Types of Guards:
Total machine safety can explained as follows:
Safety by Construction:
It indicates parts’ so constructed as to cause no hazard, viz shaft, sliding- and link mechanism so located or with slew speed that their contact is net dangerous, Built-in-safety is he similar work for designing and constructing new machinery in such a way to make the dangerous.
Safety by position:
This work used by section 21 of the Factories Act It means the situation (out reach) Dr position in such a way that normally it not possible to touch the dangerous parts. However intentional contact should prevented moving feed opening can made safe by position parts safe y deep housing or position etc.
If gravity or remote feeding device is applied. But, then, it is a type of indirect guarding. A distance of 2.6. m or 8.-6 is considered safe by position.
Safety by Guarding:
This is met important as ether methods are net always possible, Depending upon the dangerous part, its size, position, speed etc. a guard should be selected. Generally the parts to’ be guarded fall within three categories’:
The prime mover
Transmission parts from the prime mover to. the machine and the transmission parts in the machine itself. It is desirable to minimize them and enclose completely
Operating parts of machine, of which the points of dangerous operation need effective guarding
A machine guard means any enclosure, barrier or device constructed to prevent a person or his clothing corning into. contact with dangerous parts of the machine. The point of operation Ming or any other necessary operation is accomplished. A guard for its it is know as the point of operation guard.
Some Types of Guards:
Various types of guards shown classified in the table on page-368 their suitability should selected. Preference should given to the simplest type of guard ensuring complete safety. Some described below and some in subsequent par a
Fixed types of guards:
They are type of guards which are simple, easy to provide and. cover parts as well as throwing particles if any. They are of various types, materials and design. A minimum thickness of 1.2. mm is recommended for sheet metal. Guard opening and its distance from the distance are prescribed and formula are also available, ‘but it is rater a matter of fact of individual requirement. They should be close fit, robust and should withstand speed. Vibration, impact etc. They should be properly fitted by clamps, bolts etc. They require special tool for their removal.
Fixed limited access guard
provides minimum opening in the guard to insert and remove the job(material). It disallows finger to trap. If the material jammed, it requires special tool and penning and refitting of the guard. They are used on power presses.
Fixed adjustable access guard
provides opening through or around guard to accommodate materials of different sizes. Guards on band saws, jigsaws can raised or lowered as per the thickness to cut Such guard on circular saw or drill 1 too adjusts automatically as the job or tool moves its disadvantage that it gives little protection when thin material processed.
Distance or Barrier Guards
make it physically difficult for people to gain access. Nip guard to inuring rolls and fixed railing to planning or shaping machine are of this type.
make certain that the machine cannot operated until the guard screen in position and conversely the guard cannot removed until the working parts have stopped Mechanical, electrical, hydraulic or pneumatic systems used to actuate the guard. Mechanical interlocking of a card machine and electrical (limit or micro switches) interlocking of headstock covers of may textile machinery such example many times the interlocking vis by-passed or made ineffective which not good. This is its disadvantage. Correct position of micro switch is most important.
actuated by anyone approaching beyond the safe position and operate a stop or reverse control viz. trip rod, hand trip on a rubber mill, electronic eye, platen printing guard, calendars” or dough brakes.
activates the machine when the guard closed and opening the guard stops it. Thus, the guard acts as on-off switch. Such guard useful for the machine, which can brought to rest very rapidly.
will ensure that the operator prevented form coming into contact with dangerous parts when the machine set in motion accidentally. This guard itself actuated by the movement of the dangerous part. It can only be use where sufficient time is available to remove the body part from the d ‘danger zone viz. sweep- knock or pus away guard on a power press or pattern printing .machine. Because of its stroke hazard it hardly used. Photo-electric guard ( device) operates to stop the dangerous part when the light curtain interrupted .
Safety by Machine Controls:
These should be differentiated from incidental safety device (explained din next part) which are external and work like guard for protection. But the machine itself has many controls as its inherent or attached elements. All levers, buttons, brakes, pedals, switches, handles, wheels, auto controls etc. machine controls should clearly identified and suitably placed for ease of operation. Their purpose and direction of movement shall marked. Each stop button should accompany start button and they should sunk to prevent accidental operation. Where there more controls nearly placed or on one board clear instruction of their use must marked to prevent heir false operation.
Safety by Precautions and maintenance:
Above par as highlight the need of utmost precautions in safe operation and maintenance of all safety guards, devices and controls. A man ha made them and a man can make them ineffective or misuse. Therefore all precautionary operating measures are necessary in addition to the machine guarding. The machine operators should made aware or hazards in their works, location and operation of machine controls, regular checking of guards, warning not to make the guards ineffective. Repairs adjustment etc. by specially trained person need of wearing tight fitting clothing and protective equipment necessary and using right tools and equipment’s.
Other Types of Guards:-
Incidental Safety Devices and Methods:
Some incidental safety devices (indirect guards) equally useful as machine guarding are as below:
Two Hand control
Two’ push buttons required to operated simultaneously thus keeping the operator’ hands away from the dangerous parts. Such devices does not protect and another’ man, prone to faults and cause difficulties on electrically, hydraulically or pneumatically powered machines. Therefore such device alone us bit advisable. It used on garment presses etc.
This uses photo-electric cell and a light as explained earlier. Electromagnetic Sensor; This uses a sensor of electromagnetic field, a coupler and interconnecting cable and a control unit interruption of the filed by an operator’s hand causes an electric signal which initiate the desired control action’ Mechanical Feed: A positioning device like a rotating table moves the parts or material into the point of operation where the hazard exists thus avoiding human contact
Tools with guards viz. tong, magnetic lifting rod etc. used to place material in a press with an intention to save the hand there. Pedal Guard: Such guard on foot-pedal of a power press prevents accidental foot- stroke on the pedal.
Ultrasonic Device: Inaudible high-frequency .sound senses the presence of any part in the danger Zone. As sound attenuates over distance its application limited. Feed Hopper: It extends the feed length to prevent access. It can used on pug mills etc.
Guarding of Different Machines:
Some sample specific guarding suggested below as examples. The changes necessary as per Own requirement must incorporated.