Note: Descriptions are shown in the official language in which they were submitted.
`` ~32~
ABRASIVE BLASTING APPARATUS
This invention relates to abrasive blasting
apparatus especially but not exclusively a wet abrasive
bla~ting apparatus.
In wet abrasive blasting apparatus the abra3ive
medium is entrained in a pressurised liquid flow or
~aseous-erltrailled liquid flow ~hereinafter for
convenience simply referred to as "pressurised fluid
flow") and is directed against the surface or other
article to be treated by a controllable nozzle. It is
common practice with such an apparatus to add a dry
abrasive mer~ium into a gaseous stream and then to add
liquid to wet the abrasive medium prior to its e~ress
from the nozzle outlet so that dust generation at the
work area is reduced.
This liquid is normally delivered into the abra~ive
and pressuri~ed fluid flow by & separate pump the
inclusion of whioh makes the co t of the bla~ting
apparatus more expensive than is desirable, renders the
blasting apparatus more prone to breakdown, and requires
a greater technical knowledge of the operator. A further
disadvantage is that variations in the entrainin~ fluid
pressure require either manual adju~tments of the
pressure outflow from the pump, or the provision of a
pressure balancing control means between the entrainin~
fluid supply and the pump.
As a result, control of the apparatus with
particular reference to the abra~ive medium/liquid
outrlow is difficult, in the first instance, with
oonsequent variation in the efficiency of the apparatus,
an(l, in the second instance, the cost of the apparatus is
further increased by the need to prtavide the pre~Yure
balancing control means which, in any case, does not
provide instantaneous adjustment of the pump upon
~ariations in entrairlin~ fluid pressure occurring, a~ain
with adverse effect3 on the efficiency of the apparatus.
~ 32~3
It is an object of the present invention to provide
an apparatus for wet abrasive blasting which obviates or
miti~ates the aforesaid disadvantages of cost~ varying
control and efficiency.
The apparatus according to this invention may be
used dry, or the apparatus may, more generally, be
employed for purposes other than abra~ive blasting. More
detailed references to these alternative uses will be
made .later.
Generally, therefore, apparatus according to the
present invention comprises a plurality of receptacle~
for colltaining media to be mixed and a source of
pressurised fluid adapted to be placed in communication
with the receptacles to entrain the media out of the
receptacles for delivery out of a pipe, duct or similar
connected to the source and to the receptacles,
charaoterised in that a means is provided for directing
pressurised fluid from the source into at lea~t one of
the receptacles behind the media in terms of media
outflow from the receptacle and in that a communication
is provided between the receptacles to provide a
substantially balanced fluid pressure system between the
receptacles.
Also according to the present invention -there is
provided a method of mixing a plurality of separately-
contained media, by entraining the media from their
containers into a flow of pressurised fluid and
characterised in that the pressurised fluid i~
simultaneously applied to the media in their container~
to assist egres~ o~ the media into the entraining ~low
and in that a communication exist~ between the container~
substantially to balance the fluid pre~sure system
between the containers.
More specifically there i~ provided an appara-tus for
wet abrasive blasting comprisin~ a receptacle for a
liquid~abrasive medium, a receptacle for liquid and
delivery line along which an entraining pre~surised fluid
is adapted to be fed and with which the receptacles are
adapted to communicate, characterised in that a meana
adapted ~o deliver said pressurised fluid into at least
one of said receptacles is provided and that a
communication exists between the receptaclea
substantially to balance the fluid pressure aystem
between the receptacles themselves and the receptaclea
and the delivery pipe to facilitate outflow of
liquidJabrasive medium and the liquid into the entraining
~luid flowing along the delivery line.
Preferably the receptacles are coaxial and
conGentric.
Prererably an inner receptacle contain~ the
liquid~abrasive medium, while an outer and surroundin~
receptacle contains the liquid. i~
Preferably, the communication between each
receptacle and the delivery pipe ia valve-controlled.
Preferably, the pressurised fIuid ia delivered to
the interior of the inner receptacle and a communication
is provided between the inner receptacle and the outer
receptacle to provide the balanced fluid preasure system.
Preferably, at least one of the receptacles is
provided with a fast pressurised fluid exhaust, which is
normally closed.
Preferably, the liquid is water with or without
additives e.g. rust inhibitora. Preferably the
pressurised fluid is air.
Preferably, within the inner receptacle water i~ fed
in firqt Eollowed by abrasive~ such, for example, aa sand
to ensure effective mixing and to prevent clogging at the
receptacle outlet.
The present invention, therefore, provides a
pumpless wet abrasive blas-ting apparatua and aa the
entrainin~ pressuri~ed fluid is also applied directly to
the liquid/abrasive medium and the separate liquid there
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is instantaneous and equal adjustment to the entraining
pressurised fluid and direct pressurised fluid upon any
pressure variations occurring at the pressuri~ed fluid
source.
An embodiment o~ the present invention will now be
described, by way of example, with reference to the
accompanying drawing, in which:-
Fi~ure 1 i5 a part sectional elevation of an
apparatus for wet abrasive blasting according to the
lQ p~esent invention; and
Figure 2 is a corresporlding plan view.
The apparatus comprises two co-axial concentric
receptacles or chambers 10 and 11. The inner chamber 10
serves to contain the abrasive medium which is for
example sand, which sand may be wet sand. With the
present invention it is not nece~sary as i~ customary
with wet abrasive blasting apparatus using sarld as the
abrasive medium to employ dry sand which is often
delivered to the apparatus bagged. As a consequence the
present invention provides a wet abrasive blastin~
apparatus in ~hich it is possible to re-use wet ~and. The
inner chamber 10 in use also, of course, contains water
and it is to be noted that the water i~ always introduced
first into the inner chamber 10 followed by the sand ~or
other solid abrasive medium) to ensure that there is
ef~ective mixing of the sand and water and no clo~ging at
the outlet 12 of the inner chamber. The introduction of
the sand into the water in the inner chamber 10 causes
the sand to sink through the water thus gettin~ wet
immediately. The introduction of pre~suri~ed air into the
inner chamber 10, as hereafter described, causes a
swirling- action in the inner chamber 10 to complete the
mixin~. The outlet 12 i~ disposed at the bottom of the
chamber 10 and the inlet 13 of the inner chamber 10 is
provided at the top of same.
13~3~
The outer chamber 11, in use, contains additional
water for ~ddition to the sand/water mixture egre~sin~
from the inner chamber 10 as will be described later.
There is at least one hole 14 providing a
communication between the outer chamber 11 and the inner
chamber 10, which hole 14 is disposed at the upper end of
both chambers 10, 11.
The inlet 13 to the inner chamber 10 is controlled
by àn air lock valve, for example a mushroom-type valve,
15, which valve 15 is closed on application thereto of
pressurised air.
The apparatus has as its operational or motive fluid
pressurised air which passes from a pressurised air
source, such for exa~ple as a pressurised air ~ains ~not
shown) to a delivery pipe system generally indicated at
16,
~ir under pressure is delivered from a source (not
showrl), possibly an air compressor to the pipe system 16
at the main inlet 17 controlled by a valve 18. .
20Pressurised air is dellvered to the valve 15 by a
pipe 19, which air then flows from the inner chamber 10
into the outer chamber 11 via the hole 14.
Pressur;sed air is also delivered by a pipe 20,
valve controlled as indicated at 21 to an abrasive
blasting hose and nozzle ~not shown) coupled to the pipe
20 by a bayonet joint connection as indicated at 38. The
noæzle of the abrasive blasting hose is provided with a
deadman's handle so that the abrasive blasting operation
is controlled by the operator (release of the handle
closin~ the nozzle and discontinuing the abrasive
blasting operation).
Preferably the blasting nozzle i8 of the lance type
and not a conventional venturi nozzle as it has been
found that abrasive tends to lod~e in and clog a venturi
nozzle durin~ use of the apparatus. The lance provides an
outflow for the pressurised fluid which ha~ a smaller
~32~
bore than that of the delivery pipe 20 effectively to
concentrate the presgurised fluid flow therethrou~h ~o
that it can be appropriately directed by the operator. It
has beerl ~ound that the lance operates effectively when
the ratio of the diameters of the pipe 20 and of the
lance is in the range 1.5 : 1 to 10 : 1 inclusive with a
1ance that is at least 100 mm in length. Typically, the
diameter of the bore -of the lance is of the order of 15
mm l'or a ~5 mm diameter pipe 20 for delivery of
pressurised air at 10 cubic metres per minute at 100 psi.
The length of the lance is usually of the order of 450 mm
to enable the operator to distance himself from the
blasting and grip the lance effectively.
The chambers 10 and 11 communicate with the pipe 20
via pipes 22 and Z3 respectively each of which i~
respectively controlled by a valve 24, ~5.
Thus the pipes 2Z, 23 provide communication between
the bottom of the chamber 10 and Il with the pipe 20.
Adjacent the top of the outer chamber 11 there is
provided a fa~t exhaust pipe 26 controlled by a valve 27.
Water is supplied to the inner and outer chamber~
~rom for examp]e a mains water supply (not shown) by a
pipe 28 incorporatin~ a non-return valve 29 and an
open~close valve 30. The water is delivered directly into
the chamber 11 by the pipe 28 to whioh is connected a
pipe 31 for delivering water into the inner chamber 10,
this pipe being valve controlled as indicated at 32.
A water level control or overflow pipe 33
communicates with the inner chamber 10, this pipe 33 also
being valve controlled a~ indicated at 34.
The various valves are indicated as being manually
controlled but it is clearly to be understood that these
valves can be subject to automatic control in any
convenient manner.
~32~4~
To render the apparatus ready ~or use the valvea 18,
Zl, 24, 25, 27, 30, 32 and 34 are all closed. Valves 30
and 32 are then opened to allow water to flow into the
inner and outer chambers 10, 11. A given quantity of
S abrasive medium ~or example sand ~wet or dry) i then fed
through the inlet 13 which is open owing to no air
pressure being supplied to the valve 16 to close game.
Water continues to be fed into the chambers 10 and 11,
and, when the required total volume of sand and water is
delivered into the inner chamber 10, water will.flow out
of the pipe 33. At this stage, the valve 32 i~ closed
followed by the valve 34. When ~ufficient water has been
fed into the chamber 11, the valve 30 is al~o clo~ed.
The valve 17 is then opened cau ing the valvs 15 to
be moved to the closed position and pres urised air to be
introduced into the inner chamber and, through the
communicat;on hole 14 J into the outer chamber 11.
Valve 21 i5 now opened allowin~ pres~uri~ed air to
flow along the pipe towards the ho3e and no~zla ~not
~hown). Valves 2~ and 26 are then opened to the desired
degree to allow the water/sand mixture from the chamber
10 and additional water from the chamber 11 to be moved
into, and be entrained by, the air~treAm for deli~ery
alon~ the hose out of the nozzle whence it is directed
against the surface or other article to be abra~ive
blasted.
The sand/water mixture and the additional water are
subjected to the same air pres~ure in the upper part o~
the chambers~10 and 11 as that which is used to entrain
them out o~ their re~pective chamber~.
Thus, any variation in the air pressure at source is
automatically and instantaneously applied to both the
entrainin air and the internal air contained within the
chambers 1~ and 11.
132~3
At any stage, the valve 24 can be closed, and water
only from the chamber 11 be fed into the airstream, for
the purposes of washing down the work area.
Alternatively, the valves 24 and 25 can be closed
leaving air travellin~ through the hose and nozzle, ~or
blowing or drying purposes.
During operation, the air feed pressure can be
varied up or down in order to achieYe different rates of
working or different types or levelq of finish on the
work area. A pressure gauge may, in these circumstances,
be included in the air inlet line 17 in order that the
operator can more accurately jud~e the working pre~8ure.
The normal sequence of operations for shutting of~
the apparatus is first of all to close the valve 24 to
~reverlt any further emission o~ abrasive. When all of the
abrasive ill the hose has cleared, the valve 25 may be
closed to prevent any further water going down the line.
After all the water has cleared from the hose, the valves
~1 and t8 are closed. The valve 27 may then be opened to
allow fast reduction of the air pressure in vessels 10
and 11, which in turn allows air lock valve 15 to open.
If, for any reason during normal operation, an
emergency stop is required, this- can be acti~ated
manually, or triggered automatically (by relea~e of the
deadman's handle, for example), by opening the valve 27,
preferably with a simultaneous closure of the valve 18.
Means is provided to effect fast filling of the
chamber 10 with substances which do not flow quickly on
their own (e.f. wet sand or slurry). Such means ConQists
of a water jet 35 situated inside and in close proximity
to the wall of the filling hopper 36 at the top o~ the
apparatus. The jet 35 is circum~erentially-directed that
is swirls water round the hopper area, when required~ and
enables the entry of the material throu~h the open inlet
13 and into the chamber 10. A valve 37 controls the flow
of water to the jet 35.
~ 3 ~ i3
It is to be noted that additives can be included in
either the water in the chamber lO, or alterna~ively, in
the water in the chamber 11, such an additive bein~, for
e.~ample, a rust inhibitor if the surface or article bein~
treated is formed o~ metal J or an a~ti-freeze material
for low temperature working. Alternatively, the additive
may be introduced in powder or granular form, oixed with
the abrasive. Because the total volume of material in
both chambers is known at commencement of the operational
sequence, pre-measured doses of additive can be included
in either chamber to give an accurate dilution of the
additive.
The wet abrasive blasting apparatus described above
can be used dry and in thi case the dry abra~ive or
other abrasive medium is simply contained within the
chamber lO, the water supply system being closed off and
the sand or other abrasive medium being entrained along j-~
pipe 20 throu~h the pipe 22 via the open valve 24, the j'
sand being subjected to the internal air pres~ure equal
to the entraining air pressure as described above.
The apparatus can also be used for ice blasting and
in this case the inner chamber will contain ice particle~
and water and the outer chamber l1 will contain water. It
is to be noted that the ice particles formed from water
will be prevented from coagulating ~freezing togetherl by
introducing suitable additives into the water prior to
freezing. 9uitable additive3 would be for example poly-
phosphates.
The above described apparatus can, as afore~aid, be
used either wet or dry as described and it can be used
for washing down using water only from chamber lO or even
from chambers 10 and ll.
The apparatus provides faster cleaning than known
wet abrasive blasting apparatus (all other operational
factors being equal). It can be up to-20% fa~er or even
more in certaln circumstances. The reason for this i3
- - - L 3 ~
that each particle of abrasive, having bein~ soaked under
pressure, i~ enclosed in a film of water so that its
effective weight is increased as it leaves the blast
nozzle. Thus its momentum is greater and it does more
work when it strikes the workpiece surface.
The apparatus is not subject to "choking" as are
known apparatus which, on occasion, become blocked at the
abrasive outlet of the pressure vessel. In practice, with
t.he known apparatus, the~e blockages are usually relieved
by turning off the main air supply ~e.g. closing valve
21) momentarily. ~i;
The apparatus is relatively cheap to manufacture
compared with known apparatus.
There is les~ wastage of abrasive on site since with
15 the apyaratu~ according to the present in~ention all ~`~
spent abrasive can be re-used in the wet condition i.e.
it is not necessary to dry same. -i~
The apparatus can be readily used in high humidity ~J
areas since conta~ination by moisture will not adversely
affect it.
The apparatus is spark free and static free. It is
pumpless as will be clear from the above and due to the
lack of pump there is obviou ly no need to provide a pump
driving generator.
The apparatus has no mechanical working part~ and
due to the simple nature of the apparatus all parts can
easily be chan~ed and renewed in a short time.
The apparatus i~ safe to use and as a result can be
used by unskilled labour.
The apparatus, when used in a wet-blasting process,
produces far less air-borne dust than comparable known
apparatus, and therefore far le~s fall-out at any gi~en
distance from the work area. This makes it environ-
mentally more acceptable.
~ 3 ~
Finally, the apparatus can be used with a wide range
of easily obtainable abrasives wet and dry and in use it
i~ considered that there will be a lower usa~e of
abras;ve than with other wet abrasive blasting systems
~in the region of 20% le3s ~ and the apparatus involve~
less clearing up on site than conventional wet abra~ive
blasting apparatus.
The apparatus according to the present invention is
extremely versatile and can be used, inter alia, as
~0 follows: ~
1. Wet or dry abrasive cleaning of stone, brick,
terracotta, steel, iron, and all other hard or semi-
hard surfaces.
2. Stripping of paints and other coatings from the~e
surfaces, either in one operation or layer by layer.
3. Wash;ng off of these surfaces.
4. Removal of contaminant from surface~, e.g. radio-
active contamination or biolo~ical contamination
~pos~ibly using chemical additive~ in the water to
improve the efficiency of the treatment); removal of
oils and greases from surfaces (possibly using hot
water, or solvents in place of water, to speed
removal).
5. Removal of graffiti from stone and other surface
6. Texturin~ of surfaces either for ae~thetic
appearance or as a preparation for over ooating or
bonding of the surface; the exposing of grain on
timber surfaces; the 'frosting' of glass to make it
opaque; the roughenin8 or matting of plastic and all
other surfaces.
7. Engraving of glass, stone, plastic, and other
surfaces, using suitable mask~ where appropriate.
8. Mixing of materials, dilution of mixes, and spray
application of material~, the mixing of substances
in one or more forms (such ag solids in powder,
granlllar or fibrous form, or semi~solid materials,
~ 3 ~ 3
or liquids) with themselves or with each other, and
the spray or 'bla~t' application of the re~ultant
mixes. For example, the mixing and application of
renders, slurries, coatin~s, paints, adhesives/ de-
icing mixes (e.g. mixin~ salt with sand or gravel
and sp~aying onto roads liable to freezing, or de-
icing mixes onto aircraft), the mixing of plant
seeds into culture media and the ~pray applicatian
of such; the mixing and spraying of fertiliser~ and
weedkiller~ onto agricultural land; the mixing of or
coating of textile fibres with bonding aeent~ and
their spray application in, for exampLe, bonded
fabric production; the impregnation of surfaces with
another substance; the variegated colouring of
surfaces such as floors, ~alls, tiles, by using
different coloured materials in the different
chambers or of different densities on one chamber.
Modifications may be made to the above described
apparatus. ,~ ~?
For example a porous wall may be provided between 1-
the chambers lO, ll in order to allow for the movement
of, say, a liquid from chamber ll into chamber lO. For
example, when ice blasting, ice and water would be put
into chamber lO, and water into chamber ll. If the water
in chamber 10 is reduced too much during the blastin~
operation, then water can percolate from chamber ll to
chamber 10 and so prevent clogging of the ice in chamber
10 .
In another embodiment of the invention, an outer
chamber is used for the abrasive/liquid medium and an
inner chamber for the liquid medium. Here, the inner
chamber can be of a small volume with respect to the
outer chamber and a porous wall can be used to divide the
chambers so that the liquid flow~ from the outer chamber
into the inner chamber to charge it with liquid prior to
and during the blasting to obviate the need far separate
~2a~
pipework and other filling means. Some ~f the abrQsiYe
may al~o pass into the inner chamber through the wall but
this does not inhibit the mixing and blasting proceYs-
However, thls is preferably prevented by making the pore
size in the wall such that passage of the abrasive
therethrough is prevented. Effectively, in this
embodimetlt the inner cha~ber is reduced to a porous pipe
located in the outer chamber and communicating therewith
above the level of the media contained therein, through
whîch pipe liquid can be drawn off from the liquid/
abrasive medium and entrained separately in the
pressurised fluid from the abrasive/liquid medium.
The apparatus may comprise more than two chambers
provided all the chambers are in communicatio~ so that
there is in the chambers air pressure equal to the
entraining fluid pressure.
The chambers may be located one within the other and
be coaxial and concentric as in ths above described
apparatus or they may be dispo~ed in side-by-~ide
relationship either parallel one with another or in
juxtaposed coaxial relationship.
The chambers may in fact be separate one from
another and there may be two or more chambers provided
there is communication between them to ensure common
t`luid pressure within all the chambers, which pressure i8
equal to and variable with the entrainin~ fluid pressure.
