Abstract:
A method and apparatus for cleaning pipes with the aid of a blasting medium in which a deflecting member surrounding a nozzle is blown through a pipe by the blasting medium blowing through the nozzle. The movement of the deflecting member and nozzle can be controlled with either a draw-rope from the upstream end of the pipe or a rod from the downstream end. Dry ice, sugar, or chemical agents may be added to the blasting medium as an blasting means.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a blasting method for cleaning pipes, and to a device which is suitable for carrying out this method. 
     2. Description of the Related Art 
     Blasting devices are generally used to clean surfaces with the aid of a mostly gaseous blasting medium to which an abrasive blasting means such as sand or the like can be added. It is also known to use dry ice or dry snow as blasting means (DE-A-195 35 557). The use of dry ice has the advantage that the materials to be cleaned off and subsequently disposed of are not increased by additional blasting means, since dry ice evaporates after use. 
     The dry ice exerts a cleaning effect through: 
     1. Thermal shock-induced embrittlement of the material to be cleaned off, accompanied by crack formation (thermal stresses). 
     2. Penetration of particles into the cracks, produced by thermal stresses, in the materials to be cleaned off, followed by a sudden increase in the volume of the particles during the transition to the gaseous state (sublimation), which leads to ‘blasting off’ the materials to be cleaned off. 
     3. Kinetic energy when the particles strike the materials to be cleaned off at high speed. 
     With regard to quick and economic cleaning of relatively large surfaces, it is desirable for the jet produced by the blasting nozzle to be as widely fanned out as possible. Known for this purpose are flat nozzles which produce a jet widened in a fan-like fashion. However, there is still a disadvantage in using abrasive blasting means in that the particles of the blasting means impinge on the tapering walls of the nozzle, with the result that either there is an increased wear at the nozzle or, in the case of dry ice, the particles of the blasting means are smashed into finer particles which no longer have any appreciable abrasive effect. 
     U.S. Pat. No. 5,664,992 discloses a blasting method in which the blasting nozzle is at first tapered and then expands again, so that an acceleration of the blasting medium is achieved. A spindle-shaped deflecting member is moved through the pipe together with the blasting nozzle and deflects the abrasive blasting means onto the pipe wall. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to create a blasting method and a blasting device which permit efficient and thorough cleaning of the inner surfaces of pipes or other hollow bodies, in particular by using dry ice. 
     This object is achieved by means of the features specified in the independent patent claims. Advantageous refinements of the invention follow from the sub-claims. 
     When, as in claim  1 , the deflecting member moves through the pipe alone, that is to say without the nozzle, then the movement of the deflecting member must be braked, so that its speed is always lower than the flow velocity of the blasting medium, and the desired deflecting effect is achieved. This braking action is achieved with the aid of a draw-rope or, from the opposite end of the pipe, with the aid of a rod. 
     The flow of the blasting medium can in this case be generated with the aid of a pressure fan or suction fan arranged at one end of the pipe to be cleaned. 
     The centering of the deflecting cone on the pipe axis can be achieved. either purely aerodynamically or with the aid of at least three flexible guide bars or skids which form a guide for the deflecting cone as it moves through the pipe. With regard to the ability to traverse bends, the deflecting cone can also itself be flexible. Instead of the deflecting cone, it is also optionally possible to provide, for example, a spherical deflecting member. 
     In the method according to claim  3  is blasting nozzle is employed which is moved through the pipe, which blasting nozzle continuously tapers to a constriction in an upstream section and expands again continuously downstream starting from the constriction, and a deflecting cone is arranged downstream of the constriction and coaxially with the blasting nozzle, as in U.S. Pat. No. 5,664,992. According to the invention, the deflecting cone is connected to the blasting nozzle via a plurality of holding webs distributed over the circumference of the blasting nozzle, with the result that the vertex of the deflecting cone is always held at a defined spacing from the constriction in the blasting nozzle. Dry ice is used as the blasting means. It is advantageous in this context that the deflecting member is suspended not in the middle, but on the circumference of the nozzle so that the pellets, which are sensitive to shocks, are not prematurely broken up. 
     The performance of the pressure source in terms of pressure and volume is preferably adapted to the blasting nozzle such that the blasting medium reaches the speed of sound at the constriction of the nozzle. Because of the Laval effect, the blasting medium can than accelerate to ultrasonic velocity in the downstream part of the nozzle, a particularly intensive cleaning action being achieved thereby. A stationary shockwave in the form of a Mach cone forms at the vertex of the deflecting cone. This shockwave presumably contributes to leading the blasting means away from the surface of the deflecting cone. 
     Inasmuch as a certain ability of the device to traverse bends is desired when cleaning pipes, the holding webs and a lance supporting the blasting nozzle can be elastically flexible. 
     Skids or other centering devices can be provided for centering the blasting nozzle in the pipe. If the blasting nozzle is drawn through the pipe, it is also possible to utilize aerodynamic self-centering effects for centering the blasting nozzle. 
     In the case of the device according to claim  8 , the outside diameter of the nozzle need not itself be greater than the outside diameter of the deflecting member, with the result that a slim design is achieved which is also suitable for pipes of small inside diameter. 
     Since the deflection of the blasting medium and of the blasting means is effected by the deflecting member, there is a high degree of freedom of design as regards the configuration of the actual nozzle. In particular, the nozzle can be constructed as a Laval nozzle which can be used to reach high flow velocities of the blasting medium, possibly even ultrasonic flows. 
     The use of dry ice has so far been of little effect in cleaning materials or coatings, in the case of which the shock cooling approximately −80° C.) does not lead, or leads only to a small extent, to shock induced embrittlement of the material followed by crack formation, for example in the case of hardened deposits of lime, hard deposits of organic substances, or deposits of gypsum. Since the shock cooling does not lead here to thermal stresses or cracks, the dry ice particles cannot penetrate into the material or between the material to be cleaned and the workpiece surface, and thus also cannot lead to blasting off through sudden sublimation. The kinetic energy with which the relatively soft dry ice strikes then exhibits only a slight effect. 
     An improvement in the action which also permits materials which cannot be removed by dry ice alone to be cleaned away is achieved by adding to the dry ice an additional blasting means which is lightly to strongly abrasive. 
     The additional blasting means can be a lightly abrasive blasting means. It Is also possible, optionally, to add a strongly abrasive blasting means such as, for example, blasting granules. The addition of chemical means, for example lime-dissolving means, is likewise possible. It can also be expedient to add a cold gas, for example cooled N2 or the like, to the blasting medium in order to stabilize the dry ice pellets. 
     The additional blasting means are to be of such a nature/metered in such a way that they do not entail any increase in waste, or only the smallest possible increase, and cause no damage—for example by subsequent corrosion—to the surfaces to be cleaned. 
     It is therefore particularly advantageous to add additional blasting means which are water-soluble, are compatible with water and sewage treatment plants in the resulting small amounts of residues and do not cause any corrosive after-effects. The additional means should, in addition, be resistant to cold, and/or the abrasiveness should be further intensified by the low temperatures. On the other hand, the additional blasting means are not allowed to impair the way the dry ice works as blasting means. For example, sugar in crystalline or pulverized form is suitable. 
     The addition of the additional blasting means can be performed by mixing with dry ice. The mixing ratio can be selected depending on requirements. 
     The additional blasting means can also be (additionally) inducted by the dynamic pressure of the blasting medium (injection nozzle). This induction can be performed by a branching line in the nozzle, or also in the line feed between the dry tee feeding device and the blasting nozzle. 
     In the case of constrictions caused by contamination, for example, it is possible for a counterpressure of the blasting medium to occur in the blasting nozzle when pipelines are being cleaned by means of a conical nozzle or a blasting adapter attached to the pipe end. It is advantageous in this case for the additional blasting means to also be introduced under pressure into the stream of the blasting medium. The feeding of the additional blasting means can likewise be performed in this case at the blasting nozzle or the blasting adapter, or in the line feed between the dry ice feeding device and the blasting nozzle or the blasting adapter. 
     The pressure of the blasting medium with the aid of which the additional blasting means is fed should be the same as the pressure of the main stream, or at least so high as to avoid a build-up of the additional blasting means due to counterpressure, and to, achieve a uniform jet of the blasting media and blasting means brought together. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred exemplary embodiments are explained in more detail below with the aid of the drawing, in which: 
     FIG. 1 shows a diagrammatic longitudinal section through a section of a pipe, and a blasting device according to the invention; 
     FIG. 2 shows a diagrammatic longitudinal section through a blasting device in accordance with a modified exemplary embodiment; 
     FIG. 3 shows an axial section through a blasting device in accordance with a further exemplary embodiment; 
     FIG. 4 shows a partially broken-open side view of the essential element of a blasting device in accordance with another exemplary embodiment; 
     FIG. 5 shows a diagrammatic longitudinal section through a section of a blasting nozzle with a feed line for an additional blasting means; and 
     FIG. 6 shows a sketch of the principle of a blasting device in accordance with a further exemplary embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The blasting device shown in FIG. 1 has, in a way known per se, a pressure source  10 , for example a compressed-air compressor, which is connected to a blasting nozzle  14  via a flexible pressure hose  12 . For the purpose of metering a blasting means, for example dry ice, into the compressed air stream, a metering device  16 , likewise known per se, can be-provided in the compressed air line between the compressor and the blasting nozzle. 
     In the example shown, the blasting nozzle  14  is part of a probe  18  which can be pulled or pushed axially through the interior of a pipe  20  to be cleaned. The blasting head can be pushed or pulled by the pressure hose  12 , a lance or a draw-rope attached at the opposite end of the blasting head. 
     The blasting nozzle  14  is constructed as a Laval nozzle, and consequently has an upstream section  22  which continuously tapers in an approximately conical fashion to a constriction  26 , starting from a coupling piece  24  for the pressure hose. Adjoining the upstream section  22  is a downstream section  28  which expands again continuously starting from the constriction  26 . Because of the tapering of the upstream section  22 , the flow velocity of the compressed air increases towards the constriction  26 . Given adequate power of the pressure source  10  in terms of pressure and volume, the compressed air at the constriction  26  reaches the speed of sound, while the pressure there decreases to the Laval pressure. The gradual expansion of the downstream section  28  of the blasting nozzle results in the compressed air being further accelerated downstream of the constriction  26 , and thus in a multiple of the speed of sound being reached. 
     Also belonging to the probe  18  is a deflecting cone  30  which is aligned coaxially with the blasting nozzle  14  and projects with its vertex into the gas jet emerging from the blasting nozzle. The approximately conical deflecting surface  32  of the deflecting cone  30  is rounded in a slightly concave fashion in longitudinal section in the example shown. In the example shown, the cone angle at the vertex is approximately  120 . 
     The sections  22  and  28  of the blasting nozzle are of approximately the same length, and in the example shown the opening cross section at the mouth  34  is twice the cross section at the constriction  26 . 
     In the embodiment shown, the vertex of the deflecting cone  30  is situated exactly at the level of the mouth  34  of the blasting nozzle  14 . The vertex of the deflecting cone can optionally also project somewhat into the blasting nozzle. In this case, the cross section belonging to the deflecting cone must be taken into account when configuring the downstream section  28  of the Laval nozzle. 
     The ultrasonic jet emerging from the blasting  5  nozzle  14  is radially deflected in all directions by the deflecting cone  30 , with the result that it takes the form of an envelope of a cone and strikes the inner wall of the pipe  20  uniformly in this form. Because of aerodynamic effects, the blasting means entrained in the gas jet is likewise deflected radially outwards, and thus develops its abrasive effect on the wall of the pipe  20 , while only a negligibly small portion of the entrained particles come into contact with the deflecting cone  30 . 
     In the exemplary embodiment according to FIG. 1, the deflecting cone  30  is held on the blasting nozzle  14  with the aid of three bars  36  arranged at angular spacings of  1200 . This ensures that the vertex of the deflecting cone  30  is always precisely centered on the axis of the blasting nozzle  14 . The bars  36  can have a triangular or lens-shaped cross section and form a type of cutting edge on the inner side, so that they do not form an appreciable obstacle to the emerging blasting means. 
     The opposite ends of the bars  36  are let into corresponding longitudinal grooves in the outer surfaces of the blasting nozzle  14  and of the deflecting cone  30 , and fastened by welding or in another way. This produces a configuration of the probe  18  which is particularly small overall and is also suitable for cleaning pipes  20  of narrow cross section. 
     FIG. 2 shows an embodiment of the blasting head  18  which is suitable for pipes of larger cross section, or also for blasting freely accessible surfaces. The vertex of the deflecting cone  30  here projects somewhat into the mouth of the blasting nozzle  14 . The downstream section  28  of the blasting nozzle is expanded somewhat more strongly towards the mouth than in the case of the exemplary embodiment according to FIG. 1, with the result that the cross-sectional ratio between the free exit surface at the mouth and the cross-sectional surface at the constriction  26  is again approximately 2:1. 
     The bars  36  are constructed here as round bars which engage with, thinner end sections  38  in corresponding axial bores  40  of the deflecting cone  30  and of the blasting nozzle  14 . The end sections  38  and the bores  40  can be provided with right-hand and left-hand threads so that the bars can be screwed to the blasting nozzle and the deflecting cone. The bores  40  of the deflecting cone  30  are expanded in steps at the end facing the blasting nozzle  14 , and hold the thicker middle section of the round bars  36 , thus producing a cleaner connection of the round bars to the deflecting surface of the cone. 
     In the example shown, the thicker middle sections of the round bars  36  abut the end face of the blasting nozzle  14  obtusely, with the result that a defined spacing is maintained between the blasting nozzle and the deflecting cone  30 . However, it is also optionally possible for the arrangement to be made such that the round bars also engage in expanded bores in the blasting nozzle  14 . In this case, the axial spacing between the deflecting cone  30  and the blasting nozzle  14  can vary steplessly within certain limits, making it possible to optimize the jet characteristic. 
     The blasting device shown in FIG. 3 is used to clean the inner surfaces of a pipe  110  with the aid of a solid or liquid blasting medium with or without blasting means. 
     A nozzle  112  in the form of an adapter which can be coupled to the pipe end is used to introduce the blasting medium into the pipe under high pressure. In the example shown, the nozzle  112  simply has at its front end an outer cone  114  which engages in the pipe end and bears tightly against the inner wall of the pipe when the nozzle is held by hand with a light pressure against the pipe end. A pressure hose (not shown) can be coupled to the opposite end of the nozzle, and is used to feed the blasting medium. 
     Also belonging to the blasting device is a deflecting member  116  constructed separately from the nozzle  112 . In the example shown, the deflecting member  116  has an elongated shape resembling a ship and having a conically constructed upstream end  118 . The cross-sectional shape of the deflecting member  116  is adapted to the cross-sectional shape of the pipe  110 , and is therefore circular in the case of round pipes. The outside diameter of the deflecting member is somewhat smaller than the inside diameter of the pipe  110 . 
     Fastened in an axial bore  120  of the deflecting member  116  is a draw-rope  122  which runs through the pipe  110  and through the mouth of the nozzle  112 , and emerges from the nozzle  112  outside the pipe  110  through an oblique lateral opening  124 . The free end of the draw-rope  122  is held by hand, wound off from a winding device (not shown), or slackened in steps with the aid of a lever-operated self-retaining locking mechanism such as is known, for example, from cartridges for pressing out pasty compounds. 
     The blasting medium dispensed by the nozzle  112  flows at high velocity through the pipe  110  and strikes the conical end  118  of the deflecting member  116 , and is thereby deflected radially outwards, with the result that it strikes the pipe wall obliquely and cleans the inner surface of the pipe. A blasting means with a moderately abrasive effect, for example dry ice, can be added to the blasting medium. To feed the blasting means, the nozzle  112  can be provided with openings corresponding to the opening  124 . Other additives can also be fed to the blasting medium through these openings, for example in order to treat the pipe wall chemically or to “coat” it to repel lime or dirt. 
     The blasting means is deflected by the deflecting member  116  just like the blasting medium, the result being intensive cleaning of the pipe wall. It has emerged that because of the fluid-dynamic effects, the particles of the blasting means hardly strike the surface of the deflecting member, but are deflected with the flow such that they strike the pipe wall directly. The blasting medium and the blasting means, as well as the material possibly removed from the pipe wall pass through the annular interspace between the deflecting member and the pipe wall and are removed via the pipe end opposite the nozzle  112 . 
     If the draw-rope  122  is gradually slackened, the deflecting member  116  moves in a self-centered fashion through the pipe, with the result that the pipe  10  can gradually be cleaned over the entire length. 
     FIG. 4 shows an exemplary embodiment of the deflecting member  116 , which is suitable for even smaller pipe diameters. 
     The deflecting member according to FIG. 4 has a ship-shaped upstream part  126  and a conical downstream part  128  constructed as a separate component. The two parts  126 ,  128  can be screwed to one another or fastened on one another in another way. The upstream part has a conically expanding section  130 , a shorter cylindrical section  132  and a conically tapering section  134  which follow one another in the prescribed sequence in the direction of flow. Together with the cylindrical pipe wall, the part  126  forms an annular nozzle whose cross section firstly tapers, as in the case of a Laval nozzle, and then expands again. It is possible in this way to achieve a very high flow velocity, possibly an ultrasonic velocity, downstream of the part  126  by means of the Laval effect. The conical part  128  forms the actual deflecting member, which then directs the blasting medium and the particles of the blasting means onto the pipe wall at high speed. However, the blasting medium can also already be directed for the first time onto the pipe wall by the section  130 . 
     The deflecting member  116  according to FIG. 4 has the axial bore  120  and has, moreover, in its cylindrical section  132  a transverse bore  136  which is provided with an internal thread, and which permits the draw-rope  122  to be fixed using a grub screw. 
     If a strongly abrasive blasting means is used, the draw-rope can be damaged and tear. In this case, it is expedient to delay the movement of the deflecting member  116  with the aid of a rod  138  which is inserted into the pipe  110  from the opposite end and guided by hand or machine. The section  134  and the conical part  128  of the deflecting member have an axial bore  140  with a larger diameter, into which the rod  138  can be inserted or screwed. 
     Finally, the deflecting member  116  can also have a friction member or scraper  142 , which is illustrated in FIG. 4 by dots and dashes. The scraper  142  bears with its blades, preferably under elastic pretensioning, against the inner wall of the pipe, and thus produces a braking effect which delays the movement of the deflecting member  116 . Thus, it is possible, if appropriate, to dispense with the rod  138  or the draw-rope  122 . At the same time, the scraper  142  loosens contaminants adhering to the pipe wall. In the example shown, the scraper  142  serves the purpose of preliminary cleaning and loosens the contaminants before they are completely removed by the jet deflected by the deflecting member. It is also possible, however, as an option or in addition to provide a towed scraper on the deflecting member for the purpose of subsequently cleaning the blasted surface. The blades of the scraper  142  can be given a slight helical setting so that, as it moves through the pipe, the deflecting member rotates about its longitudinal axis. 
     FIG. 5 shows a blasting nozzle  210  which is placed with its tip against one end of a pipe  212  to be cleaned, and to which there is fed via a line  214  a gaseous blasting medium (air) to which dry ice has already been added. The blasting nozzle is used to introduce the blasting medium and the blasting means into the pipe  212 . Since a nozzle action is not mandatory in this case, the blasting nozzle is more accurately also denoted as a blasting adapter. An additional blasting means, for example crystal sugar, is fed via an inlet  216  provided on the side of the blasting nozzle. The feed is preferably performed with the support of compressed air, but can also be performed by simply using the jet pump principle on the basis of the underpressure produced in a conical part  218  of the blasting nozzle. A side channel  222  opening obliquely into the main channel is constructed in a head part  220  of the blasting nozzle which adjoins downstream. 
     Shown diagrammatically in FIG. 6 is a dry ice feeding device  224  which is connected via the line  214  to the blasting nozzle  210  placed against one end of the pipe  212 . Connected to the opposite pipe end is an end piece  226  which is connected in the example shown to two suction fans  228 . 
     A draw-rope  230  enters the pipe  212  through the side channel  222  of the blasting nozzle  210  and emerges again at the a opposite end of the pipe through an opening in the end piece  226 . A deflecting member  232  can be pulled through the pipe  212  in the longitudinal direction with the aid of this draw-rope. 
     The two suction fans  228 , working in parallel, have a substantially higher delivery capacity than can be produced using conventional compressors or vaporizers, and therefore permit a high flow velocity to be maintained in the interior of the pipe even in the case of pipes  212  of relatively large diameter. The ambient air is inducted via the nozzle  210  and dry ice is added to it in the dry ice feeding device  224 . The additional blasting means can be added optionally via the inlet  216 . Inside the pipe  212 , the air on the deflecting member  222 , to which blasting means have been added, is accelerated again and deflected onto the pipe wall, thus producing an intensive cleaning action. The end piece  226  contains an eliminating device or a filter for the material removed and, if appropriate, the solid additional blasting means. The eliminating device, for example in the form of a cyclone, can also be integrated into the suction fan  228 .