Unit - 3

Design of Keys, Shaft and Couplings

Q1) Explain various types of keys.

A1)

Types of Keys Common sorts of keys are:

1. Sunk keys

2. Saddle keys

3. Tangent keys

4. Round keys

5. Splines

Sunk Keys

A sunk key's a key wherein 1/2 of the thickness of key suits into the keyway with inside the shaft and 1/2 of with inside the keyway of the hub.

The sunk keys are of the subsequent types:

Rectangular sunk key:

It is the best sort of key and has a square cross-segment.

A taper of approximately 1 in one hundred is supplied on its pinnacle side.

Square sunk key:

Rectangular sunk key having same width and thickness is known as rectangular sunk key.

Parallel sunk key:

If no taper is supplied at the square or rectangular sunk key, its miles known as parallel sunk key i.e. its miles uniform in width and thickness throughout. It is used wherein the pulley, tools or different mating piece is needed to slip alongside the shaft.

Gib-head key:

It is a square sunk key with a head at one quit called gib head that is supplied to facilitate the elimination of key.

Feather key:

Feather key's a parallel key made as a crucial a part of the shaft with the assist of machining or the usage of set-screws. It allows axial motion and has a sliding suit with inside the key manner of the shifting piece.

Woodruff key:

Woodruff key's a sunk key with inside the shape of a semicircular disc of uniform thickness. Lower part of the important thing suits into the round keyway of the shaft. It may be used with tapered shafts as it could tilt and align itself at the shaft.

Saddle Keys

Slot for this sort of is supplied best with inside the hub as proven in Figure Torque is transmitted with the aid of using friction best and cannot consequently transmit excessive torque and is used best for mild applications.

The saddle keys are of types:

Flat Saddle Key and Hollow Saddle Key.

In flat saddle key, the lowest floor touching the shaft is flat and it sits at the flat floor machined at the shaft. Hollow saddle key has a concave floor at the lowest to suit the ground floor of the shaft. Chances of slip in case of the flat saddle key are surprisingly lesser and may transmit greater electricity than the whole saddle key.

Tangent Keys

Tangent keys are proven in Figure

These are used to transmit excessive torque. They can be used as an unmarried key or a couple at proper angles. Single tangent key can transmit torque best in a single direction.

Round Keys

The spherical keys have a round cross-segment and suit into holes drilled in part with inside the shaft and in part with inside the hub.

Slot is drilled after the meeting so the shafts may be well aligned. These are used for low torque transmission.

Splines

A range of keys made as a crucial a part of the shaft are known as splines. Keyways are supplied with inside the hub. These are used for excessive torque transmission e.g. In car transmission. Splines additionally allow the axial motion.

Q2) Explain design of sunk key.

A2)

Design of Sunk Keys

Figure indicates the forces performing on a square key having width w and peak h. Let l be the duration of the important thing.

Torque is transmitted from the shaft to the hub thru key. Shaft applies a pressure P on the important thing and the important thing applies a same pressure at the hub.

Therefore the secret's acted upon with the aid of using same forces of value P, one implemented with the aid of using the shaft (at the decrease portion) and the opposite due to the response of hub (at the top portion).

As those forces aren't in equal plane, they represent a pair which attempts to tilt the important thing.

Therefore same and contrary forces P’ additionally act on the important thing, which offer a resisting couple that maintains the important thing in position.

As the precise place of pressure P isn't known, to simplify the evaluation it's far assumed that the pressure P acts tangential to the shaft. If T is the torque transmitted,

P = T/d/2

Where, d = diameter of the shaft

In the design of key two types of failures are considered, shear failure and crushing failure.

Area resisting shear failure = w l

Shear stress, τ =  

Crushing Area = l h/2

Crushing stress, σcrushing =

Tables are available which give standard cross-sections for square and rectangular keys corresponding to different shaft diameters. But in the absence of such data, following relations are generally used:

For Rectangular Key:  w = d / 4 and  h = d / 6

For Square Key:         w = h = d /4

For a known diameter of shaft, w and h can be calculated using these relations and then using the above strength equations required length of the key is calculated for given values of allowable stresses. Length is calculated both for shear and crushing and then maximum value out of the two is considered.

Q3) Explain types of pins.

A3)

Classification of pins:

Exist an extensive type of trendy pins sorts and dimensions, in addition to unique designs to precise applications. Industrial pins may be categorized in an effort to his feature and bureaucracy into numerous categories, which includes: dowel pins, spring pins, cotter pins and twine clips, hitch and lynch pins or unique pins.

DOWEL PINS

Dowel pins are commercial fasteners which are used to sign up for or extra objects together. They are short, cylindrical rods that may be made of various substances which includes wood, steel and polymer. Exists numerous kinds of dowel pins how we will see below: -

Drive pins

Have an interference match and have to be hammered right into a mating hollow. They are not unusual place for rotary and transferring applications.

Groove pins

Are engraved with longitudinal or helical grooves. These grooves are intended for adhesives to alleviate hydraulic strain and enhance holding.

Knurled pins

Have a knurled floor to enhance the pin's grip. Most of this knurled floor are straight, helical and diamond knurls.

Pull dowel pins

Have a threaded hollow at one stop so a screw may be inserted. It is mainly used to help the eliminating of the pin from a blind hollow Tapered pins those pins have the shape of a truncated cone.

SPRING PINS:

Spring pins have a frame diameter which is bigger than the hollow diameter. The spring motion of the pin lets in it to compress because it assumes the diameter of the hollow.

A spring pin is taken into consideration are cost-effectives due to the fact the radial pressure exerted through the pin retains it with inside the hollow save you loosening created through vibration or surprise and requiring less training than different kinds of pins. There are kinds of spring pins:

Coiled spring pin

Additionally referred to as spiral pin, this sort of pin offers a great flexibility in diameters, uniform electricity and identical pressure distribution, additionally are shock-soaking up fastening elements.

Slotted spring pin

Additionally called roll pins, slotted spring pins are headless cylindrical pins rolled from a strip of fabric with a slot of the whole period to permit the pin to have a few flexibility at some point of insertion.

Q4) What are the types of pins?

A4)

Linch pins

Are designed to maintain a rotating tool on its axle, however it could additionally be used as a fastener as well. Both of those kinds of pins require predrilled holes in shafts and a few shape of a lock to be effective.

Hitch pins

Hyperlink mating additives and are held in function on one cease by the usage of cotter pin, and with inside the different cease a bend or cope with to save you removal. This sort of pin can attain an enormous load constantly that it won’t be carried out on the cotter pin.

Clevis pin

Is a hardware piece with a head, a cylindrical frame and a hollow that is routed thru a mating clevis fastener to bring together additives? This pins are designed to soak up lateral pressure and rotate to permit freedom of motion for supported objects.

A cotter pin is needed to save you the clevis pin from loosening.

Exist generic Clevis pins with numerous holes for regulate the pin to exceptional applications, as we will see at the proper picture.

Design of Pins:

Round and taper pins are easy cylindrical pins without or with a taper and they provide powerful method of fastening pulleys, gears or levers to a shaft. It can be equipped such that 1/2 of the pin lies with inside the hub and the alternative 1/2 of with inside the shaft as proven in figure.

The pin can be pushed thru the hub and the shaft as in figure or as in figure these joints supply fantastic grip and the pins are subjected to a shear load. For example, for the shaft with inside the assembly proven in figure, the pin is beneath   double shear and we have

Where d is the diameter of the pin at hub-shaft interface, τ is the yield strength in shear of the pin material and T is the torque transmitted.

Q5) What are the theories of failure?

A5)

Theories of failure:

Theories of failure describe the elastic failure of the mechanical additives. At the time of running gadget additives subjected to diverse masses which motive unique kinds of pressure in it.

Theories of failure assist us to decide the secure dimensions of the gadget additives whilst they're subjected to bi-axial or tri-axial kingdom of stresses. Anything is failed if the precipitated pressure exceeds the elastic restriction and everlasting deformation of the thing takes location.

In brittle failure the direct separation takes location with none sort of considerable elongation while in ductile failure we are able to see considerable inelastic elongation earlier than the failure

Both kinds of failure depend upon the form of cloth with the aid of using which gadget thing is made. All the mechanical additives failed whilst elastic restriction is reached to a positive fee and yielding starts. Different theories were proposed for unique substances and failures.

These theories are used to acquire the connection among stresses precipitated beneath bi-axial and tri-axial kingdom of pressure situations and the cloth residences that are received with the aid of using the anxiety check or compression check.

These residences are Sut (remaining energy in anxiety), Syt (yield energy in anxiety) and so on. The yielding within side the cloth relies upon the numerous pressure additives.

The failure of any mechanical element relies upon different factors like residences of cloth, form of loading and temperature etc. as an example an energy screw subjected to torsional second in addition to axial force, an overhang crank is subjected to blended bending and torsional second, equal with inside the case of bolts of the bracket that are subjected to forces that reasons tensile pressure and shear pressure, in which as crank shafts and connecting rods are examples of the ones additives that are subjected to complicated masses.

Before designing of any gadget element numerous experiments are executed on them to acquire secure running pressure beneath blended loading situations.

These experiments assist us to decide the unique residences of the substances beneath comparable loading situations.

But every so often it isn't feasible to carry out those exams for unique feasible mixtures of load to acquire mechanical residences. Generally maximum of the mechanical residences of anything are received with the aid of using anxiety check that's executed on UTM (Universal Testing Machine).

These residences are yield energy, remaining tensile energy and percent of elongation. Theories of failure supply a courting among the energy of gadget thing that are subjected to complicated kingdom of stresses with the mechanical residences that are received throughout the anxiety check.

Following are the important thing factors that are beneficial in higher information of theories of failure:

σ1, σ2 and σ3 are the precept stresses precipitated at a factor at the gadget element in 3 mutual perpendicular guidelines because of the unique loading situations. We use unique theories to acquire the connection among σ1, σ2 and σ3 with the cloth residences like Syt (yield shear energy in anxiety), Sot (remaining energy in anxiety), Sys (yield energy in shear) and element of protection FOS (N).

Under uniaxial kingdom of pressure situation i.e. most effective σ1 is appearing at the gadget thing then the energy criterion and all theories of failure will supply the equal end result so we don't have any requirement of idea of failure in case of uniaxial kingdom of pressure situation.

In case of bi-axial and tri-axial kingdom of pressure situations all of the theories of failure will offer unique results. So for the secure layout of anything beneath bi-axial and tri-axial kingdom of pressure situation suitable idea of failure ought to be selected.

Under bi-axial and tri-axial kingdom of pressure situations all of the theories of failure offer nearly equal end result whilst σ1 could be very massive compared to the σ2 and σ3.

Q6) Explain Maximum Principle Stress Theory.

A6)

Maximum Principle Stress Theory:

This idea changed into proposed with the aid of using W.J.M Rankin. This is one of the oldest and easy theories. According to this idea the failure within side the mechanical issue takes area while they're subjected to bi-axial or tri-axial kingdom of strain after which the cost of most precept strain reaches the yield electricity or final electricity of the fabric.

In this idea simplest most precept stresses are take into account, relaxation all of the precept stresses have now no longer any effects on it. If we take into account 3 precept stresses σ1, σ2 and σ3 at a factor on a device issue then σ1 > σ2 > σ3.

The situation of the failure is,

σ1 = Syt or σ1 = Sut       

Maximum precept strain idea is taken into consideration because the first-class idea of failure for brittle substances, however it's also appropriate for ductile substances beneath  the subsequent kingdom of strain conditions:- Uniaxial kingdom of strain situation simplest Bi-axial kingdom of strain situation while precept stresses are like in nature.

Here σ2 is not noted due to not like nature. Hydrostatic kingdom of strain situation i.e. while σ1 = σ2 = σ3.

Graphical Representation:

A rectangular represents the kingdom of stresses beneath = this idea. Square is split into 4 quadrants i.e. in first quadrant each σ1 and σ2 are fantastic or tensile in nature. In 2nd quadrant σ1 is poor i.e. compressive in nature and σ2 is fantastic. In 1/3 quadrant each σ1 and σ2 are poor i.e. compressive in nature and in closing i.e. fourth quadrant σ1 is fantastic and σ2 is poor

Q7) Explain Maximum Shear Stress Theory

A7)

This idea changed into proposed with the aid of using Coulombs and Guest.

According to this idea the failure of any mechanical issue happens while it's far subjected to bi-axial or tri-axial stresses after which the most shear strain at any factor of the issue reaches as much as the cost that's identical to the most shear strain within side the preferred specimen of the anxiety check while yielding is In the anxiety check the specimen is subjected to the uniaxial kingdom of strain i.e. σ2 = 0. So the most shear is identical to the 1/2 of the distinction among the most and minimal precept strain.

Therefore the most shear in easy anxiety is identical to the 1/2 of of the tensile strain. Design equation of most shear strain idea is,

Absolute T max = Syt or (σ1 – σ2)/2 = Syt

This idea isn't appropriate for ductile substances as it will provide over secure layout for ductile additives. This idea isn't relevant to substances subjected to hydrostatic kingdom of stresses, in this example shear strain is sort of 0 because of this that the failure with inside the fabric will now no longer happens that's impossible. Graphically a Hexagon represents the strain distribution which indicates that the substances will attain its elastic restriction while the stresses (σ1and σ2) cross outdoor the region.

Q8) What is total strain energy theory?

A8)

Total Strain Energy Theory:

This idea changed into given with the aid of using Beltrami Haigh’s. According to this idea the engineering additives beneath the complicated stresses fails while the whole stress strength with inside the frame is identical to the stress strength at elastic limits in easy anxiety.

This idea states that after a cloth deformed completely because of the diverse stresses. The cost of those stresses boom regularly from 0 cost because of this we are able to say that the preliminary stress strength is unbiased of the character of stresses and is sort of constant.

The layout equation consistent with this idea is,

σ12 + σ22+ σ32 – 2µ (σ1σ2 + σ2σ3 + σ3σ1) = (Syt)2

This idea is relevant for the ones brittle substances who has elastic restriction strain in anxiety and compression are different. The graphical illustration of this idea is proven with the aid of using the Ellipses that are inscribed with the aid of using the parallelogram. The fabric mechanical issue reaches its elastic restriction while the stresses (σ1and σ2) fall outdoor the ellipse.

Q9) Explain maximum strain energy theory.

A9)

Maximum Shear Strain Energy Theory:

This idea is likewise called the most distortion strength idea. This idea changed into given with the aid of using M.T. Huber and R. Von Mises.

This idea states that the inelastic motion at any factor with inside the engineering issue begins off evolved because of diverse stresses while the stress strength of distortion in keeping with unit quantity is absorbed at a factor is identical to the stress strength of distortion absorbed in keeping with unit quantity at any factor in a bar that's confused to the elastic restriction beneath the uniaxial kingdom of strain with inside the easy anxiety or compression check.

So we are able to say that the part of the stress strength produce alternate with inside the form of the detail is meant to be absolutely answerable for the failure of the fabric with the aid of using yielding.

This idea is taken into consideration because the first-class and secure amongst all of the theories for designing any mechanical issue. The layout equation consistent with this idea is,

(σ1-σ2)2 + (σ2-σ3)2 + (σ3-σ1)2 = 2 (Syt)2

Q10) What are the shaft materials?

A10)

It typically has round cross-segment and may be stable or hollow. Shafts are supported at the bearings and transmit torque with the assist of gears, belts and pulleys etc. Shafts are typically subjected to bending second, torsion and axial pressure or a mixture of those three.

So the shafts are designed relying upon the mixture of masses its miles subjected to. Spindle stub and axle are a few vital forms of shaft. Small shaft is known as spindle. Shaft crucial a part of the top mover is known as stub shaft.

An axle is a non-rotating member that includes no torque and is used to help rotating wheels, pulleys etc. And consequently is subjected to bending second only.

Shaft Materials

• Hot-rolled simple carbon metallic is the least highly-priced fabric used for shafts.
• These basically require machining to do away with the scales of warm rolling process.
• Cold rolled simple carbon metallic gives higher yield power and persistence power however the bloodless running induces residual stresses.
• Surface is clean in this example and quantity of machining consequently is minimal. It is used for widespread motive transmission shafts.
• When a shaft is to paintings beneath intense loading and corrosive situations and require greater power, alloy steels are used, typically having Ni, Cr, Mo and V as alloying elements.
• Alloy steels are highly-priced.
• Sometimes shafts are warmth dealt with to enhance hardness and surprise resistance and floor hardening strategies also are used if excessive put on resistance is the requirement.
• As the shafts transmitting electricity are subjected to fatigue loading, consequently better issue of protection of three to four is used on the idea of yield power for static load analysis.

Q11) Explain design of shaft.

A11)

Design of Shafts

Shafts are designed on the idea of power or pressure or both.

Design primarily based totally on power is to make certain that pressure at any vicinity of the shaft does now no longer exceed the fabric yield pressure.

Design primarily based totally on pressure is to make certain that most deflection (due to bending) and most twist (because of torsion) of the shaft is in the allowable limits.

Rigidity attention is likewise very vital in a few instances for instance function of an equipment hooked up at the shaft will alternate if the shaft receives deflected and if this fee is greater than a few allowable limit, it is able to result in excessive dynamic masses and noise with inside the gears.

In designing shafts on the idea of power, the subsequent instances can be considered:

(a) Shafts subjected to torque

(b) Shafts subjected to bending second

(c) Shafts subjected to mixture of torque and bending second

(d) Shafts subjected to axial masses further to mixture of torque and bending second

Q12) Explain Shafts Subjected to Torque.

A12)

Shafts Subjected to Torque

Maximum shear stress developed in a shaft subjected to torque is given by,

Where T = Twisting moment (or torque) acting upon the shaft,

J = Polar moment of inertia of the shaft about the axis of rotation

=               for solid shafts with diameter d

=             for hollow shafts with do and di as outer and inner diameter.

r = Distance from neutral axis to the outer most fibre = d/2 (or do/2)

So dimensions of the shaft subjected to torque can be determined from above relation for a known value of allowable shear stress, [τ].

Shafts Subjected to Bending Moment

Maximum bending stress developed in a shaft is given by,

Where M = Bending Moment acting upon the shaft,

I  = Moment of inertia of cross-sectional area of the shaft about the axis of rotation

=               for solid shafts with diameter d

=        for hollow shafts with do and di as outer and inner diameter.

y  = Distance from neutral axis to the outer most fibre = d / 2 (or do/2)

So dimensions of the shaft subjected to bending moment can be determined from above relation for a known value of allowable tensile stress

Q13) What is torsional rigidity?

A13)

Torsional Rigidity

For a shaft subjected twisting moment, the angle of twist is given by,

θ =

Where, T = Torque applied

L = Length of the shaft

J = Polar moment of inertia of the shaft about the axis of rotation

G = Modulus of rigidity of the shaft material

Therefore for the known values of T, L and G and allowable value of angle of twist, diameter of the shaft can be calculated.

Q14) Explain A.S.M.E. Code for Shaft Design

A14)

According to A.S.M.E. Code, the bending and twisting moment are to be multiplied by factors kb and kt respectively, to account for shock and fatigue in operating condition. Therefore, if the shaft is subjected to dynamic loading, equivalent torque and equivalent bending moment will become:

       And         

Table: Values of kb and kt for different types of loading

Q15) Explain design of coupling in detail.

A15)

• A shaft coupling is one of the maximum not unusual place device factors due to the fact it's miles simply so critical in energy transmission systems. Thus, they locate use in plenty of programs and carrier environments.
• As an end result, designers and engineers have designed many versions of couplings for unique carrier situations and environments over the years.
• This article will familiarize you with the specific sorts of couplings and talk selecting the proper alternative on your application. A coupling is a mechanical tool that connects comparable or diverse shafts in machines to transmit energy and motion.
• It is often a brief connection (however may be everlasting in a few instances) and able to elimination for carrier or replacement. A coupling can be inflexible or bendy.
• Due to the supply of many designs, there may be stark variations with inside the production and feature of sorts of mechanical couplings. Some couplings can hook up with shafts without transferring the shaft, at the same time as maximum would require shaft motion for fitting.
• In maximum instances, a coupling does now no longer alternate the path of movement or angular velocity, in contrast to gears. It can't be related or disconnected mid-operation, in contrast to clutches.
• Couplings can best switch torque over quick distances, for longer distances chain drives and belt drives are higher alternatives.
• Couplings are regularly paired with lead screw assemblies to attach the screw shaft in-line to a motor. The coupling works through keeping a sturdy however bendy connection always among shafts to switch movement from one shaft to another.
• It does so in any respect values of hundreds and misalignment without allowing any relative movement among the 2 shafts.

Unit - 3

Unit - 3

Unit - 3

Design of Keys, Shaft and Couplings

Q1) Explain various types of keys.

A1)

Types of Keys Common sorts of keys are:

1. Sunk keys

2. Saddle keys

3. Tangent keys

4. Round keys

5. Splines

Sunk Keys

A sunk key's a key wherein 1/2 of the thickness of key suits into the keyway with inside the shaft and 1/2 of with inside the keyway of the hub.

The sunk keys are of the subsequent types:

Rectangular sunk key:

It is the best sort of key and has a square cross-segment.

A taper of approximately 1 in one hundred is supplied on its pinnacle side.

Square sunk key:

Rectangular sunk key having same width and thickness is known as rectangular sunk key.

Parallel sunk key:

If no taper is supplied at the square or rectangular sunk key, its miles known as parallel sunk key i.e. its miles uniform in width and thickness throughout. It is used wherein the pulley, tools or different mating piece is needed to slip alongside the shaft.

Gib-head key:

It is a square sunk key with a head at one quit called gib head that is supplied to facilitate the elimination of key.

Feather key:

Feather key's a parallel key made as a crucial a part of the shaft with the assist of machining or the usage of set-screws. It allows axial motion and has a sliding suit with inside the key manner of the shifting piece.

Woodruff key:

Woodruff key's a sunk key with inside the shape of a semicircular disc of uniform thickness. Lower part of the important thing suits into the round keyway of the shaft. It may be used with tapered shafts as it could tilt and align itself at the shaft.

Saddle Keys

Slot for this sort of is supplied best with inside the hub as proven in Figure Torque is transmitted with the aid of using friction best and cannot consequently transmit excessive torque and is used best for mild applications.

The saddle keys are of types:

Flat Saddle Key and Hollow Saddle Key.

In flat saddle key, the lowest floor touching the shaft is flat and it sits at the flat floor machined at the shaft. Hollow saddle key has a concave floor at the lowest to suit the ground floor of the shaft. Chances of slip in case of the flat saddle key are surprisingly lesser and may transmit greater electricity than the whole saddle key.

Tangent Keys

Tangent keys are proven in Figure

These are used to transmit excessive torque. They can be used as an unmarried key or a couple at proper angles. Single tangent key can transmit torque best in a single direction.

Round Keys

The spherical keys have a round cross-segment and suit into holes drilled in part with inside the shaft and in part with inside the hub.

Slot is drilled after the meeting so the shafts may be well aligned. These are used for low torque transmission.

Splines

A range of keys made as a crucial a part of the shaft are known as splines. Keyways are supplied with inside the hub. These are used for excessive torque transmission e.g. In car transmission. Splines additionally allow the axial motion.

Q2) Explain design of sunk key.

A2)

Design of Sunk Keys

Figure indicates the forces performing on a square key having width w and peak h. Let l be the duration of the important thing.

Torque is transmitted from the shaft to the hub thru key. Shaft applies a pressure P on the important thing and the important thing applies a same pressure at the hub.

Therefore the secret's acted upon with the aid of using same forces of value P, one implemented with the aid of using the shaft (at the decrease portion) and the opposite due to the response of hub (at the top portion).

As those forces aren't in equal plane, they represent a pair which attempts to tilt the important thing.

Therefore same and contrary forces P’ additionally act on the important thing, which offer a resisting couple that maintains the important thing in position.

As the precise place of pressure P isn't known, to simplify the evaluation it's far assumed that the pressure P acts tangential to the shaft. If T is the torque transmitted,

P = T/d/2

Where, d = diameter of the shaft

In the design of key two types of failures are considered, shear failure and crushing failure.

Area resisting shear failure = w l

Shear stress, τ =  

Crushing Area = l h/2

Crushing stress, σcrushing =

Tables are available which give standard cross-sections for square and rectangular keys corresponding to different shaft diameters. But in the absence of such data, following relations are generally used:

For Rectangular Key:  w = d / 4 and  h = d / 6

For Square Key:         w = h = d /4

For a known diameter of shaft, w and h can be calculated using these relations and then using the above strength equations required length of the key is calculated for given values of allowable stresses. Length is calculated both for shear and crushing and then maximum value out of the two is considered.

Q3) Explain types of pins.

A3)

Classification of pins:

Exist an extensive type of trendy pins sorts and dimensions, in addition to unique designs to precise applications. Industrial pins may be categorized in an effort to his feature and bureaucracy into numerous categories, which includes: dowel pins, spring pins, cotter pins and twine clips, hitch and lynch pins or unique pins.

DOWEL PINS

Dowel pins are commercial fasteners which are used to sign up for or extra objects together. They are short, cylindrical rods that may be made of various substances which includes wood, steel and polymer. Exists numerous kinds of dowel pins how we will see below: -

Drive pins

Have an interference match and have to be hammered right into a mating hollow. They are not unusual place for rotary and transferring applications.

Groove pins

Are engraved with longitudinal or helical grooves. These grooves are intended for adhesives to alleviate hydraulic strain and enhance holding.

Knurled pins

Have a knurled floor to enhance the pin's grip. Most of this knurled floor are straight, helical and diamond knurls.

Pull dowel pins

Have a threaded hollow at one stop so a screw may be inserted. It is mainly used to help the eliminating of the pin from a blind hollow Tapered pins those pins have the shape of a truncated cone.

SPRING PINS:

Spring pins have a frame diameter which is bigger than the hollow diameter. The spring motion of the pin lets in it to compress because it assumes the diameter of the hollow.

A spring pin is taken into consideration are cost-effectives due to the fact the radial pressure exerted through the pin retains it with inside the hollow save you loosening created through vibration or surprise and requiring less training than different kinds of pins. There are kinds of spring pins:

Coiled spring pin

Additionally referred to as spiral pin, this sort of pin offers a great flexibility in diameters, uniform electricity and identical pressure distribution, additionally are shock-soaking up fastening elements.

Slotted spring pin

Additionally called roll pins, slotted spring pins are headless cylindrical pins rolled from a strip of fabric with a slot of the whole period to permit the pin to have a few flexibility at some point of insertion.

Q4) What are the types of pins?

A4)

Linch pins

Are designed to maintain a rotating tool on its axle, however it could additionally be used as a fastener as well. Both of those kinds of pins require predrilled holes in shafts and a few shape of a lock to be effective.

Hitch pins

Hyperlink mating additives and are held in function on one cease by the usage of cotter pin, and with inside the different cease a bend or cope with to save you removal. This sort of pin can attain an enormous load constantly that it won’t be carried out on the cotter pin.

Clevis pin

Is a hardware piece with a head, a cylindrical frame and a hollow that is routed thru a mating clevis fastener to bring together additives? This pins are designed to soak up lateral pressure and rotate to permit freedom of motion for supported objects.

A cotter pin is needed to save you the clevis pin from loosening.

Exist generic Clevis pins with numerous holes for regulate the pin to exceptional applications, as we will see at the proper picture.

Design of Pins:

Round and taper pins are easy cylindrical pins without or with a taper and they provide powerful method of fastening pulleys, gears or levers to a shaft. It can be equipped such that 1/2 of the pin lies with inside the hub and the alternative 1/2 of with inside the shaft as proven in figure.

The pin can be pushed thru the hub and the shaft as in figure or as in figure these joints supply fantastic grip and the pins are subjected to a shear load. For example, for the shaft with inside the assembly proven in figure, the pin is beneath   double shear and we have

Where d is the diameter of the pin at hub-shaft interface, τ is the yield strength in shear of the pin material and T is the torque transmitted.

Q5) What are the theories of failure?

A5)

Theories of failure:

Theories of failure describe the elastic failure of the mechanical additives. At the time of running gadget additives subjected to diverse masses which motive unique kinds of pressure in it.

Theories of failure assist us to decide the secure dimensions of the gadget additives whilst they're subjected to bi-axial or tri-axial kingdom of stresses. Anything is failed if the precipitated pressure exceeds the elastic restriction and everlasting deformation of the thing takes location.

In brittle failure the direct separation takes location with none sort of considerable elongation while in ductile failure we are able to see considerable inelastic elongation earlier than the failure

Both kinds of failure depend upon the form of cloth with the aid of using which gadget thing is made. All the mechanical additives failed whilst elastic restriction is reached to a positive fee and yielding starts. Different theories were proposed for unique substances and failures.

These theories are used to acquire the connection among stresses precipitated beneath bi-axial and tri-axial kingdom of pressure situations and the cloth residences that are received with the aid of using the anxiety check or compression check.

These residences are Sut (remaining energy in anxiety), Syt (yield energy in anxiety) and so on. The yielding within side the cloth relies upon the numerous pressure additives.

The failure of any mechanical element relies upon different factors like residences of cloth, form of loading and temperature etc. as an example an energy screw subjected to torsional second in addition to axial force, an overhang crank is subjected to blended bending and torsional second, equal with inside the case of bolts of the bracket that are subjected to forces that reasons tensile pressure and shear pressure, in which as crank shafts and connecting rods are examples of the ones additives that are subjected to complicated masses.

Before designing of any gadget element numerous experiments are executed on them to acquire secure running pressure beneath blended loading situations.

These experiments assist us to decide the unique residences of the substances beneath comparable loading situations.

But every so often it isn't feasible to carry out those exams for unique feasible mixtures of load to acquire mechanical residences. Generally maximum of the mechanical residences of anything are received with the aid of using anxiety check that's executed on UTM (Universal Testing Machine).

These residences are yield energy, remaining tensile energy and percent of elongation. Theories of failure supply a courting among the energy of gadget thing that are subjected to complicated kingdom of stresses with the mechanical residences that are received throughout the anxiety check.

Following are the important thing factors that are beneficial in higher information of theories of failure:

σ1, σ2 and σ3 are the precept stresses precipitated at a factor at the gadget element in 3 mutual perpendicular guidelines because of the unique loading situations. We use unique theories to acquire the connection among σ1, σ2 and σ3 with the cloth residences like Syt (yield shear energy in anxiety), Sot (remaining energy in anxiety), Sys (yield energy in shear) and element of protection FOS (N).

Under uniaxial kingdom of pressure situation i.e. most effective σ1 is appearing at the gadget thing then the energy criterion and all theories of failure will supply the equal end result so we don't have any requirement of idea of failure in case of uniaxial kingdom of pressure situation.

In case of bi-axial and tri-axial kingdom of pressure situations all of the theories of failure will offer unique results. So for the secure layout of anything beneath bi-axial and tri-axial kingdom of pressure situation suitable idea of failure ought to be selected.

Under bi-axial and tri-axial kingdom of pressure situations all of the theories of failure offer nearly equal end result whilst σ1 could be very massive compared to the σ2 and σ3.

Q6) Explain Maximum Principle Stress Theory.

A6)

Maximum Principle Stress Theory:

This idea changed into proposed with the aid of using W.J.M Rankin. This is one of the oldest and easy theories. According to this idea the failure within side the mechanical issue takes area while they're subjected to bi-axial or tri-axial kingdom of strain after which the cost of most precept strain reaches the yield electricity or final electricity of the fabric.

In this idea simplest most precept stresses are take into account, relaxation all of the precept stresses have now no longer any effects on it. If we take into account 3 precept stresses σ1, σ2 and σ3 at a factor on a device issue then σ1 > σ2 > σ3.

The situation of the failure is,

σ1 = Syt or σ1 = Sut       

Maximum precept strain idea is taken into consideration because the first-class idea of failure for brittle substances, however it's also appropriate for ductile substances beneath  the subsequent kingdom of strain conditions:- Uniaxial kingdom of strain situation simplest Bi-axial kingdom of strain situation while precept stresses are like in nature.

Here σ2 is not noted due to not like nature. Hydrostatic kingdom of strain situation i.e. while σ1 = σ2 = σ3.

Graphical Representation:

A rectangular represents the kingdom of stresses beneath = this idea. Square is split into 4 quadrants i.e. in first quadrant each σ1 and σ2 are fantastic or tensile in nature. In 2nd quadrant σ1 is poor i.e. compressive in nature and σ2 is fantastic. In 1/3 quadrant each σ1 and σ2 are poor i.e. compressive in nature and in closing i.e. fourth quadrant σ1 is fantastic and σ2 is poor

Q7) Explain Maximum Shear Stress Theory

A7)

This idea changed into proposed with the aid of using Coulombs and Guest.

According to this idea the failure of any mechanical issue happens while it's far subjected to bi-axial or tri-axial stresses after which the most shear strain at any factor of the issue reaches as much as the cost that's identical to the most shear strain within side the preferred specimen of the anxiety check while yielding is In the anxiety check the specimen is subjected to the uniaxial kingdom of strain i.e. σ2 = 0. So the most shear is identical to the 1/2 of the distinction among the most and minimal precept strain.

Therefore the most shear in easy anxiety is identical to the 1/2 of of the tensile strain. Design equation of most shear strain idea is,

Absolute T max = Syt or (σ1 – σ2)/2 = Syt

This idea isn't appropriate for ductile substances as it will provide over secure layout for ductile additives. This idea isn't relevant to substances subjected to hydrostatic kingdom of stresses, in this example shear strain is sort of 0 because of this that the failure with inside the fabric will now no longer happens that's impossible. Graphically a Hexagon represents the strain distribution which indicates that the substances will attain its elastic restriction while the stresses (σ1and σ2) cross outdoor the region.

Q8) What is total strain energy theory?

A8)

Total Strain Energy Theory:

This idea changed into given with the aid of using Beltrami Haigh’s. According to this idea the engineering additives beneath the complicated stresses fails while the whole stress strength with inside the frame is identical to the stress strength at elastic limits in easy anxiety.

This idea states that after a cloth deformed completely because of the diverse stresses. The cost of those stresses boom regularly from 0 cost because of this we are able to say that the preliminary stress strength is unbiased of the character of stresses and is sort of constant.

The layout equation consistent with this idea is,

σ12 + σ22+ σ32 – 2µ (σ1σ2 + σ2σ3 + σ3σ1) = (Syt)2

This idea is relevant for the ones brittle substances who has elastic restriction strain in anxiety and compression are different. The graphical illustration of this idea is proven with the aid of using the Ellipses that are inscribed with the aid of using the parallelogram. The fabric mechanical issue reaches its elastic restriction while the stresses (σ1and σ2) fall outdoor the ellipse.

Q9) Explain maximum strain energy theory.

A9)

Maximum Shear Strain Energy Theory:

This idea is likewise called the most distortion strength idea. This idea changed into given with the aid of using M.T. Huber and R. Von Mises.

This idea states that the inelastic motion at any factor with inside the engineering issue begins off evolved because of diverse stresses while the stress strength of distortion in keeping with unit quantity is absorbed at a factor is identical to the stress strength of distortion absorbed in keeping with unit quantity at any factor in a bar that's confused to the elastic restriction beneath the uniaxial kingdom of strain with inside the easy anxiety or compression check.

So we are able to say that the part of the stress strength produce alternate with inside the form of the detail is meant to be absolutely answerable for the failure of the fabric with the aid of using yielding.

This idea is taken into consideration because the first-class and secure amongst all of the theories for designing any mechanical issue. The layout equation consistent with this idea is,

(σ1-σ2)2 + (σ2-σ3)2 + (σ3-σ1)2 = 2 (Syt)2

Q10) What are the shaft materials?

A10)

It typically has round cross-segment and may be stable or hollow. Shafts are supported at the bearings and transmit torque with the assist of gears, belts and pulleys etc. Shafts are typically subjected to bending second, torsion and axial pressure or a mixture of those three.

So the shafts are designed relying upon the mixture of masses its miles subjected to. Spindle stub and axle are a few vital forms of shaft. Small shaft is known as spindle. Shaft crucial a part of the top mover is known as stub shaft.

An axle is a non-rotating member that includes no torque and is used to help rotating wheels, pulleys etc. And consequently is subjected to bending second only.

Shaft Materials

• Hot-rolled simple carbon metallic is the least highly-priced fabric used for shafts.
• These basically require machining to do away with the scales of warm rolling process.
• Cold rolled simple carbon metallic gives higher yield power and persistence power however the bloodless running induces residual stresses.
• Surface is clean in this example and quantity of machining consequently is minimal. It is used for widespread motive transmission shafts.
• When a shaft is to paintings beneath intense loading and corrosive situations and require greater power, alloy steels are used, typically having Ni, Cr, Mo and V as alloying elements.
• Alloy steels are highly-priced.
• Sometimes shafts are warmth dealt with to enhance hardness and surprise resistance and floor hardening strategies also are used if excessive put on resistance is the requirement.
• As the shafts transmitting electricity are subjected to fatigue loading, consequently better issue of protection of three to four is used on the idea of yield power for static load analysis.

Q11) Explain design of shaft.

A11)

Design of Shafts

Shafts are designed on the idea of power or pressure or both.

Design primarily based totally on power is to make certain that pressure at any vicinity of the shaft does now no longer exceed the fabric yield pressure.

Design primarily based totally on pressure is to make certain that most deflection (due to bending) and most twist (because of torsion) of the shaft is in the allowable limits.

Rigidity attention is likewise very vital in a few instances for instance function of an equipment hooked up at the shaft will alternate if the shaft receives deflected and if this fee is greater than a few allowable limit, it is able to result in excessive dynamic masses and noise with inside the gears.

In designing shafts on the idea of power, the subsequent instances can be considered:

(a) Shafts subjected to torque

(b) Shafts subjected to bending second

(c) Shafts subjected to mixture of torque and bending second

(d) Shafts subjected to axial masses further to mixture of torque and bending second

Q12) Explain Shafts Subjected to Torque.

A12)

Shafts Subjected to Torque

Maximum shear stress developed in a shaft subjected to torque is given by,

Where T = Twisting moment (or torque) acting upon the shaft,

J = Polar moment of inertia of the shaft about the axis of rotation

=               for solid shafts with diameter d

=             for hollow shafts with do and di as outer and inner diameter.

r = Distance from neutral axis to the outer most fibre = d/2 (or do/2)

So dimensions of the shaft subjected to torque can be determined from above relation for a known value of allowable shear stress, [τ].

Shafts Subjected to Bending Moment

Maximum bending stress developed in a shaft is given by,

Where M = Bending Moment acting upon the shaft,

I  = Moment of inertia of cross-sectional area of the shaft about the axis of rotation

=               for solid shafts with diameter d

=        for hollow shafts with do and di as outer and inner diameter.

y  = Distance from neutral axis to the outer most fibre = d / 2 (or do/2)

So dimensions of the shaft subjected to bending moment can be determined from above relation for a known value of allowable tensile stress

Q13) What is torsional rigidity?

A13)

Torsional Rigidity

For a shaft subjected twisting moment, the angle of twist is given by,

θ =

Where, T = Torque applied

L = Length of the shaft

J = Polar moment of inertia of the shaft about the axis of rotation

G = Modulus of rigidity of the shaft material

Therefore for the known values of T, L and G and allowable value of angle of twist, diameter of the shaft can be calculated.

Q14) Explain A.S.M.E. Code for Shaft Design

A14)

According to A.S.M.E. Code, the bending and twisting moment are to be multiplied by factors kb and kt respectively, to account for shock and fatigue in operating condition. Therefore, if the shaft is subjected to dynamic loading, equivalent torque and equivalent bending moment will become:

       And         

Table: Values of kb and kt for different types of loading

Q15) Explain design of coupling in detail.

A15)

• A shaft coupling is one of the maximum not unusual place device factors due to the fact it's miles simply so critical in energy transmission systems. Thus, they locate use in plenty of programs and carrier environments.
• As an end result, designers and engineers have designed many versions of couplings for unique carrier situations and environments over the years.
• This article will familiarize you with the specific sorts of couplings and talk selecting the proper alternative on your application. A coupling is a mechanical tool that connects comparable or diverse shafts in machines to transmit energy and motion.
• It is often a brief connection (however may be everlasting in a few instances) and able to elimination for carrier or replacement. A coupling can be inflexible or bendy.
• Due to the supply of many designs, there may be stark variations with inside the production and feature of sorts of mechanical couplings. Some couplings can hook up with shafts without transferring the shaft, at the same time as maximum would require shaft motion for fitting.
• In maximum instances, a coupling does now no longer alternate the path of movement or angular velocity, in contrast to gears. It can't be related or disconnected mid-operation, in contrast to clutches.
• Couplings can best switch torque over quick distances, for longer distances chain drives and belt drives are higher alternatives.
• Couplings are regularly paired with lead screw assemblies to attach the screw shaft in-line to a motor. The coupling works through keeping a sturdy however bendy connection always among shafts to switch movement from one shaft to another.
• It does so in any respect values of hundreds and misalignment without allowing any relative movement among the 2 shafts.