An Improved Mode of Producing and Applying a Sand-blast, and Apparatus to be used therefor.
Year: 1893

page_text: Date of Application, 22nd June, 1893
Complete Specification Left, 12th Dec., 1893-Accepted, 13th Jan., 1894
PROVISIONAL SPECIFICATION.
An Improved Mode of Producing and Applying a Sand-blast, and
Apparatus to be used therefor.
I JEREMIAH EUGENE MATHEWSON of Bellefield Works, Sheffield in the County
of York, Engineer, do hereby declare the nature of this invention to be as
follows:-
:-
The object of this invention is to increase the efficiency of the sand-blast
employed in operating upon the surfaces of metal, wood, glass, stone, &c., when
compressed air or gas is used, in contra-distinction to steam, as the motive force,
where the latter is unavailable.
Hitherto the sand blast has been generally obtained, whether the motive force
used was steam or compressed air, by the creation of a partial vacuum, followed
up by an inward rush of atmospheric air, which carried forward by the sand to the
steam or air jet, and greatly reduced the intensity of the blast, thereby necessitating
an undue expenditure of power, to secure an efficient velocity in the sand blast.
Instead of allowing atmospheric air to rush forward with the sand in response to the
air jet which creates the impelling power, I now propose, when using compressed
air or equivalent gas for sustaining the blast, to conduct air of like pressure into
the sand hopper, and thus to ensure the even flow of the sand (unmixed with atmo-
spheric air) out of the hopper, by its own specific gravity, so as to mix with the
jet of compressed air, and move forward under its impulse, to reach the work
presented to its action.
The jet of air used to impart the impelling force to the sand, has served its
purpose when the required motion has been given to the sand, and if it is allowed
to strike the work along with the sand, its action will be to detract somewhat
from the efficiency of the sand blast, besides being liable to disturb the stencil
material.
The impact of the sand upon the work will, as is well known, cause a partial
disintegration of the sand, and of the surface of the work under treatment, and
the dust thus produced it is most desirable to separate from the falling grains of
sand, which still remain suitable for use in future work.
To provide against the detrimental action of the spent air above referred to, I
prolong the blast pipe by another pipe or tube of gradually increasing diameter,
which allows the air to expand and lose its density to some extent, and in order to
separate the dust created by the operation of the sand-blast from the useful sand,
I cause a separate current of air to meet the current of spent air passing with the
sand towards the work, and draw away the dust.
The apparatus which I employ in carrying out the object of my invention, may
be constructed to deliver the blast in a horizontal, or any other direction, but in
any case, substantially the same arrangement is retained.
Supposing a horizontal blast of sand to be required, I provide a novel construction
of hopper, which consists of three compartments, set one above the other; the
uppermost is open to the atmosphere, and is supplied by hand with sand, which
is discharged by valves, from time to time, into the second compartment, which
is made air-tight. This second compartment is similarly fitted with valves for
discharging the sand into the third compartment, or hopper proper, the vent of
which opens for the continuous discharge of the sand into a horizontal blast pipe
leading from the compressed air supply. By this arrangement, fresh sand can
be supplied to the apparatus without stopping the working.
Leading from the main air supply pipe, is a pipe with two branches, one of which

page_text: delivers air into the second, and the other into the third, or lowermost, compartment
of the hopper.
By supplying compressed air to the second compartment, not only can the supply
valves be automatically closed, but the sand supplied thereto will be allowed to
fall by gravity, unaccompanied by any rush of air, into the third compartment.
The air admitted to the third compartment balances the pressure in the second,
and hence the free down-flow of the sand. It also facilitates the discharge of the
sand from the third compartment into the blast pipe, and assists in ensuring the
production of an energetic sand blast. The upper branch of the air pipe is
furnished with a cock for cutting off the compressed air, and a regulatable outlet
for the escape of the compressed air will be provided in the second compartment.
The removal of the pressure from this compartment, when a fresh supply of sand is
required, will allow of such fresh supply being delivered thereto from the first
compartment, preparatory to being discharged, in turn, into the third compartment,
or hopper proper.
To the end of the blast pipe, I may connect another pipe of gradually increasing
diameter, which allows for the expansion of the current of compressed air after
the sand has acquired a powerful momentum, and prevents its mixing with and
carrying forward the surrounding atmosphere. This expansion serves also to arrest
the air in its forward movement, and facilitates the dealing with the dust arising
from the action of the blast. The sand blast, in rushing from the conical pipe to
the work, may pass through a vacuum chamber, the partial vacuum in which is
created by discharging a jet of air from the main supply into an exit pipe, which is
open to the chamber, or by other convenient means.
The effect of this arrangement is to induce an inflow of air from the atmosphere
at the opening made for the exit of the sand blast, which inflow overcomes the
outwardly-passing air current, and draws inwards the floating dust, the result of
the pulverisation of the grains of sand and of the surface of the work.
In producing a vertical sand-blast apparatus, I fix the blast pipe centrally in the
hopper, composed, as before, of three compartments. The lower end of this blast
pipe opens into a compressed air chamber, and immediately below the pipe a table
is fixed to receive the sand as it falls from the hopper. The sand is then carried
upwards by the current of compressed air, and discharged against the work, say, a
plate of glass, which, in this instance, will close the opening of the case opposite
the delivery end of the blast pipe.
In this arrangement, the conical tube and vacuum chamber may be used as before
described.
Dated this 22nd day of June 1893
NEWTON & SON,
Agents for the Applicant.
COMPLETE SPECIFICATION.
An Improved Mode of Producing and Applying a Sand-blast, and
Apparatus to be used therefor.
I, JEREMIAH EUGENE MATHEWSON of Bellefield Works, Sheffield in the
County of York, Engineer, 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:-
The object of this invention is to increase the efficiency of the sand-blast
employed in operating upon the surfaces of metal, wood, glass, stone, etc., when
compressed air or gas is used, in contradistinction to steam, as the motive force.
Hitherto the sand-blast has been generally obtained, whether the motive force
used was steam or compressed air, by a kind of injector producing a partial
vacuum in the sand pipe, the sand being carried forward to the steam on air jet

page_text: by an inward rush of atmospheric air. This inward rush of air it has been found
considerably reduces the intensity of the blast, and necessitates an undue
expenditure of power to secure an efficient velocity in the sand-blast.
Instead of allowing atmospheric air to rush forward with the sand in response
to the compressed air which, producing the vacuum, creates the impelling power,
1 now propose to allow the sand to fall from the hopper, by its own specific
gravity, directly into, and so as to mix with, the compressed air current, and
move forward under its impulse into the blast pipe, where it receives its maximum
velocity, and thence to the work presented to its action.
In order to do this in the ordinary way, it is found necessary to have a column
of sand in the hopper of considerable height, varying with the pressure of the
compressed air, so as to prevent the air, so to speak, blowing the sand back into
the hopper. Such an arangement would be extremely inconvenient under high
pressures, as a very high column would be required, and I therefore overcome
the inconvenience by equalising the pressure above and below the sand.
For this purpose, I conduct air of equal pressure with that used for the sand-
blast, into the sand hopper, above the sand, which counterbalances that below the
hopper, and thus ensure the even flow of the sand out of the hopper.
The jet of air used to impart the impelling force to the sand, has severed its
purpose when the required motion has been given to the sand, and if it is allowed
to strike the work along with the sand, its action will be to detract somewhat from
the efficiency of the sand-blast, besides being liable to disturb the stencil material
which protects that portion of the surface of the article being operated upon,
which it is not desired to cut with the sand-blast.
The impact of the sand upon the work will, as is well known, cause a partial
disintegration of the sand, and of the surface of the work under treatment, and
the dust thus produced it is in some cases desirable to separate from the falling
grains of sand, which still remain suitable for use in future work.
To provide against the detrimental action above referred to, of what I may
term the spent air, I prolong the blast pipe by another pipe or tube of gradually
increasing diameter, which allows the impelling air to expand (without mixing
with the surrounding air), and thereby lose its density to a great extent, and in
order to separate the dust created by the operation of the sand-blast from the
useful sand, and also to arrest entirely the jet of propelling, but now spent air, I
may cause a separate current of air to meet the current of "spent air" passing
with the sand towards the work, so as to carry away the dust, and stop the
movement of the "spent air."
The apparatus which I employ in carrying out the object of my invention, may
be constructed to deliver the blast in a horizontal, or any other direction, but in
any case substantially the same arrangement is retained.
In the accompanying drawings,
Fig. 1, Sheet I, is a sectional elevation of an apparatus adapted for a horizontal
sand blast.
Fig. 2, Sheet II, shows an apparatus adapted for a vertical blast.
Fig. 3, Sheet III, shows two ways in which the sand hopper may be adapted to
the blast pipe or jet.
Referring now to the apparatus shown at Fig. 1, which i term the horizontal
blast apparatus, A is a cylinder, which is divided into three compartments, 1, 2, 3,
by hopper or other shaped partitions B B', having openings B³, by which the
sand can pass from one compartment to the other. The uppermost compartment, 1,
may be open to the atmosphere, and is supplied by hand with sand, which is
discharged by a valve or valves C (closing the openings B in the partition B),
from time to time, into compartment. 2. The compartment 2 is similarly fitted
with valves C, closing the openings B² in the partition B', for discharging the
sand into compartment 3, and into a sand hopper A¹ contained therein. This
hopper A opens for the continuous discharge of the sand into a tubular passage,
which I term, for convenience, the contact chamber D, because it is here that the

page_text: stream of sand to form the cutting medium, and the compressed air current to
propel it forward to its work, come in contact. By this arrangement of apparatus,
fresh sand can be supplied to the apparatus without stopping the working.
E is the main air supply pipe, in direct communication with compartment 3,
and leading therefrom is a pipe F, which delivers air into compartment 2, both
pipes E and F being provided with suitable cut-off valves. F¹ is an air outlet
from compartiment 2, provided with a cut-off valve.
By supplying compressed air to compartment 2 (the valve in F1 being closed),
as well as into compartment 3, the valves C in the partition B will be automati-
cally closed, and the sand in the compartment will be allowed to fall by gravity
(the pressure of air in compartments 2 and 3 being equal) through the opening B2
in the partition B', unaccompanied by any rush of air into compartment 3. The
air admitted to compartment 3 is of equal pressure above the sand in the hopper,
and at the outlet in the contact chamber D, and hence the free down-flow of the
sand into the "contact chamber" D, whence it is projected forward to form
the sand-blast. The removal of the pressure from compartment 2 (by closing the
valve in F), when a fresh supply of sand is required, will allow of such fresh
supply being delivered thereto from compartment 1, preparatory to being
discharged, in turn, into the hopper proper in compartment 3.
Although I have described the sand box A as consisting of three compartments,
which is the most perfect form, and one that is necessary to a continuous working,
it will be obvious that where the sacrifice of a little time for renewing the sand
supply is practically no objection, the intermediate compartment 2 may be
dispensed with, the working of the apparatus being stopped while the sand supply
is renewed.
Such an arrangement is practically illustrated in Sheet II.
The "contact chamber "D shown in Fig. 1, consists of a main tubular portion
or body D, having on its upper side a funnel-shaped portion D', in which the sand
hopper A is inserted. One end of the body D is open to the compressed air
supply, and the other end may receive the blast pipe or jet D2 (see Fig. 3).
The body D is of fairly large diameter, and inside, across its diameter, I provide
a plate D³, to catch the sand as it drops from the hopper. The air will pass
freely around this plate D³, and beyond this plate the body D may be contracted
to receive the blast pipe D2, as shown by dotted lines, Fig. 3.
According to this arrangement, the compressed air does not attain its maximum
velocity until it enters the blast pipe D2 (a part of the apparatus which can readily
be renewed, when worn out), and thus the abrasion of the body D, caused by the
rapid passage of the sand therein, is avoided, and the continued renewal of the
parts is rendered unnecessary.
The simplest form of blast apparatus is shown in Fig. 3, the blast pipe D' being
drawn in dotted lines, as before referred to. The same figure also shows the
lengthening of the body D by a flexible pipe H, the blast pipe D' being fitted to
the outer end of this pipe. In this arrangement, it will be seen that practically the
maximum diameter of the body D is retained in the conducting pipe H, so that the
sand will pass comparatively slowly along this pipe, without abrading the interior
surface, and will not attain its maximum velocity until it reaches the blast
pipe D².
*The employment of a contact chamber, as described, enables me, for the first
time, to make use of a flexible conducting pipe to convey the current of mixed
sand and compressed air to the blast pipe or jet, without destroying the flexible
tube.
In adapting the invention to a vertical sand-blast apparatus, I may also use three
compartments in the sand box A, but in the apparatus shown in Sheet II, I have
dispensed with the intermediate compartment 2, and I fix the blast pipe D2
centrally of the apparatus or casing A. The lower end of this blast pipe D opens
into the equivalent for (and which, for present purposes I will continue to call) the
contact chamber D, which is situate within the sand hopper A¹º, and in the

page_text: compartment 3, which also forms the compressed air chamber. Immediately below
the opening of the "contact" chamber D, and at a suitable distance therefrom, a
table L is fixed, to receive the sand as it falls from the hopper proper A¹º.
From
this table L, the sand is carried upwards (by the current of compressed air rushing
in round the edge of the table) through the contact chamber D and blast pipe D², or
jet, and is discharged against the work, say, a plate of glass, which in this instance
will close the opening of the case A, opposite the delivery end of the blast pipe.
To the end of the blast pipe D³, I may connect another pipe of gradually
increasing diameter I (see Figs. 2 and 3), which allows for the expansion of the
current of compressed air after the sand has acquired a powerful momentum in the
blast pipe D', and thus prevent its mixing with, and carrying forward, the sur-
rounding atmosphere. This expansion serves also to arrest the current of air in its
forward movement, and facilitates the dealing with the dust arising from the action
of the blast. The sand blast, in rushing from the conical pipe I to the work, will
pass through what, in effect, is a vacuum chamber, the compartment 1* (which is
enclosed) in this case serving that purpose, and out at an opening J. in a transverse
partition J. A partial vacuum in the compartiment 1 is created by an air injector K
discharging a jet of air into an exit pipe J, which is open to the lower part of the
vacuum chamber or compartment 1, or by other convenient means.
The air supplying the injector K passes from the compartment 3 with which the
injector is connected.
The effect of this injector K is to induce an inflow of air from the atmosphere
at the opening J made in the partition J', for the exit of the sand blast, which
inflow overcomes the outwardly passing air current, and draws inwards the floating
dust (the result of the pulverisation of the grains of sand and of the surface of the
work) and discharges the dust, by the exit pipe J³, to the external air, or to a
settling chamber, as may be desired.
In the arrangement of the flexible tube Fig. 3, the conical tube I may be used
as before described.
☐ As, in the vertical arrangement Fig. 2, the compartment 1 becomes the vacuum
chamber, the sand is preferably contained in a hopper 1* placed therein, otherwise
it would be liable to be discharged from the chamber by the working of the injector.
It will be obvious, however, that the exit pipe J' may be continued upwards, within
the compartment 1, to the height, say, of the top of the hopper 1*, if desired, and.
the hopper might then be dispensed with.
Between the compartments 1 and 3, is a partition B, provided with openings B²,
to allow the sand to pass, the said openings being closed by valves C, as before
described. The partition J' also has openings by which the sand, after it has
struck the object, may be returned to the hopper 1°.
It will be obvious that the arrangement for equalising the pressure both above
and below the sand, is also applicable to a single-compartment apparatus worked
by compressed air or gas.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. A sand-blast apparatus in which a stream of sand issuing from a reservoir, is
projected forward by the direct action of a current of compressed air or gas, and a
portion of the compressed propelling fluid is conveyed to the sand reservoir, so as
to obtain an equal pressure both above and below the sand, whereby the dropping
of the sand from the reservoir into the propelling current, by gravity, in ensured,
as set forth.
2. A sand-blast apparatus for compressed air or gas, consisting of a sand-box A,
divided into two or more compartments by partitions provided with valved openings,
means for supplying compressed air to the compartments, a "contact" chamber D,
provided with a blast pipe or jet D2, a conical extension I, and a vacuum chamber
provided with an air injector, substantially as herein shown and described.

page_text: 3. In a sand-blast apparatus for compressed air or gas, the use of means whereby
the propelling medium is allowed to expand on leaving the blast pipe or jet, and
thereby practically lose its velocity, without detriment to the speed of the current
of sand, as set forth.
4. In a sand-blast apparatus for compressed air or gas, arresting the forward
motion of the propelling medium, and also collecting the dust produced by the
pulverisation of the sand and the surface acted upon, by means of a vacuum
produced in the apparatus by an air or other suitable injector, as set forth.
" contact
5. In a sand-blast apparatus for compressed air or gas, the use of a
chamber" of varying length, in connection, at one side, with the compressed air
supply, and at the other with the blast pipe or jet, and in which the combined sand
and air may be carried forward at a comparatively slow rate of speed, without injury
to the parts, for a considerable distance, and in any direction, to the contracted
blast pipe or jet, where it will attain its maximum velocity, as and for the purpose
set forth.
Dated this 20th day of November 1893