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Surface of the hose is usually
made of elasomer NBR, which has a weak resistance against ozone. This is
the reason why ozone may cause cracks within the tube. A good protection
can be achieved by mixing antioxidants into the tube material during
hose production. However, this is not possible for aircraft refueling
hoses. The solution for this problem is to store and transport these
hoses with closed ends.
OZONE AND PROTECTION OF THE
HOSES
 Ozone is part of the air that we breathe, and its content in
the air is only 0,000014%. Ozone is created by chemical reaction of an
atom oxygen and molecule oxygen: O + O2 --- O3.
It is created at a height of
approximately 30 km by the effect of UV rays. A small part of it drifts
to the ground. Another reason for ozone on the earth surface is the
chemical reaction of nitrogen oxides and hydrocarbons due to strong sun
insolation. But also UV tanning lams, welding torches, electric motors
and thunderstorms are sources for ozone creation.
The resistance of rubber
materials against ozone varies greatly. Elastomers such as EPDM (Ethylene-propylene-dien)
and CSM (Hypalon) are
not damaged by ozone. On the other hand, CR (Chloroprene), which is a
common cover material of refueling hoses, must be protected by
antioxidants in order to be ozone resistant.
Due to the necessary oil and
fuel resistance the tube of refueling hoses is normally made of NBR,
which has a weak resistance against ozone. If we mix NBR with
antioxidants, we will protect hoses against ozone. This procedure,
however, can not be used in the case of aircraft refueling hoses since
effective antioxidants may lead to a strong discoloration of the fuel.
Consequently, aircraft refueling hoses should be stored and transported
with closed ends. In this way, we will prevent UV rays to get into the
hose and therefore we will unable creation of ozone inside the tube. |
