Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
2000-05-24
2001-11-13
Morgan, Eileen P. (Department: 3723)
Abrading
Abrading process
Utilizing fluent abradant
C451S076000, C451S102000
Reexamination Certificate
active
06315639
ABSTRACT:
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 a
Morgan Eileen P.
Rothwell Figg Ernst & Manbeck
Shakeri Hadi
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