Vibration

Vibration:

Types of Vibrations

There are three types of vibrations:

1. Free or normal vibrations

2. Damped vibrations

3. Forced vibrations

When a body which is held in position by elastic constraints is displaced from its equilibrium position by the application of an external force and then released, the body commences to vibrate assuming that there are no external or internal resistances to prevent the motion and the material of constraints is perfectly elastic, the body will continue vibrating indefinitely. In that case at the extreme positions of oscillations; the energy imparted to the body by the external force is entirely stored in the elastic constraint as internal or elastic or strain energy. When the body falls back to its original equilibrium position, whole strain energy is converted into the kinetic energy which further takes the body to the other extreme position, when again the energy is stored in the elastic constraint; at the expense of which the body again moves towards its initial equilibrium position; and this cycle continues repeating indefinitely. This is how the body oscillates between two extreme positions. A vibration of this kind in which, after initial displacement, no external forces act and the motion is maintained by the internal elastic forces are termed as natural vibrations.

Free Vibrations

Consider a bar of length l, diameter d, the upper end of which is held by the elastic constraints and at the lower end, it carries a heavy disc of mass m.

The system may have one of the three simple modes of free vibrations given below:

a. Longitudinal vibrations

b. Transverse vibrations

c. Torsional vibrations

a. Longitudinal Vibrations

When the particles of the shaft or disc move parallel to the axis of the shaft as shown in fig. Than the vibrations are known as longitudinal vibrations.

b. Transverse Vibrations

When the particles of the shaft or disc move approximately perpendicular to the axis of the shaft shown in fig. Then the vibrations are known as transverse vibrations.

c. Torsional Vibrations

When the particles of the shaft or disc move in a circle about the axis of the shaft, thenthe vibrations are known as torsional vibrations. Before studying frequencies of general vibrations we must understand degree of freedom.

Natural Frequency of Free Longitudinal Vibrations

The natural frequency of the free longitudinal vibrations may be determined by the following three methods.

1. Equilibrium Method

2. Energy Method

3. Rayleigh’s Method

Damping Factor or Damping Ratio

The ratio of damping coefficient C to the critical damping coefficient Cc is known as damping factor or damping ratio. Mathematically,

Damping factor = C/ Cc = C/2mwn (Cc =2mwn)

The damping factor is the measure of the relative amount of damping in the existing system with that necessary for the critical damped systems.

TRANSVERSE & TORSIONAL VIBRATIONS

Generally when the particles of the shaft or disc move in a circle about the axis of the shaft as already discussed in previous chapter, then the vibrations are known as torsional vibrations. In this case, the shaft is twisted and alternately and the torsional shear stresses are induced in the shaft.

When the particles of the shaft or disc move in a circle about the axis of the shaft as shown in fig as already explained in previous chapter , then the vibrations are known as known as transverse vibrations. Natural Frequency of Free Transverse Vibrations Due to Point Load Acting Over a Simple Supported Shaft

Natural Frequency of Free Transverse Vibrations of a Shaft Fixed at Both Ends Carrying a Uniformly Distributed Load

Natural Frequency of Free Transverse Vibrations for a Shaft Subjected to a Number of Point Loads Critical or Whirling Speed of a Shaft In general, a rotating shaft carries different mountings and accessories in the form of gears, pulleys, etc. When the gears or pulleys are out on the shaft, the centre of gravity of the pulley of gear does not coincide with the centre of the bearings or with the axis of the shaft, when the shaft is stationary, This means that the centre of gravity of the pulley of gear is at a certain distance from the axis of rotation and due to this, the shaft is subjected to centrifugal force. This force will bend the shaft, which will further increase the distance of centre of gravity of the pulley or gear from the axis of rotation. This correspondingly increases the value of centrifugal force, which further increases the distance of centre of gravity from the axis rotation. This effect is cumulative and ultimately the shaft fails. The bending of shaft not only depends upon the value of eccentricity (distance between centre of gravity of the pulley and the axis of rotation)But also depends upon the speed at which the shaft rotates. The speed, at which the shaft runs so that the additional deflection of the shaft from the axis of rotation becomes infinite, is known as critical or whirling speed.

Balancing

Balancing:

Balancing of Rotating Masses

Balancing A Single Rotating Masses

If a mass of M kg is fastened to a shaft rotating at w rad/s at radius r meter, the centrifugal force, producing out of balance effect acting radially outwards on the shaft will be equal Mw2rNewton. This out of balance in any one of the following two ways:

a. By introducing single revolving mass in the same transverse. Introduce a second mass B kg, called the balance mass, diametrically opposite to M at radius R rotating with sameangular speed of w rad/s fig

For complete balance, the centrifugal force of the two masses must be equal an opposite in the plane of rotation.

Mw2r = Bw2R

Mr = BR

Or hence for such balance the product of mass and its radius must be equal to the product of balance mass and its radius. The product BR or Mr is very often called the mass moment.

b. By introducing two masses one in each in two parallel transverse planes.

Sometimes it is not possible to introduce balance mass in the same transverse plane in which disturbing mass M is placed .in that case two masses can be placed one each in two parallel transverse planes to affect a complete balance. it may be remembered that one revolving mass in one plane cannot be balanced by another mass revolving in another parallel plane, as, no doubt balancing mass can be adjusted such that centrifugal forces may be equal and opposite indirection but at the same time will give rise to a couple which will remain unbalanced.

So let M be the distributing mass and B1, B2 be the balance masses placed at radius of r, b1 and b2 respectively from the axis of rotating , let the distances of planes of revolution ofB1 and B2 from that of M be a and c respectively and between B1 and B2d.

Balancing of Several Coplanar Rotating Masses

If several masses are connected to s shaft at different radii in one plane perpendicular to the shaft and the shaft is made to rotate, each mass will set up out of balance centrifugal force on the shaft. In such a case complete balance can be obtained by placing only one balance mass in the same plane whose magnitude and relative angular position can be determined by means of a force diagram. Since all the masses are connected to the shaft, all will have the same angular velocity w, we need not calculate the actual magnitude of centrifugal force of any, but deal only with mass moments.

If the three masses (M1, M2 and M3 are fastened to shaft at radiir1, r2 and r3 resp.

In order to determine the magnitude of balance mass B to be placed at radius b we proceed as follows.

1. Find out mass moment of each weight i.e. M1r1, M2r2 etc.

2. Draw vector diagram for these mass moments at a suitable scale. Commencing at p draw pq to represent M1r1 from q to draw qr to represent M 2r2. and from r draw rs to represent M3r3

3. The closing side sp (from s to p and not from p to s represents the magnitude and direction of balancing mass moment Bb.

4. Measure sp on the scale considered and divided by b, the quotient will be themagnitude of balance mass B.

Balancing of Several Masses in Different Parallel Planes

The technique of tackling this problem is to transfer the centrifugal force acting in each plane to a single parallel plane which is usually termed as reference plane and thereafter the procedure for balancing is almost the same as for different forces acting in the same plane.

Balancing of Reciprocating Masses

Acceleration and force of reciprocating parts. To find acceleration of reciprocating parts such as crosshead or piston, consider asimple crank and connecting rod arrangement Inwhich P is the piston or crosshead whose acceleration is to be determined.

Let

r = length of crank ;

L = length of connecting rod;

x = movement of piston or cross head at any instant from its outermost position when revolves θ radian from its inner dead center position.

CAM

 

CAM

Cams come under higher pair mechanisms. As we already know that in higher pair the contact between the two elements is either point or line contact, instead of area in the case of lower pairs.

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In CAMs, the driving member is called the cam and the driven member is referred to as the follower. CAM is used to impart desired motion to the follower by direct contact. Generally the CAM is a rotating or reciprocating element, where as the follower may de rotating, reciprocating or oscillating element. Using CAMs we can generate complex, coordinate movements that are very difficult with other mechanisms. And also CAM mechanisms are relatively compact and easy it design. Cams are widely used in automatic machines, internal combustion engines, machine tools, printing control mechanisms and so on. Along with cam and follower one frame also will be there with will supports the cam and guides the follower.

A follower can be classified in three ways

  1. According to the motion of the follower.
  2. According to the nature of contact.
  3. According to the path of motion of the follower

According to the motion of the follower

1. Reciprocating or Translating follower

: When the follower reciprocates in guides as the can rotates uniformly, it is known as reciprocating or translating follower.

2. Oscillating or Rotating follower

: When the uniform rotary motion of the cam is converted into predetermined oscillatory motion of the follower, it is called oscillating or rotating follower

According to the nature of contact:

1. The Knife-Edge follower

: When contacting end of the follower has a sharp knife edge, it is called a knife edge follower. This cam follower mechanism is rarely used because of excessive wear due to small area of contact. In this follower a considerable thrust exists between the follower and guide.

2. The Flat-Face follower

: When contacting end of the follower is perfectly flat faced, it is called a flat faced follower. The thrust at the bearing exerted is less as compared to other followers. The only side thrust is due to friction between the contact surfaces of the follower and the cam. The thrust can be further reduced by properly offsetting the follower from the axis of rotation of cam so that when the cam rotates, the follower also rotates about its axis. These are commonly used in automobiles.

3. The Roller follower

: When contacting end of the follower is a roller, it is called a roller follower. Wear rate is greatly reduced because of rolling motion between contacting surfaces. In roller followers also there is side thrust present between follower and the guide. Roller followers are commonly used where more space is available such as large stationary gas or oil engines and aircraft engines.

4. The Spherical-Faced follower

: When contacting end of the follower is of spherical shape, it is called a spherical faced follower. In flat faced follower�s high surface stress are produced. To minimize these stresses the follower is machined to spherical shape.

According to the path of motion of the follower:

1. Radial follower

: When the motion of the follower is along an axis passing through the centre of the cam, it is known as radial follower.

2. Off-set follower

: When the motion of the follower is along an axis away from the axis of the cam centre, it is called off-set follower.

A Cam can be classified in two ways:

1. Radial or Disc cam

: In radial cams, the follower reciprocates or oscillates in a direction perpendicular to the cam axis.

2. Cylindrical cam

: In cylindrical cams, the follower reciprocates or oscillates in a direction parallel to the cam axis. The follower rides in a groove at its cylindrical surface.

CAM NOMENCLATURE

The various terms we will very frequently use to describe the geometry of a radial cam are defined as fallows.

1. Base Circle

: It is the smallest circle, keeping the center at the camcenter, drawn tangential to cam profile. The base circle decides the overall size of the cam and thus is fundamental feature.

2. Trace Point

: It is a point on the follower, and it is used to generate the pitch curve. Its motion describing the movement of the follower. For a knife-edge follower, the trace point is at knife-edge. For a roller follower the trace point is at the roller center, and for a flat-face follower, it is a t the point of contact between the follower and the cam surface when the contact is along the base circle of the cam. It should be note that the trace point is not necessarily the point of contact for all other positions of the cam

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The various terms we will very frequently use to describe the geometry of a radial cam are defined as fallows.

3. Pitch Curve

: It is the curve drawn by the trace point assuming that the cam is fixed, and the trace point of the follower rotates around the cam, i.e. if we hold the cam fixed and rotate the follower in a direction opposite to that of the cam, then the curve generated by the locus of the trace point is called pitch curve.
For a knife-edge follower, the pitch curve and the cam profile are same where as for a roller follower they are separated by the radius of the roller.

4. Pressure Angle

: It is the measure of steepness of the cam profile. The angle between the direction of the follower movement and the normal to the pitch curve at any point is called pressure angle. Pressure angle varies from maximum to minimum during complete rotation. Higher the pressure angle higher is side thrust and higher the chances of jamming the translating follower in its guide ways. The pressure angle should be as small as possible within the limits of design. The pressure angle should be less than 450 for low speed cam mechanisms with oscillating followers, whereas it should not exceed 300 in case of cams with translating followers. The pressure angle can be reduced by increasing the cam size or by adjusting the offset.

5. Pitch Point

: The point corresponds to the point of maximum pressure angle is called pitch point, and a circle drawn with its centre at the cam centre, to pass through the pitch point, is known as the pitch circle.

6. Prime Circle

: The prime circle is the smallest circle that can be drawn so as to be tangential to the pitch curve, with its centre at the cam centre. For a roller follower, the radius of the prime circle will be equal to the radius of the base circle plus that of the roller where as for knife-edge follower the prime circle will coincides with the base circle.

DESCRIPTION OF THE FOLLOWER MOTION

The cam is assumed to rotate at a constant speed and the follower rotates over it. A complete revolution of cam is described by displacement diagram, in which follower displacement i.e. the movement of the trace point, is along y axis and is plotted against the cam rotation �


. The maximum follower displacement is referred to as the lift L of the follower. The inflexion points on the displacement diagram i.e., the points corresponding to the maximum and minimum velocities of the follower correspond to the pitch points. In general the displacement diagram consists of four parts namely.

1. Rise

: The movement of the follower away from the centre of the cam. The follower rises upwards in this motion.

2. Dwell

: In this phase there is no movement of the follower. In this dwell, the distance between the centre of the cam and the contact point is maximum.

3. Return

: The movement of the follower towards the cam centre.

4. Dwell

: The movement of the follower is not present in this phase. In this dwell, the distance between the centre of the cam and the contact point is minimum.

Construction of Displacement Diagrams

Though the follower can be made to have any type of desired motion, we are going to discus the construction of the displacement diagrams for the basic follower movements as mentioned below.

  1. Uniform motion and its modifications.
  2. Simple harmonic motion.
  3. Uniform acceleration motion i.e. parabolic motion.
  4. Cycloidal motion.

In uniform motion the velocity of the followers is constant. As the displacement is from y = 0 to y = L then the cam rotates from θ = 0 to θ = θri, and thus the straight line joining the two points (θ = 0, y = 0) and (θ = θri, y = L) represents the displacement diagram for uniform motion.

Uniform motion and its modifications

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As there is an instantaneous change from zero velocity at the beginning of the rise and a change to zero velocity at the end of the rise, the accelerations at this instance attain a very high value. To avoid this, the straight line of the displacement diagram is connected tangentially to the dwell at both ends of the rise by means of smooth curves of any convenient radius and the bulk of the displacements take place at uniform velocity, whish is represented as straight line as shown in the diagram. So, most part of the time the velocity of the follower is uniform.

  1. Simple harmonic motion.

The displacement diagram for simple harmonic motion can be obtained as shown in figure.5. The line representing angle �


ri is divided into a convenient number of equal lengths. A semicircle of diameter L is drawn as shown and divided into same number of circular arcs of equal length. Horizontal lines are drawn from the points so obtained on the semicircle, to meet the corresponding vertical lines through the points on the length �


ri. For SHM we always have finite velocity, acceleration, jerk, and higher order derivatives of displacements.

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Uniform Acceleration motion

In such cam and followers, there is acceleration in the first half of the follower motion whereas it is deceleration during the later half. With dwell at the beginning and at the end of the rise, when lift of the follower has to take place in a given time, it is easy to show that the maximum acceleration will be the least if the first half of the rise takes place at a constant acceleration and the remaining displacement is at a constant deceleration of same magnitude. For this reason the parabolic motion is very suitable for high speed cams as it minimizes inertia force.
While locating the vertical divisions in the displacement diagram, the fact used is that at constant acceleration the displacement is proportional to the square of the time i.e. it is proportional to the square of the cam rotation as the cam rotates at constant speed. The displacement diagram for such cam and followers is shown in figure 6.(a). This is also applicable for deceleration.

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Modified Uniform Acceleration motion

For cam operating valves of internal combustion engines, the modified uniform acceleration motion is used for the follower. It is desired that the valves should open and close quickly, at the same time maintain the aforementioned advantage of parabolic motion. In modified parabolic motion, the acceleration f1 during the first part of the rise is more than the deceleration f2 during the rest of the rise as shown in fig.6(b).

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Let
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Then it is easy to prove that,
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Where,
clip_image016= angle of cam rotation when the acceleration is f1,
     K θa = angle of cam rotation when the deceleration f2.
The lift L is given by,
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Where
     L1 = rise with acceleration clip_image018, and
     K L1= rise with deceleration f2.

.

Cycloidal Motion

Cycloidal motion is obtained by rolling a circle of radius L/(2п) on the ordinate of the displacement diagram. A point P rolling on the ordinate describes a cycloid. A circle of radius L/(2п) is drawn with centre at the end A of the displacement diagram. This circle is divided into equal number of divisions as the abscissa of the diagram representing the cam rotation θri. The projections of the on the circumference are taken on the vertical diameter, represented by 1’, 2’,…6’. The displacement diagram is obtained from the intersection of the vertical lines through the points on the abscissa and the corresponding lines parallel to OA. The following figure will show the displacement diagram for Cycloidal motion with construction details.

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Gears Trains

 

Gears Trains

A gear train is two or more gear working together by meshing their teeth and turning each other in a system to generate power and speed. It reduces speed and increases torque. To create large gear ratio, gears are connected together to form gear trains. They often consist of multiple gears in the train.The most common of the gear train is the gear pair connecting parallel shafts. The teeth of this type can be spur, helical or herringbone. The angular velocity is simply the reverse of the tooth ratio.Any combination of gear wheels employed to transmit motion from one shaft to the other is called a gear train. The meshing of two gears may be idealized as two smooth discs with their edges touching and no slip between them. This ideal diameter is called the Pitch Circle Diameter (PCD) of the gear.

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Simple Gear Trains

The typical spur gears as shown in diagram. The direction of rotation is reversed from one gear to another. It has no affect on the gear ratio. The teeth on the gears must all be the same size so if gear A advances one tooth, so does B and C.

Simple Gear Trains

The typical spur gears as shown in diagram. The direction of rotation is reversed from one gear to another. It has no affect on the gear ratio. The teeth on the gears must all be the same size so if gear A advances one tooth, so does B and C.

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Compound Gear train

Compound gears are simply a chain of simple gear trains with the input of the second being the output of the first. A chain of two pairs is shown below. Gear B is the output of the first pair and gear C is the input of the second pair. Compound Gear train

Gears B and C are locked to the same shaft and revolve at the same speed.

For large velocities ratios, compound gear train arrangement is preferred.

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Reverted Gear train

Is a compound gear train in which the driver and driven gears are coaxial.. These are used in speed reducers, clocks and machine tools.

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Epicyclic gear train:

Epicyclic means one gear revolving upon and around another. The design involves planet and sun gears as one orbits the other like a planet around the sun. Here is a picture of a typical gear

box.

This design can produce large gear ratios in a small space and are used on a wide range of applications from marine gearboxes to electric screwdrivers.

Basic Theory

The diagram shows a gear B on the end of an arm. Gear B meshes with gear C and revolves around it when the arm is rotated. B is called the planet gear and C the sun.

First consider what happens when the planet gear orbits the sun gear.

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Observe point p and you will see that gear B also revolves once on its own axis. Any object orbiting around a center must rotate once. Now consider that B is free to rotate on its shaft and meshes with C.

Suppose the arm is held stationary and gear C is rotated once. B spins about its own center and the number of revolutions it makes is the ratio tC/tB. B will rotate by this number for every complete revolution of C.

Now consider that C is unable to rotate and the arm A is revolved once. Gear B will revolve 1+ tC/tB because of the orbit. It is this extra rotation that causes confusion. One way to get round this is to imagine that the whole system is revolved once. Then identify the gear that is fixed and revolve it back one revolution. Work out the revolutions of the other gears and add them up. The following tabular method makes it easy.

Suppose gear C is fixed and the arm A makes one revolution. Determine how many revolutions the planet gear B makes.

Step 1 is to revolve everything once about the center.

Step 2 identify that C should be fixed and rotate it backwards one revolution keeping the arm fixed as

it should only do one revolution in total. Work out the revolutions of B.

Step 3 is simply add them up and we find the total revs of C is zero and for the arm is 1.

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The number of revolutions made by B is (1+ tC/tB ) Note that if C revolves -1, then the direction of B is opposite so + tC/tB .

Gear-Tooth Action

Gear-Tooth Action

Fundamental Law of Gear-Tooth Action

Figure 5 shows two mating gear teeth, in which

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Figure 5 Two gearing tooth

Tooth profile 1 drives tooth profile 2 by acting at the instantaneous contact point K.

N1N2 is the common normal of the two profiles.

N1 is the foot of the perpendicular from O1to N1N2

N2 is the foot of the perpendicular from O2to N1N2.

Although the two profiles have different velocities V1 and V2 at point K, their velocities along N1N2 are equal in both magnitude and direction. Otherwise the two tooth profiles

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If the velocity ratio is to be constant, then P must be a fixed point. That is the the tangent

drawn at the pitch point must intersect the line of centres at a fixed point.

Point P is very important to the velocity ratio, and it is called the pitch point. Pitch point

divides the line between the line of centers and its position decides the velocity ratio of the

two teeth. The above expression is the fundamental law of gear-tooth action. ]

Path of contact:

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Consider a pinion driving wheel as shown in figure. When the pinion rotates in clockwise, the contact between a pair of involute teeth begins at K (on the near the base circle of pinion or the outer end of the tooth face on the wheel) and ends at L (outer end of the tooth face on the pinion or on the flank near the base circle of wheel).

MN is the common normal at the point of contacts and the common tangent to the base circles. The point K is the intersection of the addendum circle of wheel and the common tangent. The point L is the intersection of the addendum circle of pinion and common tangent.

The length of path of contact is the length of common normal cut-off by the addendum circles of the wheel and the pinion. Thus the length of part of contact is KL which is the sum of the parts of path of contacts KP and PL. Contact length KP is called as path of approachand contact length PL is called as path of recess.

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Arc of contact: Arc of contact is the path traced by a point on the pitch circle from the beginning to the end of engagement of a given pair of teeth. In Figure, the arc of contact is EPF or GPH.

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NOMENCLATURE of GEAR

NOMENCLATURE of GEAR

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Addendum: The radial distance between the Pitch Circle and the top of the teeth.

Arc of Action: Is the arc of the Pitch Circle between the beginning and the end of the engagement of a given pair of teeth.

Arc of Approach: Is the arc of the Pitch Circle between the first point of contact of the gear teeth and the Pitch Point.

Arc of Recession: That arc of the Pitch Circle between the Pitch Point and the last point of contact of the gear teeth.

Backlash: Play between mating teeth.

Base Circle: The circle from which is generated the involute curve upon which the tooth profile is based.

Center Distance: The distance between centers of two gears.

Chordal Addendum: The distance between a chord, passing through the points where the Pitch Circle crosses the tooth profile, and the tooth top.

Chordal Thickness: The thickness of the tooth measured along a chord passing through the points where the Pitch Circle crosses the tooth profile.

Circular Pitch: Millimeter of Pitch Circle circumference per tooth.

Circular Thickness: The thickness of the tooth measured along an arc following the Pitch Circle

Clearance: The distance between the top of a tooth and the bottom of the space into which it fits on the meshing gear.

Contact Ratio: The ratio of the length of the Arc of Action to the Circular Pitch.

Dedendum: The radial distance between the bottom of the tooth to pitch circle.

Diametral Pitch: Teeth per mm of diameter.

Face: The working surface of a gear tooth, located between the pitch diameter and the top of the tooth.

Face Width: The width of the tooth measured parallel to the gear axis.

Flank: The working surface of a gear tooth, located between the pitch diameter and the bottom of the teeth

Wheel:Larger of the two meshing gears is called wheel..

Pinion: The smaller of the two meshing gears is called pinion.

Land: The top surface of the tooth.

Line of Action: That line along which the point of contact between gear teeth travels, between the first point of contact and the last.

Module: Ratio of Pitch Diameter to the number of teeth..

Pitch Circle: The circle, the radius of which is equal to the distance from the center of the gear to the pitch point.

Diametral pitch: Ratio of the number of teeth to the of pitch circle diameter.

Pitch Point: The point of tangency of the pitch circles of two meshing gears, where the Line of Centers crosses the pitch circles.

Pressure Angle: Angle between the Line of Action and a line perpendicular to the Line of Centers.

Profile Shift: An increase in the Outer Diameter and Root Diameter of a gear, introduced to lower the practical tooth number or acheive a non-standard Center Distance.

Ratio: Ratio of the numbers of teeth on mating gears.

Root Circle: The circle that passes through the bottom of the tooth spaces.

Root Diameter: The diameter of the Root Circle.

Working Depth: The depth to which a tooth extends into the space between teeth on the mating gear.

Gears and Gear types

Gears:

Introduction: The slip and creep in the belt or rope drives is a common phenomenon, in the transmission of motion or power between two shafts. The effect of slip is to reduce the velocity ratio of the drive. In precision machine, in which a definite velocity ratio is importance (as in watch mechanism, special purpose machines..etc), the only positive drive is by means of gears or toothed wheels.

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TYPES OF GEARS

According to the position of axes of the shafts.

Parallel

1.Spur Gear

2.Helical Gear

3.Rack and Pinion

b. Intersecting

Bevel Gear

c. Non-intersecting and Non-parallel

worm and worm gears

SPUR GEAR

• Teeth is parallel to axis of rotation

• Transmit power from one shaft to another parallel shaft

• Used in Electric screwdriver, oscillating sprinkler, windup alarm clock, washing machine and clothes dryer

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Helical Gear

• The teeth on helical gears are cut at an angle to the face of the gear

• This gradual engagement makes helical gears operate much more smoothly and quietly than spur gears

• One interesting thing about helical gears is that if the angles of the gear teeth are correct, they can be mounted on perpendicular shafts, adjusting the rotation angle by 90 degrees

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Herringbone gears

To avoid axial thrust, two helical gears of opposite hand can be mounted side by side, to cancel resulting thrust forces

Herringbone gears are mostly used on heavy machinery.

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Rack and pinion

Rack and pinion gears are used to convert rotation (From the pinion) into linear motion (of the rack)

• A perfect example of this is the steering system on many cars

Bevel gears

Bevel gears are useful when the direction of a shaft’s rotation needs to be changed

• They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well

• The teeth on bevel gears can be straight, spiral or hypoid

• locomotives, marine applications, automobiles, printing presses, cooling towers, power plants, steel plants, railway track inspection machines, etc.

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WORM AND WORM GEAR

Worm gears are used when large gear reductions are needed. It is common for worm gears to have reductions of 20:1, and even up to 300:1 or greater

• Many worm gears have an interesting property that no other gear set has: the worm can easily turn the gear, but the gear cannot turn the worm

• Worm gears are used widely in material handling and transportation machinery, machine tools, automobiles etc

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