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(11) | EP 0 041 810 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method of abrading surfaces by means of an abrasive jet, and apparatus therefor |
| (57) A method of and apparatus for abrading a surface (1) in which abrasive particles
are projected at high velocity against the surface to be treated and in which the
difficulty of separating dirt or other material particularly bitumastic, adhesive
and chlorinated rubber compounds from the particle for recirculation to be used again,
is effectively overcome by applying a cooling medium (17) as a cryogenic fluid (e.g.
liquid nitrogen) to keep the temperature of the removed dirt and/or particles rebounded
from the surface at a value such that some or most of the dirt can be separated from
the particles. The cooling medium may be applied to the surface to be treated in advance
of the machine as it moves over the surface but is preferable also introduced into
a flow of air drawn into the machine to assist the passage of rebounding particles
and removed dirt along the recirculation path to the seperator. |
[0001] The invention relates to a method of abrading a surface and to abrading machines for blasting a surface to be treated with an abrasive so as to clean and/or retexture the surface.
[0002] Various abrading machines of the kind referred to are known inter alia from U.S. Patent Specifications Nos. 3,034,262, 3,380,196 and 3,691,689 and British Patent Specifications Nos. 1,496,268 and 1,542,495. In the case of British Patent Specification No. 1,542,495 a machine is described in which abrasive particles such as grit or shot, are projected by a vaned centrifugal blast wheel rotating at high speed, with great force along an incident path, through an opening in the machine defining a blast zone, into contact with the surface. The spent particles together with dirt or other material dislodged from the surface, travel upwardly from the blast zone along a rebound path possibly assisted by a stream of fluid entering the machine in the region of the blast zone, such that the energy of rebounding particles and the force exerted on the particles by the fluid are together sufficient to carry the spent abrasive particles along a recirculation path to the projecting means and including a separator for separating out dirt or other material -removed from the surface.
[0003] Dirt to be cleaned from the surface may be of various kinds, for example dust, paint, oil, rust, or other contaminants or coverings, and mixtures of them: these will be referred to herein for brevity as "dirt".
[0004] A machine of the type referred to above may be required to clean various kinds of surfaces having various kinds of surface contaminants. For example a concrete floor surface may be covered with a mixture of oil and dust, or a metallic tank surface may be covered with a mixture of paint and rust, and so on. However difficulty has been encountered in cleaning surfaces which are contaminated with some kinds of dirt, for example bitumastic, adhesive, or chlorinated rubber type compounds. In a machine of the type referred to above, considerable heat is generated inside the casing of the machine as a consequence of the blast cleaning process, and this heat is sufficient to keep plastic bitumastic for example removed from the surface being cleaned. Since the removed bitumastic remains plastic, it becomes bonded to the abrasive grit when the latter is rebounded from the surface for reclaim and return to a hopper which feeds grit to the blast wheel.- This can cause blockage in the return feed system.
[0006] According to one aspect of this invention we propose a method of cleaning or abrading a surface comprising the steps of projecting by means of a machine abrasive particles at high velocity against the surface to be cleaned, moving the machine over the surface while projecting the abrasive particles to remove dirt or other material from the surface and using a cooling medium to keep the temperature of the removed dirt or other material and/or particles rebounded from the surface at a value such that some or most of the dirt can be seperated from the particles before the latter is returned to a projecting device of the machine.
[0007] According to another aspect of this invention we propose an abrading machine of the kind in which abrasive particles are projected at high velocity against a surface to be treated while moving the machine over the surface, to remove dirt or other material therefrom and in which particles rebounding from the surface are recirculated to be used again, along a rebound path including a seperator for seperating removed dirt or other material from the particles, and comprising means for applying a cooling medium to the surface to be treated and/or to the abrasive particles so as to keep the termperature of the removed dirt or other material and/or the particles rebounded from the surface at a value such that some or most of the dirt can be seperated from the particles for recirculation.
[0008] In one embodiment, the cooling medium, which is preferably a cryogenic fluid such as liquid nitrogen, is applied to the ahead surface/of the machine as it is being moved so that the surface struck by the abrasive particles is a cooled surface, the means by which cooling medium is applied comprising a reservoir for the cooling medium and a hood mounted in advance (with respect to the direction in which the machine is to be moved) of a blast zone in which particles contact the surface to be treated, and housing one or more nozzles or the like connected to the reservoir for directing cooling medium onto the surface.
[0009] As described above, air may be drawn into the machine through the blast zone in order to assist the passage of rebounding particles and removed dirt or other material along the recirculation path to the seperator. In such cases, cooling medium can, with advantage alternatively or preferably in addition, be introduced into this air flow.
[0010] In the preferred embodiment, the blast zone which is normally sealed to the surface by a depending skirt seal, is connected to the interior of the hood which has an air inlet from atmosphere preferably fitted with a check or non-return valve. With this arrangement air is drawn into the hood and there mixes with or entrains cooling medium in the form, for example, of.nitrogen vapour generated upon contact of liquid nitrogen with the surface, the mixture then flowing via the blast zone into the machine.
[0011] This embodiment has the advantage of economy since the cold nitrogen vapour generated in the hood which would otherwise escape into the atmosphere as an unsightly and inconvenient mist or cloud, is not wasted but used to further cool the particles and/or removed dirt in the blast zone.
[0012] Embodiments of this invention will now be described by way of example, with reference to the accompanying drawings of which:
Figure 1 is a diagrammatic sectional side view of an abrading machine in accordance with the-present invention;
Figure 2 is a view similar to Figure 1 but of another embodiment of abrading machine in accordance with the present invention; and
Figure 3 is a diagram showing the flow of gases through the abrading machine of Figure 2.
[0013] Referring to Figure 1, a blast cleaning machine is mounted on wheels 2 (one of which is shown) for movement of the machine over a surface 1 to be cleaned. The movement is to the left as viewed in the drawing. It will be assumed that the surface 1 is a concrete or steel surface which is contaminated with dirt in the form of bitumastic, or an adhesive substance, or a chlorinated rubber type compound, which dirt is to be removed, so as to clean the surface. Details of the machine are not shown, since most of its construction is well known. It has an enclosed area defined by a casing and including a rectangular arrangement of seals 3 which define an area (sometimes called the "blast zone") being cleaned as the machine is moved over the surface 1. The seals include a front seal, two side seals, and a rear seal. A vaned blast wheel is rotated at high speed by a motor 4 in known manner, to project abrasive grit, usually in the form of fine steel shot, obliquely downwards in a passage 5 in the casing, so as to strike with great force on the surface 1 in the area or blast zone surrounded by the seals 3. A control panel is indicated at 6. The projected grit breaks up and removes dirt from the blast zone as the machine moves slowly forward. The projected grit, with removed dirt, rebounds from the blast zone and passes up a reclaim channel 7 within the casing to a separator 8 where the dirt is separated from the shot and the dirt is drawn to a draught-creating fan 9 and removed in the direction of the arrow 10 to a dirt-collecting container (not shown). The shot falls from the separator 8 into a hopper 11 for return by a passage 12 to the blast wheel for reuse, that is, for projection again down the passage 5. The casing is a closed system so that the draught created by the fan assists in causing the rebounded grit and dirt to pass up the reclaim channel 7. Since in general the removed dirt is lighter in weight than the grit or steel shot, the removed dirt is carried into the air stream from the separator 8 to the fan 9. Air is drawn into the casing primarily through the rear one of the seals 3, as indicated by the arrow 13. As so far described, the machine and its method of operation are well known.
[0014] Just ahead of the front seal is a small hood 14, open at its lower face, and housing a nozzle 15 for directing a metered quantity of freezing nitrogen gas against the surface 1 so that dirt on the surface is strongly cooled when the machine is over it and the abrasive grit is being projected to remove the dirt. The cooling effect tends to prevent the removed rebounded dirt particles adhering to the rebounded abrasive grit. The effect may be enchanced if nitrogen gas is also fed by a feed device 16 through the rear seal and into the blast zone, so that air being drawn into and through the machine is cold. It is preferred that both devices 2 and 16 should be used, but it is envisaged that either could be used without the other.
[0015] A tank 17 for liquid nitrogen is carried as shown on the machine, feeding the nozzle 15 by a pipe 18 and the feed device 16 by a pipe 19, controlled by a valve 20.
[0016] Figures 2 and 3 show a machine similar to that shown in Figure 1 except that the interior of the hood 14 communicates via a pipe 30 with an inlet manifold 32 arranged at the trailing (with respect of the intended motion of the machine) edge of the rectangular arrangement of seals 3. Also the hood 14 has an inlet 34 through which air is drawn, preferably, via a non-return or check valve 36, into the hood 14 and a mixture of air and cold nitrogen vapour, flows through the pipe 30 to the blast zone inlet manifold 32. If this flow is inadequate having regard to the suction created by the fan, air 13 may also be induced directly into the manifold 32 via a further check valve 38. In an alternative embodiment (not illustrated) the inlet 34 and check valve 36 may be omitted so that the entire induced airflow passes through the check valve 38 and mixing with the cold nitrogen vapour occurs within the inlet manifold 32.
1. A method of cleaning or abrading a surface comprising the steps of projecting by
means of a machine abrasive particles at high velocity against the surface to be cleaned,
moving the machine over the surface while projecting the abrasive particles to remove
dirt or other material from the surface and using a cooling medium to keep the termperature
of the removed dirt or other material and/or particles rebounded from the surface
at a value such that some or most of the dirt can be seperated from the particles
before the latter is returned to a projecting device of the machine.
2. A method according to claim 1 wherein the cooling medium is applied to the surface
ahead of the machine as it is being moved so that the surface struck by the abrasive
particles is a cooled surface.
3. A method according to claim 1 or claim 2 wherein cooling medium is applied to a
zone within the machine in which zone the particles come into contact with the surface
being cleaned.
4. A method according to any one of the preceding claims wherein the cooling medium
is a cryogenic fluid.
5. A method according to any one of claims 1 to 3 wherein a cryogenic fluid is applied
to the surface-ahead of the machine, the cold vapour generated upon application of
the fluid to the surface being applied to a zone within the machine in which zone
the grit comes into contact with the surface being cleaned.
6. An abrading machine of the kind in which abrasive particles are projected at high
velocity against a surface to be treated while moving the machine over the surface,
to remove dirt or other material therefrom and in which particles rebounding from
the surface are recirculated to be used again, along a rebound path including a seperator
for seperating removed dirt or other material from the particles, and comprising means
for applying a cooling medium to the surface to be treated and/ or to the abrasive
particles so as to keep the temperature of the removed dirt or other material and/or
the particles rebounded from the surface at a value such that some or most of the
dirt can be seperated from the particles for recirculation.
7. A machine according to claim 6 wherein the cooling medium applying means comprises
a reservoir for the cooling medium and a hood mounted in advance (with respect to
the direction of movement of the machine) of a blast zone in which particles contact
the surface to be treated and housing one or more nozzles or the like connected to
the reservoir for directing cooling medium onto the surface.
8. A machine according to claim 6 or claim 7 which comprises dependent sealing means
around the periphery of an opening in the machine defining a blast zone in which particles
strike the surface to be treated and a means arranged to draw air through the blast
zone into the machine wherein the cooling medium applying means comprises means for
introducing cooling medium into the flow or air drawn into the machine.
9. A machine according to claim 7 which comprises dependent sealing means around the
periphery of an opening in the machine defining a blast zone in which particles strike
the surface to be treated and means arranged to draw air into the blast zone and through
the machine, wherein the hood has an air inlet from atmosphere and the interior of
the hood is connected to the blast zone so that air drawn into the hood mixes with
or entrains cooling medium in the hood, and flows via the blast zone into the machine.
10. A machine according to any one of claims 6 to 9 wherein the cooling medium is
a cryogenic fluid.