilled white iron, a grey iron with chilled edge, a sound grey iron or a week open grained structure - depending upon the section thickness of the casting. For this reasons the standards specify the grey irons by reference to its strength not by composition, nor by the strength of the casting, but by the strength when cast into test bars of fixed diameter.
Tensile strength : Earlier standards used to specify tensile strength for different as cast test bar diameters. The definition of grade was based on tensile strength of 30 mm diameter test bar. Larger test bars showed less strength, and vice versa. It should be understood that the tensile strength obtained from the test bar does not indicate the strength of the casting, but the quality of the melting process and the molten metal. Strength of a particular section in a casting is dependent upon the cooling rate of the particular portion, and can be roughly correlated to the tensile strength results.
Transverse test : In other words Bend test to determine the transverse rupture stress. This is another way for melt quality and the results show good correlation with the tensile strength results.
The compression test : On specimen L/D 2:1. The compression strength is generally 3 to 4 times its tensile strength. Grey iron actually fractures at its maximum compression strength. In this respect it differs from the steel, malleable iron and other metals which deform plastically.
Hardness Test : Brinell hardness test is most commonly accepted test. It should be remembered that the Brinell hardness number is not independent of the test load.
• The diameter of the impression should be within 0.25 to 0.5 of the ball diameter. This is ensured by selecting ball diameter and test load (3000 Kf and 10 mm diameter ball, or 750 Kg and 5 mm ball - p/d2)
• Above 450 BHN, the ball tends to distort appreciably.
There is no clear relation between the hardness and tensile strength value for grey cast iron, as there is for steels.
Similarly there is no clear relationship between hardness and wear resistance.
Modulus of Elasticity : is measured by the slope of the stress-strain curve. For cast iron it is not a straight line as steels. Graphite flakes or nodules give dispersed discontinuities modifying stress strain response. The broken matrix carries a complex stress with high local stress at graphite flakes because of which the recoverable total strain does not follow a straight line.
Normal graphite structures show higher tensile, lower hardness, lower Eo values and higher total strain at failure than undercooled graphite structures.
Higher phosphorus irons show higher tensile, higher hardness, lower total strain at failure and little change in Eo values.
Annealing to ferritic state lowers tensile, hardness and Eo values
Dimensional stability under stress : For large castings, where maintenance of the higher dimensional accuracy is required – as in machine tools – initial deformation can be virtually eliminated by prestressing for a suitable period of time to a stress higher than that to be subsequently imposed.
Stress relieving is another method.
Damping Capacity : To absorb vibrational stresses – amount of energy absorbed per oscillation.
Increasing carbon equivalent increases damping capacity
Increasing cooling rate, causing refinement of matrix and graphite structures decreases damping capacity.
Annealed ferritic structures, and hardened structures have higher damping capacities than as cast structures.
Sliding Lubricated Wear –
Cast iron is an extremely good bearing material which can be used for applications from textile spindles (low load at 10000 rpm) to heavy planing machines (heavy load at few strokes per minute).
It is well known that under sliding lubricated wear against hardened steel surface, the greater wear may occur in hardened steel than in ordinary cast iron.
The presence of graphite contributes to the initial running in period to avoid seizing and scoring. The amount of graphite on the running surface is very small, and its effect is therefore likely to be confined to the initial period only.
Fully pearlitic matrix is normally preferable to one containing mainly free ferrite. Irons containing a high phosphorus content (> 0.7%) are more resistant under marginal lubricated wear. Iron containing such high phosphorus levels as tolerate 5- 10 % of free ferrite associated with moderately coarse flake graphite.
Surface hardness is only one of the factors affecting cylinder bore wear.
Machinability
Main criteria is chip cutting and removal. The coefficient of friction between the chip and the tool governs the character of chip.
For ductile materials, high coefficient of friction leads to a discontinuous chip.
Low coefficient of friction leads to a continuous chip and built up of metal on the tool.
For cast irons, which falls under brittle materials category, the discontinuous bricks will form for all coefficients of friction. Actual machinability depends on the different constituents of microstructure.
Graphite
• Provides dicsontinuities to facilitate chip breakage
• Provides anti-welding lubricant
• Form of graphite is less significant, than the quantity
• Coarse graphite machines better than fine undercooled graphite – but cannot produce better surface finish.
Ferrite
• Low hardness, however low ductility due to silicon content
• Increases machinability
Pearlite
• In general increasing amount of pearlite decreases machinability
• Coarse pearlite ismore readily machinable than fine pearlite
Phosphide eutietic
• the machinability reduces slightly above 0.5 % Phosphorus.
• Upto 1.4% phosphorus the castings are quite freely machinable, provided the ternary eutestic is absent. Carbides drastically reduce the machinability.
Carbides
• Free carbide markedly reduce the machinability and decrease tool life.
Typical points to check for machinability problems
Poor machinability – without hardspots
• Excessive machining allowance – leading to increased depth of cuts
• Higher strength and hardness
• Imperfect tools and speed / feeds
• Raw material sources
Hard Spots
• Too low carbon equivalent
• Variation in metal composition
• Unbalanced sulphur / manganese ratio – leading to hard center of casting. First metal out from cupola is likely to have high sulphur.
• Segregation of phosphorus/carbide complex – typically in thick castings where carbide forming elements are added.
• Hard spots due to trace elements is raw materials
Hard skin
• Typically for heavy castings
• Burnt on sand
• Deep oxidation of metal
• Sometimes a soft skin formed due to decarburisation also can produce a graphite free pearlite skin leading to heavy tool wear.
Main difference between the molten cast irons and steels is that the liquid cast iron is a micro heterogeneous system which is not in equilibrium. It consists of carbon saturated iron and microgroups of carbon. An iron may solidify as grey, white or mottled depending upon the eutectic value and the rate of cooling.
Composition has effect on eutectic value. To simplify the effect of composition, a concept of carbon equivalent value has been developed. (CE). A commonly accepted definition of CE is Total Carbon % + (Si% / 3 + P% / 3). This carbon equivalent value tells whether the iron will be hypo eutectic, or hyper eutectic. In general, the lower the C value, the greater is the tendency for an iron to solidify white or mottled.
• Hypo eutectic irons do not solidify with the formation of graphite. Instead the solidification takes place by formation of austenite dendrites. The interdendritic areas remain high in carbon and solidify as a eutectic of iron carbide and austenite - called as ledeburite.
• Hyper eutectic irons solidify by the direct formation of graphite from the melt in the form of KISH generally appearing as long straight flakes. Graphite phase continues to solidify till the eutectic temperature. The eutectic graphite as a general rule solidifies as flake graphite.
ASTM A247 defines the graphite shape, size and distribution. ISO 945 has also accepted these definitions with extensions of additional graphite forms.
Type C : Kish, straight, thick chunkey flakes.
Type A : Normal Flakes –
Type D/E : Undercooled – is normally associated with rapid cooling, and is particularly common in thin sections. It can also be produced by other means like addition of titanium.
Type B : Rosettes type - is typical of slightly less rapid cooling.
Both Rosette and Under cooled graphites are frequently associated with ferrite, since the larger surface area of graphite flakes reduces the distance required to be traveled by carbon atoms during gamma to alpha cooling.
Other forms of graphite : Trace elements like lead (above 0.0007%) results in Widmannstatten graphite. Tellurium results in Mesh type graphite. Both these types of structures result in drastic reduction in strength of Cast Iron.
Manganese has its chief function to neutralise the sulphur content by formation of Manganese sulphide and to prevent formation of more harmful iron sulphide. This is possible if manganese contents equals 1.7 x sulphur percent + 0.3 %. When sulphur content is not balanced by the manganese content, anomolous inverse chilling effect may occur, indicated by free carbide in the center of an other wise grey section.
Mechanical Properties.
Although the structural constituents of steel can all be present in cast iron, there are two important constituents not normally present in steel which are responsible for major characteristics of cast iron - graphite and phosphorus. Effect of graphite on purely mechanical properties is essentially that of a void. Phosphorus forms a low melting point eutectic forming a brittle network affecting shock resistance and hydraulic soundness.
The structure and strength of grey iron castings are mainly governed by the amount and form of graphite - ie not only on the composition but also on the section thickness of the casting or the rate of cooling. Thus the metal cast from the same ladle may produce -a chilled white iron, a grey iron with chilled edge, a sound grey iron or a week open grained structure - depending upon the section thickness of the casting. For this reasons the standards specify the grey irons by reference to its strength not by composition, nor by the strength of the casting, but by the strength when cast into test bars of fixed diameter.
Tensile strength : Earlier standards used to specify tensile strength for different as cast test bar diameters. The definition of grade was based on tensile strength of 30 mm diameter test bar. Larger test bars showed less strength, and vice versa. It should be understood that the tensile strength obtained from the test bar does not indicate the strength of the casting, but the quality of the melting process and the molten metal. Strength of a particular section in a casting is dependent upon the cooling rate of the particular portion, and can be roughly correlated to the tensile strength results.
Transverse test : In other words Bend test to determine the transverse rupture stress. This is another way for melt quality and the results show good correlation with the tensile strength results.
The compression test : On specimen L/D 2:1. The compression strength is generally 3 to 4 times its tensile strength. Grey iron actually fractures at its maximum compression strength. In this respect it differs from the steel, malleable iron and other metals which deform plastically.
Hardness Test : Brinell hardness test is most commonly accepted test. It should be remembered that the Brinell hardness number is not independent of the test load.
• The diameter of the impression should be within 0.25 to 0.5 of the ball diameter. This is ensured by selecting ball diameter and test load (3000 Kf and 10 mm diameter ball, or 750 Kg and 5 mm ball - p/d2)
• Above 450 BHN, the ball tends to distort appreciably.
There is no clear relation between the hardness and tensile strength value for grey cast iron, as there is for steels.
Similarly there is no clear relationship between hardness and wear resistance.
Modulus of Elasticity : is measured by the slope of the stress-strain curve. For cast iron it is not a straight line as steels. Graphite flakes or nodules give dispersed discontinuities modifying stress strain response. The broken matrix carries a complex stress with high local stress at graphite flakes because of which the recoverable total strain does not follow a straight line.
Normal graphite structures show higher tensile, lower hardness, lower Eo values and higher total strain at failure than undercooled graphite structures.
Higher phosphorus irons show higher tensile, higher hardness, lower total strain at failure and little change in Eo values.
Annealing to ferritic state lowers tensile, hardness and Eo values
Dimensional stability under stress : For large castings, where maintenance of the higher dimensional accuracy is required – as in machine tools – initial deformation can be virtually eliminated by prestressing for a suitable period of time to a stress higher than that to be subsequently imposed.
Stress relieving is another method.
Damping Capacity : To absorb vibrational stresses – amount of energy absorbed per oscillation.
Increasing carbon equivalent increases damping capacity
Increasing cooling rate, causing refinement of matrix and graphite structures decreases damping capacity.
Annealed ferritic structures, and hardened structures have higher damping capacities than as cast structures.
Sliding Lubricated Wear –
Cast iron is an extremely good bearing material which can be used for applications from textile spindles (low load at 10000 rpm) to heavy planing machines (heavy load at few strokes per minute).
It is well known that under sliding lubricated wear against hardened steel surface, the greater wear may occur in hardened steel than in ordinary cast iron.
The presence of graphite contributes to the initial running in period to avoid seizing and scoring. The amount of graphite on the running surface is very small, and its effect is therefore likely to be confined to the initial period only.
Fully pearlitic matrix is normally preferable to one containing mainly free ferrite. Irons containing a high phosphorus content (> 0.7%) are more resistant under marginal lubricated wear. Iron containing such high phosphorus levels as tolerate 5- 10 % of free ferrite associated with moderately coarse flake graphite.
Surface hardness is only one of the factors affecting cylinder bore wear.
Machinability
Main criteria is chip cutting and removal. The coefficient of friction between the chip and the tool governs the character of chip.
For ductile materials, high coefficient of friction leads to a discontinuous chip.
Low coefficient of friction leads to a continuous chip and built up of metal on the tool.
For cast irons, which falls under brittle materials category, the discontinuous bricks will form for all coefficients of friction. Actual machinability depends on the different constituents of microstructure.
Graphite
• Provides dicsontinuities to facilitate chip breakage
• Provides anti-welding lubricant
• Form of graphite is less significant, than the quantity
• Coarse graphite machines better than fine undercooled graphite – but cannot produce better surface finish.
Ferrite
• Low hardness, however low ductility due to silicon content
• Increases machinability
Pearlite
• In general increasing amount of pearlite decreases machinability
• Coarse pearlite ismore readily machinable than fine pearlite
Phosphide eutietic
• the machinability reduces slightly above 0.5 % Phosphorus.
• Upto 1.4% phosphorus the castings are quite freely machinable, provided the ternary eutestic is absent. Carbides drastically reduce the machinability.
Carbides
• Free carbide markedly reduce the machinability and decrease tool life.
Typical points to check for machinability problems
Poor machinability – without hardspots
• Excessive machining allowance – leading to increased depth of cuts
• Higher strength and hardness
• Imperfect tools and speed / feeds
• Raw material sources
Hard Spots
• Too low carbon equivalent
• Variation in metal composition
• Unbalanced sulphur / manganese ratio – leading to hard center of casting. First metal out from cupola is likely to have high sulphur.
• Segregation of phosphorus/carbide complex – typically in thick castings where carbide forming elements are added.
• Hard spots due to trace elements is raw materials
Hard skin
• Typically for heavy castings
• Burnt on sand
• Deep oxidation of metal
• Sometimes a soft skin formed due to decarburisation also can produce a graphite free pearlite skin leading to heavy tool wear.
Sunday, February 13, 2011
OUTLOOK SHORTCUT KEYS
Alt + S -Send the email
Ctrl + C -Copy selected text
Ctrl + X -Cut selected text
Ctrl + P -Open print dialog box
Ctrl + K -Complete name/email typed in address bar
Ctrl + B -Bold highlighted selection
Ctrl + I -Italicize highlighted selection
Ctrl + U -Underline highlighted selection
Ctrl + R -Reply to an email
Ctrl + F -Forward an email
Ctrl + N -Create a new email
Ctrl + Shift + A -Create a new appointment to your calendar
Ctrl + Shift + O -Open the outbox
Ctrl + Shift + I -Open the inbox
Ctrl + Shift + K -Add a new task
Ctrl + Shift + C -Create a new contact
Ctrl + Shift+ J -Create a new journal entry
Ctrl + C -Copy selected text
Ctrl + X -Cut selected text
Ctrl + P -Open print dialog box
Ctrl + K -Complete name/email typed in address bar
Ctrl + B -Bold highlighted selection
Ctrl + I -Italicize highlighted selection
Ctrl + U -Underline highlighted selection
Ctrl + R -Reply to an email
Ctrl + F -Forward an email
Ctrl + N -Create a new email
Ctrl + Shift + A -Create a new appointment to your calendar
Ctrl + Shift + O -Open the outbox
Ctrl + Shift + I -Open the inbox
Ctrl + Shift + K -Add a new task
Ctrl + Shift + C -Create a new contact
Ctrl + Shift+ J -Create a new journal entry
Sunday, February 6, 2011
Analog Transducers
The simplest analog position transducer is the resistance potentiometer, the resistance element in which is usually a deposited-film rather than a wirewound type. Very stable resistance elements based on conductive plastics, with resolution to a few microinches and operating lives in the 100 million rotations, are available, capable of working in severe environments with high vibrations and shock and at temperatures of 150 to 200°C. Accuracies of a few hundredths, and stability of thousandths, of a per cent, can be obtained from these units by trimming the plastics resistance element as a function of angle.
Performance of resistance potentiometers deteriorates when they operate at high speeds, and prolonged operation at speeds above 10 rpm causes excessive wear and increasing output noise. An alternative to the resistance potentiometer is the variable differential transformer, which uses electrical coupling between ac magnetic elements to measure angular or linear motion without sliding contacts. These units have unlimited resolution with accuracy comparable to the best resistance potentiometers but are more expensive and require compatible electronic circuits. A variable differential transformer needs ac energization, so an ac source is required. A precision demodulator is frequently used to change the ac output to dc. Sometimes the ac output is balanced against an ac command signal whose input is derived from the same ac source. In dealing with ac signals, phase-angle matching and an accurate amplitude-scale factor are required for proper operation. Temperature compensation also may be required, primarily due to changes in resistance of the copper windings. Transducer manufacturers will supply full sets of compatible electronic controls.
Performance of resistance potentiometers deteriorates when they operate at high speeds, and prolonged operation at speeds above 10 rpm causes excessive wear and increasing output noise. An alternative to the resistance potentiometer is the variable differential transformer, which uses electrical coupling between ac magnetic elements to measure angular or linear motion without sliding contacts. These units have unlimited resolution with accuracy comparable to the best resistance potentiometers but are more expensive and require compatible electronic circuits. A variable differential transformer needs ac energization, so an ac source is required. A precision demodulator is frequently used to change the ac output to dc. Sometimes the ac output is balanced against an ac command signal whose input is derived from the same ac source. In dealing with ac signals, phase-angle matching and an accurate amplitude-scale factor are required for proper operation. Temperature compensation also may be required, primarily due to changes in resistance of the copper windings. Transducer manufacturers will supply full sets of compatible electronic controls.
Gearing
In a closed-loop system, gearing may be used to couple a high-speed, lowtorque
motor to a lower-speed, higher-torque load. The gearing must meet requirements
for accuracy, strength, and reliability to suit the application. In addition, the closed loop requires minimum backlash at the point where the feedback sensor is coupled. In a velocity- controlled system, the feedback sensor is a tachometer that is usually coupled directly to the rotor shaft. Backlash between motor and tachometer, as well as torsional compliance, must be minimized for stable operation of a high-performance system. Units combining motor and tachometer on a single shaft can usually be purchased as an assembly. By contrast, a positioning system may use a position feedback sensor that is closely coupled to the shaft being positioned. As with the velocity system, backlash between the motor and feedback sensor must be minimized for closed-loop stability. Antibacklash gearing is
frequently used between the gearing and the position feedback sensor. When the position feedback sensor is a limited rotation device, it may be coupled to a gear that turns faster than the output gear to allow use of its full range. Although this step-up gearing enhances it, accuracy is ultimately limited by the errors in the intermediate gearing between the position sensor and the output. When an appreciable load inertia is being driven, it is important that the mechanical stiffness between the position sensor coupling point and the load be high enough to avoid natural torsional resonances in the passband.
motor to a lower-speed, higher-torque load. The gearing must meet requirements
for accuracy, strength, and reliability to suit the application. In addition, the closed loop requires minimum backlash at the point where the feedback sensor is coupled. In a velocity- controlled system, the feedback sensor is a tachometer that is usually coupled directly to the rotor shaft. Backlash between motor and tachometer, as well as torsional compliance, must be minimized for stable operation of a high-performance system. Units combining motor and tachometer on a single shaft can usually be purchased as an assembly. By contrast, a positioning system may use a position feedback sensor that is closely coupled to the shaft being positioned. As with the velocity system, backlash between the motor and feedback sensor must be minimized for closed-loop stability. Antibacklash gearing is
frequently used between the gearing and the position feedback sensor. When the position feedback sensor is a limited rotation device, it may be coupled to a gear that turns faster than the output gear to allow use of its full range. Although this step-up gearing enhances it, accuracy is ultimately limited by the errors in the intermediate gearing between the position sensor and the output. When an appreciable load inertia is being driven, it is important that the mechanical stiffness between the position sensor coupling point and the load be high enough to avoid natural torsional resonances in the passband.
Stepper Motors
In a stepper motor, power is applied to a wound stator, causing the
brushless rotor to change position to correspond with the internal magnetic field. The rotor maintains its position relative to the internal magnetic field at all times. In its most common mode of operation, the stepper motor is energized by an electronic controller whose current output to the motor windings defines the position of the internally generated magnetic field. Applying a command pulse to the controller will change the motor currents to reposition the rotor. A series of pulses, accompanied by a direction command, will cause rotation in uniformly spaced steps in the specified direction. If the pulses are applied at a sufficiently high frequency, the rotor will be carried along with the system's inertia and will rotate relatively uniformly but with a modulated velocity. At the other extreme, the response to a single pulse will be a step followed by an overshoot and a decaying oscillation. Where the application cannot permit the oscillation, damping
can be included in the controller. Stepper motors are often preferred because positions of the rotor are known from the number of pulses and the step size. An initial index point is required as an output position reference, and care is required in the electronic circuits to avoid introducing random pulses
that will cause false positions. As a minimum, the output index point on an appropriate shaft can verify the step count during operation.
brushless rotor to change position to correspond with the internal magnetic field. The rotor maintains its position relative to the internal magnetic field at all times. In its most common mode of operation, the stepper motor is energized by an electronic controller whose current output to the motor windings defines the position of the internally generated magnetic field. Applying a command pulse to the controller will change the motor currents to reposition the rotor. A series of pulses, accompanied by a direction command, will cause rotation in uniformly spaced steps in the specified direction. If the pulses are applied at a sufficiently high frequency, the rotor will be carried along with the system's inertia and will rotate relatively uniformly but with a modulated velocity. At the other extreme, the response to a single pulse will be a step followed by an overshoot and a decaying oscillation. Where the application cannot permit the oscillation, damping
can be included in the controller. Stepper motors are often preferred because positions of the rotor are known from the number of pulses and the step size. An initial index point is required as an output position reference, and care is required in the electronic circuits to avoid introducing random pulses
that will cause false positions. As a minimum, the output index point on an appropriate shaft can verify the step count during operation.
Mechanical Stiffness
When output motion must respond to a rapidly changing input
command, the control system must have a wide bandwidth. Where the load mass (in linear motion systems) or the polar moment of inertia (in rotary systems) is high, there is a possibility of resonant oscillations. For the most stable and reliable systems, with a defined load, a high system mechanical stiffness is preferred. To attain this stiffness requires strengthening shafts, preloading bearings, and minimizing free play or backlash. In the best-performing systems, motor and load are coupled without intervening compliant members. Even tightly bolted couplings can introduce compliant oscillations resulting from extremely minute slippages caused by the load motions.
Backlash is a factor in the effective compliance of any coupling but has little effect on the resonant frequency because little energy is exchanged as the load is moved through the backlash region. However, even in the absence of significant torsional resonance, a highgain control system can “buzz” in the backlash region. Friction is often sufficient to eliminate this small-amplitude, high-frequency component. The difficulty with direct-drive control systems lies in matching motor to load. Most electric motors deliver rated power at higher speeds than are required by the driven load, so that load power must be delivered by the direct-drive motor operating at a slow and relatively inefficient speed. Shaft power at low speed involves a correspondingly high torque, which requires a large motor and a high-power controller. Motor copper loss (heating) is high in delivering the high motor torque. However, direct-drive motors provide maximum
load velocity and acceleration, and can position massive loads within seconds of arc (rotational) or tenths of thousandths of an inch (linear) under dynamic conditions.
Where performance requirements are moderate, the required load torque can be traded
off against speed by using a speed-changing transmission, typically, a gear train. The transmission effectively matches the best operating region of the motor to the required operating region of the load, and both motor and controller can be much smaller than would be needed for a comparable direct drive.
command, the control system must have a wide bandwidth. Where the load mass (in linear motion systems) or the polar moment of inertia (in rotary systems) is high, there is a possibility of resonant oscillations. For the most stable and reliable systems, with a defined load, a high system mechanical stiffness is preferred. To attain this stiffness requires strengthening shafts, preloading bearings, and minimizing free play or backlash. In the best-performing systems, motor and load are coupled without intervening compliant members. Even tightly bolted couplings can introduce compliant oscillations resulting from extremely minute slippages caused by the load motions.
Backlash is a factor in the effective compliance of any coupling but has little effect on the resonant frequency because little energy is exchanged as the load is moved through the backlash region. However, even in the absence of significant torsional resonance, a highgain control system can “buzz” in the backlash region. Friction is often sufficient to eliminate this small-amplitude, high-frequency component. The difficulty with direct-drive control systems lies in matching motor to load. Most electric motors deliver rated power at higher speeds than are required by the driven load, so that load power must be delivered by the direct-drive motor operating at a slow and relatively inefficient speed. Shaft power at low speed involves a correspondingly high torque, which requires a large motor and a high-power controller. Motor copper loss (heating) is high in delivering the high motor torque. However, direct-drive motors provide maximum
load velocity and acceleration, and can position massive loads within seconds of arc (rotational) or tenths of thousandths of an inch (linear) under dynamic conditions.
Where performance requirements are moderate, the required load torque can be traded
off against speed by using a speed-changing transmission, typically, a gear train. The transmission effectively matches the best operating region of the motor to the required operating region of the load, and both motor and controller can be much smaller than would be needed for a comparable direct drive.
Electromechanical Control Systems
Wiring is the simplest way to connect components,
so electromechanical controls are more versatile than pure hydraulic or pneumatic
controls. The key to this versatility is often in the controller, the fundamental characteristic of which is its power output. The power output must be compatible with motor and load requirements. Changes to computer chips or software can usually change system performance to suit the application.
When driving a dc motor, for instance, the controller must supply sufficient power to match load requirements as well as motor operating losses, at minimum line voltage and maximum ambient temperature. The system's wiring must not be greatly sensitive to transient or steady-state electrical interference, and power lines must be separated from control signal lines, or appropriately shielded and isolated to avoid cross-coupling. Main lines to the controller must often include electrical interference filters so that the control system does not affect the power source, which may influence other equipment connected to the same source. For instance, an abruptly applied step command can be smoothed out so that heavy motor inrush currents are avoided. The penalty is a corresponding delay in response.
Use of current limiting units in a controller will not only set limits to line currents, but will also limit motor torque. Electronic torque limiting can frequently avoid the need for mechanical torque limiting. An example of the latter is using a slip clutch to avoid damage due to overtravel, the impact of which usually includes the kinetic energy of the moving machine elements. In many geared systems, most of the kinetic energy is in the motor.
Voltage limiting is less useful than current limiting but may be needed to isolate the motor from voltage transients on the power line, to prevent over speeding, as well as to protect electronic components.
so electromechanical controls are more versatile than pure hydraulic or pneumatic
controls. The key to this versatility is often in the controller, the fundamental characteristic of which is its power output. The power output must be compatible with motor and load requirements. Changes to computer chips or software can usually change system performance to suit the application.
When driving a dc motor, for instance, the controller must supply sufficient power to match load requirements as well as motor operating losses, at minimum line voltage and maximum ambient temperature. The system's wiring must not be greatly sensitive to transient or steady-state electrical interference, and power lines must be separated from control signal lines, or appropriately shielded and isolated to avoid cross-coupling. Main lines to the controller must often include electrical interference filters so that the control system does not affect the power source, which may influence other equipment connected to the same source. For instance, an abruptly applied step command can be smoothed out so that heavy motor inrush currents are avoided. The penalty is a corresponding delay in response.
Use of current limiting units in a controller will not only set limits to line currents, but will also limit motor torque. Electronic torque limiting can frequently avoid the need for mechanical torque limiting. An example of the latter is using a slip clutch to avoid damage due to overtravel, the impact of which usually includes the kinetic energy of the moving machine elements. In many geared systems, most of the kinetic energy is in the motor.
Voltage limiting is less useful than current limiting but may be needed to isolate the motor from voltage transients on the power line, to prevent over speeding, as well as to protect electronic components.
Sunday, January 30, 2011
CAREER OPPORTUNITIES IN INVESTMENT MANAGEMENT
By |
— Dr. Sanjay Tiwari |
One of the most important instruments of investment through stock market is the mutual funds. The companies or organisations which facilitate this type of investment are known as Asset Management Companies (AMCs). These AMCs are responsible for the investment made by investors and thereby MF agents are the key channels for apprising the large number of investors of options for investment. MF’s agents, distributors, bank employees handling Mutual Fund marketing have to be informed fund advisors. The following is the detail of career positions available in MF segment:
Fund Managers are the people or experts who are responsible for managing the Asset Under Management (AUM) of any AMC which is contributed by the heavy amount of investment in equity and debt market. They not only manage the investment but also provide advice to their clients who may be institutional or individual. They have the responsibility to track the market returns and give good returns to their clients who have shown confidence in their expertise. Simultaneously they keep on changing their capital structure i.e. debt-equity mix for balanced investment decisions. The criteria for becoming fund manager depends upon the professional degree like MBA in finance and more important the inclination towards Mutual Fund risk-return analysis.
Distributors are appointed by the AMCs who educate the investor sufficiently. Individuals form the largest segment in the distribution category. They perform the role of marketing distribution channels and facilitate individuals to purchase some funds.
Lead Managers are the functionaries who co-ordinate with intermediaries, campaign for the scheme and approach potential investors. Expert professionals having exposure to risk-return conceptual knowledge and practical skills are employed by these organisations.
Dealers execute trades and act as intermediaries between the investors and the equity/debt markets. The dealers have to comply with all the formalities of sale and purchase. A person with a financial background, thorough understanding of stock market operations, communication skills and acumen can be a dealer.
Operations related career in stock market There are some other positions available in stock market and its operations. These may be categorised into the fund accounting group, the custody group, the financial control group and the MIS & audit group.
The fund accounting group calculates Net Asset Value of funds on a daily basis and maintains books. The custody group make a liaison with custodians appointed by the AMC. MFs buy and sell huge volumes of securities. The custodians appointed ensure the safe custody of these funds and ready availability. Therefore, the people are required to run these day to day operational activities. The skills, inclination and professional qualifications are desired.
Registrar and transfer agents process the applications and dispatch Unit certificates to unit holders within the Security & Exchange Board of India specified time-frames.
Career with Regulatory Bodies, Rating Agencies and Depositories
To regulate the capital market SEBI (Securities and Exchange Board of India) was constituted in 1992. As a regulator of stock market, mutual funds and derivative, this body has expanded its business and operation which require professionals from varied backgrounds; finance, accounting, auditing, investment, credit rating, consultancy, mutual funds, law, derivatives products etc. IRDA as a regulator of insurance business in India requires some investment experts for their valuable advises based on sound analysis of investment of their insurance products. With the opening up of the insurance sector, private and foreign players have emerged on Indian insurance scene which also provides ample opportunities for professionals associated with investment management profession.
Similarly, to advise the individual investors on their investment related to equity and debt based on respective ratings of the financial instruments, various credit rating agencies have been formed i.e. CRISIL, CARE, ICRA which are always in need of professionals in investment analysis such as; credit analysis, rating analysis, industry analysis, portfolio analysis, economic analysis etc. CRISIL has started courses in financial planning for professionals.
Career in Depositories
Depositories are the organisations responsible for recording, maintaining, authenticating and facilitating paperless trading of financial securities. These also act as clearing houses and provide services related to DMAT account and transactions clearance. Some of the depositories working in India are; National Securities Depositories Ltd. (NSDL), Central Depositories Services Ltd. (CDSL) and Stock Holding Corporation of India (SHCIL). For running the business operations of these depositories CA/ICWAI/CS/CFA/MBA with some experience in stock exchanges, custodians, brokerage firms, banks and financial services companies from reputed institutes/universities are required.
Research and Consultancy
Investment firms and institutions differ in the number of professionals they employ in the research and consultancy departments. Equity research can be a one man outfit or a department with a team of professionals drawn from diverse disciplines. Mutual Funds, FIIs, institutional investors, broking houses hire research specialists. Print and electronic media also offer opportunities for professionals’ expert advice on stock investment and volatility.
The following academic and personal prerequisites are essential to seek a career in investment management:
. Degree/diploma/course in investment management/stock market operations
. Knowledge of finance, business, mathematics, accounting, economics, computers
. Analytical ability and communication skills of expected standard
. Acumen, interest and inclination towards investment market
. Knowledge of financial institutions, tax, financial planning, legal aspects of capital market
. Creative ability to take decisions based on sound analysis
. Zeal to learn latest development with persuasive traits and patience.
Now let’s have a look at some intuitions offering programmes/courses in investment management:
Name of the Programme/Course : MBA/PGDM/PGDBA with finance specialisation
Institutions/Universities : IIMs, Universities (Central and State)/Institutions
Duration : Two Years
Eligibility : Graduation with 50% with valid score in CAT/MAT/Test conducted by universities
Address : Website of related institutions
Name of the Programme/Course : Courses and NCFM modules on stock market operations, surveillance, dealers’, derivatives, currency derivatives, investment analysis and portfolio management, depository operations etc.
Institutions/Universities : National Stock Exchange of India, Mumbai
Duration : Depending upon the course/module
Eligibility : Depending upon the course/module
Address : nse- india.org
Name of the Programme/Course : Post-graduate membership course in capital market and financial services.
Institutions/Universities : Institute of Company Secretaries of India, New Delhi
Duration : —
Eligibility : —
Address : Institute of Company Secretaries of India, New Delhi.
Now let us understand the terminology used in this article:
Investment
It is the amount invested in some financial asset i.e. equity and debt to get some return at a given level of risk.
Investment Management
It is the study of analysing risk and return on investment using analytical techniques.
Credit Rating
The relative performance given in terms of grade to the financial asset depending upon the risk. Credit rating agencies determine a set of criteria for rating the instruments on their safety and advise the investors accordingly.
Risk
The probability of getting return from investment in financial asset.
Industry Analysis
Evaluation of the performance of industry based on certain parameters.
Portfolio Management
Analysing the risk-return profile of a group of securities. It is done to minimize the risk and neutralize its impact on other securities.
ETF
It stands for Exchange Traded Funds. A popular financial instrument whose trading is done through stock exchanges. Gold ETFs are instruments whose value depends upon the gold prices and these can be easily traded through exchanges.
(Concluded)
(The author is Associate Professor (Management), Central University of Haryana, Mahendergargh
e-mail: stiwarigju@rediffmail.com)
ref - http://www.employmentnews.gov.in/CAREER-OPPORTUNITIES-IN-INVESTMENT2.asp
Career in Soft Skills Training
By |
Anurag Kumar Of late, soft skills have emerged as a tool with enough power to make or break your career. How often do we encounter technically talented people who excel in their jobs, but whose career stalls beyond a certain point because they lack the social communication and relationship building skills to manage, work with and lead other people? Soft skills is an umbrella term which includes communicative skills, listening skills, team skills, Leadership quality, creativity and logic, problem solving skills, diplomacy and change readiness, among others. Soft skills are generally gifted and cannot be learnt from a book. Roots of soft skills can be traced back to one’s ‘Sanskaras’ (Family Values). Still, formal training can, of course, give you a fresh perspective, and teach you tips and techniques if you need to improve specific skills, but if you really want to ingrain soft skills into your personality, you have to become a keen observer, an eager learner and an assiduous workman religiously putting to practice all that you have learnt. Here are a few soft skills which may help you improve your career prospects and enhance your personality as a whole. Effective Communication Skills Effective communication skills include oral Skills for public speaking, presentations, negotiating, conflict resolutions, knowledge-sharing; Writing Skills for preparing reports, proposals, instruction manuals, writing memos, notices, official correspondence etc. It also includes a combination of verbal and non-verbal skills. Since our official medium of communication is English, certain amount of proficiency is needed in it. As English for us is a second language and not our mother tongue, so a constant practice at home/hostel, followed by language-lab sessions, is need of the hour. Those institutes that want their students to get placed in MNCs and reputed companies, must give this a deep and urgent thought. Quality job depends as much as on knowledge of the respective subject as on good communication skills. Interpersonal and Teamwork Skills Interpersonal and teamwork skills contribute to higher productivity and better environment as people work together to reach common goals. Some individuals are born leader or intuitively adopt the traits required in team work. However, in general, these skills need to be taught or can be learnt through practice and awareness. This skill has four dimensions namely—Cooperation, Communication, Work Ethic and Leadership. Cooperation requires demonstrating the ability to compromise on their views, treating team members with respect, and working within a consensus of the team. Communication here requires a dynamic interaction among team members and inviting and providing feedback and resolving conflict. Work ethics includes accepting responsibility for assigned work, completing any assigned tasks and doing so on-time, and offering assistance to other team members when required. It is certainly desirable for each team member to demonstrate leadership. This includes helping to provide structure by initiating action, clarifying concepts and problems, and summarizing activities and results. Personal Skills Many people wonder why they do not have the success they want in business! Most of the time, the reason will be right under their nose; they are just unable to see it. The first thing that someone should ask is, "Am I successful in my personal life and relationships?” Personal skills are those skills which make you not only acceptable and respectable in society and at the work place but also help you in getting a good job and better career growth. They include ability to make decision, Alertness, Assertiveness, Attention to details, calmness, Commitment, Cooperation, Emotional stability, Empathy, Flexibility, Generosity, Tolerance, self-confidence, self-control, self-reliance, self-respect, Honesty, and sense of humor among others. Problem-Solving and Other Cognitive Skills In your day to day life, you often come across such situations where you are unable to make right decisions. You are more likely to get into such conditions when you are working in an organization. To deal with such stresses, you need to develop some skills which may help you in making decisions, developing creative and innovative solutions, developing practical solutions, showing independence and initiative in identifying problems and solving them, applying a range of strategies to problem-solving, applying problem-solving strategies across a range of areas. Adaptability and Work Ethics It is a well-known fact that contemporary organizations evolve and change rapidly, given the fast pace of technological change over the last hundred years of industrial era. Consequently, an employee in a contemporary organization must not only be willing to work hard but also possess the flexibility and ability to respond to rapid change. An employer requires a whole set of skills to develop adoptability like communicating across cultures, getting along with others in a multi-cultural work environment, respect for others’ faith and belief systems, avoiding racial/cultural discrimination at the workplace. Work ethic is a set of values based on the moral virtues of hard work and diligence. It is also a belief in moral benefit of work and its ability to enhance character of the employer or any individual. A work ethic may include being reliable, having initiative or maintaining social skills. Apart from that a sense of responsibility, honesty and commitment may also be included in it. In order to posses these above discussed skills you need to be self-aware i.e. you need to cultivate positivism in your thought and approach. You should also know how to live consciously and try to put your words into action. Reading is yet another way to improve your skills and can help you develop a better perspective of the world and the things around you. You should also open yourself to new ideas and experiences and be willing to adapt to changes if it makes the things go easier. The last but not the least you should always remember is that you need to practice and practice these skills with dedication. Practice improves your performance, helps you discover and overcome shortcomings and mistakes and gives you confidence. Career Prospects
Education Though there are a number of institutes that are offering courses in soft skills, here are a few institutes who organize short term course for soft skill training:
After completing the course, one can get a job in any public or private organization, educational institute, or can set his own training centers. Initially, the trainer can earn somewhere between Rs. 10,000 to Rs. 20,000 per month which increases over the years. About the Author Anurag Kumar is presently working on his Ph. D Thesis in the Department of Humanities and Social Sciences, Indian Institute of Technology Roorkee. Address for Correspondence: Anurag Kumar C/o Dr. Nagendra Kumar 60/1 Ravindra Lok Colony IIT Roorkee- 247667 Email Id: anuragkumar.lko@gmail.com; anu_pandeylu@yahoo.co.in ref - http://www.employmentnews.gov.in/Career_in_Soft_Skills_Training.asp |
Friday, January 28, 2011
Bearings
Bearings
• The interface between moving parts that should minimize friction and wear.
Plain Bearings
• Generally used in low speed machines.
• The main bearing action comes from the lubricant.
Solid Bearings
• This looks like a section of tube that is placed in a hole, and the shaft rotates inside.
• Typical materials are,
- bronze
- sintered bronze (with graphite)
- cast iron
• Made for slowly rotating equipment
• lubrication is required, and problems will arise when not properly maintained.
• Available in standard sizes.
Split Bearings
• Used on large machines at low speeds.
• The two halves of the bearings are adjusted in position using shims.
• Typical materials include,
- bronze
- bronze with babbitt
- babbitt lined metal
• Oil grooves are used for lubrication.
Thrust Bearings
• Opposses axial thrusts of rotating shafts.
• Uses shoes of a variety of shapes,
- flat
- kidney shaped
• An oil wedge approach is used to support the bearing.
Rolling Bearings
• Advantages,
- low friction at all times
- compact
- high accuracy
- low wear
- come in standard sizes
Ball Bearings
• Low friction, high speeds, low loads.
• ball bearings are packed between two rotating rings.
• The grooves that contain the ball bearings is given different shapes for different loading conditions.
Roller Bearings
• For heavy loads at medium or high speeds.
• The various roller bearings are designed for loads (radial and axial) and packing space.
Thrust Bearings
• A set of rollers or balls are held between two washers.
• Designed mainly for lower speed axial loads and occasionally light radial loads.
• The interface between moving parts that should minimize friction and wear.
Plain Bearings
• Generally used in low speed machines.
• The main bearing action comes from the lubricant.
Solid Bearings
• This looks like a section of tube that is placed in a hole, and the shaft rotates inside.
• Typical materials are,
- bronze
- sintered bronze (with graphite)
- cast iron
• Made for slowly rotating equipment
• lubrication is required, and problems will arise when not properly maintained.
• Available in standard sizes.
Split Bearings
• Used on large machines at low speeds.
• The two halves of the bearings are adjusted in position using shims.
• Typical materials include,
- bronze
- bronze with babbitt
- babbitt lined metal
• Oil grooves are used for lubrication.
Thrust Bearings
• Opposses axial thrusts of rotating shafts.
• Uses shoes of a variety of shapes,
- flat
- kidney shaped
• An oil wedge approach is used to support the bearing.
Rolling Bearings
• Advantages,
- low friction at all times
- compact
- high accuracy
- low wear
- come in standard sizes
Ball Bearings
• Low friction, high speeds, low loads.
• ball bearings are packed between two rotating rings.
• The grooves that contain the ball bearings is given different shapes for different loading conditions.
Roller Bearings
• For heavy loads at medium or high speeds.
• The various roller bearings are designed for loads (radial and axial) and packing space.
Thrust Bearings
• A set of rollers or balls are held between two washers.
• Designed mainly for lower speed axial loads and occasionally light radial loads.
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