Patent Grant
7775857
This application claims the benefit of Belgian Application No. 2006/0390 filed Jul. 14, 2006, which is hereby incorporated by reference in its entirety.
This invention relates to a device for particle blasting, comprising:
In particular, this invention relates to a device for dry ice blasting.
In order to tackle stubborn dirt, we all too readily turn to the heavy-duty means: sandblasting, corrosive products and solvents, high-pressure cleaning, sanding, brushes etc.
These solutions are far from ideal, as they are often aggressive, harmful to the substrate, downright dangerous, or even environmentally polluting. Yet there is a solution that is effective, efficient and virtually universally usable: dry ice blasting.
Dry ice blasting uses solid CO2 pellets as the particles and a carrier gas, preferably compressed air, to accelerate the pellets in the direction of the surface to be treated.
A dry ice device is generally composed of a feed hopper filled with particles, a mixing device for mixing the particles with the carrier gas, and one or more discharge means to which a gun can be connected in order to project the particles towards the surface to be treated. In most cases the mixing device will regulate the particle consumption.
There are various types of mixing devices for such dry ice devices. A commonly used type is the driven rotor with holes. Such a type is disclosed in European patent application EP 1 340 592. According to this patent application, the mixing device comprises a disc rotatably disposed between two non-rotatable plates and rotatable about a vertical axis. The disc has two functions:
Varying the speed of rotation of the disc can regulate the particle consumption.
Another type of mixing device used is disclosed in the international patent publication WO 03089193. According to this patent publication, the mixing device comprises a cylinder, which on its outer circumference is provided with cavities or recesses. The cylinder is rotatable about a horizontal axis and is disposed between a top chamber where the openings are filled with particles from the feed hopper and a bottom chamber where the particles are mixed into the carrier gas flow. The particle consumption can likewise be regulated by varying the speed of rotation of the disc.
Since the design of the known devices is fairly complex, one of the great challenges of the known systems is to achieve a good seal between the rotating rotor and the non-rotatable discs or chambers. The device wherein the rotor is rotatable about a vertical axis makes use of sealing discs disposed in a stationary position above and below the rotor, and partially or fully covering the rotor. The pressure at which the seal is produced can be regulated by means of springs or sealing elements, which make the construction of the whole unit even more complex.
The seal of the mixing devices with a rotor that is rotatable about a horizontal axis has to be provided on the outer circumference, which results in a very complex construction of the top and bottom chamber, and in high motor torque. In order to maintain the seal at raised pressure and without a high motor torque, complex bottom chambers with flexible inside walls and various seals have already been developed. SUMMARY OF THE INVENTION
The object of the invention is to provide a device for particle blasting wherein the seal of the mixing device can be achieved in a simple manner.
The object of the invention is achieved by providing a device for particle blasting comprising:
Since both the supply channel and the discharge channel provided are situated in one and the same element, a very simple arrangement is obtained, and said arrangement has yet another advantage. It is namely that, if the pressure of the carrier gas gets lost during rotation of the distribution disc, in the known devices, as a result of the force of gravity, the inlet and/or outlet of the carrier gas channel will be filled with particles. If the particles are solid CO2 pellets, it can happen that the inlet and/or outlet of the channel is/are blocked as a result of the frozen pellets. In the device according to this invention there is no risk of the inlet or outlet becoming blocked with pellets if the pressure of the carrier gas gets lost and the distribution disc continues to rotate, since the pellets will not leave the cavities in the distribution disc as a result of the force of gravity.
The carrier gas used in the device according to the invention is in particular compressed air, but it can also be another known carrier gas. The particles are preferably CO2 pellets or a mixture of CO2 pellets and another material such as, e.g., silicates, salt crystals and the like. The particles can be supplied to the device in the form of scrapings (e.g. from blocks), flakes or powder.
In a preferred embodiment of the device according to the invention a dividing wall is provided between the supply channel and the discharge channel, and the channels are provided in order to achieve the said connection at the level of the dividing wall.
According to a more preferred embodiment of the device according to the invention, the mixing device comprises a non-rotatable sealing plate, which is disposed between the mixing plate and the rotatable distribution disc. In a preferred embodiment the said non-rotatable sealing plate is composed of a plurality of layers, so that, inter alia, the layer that could possibly be subject to wear is easy to replace.
According to a special embodiment of the device according to the invention, the said sealing plate comprises at least one first aperture, which is in communication with the second supply means, and the said sealing plate comprises at least one second aperture at the level of the dividing wall, the second aperture connecting to both the supply channel and the discharge channel.
According to a preferred embodiment of the device according to the invention, the mixing device comprises cutting means for reducing the size of the particles fed in. The cutting means are preferably disposed between the mixing plate and the rotatable distribution disc.
In a particularly advantageous embodiment of the device according to the invention the rotatable distribution disc comprises at least one series of cavities placed at regular intervals and at equal distances relative to the centre point of the disc, which cavities during rotation of the distribution disc form a temporary connection between the at least one supply channel and the at least one discharge channel. During rotation of the distribution disc the cavities placed at regular intervals and at equal distances relative to the centre point of the disc will preferably connect alternately to the first and second apertures. In a special embodiment of the device according to the invention the number of cavities per series is an odd number. If this is combined with two filling apertures, two first apertures and two second apertures which give access to the discharge channel, it results in uniform mixing of the particles with the carrier gas and, furthermore, the undesirable pulsing (jolting) effect is reduced.
Even better mixing of the particles with the carrier gas is obtained in a special embodiment of the device according to the invention, wherein the rotatable distribution disc comprises a first series and a second series of cavities, the said series of cavities being placed at a first and a second distance respectively from the centre point of the disc. In particular, the first and second series of cavities are in an offset position relative to each other.
According to a preferred embodiment of the device, the device comprises pressure means for pressing the rotatable distribution disc against the mixing plate. The said pressure means preferably press the rotatable distribution disc against the mixing plate along one side.
In particular, the said pressure means comprise a pressure chamber, and the pressure exerted by the pressure chamber is proportional to the pressure of the carrier gas. This has the advantage that a pressure-dependent seal is achieved and unnecessary friction and subsequent wear at lower pressures is avoided. In a preferred embodiment the said pressure chamber is situated outside the mixing device.
In a most special embodiment of the device according to the invention the said device is a dry ice blasting device.
In order to explain the features of this invention further and to indicate additional advantages and details of it, there now follows a more detailed description of a device for pellet blasting according to the invention. It should be clear that nothing in the description that follows can be interpreted as a limitation of the protection for the device according to the invention demanded in the claims.
In this description reference is made by means of reference numerals to the appended drawings, wherein:
Dry ice blasting is a blasting technique that is comparable to sandblasting or high-pressure water blasting, but it makes use of, inter alia, solid CO2 pellets, also known as “dry ice pellets”, powder or flakes as the pellets. The great difference from the other blasting techniques is twofold. On the one hand, the pellets are very cold (−78° C.), with the result that the contamination layer suddenly cools down and shrinks. This means that this layer comes away easily from the substrate. On the other hand, the CO2 pellets sublime after they have touched the surface, which means that no additional waste is generated. This is directly one of the greatest advantages of dry ice blasting.
A device for particle blasting according to this invention and as illustrated in
The mixing device as illustrated in
As illustrated in
The sealing plate (9), illustrated, inter alia, in
A dividing wall (8) is provided between both the right supply channel (6a) and the right discharge channel (7a) and the left supply channel (6b) and the left discharge channel (7b). The dividing walls (8) ensure that the carrier gas flow will be deflected in the direction of the rotatable distribution disc (1) situated below. The dividing wall can close off the passage between supply channel and discharge channel either fully or only partially. In the latter case, part of the carrier gas will flow directly from supply channel to discharge channel, resulting in a reduced pulsating or jolting effect of the carrier gas to the gun.
The mixing plate (3) has at least one filling aperture (14), preferably having two, which connect to the second supply means. The particles from the feed hopper (13) fall through the filling apertures (14) and the first apertures (10) into the cavities (2) of the rotatable distribution disc (1). The filling of the cavities (2) can be aided by a rotatable knife (17) mounted on the upper side of the mixing plate (3). The cavities (2) remain filled with particles until they pass below a second aperture (11). At that moment the cavities (2) form part of the carrier gas flow path, and the particles that are present in the cavities (2) are entrained with the carrier gas and sent to the discharge channel (7). The mixture of particles/carrier gas then leaves the mixing device through the fourth aperture (16). In order to project the mixture towards the surface to be treated, a gun is connected by means of a hose or tube to said fourth aperture (16). By providing two fourth apertures, it is also possible to connect two guns to the mixing device.
Before the cavities (2) pass along the filling aperture and are filled again, they first pass along a venting channel (18). As illustrated in
The mixing device is designed in such a way that the particles undergo a minimal collision before the particles go into the discharge channel (7). This is achieved by making the second apertures (11) sufficiently large and providing a smooth discharge channel (7). This contrasts with the known systems, which are provided with apertures or openings on their outer circumference. In the case of such systems the particles, before being sent to the discharge channel, will first pass into a larger chamber, where a certain turbulence is present.
The rotatable distribution disc (1) (see, for example,
The rotatable distribution disc (1) comprises a first series and a second series of cavities (and possibly a third series of cavities), the said series of cavities (2) being placed at a first and second distance (and third distance) respectively from the centre point of the disc (1). If the first and second series of cavities are in an offset position relative to each other, this results in even more uniform mixing of the particles with the carrier gas.
The diameter of the distribution disc (1) and the dimensions of the cavities (2) are selected in such a way that, on the one hand, the friction between distribution disc (1) and sealing plate (9) is kept limited and that, on the other hand, sufficient particles can be mixed with the carrier gas without the speed of rotation becoming so high that the cavities would be only partially filled. Typical speeds of rotation lie in the order of magnitude of 5 to 100 rpm.
In the case of devices working with two filling apertures (14) and two second apertures (11) that connect to both the supply channel (6) and the discharge channel (7), the cavities will be emptied at the first second aperture by a gas flow flowing according to the direction of rotation of the rotatable distribution disc (1), while in the second, second aperture the cavities are emptied by a gas flow flowing in a direction opposite to the direction of rotation of the distribution disc (1). This prevents any build-up of dry ice in the cavities (2).
Where, as shown in
The device according to the invention is designed in such a way that all moving parts are disposed symmetrically relative to the rotating shaft, and that the pressure with which the seal is produced is in line with the moving shaft. As a result of the symmetrical positioning of both inlets and outlets, no moment of force is generated relative to the rotating shaft. The advantage of this symmetrical design is uniform wear of the rotatable distribution disc (1) and mixing plate (3), and also a great reduction in the wear of these parts. This results in a consistent seal during the service life. Although this is less good for the balance, force and pulsations of the particles, this device also relates to a device with one filling aperture (14), one supply channel (6), one discharge channel (7) and one second aperture (11).
The device according to the invention is designed in such a way that assembly and disassembly are very easy.
In order to have minimal leakage losses of carrier gas when the blow pressure (pressure of the carrier gas) is increased, and in order to limit the friction and use of the distribution disc (1) when the blow pressure is reduced, the seal is preferably made dependent upon the pressure of the carrier gas. In the known mixing devices the pressure-dependent seal is achieved directly at the interface with the rotor (1) and is consequently exposed to very low temperatures as a result of the dry ice. This has the disadvantage that the different components needed to achieve the seal have to meet specific requirements.
In the device according to the invention the pressure-dependent seal is achieved outside the mixing device, and consequently outside the cold zone, with the result that there is no need for specific material. This is achieved as follows: The rotatable distribution disc (1) is mounted on a rotating shaft (19), which is fitted through the hollow shaft of the reductor (21), which is driven by a motor (20). Below the reductor (21), the hollow shaft is supported by a piston (22), which receives counterpressure from a pressure chamber (23) situated on the bottom of the device. The bearing (24) provided on the upper side of the piston (22) prevents the piston (22) and the pressure chamber from rotating. This results in a very simple arrangement. Since the pressure of the pressure chamber (23) is proportional to the blow pressure, a pressure-dependent seal is achieved.
In order to make the pressure of the pressure chamber (23) proportional to the blow pressure, it is obvious to regulate the pressure circuit of the pressure chamber by means of the same pressure valve as that of the blow pressure. Notwithstanding that, this invention also comprises a system wherein the pressure in the pressure chamber (23) is regulated by means of a separate pressure valve. The present invention also relates to systems wherein the sealing pressure is not regulated by means of a pressure chamber, but by means of springs or other means making it possible to achieve a certain pressure between mixing plate (3) and distribution disc (1).
In addition, the rotatable distribution disc (1) is mounted on the hollow shaft in such a way that the connection is not rigid, which makes it possible to accommodate minor alignment differences.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006/0390 | Jul 2006 | BE | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4703590 | Westergaard | Nov 1987 | A |
| 5445553 | Cryer et al. | Aug 1995 | A |
| 5492497 | Brooke et al. | Feb 1996 | A |
| 20030064665 | Opel | Apr 2003 | A1 |
| Number | Date | Country |
|---|---|---|
| 10 2004 045770 | Aug 2005 | DE |
| 1 340592 | Sep 2003 | EP |
| Number | Date | Country | |
|---|---|---|---|
| 20080013399 A1 | Jan 2008 | US |
