Engine components

Reciprocating IC Engine look quiet simple but they are highly complex machines. There are two types of engines, viz., spark-ignition (SI) and compression ignition (CI) engine.

A cross section of single cylinder spark ignition engine with overhead valves is shown in figure.

EC & IC Engines

External combustion engines are those in which combustion takes place outside the engine whereas in internal combustion engines, combustion takes place within the engine.

For example:

In a steam engine or steam turbine, the heat generated due to the combustion of fuel is employed to generate high pressure steam which is used s a working fluid in a reciprocating engine or a turbine.

In case of gasoline or diesel engines, the product of combustion generated by combustion of fuel and air within the cylinder form the working fluid.

Classification of heat engine

Engines whether IC or EC are of two types, viz.,

• Rotary engine
• Reciprocating engine

A detailed classification is given in figure

Of the various types of heat engines, the most widely used ones are the reciprocating IC Engine, the gas turbine and the steam turbine.

ENGINE

An engine is a device which transforms one form of energy into another form. However, the efficiency of conversion plys an important role. Normally most of the engines covert thermal energy into mechanical work and therefore they are called 'heat engines'.

Heat engine is a device which transforms the chemical energy of a fuel into thermal energy and utilizes this energy to perform useful work.

Heat engines can be broadly classified into two categories:

• Internal combustion engines (IC Engines)
• External combustion engines (EC Engines)

FIRE EXTINGUISHER

Dry Powder Extinguishers

These extinguishers filled with dry powder may be of the gas pressure or stored air pressure type. They are suitable for use on both Type 2 and Type 3 kind of fires.

Foam Extinguishers

These are of two main types commonly called mechanical foam and chemical foam type of fire extinguishers. They are effective against Type 2 kind of fires.

Carbon Dioxide Type Fire Extinguishers

These are filled with the carbon dioxide. It is operated by means of a plunger, lever trigger or by opening a valve. It is fitted with a distinctively shaped discharge horn. This type of fire extinguisher has only limited effectiveness against Type 1 kind of fires but is suitable for extinguishing type 2 and 3 kinds of fires.

Water Filled Fire Extinguishers

The soda acid kind is the most common kind of water extinguishers. They are most suitable for extinguishing  fire for type 1.

Vaporizing Liquid Type Fire Extinguishers

They may be filled with either carbon tetrachloride (CTC.) or chlorobromethane (CBM). Where CTC kinds of extinguishers may be of the pump, gas cartridge or stored pressure type and CBM may be either gas cartridge or stored pressure. These extinguishers are most effective against electrical kind of fire (Type 3).

Stored Air Pressure Type Extinguishers

In stored air pressure type extinguishers, the container is pressurized with air when the extinguisher is filled. The extinguisher is trigger operated and operation can be stopped at any time by releasing the trigger grip. It is suitable for type 1 kind of fire only.

Gas Pressure Type Extinguishers

In gas pressure type extinguishers the water is expelled under pressure provided by carbon dioxide gas released from cartridge filled inside the container. It is suitable for Type 1 kind of fire.

TYPES OF FIRE

Type 1

 Fires occurring due burning of ordinary combustible materials such as wood, cloth and paper.  Pouring water is the most effective way for extinguishing this kind of fire.

Type 2 

Fires occurring due burning of flammable liquids such as oils, petrol, grease and fat. For extinguishing this kind of fire water must never be used, as it excludes oxygen.

Type 3 

Fires in this category involve live electrical equipment. The extinguishing agent must be non-conducting of electricity and water must never be used for extinguishing this kind of fire.

FIRE PREVENTION

• The maximum number of workers and officers should be trained with fire fighting systems and equipments.
• Keep all flammable liquids in closed containers or in safe cylinders.
• An industry must have effective fire warning signals.
• All doors should be opened towards outside the workroom as means of escape in case of fire.
• The doors and windows to be used as exit in case of fire should be easily located. These should be marked with red letters of adequate size.
• Always select the least flammable liquid that will serve the purpose.
• One should provide ventilation to prevent any accumulation of vapors.
• Always provide suitable and adequate means of fire extinguishment.
• Every operator should be familiar with the location of fire extinguishers and their use (operation).
• Proper distance should always be there in between the heating device and any combustible material.
• Electrical wiring should be proper.
• Always prohibit smoking, open flames and sparks near the flammable materials.
• A free passageways and easily open-able windows should be always provided.
• Always provide suitable means for the safe storage and handling of all fuels used.
• Use of flammable liquids should be minimized.
• Safe disposal for the flammable liquid wastes must be provided.
• No one is permitted to accumulate fuels or other combustibles near the source of open fire or spark.

ELECTRICAL SAFETY MEASURES

• All metallic parts, externally accessible must always be earthed.
• No inflammable materials are kept near electrical appliances, electric line wires or electric control panels.
• Electric safety devices like fuse, circuit breakers over-tripping must always be used wherever required.
• All defective and worn-out electric fittings must be replaced.
• No untrained persons should be allowed to repair electrical faults.
• Safety belts, helmet, rubber gloves, boots with rubber soles, and other safety items always are used by electrician while dealing or working with high voltage. These appliances should be provided to all electric mechanics.
• Overloading of any electric circuit must be avoided.
• The electric appliances when not in use must be dis-connected from main supply.
• Power supply should be switched off always during maintenance work. Only authorized person should be allowed to switch on and off’ the power supply.
• One should avoid touching metal case of any electrical apparatus when it is in operation.
• Proper type of wiring should always be provided in all locations.
• Periodical inspection should be done to detect the damages.
• Always avoid overloading on any single point.
• Good standards of safety items must be maintained as per norms.

SAFETY PRECAUTIONS WHILE WORKING IN WELDING SHOP-2

 Arc welding

• One should use protective clothing and eye protection devices while performing arc welding operation, otherwise radiation from electric arc will damage the retina of eyes.
• One has to be sure that other people standing nearby also uses eye-protection devices from ultraviolet rays.
• Always use ear protection devices such as muffler because excessive noise caused during the process of arc welding may cause temporary or permanent hearing loss.
• Welder should keep clothing and gloves dry.
• Always keep welding cables free of grease and oil.
• One should prevent the non-insulated portion of the electrode holder from touching the welding ground or job-piece when the current is on.
• Always keep the body insulated from both the work and the metal electrode holder.
• One should carry out the welding process by standing on the insulating material like dry wood rather than on a grounded metal structure.
• It is easier and safer to establish an arc on a clean surface than on a dirty or rusty one.
• Always turn the welding machine off when it is not in use.
• One should not change the polarity switch when the machine is under use. This will burn the surface of the switch and the resulting arc can cause injury to the welder.
• Always avoid using electrode holders with defective jaws or poor insulation.

SAFETY PRECAUTIONS WHILE WORKING IN WELDING SHOP-1

Gas welding

• One should never use a leaking gas cylinder.
• One should never handle oxygen cylinders, valves, regulators, hoses or fittings with oily hands.
• Welder must not mix the gases in one cylinder.
• One should never transfer the gas from one cylinder to another.
• One should clearly mention the type of gas on the cylinder (i.e. oxygen, acetylene, etc.).
• One should use nose masks where the local exhaust ventilation is not practicable. Insist the safety officer to provide proper ventilation system.
• Always avoid skin contact with fluxes, which contain fluorides. If they will penetrate the skin, they produce severe irritation.
• One should never weld the parts, which are coated with toxic material such as lead, cadmium, zinc, mercury, or paint containing toxic. Any such coatings must be removed prior to welding.
• Acetylene gas should not be brought in direct contact with the unalloyed copper (except in torch) as it may result in a violent explosion.

SAFETY PRECAUTIONS WHILE WORKING IN CASTING SHOP

• One should use mask to avoid excessive inhalation of the dust, which may cause serious problem to health.
• Always wear protective clothes to keep safe from the heat radiating from the melting process.
• All foundry men should wear protective clothes, glasses, shoes, and gloves while handling molten metal for casting process.
• One should be alert as severe burn injury can result from spillage of the molten metal.
• Always use proper ventilation to protect from molten metal fumes and gases that evolve from the mould during pouring.
• One should not touch hot moulds and castings.
• Always use earplugs to safeguard against the heavy noise.
• One should always keep clean the work area.

SAFETY PRECAUTIONS WHILE WORKING ON LATHE MACHINE

• One should always be sure that all guards are in place before running the machine.
• Always clamp the work and tool properly with correct size of work and tool holding device.
• Always keep the machine clear of tools.
• Machine should be stopped before making measurements or adjustments.
• Wear an apron or a properly fitted shop coat. Goggles should also be used.
• One should remove necktie, wrist watch and jewellery while working.
• One should not operate the lathe until he knows the proper procedure.
• One should check the work frequently when it is being machined.
• One should check the face-plate or chuck by hand to be sure that there is no danger of the work striking any part of the lathe.
• Stop the machine and remove chips with pliers. One should not remove the chips by hand.

SAFETY GUIDELINES WHILE WORKING ON GRINDING MACHINE

• Grinding wheels badly worn or cracked should be replaced.
• The grinding wheel should be properly balanced while mounting.
• One should ensure that no combustible or flammable materials are nearby that could be ignited by sparks generated by grinding wheels during grinding operations.
• One should allow the grinding wheel to reach full speed before stepping it into the grinding position.
• Faulty wheels usually break at the start of an operation.
• Always use the face of the grinding wheel that is meant for grinding.
• One should slowly move job-pieces across the face of wheel in a uniform manner. This will keep the wheel sound.
• Grinding wheels should be checked properly timely for soundness. Suspend the wheel on a string and tap it. If the wheel rings, it is probably sound.
• One should not use a grinding wheel that has been dropped or dealt with a heavy blow, even if there is no apparent damage.
• Before using a new grinding wheel, let it run for a few seconds at the full speed to check and make sure that it is perfectly balanced.
• One should not operate the grinding wheel beyond its bursting speed.
• Follow the manufacturer’s instructions for the correct use of the grinding wheels.
• Always wear goggles during grinding or allied processes.

SAFETY PRECAUTIONS WHILE WORKING IN MACHINE SHOP

The following safety precautions or guidelines are generally adopted for every metal cutting or machining shop. They must be strictly followed for safety. Specific safety guidelines for some of the machine processes like lathe, drilling, shaping, planning slotting, grinding, milling, and finishing operations are described below:

• Use the correct tools and work holding devices recommended for the process.
• Hold the work piece and tool securely on the machine.
• Clamp the tool correctly. An overhanging tool may cause catastrophic failure of the tool, work piece or the machine tool.
• Do not try to remove chips from the machine with bare hands. Never use compressed air from mouth, use brush.
• Do not touch a job-piece with bare hands while doing inspection or removing it from the machine. Use gloves always.
• Operate the machine at recommended operating conditions based on work material and tool material combination and other cutting conditions specified.
• Use recommended coolant depending upon work-tool material combination.
• During machining ductile materials, use chip breakers and chip guards.
• Re-sharp the tools immediately when it starts producing rough surfaces on the job-piece or produces chatter.
• Never run the machines at speed higher than recommended. It may produce vibrations & chatter and may damage job-piece, tool, or both.
• Provide sufficient approach and over travel distances wherever necessary.
• In case of power failures, switch off the machine and retrieve tool from the work piece.
• Always wear goggles to protect eyes from flying chips.
• Machines are governed by the old clinch garbage input-output. The skill of the operator is often the limiting factor for the machining operation.
• Stop machine before attempting to clean, removing tool or work piece.

SAFETY PRECAUTIONS WITH CUTTING TOOLS-5

 Abrasives

• If the lathe is used for polishing, make sure that the machine is protected from the abrasive grains that fall from the polishing wheels during polishing. They can cause rapid wear of the precision parts.
• Do not rub fingers or hand across a piece that has just been polished by abrasive.
• Cuts and burns should always be treated immediately by using first aid facility.
• Always remove all the abrasive particles by washing them thoroughly after the polishing operation.

SAFETY PRECAUTIONS WITH CUTTING TOOLS-4

 Reamers

• One should remove all bars from the reamed holes.
• Never use your hands to remove chips and cutting fluids from the reamer and work. Use a piece of cotton to remove waste. 

SAFETY PRECAUTIONS WITH CUTTING TOOLS-3

 Saws

• Never test the sharpness of the blade by a running a finger across the teeth.
• Do not brush the chips away with your hand.
• All hard blades can shatter and produce flying chips. Wear your toggles & goggles.
• One should make sure that the blade is properly tensioned.
• Store the saw so that you will not accidentally reach into the teeth when you pick it up.
• If the blade breaks while you are on cutting stroke, your hand may strike the works and cause an injury. Therefore saw operator should work carefully. 

SAFETY PRECAUTIONS WITH CUTTING TOOLS-2

 Chisels

• Always hold the chisel in a way that the hammer blow may not miss the chisel to injure your hand.
• Edges of metal cut with the chisel are often sharp and cause bad cuts.
• Flying chips are dangerous. Wear transparent plastic safety goggles and use a shield when using a chisel to protect yourself and those working near you.
• Sharp edges of chisels are removed by grinding or filing.
• Mushroomed head of the chisel should be removed by grinding. 

SAFETY PRECAUTIONS WITH CUTTING TOOLS-1

 Files

• Always use a file card to clean the file. Never use your hand. The chips may penetrate in hand and cause a painful infection.
• Never use a file without a handle.
• Short burns formed in filling may cause serious cuts. Always use a piece of cloth to wipe the surface being field.
• Files are highly brittle and should never be used as a hammer otherwise the file will break.
• Never hammer on a file. It may shatter and chips may fly in all directions.

SAFETY PRECAUTIONS WITH HAND TOOLS-3

 Hammers

1. One should not operate the hammer unless its head is tightly fixed to the handle.
2. Place the hammer on the bench carefully. A falling hammer can cause serious foot injuries.
3. Never strike two hammers together. The faces are very hard and the blow might cause a chip to break off.
4. Never hold the hammer too far on the handle when striking a blow.
5. Unless the blow is struck squarely, the hammer may glance at the work.

SAFETY PRECAUTIONS WITH HAND TOOLS-2

 Wrenches

1. One should not hammer a wrench to loosen a stubborn fastener, unless the tool has been specially designed for such treatment.
2. Always pull on a wrench. One can have more control over the tool if pulling instead of pushing is done, and there is less chance of injury.
3. It is dangerous practice to lengthen the wrench handle for additional leverage. Use a larger wrench.
4. Choose a wrench that fit properly. A loose fitting wrench may slip and round off the corners of the bolt head and nut.
5. When using wrenches, clean grease or oil from the floor in the work area. This will reduce the possibility of slipping and losing balance. 

SAFETY PRECAUTIONS WITH HAND TOOLS-1

 Screw Drivers

1. When working on electrical equipment use only a screw driver with an approved handle.
2. One should wear goggles when re-sharpening screw-driver tips.
3. Screws with burred heads are dangerous and must be replaced or the burrs should be removed with file or an abrasive cloth.
4. One should use the correct tip of screw drivers while screwing. Too narrow or too wide tip will damage the work. 

SAFETY PRECAUTIONS IN WORKSHOP

 General Safety Precautions while Working in a Workshop: 

• One should not leave the machine ON even after the power is OFF and until it has stopped running completely.
• Operator should not talk to other industrial persons when he is operating a machine. 
• One should not oil, clean, adjust or repair any machine while it is running. Stop the machine and lock the power switch in the OFF position. 
• One should not operate any machine unless asked to do so by the authorized person in the shop.
• Always check whether work and cutting tools on any machine are clamped securely before starting. 
• The floor should be kept clean and clear of metal chips or curls and waste pieces.
• Defective guards must be replaced or repaired immediately.
• One should not operate any machine in absence of supervisor or instructor.
• All set screws should be of flush or recessed type. Projecting set screws are very dangerous because they catch on sleeves or clothing.
• One should not try to stop the machine with hands or body.
• Only trained operator should operate machine or switches as far as possible.
• Always take help for handling long or heavy pieces of materials.
• Always follow safe lifting practices.
• No one should run in the shop at work time.
• Always keep your body and clothes away from moving machine parts. Get first aid immediately for any injury.
• Stop the machine before making measurements or adjustments.
• Never wear necktie, loose sweater, wristwatch, bangles, rings, and loose fitting clothing while working in workshop.
• Always wear overcoat or apron.
• Stop machines before attempting to clean it.
• Make sure that all guards are in their place before starting to operate a machine. 
• Be thoroughly familiar with the ‘stop’ button and any emergency stop buttons provided on the machines.
• Remove burrs, chips and other unwanted materials as soon as possible.
• Do not leave loose rags on machines.
• Wash your hands thoroughly after working to remove oils, abrasive particles, cutting fluid, etc.
• Report all injuries to the foreman, howsoever small. Cuts and burns should be treated immediately.
• Keep your mind on the job, be alert, and be ready for any emergency.
• Always work in proper lighting.
• One should not lean against the machines.

CAUSES OF ACCIDENTS-4

The other general causes of accidents in workshops are listed below:

1. Ignorance in working with equipments, i.e., hand tools, cutting tools and machine tools.
2. Operating machine and equipments without knowledge.
3. Extra curiosity to work without knowing.
4. Due to poor working conditions.
5. Due to speedy work.
6. Improper method of work.
7. Due to use of improper tools.
8. Due to lack of discipline.
9. Due to carelessness.
10. Due to over confidence.
11. Because of excessive over times duty by industrial workers.
12. Lack of cleanliness.
13. Due to poor planning. 

CAUSES OF ACCIDENTS-3

Mechanical Causes 

• Continued use of old, poorly maintained or unsafe equipment may result in accidents.
• Accidents commonly occur due to use of unguarded or improperly guarded machines or equipments.
• Unsafe processes, unsafe design and unsafe construction of building structure may lead to accidents in the plant.
• Accidents occur due to improper material handling system and improper plant layout. 
• Accidents may occur due to non use of safety devices such as helmets, goggles, gloves, masks etc.

CAUSES OF ACCIDENTS-2

Environmental Causes 

• Accidents may occur during working at improper temperature and humidity, as it causes fatigue to the workers.
• The presence of dust fumes and smoke in the working area may cause accidents. 
• Poor housekeeping, congestion, blocked exits, bad plant layout etc. may cause accidents. 
• Accidents occur due to inadequate illumination. 
• Improper ventilation in the plant may lead to industrial accidents.

CAUSES OF ACCIDENTS-1

The accidents may take place due to human causes, environmental causes and mechanical causes. These causes are discussed as under.

Human Causes 

• Accidents may occur while working on unsafe or dangerous equipments or machineries possessing rotating, reciprocating and moving parts. 
• Accidents occur while operating machines without knowledge, without safety precautions, without authority, without safety devices. 
• Accidents generally occur while operating or working at unsafe speed. 
• Accidents may occur while working for long duration of work, shift duty etc. 
• Accidents commonly occur during use of improper tools. 
• Accidents may occur while working with mental worries, ignorance, carelessness, nervousness, dreaming etc. 
• Accidents occur because of not using personal protective devices.

EFFECT OF ACCIDENTS

The adverse effects of the accident are given as under— 
(A) Effect on the owner of factory 

• Direct cost of an accident 
• Compensation paid to the workers. 
• Money paid for treatment. 
• Monetary value of damaged tools, equipments and materials. 
• Indirect cost of an accident 
• Lost time of the injured worker. 
• Time lost by other employees. 
• Delays in production. 
• Time lost by supervisors, safety engineers etc. 
• Lowered production due to substitute workers. 

(B) Effect on worker 

• The industrial workers may get temporary or permanent disability. 
• If the industrial worker dies, his family loses the earner and the compensation never equals to his earnings. 
• Accident also affects the morale of the employees working in the manufacturing environment. 

(C) Effect on society 
Work connected with injuries put a considerable burden on society. It is given as under:

• Cost of accidents is included in the products, so the society has to pay more prices for the industrial products. 
• If some industrial workers do not come under compensation act, the need for help from society is much greater. 
• Loss of production hours may causes fewer products in market. So more prices if demand is more than production.

ACCIDENTS

The accidents are the mishaps leading injury to man, machines or tools and equipment and may cause injury and result either death or temporary disablement or permanent disablement of the industrial employees.

There are various types of common accidents  as follows: 

• Near Accident: An accident with no damage or injury is called near accident. 
• Trivial: An accident with very less damage is called trivial. 
• Minor Accident: It is an accident with damage and injury more than trivial. 
• Serious Accident: An accident with heavy damage and lot of injury is called serious accident. 
• Fatal: It is an accident with very heavy damage. There may be loss of lives also.

INVERSIONS OF DOUBLE SLIDER

Elliptical trammel
It is a device used to trace ellipses. Here frame is fixed and the sliders translates inside it making every points on the connecting rod to trace an ellipse.






Oldham Coupling
It is a device used to connect two parallel offset beams. Here sliders are perpendicular to each other connected by a disc. Their translation results in the rotation of frame.

Watch mechanism of Elliptical Trammel

Watch mechanism of Oldham Coupling

INVERSIONS OF SINGLE SLIDER

First inversion
frame is fixed and slider reciprocates.
Example:
Reciprocating engine



Second inversion
Crank is fixed hence cylinder acts as crank (i.e.,it rotates).
Example:
- Witworth quick return motion mechanism
- Rotary engine


Third inversion
Connecting rod is fixed hence cylinder acts as connecting rod (i.e., it oscillates).
Example:
- Oscillating cylinder engine
- Crank and slotted lever mechanism



Fourth inversion
Slider is fixed
Example:
Handpump

Watch mechanism of Reciprocating Engine

Watch mechanism of Rotary Engine (Gnome)

Watch mechanism of Osillating Engine

Watch mechanism of Hand Pump

SLIDER CRANK CHAIN

When one of the turning pair of a four bar chain is replaced by a sliding pair then it is called as single slider crank chain.

It is also possible two replace two sliding pairs of a four bar chain to get double slider crank chain.

Different mechanisms obtained by fixing different links of a kinematic chain are termed as inversions.

KINEMATIC CHAIN

A kinematic chain is a assembly of links in which relative motion of links is possible and the motion of each relative to other is definite.

Degree of freedom of a plane mechanism can be calculated using GRUEBLER'S CRITERION, i.e., F=3(N-1)-2P-Q where each movable link possess 3 degree of freedom.

For linkages with single degree of freedom KUTZBACK'S CRITERION is followed, i.e., 2P=3N-4 

In the above equations-
N = total number of links in a mechanism
:. N-1 = number of movable links
F = degree of freedom
P = number of pairs having one degree of freedom
Q = number of pairs having two degree of freedom

DEGREE OF FREEDOM

An unconstrained rigid body in space can describe the following independent motions:

1. Translational motion along any three mutually perpendicular axes (x, y, or z)
2. Rotational motion about these axes

• A rigid body possess 6 degree of freedom
• for a body, number of restraints can never be-
• six (joint becomes solid)
• zero (joint is disconnected)

Degree of freedom of a pair is defined as the number of independent relative motion, both translational and rotational.

Degree of freedom of a pair = 6 - number of restraints

KINEMATIC PAIR- RELATIVE MOTION

On the basis of nature of relative motion kinematic pairs can be classified as:
* Sliding Pair
* Turning Pair
* Rolling Pair
* Helical Pair
* Spherical Pair

Sliding Pair
If two links have sliding motion relative to each other.
Example:
A rectangular rod in a rectangular hole

Turning Pair
When one link has a revolving motion relative to other.
Example:
Circular shaft revolving inside a bearing

Rolling Pair
If links of pair have rolling motion relative to each other.
Example:
Ball and roller bearings

Helical Pair (Screw Pair)
When the links of a pair have turning as well as sliding motion.
Example:
nut-bolt

Spherical Pair
If one of the two links is spherical and it turns inside the other.
Example:
Ball and socket joint

KINEMATIC PAIR- MECHANICAL CONSTRAINT

According to nature of mechanical constraint kinematic pairs can be classified as:
* Closed pair
* Unclosed pair

Closed Pair
- When the elements of the pair are held together mechanically
- Elements are geometrically identical
- Contact can be broken only by destruction of atleast one member
Example:
Screw pair



Unclosed Pair
- When elements are connected either by force of gravity or by spring action
- Links are not held together mechanically
Example:
Cam and follower pair

KINEMATIC PAIR- NATURE OF CONTACT

According to nature of contact kinematic pairs can be classified as:

* Higher Pair
* Lower Pair

HIGHER PAIR

When the pairs has point or line contact. Or the contact surface is dissimilar.

Example:

- Ball and roller bearings

- Cam and follower pair, etc...

 

LOWER PAIR

When the pairs has surface or area contact. Or the contact surface is similar.

Example:

- Nut turning on a screw

- Universal joint, etc...

KINEMATIC PAIR

When two links combine to form a pair such that the motion between them is completely or successfully constrained, then they are termed as kinematic pair.

They can be classified according to:

- Nature of contact
- Nature of mechanical constraint
- Nature of relative motion

CONSTRAINT MOTION

There are 3 types of constraint motion:


Completely constraint motion:-

when the motion between 2 elements of a pair is in definite direction irrespective of the direction of the force applied.

Example:

sliding pair

turning pair

Incompletely constraint motion:-

when the motion between 2 elements of a pair is possible in more than one direction depending on the fore applied.

Example:

a circular shaft without collar

Successfully constraint motion:-

when motion between 2 elements of a pair is possible in more than one direction but is constrained to remain in one direction by application of external forces.

Example:

Foot step bearing

MOTION

Motion is a change in position of an object with respect to time. 

Motion is typically described in terms of displacement, distance (scalar), velocity, acceleration, time and speed.

Machines

When mechanisms combine to produce work they are termed as machines.

Example:
- Engine is a machine and reciprocation of piston inside cylinder due to rotation of crank is a mechanism

- Lathe machine
- Shaper machine
- Slotter machine
- Drilling machine
- Sewing machine
- Washing machine which works on electrical mechanism
- Grinder, etc....

Mechanism

if a number of bodies are connected in such a way that the motion of one constrains the motion of other, or gives a predictable motion then it is called as mechanism.

Examples:

motion of hands of clock

internal combustion engine

rope drives

chain drives

gears, etc...

watch mechanism of a watch