SAFETY PRECAUTION
GENERAL
INTRODUCTION
Good housekeeping in the hangar, workshops, and on-flight line area is essential for safe and efficient maintenance of these
places where technicians may work on shift. The outgoing shift should make sure
that all equipment, tools, and other items used during their shift are removed
and properly stored in their respective stores.
CAUTION.
Caution notices are used throughout instructions and maintenance manuals to warn workers of certain processes or steps to follow in reaching the next assembly.
This will help you to
(1)
Avoid
missing important processes in a complicated assembly
(2)
Warn you of a special process that must be performed
(3)
Warn you of a previously carried out step of some
importance in this continuous process.
WARNING.
Warning
notices make the reader aware of a personal safety hazard, to adhere to, or to
avoid. These warnings are set in such a way you do not get injured by some
hazard. Remember accidents happen because we become over-familiar with a
process or from some unforeseen circumstance. Therefore, observe warnings,
caution, and any other signs in the maintenance of equipment and work practices.
CAUSES
OF ACCIDENTS.
a.
Failure to comply with safety regulations.
b.
Incorrect use of tools and equipment.
c.
Negligence and irresponsibility.
CONSEQUENCES.
a. Injury to personnel.
b. Damage to equipment.
c. Loss of time.
ACCIDENCE PREVENTION.
a. By being fully conversant with the
safety regulations and diagrams.
b. Correct
use of tools and equipment.
c. Sense of responsibility.
FIRST AIDS
Every hangar and
workshop should maintain an accident report book and first-aid box. Any
accident must be reported to NCO I/C and be recorded
WORKSHOP SAFETY
SAFETY REQUIREMENTS IN WORKSHOP / MACHINE SHOP.
a.
A machine should never start until it has been
determined that all conditions of safety operations have been complied with.
b.
Find and use always the quick way of stopping the
machine, in case of emergency.
c.
Suitable fences and guards should be in place before
commencing the job and these should be removed only for the purpose of authorized
inspection and adjustment of machinery.
d.
No adjustment,
repair, or oiling should be attempted while the machine is running.
e.
Lathe face plates, and driving plates chucks are to be
mounted or removed when the mandrel is at rest.
f.
Machine should not be left unattended while the power
is “ON”.
g.
The machine fitting must not be braked by hand in order
to bring the machine to rest after switching off the power.
h.
Hands should not be taken near the cutting edges of the
tool when the machine operations are in progress.
i.
Adjust and secure tools properly before commencing the
job.
j.
The use of the cooling mixture is very essential, as it
preserves the cutting edges of the tool, and prevents the distortion of the
work.
k.
Tight fitting clothes must be worn, as loose clothing is
likely to be caught in the machine.
SAFETY REQUIREMENTS OF HAND TOOLS.
a.
Always select the proper and suitable tool for the
work.
b.
Use tools only for the work for which they are intended.
c.
Never allow the cutting edges or teeth of tools to come
into contact with anything except the job.
d.
Tools like files should never be used without handles.
e.
Never use pliers as a spanner.
f.
Replace chisels, gauges, and pointed marking tools in
the box or tray after use.
g.
Precision instruments must be cleaned and oiled properly
after use.
h.
Keep hand tools clean and free from corrosion, by
wiping the metal part with an oily rag, after use.
SAFETY OF DRILLING MACHINE.
a.
Before using the machine, mark the sport to be drilled
and punch them surrounded by a circle.
b.
Proper size of a drill with proper cutting angles must be
selected.
c.
Before drilling an exact size of the hole, a smaller size hole is to be drilled.
d.
Always hold work in a vise or clamp to the
drill table.
e.
Proper speed and feed must be selected as per the work
and size of the drill.
f.
The drill must never be forced with a jerk but a slow
and continuous pressure is sufficient.
g.
Drill must be taken out occasionally while drilling
deep and blind holes.
h.
Remove
chips with a brush, never by hand.
i.
Proper coolant must be used and in no case, a piece of
rag be used for the coolant.
j.
Attempt of changing speed and feed should not be made
while the machine is running.
k.
After the operation, the machine should be cleaned well
and oiled.
SAFETY OF GRINDING MACHINE.
a.
Always wear safety glasses or goggles, or a face shield
b.
Inspect the grinding wheel for cracks before putting it on
a machine.
c.
The spindle nut should be set up light enough to hold
the wheel securely.
d.
When grinding wheels are removed from the machine handle
them carefully and store them in a dry place.
e.
Never grind soft material such as Aluminum, Brass, wood, etc.
f.
Do Not Exert excessive pressure on the machine.
g.
In any grinding machine, it is necessary for the work
to be supported properly and for the operator to keep his hands away from
the revolving wheel and work.
h.
Never use the side of the grinding wheels.
i. The gap between the work rest and wheel should not be more than 1/28”.
Safety Boots
Head gear
Chemical gloves
Figure 2.1.7-j Eye
protector Figure
2.1.7-k Disposal Dust, Mark
FIRE SAFETY.
TYPES OF FIRE.
a. Class
“A” Fires.
Fires
in ordinary combustible materials such as Wood Cloth Paper Upholstery materials
etc.
b. Class
“B” Fires.
Fires in inflammable
petroleum products or other combustible liquids grease solvents paints etc.
c. Class
“C” Fires.
Fires
involving energized electrical equipment.
d.
Class
“D” Fires.
Fires in flammable
metal. Eg: magnesium, sodium potassium in the shop. Aircraft wheels and brakes any one of these fires can
occur during maintenance or operations.
CAUSE OF FIRE
These things are
required for a fire.
a. Combustible
b. Heat
Fire triangle
2.1.8.3 PRINCIPLE
OF EXTINGUISHING FIRE
Remove any one of these things. Heat Oxygen or
Combustible Substance.
v
COOLING
- below kindling point
v
EXCLUDING
- the oxygen supply - Smothering
v
SEPARATING- the
fuel the oxygen - starvation
2.1.8.4 EXTINGUISHING AGENTS
RESPONSE
Class A – Fires - Respond
best to water or WATER – Type extinguishes which cool the combustible-
substance below the combustion temperature- COOLING.
Class B-Fires - Respond Best to Carbon Dioxide (Co2)
Halogens and Dry Chemicals water is in- effective on class B fires and causes
the fire to spread SMOTHERING.
Class C- Fires - Halogenated
Hydrocarbons Are Very Effective On Class
“C” Fires. The Vapors Reacts Chemical with the Flame to Extinguish Fire. Water or Foam must not be used on Electrical fire as it aggravates current leakage.
CLASS D- Fires - Respond
to the application of Dry Powder which prevents Oxidation and the Resulting
Flame. The application may be from an extinguisher, A Scoop, or a Shovel. Manufacturer's
recommendations should be followed at all times. Under no circumstance should a person use Water on a Metal Fire it will cause the fire to burn more violently and
can cause an explosion.
a.
Fire
extinguishing agents - may be categorized under three groups.
(1) Water and
water-based agents
(2)
Dry – Chemicals
b. Four types of Chemicals are used.
(1) Sodium Bicarbonate (formula – H)
For class B &
C Fires
(2) Ammonium Phosphate (multi-purpose)
For
class B & C Fires
(3) Potassium
Bicarbonate (purple - k)
For
High-risk class B & C Fires
(4) Multi-Purpose Dry Chemical (ABC)
For use
on class B & C Fires
c. GASES
` (1) Carbon
dioxide
Use on class B & C fires. Extinguishes flames by dissipating oxygen in the immediate
area.
(2) Halogenated
hydrocarbons
Used for Metal Fires &
Wheel Brakes this type is Not recommended for aircraft use since they leave residual dust or power which is difficult to clean up and causes damage to Electronic
Equipment.
Fire
Extinguisher
METALLURGY
INTRODUCTION
Since age’s man has been using different materials for
different uses, for example cotton wood (for furniture fuel). Etc. some of
these materials are obtained directly from natural resources and others are
developed by research in laboratories to suit individual requirement.
Historians have proved that in the beginning. The man depended only on his
physical strength for survival, latter he found the usefulness of stone wood
and fire. The quest for a stronger material than wood and stone lead him to
metal and other material like plastics rubber glass ceramics etc.
a.
In modern engineering technology a wide range of
material is used these materials are generally classified as,
b.
In the ensuing chapters, we will learn more about
metals. First what is a metal? Metal is a substance which possesses certain
physical properties.
They are:
(1)
They
conduct heat or electricity.
(2)
They generally have ringing tones.
(3)
They have metallic luster or shine
(4)
They are dense in other words they are heavier than
water.
c.
Metals are further categorized as ferrous and
non-ferrous metals. Only iron and their alloys are called ferrous metals. Some
metals are not easily affected by acids or salts, e .g Gold, Silver, Platinum
etc. these are called precious metals.
d.
All metals have the following properties though the
degree of these properties may vary from metal to metal:
(1) Physical properties.
(i) Tightness
and porosity.
(ii) Thermal
and Electrical Conductivity.
(iii) Thermal
Increase.
(iv) Heat
capacity
(2) Mechanical properties
(i) Elasticity
(ii) Ductility
(iii) Malleability
(iv) Brittleness
(v) Hardness
(vi) Tenacity
(vii) Plasticity
(viii) Fusibility
In general engineering the most commonly used metal is
steel. In an aircraft, aluminum and its alloys are used for structure or
airframe while steel and special alloys are used for aero-engines. Aluminum and
its alloys are also known as light alloys as these are comparatively lighter
than other metals.
DEFINITIONS OF ENGINEERING TERMS.
a. Brittleness.
The
liability of a metal to fracture on receiving a blow or shock.
b. Hardness.
The ability of a material to resist
abrasion, penetrating, indentation or cutting action.
c. Toughness.
The
property of resisting breakages when subjected to bending sudden blow or twist.
d. Tenacity.
The property
of resisting breakages when the application of a pulling force.
e.
Malleability
The
property of being permanently extended for patterned by hammering, rolling or
pressing without rupture.
f.
Ductility
The property ware by a metal can be
drawn out in to a wire with out cracking.
g.
Elasticity
The capacity of a material to its
original dimension on the removal of distortion forces.
h.
Conductivity
The
ability or capacity of a metal to conduct heat or electricity.
i.
Fusibility
The
capacity of being melted
j.
Fatigue
The
diminishing resistance to fracture caused by fluctuating stresses
k.
Drawing
Pulling
a metal through a die or succession of dies in order to produce a required
cross sectional shape.
l.
Extrusion.
Forcing a material through a die of the required shape by
means of hydraulic press
m.
Forging
The operation of shaping
hot metal by means of hammers or presses.
n.
Spinning.
Shaping sheet metal by
applying pressure while revolving.
o.
Stamping.
Shaping or cutting by
means of dies in a press.
p.
Swaging
Shaping by pressure or
by hammering the metal in a die of required shape.
q. Tolerance.
A permissible range of dimension of
finish components provided to cover unavoidable in accuracies in
manufactures.
q.
Backlash.
The
clearance between the meshing gear teeth or splined members which must
be taken up before diving in the reverse direction.
r. Clearance.
The
space provided between two working parts to allow for freedom of movement,
lubrication and variation of size or position due to heat or distortion.
FERROUS
METAL
PIG IRON
Pig iron is obtain by
heating iron ore with coke and lime stone in big blast furnace coke provide
fuel or maintain the heat required and carbon in the form of carbon monoxide
from the core combines with the iron
oxide reducing them to iron. Lime stone serves as flux and combines with
nonmetallic portion of the ore to form a molten SLAG. Hot air is blown into the
lower portion of the furnace. As the action from proceeds the molten iron and
slag fall to the bottom of the furnace. SLAG floating on the top of the iron
from time to time SLAG is tapped off from the hole shown and molten iron from
the hearth.
Pig iron is the basis form of iron with little
impurities it is weak brittle and needs further processing before being used
for engineering purpose.
2.2.3.2
CAST IRON
Cast iron
obtains by re-melting pig iron, in small furnace called cupola Cast iron is
brittle, weak and fairly soft it can be cast very easily. Marling out tables, Bases of mechanic tools,
Bodies of eclectic machines, Beds of engines etc.
WROUGHT IRON
Wrought iron is produced
from pig iron by paddling process. In this process nearly all the carbon and
other elements present in the pig iron are oxidized. Carbon monoxide bubbles
from the masses of molten iron and burns at its surface slag rises up and flow
out from the slag notch.
HEAT
TREATMENT
a. Principles of heat treatment
(1) Purpose.
To
chance mechanical property or combination of technical properties so that the
metal will be more useful. Serviceable and safe for definite purpose.
(2) Principle.
Heat treatment is a series of
operations involving the heating and cooling of metals in the solid state. By
heat treating a metal can be made harder stronger. More resistance of impact
more ductile and softer.
(3) Common forms of heat treatment for
ferrous metals are Annealing, Hardening,
Tempering, Normalizing and Casehardening.
HEAT
TREATMENT PROCESS
a. Annealing
Objects
of annealing are to
(1)
Make
steel soft
(2)
Improve Mach inability
(3)
Bring back Ductility and Toughness
(4)
Reduce internal stress
(5)
Refine crystalline structure.
The
metal is heated to annealing temperature and cooled slowly by keeping under
sand, lime or ashes. Annealing of Steel
produces fine grained, soft, ductile, lowest strength metal without internal
stresses or strains.
b. Normalizing
Normalizing of steel removes internal stresses set up
heat treating welding, casting, forming, machining etc. Air craft steels are
often used in the normalized steel for better physical properties. All welded
parts should be normalized after fabrication.
(1)
Objects
of normalizing
(2)
To
reduce grain (crystal) size
(3)
To
reduce internal stress
(4)
To
improve Mach inability, Strength etc.
Normalizing is accomplished by heating the
steel 40 oC to 50 oC above the upper critical point.
Soaked at that temperature for a short period of time and then cooled slowly in
still open air.
c. Hardening
Hardening treatment consists of heating the steel to a
temperature just above the upper critical point soaking or holding for the
required length of time, and then cooling it rapidly by plunging the hot steel
in to oil of brine. Treatment of hardening to steel in order to harden it to
certain depth.
As a result of rapid cooling austenite so formed does not
get sufficient time to be transformed to perlite and cementite but is forced to
form a solid solution of carbon in ferrite called marten site which being hard
and brittle makes steel hard and brittle.
d. Tempering
Tempering
involves heating steel to much below the lower critical point (23 oC
to 300 oC) and cooled in still air after removed from the furnace.
This process causes a partial transformation of marten site back to partite
again their by taking away some of the hardness but making steel tougher.
e. Case hardening
Case
hardening produces a hard ware resistant surface or case over a tough interior
core. Low carbon and low carbon steel are best suited to case hardening. High
carbon steel when case hardened, the hardness penetrates the core and cause
brittleness.
f. Low carbon steel when case hardened
depth may be about 1.5 mm and mild steel may be up to about 2 mm, while the
core process almost of softness as of the original sample. The surface of the
metal is changed chemically by introducing a high carbide or Nitride center and
the core is unaffected chemically.
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