14 APPENDIX
Mitsubishi Diesel Engine S16R & S16R2 OPERATION & MAINTENANCE MANUAL
213
Pub. No. K29001-00320 Revision: 1
Necessity of LLC
In recent years, with increasing in performance, the
engine is inclined to be compact, lightweight, high
output power, lower fuel consumption and low
emission, however engine coolant is used under
severe conditions such as continuous long
operation, high temperature, high flow rate and
others. Furthermore, many different materials such
as steel, aluminum, copper, solder, and rubber are
used in the cooling system, and they are also
subject to the severe conditions described above.
Those materials have different ionization
characteristics, and this difference accelerates
corrosion through the medium of engine coolant.
To prevent such a problem, it is necessary to use
the LLC containing additives that prevent rust.
Characteristics of LLC Additives
LLC contains several chemicals in such proportions
as to produce chemical reactions that suppress
corrosion (ionization) of engine parts that contact
with the coolant. LLC loses its effectiveness by
hours of use as well as lapse of time.
Furthermore, if the chemicals are not well
proportioned to match the metals used in the
cooling system, certain chemicals in the LLC
become rapidly used up, and it results in corrosion
of metals to be protected. Consequently, other
corrosion preventing chemicals react with
dissolving metals, by which corrosion is
accelerated. This condition generates more severe
corrosion than when plain soft water is used. This is
a typical problem caused by the use of
inappropriate LLC.
Examples of Abnormalities
Caused by LLC (Amine Type)
■
Corrosion of Iron Parts
Amines are generally effective in suppressing the
rusting of ferrous metals, but they are said to cause
problems for copper parts. If copper corrosion
occurs in the cooling system due to lowering of
copper type antirust, dissolved copper will deposit
on iron parts. A difference in electrical potential
occurs between the copper deposits and the iron,
causing corrosion of iron which has a higher
ionization characteristics, resulting in problems
such as pitting at an early stage.
■
Corrosion of Aluminum Parts
Silicate is highly effective in protecting aluminum
against rusting. However, it is unstable in a solution
in which the pH is 9 or lower, and can turn to gel and
precipitate in the solution. For this reason, the pH is
usually specified to be about 10 to ensure a high
alkaline level. This means, after silicate is used up,
the high alkalinity causes chemical attacks on
aluminum. To prevent this problem, proper
maintenance of the coolant is required. For
example, rapid wear of the water pump mechanical
seal due to gelification of silicate salt has been
observed.
■
Pitting and Clogging of Heat
Exchanger
When LLC deteriorates or when its concentration in
the coolant becomes low, the anti-corrosion
performance of LLC lowers and it results in the
corrosion of metals.
Brass and solder tend to corrode faster than other
metals, and corrosion of these metals is said to
cause troubles such as water leak and clogging in
the heat exchanger.
Содержание S16R
Страница 215: ......