IMPROVEMENTS IN THE MANUFACTURE OF ASBESTOS MICRO-MEMBRANES FOR FILTERING PURPOSES
Year: 1885

page_text: I, OLIVER IMRAY of N° 28 Southampton Buildings Chancery Lane in the.
county of Middlesex, Fellow of the Institute of Patent Agents do hereby declare
the nature of my invention for "IMPROVEMENTS IN THE MANUFACTURE OF
ASBESTOS MICRO-MEMBRANES FOR FILTERING PURPOSES "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 the process of manufacture of thin layers of asbestos-
felt for filtering purposes, for which Letters Patent N° 2087, dated April 24th 1883
were granted to me, and it consists, firstly in a novel method of finely and
uniformly subdividing asbestos, so as to render it available for forming a felt
capable of retaining the smallest bodies that are in existence, and it further consists
in certain improvements of the process by which the finely subdivided asbestos fibres
are formed into a layer of felt supported by a woven fabric, made of textile fibre yarn,
instead of the electro-plated wire-gauze previously used. The sheets of felt thus
produced are cut in pieces of the desired size, and after their margins have been
rendered impermeable by any suitable means, they are fastened to metal gratings.
To prepare the finely subdivided asbestos, which on account of its purpose I call
micro-membrane stuff, and the fibres and small sticks of which are of smaller
diameters than 50,000 of an inch, only those sorts of asbestos can be used, the
fibres of which are sufficiently elastic to give when treated by an edge roller, a
woolly product and not a powdery one. The fibres of the asbestos reduced to
wooly appearance are next to be reduced in length so as not to contain particles of
greater length than 0.2. This result is obtained either by treating the mass in
the vertical mill for a greater length of time, or by pounding the same in a
pounding mill, or by subdividing it by means of a rag-engine having its knives
adjusted to a distance of from 0.2 to 0.04m. The most satisfactory results have
been obtained when using a so-called Favorita" mill, constructed by Mr. Gläser
of Vienna, Austria.
"

page_text: Once reduced to the state above described namely subdivided into fibres of a
length of about 0.2ms, and a diameter of about 250.000 of an inch, the asbestos is
soaked in water during several days or boiled in water, in order to wet and loosen
all its fibres. Afterwards, an equal weight of granulated crystalline carbonate of
lime or of magnesia or of granulated shells is added to the mass, the largest grains of
the granulated substances having no larger diameter than from 0.12 to 0.2 ins. With
the aid of a stirrer and with the necessary quantity of water, the mixture is
reduced to a homogeneous magma, which is then passed repeatedly through a paint-
mill or a so called "Favorita" mill. The grinding of the mass is carried on, until
it no longer presents a granular appearance to the naked eye. To ascertain
whether the necessary degree of subdivision is reached, about .0016 cubic ins.
C/4 of a cubic centimeter) of the mass is brought into a bottle with about of a
pint (½ litre) of water and the whole is well agitated. If the shaken liquid
assumes the aspect of a thoroughly homogeneous emulsion of milky appearance in
which the naked eye distinguishes fibres but no lumps, the grinding process is to be
considered as finished; in the contrary case it ought to be continued. When the
asbestos fibres are ground with the granulated crystalline minerals, the sharp edges
and points of the latter act upon the fibres like as many wedges and chisels, and
in consequence thereof, the subdivision thus carried through is the finest one that
can be attained.
The shorter the asbestos fibres have been made by the preceding preparation, the
sooner the desired result, indicated by the proof above described, will be obtained,
and the farther the subdivision is carried through, the more homogeneous the
emulsion will look, and the more dense and uniform will be the asbestos felt, made
of the said fibres and destined to perform the office of a filtering material. As
however the solidity of the felt membrane depends directly on the length of the
fibres, a certain limit should not be exceeded, and in all cases, the special purpose
for which the filter is intended should be kept in view.
The next operation is the elimination of the granules of limestone or magnesite,
as these granules would be a detrimental element in the asbestos felt. To this end
the semi-fluid mass, produced by the grinding process is first diluted by water to
the consistency of rather thick milk, and afterwards it is treated with diluted
hydrochloric or sulphuric acid. This treatment is performed in a leaden vessel
provided with a stirrer, and while this latter is operating continuously, the
diluted hydrochloric or sulphuric acid is allowed to pour into said vessel in a thin
stream, until all particles of limestone or magnesite are dissolved. A brisk
effervescence is caused by the escape of carbonic acid, and the bubbles of the car-
bonic acid gas, in expanding as they are developed, act as numerous separating and
stirring-up forces upon the bundles of asbestos fibres. The fact whether the
decomposition in view has been fully accomplished is ascertained after 24 hours,
with the aid of blue litmus-paper, which should no longer be reddened by the
milky liquid, and by the addition of a small quantity of acid, which should cause
no effervescence.
If neither of these two phenomena takes place, the micro-membrane stuff is to be
regarded ready for use.
The manufacture of the filtering material proper is effected by immersing into a
vessel filled with water, the woven fabric made of vegetable or animal fibres, and
stretched over a wooden frame, the micro membrane stuff suspended in water being
successively poured into said vessel and the water drawn off through a hole in the
bottom against which the said frame is tightly held.
In the accompanying drawing, forming part of this specification, and in which
similar letters of reference indicate corresponding parts in all the figures,
Fig. 1 is a plan of the frame over which the woven fabric is to be stretched.
Fig. 2 is a sectional side elevation of the said frame.
Fig. 3 is a similar view to a larger scale of one border of the frame, shewing in
what manner the woven fabric is fastened.

page_text: asbestos felt.
of an apparatus what may be used for preparing the
Fig. 5 is a sectional elevation to a larger scale of the flat cup through which the
water with the asbestos fibres suspended therein flows into the vessel containing
the immersed frame.
The frame A over which the woven fabric of vegetable or animal origin is
stretched is a simple wooden frame, the dimensions of which correspond to those
of the hereinafter described india rubber lining on the bottom of the sediment
trough. The upper surface of the said frame A is covered with brass wire-gauze
made of wire from 0.004ins to 0.008in thick and having meshes from 0.004in to
0.006 in wide; the outer surface or circumference of the frame is made tapering
toward the top. The woven fabric B, consisting of yarn from 0.004in to 0.006in
thick and having meshes about 0.004in wide being placed upon the frame A, the
said fabric is stretched by placing upon the frame A a second frame A¹, closely
fitting the frame A by its tapering inner edges and thus jamming the edges of the
fabric. By means of an indiarubber lining a secured to the outer frame A¹,
friction is increased and consequently a more perfect stretching of the fabric B
obtained.
Thus prepared, the fabric B stretched over the frame A is inserted into the
apparatus in which the asbestos felt is formed by the precipitation of the micro-
membrane stuff from the water in which it has been suspended. This apparatus
essentially consists of an open vessel or trough C into which the frame A A¹
carrying the woven fabric B. can be so inserted as to tighten by its bottom
surface round the outlet provided in the bottom of the trough C. Above the said
trough is arranged a sort of funnel D into which the micro-membrane stuff is
filled and beneath the trough C are situated two reservoirs E E'; from the
reservoir E, water may be conveyed to the funnel D by means of pneumatic
pressure, and into the other reservoir E¹ the water contained in the trough C may
be drawn off'; the contents of the reservoir E¹ may also be caused by pneumatic
pressure to rise back into the trough C.
The bottom of the precipitation trough C has an india-rubber tube c¹ secured to
it, which tube surrounds the funnel-shaped outlet socket c along a line answering to
the shape of frame A in order that the said frame when laid down upon this india
rubber tube c¹ and pressed down upon the same may form a watertight enclosure
round the outlet, and thus the liquid will be bound to pass through the woven
fabric. The frame A is pressed down upon the india rubber tube c¹ by means
of wedges c² pushed in between the upper surface of the frame and pins c³ pro-
jecting from the inner side of the precipitation trough C.
The frame A A¹ being inserted in the described manner, and the communication
between the trough C and the reservoir E shut off by means of the cock c', water
from the reservoir E' is caused to rise into the trough C in sufficient quantity to
cover the frame at a height of at least 6 whereupon the stop cock c* in the
tube co, connecting the reservoir E, to the trough C is shut.
The funnel D also having its cock d closed, is then filled with coarser micro-
membrane stuff in the proportion of from 300 to 450 grains per 10.5 square feet
of fabric, and afterwards a sufficient quantity of water to fill the funnel D is
allowed to rise from the reservoir E. To this end the cock or valve e¹ in the tube e
is opened, and compressed air having an excess of pressure of about 1/3 of an
atmosphere, is permitted to enter the reservoir E through the pipe e communicating
with both reservoirs E and E¹; when operations are commenced the reservoir E
ought to be full and reservoir E¹ nearly empty. The water pouring into the
funnel D reduces the micro-membrane stuff therein contained to a homogeneous
emulsion, and as soon as said funnel is full, the water supply is shut off and cock d
is opened to allow the asbestos emulsion to flow into the precipitation trough C.
The flowing out takes place through an india rubber tube d¹, the lower end of
which, extending below the water surface, carries a dish shaped disc d³, by which

page_text: the emulsion is caused to diffuse itself in all directions, while flowing over the
edge of the said disc. To promote the diffusion of the asbestos fibres above the
woven fabric, destined to form the bed or support of the mineral felt, the tube d¹
is moved to and fro by the hand while the outflow takes place.
When the funnel D is wholly emptied, the valve d is shut again and another
portion of micro membrane stuff namely about 150 grains of fine stuff per
10.5 square feet of the fabric is put into said funnel and then water is allowed to
enter the same in the way heretofore described, with the difference however that
at the moment when the emulsion is drawn off into the precipitation trough C, this
latter is put in communication with the empty reservoir E'; to this end the cock c¹
in the pipe c³, connecting the outlet c to the reservoir E, is opened. At the same
time the three-way cock e³ arranged in the air conduit e, between the reservoirs E
and E,, and the box or seat of which communicates with a second conduit e* for
compressed air, is turned in such a manner as to cut off communication between
the two reservoirs E E₁, while the compressed air continues to flow through pipe es
into the reservoir E, and the air driven out from the reservoir E₁, by the entering
liquid, escapes through the opened cock c*.
With the described positions of all cocks or valves possibility is afforded for
causing the water contained in the reservoir E to flow continuously from the
reservoir E through pipe e, funnel D precipitation trough C and pipe co, into the
reservoir E¹. To avoid the formation of eddies in the precipitation trough C, the
upper mouth of the funnel shaped outlet socket c is covered by a disk c, which
allows free passages on its circumference only.
The trough C and the reservoirs E and E¹ are of equal capacity, and consequently,
as soon as the outflow of water from pipe e ceases, that is to say, as soon as the
reservoir E, is full, the valve c' in the pipe which connects the outlet-socket c to
the reservoir E should be opened. Obviously, the supply of compressed air is then
checked, and the three-way cock e³ allows the air displaced from the reservoir E by
the entering liquid to escape.
When the level of the liquid has descended nearly to the surface of the fabric
covered with the asbestos felt, the last portion of the water is caused to pass
through the asbestos felt very slowly, this being effected by partly shutting the
cock c. By this proceeding a dead appearance of the asbestos-felt is finally obtained,
indicating that the surface of the liquid has fallen beneath the layer of felt. The
cock in the upward curved pipe c¹o communicating with the bottom portion of
the trough C inside the india rubber tube c¹ is now opened, in order to admit the
outer air beneath the fabric B and at the same time the three-way cock c³ is
wholly opened again, to permit the remaining water to rapidly flow into the
reservoir E'.
With reference to the described process, it should be observed that in those
places of the asbestos felt, where the density of the layer is less, in consequence of
à non-uniform stratification of the asbestos fibres first precipitated, the velocity of
the passing water will obviously be greater and thus a greater quantity of fibres
will be there deposited in the subsequent course of the process; on the other hand
the velocity of the water will be smaller in the portions of the felt grown denser at
the beginning, and in this manner the formation of the sediment is automatically
regulated so as to give an absolutely uniform felt.
The layer of asbestos felt, supported by a woven fabric and made in the
described way is then withdrawn from the precipitation trough and is vertically
Buspended in a drying kiln, the temperature of which is so regulated that the
drying process is finished in from 3 to 4 hours. When dried, the felt grows
perfectly white and adheres very closely to the woven fabric without a cement.
"
The water contained in the apparatus may be used several times, that is to say
the water sunk down into the reservoir E' inay be caused by pneumatic pressure,
to rise again into the precipitation trough C. By means of the described apparatus
from 3 to 4 complete processes can be carried through in an hour.

page_text: 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 described process of splitting asbestos into the finest fibres the said
process consisting in grinding the coarsely subdivided asbestos with granulated
crystalline carbonates or shells soluble in acids and having a degree of hardness of
from 3 to 4.5.
2. The described process of eliminating the said granular particles from the
mass of asbestos fibres and mineral particles and of simultaneously loosening the
mass, the said process consisting in the treatment of the mass with an acid which
dissolves the granular particles and causes the development of carbonic acid, the
expanding bubbles of which loosen the clusters of fibres.
3. The described filtering material, consisting of a woven fabric of vegetable or
animal origin provided with a thin layer of asbestos-felt, made of the finest fibres
that can be obtained.
4. The described process of making the asbestos felt, the said process consisting
in the precipitation of the asbestos fibres, suspended in water, upon the stretched
fabric.
5. In the described process of making the asbestos felt for the purpose of
producing a uniform sediment adding the asbestos fibres by separate portions and
inducing a suction at the lower surface of the fabric by drawing off the water
below the same.
6. The joining of the asbestos-felt to the woven fabric by first forcing the fibres
onto said fabric by means of suction acting upon the underside of the fabric and
afterwards drying the layer of felt so produced.
Dated this 12th day of May 1885.
ABEL & IMRAY,
Agents for the Applicant,
28, Southampton Buildings,
London, W.C.