1) The document describes a method for protecting fire extinguishers from corrosion by applying a coating to the interior of the extinguisher body. 2) The coating is produced by mixing equal parts of distilled bitumen and air blown bitumen, heating the mixture, and applying it to the pre-heated interior walls of the extinguisher body. 3) The bitumen coating provides a durable, waterproof layer that prevents corrosion even if the metal body is bent, and remains effective over prolonged use.

1. * GB780098 (A)
Description: GB780098 (A) ? 1957-07-31
Improvements in or relating to the protection of fire extinguishers against
corrosion
Description of GB780098 (A)
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PATENT SPECIFICATION
780,098 Date of filing Complete Specification: Feb. 24, 1956.
Application Date: March 10, 1955.
No. 7104/55.
Complete Specification Published: July 31, 1957.
Index at acceptance: -Class 123(1), D1.
International -Classification:-F061.
COMPLETE SPECIFICATION
Improvements in or relating to the Protection of Fire Extinguishers
against Corrosion I, HAROLD HUTCHINSON, a British Subject, of Attifyre
Limited, Shaftsbury Road, Acton, London W.3., do hereby declare the
invention, Tfor which I pray that a patent may be granted to me, and
the method by which it is to be performed, to be particularly
described in and by the following statement:-
This invention relates to fire extinguishers of the kind comprising a
metal body adapted to contain a liquid charge which is either water
from a domestic supply or a solution with a water base.
Fire extinguishers of the kind above referred to have hitherto been
subject to the disadvantage that in course of time they are liable to
become corroded, particularly near the water level line inside the
extinguisher, and experience has shown that this is particularly - so

2. in the case of extinguishers of the water type. Various types of
coating have been employed to retard or inhibit this corrosion, in
particular rubberised coatings employing chlorinated rubber mixtures,
latex, and the like. - Also, various types of plastic or paint
coatings have been employed, but all these suffer from weaknesses,
which [may be hardening through age, deterioration through changes of
temperature and the oxidising effect of the water/air mixture inside
the extinguisher, and especially the lack of adequate and permanent
bonding between the coating and the steel body of the extinguisher,
permitting the coating either to peel away, flake or crack, or
eventually become porous after prolongedt use or storage.
The object of the present invention is to overcome the disadvantages
described in the preceding paragraph and to provide a simple and
effective method of applying a durable protective coating to the
interior of a fire extinguisher body. According to the invention a
method of internally Icoating a fire extinguisher body of the kind
above described consists in preparing a mixture of distilled bitumen
and air blown [Price 3s. 6d.] bitumen, in pre-heating the fire
extinguisher body and in applying thereto a quantity of the melted
bitumen mixture.
In carrying the invention into effect and in the preferred manner the
coating for the interior of a fire extinguisher body is produced by
first preparing a mixture of crude oil based steam distilled bitumen
and crude oil based air blown bitumen in approximately equal
proportions by heating to a temperature of the order of 190 degrees C.
The extinguisher body is then pre-heated to a temperature
(approximately 210 degrees C.) higher than the melting point of the
bitumen mixture, and thereafter a quantity of the melted mixture is
applied to the internal walls of the extinguisher.
A convenient method of applying the mixture to the internal surface of
the fire extinguisher body is to fill the body with the hot bitumen
mixture and immediately drain it by inverting its position. This
operation removes the surplus bitumen mixture and leaves a uniform
tcoating over the entire surface of the extinguisher body which after
cooling is ready for use and retains its characteristic as a uniform
coating for an indefinite period.
The application of the bitumen mixture in the manner described has
been found to prodtce a!comnplete bonding between the bitumen mixture
and the metal which is of such durability that the coating mixture
will not crack or flake from the metal even should the metal be bent
at an acute angle. The coating itself remains slightly pliable under
all climatic and temperature variations. The coating described also
possesses the advantage that it is com.
pletely waterproof, is unaffected by prolonged contact with water

3. and/or air, and as a consequence will avoid altogether the danger of
liquid percolating through cracks or flakes and causing invisible
corrosion between the coating and the metal wall of the extinguisher.
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* 5.8.23.4; 93p