Need and Importance of Machine Guarding:
Need and Importance of Machine Guarding: Basic need of machine guarding is to protect against contact with the dangerous and moving parts of a machine work in process and failure due to mechanical, electrical, chemical or human causes, the guards remove workers fear and thereby increase the production. They allow the operation higher speeds and compensate .the expenditure on guarding.
Groups of Dangerous Parts:
According to Motions:
Dangerous parts to be guarded according to their, motions are generally classified as follows:
Rotary Motions :
- Rotating parts alone viz. shafts, coupling, spindles etc.
- In-running nips subdivided as-
- Between parts rotating in opposite direction-gears, rolls etc.,
- Between_rotating and tangentially moving parts- conveyors, belt drives etc.
- Between rotating and fixed parts-grinding wheel, paper machine felt or roll etc.
(1) Reciprocating sliding motions and fixed parts:-
- Approach type-danger of crushing, viz. slides
- A rams, on power presses and forging hammers, pistons, cross rod of a steam engine and reverting I machines.
- Passing types-danger of shearing, viz. planning machine, shaper, spot welder clamping fixtures guillotine and the shear, powers press etc.
(2) Single sliding motion-abrasive or sharp nature of objects such as saws o crocodile clips on belts.
Rotating Sliding Motion:
Cam gear having sliding and running movement etc., fall within this group.
Oscillating Motions Trapping pints between two moving parts or between a moving part and fixed object viz. a pendulum, crankshaft etc.
According to H. A. Hepburn
25 groups of intrinsically dangerous parts of machinery as classified by H. A Hepburn are follow
a. Single Revolving Units – Risk of entanglement
- Revolving open arm pulleys and other discontinuous rotating parts-Fan blades, spur gear wheels etc.
- Revolving worms or spirals in castings – Meat minces, rubber extrude, spiral conveyers.
- Projections on revolving parts – Keys heads, set screws, cotter pins, comp ling belts etc.
- Revolving shafts, spindles, mandrels and bars – Drills, reamers boring bar, stock bar milling etc.
b. Single Revolving Units – Risk of cutting or abrading
- Revolving high speed cages in castings – Hydro-extractors, centrifuge.
- Revolving or oscillating mixer arms in castings – dough mixture, rubber solution mixture
- Abrasive wheels grinding wheels etc.
- Revolving drums and cylinders-uncased – rambler, shaking barrels, rag digesters etc.
- Revolving cutting tools – Circular saws, milling cutters, shears, routers chain martises.
C. In Running Parts – Risk of nipping and tearing :
- In running nips of the belt and pulley type-pulley-belt, chain and sprocket gear, conveyor belt etc.
- Revolving beaters, spiked cylinders and drums-Scutchers, cotton openers, laundry washers. In running nips between pairs of revolving parts-Gear wheels, friction wheels, calendar bowls. mangle rolls etc. Nips between gears and rack strips.
- Reciprocating Tools or Parts – Risk of cutting or crushing
- Moving balance weights and dead weights-HydranJic accumulators, balance weight on slotting machine etc.
- Reciprocating knives and saws-Guillotines for metal, rubber and paper cutting, trimmers, perforators etc.
- Nips between reciprocating and fixed parts other than tools and dies-sliding table and fixture, shaping machine and fixture.
- Closing nips between platen motions-Letter press platen printing machine, power presses.
- Reciprocating tools and dies-Power presses, drop stamps, relief stamps, bending press, revolting press.
- Nips Between revolving wheels or cylinders in pans or on tables-Sand mixtures, edge runners, crushing mill, mortar mill etc.
- Nips between revolving wheels or cylinders in pans or on tables-Sand mixtures, edge runners, crushing mill, mortar mill etc.
- Pawl and notched wheel devices for intermittent feed motions
- Nips between fixed parts and unidirectional moving parts-Buckets or hoppers or conveyors against tipping-bars etc.
- Nips between connecting rods or links and rotating wheels, cranks or disc-Flat bed printing machine, jacquard loom, and automatic looms.
- Planer tool feed motion, power press dial feed table etc.
- Running Edges Risk of cutting
- Cutting edges of endless band cutting machines-Band saws, band knives.
- Projecting belt fasteners and fast running belts-Boll and nut fasteners, wire pin fasteners, centrifuge belt etc.