Motorized Ramming Machine

MOTORIZED RAMMING MACHINE CHAPTER-1 INTRODUCTION

Here we fabricate the model for ramming machine it is used to set the loose sand sand in found foundri ries es.. It mini minimi mize zess the work work load load of man man powe powerr. Most Mostly ly ramm rammin ing g machines are using the vibrating table with the arrangement of zigzag movement and it needs more current to carry out this process. To avoid this we are using cam with return return spring spring arrang arrangeme ement nt for the ramming ramming machine machine..

The project project consists consists of the

foll follow owin ing g part partss ramm rammin ing g tool tool,, etu eturn rn spri spring ng,, Hand Handle le with with scre screw w rod, rod, !am !am arrang arrangeme ement nt and Motor Motor with with worm worm gear gear arran arrangem gement ent.. " sand rammer is a piece of e#uipment used in foundry sand testing to make test specimen of molding sand by compacting bulk material by free fi$ed height drop of fi$ed weight for % times. It is also used to determine compatibility of sands by using special specimen tubes and a linear scale. Mechanism

&and rammer consists of calibrated sliding weight actuated by cam, a shallow cup to accommodate specimen tube below ram head, a specimen stripper to strip compacted specimen out of specimen tube, a specimen tube to prepare the standard specimen of '( mm diameter by '( mm height or ) inch diameter by ) inch height for an "*& standard specimen. Specimen Preparatin Preparatin

The cam is actuated by a user by rotating the handle, causing a cam to lift the weight and let it fall freely on the frame attached to the ram head. This produces a standard compacting action to a pre+measured amount of sand. ariety of standard specimen for -reen &and and &ilicate based !/ )0 sand are prepared using a sand rammer along with accessories Specimen D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

T!pe " sand Page

!ompression !ylindrical0

-reen &and and &ilicate based sand

Tensile &pecimen

&ilicate based sand

Transverse &pecimen

&ilicate based sand

The object for producing the standard cylindrical specimen is to have the specimen become ) inches high plus or minus 12%) inch0 with three rams of the machi machine ne.. "fter fter the the speci specime men n has has been been prep prepar ared ed inside inside the spec specim imen en tube tube,, the the specimen can be used for various standard sand tests such as the permeability test, the green sand compression compression test, the shear test, or other standard standard foundry foundry tests. The sand rammer machine can be used to measure compactability of prepared sand by filling the specimen tube with prepared sand so that it is level with the top of the tube. The tube is then placed under the ram head in the shallow cup and rammed three times. !ompactability in percentage is then calculated from the resultant height of the sand inside the specimen tube. " rammer is mounted on a base block on a solid foundation, which provides vibration damping to ensure consistent ramming. Prere#$isites%

3rere#uisite 3rere#uisite e#uipments e#uipments for sand rammer rammer may vary from case to case basis or testing scenario4 Case 14 If the prepared sand is ready •

Tube filler accessory to fill sample tube with sand. "dvantage is it lets the sand fill in from fi$ed distance and riddles it before filling.

Case &% 5$periment by preparing new sand sample If sand needs to be prepared before making specimen following e#uipments may be needed •

6aboratory sand muller or laboratory sand mi$er for core sands0

Case '% *or low compressive strength sands and mi$tures4 •

&plit specimen tube

CHAPTER-& D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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!ompression !ylindrical0

-reen &and and &ilicate based sand

Tensile &pecimen

&ilicate based sand

Transverse &pecimen

&ilicate based sand

The object for producing the standard cylindrical specimen is to have the specimen become ) inches high plus or minus 12%) inch0 with three rams of the machi machine ne.. "fter fter the the speci specime men n has has been been prep prepar ared ed inside inside the spec specim imen en tube tube,, the the specimen can be used for various standard sand tests such as the permeability test, the green sand compression compression test, the shear test, or other standard standard foundry foundry tests. The sand rammer machine can be used to measure compactability of prepared sand by filling the specimen tube with prepared sand so that it is level with the top of the tube. The tube is then placed under the ram head in the shallow cup and rammed three times. !ompactability in percentage is then calculated from the resultant height of the sand inside the specimen tube. " rammer is mounted on a base block on a solid foundation, which provides vibration damping to ensure consistent ramming. Prere#$isites%

3rere#uisite 3rere#uisite e#uipments e#uipments for sand rammer rammer may vary from case to case basis or testing scenario4 Case 14 If the prepared sand is ready •

Tube filler accessory to fill sample tube with sand. "dvantage is it lets the sand fill in from fi$ed distance and riddles it before filling.

Case &% 5$periment by preparing new sand sample If sand needs to be prepared before making specimen following e#uipments may be needed •

6aboratory sand muller or laboratory sand mi$er for core sands0

Case '% *or low compressive strength sands and mi$tures4 •

&plit specimen tube

CHAPTER-& D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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(ITERATURE SUR)E*

The 7et 75T+(T ) in. 8ench Model &and ammer delivers fast, powerful blows for for ramm rammin ing g smal small, l, mediu medium m and and larg largee form forms. s. The The heat+ heat+tr trea eate ted d pisto piston n provi provide dess suff suffic icie ient nt forc forcee and and stur sturdi dine ness ss to outl outlas astt any any indu indust stri rial al envi enviro ronm nmen ent. t. It is ergonomically designed to provide greater ease of handling with reduced operator fatigue.

*eatures4 •

Heat treated cylinder and chrome+plated piston provide corrosion resistance in any industrial environment

•

5rgonomically designed providing greater ease of handling with reduced operator fatigue

•

9esigned for fast, compacting blows increasing productivity

•

6ight to medium duty applications

•

5#uipped with rubber butt

Includes4 •

) in. 8ench Model &and ammer + ''::%)

DEDAN +IMATHI UNI)ERSIT* O, TECHNO(OG*

The automatic rammer is used for ramming the sand uniformly around the pattern. It can be used even in small scale industries. To operate this rammer an air compressor is needed. " 8utt which is attached to the bottom of the piston rod does the operation of ramming. The pressure developed developed inside the cylinder reciprocates the piston and hence the butt. This rammer is handled by an operator just by moving it over the molding sand. The butt rams the sand at places moved and the sand is uniformly rammed. This rammer D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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reduces the ramming time and labor. 9ue to this the cost is reduced considerable. &o this machine finds application application in foundries. foundries. ).

The rammer can be handled by an operator without feeling uneasiness. ;o separate skill is re#uired to operate this rammer. The operation is #uick and hence it is a time saving one. The operation is easy and consumes less cost. 9ue to the above reasons it finds its e$tensive application in manufacturing industries. It has an e$tensive application in both large scale and small scale industries because of its economy and easy handling "utomat "utomation ion can be achiev achieved ed through through compute computers, rs, hydraul hydraulics ics,, pneuma pneumatic tics, s, robotics, etc et c., of these these source sources, s, pneum pneumatic aticss form form an attra attracti ctive ve medium medium for low low cost autom automatio ation. n. The The main advantages of all pneumatic systems are economy and simplicity. "utomation plays an important role in mass production. ;owadays almost all the manufacturing process is being atomized in order to deliver the the produc oductts at a faste ster rate. The rammer ramm er can be handle han dled d by an operato oper atorr withou wit houtt feeling feel ing uneasiness. ;o separate skill is re#uired to operate this rammer. The operation is #uick and hence it is a time saving one. The operation is easy and consumes less cost. 9ue to the above reasons it finds its e$tensive application in manufacturing industries. It has an e$tensive application in both large scale and small scale industries because of its economy and easy handling. • • • • •

• •

&trength uniform ramming of sand is obtained by this rammer. The time consumption for ramming is reduced greatly. &killed labor is not re#uired. 5asy operation It can be transported easily from one place to another since dismantling and assembling is simple. It reduces more labor for ramming operation. Maintenance is easy.

D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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reduction of production time and elimination of more labor for ramming operation reduce production cost, thereby the economy is greatly achieved.

CHAPTER-' S*STEM ,UNCTION

OR+ING PRINCIP(E%

Here we are using the table with the support of return spring arrangement and below of this we are placing the cam mechanism with rotation movement. The The rota rotati tion on movem ovemen entt for for cam cam is give given n by the the moto motorr with with worm worm gear gear arrangement for the vibrating operation. The supporting shaft on either side of the table holds the molding bo$ preventing it from falling while the operation takes place. The motor will rotate the worm gear arrangement and that will rotate the cam mechanism hence the table moves up and down. The ramming


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tool is rotated by means of handle to seat on the molding sand and to set the sand firmly in the molding bo$. AD)ANTAGES 

-et good output



5asy to operate



5asy to maintain

DISAD)ANTAGES 

;ut should be tightened every time manually

APP(ICATION •

It is applicable in foundries.

INDUSTRIA( APP(ICATION O, RAMMING

The rammer can be handled by an operator without feeling uneasiness. ;o separate skill is re#uired to operate this rammer. The operation is #uick and hence it is a time saving one. The operation is easy and consumes less cost. 9ue to the above reasons it finds its e$tensive application in manufacturing industries.

It has an

e$tensive application in both large scale and small scale industries because of its economy and easy handling. The manufacturing operation is being atomized for the following reasons. 

To achieve mass production



To reduce man power



To increase the efficiency of the plant



To reduce the work load



To reduce the production cost



To reduce the production time



To reduce the material handling


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

To reduce the fatigue of workers



To achieve good product #uality



6ess maintenance

CHAPTER-. /ASIC MOTOR THEOR*

Intrd$ctin

It has been said that if the "ncient omans, with their advanced civilization and knowledge of the sciences, had been able to develop a steam motor, the course of history would have been much different. The development of the electric motor in modern times has indicated the truth in this theory. The development of the electric motor has given us the most efficient and effective means to do work known to man. 8ecause of the electric motor we have been able to greatly reduce the painstaking toil of man=s survival and have been able to build a civilization which is now reaching to the stars. The electric motor is a simple device in principle. It converts electric energy into mechanical energy. /ver the years, electric motors have changed substantially in design, however the basic principles have remained the same. In this section of the "ction -uide we will discuss these basic motor principles. >e will discuss the phenomena of magnetism, "! current and basic motor operation. Ma0netism

;ow, before we discuss basic motor operation a short review of magnetism might be helpful to many of us. >e all know that a permanent magnet will attract and hold metal objects when the object is near or in contact with the magnet. The permanent magnet is able to do this because of its inherent magnetic force which is referred to as a ?magnetic field?. In *igure 1 , the magnetic field of two permanent magnets are represented by ?lines of flu$?. These lines of flu$ help us to visualize the magnetic field of any magnet even though they only represent an invisible phenomena. The number of lines of flu$ vary from one magnetic field to another. The D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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stronger the magnetic field, the greater the number of lines of flu$ which are drawn to represent the magnetic field. The lines of flu$ are drawn with a direction indicated since we should visualize these lines and the magnetic field they represent as having a distinct movement from a ;+pole to a &+pole as shown in *igure 1. "nother but similar type of magnetic field is produced around an electrical conductor when an electric current is passed through the conductor as shown in *igure )+a. These lines of flu$ define the magnetic field and are in the form of concentric circles around the wire. &ome of you may remember the old ?6eft Hand ule? as shown in *igure )+b. The rule states that if you point the thumb of your left hand in the direction of the current, your fingers will point in the direction of the magnetic field.

Figure 1 - The lines of flux of a magnetic field travel from the N-pole to the S-pole.


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Figure 2 - The flow of electrical current in a conductor sets up concentric lines of magnetic flux around the conductor.

Figure 3 - The magnetic lines around a current carrying conductor leave from the N pole and re-enter at the S-pole. >hen the wire is shaped into a coil as shown in *igure %, all the individual flu$ lines produced by each section of wire join together to form one large magnetic field around the total coil. "s with the permanent magnet, these flu$ lines leave the north of the coil and re+enter the coil at its south pole. The magnetic field of a wire coil is much greater and more localized than the magnetic field around the plain conductor before being formed into a coil. This magnetic field around the coil can be strengthened even more by placing a core of iron or similar metal in the center of the core. The metal core presents less resistance to the lines of flu$ than the air, thereby D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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causing the field strength to increase. This is e$actly how a stator coil is made@ a coil of wire with a steel core.0 The advantage of a magnetic field which is produced by a current carrying coil of wire is that when the current is reversed in direction the poles of the magnetic field will switch positions since the lines of flu$ have changed direction. This phenomenon is illustrated in *igure A. >ithout this magnetic phenomenon e$isting, the "! motor as we know it today would not e$ist.

Figure  - The poles of an electro-magnetic coil change when the direction of current flow changes. Ma0netic Prp$sin 2ithin a Mtr


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Figure ! Magnetic 3ropulsion within a Motor The basic principle of all motors can easily be shown using two electromagnets and a permanent magnet. !urrent is passed through coil no. 1 in such a direction that a north pole is established and through coil no. ) in such a direction that a south pole is established. " permanent magnet with a north and south pole is the moving part of this simple motor. In *igure '+a the north pole of the permanent magnet is opposite the north pole of the electromagnet. &imilarly, the south poles are opposite each other. 6ike magnetic poles repel each other, causing the movable permanent magnet to begin to turn. "fter it turns part way around, the force of attraction between the unlike poles becomes strong enough to keep the permanent magnet rotating. The rotating magnet continues to turn until the unlike poles are lined up. "t this point the rotor would normally stop because of the attraction between the unlike poles. *igure '+b0 If, however, the direction of currents in the electromagnetic coils was suddenly reversed, thereby reversing the polarity of the two coils, then the poles would again be opposites and repel each other. *igure '+c0. The movable permanent magnet would then continue to rotate. If the current direction in the electromagnetic coils was changed every time the magnet turned 1B( degrees or halfway around,then the magnet would continue to rotate. This simple device is a motor in its simplest form. "n actual motor is more comple$ than the simple device shown above, but the principle is the same. AC C$rrent

How the current is reversed in the coil so as to change the coils polarity, you ask. >ell, as you probably know, the difference between 9! and "! is that with 9! the current flows in only one direction while with "! the direction of current flow changes periodically. In the case of common "! that is used throughout most of the

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vary in #uantity. >e can have a ' amp, 1( amp or 1(( amp flow for instance. >ith pure 9!, this means that the current flow is actually ',1(, or 1(( amps on a continuous basis. >e can visualize this on a simple time+current graph by a straight line as shown in *igure :.

Figure " - #isuali$ation of %& 8ut with "! it is different. "s you can well imagine, it would be rather difficult for the current to be flowing at say 1(( amps in a positive direction one moment and then at the ne$t moment be flowing at an e#ual intensity in the negative direction. Instead, as the current is getting ready to change directions, it first tapers off until it reaches zero flow and then gradually builds up in the other direction. &ee *igure C. ;ote that the ma$imum current flow the peaks of the line0 in each direction is more than the specified value 1(( amps in this case0. Therefore, the specified value is given as an average. It is actually called a ?root mean s#uare? value, but don=t worry about remembering this because it is of no importance to us at this time. >hat is important in our study of motors, is to realize that the strength of the magnetic field produced by an "! electro+magnetic coil increases and decreases with the increase and decrease of this alternating current flow. /asic AC Mtr Operatin

"n "! motor has two basic electrical parts4 a ?stator? and a ?rotor? as shown in *igure B. The stator is in the stationary electrical component. It consists of a group of individual electro+magnets arranged in such a way that they form a hollow cylinder, with one pole of each magnet facing toward the center of the group. The term, ?stator? D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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is derived from the word stationary. The stator then is the stationary part of the motor. The rotor is the rotating electrical component. It also consists of a group of electro+ magnets arranged around a cylinder, with the poles facing toward the stator poles.

Figure ' - #isuali$ation of (&. The rotor, obviously, is located inside the stator and is mounted on the motor=s shaft. The term ?rotor? is derived from the word rotating. The rotor then is the rotating part of the motor. The objective of these motor components is to make the rotor rotate which in turn will rotate the motor shaft. This rotation will occur because of the previously discussed magnetic phenomenon that unlike magnetic poles attract each other and like poles repel. If we progressively change the polarity of the stator poles in such a way that their combined magnetic field rotates, then the rotor will follow and rotate with the magnetic field of the stator.


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Figure ) - *asic electrical components of an (& motor. This ?rotating magnetic fields of the stator can be better understood by e$amining *igure D. "s shown, the stator has si$ magnetic poles and the rotor has two poles. "t time 1, stator poles "+1 and !+) are north poles and the opposite poles, "+) and !+1, are south poles. The &+pole of the rotor is attracted by the two ;+poles of the stator and the ;+pole of the rotor is attracted by the two south poles of the stator. "t time ), the polarity of the stator poles is changed so that now !+) and 8+1 and ;+poles and !+1 and 8+) are &+poles. The rotor then is forced to rotate :( degrees to line up with the stator poles as shown. "t time %, 8+1 and "+) are ;. "t time A, "+) and !+1 are ;. "s each change is made, the poles of the rotor are attracted by the opposite poles on the stator. Thus, as the magnetic field of the stator rotates, the rotor is forced to rotate with it.


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Figure + - The rotating magnetic field of an (& motor. /ne way to produce a rotating magnetic field in the stator of an "! motor is to use a three+phase power supply for the stator coils. >hat, you may ask, is three+phase powerE The answer to that #uestion can be better understood if we first e$amine single+phase power. *igure C is the visualization of single+phase power. The associated "! generator is producing just one flow of electrical current whose direction and intensity varies as indicated by the single solid line on the graph. *rom time ( to time %, current is flowing in the conductor in the positive direction. *rom time % to time :, current is flowing in the negative. "t any one time, the current is only flowing in one direction. 8ut some generators produce three separate current flows phases0 all superimposed on the same circuit. This is referred to as three+phase power. "t any one instant, however, the direction and intensity of each separate current flow are not the same as the other phases. This is illustrated in *igure 1(. The three separate phases current flows0 are labeled ", 8 and !. "t time 1, phase " is at zero amps, phase 8 is near its ma$imum amperage and flowing in the positive direction, and phase ! is near to its ma$imum amperage but flowing in the negative direction. "t time ), the amperage of phase " is increasing and flow is positive, the amperage of phase 8 is decreasing and its flow is still negative, and phase ! has dropped to zero amps. " complete cycle from zero to ma$imum in one direction, to zero and to D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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ma$imum in the other direction, and back to zero0 takes one complete revolution of the generator. Therefore, a complete cycle, is said to have %:( electrical degrees. In e$amining *igure 1(, we see that each phase is displaced 1)( degrees from the other two phases. Therefore, we say they are 1)( degrees out of phase.

Figure 1, - The pattern of the separate phases of three-phase power. To produce a rotating magnetic field in the stator of a three+phase "! motor, all that needs to be done is wind the stator coils properly and connect the power supply leads correctly. The connection for a : pole stator is shown in *igure 11. 5ach phase of the three+phase power supply is connected to opposite poles and the associated coils are wound in the same direction. "s you will recall from *igure A, the polarity of the poles of an electro+magnet are determined by the direction of the current flow through the coil. Therefore, if two opposite stator electro+magnets are wound in the same direction, the polarity of the facing poles must be opposite. Therefore, when pole "1 is ;, pole ") is &. >hen pole 81 is ;, 8) is & and so forth.


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Figure 11 - ethod of connecting three-phase power to a six-pole stator.

*igure 1) shows how the rotating magnetic field is produced. "t time1, the current flow in the phase ?"? poles is positive and pole "+1 is ;. The current flow in the phase ?!? poles is negative, making !+) a ;+pole and !+1 is &. There is no current flow in phase ?8?, so these poles are not magnetized. "t time ), the phases have shifted :( degrees, making poles !+) and 8+1 both ; and !+1 and 8+) both &. Thus, as the phases shift their current flow, the resultant ; and & poles move clockwise around the stator, producing a rotating magnetic field. The rotor acts like a bar magnet, being pulled along by the rotating magnetic field.


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Figure 12 - ow three-phase power produces a rotating magnetic field.

Figure 13 - &onstruction of an (& induction motor/s rotor.


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This is no e$ternal power supply. "s you might imagine from the motor=s name, an induction techni#ue is used instead. Induction is another characteristic of magnetism. It is a natural phenomena which occurs when a conductor aluminum bars in the case of a rotor, see *igure 1%0 is moved through an e$isting magnetic field or when a magnetic field is moved past a conductor. In either case, the relative motion of the two causes an electric current to flow in the conductor. This is referred to as ?induced? current flow. In other words, in an induction motor the current flow in the rotor is not caused by any direct connection of the conductors to a voltage source, but rather by the influence of the rotor conductors cutting across the lines of flu$ produced by the stator magnetic fields. The induced current which is produced in the rotor results in a magnetic field around the rotor conductors as shown in *igure 1A. This magnetic field around each rotor conductor will cause each rotor conductor to act like the permanent magnet in the *igure D e$ample. "s the magnetic field of the stator rotates, due to the effect of the three+phase "! power supply, the induced magnetic field of the rotor will be attracted and will follow the rotation. The rotor is connected to the motor shaft, so the shaft will rotate and drive the connection load. That=s how a motor worksF &imple, was it notE


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Figure 1 - ow voltage is induced in the rotor0 resulting in current flow in the rotor conductors.

CHAPTER-3 POER SUPP(* UNIT

/(OC+ DIAGRAM%

CIRCUIT DIAGRAM


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Descriptin

"! power is easily in bulk from through different methods, but generally for many power control circuits and other industrial application 9! power is very much re#uired. Hence "! power necessarily has to be converted into 9! power by means of electronic rectifier, which is simpler, cheaper, and highly efficient compared to rotary converters or 9! generators. The Grecti"ier is a circuit, which converts "! oltage and currents into pulsating 9! voltages and currents. It consists of 9! components and the unwanted ac ripple or harmonic components, which can be removed by using filter circuit. Thus the output obtained will be steady 9! voltage and magnitude of 9! voltage can be varied by varying the magnitude of "! oltage. ectifiers are grouped into two categories depending on the period of conduction. a0 Half >ave ectifier

b0 *ull >ave ectifier.

In this power supply unit we are using *ull+>ave ectifier.

,$-a4e Recti"ier

" Gfull wave rectifier is one which converts "! voltage into a pulsating 9! voltage using both half+cycles of the applied input voltage. It typically uses two diodes, one of which conducts and provides output during one half+cycle i.e., positive2negative0 and other diode conducts during the other half+cycle i.e. negative2positive0. ,iters

It is a circuit, which removes, ripples unwanted ac components0 present in the pulsating dc voltage.


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Re0$atr

It is a circuit which maintains the terminal voltage as constant even if the input voltage varies or load current varying.

*ull wave rectifier rectifies the full cycle in the waveform i.e. it rectifies both the positive and negative cycles in the waveform. >e have already seen the characteristics and 2r5in0 " Ha" a4e Recti"ier . This *ull wave rectifier has an

advantage over the half wave i.e. it has average output higher than that of half wave rectifier. The number of "! components in the output is less than that of the input. The full wave rectifier can be further divided mainly into following types. 1. !enter Tapped *ull >ave ectifier ). *ull >ave 8ridge ectifier Center Tapped ,$ a4e Recti"ier%

!enter tap is the contact made at the middle of the winding of the transformer.

Center Tapped ,$ a4e Recti"ier Circ$it Dia0ram

In the center tapped full wave rectifier two diodes were used. These are connected to the center tapped secondary winding of the transformer. "bove circuit diagram shows the center tapped full wave rectifier. It has two diodes. The positive terminal of two


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diodes is connected to the two ends of the transformer. !enter tap divides the total secondary voltage into e#ual parts. Center Tapped Full Wave Rectifier Working:

The primary winding of the center tap transformer is applied with the "c voltage. Thus the two diodes connected to the secondary of the transformer conducts alternatively. *or the positive half cycle of the input diode 91 is connected to the positive terminal and 9) is connected to the negative terminal. Thus diode 91 is in forward bias and the diode 9) is reverse biased. /nly diode 91 starts conducting and thus current flows from diode and it appears across the load 6. &o positive cycle of the input is appeared at the load. 9uring the negative half cycle the diode 9) is applied with the positive cycle. 9) starts conducting as it is in forward bias. The diode 91 is in reverse bias and this does not conduct. Thus current flows from diode 9) and hence negative cycle is also rectified, it appears at the load resistor 6. 8y comparing the current flow through load resistance in the positive and negative half cycles, it can be concluded that the direction of the current flow is same. Thus the fre#uency of rectified output voltage is two times the input fre#uency. The output that is rectified is not pure, it consists of a dc component and a lot of ac components of very low amplitudes. Peak Inverse Voltage (PIV) of Centre Tap Full Wave Rectifier:

3I is defined as the ma$imum possible voltage across a diode during its reverse bias. 9uring the first half that is positive half of the input, the diode 91 is forward bias and thus conducts providing no resistance at all. Thus, the total voltage s appears in the upper+half of the ac supply, provided to the load resistance . &imilarly, in the case of diode 9) for the lower half of the transformer total secondary voltage developed appears at the load. The amount of voltage that drops across the two diodes in reverse bias is given as 3I of 9)  m J m  )m D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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3I of 91  )m m is the voltage developed across upper and lower halves. Pea5 C$rrent%

The peak current is the instantaneous value of the voltage applied to the rectifier. It can be written as s  sm &inwt 6et us assume that the diode has a forward resistance of * ohms and a reverse resistance is e#ual to infinity, thus current flowing through the load resistance 6 is given as Im  sm 2  , J 60 O$tp$t C$rrent%

&ince the current is same through the load resistance 6 in the two halves of the ac cycle, magnitude of dc current Idc, which is e#ual to the average value of ac current, can be obtained by integrating the current i1 between ( and pi or current i) between pi and )pi.


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Trans"rmer Utii6atin ,actr%

This can be calculated by considering primary and secondary windings separately. Its value is (.:D%.This can be used to determine transformer secondary rating.


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INPUT AND OUTPUT A)E,ORM O, ,U(( A)E RECTI,IER


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CHAPTER-7 COMPONENT DETAI(S

6.1 12V DC GEARED MOTOR:

Descriptin%

The 1) 9! -eared Motor can be used in variety of robotics applications and is available with wide range of 1( 3M. Speci"icatin%

8

6ength4 B(mm

8

Tor#ue4 1.' kg.cm

8

&haft 9iameter4 :mm

8

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79& RESISTOR


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" resistr is a two+terminal electronic component having a resistance 0 that produces a voltage 0 across its terminals that is proportional to the electric current I0 flowing through it in accordance with /hm=s law4 V : IR

esistors are elements of electrical networks and electronic circuits and are ubi#uitous in most electronic e#uipment. 3ractical resistors can be made of various compounds and films, as well as resistance wire wire made of a high+resistivity alloy, such as nickel+chrome0. The primary characteristics of a resistor are the resistance, the tolerance, the ma$imum working voltage and the power rating. /ther characteristics include temperature coefficient, noise, and inductance. 6ess well+known is critical resistance, the value below which power dissipation limits the ma$imum permitted current, and above which the limit is applied voltage. !ritical resistance is determined by the design, materials and dimensions of the resistor. esistors can be integrated into hybrid and printed circuits, as well as integrated circuits. &ize, and position of leads or terminals0, are relevant to e#uipment designers@ resistors must be physically large enough not to overheat when dissipating their power.

RESISTOR )A(UE IDENTI,ICATION% ;Cr cdin0 methd<


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The color code chart is applicable to most of the common four band and five band resistors. *ive band resistors are usually precision resistors with tolerances of 1K and )K. Most of the four band resistors have tolerances of 'K, 1(K and )(K.


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The color codes of a resistor are read from left to right, with the tolerance band oriented to the right side. Match the color of the first band to its associated number under the digit column in the color chart. This is the first digit of the resistance value. Match the second band to its associated color under the digit column in the color chart to get the second digit of the resistance value. Match the color band preceding the tolerance band last band0 to its associated number under the multiplier column on the chart. This number is the multiplier for the #uantity previously indicated by the first two digits four band resistor0 or the first three digits five band resistor0 and is used to determine the total marked value of the resistor in ohms. To determine the resistor=s tolerance or possible variation in resistance from that indicated by the color bands, match the color of the last band to its associated number under the tolerance column. Multiply the total resistance value by this percentage.

79' CAPACITOR

" capacitr formerly known as cndenser0 is a passive electronic component consisting of a pair of conductors separated by a dielectric insulator0. >hen there is a potential difference voltage0 across the conductors, a static electric field develops in the dielectric that stores energy and produces a mechanical force between the


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conductors. "n ideal capacitor is characterized by a single constant value, capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. !apacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass, in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to particular fre#uencies and for many other purposes. The effect is greatest when there is a narrow separation between large areas of conductor@ hence capacitor conductors are often called ?plates?, referring to an early means of construction. In practice the dielectric between the plates passes a small amount of leakage current and also has an electric field strength limit, resulting in a breakdown voltage, while the conductors and leads introduce an undesired inductance and resistance.

79. DIODE

In electronics, a dide is a two+terminal electronic component that conducts electric current in only one direction. The term usually refers to a semicnd$ctr dide, the most common type today. This is a crystalline piece of semiconductor

material connected to two electrical terminals. L1 " 4ac$$m t$=e dide now little used e$cept in some high+power technologies0 is a vacuum tube with two electrodes4 a plate and a cathode. The most common function of a diode is to allow an electric current to pass in one direction called the diode=s forward direction0 while blocking current in the opposite direction the reverse direction0. Thus, the diode can be thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to e$tract


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modulation from radio signals in radio receivers. However, diodes can have more complicated behavior than this simple on+off action. This is due to their comple$ non+ linear electrical characteristics, which can be tailored by varying the construction of their 3+; junction. These are e$ploited in special purpose diodes that perform many different functions. *or e$ample, specialized diodes are used to regulate voltage Nener diodes0, to electronically tune radio and T receivers varactor diodes0, to generate radio fre#uency oscillations tunnel diodes0, and to produce light light emitting diodes0. Tunnel diodes e$hibit negative resistance, which makes them useful in some types of circuits. 9iodes were the first semiconductor electronic devices. The discovery of crystals= rectifying abilities was made by -erman physicist *erdinand 8raun in 1BCA. The first semiconductor diodes, called cat=s whisker diodes, developed around 1D(:, were made of mineral crystals such as galena. Today most diodes are made of silicon, but other semiconductors such as germanium are sometimes used.

DIODE 1N.>>1?@ ,EATURES

O -lass passivated O High ma$imum operating temperature O 6ow leakage current O 5$cellent stability O "vailable in ammo+pack. DESCRIPTION

ugged glass package, using a high temperature alloyed construction. This package is hermetically sealed and fatigue free as coefficients of e$pansion of all used parts is matched.


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793 TRANSISTOR

" transistr is a semiconductor device used to amplify and switch electronic signals. It is made of a solid piece of semiconductor material, with at least three terminals for connection to an e$ternal circuit. " voltage or current applied to one pair of the transistor=s terminals changes the current flowing through another pair of terminals. 8ecause the controlled output0 power can be much more than the controlling input0 power, the transistor provides amplification of a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits. The transistor is the fundamental building block of modern electronic devices, and is ubi#uitous in modern electronic systems. *ollowing its release in the early 1D'(s the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things. /C3.@?3. ;NPN TRANSISTOR<


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S2itchin0 and Appicatins

P High oltage4 8!'A:, !5/:' P 6ow ;oise4 8!'AD, 8!''( P !omplement to 8!'': ... 8!':(


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797 TRANS,ORMER

" trans"rmer is a static device that transfers electrical energy from one circuit to another through inductively coupled conductorsQthe transformer=s coils. " varying current in the first or primary winding creates a varying magnetic flu$ in the transformer=s core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force 5M*0 or ?voltage? in the secondary winding. This effect is called mutual induction. If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding # s0 is in proportion to the primary voltage # p0, and is given by the ratio of the number of turns in the secondary  N s0 to the number of turns in the primary  N p0 as follows4

/ASIC PRINCIP(ES

The transformer is based on two principles4 first, that an electric current can produce a magnetic field electromagnetism0, and, second that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil electromagnetic induction0. !hanging the current in the primary coil changes the magnetic flu$ that is developed. The changing magnetic flu$ induces a voltage in the secondary coil. D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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An idea trans"rmer

"n ideal transformer is shown in the adjacent figure. !urrent passing through the primary coil creates a magnetic field. The primary and secondary coils are wrapped around a core of very high magnetic permeability, such as iron, so that most of the magnetic flu$ passes through both the primary and secondary coils. Ind$ctin a2

The voltage induced across the secondary coil may be calculated from *araday=s law of induction, which states that4

where # s is the instantaneous voltage, N s is the number of turns in the secondary coil and R is the magnetic flu$ through one turn of the coil. If the turns of the coil are oriented perpendicular to the magnetic field lines, the flu$ is the product of the magnetic flu$ density * and the area ( through which it cuts. The area is constant, being e#ual to the cross+sectional area of the transformer core, whereas the magnetic field varies with time according to the e$citation of the primary. &ince the same magnetic flu$ passes through both the primary and secondary coils in an ideal transformer ,L)D the instantaneous voltage across the primary winding e#uals


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Taking the ratio of the two e#uations for # s and # p gives the basic e#uation for stepping up or stepping down the voltage

N p2 N s is known as the turns ratio, and is the primary functional characteristic of any transformer. In the case of step+up transformers, this may sometimes be stated as the reciprocal, N s2 N p. Turns ratio is commonly e$pressed as an irreducible fraction or ratio4 for e$ample, a transformer with primary and secondary windings of, respectively, 1(( and 1'( turns is said to have a turnSs ratio of )4% rather than (.::C or 1((41'(. Detaied peratin

The simplified description above neglects several practical factors, in particular, the primary current re#uired to establish a magnetic field in the core, and the contribution to the field due to current in the secondary circuit. Models of an ideal transformer typically assume a core of negligible reluctance with two windings of zero resistance. L%) >hen a voltage is applied to the primary winding, a small current flows, driving flu$ around the magnetic circuit of the core.L%) The current re#uired to create the flu$ is termed the magneti$ing current . &ince the ideal core has been assumed to have near+zero reluctance, the magnetizing current is negligible, although still re#uired, to create the magnetic field. The changing magnetic field induces an electromotive force 5M*0 across each winding. &ince the ideal windings have no impedance, they have no associated voltage drop, and so the voltages 3 and & measured at the terminals of the transformer, are e#ual to the corresponding 5M*s. The primary 5M*, acting as it does in opposition to the primary voltage, is sometimes termed the ?back 5M*?.L%A This is in accordance with 6enz=s law, which states that induction of 5M* always opposes development of any such change in magnetic field.


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Practical considerations: Leakage flux

The ideal transformer model assumes that all flu$ generated by the primary winding links all the turns of every winding, including itself. In practice, some flu$ traverses paths that take it outside the windings. L%' &uch flu$ is termed leaage flux, and results in leakage inductance in series with the mutually coupled transformer windings. 6eakage results in energy being alternately stored in and discharged from the magnetic fields with each cycle of the power supply. It is not directly a power loss see ?&tray losses? below0, but results in inferior voltage regulation, causing the secondary voltage to not be directly proportional to the primary voltage, particularly under heavy load. Transformers are therefore normally designed to have very low leakage inductance. ;evertheless, it is impossible to eliminate all leakage flu$ because it plays an essential part in the operation of the transformer. The combined effect of the leakage flu$ and the electric field around the windings is what transfers energy from the primary to the secondary. In some applications increased leakage is desired, and long magnetic paths, air gaps, or magnetic bypass shunts may deliberately be introduced in a transformer design to limit the short+circuit current it will supply. 6eaky transformers may be used to supply loads that e$hibit negative resistance, such as electric arcs, mercury vapor lamps, and neon signs or for safely handling loads that become periodically short+ circuited such as electric arc welders.


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"ir gaps are also used to keep a transformer from saturating, especially audio+ fre#uency transformers in circuits that have a direct current component flowing through the windings. 6eakage inductance is also helpful when transformers are operated in parallel. It can be shown that if the ?per+unit? inductance of two transformers is the same a typical value is 'K0, they will automatically split power ?correctly? e.g. '(( k" unit in parallel with 1,((( k" unit, the larger one will carry twice the current0. E""ect " "re#$enc!

The time+derivative term in *araday=s 6aw shows that the flu$ in the core is the integral with respect to time of the applied voltage. Hypothetically an ideal transformer would work with direct+current e$citation, with the core flu$ increasing linearly with time. In practice, the flu$ rises to the point where magnetic saturation of the core occurs, causing a large increase in the magnetizing current and overheating the transformer. "ll practical transformers must therefore operate with alternating or pulsed direct0 current. The 5M* of a transformer at a given flu$ density increases with fre#uency. 8y operating at higher fre#uencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve the same impedance. However, properties such as core loss and conductor skin effect also increase with fre#uency. "ircraft and military e#uipment employ A(( Hz power supplies which reduce core and winding weight. !onversely, fre#uencies used for some railway electrification systems were much lower e.g. 1:.C Hz and )' Hz0 than normal utility fre#uencies '(  :( Hz0 for historical reasons concerned mainly with the limitations of early electric traction motors. "s such, the transformers used to step down the high over+head line voltages e.g. 1' k0 were much heavier for the same power rating than those designed only for the higher fre#uencies.


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/peration of a transformer at its designed voltage but at a higher fre#uency than intended will lead to reduced magnetizing current. "t a lower fre#uency, the magnetizing current will increase. /peration of a transformer at other than its design fre#uency may re#uire assessment of voltages, losses, and cooling to establish if safe operation is practical. *or e$ample, transformers may need to be e#uipped with ?volts per hertz? over+e$citation relays to protect the transformer from overvoltage at higher than rated fre#uency. /ne e$ample of state+of+the+art design is transformers used for electric multiple unit high speed trains, particularly those re#uired to operate across the borders of countries using different electrical standards. The position of such transformers is restricted to being hung below the passenger compartment. They have to function at different fre#uencies down to 1:.C Hz0 and voltages up to )' k0 whilst handling the enhanced power re#uirements needed for operating the trains at high speed. Unowledge of natural fre#uencies of transformer windings is necessary for the determination of winding transient response and switching surge voltages. Ener0! sses

"n ideal transformer would have no energy losses, and would be 1((K efficient. In practical transformers, energy is dissipated in the windings, core, and surrounding structures. 6arger transformers are generally more efficient, and those rated for electricity distribution usually perform better than DBK. 5$perimental transformers using superconducting windings achieve efficiencies of DD.B'K. The increase in efficiency can save considerable energy, and hence money, in a large heavily loaded transformer@ the trade+off is in the additional initial and running cost of the superconducting design. 6osses in transformers e$cluding associated circuitry0 vary with load current, and may be e$pressed as ?no+load? or ?full+load? loss. >inding resistance dominates load losses, whereas hysteresis and eddy currents losses contribute to over DDK of the no+load loss. The no+load loss can be significant, so that even an idle transformer constitutes a drain on the electrical supply and a running cost. 9esigning transformers D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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for lower loss re#uires a larger core, good+#uality silicon steel, or even amorphous steel for the core and thicker wire, increasing initial cost so that there is a trade+off between initial costs and running cost also see energy efficient transformer0. Transformer losses are divided into losses in the windings, termed copper loss, and those in the magnetic circuit, termed iron loss. 6osses in the transformer arise from4 indin0 resistance

!urrent flowing through the windings causes resistive heating of the conductors. "t higher fre#uencies, skin effect and pro$imity effect create additional winding resistance and losses. H!steresis sses

5ach time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. *or a given core material, the loss is proportional to the fre#uency, and is a function of the peak flu$ density to which it is subjected. Edd! c$rrents

*erromagnetic materials are also good conductors and a core made from such a material also constitutes a single short+circuited turn throughout its entire length. 5ddy currents therefore circulate within the core in a plane normal to the flu$, and are responsible for resistive heating of the core material. The eddy current loss is a comple$ function of the s#uare of supply fre#uency and inverse s#uare of the material thickness.LAA 5ddy current losses can be reduced by making the core of a stack of plates electrically insulated from each other, rather than a solid block@ all transformers operating at low fre#uencies use laminated or similar cores.

Ma0netstrictin D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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Magnetic flu$ in a ferromagnetic material, such as the core, causes it to physically e$pand and contract slightly with each cycle of the magnetic field, an effect known as magnetostriction. This produces the buzzing sound commonly associated with transformers that can cause losses due to frictional heating. This buzzing is particularly familiar from low+fre#uency '( Hz or :( Hz0 mains hum, and high+fre#uency 1',C%A Hz ;T&!0 or 1',:)' Hz 3"600 !T noise. Mechanica sses

In addition to magnetostriction, the alternating magnetic field causes fluctuating forces between the primary and secondary windings. These incite vibrations within nearby metalwork, adding to the buzzing noise and consuming a small amount of power.LA' Stra! sses

6eakage inductance is by itself largely lossless, since energy supplied to its magnetic fields is returned to the supply with the ne$t half+cycle. However, any leakage flu$ that intercepts nearby conductive materials such as the transformer=s support structure will give rise to eddy currents and be converted to heat. There are also radiative losses due to the oscillating magnetic field but these are usually small. !uivalent circuit

The physical limitations of the practical transformer may be brought together as an e#uivalent circuit model shown below0 built around an ideal lossless transformer.LAC 3ower loss in the windings is current+dependent and is represented as in+series resistances  p and  s. *lu$ leakage results in a fraction of the applied voltage dropped without contributing to the mutual coupling, and thus can be modeled as reactances of each leakage inductance V p and Vs in series with the perfectly coupled region.


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Iron losses are caused mostly by hysteresis and eddy current effects in the core, and are proportional to the s#uare of the core flu$ for operation at a given fre#uency. &ince the core flu$ is proportional to the applied voltage, the iron loss can be represented by a resistance  ! in parallel with the ideal transformer. " core with finite permeability re#uires a magnetizing current Im to maintain the mutual flu$ in the core. The magnetizing current is in phase with the flu$. &aturation effects cause the relationship between the two to be non+linear, but for simplicity this effect tends to be ignored in most circuit e#uivalents. >ith a sinusoidal supply, the core flu$ lags the induced 5M* by D(W and this effect can be modeled as a magnetizing reactance reactance of an effective inductance0  m in parallel with the core loss component. c and  m are sometimes together termed the magneti$ing 4ranch of the model. If the secondary winding is made open+circuit, the current 5 ( taken by the magnetizing branch represents the transformer=s no+load current. The secondary impedance s and  s is fre#uently moved or ?referred?0 to the primary side after multiplying the components by the impedance scaling factor  N p2 N s0).

The resulting model is sometimes termed the ?e$act e#uivalent circuit?, though it retains a number of appro$imations, such as an assumption of linearity. "nalysis may be simplified by moving the magnetizing branch to the left of the primary impedance, an implicit assumption that the magnetizing current is low, and then summing primary and referred secondary impedances, resulting in so+called D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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e#uivalent impedance. The parameters of e#uivalent circuit of a transformer can be calculated from the results of two transformer tests4 open+circuit test and short+circuit test. "pplications

" major application of transformers is to increase voltage before transmitting electrical energy over long distances through wires. >ires have resistance and so dissipate electrical energy at a rate proportional to the s#uare of the current through the wire. 8y transforming electrical power to a high+voltage and therefore low+ current0 form for transmission and back again afterward, transformers enable economical transmission of power over long distances. !onse#uently, transformers have shaped the electricity supply industry, permitting generation to be located remotely from points of demand. "ll but a tiny fraction of the world=s electrical power has passed through a series of transformers by the time it reaches the consumer. Transformers are also used e$tensively in electronic products to step down the supply voltage to a level suitable for the low voltage circuits they contain. The transformer also electrically isolates the end user from contact with the supply voltage. &ignal and audio transformers are used to couple stages of amplifiers and to match devices such as microphones and record players to the input of amplifiers. "udio transformers allowed telephone circuits to carry on a two+way conversation over a single pair of wires. " balun transformer converts a signal that is referenced to ground to a signal that has balanced voltages to ground, such as between e$ternal cables and internal circuits. The principle of open+circuit unloaded0 transformer is widely used for characterization of soft magnetic materials, for e$ample in the internationally standardized 5pstein frame method.

CHAPTER-@ DIMENSIONB COST ESTIMATION AND CONC(USION D.D.C.S.M. POLYTECHNIC, MECHANICAL ENGG.

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@91 DIMENSION%

@9& COST ESTIMATION


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Motorized Ramming Machine

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