EP2960027B1 - Undercutting tool for producing a blind hole - Google Patents

Description

Field of the invention

The invention relates to an undercut tool for producing a blind hole in flowable, curable mixtures. Such an undercut tool comprises a connector for connecting the undercut tool to a mold and a mandrel which is slidably mounted along a longitudinal axis of the mandrel in the connector. The longitudinal axis of the mandrel also corresponds to the longitudinal axis of the blind hole in the batch when the tool is in operation. On the basis of the longitudinal axis of the mandrel can also define a direction of action. This is parallel to the longitudinal axis of the mandrel, along which it is displaceable. The direction of action points in the direction of the mixture, i. away from the tool or mold into the interior of the mold where the batch is located. In the direction of the mixture or in the effective direction of the mandrel is closed by a cap.

The undercut tool also includes a sheath of a reversibly deformable under pressure material, which completely surrounds the mandrel in a region which is located between the connector and the cover, to the outside. The jacket has around the mandrel at least one cavity with a defined geometry. The geometry of the cavity is predetermined such that the jacket bulges locally under the action of pressure along the direction of action in the region of the cavity, whereby a blind hole with a shape corresponding to the jacket in the bulged state can be formed in the mixture which surrounds the jacket.

State of the art

Such an undercut tool is for example in the EP 2 684 659 A1 described, the disclosure of which is explicitly incorporated herein by reference.

In the prior art, a variety of products are known, which are made of flowable, curable mixture. Examples of such mixtures are clay mixtures from which roof tiles or stones are produced in the industrial sector. Another example is concrete, from which roof tiles, railway sleepers, bricks, prefabricated parts and a variety of other products can be made. Such materials are first shaped and then cured in order to make the molded article durable even without enclosing shape. For this purpose, clay mixtures are fired and concrete bonded with cement and optionally compacted by shaking. Due to these chemical and physical processes, the mixtures are deprived of water or bound in the mixtures, whereby they harden. The flowability of the mixture is different, with clay mixtures usually rather low, as these are usually given as "batzen" in compression molding and already have a certain strength when removing from the mold before curing, which prevent re-deformation of the geometric shape , not least because when pressing the water content in the clay mixture is reduced.

In order to be able to fasten further elements to bricks, bricks and other objects which are produced in the manner described above, the undercut tool described at the outset can be used to introduce blind holes into the corresponding elements before curing during the molding process.

In the DE 601 00 861 T2 For example, an apparatus for automatically forming an opening or cavity in the wall of a ceramic product during molding in the mold is described. For this purpose, a deformable mandrel is used. This contains a cavity that can be filled with a liquid from the outside and has a supply line. The shell of the molding is deformed by the pressure exerted by the liquid from the inside.

In the JP 2009-101611 A a device is shown with an elastic member which is deformable so that in a deformable material blind holes can be produced.

As mentioned above, the undercut tool comprises a connector for connecting the tool to a mold. The connecting piece can be provided with a thread, for example, so that the undercut tool can be screwed into a mold. But also an attachment via bolts or a tension can be realized with appropriate design with the connector, wherein the respective form, such as a flow mold or a mold, corresponding receiving possibilities for the undercut tool with its connector must be provided. Alternatively, the connector can also be made in one piece with the mold.

In the connecting piece of the undercut tool, a mandrel displaceable along a direction of action extending parallel to a longitudinal axis of the blind hole or of the mandrel is supported, which in the case of a connecting piece produced integrally with the mold is thus guided directly in an opening of the mold. The longitudinal axis of the blind hole also corresponds to the longitudinal axis of the mandrel, the mandrel is thus slidably mounted along its longitudinal or symmetry axis. Under the direction of action is understood to mean the direction along the longitudinal axis, which is directed into the interior of the mold, ie in the direction of the mixture, since the mandrel in this direction the mixture when closing the mold or when introduced into the mixture, supported by the cap , which usually has a diameter larger than the mandrel displaced, while the mixture remains in the generated shape when removing the mandrel from the blind hole thus produced, the blind hole thus remains. When removing the mandrel this exerts no direct effect on the mixture. The mandrel may be made of a variety of materials that are strong enough to withstand the manufacturing process of the product without damage. For example, the mandrel may be made of metal, plastic, glass, ceramic or wood.

In the direction of action, i. in the direction of the mixture of the mandrel is completed by the cap. This cap serves on the one hand to protect the mandrel, on the other hand, but also the efficient displacement of the mixture around the mandrel when creating the blind hole.

The sheath of the undercut tool is made of a reversibly deformable under pressure material and surrounds the mandrel in a region which is located between the connector and cap, outwardly completely. This area may comprise the entire length of the mandrel between the connector and cap, or even a portion. As a result, no mixture can reach the mandrel. An essential feature of the shell is the reversible deformability under pressure, wherein the pressure along the longitudinal axis of the mandrel is constructed, for example, opposite to the effective direction through the mixture when introduced into this and through the mold itself along the direction of action. For this purpose, the jacket can be made for example of an elastically deformable plastic, silicone or rubber. In cross section, the jacket is usually circular in shape, but deviating shapes such as an elliptical or polygonal shape or a combination of such shapes are possible if special blind hole geometries are required. This also includes asymmetric or other shapes for the cross-section, since the tool is not rotated in the batch like a conventional drill.

Finally, the sheath around the mandrel has at least one cavity with a defined geometry. The geometry of the cavity is predetermined so that the jacket under pressure along the longitudinal axis of the mandrel, i. locally bulges parallel to the direction of action, in the region of the cavity, whereby in the mixture surrounding the shell, a blind hole with a shape corresponding to the jacket in a bulged state can be formed. Thus, when the mandrel caused by an external force - the pressure of the mixture on the cap and the pressure of the tool-mounted connector with the mandrel on the mixture - is moved relative to the connector so that the cap approaches the connector, the buckles Coat in the region of the cavity locally, whereby the corresponding shape can be formed. Due to the at least one cavity, the jacket is at this point of small thickness than in the rear area closer to the connector, where the jacket rests directly on the mandrel. If the mantle has a multiplicity of very small cavities around the mandrel, the density of the mantle is lower at this point, which produces the same effect: the mandrel is moved in such a way that the cap moves in the direction of the connecting piece, ie counter to the effective direction out of the mold, the mantle is more deformed at the point where the cavities are located. It forms at this point a bead with a larger diameter than it has the jacket in the region of the connecting piece.

The elasticity of the material used for the jacket can be tailored to the properties, in particular the flow properties of the mixture to be cured. For conventional clay mixtures, the Shore hardness of the deformable material can be selected for example in a range between 20 Shore and 90 Shore. No special requirements are imposed on the surface finish of the jacket; it can be smooth, corrugated, grained or otherwise roughened in order to achieve the lowest possible adhesion of the batch to be processed to the jacket. Sheath, mandrel and / or cap are usually designed interchangeable. The cap may in particular be screwed onto the mandrel, the jacket can be pushed with the cap removed, for example, on the mandrel. Cover and mandrel can also be made in one piece, the mandrel can then, for example, in a corresponding slide, which is guided in the connector to be screwed. The mandrel may be freely movable in the connector, it may also be resiliently mounted, or, if required by the manufacturing process, also be driven along its longitudinal axis, wherein the drive may be electromotive, pneumatic, hydraulic or otherwise.

The shape of the blind hole is determined essentially by the geometry of the cavity and can be easily varied by the pressure. Depending on the geometry of the blind hole can be formed, for example, with the shape of a barrel, a pear or a truncated cone, in the latter case also with at least partially frustoconical shape, which tapers towards the opening of the blind hole. The at least one cavity is, for example, in the front region of the jacket in the direction of action, i. in the region in which the jacket adjoins the cover, arranged to settle the truncated cone as deep as possible in the blind hole. When using a plurality of larger cavities along the longitudinal axis of the mandrel can also produce more complex shapes of the blind hole, such as blind holes with wavy walls.

It is essential that a bulge is formed at at least one point of the blind hole, i. an area where the diameter of the blind hole is larger than its opening. This is achieved by the at least one correspondingly formed cavity in the jacket. In the simplest case, the cavity is rotationally symmetrical with respect to the longitudinal axis of the blind hole or of the mandrel. With this design, objects to be mounted in the blind hole can be connected to the cured article more easily and more resiliently against attacking forces than with straight-walled blind holes, i. would be the case with cylindrical blind holes.

In the manufacture of the blind hole with such an undercut tool, this is first connected to the mold, for example a mold. Then the mixture is filled into the mold, the mold is closed and the mixture in the mold is formed into a blank by pressing. In this case, the mandrel moves due to the pressure exerted by the mixture from its initial position - with a relaxed elastic jacket - along the longitudinal axis of the mandrel or the blind hole, in a mold against the direction of action in the direction out of the mold. As a result, the jacket is compressed and bulges locally in the region of the at least one cavity. When you end the pressing process, the mold is opened again, so that the mandrel returns to its original position. The blank is removed from the mold. In the blank remains a blind hole with the jacket in the arched state corresponding shape.

For further details of such undercutting tool is again on the EP 2 684 659 A1 The disclosure is explicitly and completely included here.

In the in the EP 2 684 659 A1 described undercutting tool is the jacket in the rear direction in the direction of action - ie in the area which is farthest from the cap, and which adjoins the connecting piece, designed widening against the direction of action, so that under pressure effect in the direction of action a Ausschalschräge can be formed, which facilitates the removal of the tool and the insertion of latching means in the blind hole in the hardened mixture.

However, the use of different shell shapes and in particular of coats of different elasticity or compressibility can lead to the Ausschalschräge is more or less pronounced depending on the coat used, that has a shape dependent on the shell. In extreme cases, the jacket material may have such properties, which lead to the fact despite the formation of a corresponding taper in the rear region in the direction of the direction of action to the cap out Ausschalschräge not formed. In addition, due to the fact that the mixture usually has a high water content, moisture accumulating in the at least one cavity between jacket and mandrel can, on the one hand, change the bulging behavior of the jacket with a corresponding quantity of liquid the shell and / or the mandrel can react in an undesirable manner, so that there forms, for example, mold or rust.

The object of the invention is an undercut tool of the type described above, as is particularly in the EP 2 684 659 A1 is described, and in particular to further develop that the disadvantages mentioned are eliminated.

Description of the invention

This object is achieved in an undercut tool of the type described above in that the undercut tool comprises a chamfer ring for generating a Ausschalschräge in the batch, wherein the chamfer ring on the cap along the longitudinal axis of the mandrel opposite side of the shell abuts this. The chamfer ring is thus on that side of the jacket, which is opposite to the direction of action, that points in the direction of the connector. The chamfer is arranged so that it tapers in the direction of the mixture, ie in the direction of the cap or in the effective direction and widens against the effective direction. The advantage of using a separate chamfer ring over incorporation into the cladding is that the formation of the clipping slope becomes independent of the choice of cladding material, and thus greater uniformity in the formation of the clipping slope is achieved. The jacket then completely encloses the mandrel between the cap and the chamfer ring to the outside.

The chamfer ring may be part of the connecting piece, but is expediently made as a separate component, which allows easy changing and allows to remove the chamfer ring from the connector so that there is no elevation left, resulting in a use of the mold without the use of the tool disadvantageous as depressions in the mixture could be noticeable. In the event that the particular shape in which the tool is used to produce objects without blind holes, therefore, a cover pin is expediently provided, which are exchanged for the mandrel, sheath and bevel ring and can be used in the tool. This cover pin preferably has a head that allows a flush finish with the surface of the tool facing the batch, so that the tool leaves no imprints in the batch when not in use. By means of the cover pin the conversion of the mold is facilitated on the production of objects without blind holes, since not the entire tool, but only the mandrel, including the jacket and chamfer ring must be removed. Similar to the mandrel and the cover pin can be screwed into a corresponding slider or a bracket on the connector or tool, the slider can then be locked to prevent sliding over corresponding locking means, alternatively, the cover pin, for example, with the slide so far be screwed that a shift along the effective direction is prevented. If the chamfer ring is made as a separate component, then it is preferably formed on a guide piece with a guide for the mandrel. In this way, the chamfer ring via the guide piece also contributes to the stabilization of the directed movement of the dome.

Particularly preferably, the mandrel opposite the guide on a Unterpassung with game. The game may for example be between 0.5 mm and 1.0 mm, preferably it is 0.75 mm. In this way it is possible to remove any press residue or clay material that may have entered the tool; they can, for example, if the mold is aligned with the tool so that the mandrel with the cover pointing upward, ie away from the earth surface, fall down or supported by a lateral tilting movement of the mandrel down out of the mold under the tool become.

In a further embodiment, the tool comprises means for securing the casing and / or chamfer ring against rotation, for the chamfer ring in particular when it is manufactured as a separate component. Such anti-rotation means are particularly useful if no rotationally symmetrical blind hole, but a blind hole with a lower symmetry - for example, elliptical or hexagonal cross-section - or a blind hole is to be generated with an asymmetric cross-section. The shape of the blind hole is better fixed in this way, a corresponding for this shape of the blind hole trained element for insertion into the blind hole then finds better support, which is not least in such situations of significant advantage in which the element is exposed to strong tensile stresses.

Appropriately, the chamfer ring on its side facing the shell on which are formed engaging under pressure in the jacket and thus prevent rotation of the shell relative to the chamfer ring. Alternatively or additionally, such formations can also be arranged or formed on the side of the covering cap facing the jacket. These formations may be formed as small teeth or barbs, which press into the elastic material of the shell, in particular when the shell is elastically compressed by the mixture in the longitudinal direction along the longitudinal axis of the mandrel or the blind hole.

If the chamfer ring is not firmly formed on the connecting piece, but rather as a separate component, it advantageously has a cross-section as outer polyhedron in its side facing away from the jacket. On the connector then an inner polygon is designed with appropriate dimensions, on which the outer polygon is placed. The chamfer ring is then formed engaging over the outer polyhedron in an inner polyhedron formed on the connector. Equivalently, the outer polyhedron can also be formed on the connecting piece and the inner polygon on the chamfer ring or the guide piece on which the chamfer ring is formed.

In the shaft of the mandrel, a groove for venting is advantageously provided in the longitudinal direction, this groove extending in the longitudinal direction of the cap opposite end of the shaft of the mandrel to at least in the region in which the shell has at least one cavity, as a rule close to the cap. In this way, moisture, which can penetrate into the cavity due to the water content of the mixture, can be removed again from the cavity without the mandrel and the jacket having to be separated from one another, ie. without the tool would have to be at least partially taken apart.

Suitably, the mandrel is also formed with a stop for setting a predetermined stroke, this stop can also be set variably. This, in cooperation with a correspondingly formed on the connector stop surface ensures that the depth of the blind hole and the compression of the shell along the longitudinal direction of the mandrel are substantially identical.

In a further preferred embodiment of the invention, the mixture facing the batch surface of the cap is convexly curved and has at each point one of zero different curvature on. Has the cap on this surface namely flat areas, as well as in the EP 2 684 659 A1 described apparatus may be the case, ie have a curvature of zero, the mixture is compressed in these areas in the production of the blind hole more compressed, so that the surface structure, especially for workpieces with a small thickness, such as roof tiles, changes what The surface in this area leads to a slightly different color shading. In roof tiles such color deviations are noticeable after assembly and change, as they occur in large numbers, the appearance of the roof as a whole, which is undesirable. By using curved surfaces, this effect can be largely prevented or limited to a region of minimal expansion at the top of the cap with a tangent perpendicular to the longitudinal direction of the blind hole or the mandrel, which is not visible. The curvature of the surface of the cap can be anywhere constant and different from zero, which corresponds to the section of a spherical surface. However, the curvature preferably varies and decreases towards the edge of the cap. This allows a better adaptation of the surface of the cap with regard to an optimized pressure distribution in the mixture.

Also with other shapes for the mixture of the surface facing the cap can be very good results. For example, it is sufficient for the surface of the cap to have a comparatively strong convex curvature only in the region of the tip facing the mixture, which lies on the symmetry axis in the case of a rotationally symmetrical cap, somewhat in a range of up to 2 mm from the axis of symmetry Outside. This is followed by a region with a concave curvature to the region of the outer edge, wherein the amount of the concave curvature is much smaller than the amount of the convex curvature, so it is weaker.

In a particularly preferred embodiment of the undercut tool, the surface of the covering cap facing the mixture is composed of a first conical surface in the region of the tip of the covering cap and of at least one second conical surface which adjoins the first conical surface; to the last conical surface then connects the mandrel or coat. Here, the cone angle - the opening angle of the cone - the first conical surface is smaller than the cone angle of the second conical surface, or take the cone angle successively.

Preferably, in the connecting piece from a region surrounding the mandrel to an outer region continuous grooves and / or openings, which may be configured, for example, as holes whose cross-section may also have other shapes attached, which serve to remove impurities. Is the tool aligned in the same way as described above, ie with an upward Cover cap, so can mixture, which has infiltrated the tool in the area of the mandrel, are transported under the action of gravity down and in an outdoor area adjacent to the outside of the mold. There, the mixture can fall into a corresponding receiving device and be transported away.

Finally, it is also advantageous to provide the cover cap and / or the mandrel and / or the chamfer ring at least partially with a layer of an anti-adhesive material or at least partially or even completely made of a material having anti-adhesive properties. The properties of the non-adherence or non-adherence here refers to the mixture, also in this way it can be ensured that the blind hole always has the same depth, since no disturbing impurities between shell, mandrel and chamfer ring or between chamfer ring and connector penetrate can, what may could prevent the mandrel is pushed by the mixture to the stop against the direction of action from the mold. For example, in the case of a cap in which the surface facing the mixture is composed of two conical surfaces, the region with the more pointed first conical surface may be made of Teflon or coated with Teflon while the region with the blunt, second conical surface is made of steel. Also, the whole cap can be made of Teflon or a similar material with anti-adhesive effect.

It is understood that the features mentioned above and those yet to be explained can be used not only in the specified combinations but also in other combinations or alone, without departing from the scope of the present invention.

Brief description of the drawings

Fig. 1

einen Querschnitt durch ein Hinterschneidungswerkzeug,

Fig.2a

eine Seitenansicht eines Dorns für das Werkzeug,

Fig.2b

einen Schnitt durch den Dorn,

Fig.3a

einen Fasenring in der Draufsicht,

Fig.3b

einen Fasenring im Querschnitt,

Fig.3c

eine Perspektivansicht eines Fasenrings,

Fig.4a

eine Ausgestaltung einer Abdeckkappe und

Fig.4b

eine weitere Ausgestaltung einer Abdeckkappe.

The invention will be explained in more detail for example with reference to the accompanying drawings, which also disclose characteristics essential to the invention. Show it

Fig. 1

a cross section through an undercut tool,

2a

a side view of a mandrel for the tool,

2b

a cut through the thorn,

3a

a bevel ring in plan view,

3b

a chamfer ring in cross section,

3 c

a perspective view of a chamfer ring,

4a

an embodiment of a cap and

4b

a further embodiment of a cap.

Detailed description of the drawings

In FIG. 1 is an undercut tool for producing a blind hole in flowable, curable mixtures shown, which is inserted into a mold 1. To connect the undercut tool with the mold 1 is a connector 2. In the connector 2, a mandrel 3 is mounted, which is slidably mounted in the connector 2 along its longitudinal axis, which also corresponds to the longitudinal axis of the blind hole. Parallel to the longitudinal axis extends a direction of action, this is defined as the direction in which a cap 4 closes the mandrel 3 in the direction of the batch. The tool also comprises a jacket 5 made of a reversibly deformable under pressure material, which completely surrounds the mandrel 3 in a region on the circumference to the outside and rests on the one side of the cap. The jacket has around the mandrel 3 at least one cavity 6 with a defined geometry. The geometry of the cavity 6 is predetermined such that the shell 5 bulges locally under the action of pressure along the longitudinal axis of the mandrel 3 in the region of the cavity 6, wherein in the mixture surrounding the shell 5, a blind hole with a jacket 5 in the bulged Condition corresponding form is formed or is formed.

The undercut tool also includes a chamfer ring 7 for creating a Ausscha bevel in the batch. The chamfer ring 7 rests on the cap 4 along the longitudinal axis of the mandrel 3 opposite side of the shell 5 of this, so that the shell completely surrounds the mandrel 3 in this area between the bevel ring 7 and cap 4 to the outside. On the outer circumference of the chamfer ring 7, a chamfer 8 is mounted, which ensures that in each case a well-defined Ausschalschräge is produced in the mixture. The chamfer ring 7 is here formed on a guide piece with a guide 9 for the mandrel 3, both form a unit. The mandrel 3 is not accurately guided in the guide 9, but has its opposite a Unterpassung with a game of about 0.75 mm. This facilitates the removal of mixture, which may possibly reach between jacket 5, mandrel 3 and / or bevel ring 7, since the jacket 5 is placed only on the mandrel 3 and received with this no permanent connection. In particular, when removing the tool, when the jacket 5 is relaxed, can penetrate into these areas, even between the jacket 5 and cap 4, in small quantities mixture. Is the tool in the form 1 arranged as in FIG. 1 shown, ie with an upwardly directed cap 4, it can be transported by the action of gravity such, the tool-contaminating mixture down. To a lesser extent, the mandrel 3 can also be tilted sideways.

The undercut tool also has means for securing the jacket 5 against rotation relative to the chamfer ring 7. For this purpose, the chamfer ring 7 on his the shell 5 side facing formations 10, which are formed engaging under pressure in the jacket 5 and thus prevent rotation of the shell 5 relative to the chamfer ring 7. These formations 10 may be formed, for example, as teeth or barbs.

In the production of clay products such as roof tiles, the metallic mold is often subjected to electrical current after pressing, which facilitates the separation of the still moist and therefore water-containing product from the mold. Of course, the cap and the mandrel can also be energized. Are both form 1, connector 2, mandrel 3, cap 4 and the slide 13 made of metal, so are current and voltage everywhere in the same ratio. However, it may be advantageous to electrically isolate the tool from the mold 1 and to provide it with its own voltage, since the field profile at the tip of the mandrel 3 and the cap 4 due to the curvature is different than in the mold 1, which is formed essentially of flat areas. To increase the conductivity, the individual elements can be acted upon by a conductivity-increasing element, such as a contact grease.

As in Fig. 2a and 2b is shown in the shaft of the mandrel 3 in the longitudinal direction of the mandrel, a groove 11 is mounted for venting. The groove 11 extends along the longitudinal direction from the cap 4 opposite end of the mandrel 3 to at least in the region in which the jacket 5 has the at least one cavity 6. Through this groove 11, moisture or mixture, which has accumulated in the cavity 6, also be transported down from the cavity 6 and out of the tool.

The in the Fig. 2a and 2b shown mandrel 3 is also provided with a stop 12, which serves to set a predetermined stroke. In this way it can be ensured that the blind hole always has the same depth. The thorn 3 itself is as in FIG. 1 shown, also connected via a thread with a slider 13 which, in cooperation with corresponding, formed on the connector 2 stops ensures that the mandrel 3 does not remain in the batch and which simultaneously the mandrel 3 also leads.

The mixture of the facing surface of the cap 4 is convexly curved and has at each point a non-zero, preferably varying and decreasing towards the edge curvature. The stop 12 is incorporated here in the mandrel 3, but can also be variably adjustable. Such a variable setting can be made for example by means of an intermediate ring, not shown, which is screwed onto the same thread with which the mandrel 3 is also screwed to the slider 13.

In the connecting piece 2 also grooves and / or holes for the removal of impurities may be introduced, which pass from a region surrounding the mandrel 3 to an outside area below the tool. Cover 4, mandrel 3 and / or chamfer ring 7 are preferably non-stick coated or made of a material having non-stick properties to prevent aggregate from attaching to these elements.

The chamfer ring 7 is in the FIGS. 3a-3c shown in detail again. In FIG. 3a is a plan view of the chamfer ring 7 shown in FIG FIG. 3b a section along the axis AA and in Figure 3c a perspective view of the chamfer ring 7 is shown. On its side facing away from the jacket of the chamfer ring 7 is formed so that it has the shape of a Außenvielkants 14 in cross section. This is especially good in the top view FIG. 3a to recognize. With this outer polygon 14 of the chamfer ring 7 engages in a formed in the connector 2, corresponding inner polygon. In this way, the chamfer ring 7 is protected against twisting against the mold.

Mandrel 3, 5 jacket and chamfer ring 7 can also be removed from the tool, the connector 2 is flush with the inner edge of the mold 1 from. In the opening of the connector 2, a cover pin, which is not shown here, can be used, which is dimensioned so that it is also flush with the inner edge of the connector 2, so that form 1, connector 2 and the surface of the Cover pin form a flat surface.

In Fig. 4 a, a cap 15 is shown, the surface facing the mixture only in the region of the tip has a convex and otherwise a concave, decreasing towards the outer edge curvature. The cap 15 is made of steel, but coated in the region of the tip with a Teflon layer 17 with anti-adhesive effect.

In Fig. 4b a further cap 16 is shown, which is made in two pieces from two cone parts. In the region of the tip, the surface of the covering cap 16 facing the mixture is designed as a cone with a first conical surface 18, and in the adjoining region between cone and mandrel 3 it is designed as a truncated cone with a second conical surface 19. The cone angle of the first conical surface 18 on the cone is smaller than the cone angle of the second conical surface 19 on the truncated cone. The cone with the first conical surface 18 is made of Teflon, the truncated cone with the second conical surface is made of steel. Both parts are connected to each other, for example glued or screwed.

With the undercut tool described above, it is possible to produce blind holes of constant quality and dimensions in flowable, curable mixtures. If no blind hole is needed, then the tool can be rebuilt so that it does not become noticeable in the mixture, but it can remain in the mold.

LIST OF REFERENCE NUMBERS

1

shape

2

joint

3

mandrel

4

cap

5

coat

6

cavity

7

Fasenring

8th

chamfer

9

guide

10

formation

11

groove

12

attack

13

pusher

14

External polyhedron

15

cap

16

cap

17

Teflon coating

18

first conical surface

19

second conical surface

Claims (15)

1. Undercutting tool for producing a blind hole in flowable, curable batch mixtures, comprising

   - a connecting piece (2) for connecting the undercutting tool to a mould (1),

   - a mandrel (3), which is mounted in the connecting piece (2) in such a way that it can be displaced along a longitudinal axis,

   - a cap (4, 15, 16) that covers the mandrel (3) in the direction of the batch mixture,

   - a jacket (5) that consists of a material reversibly deformable under pressure and completely encloses the mandrel (3) on the outside in an area located between connecting piece (2) and cap (4, 15, 16),

   - wherein the jacket (5) comprises at least one cavity (6) that surrounds the mandrel (3) and has a defined geometry, and

   - wherein the geometry of the cavity (6) is specified in such a way that the jacket (5), when under pressure exerted along the longitudinal axis of the mandrel (3), bulges out locally in the area of the cavity (6), whereby a blind hole can be formed in the batch mixture surrounding the jacket (5), said blind hole having a shape corresponding to the jacket (5) in its bulged-out state, characterized in that

   - the undercutting tool comprises a bevelled ring (7) for producing a stripping bevel in the batch mixture.
2. Undercutting tool according to claim 1, characterized in that the bevelled ring (7) is formed on a guide piece with a guide (9) for the mandrel (3).
3. Undercutting tool according to claim 2, characterized in that the mandrel (3) comprises a clearance with play with respect to the guide (9).
4. Undercutting tool according to one of claims 1 to 3, comprising means for securing the jacket (5) and/or bevelled ring (7) against rotation.
5. Undercutting tool according to claim 4, characterized in that the bevelled ring (7) and/or the cap (4, 15, 16) comprises mouldings (10) in each case on the side facing the jacket (5), which mouldings are formed to engage in the jacket (5) when under pressure and thus prevent the jacket (5) from rotating with respect to the bevelled ring (7).
6. Undercutting tool according to one of claims 4 or 5, characterized in that, on the side facing away from the jacket (5), the bevelled ring (7) has a polygonal external cross-section (14) and is formed to engage in a corresponding internal polygonal shape formed on the connecting piece (2).
7. Undercutting tool according to one of claims 1 to 6, characterized in that a groove (11) is placed in the shaft of the mandrel (3) for venting, which groove extends along the longitudinal direction from the end opposite the cap (4, 15, 16) at least into the area in which the jacket (5) comprises a cavity (6).
8. Undercutting tool according to one of claims 1 to 7, characterized in that the mandrel (3) is formed with a stop (12) for setting a predetermined stroke.
9. Undercutting tool according to claim 8, characterized in that the stop (12) is variably adjustable.
10. Undercutting tool according to one of claims 1 to 9, characterized in that the surface of the cap (4) facing the batch mixture is convexly curved and has at every point a curvature which is different from zero, preferably varying and decreasing towards the edge.
11. Undercutting tool according to one of claims 1 to 9, characterized in that the surface of the cap (15) facing the batch mixture is convex only in the area of a point and otherwise has at every point a concave curvature which is different from zero.
12. Undercutting tool according to one of claims 1 to 9, characterized in that the surface of the cap (16) facing the batch mixture is formed from a first tapered surface (18) in the area of a point of the cap and from at least a second tapered surface (19) in the area adjacent to the mandrel and/or jacket, wherein the taper angle of the first tapered surface is smaller than the taper angle of the second tapered surface.
13. Undercutting tool according to one of claims 1 to 10, characterized in that continuous grooves and/or openings, preferably bores, are introduced in the connecting piece (2) from an area surrounding the mandrel (3) to an outer area for transporting away dirt particles.
14. Undercutting tool according to one of claims 1 to 11, characterized in that the cap (4, 15, 16) and/or the mandrel (3) and/or the bevelled ring (7) are produced with at least a partial non-stick coating or at least partially from a material with non-stick properties.
15. Undercutting tool according to one of claims 1 to 12, comprising a cover pin to be exchanged for the mandrel (3), jacket (5) and bevelled ring (7).

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