Technical Seminar (Mechanical Engg.)

A Warm Welcome To One And All

VISVESVARAYA TECHNOLOGICAL UNIVERSITY BELGAUM 590002

A Techinal Seminar On

EFFECTIVE MACHINE GUARDINGSubmitted in partial fulfillment of the requirement for the award of degree BACHELOR OF ENGINEERING IN MECHANICAL ENGINEERINGSubmitted ByNIVESH KUMAR (1BY08ME032)

Under the Guidance ofAsst. Prof. Mr.Yashavantha Kumar G.A.DEPARTMENT OF MECHANICAL ENGINEERING BMS INSTITUTE OF TECHNOLOGY AVALAHALLI, YELAHANKA BANGALORE-560064.

ContentsIntroduction 2. Steps of machine safeguarding 3. Areas of machine safeguarding 4. Types of hazardous mechanical motions 5. Methods of Machine safeguarding 6. The Ergonomic of machine safeguarding 7. Designing of machine safeguards 8. Maintenance and repair safeguards 9. Requirements of safeguards 10. Conclusion 11. References1.

1. Introduction Any machine part, function, or process which may cause injury must be safeguarded. When the operation of a machine or accidental contact with it can injure the operator or others in the vicinity, the hazards must be either controlled

or eliminated. Accidents usually result from a combination of factors that includes both hazardous machine condition and careless human actions. The intent of machine safeguarding is to minimize the risk of accidents from machineoperator contact.

2 . Steps of machine safeguardingThe primary steps of machine safeguarding include: Recognize the hazards by identifying hazardous

actions and motions. Analyze the workplace and prioritize safeguarding

efforts based on the most predictable injury, the probability of occurrence and available resources. Develop and implement a systematic safeguarding

program which includes identifying safeguarding methods, selection and installation. Ensure use of safeguarding and reinforce program by

training, education and enforcement.

3 . Areas of machine safeguarding

Where mechanical hazards occur

The point of operations The power transmission apparatus The other devices

4 . Types of hazardous mechanical motions Rotating motions Reciprocating motions Transverse motionss Nip point

4.1 Rotating motionsRotating motions can grip clothing, and through mere skin contact force a limb into a dangerous position. The danger increases when projections

such as set screws, bolts, nicks, abrasions, and projecting keys or set screws are exposed on rotating parts.

Fig 4.1: examples of rotating motions

4.2 Reciprocating motionsReciprocating motions are more dangerous because during back and forth or up and down

motion the worker may be struck between the moving and stationary part . Fig 4.2 : Example of Reciprocating motion

4.3 Transverse motionTransverse motion creates a hazard because a worker may be struck or caught in a pinch or shear point by the moving part , or caught and dragged by

the parts motions .

Fig 4.3: Transverse motions of belts

4.6 Hazards caused by mechanical actions Cutting actions

Bending actions Shearing actions

Punching actions

4.6.1 Cutting actions The danger of cutting action exists at the point of operation where finger, arm and bodily injuries can occur and where flying chips or scrap material can strike the head, particularly in the area of the eyes or face .

4.6.2 Punching actionThe principle hazard occurs at the point of operation where stock is inserted, held or

withdrawn. Punching action is observed in either power presses or iron workshop .

4.6.3 Bending actionsBending action results when power is applied to a slide in order to draw or stamp metal or other materials. A hazard occurs at the point of operation where stock is inserted, held, and withdrawn.

4.6.4 Shearing actionsShearing action involves applying power to a slide or knife in order to trim or shear metal or other materials. A hazard occurs at the point of operation where stock is actually inserted, held, and withdrawn.

4.6.7 Analyze the hazards This also includes various question to be answered examples : What are the possible hazards ? How these hazards have to be overcome ? Are these safeguarding measures an economical issue

for the industry ? How these safeguarding measure be implemented in

the industry ? How effective they are and will they effect the efficiency

of the machine as well the operator working on it ?

5.0 Methods of machine safeguardsGuards : A guard prevents the entry into the danger area There are four types of machine guards:1. Fixed 2. Interlocked

3. Adjustable4. Self-adjusting

5.1 Fixed guardsFixed guards are a permanent part of the machine

no moving parts

protect only when fixed in positionshould be easy to remove and replace are only opened or removed with a tool simple, low maintenance, often the cheapest form of guarding

may interfere with production/maintenance

Examples of fixed guardsFig 5.1(a) : Shows the metal

mesh guards

Fig 5.1 (b) : shows the grinder

machine

5.2 Interlocked guardsInterlocked guards are designed to automatically shut off or disengage the machine if the guard is

opened or removedAUTOMATIC AUDIBLE ALARM AUTOMATIC VISUAL ALARM

Fig 5.2 (a): shows pictorial view of interlocked guards

Example of Interlocked guards Fig 5.2 (b): Interlocked guard on dough maker used in hotels

5.3 Adjustable guardsTypically adjusted by the operator Accommodate various sizes of stock May require additional operator training Adjustable guards are typically used on:

Tablesaws Bandsaws Power presses

Example of Adjustable guard Fig 5.3 : shows the grinding machine

5.4 Self adjusting guardsAdjusts automatically to the work Accommodate various sizes of stock May require additional operator training Self-Adjusting guards are typically used on Circular saws

Example of self adjustable guard Fig 5.4 : shows the self

adjustable guard on Circular saw

5.5 DevicesDevices may perform one of several function: Stop a machine if a body part is in danger Restrain or withdraw a hand if it is in danger

Require activation by the use of both hands Provide a barrier synchronized to the operation

Devices fall into four general types: Presence sensing devices Pullback devices Restrain devices Safety trip controls

5.6 Presence sensing devices

Detect the presence of a person, or part of a person, in a defined area and prevents the dangerous parts of machinery moving while they are in that area .

The Presence-Sensing devices are

Photoelectric presence sensing deviceElectromechanical devices

5.6.1 Photoelectric presence sensing deviceThe light curtain (photoelectric) presence sensing device uses a system of light sources and controls

that can interrupt the machine's operating cycle. If the light field is broken, the machine stops and

will not cycle. This device must be used only on machines which

can be stopped before the worker can reach the danger area .

Example of Photoelectric sensing device Fig 5.6.1 : shows the photoelectric sensing device on

power press .

5.6.3 Electromechanical devicesHas a probe or contact bar which descends to a predetermined distance when the operator

initiates the machine cycle.If there is an obstruction preventing it from

descending its full predetermined distance, the control circuit does not actuate the machine cycle.The electro-mechanical sensing device is sometimes called a Touch O-Matic.

Example of electromechanical devices

The sensing probe in contact with the operator's finger is shown.

The machine will not operate until the probe comes in contact with the material. The finger prevents this by not allowing the probe to come all the way down and contact the material .This technique is widely used in bottling industries and wrist watches belts hole making .

5.7 Pullback devicesThe pullback is primarily used on machines with stroking action . When the slide/ram is up, the operator is allowed access to the point of operation. When the slide/ram begins to descend, a mechanical linkage automatically assures

withdrawal of the hands from the point of operation.

Pullback devicesThus Pullback devices in short is Attached to Wrists Positioning Critical Adjustment Critical Maintenance Critical Training Critical Must Stop Machine immediately!

Example of pullback devicesFig 5.7 : Nylon strap is attached to the wrist band of the worker .

5.8 Restrain devicesUses cables or straps Affixes to hands May need feeding tools Adjustment critical Positioning critical

Maintenance critical Training critical Must restrain Body

5.9 GatesA gate is a moveable barrier which protects the operator at the point of operation before the machine cycle can be started .

If the gate is not permitted to descend to the fully closed position, the press will not function Fig 5.9 : Gates used in power press

6.0 Ergonomic of machine guardingPosition hazard areas against a wall Locate hazards out of reach of operators

Add enclosures or fences to restrict access Design stock feeding openings away from hazards Position the operators control station away from hazards .

7.0 Design of machine guardingShould provide a physical barrier which prevents access to dangerous parts of a machine . makes tasks such as cleaning, machine adjustment or belt changes easier - particularly if this needs to be done regularly . guards can only be removed with the aid of a tool . hinged guards must be interlocked . guard material must be of a good quality . good design will aid dust and noise reduction .

8.0 Maintenance and repair of safeguards Opening of the guards Interactions

Weights Colour coding

9.0 Requirements of safeguards Prevent contact

Be secured to the machine

Protect from falling objectsNot create new hazards Not interfere with job performance Allow for safe lubrication of the machine

ConclusionThis technical seminar helps to employers, employees, machine manufacturers, machine guard designers and fabricators, and all others with an interest in protecting workers against the hazards of moving machine parts . Even the most elaborate safeguarding system

cannot offer effective protection unless the worker knows how to use it and why. Specific training is a crucial part of any effort to provide safeguarding against machine-related hazards. One must not forget that Education is the beginning of safety .

References ILO volume 2 chapter 58.11 Machine Safeguarding. The Workplace Health and Safety Act 1995. OSHA Publication 3067, Concepts and Techniques of

Machine Safeguarding. From internet through Wikipedia .

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