speeds of 25,000 to 40,000 rpm. Routers are
normally used with a template to define a smooth
regular cut with the depth of the cut set and locked.
Hole saws are good for removing small areas of
damage on laminates, although they have a tendency
to damage honeycomb rather than cut it. Hole saws
also easily clean up damages, providing a good
surface for repairs. Backup plates should be taped to
the backside of the material being sawed to prevent
backside breakout. Fine tooth metal or diamond saws
work the best for sawing laminates.
HAZARDS AND SAFETY
Learning Objective: Recognize the different
safety precautions peculiar to working with
advanced composites materials.
The issue of personal health and safety is
paramount when working with composite materials.
With the rapid development of the new material
systems, the full effect of hazards to personnel has not
been determined; however, sensible shop practices
and procedures have to be employed to prevent
problems now and those that may appear later.
Following these safety precautions may prevent
future health problems, such as those encountered in
the case of asbestos fibers.
Airborne dust and fibrous particles are the
principal source of hazards. These particles are
generated by drilling, sanding, routing, or sawing the
composite structures. Fine, lightweight fiber particles
are easily circulated into the atmosphere, causing skin
irritation and inflammation, eye irritation, respiratory
system inflammation, pulmonary diseases (black
lung), cancer of the lung, and abdominal disorders.
Respiratory protection is required in those operations
where dust exists or is generated. Eye protection,
consisting of safety goggles or a face shield, is also
recommended for use in work involving any
operation where the likelihood of airborne fibers
exist. Broken fibers can penetrate the skin. The
fibers may become lodged beneath the skin. These
fibers are so brittle and difficult to remove that they
generally have to be cut out and the wound disinfected
to prevent infections.
Personal hygiene includes washing your hands
before and after working with composites, and your
hair should be washed at the end of each day. Wash
dust-contaminated clothing separate from other
clothing. Do not eat, drink, or smoke in the composite
Graphite dust and particles are conductors and
can cause shorts in electrical motors and avionics
circuity. Also, these dust particles can affect the
aircrafts fluid systems.
In the hydraulic system
where contamination is critical, actuating cylinder
rods can draw the dust particles into the system,
causing premature seal failures. The abrasiveness of
these dust particles can also cause failures to valves,
pumps, and other close tolerance parts. In the fuel
system, these particles can be introduced during wet
wing repairs, causing clogged filters and erroneous
readings in capacitance fuel quantity probes. The
abrasiveness of these dust particles can cause failures
to fuel controls and other close tolerance fuel valves.
Because of the necessity to use solvents while
accomplishing bonded repairs, potential health and
fire dangers must be given special consideration.
Solvents dissolve natural skin oils and result in
drying and cracking of the skin, rendering it
susceptible to infection. Additionally, these solvents
may cause irritation and allergic reactions to
If the vapors are inhaled during
prolonged and repeated exposure to moderate
concentrations, solvents can cause headache, fatigue,
nausea, or visual and mental disturbances. Extreme
exposure may result in unconsciousness and even
death. Solvent vapors may also act as an anesthetic or
cause irritation of the eyes or respiratory system. In
addition, they can result in blood, liver, and kidney
damage. Therefore, adequate ventilation should be
provided during mixing and use of adhesives,
solvents, and cleaning solvents.
To minimize or eliminate the danger of tire and
subsequent destruction of life and property,
flammable solvents should be used only in approved
areas and with methods recommended by local fire
safety authorities. Composite material fire hazards
are usually limited to solvents and resins. Flashpoints
of solvents and resins vary, but are usually around