CA1320643C

CA1320643C - Abrasive blasting apparatus

Info

Publication number: CA1320643C
Application number: CA000563648A
Authority: CA
Inventors: Bruce Nicholson; Ronald Davis
Original assignee: Gagemarch Ltd
Current assignee: Gagemarch Ltd
Priority date: 1987-04-09
Filing date: 1988-04-08
Publication date: 1993-07-27
Anticipated expiration: 2010-07-27
Also published as: GB8708499D0; IE61329B1; GR880100228A; DK492889A; DK170697B1; DK492889D0; NO885374D0; AU1544888A; AU606416B2; NO885374L; NO169702B; IE881032L; EP0358648A1; DE3866355D1; ES2008443A6; EP0358648B1; RU2051020C1; KR890700430A; WO1988007915A1; JPH02502982A

Abstract

ABSTRACT
ABRASIVE BLASTING APPARATUS
A method and apparatus for mixing separately-contained media such as would be used in a wet abrasive blasting operation comprises a receptacle (10) for a liquid/abrasive medium, a receptacle (11) for a liquid, and a delivery line (20) along which pressurised fluid is adapted to be fed. The receptacles (10, 11) communicate via pipes (22, 23) with the delivery line (20) so that the liquid and the liquid/abrasive medium are entrained by the pressurised fluid. The receptacles communicate with each other via a hole (14) to balance the fluid pressure system between them and a means (15, 19) is also provided to deliver pressurised fluid into at least one of the receptacles (10, 11) in order substantially to balance the fluid pressure system between the receptacles (10, 11) and the delivery line (20) and to facilitate outflow of the liquid/abrasive medium and the liquid into the entraining fluid. The method comprises entraining the separately-contained media such as liquid/abrasive medium and the liquid medium in a flow of pressurised fluid whilst simultaneously applying the pressurised fluid to the media in their receptacles (10, 11) in order to balance the fluid pressure system between the receptacles themselves and the receptacles and the delivery line and to assist their egress into the entraining flow.

Description

`` ~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 ~32~

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.

Claims

1. An apparatus comprising a first receptacle adapted to contain a particulate material or a particulate material and a liquid combination and including an inlet and a bottom outlet; a second receptacle to contain material to be mixed with the contents of the first receptacle and also including an inlet and a bottom outlet; a delivery line in communication with the respective bottom outlet of each of the first and second receptacles; a source of pressurised fluid connected to the delivery line; means connecting the source of pressurised fluid with the interior of one of the receptacles and capable of directing pressurised fluid into said one receptacle behind the receptacle's contents in terms of the outflow of said contents from the receptacle through the bottom outlet; and communication means between the interiors of the first and second receptacles to balance the fluid pressure both between the interiors of the receptacles and between the interiors of the receptacles and the delivery line to facilitate simultaneous outflowing of the contents of the first and second receptacles through their respective outlets into the entraining fluid flowing along the delivery line.

2. An apparatus as claimed in Claim 1, in which the first and second receptacles are located one within the other.

3. An apparatus as claimed in Claim 2, in which the first and second receptacles are separated by a porous wall.

4. An apparatus as claimed in Claim 3, in which the outer receptacle comprises the first receptacle which is adapted to contain a particulate material and a liquid combination and the inner receptacle comprises the second receptacle which is adapted to contain a liquid, the inlet of the second receptacle comprising the porous wall through which liquid can pass into the second receptacle from the first receptacle.

5. An apparatus as claimed in Claim 1, in which a valve is provided at the inlet of the first receptacle for the introduction of the particulate material or the particulate material and the liquid combination thereto, the valve being closable by the application thereto of pressurised fluid from within the fir 5 t receptacle.

6. An apparatus as claimed in Claim 1, in which a means to enable a circumferentially directed jet of liquid is provided to swirl the particulate material to assist its entry into the first receptacle through the inlet.

7. An apparatus as claimed in Claim 1, in which a lance is provided at the end of the delivery line, the lance comprising a straight-bore rigid tube of at least 100mm in length and the ratio of the diameters of the delivery line and of the lance being between 1.5:1.0 and 10:1 inclusive.

8. A method of mixing a plurality of separately contained media, at least one of which is a particulate material or a particulate material and a liquid combination, comprising the steps of providing first and second receptacles to contain said media;
providing a flow of pressurised fluid; entraining the media from the first and second receptacles into the flow of pressurised fluid; simultaneously applying the pressurised fluid behind at least one of the media in terms of said medium's outflow from said medium's receptacle; and providing a communication between the interiors of the first and second receptacles so that either the pressurised fluid or said one pressurised medium acts on the medium in the other receptacle substantially to balance the fluid pressure between the interiors of the first and second receptacles themselves and the interiors of the first and second receptacles and the flow of pressurised fluid to facilitate the simultaneous outflowing and dispersal of the media from the receptacles into the entraining pressurised fluid.

9. A method as claimed in Claim 8, in which one of the media is a liquid with a temperature above the ambient temperature.

10. A method as claimed in Claim 8, in which a porous wall is provided to separate the first and the second receptacles and in which the particulate material is ice.