Improvements in the Manufacture of Paving Blocks, Tiles, and the like.
Year: 1897

page_text: Date of Application, 1st Mar., 1897-Accepted, 17th Aor., 1897
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Paving Blocks, Tiles, and
the like.
I, WALTER SCOTT WILKINSON, of 1204 Charles Street North, Baltimore,
Maryland. United States of America, Gentleman, do hereby declare the nature of
this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
This invention relates to improvements in the manufacture of compressed paving
blocks, tiles, and the like from asphalt and other materials.
According to my said invention I form the blocks, tiles or the like by compressing
in a suitable mould, a mixture consisting of asphalt, non-calcareous hard-stone
debris, i.e. partly in fragments and partly powdered, and powdered limestone, the
asphalt used being preferably that obtained from the Pitch Lake in the Island of
Trinidad, British West Indies, and being first pulverized and then macerated and
agitated in water in order to remove soluble salts and non-bituminous organic
matters.
The asphalt after this pulverisation and maceration is treated to evaporate the
water from it, which is accomplished by placing it in a tank inside of which are
arranged coils of steam pipes. Through these pipes steam is circulated from a
boiler, in which it is generated and to which it is returned in the form of water,
the action being continuous while the evaporation of the water from the asphalt is
being effected. The asphalt is meanwhile kept agitated by jets of steam discharged
into it at the bottom of the mass in order to maintain the heavy matters in even
suspension or mixture with the lighter constituents of the asphalt and also to
hasten the operation of drying by bringing into contact with the heated surfaces of
the circulating pipes all parts of the mass in a shorter space of time than would be
the case if only the natural circulation of the material were depended upon. This
mode of preparing the asphalt is superior to the direct application of heat from a
fire or furnace, since such heat cannot be carefully regulated, and should the
asphalt or any part of it be heated beyond a proper temperature its adhesive
property is either impaired or destroyed.
The next step in the treatment of the asphalt (provided that it has been
previously allowed to cool and harden) is to melt it at a temperature of about
300 degrees Fahr. There is then added to it 12 to 13 per cent. of its weight of
heavy oil, preferably a residuum of petroleum, of a specific gravity of from
18 degrees to 22 degrees Beaume which residuum has previously been heated to
remove by evaporation any water contained therein. The oil and asphalt are kept
heated to about 300 degrees Fahr. by means of the aforesaid circulating steam
pipes, and are also agitated until they are thoroughly mixed together by means of
the before described steam jets. This mixture is known as asphaltic cement.
I will now describe the treatment of the stony material which constitutes the
larger proportion of the finished blocks, tiles or the like. Stone of non-calcareous
character, such as trap rock or basalt, is first crushed in an ordinary stone crusher,
until it will pass through a revolving screen having holes about seven-eighths of
an inch in diameter, that portion which will not pass through being returned as
tailings" to the crusher to be again subjected to the crushing operation so that
all the product of the crusher will ultimately pass through the perforations of the
evolving screen. After having passed through this screen the crushed stone is
TPQ77

page_text: delivered to a pair of steel rollers which reduce a large portion of it to dust, and
the remainder to small pieces which will pass through a revolving screen having
meshes about three-eighths of an inch square, such portions of the stone as may not
have been sufficiently reduced being returned to the rollers as "tailings" so that
the whole of the stone will be reduced to debris which will ultimately pass through
the three-eighths inch meshes of the revolving screen. From this screen the crushed,
rolled and partly pulverized hard stone is delivered into a revolving heater which
is placed over a fire of coal or petroleum, preferably the latter, because the degree
of heat can be much more easily regulated and controlled with petroleum fuel than
it can be with coal fuel.
The preparation of the limestone dust of which the blocks and tiles are partly
composed is as follows:-Limestone of good quality and hardness is crushed and
ground to powder in a suitable mill from which it is delivered into the stone heater
above referred to simultaneously with the previously described crushed and
pulverised hard stone. The percentage of limestone dust or powder requisite will
vary according to the proportion of the hard stone which is reduced to dust in the
crushing, rolling and screening process, some stone yielding a comparatively large
proportion of fine material and some a comparatively small proportion. The
percentage of limestone dust relatively to the hard stone debris may be said to
range, according to the circumstances, between 5 and 10 per cent. The revolving
stone heater mixes the hard stone debris and the limestone dust together thoroughly,
and the whole is discharged at a temperature of about 300 degrees Fahr. into an
elevator which conveys it to a bin, whence it is drawn into a measure and from this
measure discharged into a mixer or pug mill. Simultaneously with the discharge
of the crushed and pulverized hard stone and limestone material into this mixer,
a certain amount of asphaltic cement at the temperature of about 300 degrees F.
is discharged into the mixer, the proportion of cement being about 10 to 12 per cent.
of the whole. The mass is then thoroughly incorporated by means of the revolving
blades or paddles of the pug mill, until the dust or fine portions of the stony
material are mixed with the aspbaltic cement and the larger pieces are coated
therewith, the whole contents of the mixer being afterwards discharged into a
shute which conveys it to a suitable press, by means of which the material is formed
into the required blocks, tiles or the like.
The pressure delivered on blocks measuring say about 12 × 4 × 5 inches, should
be from 125 to 140 tous on the 12 x 4 inch surface, and on tiles from 75 to 100 tons.
The tiles, which may be about 8 or 9 inches square or may be hexagonal and
measure about 8 or 9 inches between their opposite faces, are only about half the
thickness of the blocks and therefore do not require so great a pressure to solidify
them. After the material has been subjected to pressure, the block, tile or the
like is delivered on to an endless chain carrier or conveyor operating in a tank or
trough filled with water which is cooled by being kept flowing or changing con-
stantly, each block or tile being submerged immediately and while hot and
remaining so from the time it leaves the press, until it has reached the extreme
end of the tank or trough when it is raised out of the water, and being in a cool
condition can be removed and piled until needed for use in paving.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. The manufacture of compressed paving blocks, tiles, and the like from a
mixture of asphalt, non-calcareous hard-stone debris, and powdered limestone, all
previously treated in the manner described, the mixing being effected while the
ingredients are in a heated state, substantially as set forth.
2. In the manufacture of compressed paving blocks tiles and the like, the
preparatory treatment of the asphalt which consists in pulverizing it and then
macerating and agitating it in water, substantially as described and for the purposes
specified.

page_text: 3. Paving blocks, tiles, and the like, manufactured in the manner hereinbefore-
described from the ingredients specified.
Dated this 13th day of February 1897.
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.