SI24359A - Arrangements and methods for abrasive flow machining - Google Patents

Abstract

The subject of the invention is the upgrading of the abrasive flow polishing preparations and processes based on the principle of a flexible / adjustable routing object, or more precisely, polishing with an abrasive flow using a moving guide (pin) in which this moving guide object (trn) with the corresponding movement the workpiece (workpiece with internal shape or workpiece with an external shape that is inserted into a suitable bed) ensures the optimal dynamics of the polishing mass, and thus more efficient machining, more even treatment of the surface, the possibility of working longer workpieces, polishing the desired detail on the workpiece, taking away the material on the desired detail of the workpiece, and shorter processing cycles. In addition, it makes it possible to use several routing objects (trunks) simultaneously, which simultaneously polish the same number of workpieces. The problem of the existing state is the processes that do not use the directional objects (trunnions), resulting in an unevenly polished surface, an uneven removal of material on the workpieces with a longer length of the shape to be polished. The invention solves these problems and leads to an increase in the efficiency and robustness of the abrasive flow polishing process.

Description

The present invention is based on the field of abrasive flow polishing. More specifically, the invention relates to new and improved embodiments, or. derivatives and processes for machining the interior surfaces of workpieces with abrasive liquids.

BACKGROUND OF THE INVENTION

Abrasive flow polishing is a well-known machining process in which the abrasive medium is extruded through the workpiece. it travels on its surface, thus processing it. The effect of abrasive particles on polishing with abrasive flux is comparable to conventional or abrasive polishing. classic sawing, grinding, gluing or honing by extruding abrasive media which flows through the surface of the workpiece in this way removes the material, forms the surface and thus forms the surface treatment. When using a suitable non-Newtonian fluid, the abrasive medium will flow through or through the workpiece surface, mostly with a plug flow. The resulting abrasive media plug can be considered as a self-contained, properly shaped file, sandstone or pressure glue extruded through a closed passage restricting flow. This results in efficient workpiece surface treatment. Unlike conventional abrasive machining processes, where the abrasive particles are fixed on a solid support part of the tool, such as a solid abrasive abrasive paper, when moving through the workpiece, in the case of abrasive flow polishing, the abrasive particles are supported by a flexible mass. This leads to a very even surface finish. WO 2009/105043 represents abrasive flow polishing equipment whose structure comprises two opposite abrasive media chambers and a workpiece inserted between them.

Abrasive media chambers are simultaneously extrusion chambers capable of extruding abrasive media from one chamber through passage into another by hydraulic or mechanical means. The surface to be machined is a hole through the workpiece and the abrasive media chambers are sealed at each end of the hole so that the hole becomes a closed passage between the two chambers. The abrasive medium is alternately extruded from one chamber to another. US • ·

No. 3,819,343 describes an abrasive medium used for abrasive flow polishing, which is a semi-solid, visco-elastic material imbued with abrasive grains. The abrasive grain is supported in place by a semi-solid, visco-elastic material.

While conventional abrasive flow polishing procedures are effective in many applications, conventional procedures are often ineffective especially when the surface to be machined is either in the form of a long and narrow passage, or where the transition or. holes through which an abrasive medium flows, consisting of several sections having sections of different sizes.

In very long and narrow passages, the required pressure and work required to move the viscous abrasive medium through the passage is very high. This places additional requirements on the mechanical stability of the hardware used for this purpose. It also increases the energy required for the machining process. Both are undesirable.

If the passage to be treated contains both sections with relatively small sections and sections with relatively large sand, the velocity of the fluid in narrower and wider sections will vary greatly. In narrow sections, the fluid velocity will be relatively high at passage, while in wide sections it will be relatively low. As a result, the abrasive effect of machining will be relatively large in narrow sections and the effect on sections with larger sections will not be satisfactory. Long narrow sections will additionally lead to an undesirable high pressure drop.

In this field there is a need in the art for methods and embodiments of abrasive flow polishing that will improve the problems mentioned above.

SUMMARY OF THE INVENTION

The present invention fulfills these needs by the methods provided and the appropriate abrasive flow polishing equipment, in which the abrasive medium is extruded through a passageway and in which the passage objects are inserted, preferably into transitions or sections of passageways having a relatively large cross-section. Routing objects cause a local decrease in the active cross-section available for fluid flow. Therefore, the speed of the abrasive medium increases locally near objects to direct the abrasive medium. As a result, the efficiency of abrasive machining increases at the point of orientation. In addition, due to the relatively short length of the area where the fluid velocity is increased (measured in the axial direction), the pressure drop increase is relatively small. Therefore, the methods of the invention provide greater efficiency

surface treatments at selected locations within the workpiece without increasing the required pressure to unacceptable limits.

If the passage to be machined includes both sections having a relatively large cross-section and sections with a relatively small cross-section, objects may be used to direct the abrasive medium to adjust the intensity of the surface treatment in such sections. By using directional objects, a relatively uniform surface treatment of the workpiece consisting of wide and narrow sections can be carried out. For example, by locally increasing the flow rate of the abrasive medium in wide portions of the passage.

The present invention thus relates to a process for machining the inner surface of a workpiece; the method comprising (i) preparing a workpiece having an inner passage defined by at least partially said inner surface to be machined, said passage having an inlet and an outlet section; (ii) providing at least one routing object in said inner passage, wherein the routing object has an outer surface, thereby forming a space between said outer surface of said at least one routing object and said inner surface of said workpiece; (iii) providing the abrasive fluid in said space so that said space is fully filled with said abrasive fluid; and (iv) executing the flow of said abrasive medium through said internal passage from said inlet to said outlet.

Preferably, the interior is completely filled with abrasive fluid.

The step that performs the flow comprises the movement of a piston in the cylinder associated with said inlet portion of said internal passage. In this way, the abrasive fluid is pumped into the restricted inner passage and / or thus a clean flow of the abrasive fluid through the inner passage is established.

Preferably, at least one routing object is attached to a solid support such as a pole or shaft. The routing object can also be attached to a rope or wire. The wire is the most flexible. Mounting the routing object on a solid support, either a pole or a shaft, enables the spatial position of the routing object to be accurately reached in said inner passage. The cross-section of the bar in a plane perpendicular to the longitudinal axis of the passage is preferably substantially smaller than the cross-section of the directional object in the plane perpendicular to the longitudinal axis of the passage. Preferably, said cross section of the bar is at least 5 or 10 times smaller than the cross section of said laughing object. A substantially larger cross-section of the routing object relative to the rod cross-section leads to a locally increased rate of abrasive medium in and around the routing object.

According to a preferred embodiment of the invention, the rod is connected to a piston.

Such an embodiment permits the movement of a routing object at the same speed and at the same frequency as the piston. This makes it very easy to control the movement and position of at least one routing object inside the passage.

In other preferred embodiments, the rod moves relative to the piston motion. This allows at least one routing object to move independently, i.e. at a different speed and frequency than the piston. The routing object may (e.g., additionally) perform rotational motion in said passage.

In other preferred embodiments of the invention, at least one routing object includes multiple routing objects. In other words, more routing objects are present. The use of multiple directional objects allows, for example, to account for multiple sections of different cross-sections within the passageway by adjusting the speed of the abrasive medium to each section, so as to ensure a uniform treatment of the passageway surface.

According to one embodiment, multiple routing objects are interconnected.

For example, multiple routing objects are interconnected so that they have a certain distance between the individual routing objects. This allows the positions of multiple routing objects to be adjusted at the same time.

To this end, multiple routing lines may be attached to one and the same pole. The movement of multiple directional objects in a passage can then be accomplished by the movement of a single pole.

The rod can be gripped with the plunger so that the multiple routing objects move parallel to the plunger.

In other preferred embodiments, multiple routing objects are interconnected in such a way as to allow independent movement independently of one another. This allows for greater flexibility in determining the longitudinal position and speed of movement of multiple directional objects in passage.

In the preferred methods of the invention, the transition is rotationally symmetrical. Alternatively, the interior of the passage may have at least one circular cross-section, preferably in a plane perpendicular to the longitudinal axis of the inner passage.

According to a preferred embodiment, the at least one routing object is rotationally symmetrical.

If both, the inner passage and the laughing object are rotationally symmetrical, the outer contour of the directional object will follow the internal contour of the passage. This leads to a very steady speed of the abrasive medium at the point of the routing object as the medium passes through the routing object.

In other preferred embodiments, the inner passage has at least one square cross section, preferably on a plane perpendicular to the longitudinal axis of the inner passage. In such cases, it is desirable that the guiding object also have at least one square cross-section, preferably in a plane perpendicular to the longitudinal axis of the inner passage. This again leads to a position in which the outer contour of at least one routing object follows the inner contour of the passage, thus achieving a more even surface treatment.

In preferred embodiments of the invention, at least one guiding object includes, is shaped or takes the form of a flat structure or. a cross section preferably oriented perpendicularly to the longitudinal axis of said inner passage (when inserted). For example, at least one routing object contains an object of circular shape or possibly rectangular plate. A round object or plate is mounted on a pole.

In highly preferred embodiments, the at least one guiding object comprises several planar shapes, preferably all oriented perpendicular to the longitudinal axis of said passage. Multiple planar shapes can be all round or all rectangular in shape.

As mentioned above, the outer contour of said at least one routing object may follow or be similar to the contour of said passage. This creates a gap between the directional object and the inner surface or inner passage, which is approximately uniform in thickness, thus passing the abrasive fluid at approximately uniform velocity over / around at least one directional object.

Preferably the abrasive fluid contains a viscous or visco-elastic fluid. Preferred fluids are non-Newtonian fluids, especially shear thickening fluids. Shear thickening liquids increase the viscosity as shear stresses increase. Such liquids have a constant flow across the cross-section through the passage through the passage, in essence the shape of the flow is squat. The splitting flow of the abrasive medium through the passage increases the shear forces on the surface to be treated, which increases the efficiency of the abrasives.

The abrasive medium also contains abrasive grains, which are solid particles with abrasive properties. Different abrasive particles can be used. For example, an abrasive fluid may contain boron carbide, aluminum oxide, calcite, corundum, diamond powder, synthetic diamond powder, moneyulite, tufa powder, sand, boron nitride, ceramic particles, ceramic iron oxide, powdered glass, steel carbide, and silicon carbide. zirconium.

The particles preferably have a medium or a an average diameter (based on particle number) of 1 pm to 4 mm, preferably 10 pm to 2 mm, or more preferably 100 pm to 1 mm. The diameter of the particle is preferably determined by micro-photography, as the largest individual dimension in the two-dimensional image of said particle in a limited micro-photograph. Automatic image analysis systems, such as the Morphologi G3 systems from Malvem Instruments Ltd., England, can be used to determine the mean diameter or. average particle diameter.

As already stated, at least one routing object is preferably moving in said passage. In this way, the location of the routing object and thus the place where it passes to efficient processing can be adjusted. The movement of the guiding object (s) in the passage can also increase the flow of the abrasive fluid, thereby increasing the trajectories performed which results in a clean flow of the abrasive medium through the passage.

For example, the movement of said at least one routing object in said passage may comprise motions parallel to the longitudinal axis of said passage, for example, the movement may include reciprocal motion parallel to the longitudinal axis of said passage.

In other preferred embodiments, said movement comprises rotational motion about an axis parallel to the longitudinal axis of said passage. This can increase the efficiency of surface treatment at the site of the routing object by the additional tangential component of the movement of the abrasive fluid across the surface being machined.

It will be understood by one of skill in the art that, according to the invention, a clean flow of the abrasive fluid is provided through said internal passage from said inlet to said outlet.

Preferred machined internal surfaces are in accordance with the invention of a metal surface.

The present invention also relates to systems, machines or devices for machining the interior surfaces of a workpiece, wherein the workpiece has an internal passage or a workpiece. through the hole. The restricted inner passageway is at least partially defined by said inner surface to be treated, said inner passageway comprising an inlet and outlet section, the apparatus comprising: (i) a first chamber comprising abrasive fluid; (ii) a joint for connecting said workpiece to said device in such a way that a liquid-tight joint is formed between said first chamber and the restricted inlet section of said internal passage; (iii) pressure build-up means the establishment of elevated pressure on a limited abrasive fluid in said first chamber, if present in said first chamber; and (iv) at least one smiling object that can be inserted into said inner passageway when said workpiece is inserted on said device, wherein the guiding object laughs abrasive fluid as such abrasive fluid flows through said inner passageway.

The arrangement of the device may also include the workpiece.

In preferred embodiments, said pressure buildup in said abrasive fluid comprises a portion of the first cylinder and a first piston movable in a restricted portion of the first cylinder.

Preferably, at least one said ridiculous object is attached to the pole.

According to a preferred embodiment, the system, machine or device further comprises, said means, a second chamber that can be coupled to the workpiece such that a fluid-tight joint is formed so that said outlet of said internal passage and said second chamber can pressure abrasive fluid when the latter is present in said second chamber.

Preferably said abrasive fluid pressure buildup in said second chamber comprises a portion of the second cylinder and a second piston inserted in said portion of the second cylinder.

• ·

The first and second pistons are preferably movable or respectively. movable such that reciprocal movement of the abrasive fluid in said inner passage can be performed. For example, bypassing said at least one smiling object when abrasive fluid is present in said first and second chambers and in said internal passage.

The inner passage may comprise at least one circular cross-section in a plane perpendicular to the longitudinal axis of said passage.

In such cases, it is particularly preferred that said at least one routing object is rotationally symmetrical.

In other embodiments, the inner passage has at least one square cross section, preferably in a plane perpendicular to the longitudinal axis of said inner passage.

In such embodiments, it is particularly preferred that the at least one routing object has at least one square cross section.

At least one guiding object includes, is shaped, or takes the form of a flat structure, or. a cross section preferably oriented perpendicular to the longitudinal axis of said inner passage.

In preferred embodiments, the planar structure is circular in shape.

In other preferred embodiments, said planar structure is rectangular in shape.

At least one guiding object may comprise multiple planar structures directed perpendicularly to the longitudinal axis of said inner passage. These can be round in shape.

According to the invention, it is generally recommended that the outer contour of said at least one directional object imitate or. is similar to the inner contour of said inner passage.

SHORT DESCRIPTION OF THE DRAWINGS

Figure 1 shows a first embodiment of the invention using a ball-shaped guidance object.

Figure 2 shows a second embodiment of the invention using a disk-shaped routing object.

Figure 3 shows a third embodiment having three disk routing objects.

Figure 4 shows an embodiment in which the directional object is independently movable from the piston.

DETAILED DESCRIPTION OF THE INVENTION with reference to the invention, it is to be understood that the object has at least one dimension in the radial direction that is at least 5 to 10 times larger than the largest dimension of the object in the axial direction .

The invention will now be described with reference to the accompanying drawings.

Figure 1 shows a first embodiment of the invention. The arrangement of the composition for machining the inner surfaces of the workpiece 5 is shown. Part of cylinder 2 and piston 1 form the first chamber. The first chamber contains abrasive medium 3. A rod 4 is attached to the piston 1 to which a directional object 6 is mounted. the shape of a sphere. The rod 4 holds the guiding object 6 at a fixed distance from the piston 1. The first chamber is connected to the workpiece 5 in such a way as to provide a fluid-tight joint. As shown by the arrow on piston 1, the piston moves vertically downward, thereby providing increased pressure of the abrasive fluid 3 in the first chamber. As the piston 1 moves downward in the first chamber, the abrasive fluid 3 is pushed (or extruded) through the inner passage 11 on the workpiece 5. In the embodiment shown in Figure 1, the inner passage 11 has an inlet at its upper end and an outlet at its lower end. The embodiment does not include a second chamber that is connected to the outlet portion of the inner passage 11, thereby expelling the abrasive fluid at the outlet portion from the assembly and not being used in cyclic mode. As would be appreciated by one of skill in the art, in order for the ridiculous object to follow an incorrectly shaped inner passage 11, the bar 4 must be made of a deformable, for example flexible material. For example, pole 4 may be made of plastic or steel. The rod 4 can also be made of wire or rope.

Figure 2 shows another embodiment of the invention. In this embodiment, the first chamber is formed by the cylindrical part 2 and the associated piston 1. The first chamber is filled with abrasive fluid

3. The piston 1 can move in a vertical direction and in this case perform alternating motion. A piston 4 is attached to the piston 4, on which the steering object 6 is additionally attached. The movement of the piston 1 affects the movement of the pole 4 and the steering object 6. They all move at the same speed and frequency. As the piston 1 moves upwards, the abrasive fluid 3 is forced into the inner passage, past the moving directional object 6 into the second chamber, which in this case is formed by the second cylindrical part 10 and the second piston 9. As will be immediately determined by the axis of the person skilled in the art , the velocity of the abrasive medium 3 in the inner passage 11 increases about the routing object 6 in proportion to the velocity in the rest of the inner passage 11 because the available cross section for the fluid flow is small / smaller. This leads to a very efficient / controlled machining of the inner surface of the workpiece 5 at and around the guide object 6. As shown by the two-way arrows on the first and second pistons 1 and 9, both pistons can move alternately. The alternating movement of the pistons 1 and 9 in combination with the parallel movement of the guiding object 6 through the inner passage leads to an effective and uniform treatment of the inner surface of the workpiece 5. Figure 3 shows a third embodiment of the invention. This embodiment includes the first and second fluid chambers formed by the parts of cylinders 2 and 10, with their respective pistons 1 and 9, individually. The alternating movement of the first and second pistons 1 and 9 causes an alternating flow of abrasive medium 3 through the inner passage 11. As can be seen in the sketch, the inner passage has parts with different cross sections. The first part, which is vertically below the second part, has a larger cross-section than the second part. With a conventional abrasive flow polisher, this would result in less efficient surface treatment in the first section having a larger cross-section. According to the invention, multiple directional objects 6, 7, 8 are present in the inner passage 11 and thus significantly affect the uniformity of processing in the first and second portions. In the embodiment shown in Figure 3, three separate routing objects 6, 7, 8 are arranged or respectively. attached to one pole 4 and consequently move at the same speed and frequency.

Figure 4 shows a fourth embodiment of the present invention. In this embodiment, the guiding object 6 is attached to a pole 4 which is independently movable from the piston 1. This allows the speed and frequency of movement of the routing object 6 to be controlled independently of the control and frequency of the piston 1. This is useful if the surface smoothness requirements in the lower part of the inner passage 11 are greater than those in the upper passage. In such cases, the guiding object 6 will be positioned primarily in the lower part of the passage 11, while at the same time the first and second pistons 1 and 9 perform their alternating movement, thus providing more efficient surface treatment in the lower part of the passage 11.

Figure 5 shows an embodiment in which the bar 4 and the guiding object 6 are rotatable about the longitudinal axis of the passage 11. The rotation of the steering object 6 in the passage 11 adds a tangential component to the usual longitudinal movement of the abrasive fluid 3 through the passage 11.

Abrasive fluid may contain the following ingredients:

Ingridients CAS Label Share% Boron carbide 74869-21-9 40-70 Polyborosiloxane polymer 104780-67-8 15-40 Grease 748669-21-9 10-30 Oleic acid 112-80-1 0.1-2

Abrasive fluid may contain abrasive particles selected from the following group: aluminum oxide, silicon carbide, boron carbide, diamond.

Preferably, at least 80% of the abrasive particles (by number) have a maximum diameter in the range of 0.01 to 2 mm, more preferably in the range of 0.02 to 1 mm and more preferably of 0.05 to 0.5 mm. Most preferably, at least 80% of the abrasive particles of the abrasive medium have a larger diameter in the range of 100 to 200 pm.

The viscosity of the abrasive medium is preferably in the range from 100 to 10000 Pas, more preferably from 1000 to 5000 Pas and most preferably from 1500 to 4000 Pas.

It should be understood that the embodiments described above serve only as examples to illustrate. They should not be construed as limiting the invention, which is defined by nothing but the appended claims.

Claims (43)

1. Abrasive flow polishing procedures are a process for treating the inner surface of a workpiece (5) by: (i) providing a workpiece (5) having an inner passage which is at least partially defined by said inner surface to be machined, the passage having an inlet and an outlet; (ii) providing at least one routing object in said internal passage; Said routing object has an outer surface, wherein a space is formed between said outer surface of said at least one routing object and said inner surface of said workpiece; (iii) providing abrasive fluid in said space so that said space is reliably filled with said abrasive fluid; and (iv) executing the flow of the abrasive medium through said interior space from said inlet portion to said outlet portion. The method of claim 1, wherein said step of performing the flow comprises moving a piston in a cylinder which is connected to said inlet portion of said internal passage. The method of claim 1 or 2, wherein the at least one said guiding object is attached to a pole. The method of claims 2 and 3, wherein said rod is attached to said piston. The method of claims 2 and 3, wherein said rod is movable relative to said ·. bat. A method according to any one of the preceding claims, wherein said at least one routing object comprises multiple routing objects. The method of claim 6, wherein said multiple routing objects are connected such that a fixed fixed distance between objects is provided by default. The method of claims 2 and 7, wherein said multiple directional objects are mounted at a fixed distance on said piston. The method of any of the preceding claims, wherein said inner passage has at least one circular cross-section in a plane perpendicular (normal) to the longitudinal axis of said passage. The method of claim 9, wherein the at least one said guiding object is rotationally symmetrical. The method of claims 1 to 8, wherein said inner passage has at least one square cross section in a plane perpendicular (normal) to the longitudinal axis of said passage. The method of claim 11, wherein said at least one routing object has at least one square cross section. A method according to any one of the preceding claims, wherein said at least one guiding object is formed from oriented planar structures when positioned in said inner passage perpendicular to the longitudinal axis of said inner passage. The method of claim 13, wherein said planar structure is disk-shaped. The method of claim 13, wherein said one flat structure is a rectangular panel. The method of claims 13 to 15, wherein said at least one laughing object comprises several planar structures directed perpendicularly (normally) to the longitudinal axis of said passage. The method of claim 16, wherein said multiple planar structures are disk-shaped. A method according to any one of the preceding claims, wherein the outer contour of said at least one routing object is followed by or. is similar to the inner contour of said inner passage. The method according to any of the preceding claims, wherein said abrasive fluid contains a fluid that thickens with the presence of shear stresses. The method according to any of the preceding claims, wherein said abrasive fluid further comprises abrasive particles selected from the following group: boron carbide, aluminum oxide, calcite, corundum, diamond powder, synthetic diamond powder, moneyulite, tuft powder, sand, boron nitride, ceramic particles, ceramic iron oxide, powdered glass, steel particles, silicon carbide, zirconium and ice particles. The method of any of the preceding claims, wherein said at least one routing object is moved in said passage. The method of claim 21, wherein said movement of said at least one guiding object comprises movement in a parallel direction to the longitudinal axis of said passage. The method of claim 22, wherein said movement includes alternating (reverse) motion that is parallel to the longitudinal axis of said passage. The method of claims 21 to 23, wherein said motion involves rotation about an axis parallel to the longitudinal axis of said passage. A method according to any one of the preceding claims, wherein a pure flow of abrasive fluid is provided through said passage from said inlet to said outlet. The method of any of the preceding claims, wherein said inner surface to be machined is a metal surface. 27. Abrasive flow polishing preparations also represent an improvement in the workpieces for machining the inner surface of a workpiece, said workpiece having an internal passage, said internal passage is at least partially defined by said internal surface to be machined, said internal passage having an inlet and an outlet del; preparation of the scope: (i) the first chamber in which the abrasive fluid is located; (ii) a joint, which means joining said workpiece with said device in such a way that a tight connection is made between said first chamber and said inlet portion of said inner passage; (iii) pressure buildup means the establishment of an elevated pressure on said abrasive fluid in said first chamber if it is located in the first chamber; and (iv) at least one directional object that can be accommodated in said inner passage when said workpiece is attached to said device, said directional object adapted to direct the abrasive fluid as this abrasive fluid flows through said inner passage. • · The device of claim 27 further comprising said workpiece. The apparatus of claims 27 and 28, wherein said purpose of applying pressure to said abrasive fluid in said first chamber includes a portion of the first cylinder and a first piston that can move in said first portion of the cylinder. 30. The device of claim 29, wherein said at least one guiding object is attached to a pole. The apparatus of claims 27 to 30, wherein the apparatus further comprises a second chamber which can be coupled to said workpiece to provide a fluid-tight connection with said outlet portion of said inner passage, said second chamber also comprising the possibility of applying pressure to said workpiece. abrasive fluid as far as it is located in said second chamber. The apparatus of claim 31, wherein said abrasive fluid pressure can be restored in said second chamber comprising a portion of the second cylinder and a second piston arranged in said portion of the second cylinder. 33. The device of claim 32, wherein said first and second pistons are movable in such a way that they perform alternate movement of the abrasive fluid in said inner passage and via said at least one guiding object when the abrasive fluid is present in said first and second chambers, and in said internal passage. The apparatus of claims 27 to 33, wherein said inner passage has at least one cross-section in circular shape in a plane perpendicular (normal) to the longitudinal axis of said passage. The apparatus of claim 34, wherein said at least one guiding object is rotationally symmetrical. The apparatus of claims 27 to 33, wherein said inner passage has at least one cross-section of a square shape in a plane perpendicular (normal) to the longitudinal axis of said inner passage. The apparatus of claim 36, wherein said at least one guiding object has at least one square cross-section. The apparatus of claims 27 to 37, wherein said at least one guiding object includes substantially planar structures oriented perpendicularly (normally) to the longitudinal axis of said inner passage. The device of claim 38, wherein said is a substantially flat disc-shaped structure. The device of claim 38, wherein said substantially planar structure is rectangular in shape. The apparatus of claims 38 to 40, wherein said at least one smiling object comprises several substantially planar structures oriented perpendicularly (normally) to the longitudinal axis of said inner passage. The device of claim 41, wherein all said multiple planar structures are disk-shaped. A device according to claims 27 to 42, wherein the outer contour of said at least one guiding object follows or is. is similar to the inner contour of said inner passage.