INTRODUCTION TO HEALTH, SAFETY, AND ENVIROMENT.

Relevance of Health Safety, and Environment  to Industry, the employer and employee, and the Community.

Health: Physical Condition.

 1. Every individual wants to be fit and healthy to enable him work to earn a living.

 2.   The employer needs his employee to be of good health to be able to perform to standard required for the achievement of set goals.

3. The community needs healthy members who will contribute effectively to community affairs- financially, physically and mentally.
4. The nation needs citizens who would pay taxes  as well as contribute physically and mentally.
5. Families need their breadwinner and companion. 

Safety: A state of being free from danger or harm (injury or damage).

 1.  Every individual wants to be safe for a worthy life.         

  2. A business organization needs its employees to be safe for continuous 

     operation to meets targets and objectives, as well as to conserve its vital

     resources.

 3. Families, communities and the nation all need their kins-folk to be safe to continue to provide needs, service, and contributions-physical, mental and financial.

Environment: The air, water, and land in which people, animals and plant live

sustain the quality of life of the people and activities located within its confines.

The foregoing paragraphs emphasize the relevance of health, safety, and environment to industry, its people, its assets, and the environment within which they are located, and the reason why every effort deserves to be made to prevent negative activities or conditions that would impact adversely on them that would in turn harm people, assets and the environment.

ACCIDENTS.

Industries activities generally involve people, machines, materials, chemicals and the

environments. In the course of operations in which these elements interacts, it does

happen that one or the elements is upon adversely and there is injury or damage, and

it is said an accident has occurred. The negative actions or situations are usually

unplanned, unexpected, and the resultant impact unwanted. Hence the definition of

an accidents as ‘an’ unplanned and unwanted occurrence caused by unsafe acts and

unsafe conditions which result in injury or damage. and sometimes both injury and

damage, or neither (the near miss)

CONSEQUENCES OF ACCIDENTS

Accidents impact adversely on the industry, its  people,plants,machinery,equipment

and the environment within which the industry is located. When an accidents occurs

in an industry, directly affected are usually-

   1.  The injured employee: physical pain, mental agony, disability (temporary or permanent), and loss of leisure, earning, and life.

   2.The company: economic loss, production loss, time, reputation, possible litigation.

       Usually affected indirectly are:-

   1. Family of injured employee: loss of breadwinner.

   2. Community: contributions-financial, mental, physical.

  3. The Nation: Taxes paid by the company and the employee.

 The reasons for which accidents are considered undesirable are usually summarized

as-

   1. humanitarian.

   2.Economic.

   3. Legal.

   4. morale.

   5. Reputation

Since these consequences are undesirable it is imperative that effort should be

directed at preventing  accidents.  This can be achieved through an understanding of

the factors responsible for the occurrence of accidents and eliminating them or

making provisions for effectively controlling them or mitigating the effect of the

occurrence.

ACCIDENT CAUSES

Research has establish that accidents are caused by unsafe acts and

unsafe conditions.

Unsafe acts are defined  are defined as actions taking or performed by someone without due regard for personal safety, that of colleagues or other persons in the vicinity .  These are acts usually contrary to rules and regulations, or accepted standard practices and procedures – they are ilegal acts .

ACCIDENT PREVENTION MEASURES.

       With the acceptance of the assertion that accidents are caused, it is also accepted that identified as being responsible for unsafe acts and the existence of unsafe conditions. They are said to act unsafely and permit the existence of unsafe conditions because of the following defects in them-

    1. Does not know: ignorance, not trained ,not instructed, not informed.

     2.Cannot: physically or mentally unable.

    3. Does not want to: wrong attitude.

      Measures to prevent accidents would therefore seek to identify and correct the unsafe acts of people and the unsafe conditions in the work environment, as well as identify and correct the defects in the people, for a permanent solution to the accidents problem. Measures adopted are therefore those of-

       1. Engineering.

        2. Education.

        3. Enforcement.

        4. Encouragement.

       Engineering takes the unsafe conditions out the work environment: Education takes the defects out of the people through training, induction,nstruction,rules, policies, procedures,seminars ,etc.;Enforcement ensures that people comply with and apply all that they have been taught and instructed to do through effective supervision,inspections,audits, and reports ;encouragement by recognition, incentives,awards,and promotion, boosts the morale of employees and makes them react more positively to the requirements of the employment, which has a salutary effect on production.

BENEFITS DERIVABLE FROM SAFE OPERATIONS.

Safety pays great dividends to all  stakeholders.

The company has to continued service of a healthy , competent and

efficient workforce, which ensures achievement of targeted

quality and quantity of production, conservation of funds that would

otherwise have been spent on medical, compensation, and lost time

bills, and greater profits.

The employee remains healthy and fit, and is in position to achieve

his life ambition. He is able to fully enjoy the company of his family

and associates, his leisure and hobbies. He remains in the

employments and is employable in an appropriate job, with full

earning capability. He has full hope of improved conditions and

elevation if he continues to give good service unhindered by injury or

ill health.

The family is happy the breadwinner is always available to provide

for them the pleasures and necessities of life.

The community continues to reap the benefits of the contributions of

a worthy member.

Government earns increased revenue from the increased profits

earned by the company, and from, the employee who pays tax from

his earnings.

•          HAZARDS AND EFFECTS MANAGEMENT PROCESS-

•          The process for those critical operations and installation should include

•           An inventory of the major hazards to the environment and to the health and safety of people of all the activities, materials, products and services; and

•          An assessments of the related risks, implementation of measures to control these risks and to recover in case of control failure.

•           Planning and procedures-adequate standards and procedures shall be in place and understood at the appropriates organization levels.preparation,review and distribution of all key reference documents shall be adequately controlled.

•          HSE; standards include;procedures;and work instructions; permit to work; concurrent operations; emergency response procedures (including medical emergencies) shall be regularly tested.

•          Implementation and monitoring- HSE performance targets shall be set to ensure progression towards the long-term goals of no harm to people and n o damage to the environment. performance indicators shall be established, monitored and results reported in away that can be externally verified. All HSE incidents and near misses with significant actual or potential consequences shall be thoroughly investigated and reported.

•          HSE RULES AND PROCEDURES.

•          HSE rules are meant to ensure that the company’s HSE objectives are realized. They enable the policy of the company to pursue the goal of no harm to people- its staff, other persons, and to protect the environment.

•          These set rules and procedures are required to be adhered to while executing any task. Strict adherence will prevent accidents that could result in injury to people, or  loss of product and lead to pollution of the environment and exposure of persons to health hazards.

•          PERSONAL PROTECTIVE EQUIPMENT  (PPE)

•          INTRODUCTION

•          The Board of Directors of the National Safety Council (US), in 1949, declared, in a former statement of policy;  ‘ The elimination of accidents is vital to the public interest.  Accidents produces economic and social loss impair individual and group productivity, cause inefficiency, and retard the advancement of standards of living’. The thus emphasis the need to prevent accidents and protect the workers , using every possible advice.

•          The primary approach in any accident prevention effort is the correction of the physical environment so that accident cannot occur.   However, it does not happen sometimes that the nature of the operations requires that the personnel should also be safe guided, by equipping them individually with Personal Protective Equipment (PPE).  Then it should be noted that these PPE should be considered only as a ‘second line or last line’ of deface in accident prevention. PPE does not prevent the accident or remove the hazard it only serves to prevent contact with the hazard , minimize the effect of the hazard on the worker or reduce the severity of the injury from the accident.  It will be wrong for a worker to deliberately expose himself to a hazard because he is wearing some form of protective equipment.

•          DEFINITION

•          Personal Protective Equipment are pieces of equipment; gadgets, and apparels used or worn by workers to protect them against the hazards, existing in their work situation or environment .

•          The provision of PPE + by management, and their use by employees is a statutory requirement ideally design to protect or minimize the impact of accidents on a worker in a work site.

•                                          TYPES AND KINDS OF PPE

1. HEAD AND PROTECTION.
2.  SAFETY HATS: These are equipment  used to protect the head against falling or flying objects, menace by bumps, liquids leaking from facilities. They are made of metal, plastic, glass fiber impregnated with resin, and some non-metallic materials.  Impact resistance is essential.   Where contact with energized circuits is possible, only hats that meet the   requirement of class B. ANSI Z89.1(i.e tested at 20 volt). They are different types shapes styles and shades for different work situation

3. EYE PROTECTION: They are various types and styles of eye protection equipment mainly, for protection of the eyes against flying objects and particles, splashes of corrosive liquids or molten metals, dust , and harmful radiations.  They include:

       Cup Goggles, Cover Goggles, Welders’ goggles, Melters’ Goggles, Protective Spectacles e.t.c .

4. FOOT PROTECTION: Consists of safety shoes boots, job master, and swamp shoes. 

5. FACE SHIELD:  They are used for the protection of the face and neck against light impact, flying particles, hazardous chemicals, heat, radiation,

6. Hand Gloves: They are used for protection of fingers palms and hands from burns, cuts, and bruises, scratched.

7. EAR PROTECTION: Assorted types and styles, design for the protection of ear from high damaging sound.  They are Ear muffs and Ear plugs.

8. RESPIRATORY EQUIPMENT: For the protection against inhalation of dangerous substances e.g. dusts, fumes, and tiny air particles.

9. OVERALL/APRONS:  Protect the body from contact with heat, corrosive and/or toxic substances.

10. FIRE SUIT: For fire fighting

                          REASONS FOR NOT WEARING PPE

It is commonly observed that some workers resent using the PPE they are

expected to wear why performing their duties.  The advance reasons with

psychological, egotistical and economic undertones these includes:-

•          Discomfort, due to weather conditions

•          Wrong Size (oversize/undersized).

•          Due not keep pace with fashion trends.

•          Exposure of grade of workers.

•          Payment for the equipment.

MEASURES TO ENSURE EFFECTIVE USE OF PPE.

Effort must be made to persuade workers to use PPE issue to them

attention should be drawn to the fact that it is statutory requirement.

They should be a proper education and the need and the importance of the use of PPE.

The following measures are recommended:-

1. EDUCATION: Workers should be thoroughly educated in the need and the importance of PPE. .These will enable them to bear whatever discomfort the equipment might cause them. They will be concerned with their safety rather than their ego.

2. CHOICE OF THE STYLE: Resentment due to vagaries of fashion can be solve by allowing employees to choose from a group of pre- selected style of PPE. They will thus have no excuse for refusing to use them.

3. AS A CONDITION FOR EMPLOYMENT: The compulsory use of PPE should be a condition for employment. 

4. FREE ISSUE OF PPE: All PPE that an employee must wear while performing his job should be provided free of charge.

5.            SANCTION FOR NOT WEARING IT: There should be penalty for an employee failing o wear provided PPE where it should be worn.

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DEVELOPMENT OF PALM FRUIT FIBRE REINFORCED COMPOSITE FOR CAR BUMPER

OBJECTIVES:

The objective of this research work is to develop new and improved material from farm waste that is necessary for Local Content addition in Automotive industry.

INTRODUCTION:

Most current researches are geared towards the engineering of Composites materials to achieve properties and characteristics that are better and more desirable than the primary metal, polymer or ceramics. These properties promote the use of Composite materials for various engineering applications.  Palm is native and widely cultivated in this environment  and palm chaff  is a waste material that could be developed as fibre  component  of  composites that could have resourceful application in the automobile industry especially in the production of  automobile bumper. It is hoped that the research will facilitate the current government Local Content initiatives and Automotive Policy. 

METHODOLOGY:

       Palm fibre preparation.

  Production of the palm fibre reinforced composite.

        Mechanical test.

       Simulation using CAD.

       Fabrication of the car bumper.

ENVISAGED CONTRIBUTION TO KNOWLEDGE:

        i.            This research will help to discover new and improved material that could be used for production Car Bumper.

      ii.            The research will help discover the industrial use of Palm chaff which is regarded as Farm waste.

           Contact us for the full project topic @shadowfactonline@gmail.com

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ELECTRICAL PANEL AND ITS COMPONENTS OF A COMPUTER NUMERIC CONTROL MACHINE PRESENTED

                   ABSTRACT

This deals with the control system of a computer numeric control machine and its associated interaction with electromechanically devices. Also, here we shall be looking at the various components such as circuit breakers, contactors, relays etc that makes this control system possible. This component’s description, operation, types and uses shall as well be discussed.

INTRODUCTION

The use of simple electrical components for the designing and constructing of a panel capable of controlling an electrical machine both in the forward and reverse directions has led to automation engineering and subsequently to Computer Numeric Control machine technology. The computer numeric control (CNC) panel is the automated design part of a CNC machine where electrical inputs are fed and controlled. Such control includes the spindle motor, the X,Y, motors, the coolant motors etc. It is made up of both electrical and electronics components. Here emphasis shall be laid on the electrical components as much of it does the control system.

Below is an outline of the various components used in a CNC control panel;

Circuit breaker

Control transformer

Motor protection switch

Contactors

Rectifier

Relays e. t. c.

CIRCUIT BREAKERS 

DESCRIPTION

break An early form of circuit breaker was described by Thomas Alva Edison in an 1879 patent application, although his commercial power distribution system used fuses.^[1] Its purpose was to protect lighting circuit wiring from accidental short-circuits and overloads.

OPERATION OF A CIRCUIT BREAKER

All circuit breakers have common features in their operation, although details vary substantially depending on the voltage class, current rating and type of the circuit breaker. The circuit breaker must detect a fault condition; in low-voltage circuit breakers this is usually done within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged with pilot devices to sense a fault current and to operate the trip opening mechanism.                           

The trip solenoid that releases the latch is usually energized by a separate battery, although some high-voltage circuit breakers are self-contained with current transformers, protection relays, and an internal control power source. Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit.

The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting the circuit.

Contacts are made of copper or copper alloys, silver alloys, and other materials.

Service life of the contacts is limited by the erosion due to interrupting the arc. Miniature and molded case circuit breakers are usually discarded when the contacts are worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts.

POLES OF A CIRCUIT BREAKER

Circuit breaker poles are usually expressed in 1p, 2p, 3p, 4p, e.t.c. this indicates the terminal(s) of the breaker.

 

TYPES OF CIRCUIT BREAKER.

Low voltage circuit breakers

Magnetic circuit breaker

Thermal magnetic circuit breaker Common trip breakers

High-voltage circuit breakers

Sulfur hexafluoride (SF₆) high-voltage circuit-breakers

Other breakers

Breakers for protections against earth faults too small to trip an over-current device:

Residual-current device (RCD, formerly known as a residual current circuit breaker) — detects current imbalance, but does not provide over-current protection.

Residual current breaker with over-current protection (RCBO) — combines the functions of an RCD and an MCB in one package. In the United States and Canada, panel-mounted devices that combine ground (earth) fault detection and over-current protection are called Ground Fault Circuit Interrupter (GFCI) breakers; a wall mounted outlet device providing ground fault detection only is called a GFI.

Earth leakage circuit breaker (ELCB) — This detects earth current directly rather than detecting imbalance. They are no longer seen in new installations for various reasons

Autorecloser — A type of circuit breaker which closes again after a delay. These are used on overhead power distribution systems, to prevent short duration faults from causing sustained outages.

Polyswitch (polyfuse) — A small device commonly described as an automatically resetting fuse rather than a circuit breaker

 

CONTROL TRANSFORMER

A control transformer is a device used to transform or "step down" a high main circuit voltage to a lower voltage which is then used to operate the control or switching components of the main circuit. These devices are commonly used in industrial starter circuits where the main circuit voltage is not suitable for use in the control circuit and where a separate control circuit feed would not be practical. For example in a starter panel designed to start a 500 volt electric motor, the contactors and relays used to switch the motor on or off would typically use electromagnetic coils rated for a far lower voltage.

 

USES OF CONTROL TRANFORMER

To supply this voltage without the need for a separate power feed, power is tapped off the main incoming 500 volt feed and passed through a control transformer which would then supply the lower control circuit voltage.

Heavy electrical machinery that starts automatically or remotely generally makes use of contactors which rely on an electromagnetic force to close them to start the machinery. This force is created by an electric coil placed in the center of a laminated steel core. These coils are typically designed to operate at fairly low voltages, ranging from 110 volts to as low as 12 volts. As these machines themselves typically run on far higher voltages, this creates the need for a separate control voltage feed.

 

Instead of having to run separate cables or install extra sets of bus bars, it is far simpler to use the main circuit voltage and step it down with a control transformer to the appropriate control voltage. Low control circuit voltages are used for various reasons including the fact that parts of the control circuit include push buttons in a remote control room, on the starter panel door, and at the machine itself. It would not be wise to have high voltages used in these applications for obvious safety reasons. It is also undesirable to have densely packed control wiring carrying very high voltages inside the starter panel either. For these reasons, lower voltages are typically used in control circuits.

Another benefit of using a control transformer is the inherent stability of the voltage supplied from a transformer as well as its ability to handle extreme peaks in demand. When the start button on a motor starter is pushed and the contactor coil energizes, there is a very brief (typically 30 to 50 milliseconds) surge in current demand known as an "inrush current". This peak can exceed 10 times the normal current flow, and transformers handle these peaks far more efficiently than a conventional supply. Using a control transformer to supply control power thus allows a lower, safer and more efficient control circuit voltage to be used in high working voltage applications. The excellent inrush current handling characteristics of transformer supplied power also makes for a more efficient power supply. Lastly, the use of lower voltages in a control circuit make for far safer use by workers using stop and start buttons in hazardous environments.

                                        Motor protection switch

Mainly used for overload and short-circuit protections of motor in AC 50/60Hz, up to 660V, 0.1 to 80A power circuit
     Full voltage starter to start and cut-off motor
     Under AC-3 load or for the overload and short-circuit protection of circuit and power equipment in power distribution network

Conform to IEC60947.2 and IEC 60947-4.1 as well as the EN60947-1 standard
     Mainly used for overload and short-circuit protections of motor in AC 50/60Hz, up to 660V, 0.1 to 80A power circuit
     Full voltage starter to start and cut-off motor
     Under AC-3 load or for the overload and short-circuit protection of circuit and power equipment in power distribution network

CONTACTOR

Contactors are electrical devices used to control electric motors, lighting, heating, and other electrical loads.

A contactor is an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings.^[1] A contactor is controlled by a circuit which has a much lower power level than the switched circuit. A contactor is composed of three different items. The contacts are the current carrying part of the contactor. This includes power contacts, auxiliary contacts, and contact springs. The electromagnet provides the driving force to close the contacts. The enclosure is a frame housing the contact and the electromagnet. Enclosures are made of insulating materials like Bakelite, Nylon 6, and thermosetting plastics to protect and insulate the contacts and to provide some measure of protection against personnel touching the contacts. Open-frame contactors may have a further enclosure to protect against dust, oil, explosion hazards and weather.

 

OPERATING PRINCIPLE

Unlike general-purpose relays, contactors are designed to be directly connected to high-current load devices. Relays tend to be of lower capacity and are usually designed for both normally closed and normally open applications. Devices switching more than 15 amperes or in circuits rated more than a few kilowatts are usually called contactors. Apart from optional auxiliary low current contacts, contactors are almost exclusively fitted with normally open contacts. Unlike relays, contactors are designed with features to control and suppress the arc produced when interrupting heavy motor currents. When current passes through the electromagnet, a magnetic field is produced, which attracts the moving core of the contactor. The electromagnet coil draws more current initially, until its inductance increases when the metal core enters the coil. The moving contact is propelled by the moving core; the force developed by the electromagnet holds the moving and fixed contacts together.

 

When the contactor coil is de-energized, gravity or a spring returns the electromagnet core to its initial position and opens the contacts .

For contactors energized with alternating current, a small part of the core is surrounded with a shading coil, which slightly delays the magnetic flux in the core. The effect is to average out the alternating pull of the magnetic field and so prevent the core from buzzing at twice line frequency.

Most motor control contactors at low voltages (600 volts and less) are air break contactors; air at atmospheric pressure surrounds the contacts and extinguishes the arc when interrupting the circuit. Modern medium-voltage motor controllers use vacuum contactors. High voltage contactors (greater than 1000 volts) may use vacuum or an inert gas around the contacts.

 

APPLICATIONS/USES

Lighting control

Contactors are often used to provide central control of large lighting installations, such as an office building or retail building. To reduce power consumption in the contactor coils, latching contactors are used, which have two operating coils. One coil, momentarily energized, closes the power circuit contacts, which are then mechanically held closed; the second coil opens the contacts.

Magnetic starter

A magnetic starter is a contactor designed to provide power to electric motors. The magnetic starter has an overload relay, which will open the control voltage to the starter coil if it detects an overload on a motor.^[

Overload relays may rely on heat produced by the motor current to operate a bimetal contact or release a contact held closed by a low-melting-point alloy. The overload relay opens a set of contacts that are wired in series with the supply to the contactor feeding the motor. The characteristics of the heaters can be matched to the motor so that the motor is protected against overload. Recently, microprocessor-controlled motor digital protective relays offer more comprehensive protection of motors.

PICTURE OF A CONTACTOR

The picture below shows the nature, appearance and connection of a typical contactor.

Motor control contactors can be fitted with short-circuit protection (fuses or circuit breakers), disconnecting means, overload relays and an enclosure to make a combination starter. Several combination starters and other switchgear and control devices can be grouped in a common enclosure called a motor control center/panel.

 

RECTIFIER

A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which is in only one direction, a process known as rectification. Rectifiers have many uses including as components of power supplies and as detectors of radio signals. Rectifiers may be made of solid state diodes, vacuum tube diodes, mercury arc valves, and other components.

A device which performs the opposite function (converting DC to AC) is known as an inverter.

When only one diode is used to rectify AC (by blocking the negative or positive portion of the waveform), the difference between the term diode and the term rectifier is merely one of usage, i.e., the term rectifier describes a diode that is being used to convert AC to DC. Almost all rectifiers comprise a number of diodes in a specific arrangement for more efficiently converting AC to DC than is possible with only one diode. Before the development of silicon semiconductor rectifiers, vacuum tube diodes and copper(I) oxide or selenium rectifier stacks were used

 

HALF-WAVE RECTIFICATION.

In half wave rectification, either the positive or negative half of the AC wave is passed, while the other half is blocked. Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer. Half-wave rectification can be achieved with a single diode in a one-phase supply, or with three diodes in a three-phase supply. The output DC voltage of a half wave rectifier can be calculated with the following two ideal equations:^[1]

FULL-WAVE RECTIFICATION.

A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to DC (direct current), and is more efficient.

However, in a circuit with a non-center tapped transformer, four diodes are required instead of the one needed for half-wave rectification.

For single-phase AC, if the transformer is center-tapped, then two diodes back-to-back (i.e. anodes-to-anode or cathode-to-cathode) can form a full-wave rectifier. Twice as many windings are required on the transformer secondary to obtain the same output voltage compared to the bridge rectifier above.

Full-wave rectifier using a center tap transformer and 2 diodes.

 

The average and root-mean-square output voltages of an ideal single phase full wave rectifier can be calculated as

 

V_r.m.s = V_p/√2

 

V_dc,V_av - the average or DC output voltage,

V_p - the peak value of half wave,

V_rms - the root-mean-square value of output voltage.

π = ~ 3.14159

 

RELAYS

DESCRIPTION

A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have two switch positions and most have double throw (changeover) switch contacts as shown in the diagram.

OPERATION OF A RELAY

Relays allow one circuit to switch a second circuit which can be completely separated from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit. There is no electrical connection inside the relay between the two circuits, the link is magnetic and mechanical. Relays are usually SPDT or DPDT but they can have many more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily available.

The relay's switch connections are usually labeled COM, NC and NO:

COM = Common, always connect to this, it is the moving part of the switch.

NC = Normally Closed, COM is connected to this when the relay coil is off.

NO = Normally Open, COM is connected to this when the relay coil is on.

Connect to COM and NO if you want the switched circuit to be on when the relay coil is on.

Connect to COM and NC if you want the switched circuit to be on when the relay coil is off.

 

Protection diodes for relays

Transistors and ICs must be protected from the brief high voltage produced when a relay coil is switched off. The diagram shows how a signal diode (eg 1N4148) is connected 'backwards' across the relay coil to provide this protection.

Current flowing through a relay coil creates a magnetic field which collapses suddenly when the current is switched off. The sudden collapse of the magnetic field induces a brief high voltage across the relay coil which is very likely to damage transistors and ICs. The protection diode allows the induced voltage to drive a brief current through the coil (and diode) so the magnetic field dies away quickly rather than instantly. This prevents the induced voltage becoming high enough to cause damage to transistors and ICs.

USES/APPLICATIONS OF RELAYS

Relays are used to switch AC and DC

Relays can switch higher voltages.

Relays are often a better choice for switching large currents (> 5A).

Relays can switch many contacts.

CONCLUSION

With the use of control panel, the production of convectional machine has become uncommon in the field of engineering and technology and subsequently makes machine automatic in operation. Today over 50% of our machines in the workshop can be operated with little or no human intervention. Therefore, for an efficient and effective maintenance of computer numeric control machines, a sound knowledge of paneling is essential.                     

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THE MACHINIST’S TRADE AND THE MACHINE SHOP

ABSTRACT

This presentation introduces the machinist’s trade, and further deals on the essential sector in the machine shop. A brief description of a machine shop equipment, processes and safety  is emphasized.

INTRODUCTION

The machinist’s trade has made possible what we today call the atomic age, the technological revolution or the electronic age. Without the machinist there would be no engines or dynamos to generate power or any  machinery to produce anything.

The machinist's trade is a great trade in its vital necessity, great in its ever-increasing interest and great in the opportunity it offers for improvement, advancement and self-actualization.

 

Many great inventors in Europe and America started as machinists in their youth. In the wider engineering world, the machinist’s trade is known as Machine Shop Engineering and also as Production engineering. The machine tool principle remains the same irrespective of the thousands of machines built and assembled.

THE MACHINIST (The Machine Operator)

This is the operator of a certain machine for doing a certain class of work in a machine shop or in a factory. The machine operator must be skilled in the use of all the attachments of the special machine. He is skilled in the operation of one machine.

The machinist is skilled in the operation of most of the machines in  the machine shop. To acquire the status of a good machinist, it involves hard work, serious study and sacrifice of money at the start. For the engineering student, knowledge of machine shop practice is absolutely necessary. To enable the engineer to design and aid in the manufacturing of  machine tools, he/she must know what these tools are able to do.

 If he/she aspires to be a production engineer, one who decides which machine tools will do certain machining operations, he must have a thorough knowledge of machine shop practice.

WHAT IS A MACHINE SHOP

It is place where metal parts are cut to the required shape and size required and put together to form mechanical units or machines. The machines so made are used directly or indirectly in the production of the necessities and luxuries of civilization. Machine workshop is the basis or foundation of all mechanical production.

 

MACHINE  SHOP EQUIPMENT

These consist of certain standard machine tools, the size, the number and kind of machine tools depending upon the product of the shop. They include the tools used at the bench and on the floor, the measuring and adjusting tools, the work-holding and tool-holding accessories and the small tools used on the machines shop.

STANDARD MACHINE TOOLS

The standard machine tools include:

•             Centre lathes and its vastly improved models

•             Milling machines

•             Shaping machines

•             Drilling machines

•             Power saws

•             Grinding machine

•             Boring machines

•             Planing machines

•             Threading machines

•             Jig mils

                  SEQUENCE OF OPERATION ON CENTRE LATHE

Sequence of operation is the systematical and orderly arrangement of all undertaking operations needed for the production of a work piece.

EXAMPLE: The work piece in figure 1 below, is to be turned on the centre lathe machine, prepare an operational sequence for the machining of the component

LATHE TURNING TOOLS (TOOL ANGLES)

•                    CLEARANCE ANGLES: The clearance angle allows the tool to bite into the work piece and reduces friction so that the tool lasts longer. Lathe tools are ground with side clearance angle  limited to between 5˚ and 10˚. If it is too small the tool rubs and wears out quickly or does not cut at all. If it is too large the tool is widened leading to short tool life and tends to ‘’dig in ‘’ and ``chatter’’ producing a poor finish on the work piece. Clearances ensure contact between the actual cutting edge of the tool and the work.

•                 RAKE ANGLE: The rake is an important angle which influences chip formation. It affects the type of chips, the cutting force, tool wear and the roughness of the finished surface. Increasing this angle makes cutting easier for ductile and low-strength materials but the strength of the cutting edge is reduced.

•                 TOOL OR WEDGE ANGLE: This is the actual angle of the tool wedge. Increasing it makes the tool stronger but increase the cutting force. Increasing it also backs up the cutting edge with greater mass of metal which conducts away the heat cutting more quickly and increases tool life and vice versa.

BENCH WORK AND FLOOR WORK

Bench work in a machine shop company involves laying or making out, assembling and the final fitting of parts. When the same operations are performed on the floor, floor work applies. The machine shop produces parts machined from stock material, finished castings, forging etc requiring machine surfaces. Cylindrical and conical  surfaces are machined on the lathe. Flat or plane surfaces are machined on a planer, shaper, milling, broaching machine or in some cases (facing) on a lathe.

Holes are drilled, reamed, counter bored and counter-sunk on a drill press or lathe machine, for exact work, grinding machines with wheels of abrasive material are used. Grinders are also coming into greatly increased use for operation formerly made with cutting tools.  In quantity production, many special machine tools and automatic machines are in use. The special tools, jigs and fixtures made for the machine parts, are held in the tool room (store) ready for machine shop.

All machining operations remove metal either to make a smoother and more accurate surface, as by planing, facing, milling e t c, or to produce  a surface not previously existing, as by drilling , punching etc. The metal is removed by a hardened steel, carbide or diamond cutting tool (machining) or an abrasive wheel(grinding).

All machining methods are classified according to the operating principle of the machine performing the work.

MACHINE TOOL HAZARDS:

Machine tool and machine shop hazards comes from various sources:

•                 Improper Guards: improper guarding of the mechanical drive (transmission) system-pulleys, belts, gears, coupling etc.

•                 Faulty wiring.

•                 Individual motor drive- electric problem caused by breaking in the insulation on the electrical controls.

•                 All machine tools have these points in common

•              They use driving power of one sort or other.

•Their tools have sharp cutting edges

•They have dangerous moving parts

•They throw off flying chips or swarf

5. Method of handling materials

6.Falling  objects

7. Difficulties chargeable to the work and not to the machine

8.Insufficient training

9. Carelessness

10. Overconfidence

11. Use of improper tools or worn out tools

CONCLUSION

       With the ideas shared in this paper, we have seen the machinist’s trade relevance and it’s usefulness in bringing into reality the conceptual designs created by the design engineer. Therefore, the need to appreciate the trade more arises.

THE PRODUCTION OF ACCURATE GEOMETRICAL SURFACE

•                 The surface may be generated by moving the work with respect to the cutting tool or the tool with respect to the work, following the geometric laws for the production of the surface.

•                 The surface  may be formed with a special shape cutting tool, moving either work or tool while the other is stationary.

•                     The forming method is general less accurate than the generating method, in as much as any irregularities in the cutter are produced on the work. In some cases  a combination of the two methods is used e.g. Thread cutting on the lathe.

 

 

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