Sealing piston for a hydraulic tool holder and hydraulic tool holder

Abstract

Sealing piston (6) for a hydraulic tool holder (2), comprising: a pin (8), a seal (10) and a head (12) which are arranged one behind the other in an axial direction (A) and thereby form a stack, - wherein the seal (10) has a circumferential sealing lip (16) for contact with and sealing against an inner wall (18) of a bore (4) of the tool holder (2), for realising a first sealing effect, - wherein the head (12) abuts and rests against a sealing seat (20) of the bore (4) and thereby closes the bore (4) to achieve a second sealing effect, wherein the head (12) is formed in two parts and has a plate (32) and a ball (34), - wherein the plate (32) is connected to the seal (10) with a first side, - wherein the plate (32) has a second side which is opposite the first side and against which the ball (34) rests in the end position, so that it is pressed into the sealing seat (20).

Description

Background of the invention

[0001] The invention relates to a hydraulic tool holder and a sealing piston for such a tool holder.

[0002] A hydraulic tool holder holds a tool or workpiece using hydraulic pressure. An example of a tool holder is an expansion chuck. To clamp or insert the tool or workpiece, the tool holder has an expansion sleeve with a wall and a pressure chamber containing a fluid. The pressure chamber is accessible via a hole in the tool holder. A sealing piston is inserted into this hole and uses this to exert pressure on the fluid and thus on the wall. The pressure and therefore the clamping of the tool or workpiece in or on the expansion sleeve can be adjusted by moving the sealing piston in the hole, e.g. by screwing it in or out. More or less pressure is exerted accordingly.

[0003] EP 1 737 594 B1 and DE 10 2017 002 144 A1 contain examples of hydraulic expansion chucks and associated sealing pistons. Furthermore, DE 69 113 984 T2 describes a tool holding device, WO 95 / 29 029 A1 describes a hydraulic clamping bush, and DE 34 17 430 A1 describes a hydraulic clamping element.

[0004] The tightness of the sealing piston within the bore of the tool holder is essential for its optimal operation. Leakage of fluid from the pressure chamber should be avoided as much as possible. However, since the sealing piston must be movable, sealing is difficult, especially since the repeated movement of the sealing piston during the clamping and unclamping of a tool or workpiece causes the sealing piston to wear over time, reducing the sealing effect. Object of the invention

[0005] Against this background, it is an object of the invention to provide an improved hydraulic tool holder and a sealing piston for use in such a tool holder. The sealing piston should ensure the highest possible tightness for as long as possible. Solution to the task

[0006] The object is achieved according to the invention by a tool holder having the features of claim 6 and by a sealing piston having the features of claim 1. Advantageous embodiments, further developments, and variants are the subject of the dependent claims. The statements relating to the tool holder also apply mutatis mutandis to the sealing piston, and vice versa.

[0007] The hydraulic tool holder has a bore into which a sealing piston is inserted. The sealing piston seals a pressure chamber of the tool holder from the environment. The sealing piston can be moved in the bore, allowing the tool holder to be clamped and released depending on the direction. A fluid is arranged in the pressure chamber, which in turn presses on a wall, e.g. of an expansion sleeve, in which a tool or workpiece can be clamped. The tool holder is therefore also referred to as an expansion clamping holder. The fluid can be an oil, for example. When the sealing piston moves in or out of the bore, pressure is exerted on the fluid and the wall, as well as on a tool or workpiece clamped in or on it.

[0008] In the present case, it is assumed, without limiting the generality, that the tool holder is an expansion chuck which has a particularly cylindrical expansion sleeve which surrounds a cavity into which a tool or a workpiece can be inserted and in which the tool or workpiece can be clamped by actuating the sealing piston.

[0009] The sealing piston comprises a pin, a seal, and a head, which are arranged one behind the other in an axial direction, thus forming a stack. The pin, the seal, and the head each extend in the axial direction, i.e., along a longitudinal axis, and are preferably rotationally symmetrical with respect to this axis. The pin, the seal, and the head are preferably arranged directly behind the other, so that the head and the pin each bear against the seal on opposite sides.

[0010] The pin serves, in particular, to actuate the sealing piston from the outside. Preferably, the tool holder has an actuator, which is also located in the bore, e.g., a screw that is threaded into the bore. The actuator presses on the pin, so that the sealing piston can be extended and retracted by actuating the actuator. Accordingly, the actuator expediently has a tool engagement for external actuation.

[0011] The seal has a circumferential sealing lip for contact with and sealing against an inner wall of the bore, to achieve a first sealing effect. The sealing lip is preferably annular. In particular, the sealing lip protrudes radially from the rest of the sealing piston. When inserted, the sealing lip rests against the inner wall; when the sealing piston moves, the sealing lip rubs along the inner wall. Overall, this results in the first sealing effect. Viewed in cross-section along the axial direction, the sealing lip protrudes from the rest of the seal and has a generally convex, i.e. outward-facing, profile. In a suitable embodiment, the sealing lip is wedge-shaped. A curved sealing lip, for example, is also suitable.

[0012] In this case, the bore has a sealing seat which forms a stop for the head when the sealing piston is retracted in the axial direction, so that in one of the sealing piston's end positions the head rests on the sealing seat and thereby closes the bore, creating a second sealing effect. When the sealing piston is retracted, i.e. when the tool holder is clamped, the sealing piston is moved inwards as a whole until the head touches the sealing seat. Moving the head beyond the sealing seat is not possible. The head then closes the bore at the level of the sealing seat, so that the seal is relieved. Advantageous relief of the seal already begins as the head approaches the sealing seat, since the head closes the bore more and more as it moves inwards, and the pressure in the pressure chambers acts more on the head and less on the seal. In the end position the head then lies sealingly against the sealing seat.

[0013] A key aspect of the invention is the double sealing effect, which is achieved by combining the seal that rests against the inner wall with an additional seal, namely the head, which rests against the sealing seat. The seal creates a first sealing effect, which is combined with a second sealing effect of the head. When the tool holder is clamped, the sealing piston is moved inwards in the bore, so that pressure is built up. This pressure acts on the seal, more precisely on the sealing lip, which is correspondingly stressed. As the tool is retracted, however, the head closes the bore and absorbs the corresponding pressure, so that the seal is correspondingly relieved. In the end position, the pressure of the pressure chamber is applied entirely to the head, and the seal is correspondingly relieved.In the clamped state, i.e., while a tool or workpiece is clamped or inserted, and especially during machining, the seal is largely or completely pressure-free. This significantly reduces wear on the seal, especially the sealing lip, and extends the service life of the sealing piston. The dual sealing effect also advantageously reduces so-called micro-leakage of fluid from the pressure chamber through the bore to the outside.

[0014] In a suitable embodiment, the sealing seat is formed in that the bore has an outer section in which the sealing piston is seated, and an inner section which is tapered compared to the outer section and thus has a diameter which is smaller than the diameter of the head. The bore is therefore tapered overall. In other words: the bore has a step when viewed in cross-section along the axial direction, which forms the sealing seat. This makes the sealing seat particularly stable. In principle, however, a variant is also possible and suitable in which the sealing seat is merely designed as a ring in the bore, so that the bore does not continue inwards with a tapered diameter, but is widened again after the sealing seat. In a suitable embodiment, the sealing seat and especially the entire inner section has a diameter (ieinner diameter) which is at least 50% and at most 80% of the diameter of the outer section.

[0015] Preferably, the sealing seat is annular, and the head is designed at the front such that it rests positively in the sealing seat in the final position. A positive fit is thus achieved between the head and the sealing seat in the final position, thereby optimally closing and sealing the bore. The head and the sealing seat are designed to complement each other.

[0016] The head has a spherical front design for a positive fit against the sealing seat in the final position. This type of head geometry is particularly easy to manufacture and simultaneously ensures optimal form-fitting engagement with the sealing seat. The head is thus designed as a spherical seal or a conical seal. The sealing seat is advantageously funnel- or conically shaped so that the sealing seat runs diagonally inward and the head is automatically and optimally centered in the sealing seat. The spherical shape of the head, in combination with an annular sealing seat, results in a particularly good sealing effect.

[0017] The head is plate-shaped on the rear side, i.e., facing outwards and towards the seal, and has a flat contact surface that rests against the seal. This advantageously results in a large-area distribution of the force from the head to the seal, especially with a spherical or conical head on the front side, i.e., tapered towards the front. The contact surface extends, in particular, perpendicular to the axial direction.

[0018] Alternatively or additionally, in an advantageous embodiment, the pin has a flat contact surface that rests against the seal. The seal is expediently enclosed on both sides by the pin and the head and arranged, in particular clamped, between two flat contact surfaces. The seal also has contact surfaces that are designed, in particular, to complement the contact surfaces of the pin and head.

[0019] The seal is preferably made of an elastic material, in particular a plastic, so that the seal adapts optimally to the bore and thereby seals in particular the pressure chamber. The material expediently has the best possible chemical resistance, especially with regard to the fluid in the pressure chamber, as well as the best possible wear resistance, temperature resistance, formability with regard to production, elasticity with regard to insertion into the bore, service life and sealing effect as well as friction properties, especially with regard to the inner wall of the bore. The seal is in particular rotationally symmetrical with respect to the longitudinal axis. Preferably, the seal is manufactured in one piece, i.e. monolithic. The seal is preferably manufactured using an injection molding process and is then accordingly an injection-molded part.

[0020] The head, on the other hand, is preferably made of a rigid material, preferably a metal, in particular steel. The head is particularly rotationally symmetrical with respect to the longitudinal axis. The head is suitably made of a similar or identical material to the inner wall of the bore, especially its sealing seat. Neither the sealing seat nor the head are thus made of an elastic material, but rather of a rigid material, resulting in a particularly robust and wear-resistant seal.

[0021] The pin is preferably made of a rigid material, preferably a metal, in particular steel. The statements regarding the head also apply accordingly to the pin. The pin is, in particular, rotationally symmetrical with respect to its longitudinal axis and is expediently a cylinder. The pin is preferably manufactured in one piece, i.e., monolithic.

[0022] The head and the pin are conveniently manufactured with clearance in relation to the bore so that both can be moved along the bore with as little friction as possible and yet are guided.

[0023] A design in which the seal is made of a material which has a higher elasticity than the pin and the head is particularly preferred. Designs in which the seal has a higher elasticity than either the pin or the head are generally also advantageous. When the tool holder is clamped, the seal is therefore primarily compressed and squeezed between the pin and the head. Because the seal is more elastic than the head and pin, the sealing piston has a variable length. A particular advantage of the elastic seal is that it accommodates tolerances which are caused by the manufacture of the sealing piston and the bore. In a suitable design, the seal is so elastic that it allows a change in length in the range from 0.1 mm to 1 mm, preferably 0.5 mm.

[0024] In a suitable design, the seal is made of plastic, and the head and pin are each made of metal. The plastic is, as described above, more elastic than the metal.

[0025] In principle, it would be conceivable for the head to be manufactured in one piece and from a single material, i.e. the head is monolithic. The head therefore has an upper side which rests against the seal, and an underside which rests against the sealing seat in the final position. The upper side is accordingly preferably flat, in particular as a plate, while the underside is convex, in particular spherical or conical. The underside therefore has a spherical section or a conical section, in particular a hemisphere or a cone or truncated cone, which extends downwards and into the interior of the bore. The spherical or conical section has a diameter which corresponds to the diameter of the head or, alternatively, is smaller, so that an additional ring is formed around the spherical or conical section on the underside.It is particularly important that the diameter of the ball or conical section is larger than the inner diameter of the sealing seat. The ball or conical section is preferably 1 / 2 to 2 times as long as the plate, measured in the axial direction. The one-piece design is advantageous because it reduces the number of parts in the sealing piston, and the head is also particularly well guided in the bore, allowing it to be optimally retracted into the sealing seat during clamping.

[0026] In the present case, however, as an alternative to a one-piece design, the head is made in two parts and has a plate and a ball. The plate has a first side that is connected to the seal and a second side that is opposite the first side and against which the ball rests, at least in the end position, so that it is pressed into the sealing seat. It is particularly important that the ball has a diameter that is larger than the inside diameter of the sealing seat. Measured in the axial direction, the ball is preferably 1 / 2 to 2 times as long as the plate. Viewed in the axial direction, the plate is arranged between the seal and the ball. The ball is either attached to the plate or loose and can therefore move relative to the plate.It is particularly important that the point-like force transmission of the ball is not transferred to the seal in a point-like manner, but that the plate acts as an intermediary, so to speak, transferring the pressure from the ball to the seal over a large area. Accordingly, the plate, as described above, is advantageously made of a rigid material, as is the ball. This two-part design is advantageous because only simple parts are used, namely a ball and a plate, which can be a disk or a cylinder, for example. The statements regarding the plate with a ball also apply analogously to a design in which the head is constructed in two parts and has a plate and a cone or truncated cone instead of a sphere. However, with the two-part design of the head, the variant with a ball is preferred.

[0027] The sealing piston has a length which is the sum of the respective lengths of the pin, the seal and the head. Furthermore, the sealing piston has a diameter which is correspondingly determined by the respective diameters of the pin, the seal and the head, whereby the maximum diameter is determined in particular by the seal, specifically its sealing lip. The lengths and diameters, i.e. generally the dimensions of the sealing piston and its individual parts, depend on the specific application and the dimensions of the tool holder. In an exemplary embodiment, the pin is one to twice as long as the seal and the seal is one to twice as long as the head, depending on whether a whole sphere or just a spherical section (or cone or conical section) is present. The sealing lip has a length which is 10% to 30% of the total length of the seal.The diameter and overall length of the sealing piston are typically in the range of a few millimeters to a few millimeters. The inner diameter of the sealing seat and the diameter of the bore are designed accordingly.

[0028] An actuator is expediently arranged in the bore for moving the sealing piston. The actuator is, for example, a screw as described above. The actuator exerts pressure on the pin and thus on the entire sealing piston, allowing it to be retracted into the bore. Pressure from the pressure chamber acts on the other side, so that the sealing piston is driven out of the bore when the actuator is released. Preferably, the bore for the actuator has an actuator stop, and the seal is designed to be compressible such that, when the sealing piston is in its end position, the actuator can still be retracted up to the actuator stop. This provides a certain degree of tolerance for pressing the head against the sealing seat. When the tool holder is clamped, the actuator and the sealing piston are initially retracted inwards into the bore until the head hits the sealing seat.The actuator can then be retracted further to the actuator stop, but the head is already in its end position. Only the seal is compressed and the pin is retracted accordingly. The actuator stop is designed, for example, as a ring-shaped, chamfered step within the bore. The actuator has a corresponding front face that strikes the actuator stop when retracted.

[0029] In a practical embodiment, the seal is positively connected to the pin or to the head, or to both, via a plug-in coupling. This means that the individual parts of the sealing piston are connected to one another in a captive manner. It also ensures optimal guidance when moving in the bore. For example, the pin and the head each have a pin which is inserted into a complementary recess in the seal. The seal then has an H-shaped cross-section along the axial direction. The contact surfaces of the pin and head are each annular. However, a design without a plug-in coupling is also advantageous; in this case, the contact surfaces are designed perpendicular to the axial direction over the entire cross-section, preferably flat, so that the head, the seal and the pin simply lie against one another and are not actually plugged together.

[0030] In addition to the bore for the sealing piston, in a preferred embodiment the tool holder has a separate filling bore and a ball seal for closing the filling bore. The filling bore serves to fill the pressure chamber with fluid and is otherwise closed in a pressure-tight manner, namely by means of the ball seal. The ball seal is designed in particular similar to the head of the sealing piston. The ball seal has a ball which rests inwards against a sealing seat of the filling bore and thereby closes it. The ball is pressed against the sealing seat by another actuator, in particular a screw which sits in a thread in the filling bore. In contrast to the sealing piston, however, the actuator in the filling bore acts directly on the ball, without an additional seal made of an elastic material arranged in between. Description of the characters

[0031] In the following, exemplary embodiments of the invention are explained in more detail with reference to a drawing. In each case, the following schematically show: Fig. 1 a tool holder with a sealing piston, Fig. 2 the sealing piston Fig. 1 in a detailed view, Fig. 3 a variant of the sealing piston from Fig. 1, Fig. 4 another variant of the sealing piston from Fig. 1. Description of the embodiment

[0032] In Fig. 1, a hydraulic tool holder 2 is shown in a cross-sectional view perpendicular to a rotational axis D. The tool holder 2 is specifically an expansion chuck. The tool holder 2 has a bore 4 extending in an axial direction A and along a longitudinal axis L. The cross-sectional view in Fig. 1 is also a sectional view along the longitudinal axis L. A sealing piston 6 is inserted into the bore 4. Two embodiments of the sealing piston 6 are shown in detail in the Fig. 2 to 4 shown.

[0033] The sealing piston 6 seals a pressure chamber (not shown in detail), which is hydraulically connected to the bore 4, from the environment. The sealing piston 6 can be moved in the bore 4 in the axial direction A, whereby the tool holder 2 can be clamped and released depending on the direction. The sealing piston 6 has a pin 8, a seal 10 and a head 12, which are arranged one behind the other in an axial direction A and thus form a stack. The pin 8, the seal 10 and the head 12 each extend along the longitudinal axis L and are rotationally symmetrical with respect to this. The pin 8, the seal 10 and the head 12 are arranged directly behind the other, so that the head 12 and the pin 9 each rest against the seal 10 on opposite sides.

[0034] The pin 8 serves to actuate the sealing piston 6 from the outside by means of an actuator 14, which is also located in the bore 4 and is a screw in this case, which is inserted into a corresponding thread. The actuator 14 presses on the pin 8, allowing the sealing piston 6 to be extended and retracted.

[0035] The seal 10 has a circumferential sealing lip 16 for contact with and sealing against an inner wall 18 of the bore 4, thus realizing a first sealing effect. The sealing lip 16 is annular here and protrudes in the radial direction R relative to the rest of the sealing head 6, i.e., perpendicular to the axial direction A. When inserted, the sealing lip 16 rests against the inner wall 18 and rubs against it as the sealing piston 6 moves, thus resulting in the overall first sealing effect. The sealing lip 16 shown here as an example is wedge-shaped, but other profiles are also suitable.

[0036] The bore 4 has a sealing seat 20 which forms a stop for the head 12 when the sealing piston 6 is retracted in the axial direction A, so that in an end position of the sealing piston 6 the head 12 as shown in Fig. 1 is clearly seen resting against the sealing seat 20 and thereby closing the bore 4, creating a second sealing effect. When the sealing piston 6 is retracted, it is moved inward until the head 12 abuts the sealing seat 20. Moving the head 12 beyond the sealing seat 20 is not possible. The head 12 then closes the bore 4 at the level of the sealing seat 20, so that the seal 10 is relieved.

[0037] The seal 10, which rests against the inner wall 18, in combination with an additional seal, namely the head 12, which rests against the sealing seat 20, then creates a double sealing effect. Fig. In the end position shown in Figure 1, the pressure of the pressure chamber is fully applied to the head 12, and the seal 10 is completely relieved of pressure. In the clamped state, i.e., while a tool or workpiece is clamped in or clamped, the seal 10 is pressure-free.

[0038] In the exemplary embodiment shown, the sealing seat 20 is formed in that the bore 4 has an outer section 22 in which the sealing piston 6 is seated, and an inner section 24 which is tapered compared to the outer section 22 and thus has a diameter d1 which is smaller than a diameter d2 of the head 12. The bore 4 is therefore tapered overall and has a step which forms the sealing seat 20. In the present case, the sealing seat 20 and also the inner section 24 have a total diameter d1 (ie inner diameter) which is at least 50% and at most 80% of the diameter d3 of the outer section 24.

[0039] The sealing seat 20 in Fig. 1 is ring-shaped and the head 12 is spherical at the front, so that in the end position the head 12 lies positively in the sealing seat 20. The sealing seat 20 is for this purpose in the embodiment of the Fig. 1 funnel- or conical-shaped and runs diagonally inwards.

[0040] As especially in the Fig. 2 to 4, the head 12 in the embodiments shown here is plate-shaped on the back and has a flat contact surface 28 which rests against the seal 10 and here also extends perpendicular to the axial direction. This results in a large-area distribution of the force from the spherical or conical head 12 on the front to the seal 10. In addition, the pin 8 also has a similarly flat contact surface 26 which rests against the seal 10, so that the latter is enclosed on both sides by the pin 8 and the head 12 and is clamped between two flat contact surfaces 26, 28. The seal 10 also has contact surfaces (not designated in more detail) which are complementary to the contact surfaces 26, 28 of the pin 8 and the head 12.

[0041] In this case, the seal 10 is made of an elastic material, specifically a plastic, so that the seal 10 optimally adapts to the bore 4 and thereby seals the pressure chamber. Furthermore, the seal 10 is manufactured in one piece, i.e., monolithic.

[0042] The head 12, on the other hand, in the present case consists of a rigid material, specifically a metal, in particular steel, and here also of a similar or the same material as the inner wall 18 of the bore 4, specifically its sealing seat 20. Neither the sealing seat 20 nor the head 12 are thus made of an elastic material, but rather each of a rigid material, resulting in a particularly robust and wear-resistant seal 10.

[0043] In this case, the pin 8 is also made of a rigid material, specifically a metal, particularly steel. The statements regarding the head 12 also apply to the pin 8. The pin is a simple cylinder and manufactured in one piece, i.e., monolithic.

[0044] The head 12 and the pin 8 are manufactured with clearance with respect to the bore 4 so that both can be moved along the bore 4 with as little friction as possible and yet in a guided manner.

[0045] In the exemplary embodiments shown, the seal 10 is made of a material which has a higher elasticity than the pin 8 and the head 12. When the tool holder 2 is clamped, the seal 10 is therefore primarily compressed and squeezed between the pin 8 and the head 12. Due to the seal 10 being elastic compared to the head 12 and pin 8, the sealing piston 6 has a variable length I1, ie the elastic seal 10 accommodates tolerances which are caused by the manufacture of the sealing piston 6 and the bore 4.

[0046] The Fig. 2 to 4 each show a variant of the sealing piston 6 in a side view. In the respective embodiment of the Fig. 2 and Fig. 4, the head 12 is manufactured in one piece and consists of a single material, ie the head 12 is monolithic. The head 12 thus has an upper side, which rests against the seal 10, and a lower side, which in the final position rests against the sealing seat 20. The upper side is accordingly preferably flat, while the lower side is convex, in Fig. 2 spherical, in Fig. 4 is conical, and the underside therefore has Fig. 2 has a spherical section 30, here specifically a hemisphere, which extends downwards. Analogously, the underside in Fig. 4 has a conical section 31 extending downward. The spherical section 30 and the conical section 31 have a diameter d4 that corresponds to the diameter d2 of the head 12 or, alternatively—as shown here—is smaller, so that an additional ring is formed on the underside around the spherical section 30 or the conical section 31. It is particularly important that the diameter d4 of the spherical section 30 or the conical section 31 is larger than the inner diameter d1 of the sealing seat 20.

[0047] In the embodiment of the Fig. 3, the head 12 is in contrast formed in two parts and has a plate 32 and a ball 34. The plate 32 adjoins the seal 10 with a first side and further has a second side, which is opposite the first side and against which the ball 34 rests in the end position, so that it is pressed into the sealing seat 20. The ball 34 has a diameter d4 which is larger than the inner diameter d1 of the sealing seat 20. The plate 32 is arranged between the seal 10 and the ball 34, viewed in the axial direction A. The ball 34 is either attached to the plate 32 or loose and thus movable relative to the plate 32. The plate 32 transmits the point-like force transmission of the ball 34 over a large area to the seal 10. The explanations apply accordingly to an embodiment not explicitly shown, in which the head 12 has a cone instead of the ball 34, e.g.a true cone with a point or a truncated cone.

[0048] The sealing piston 6 has a length I1, which is the sum of the respective lengths I2, I3, I4 of the pin 8, the seal 10, and the head 12. Furthermore, the sealing piston 6 has a diameter, which is determined by the respective diameters d5, d6, d2 of the pin 8, the seal 10, and the head 12, with the maximum diameter being determined by the seal 10, specifically its sealing lip 16. The actual lengths I1, I2, I3, I4 and diameters d2, d5, d6, i.e., the general dimensions of the sealing piston 6 and its individual parts, depend on the specific application and the dimensions of the tool holder 2.

[0049] The actuator 14, which is in Fig. 1 is used as described to move the sealing piston 6. In the embodiment shown, the Fig. 1, the bore 4 for the actuator 14 has an additional actuator stop 36 and the seal 10 is designed to be compressible in such a way that in the end position of the sealing piston 6, the actuator 14 can still be retracted up to the actuator stop 36, as in Fig. 1. This provides a certain degree of tolerance for pressing the head 12 against the sealing seat 20. When the tool holder 2 is clamped, the actuator 14 and the sealing piston 6 are initially retracted inward in the bore 4 until the head 12 abuts the sealing seat 20. The actuator 14 can then be retracted further up to the actuator stop 36, but the head 12 is already in the end position; only the seal 10 is compressed and the pin 8 is retracted accordingly. Fig. 1, the actuator stop 36 is designed as an annular and chamfered step within the bore 4 and the actuator 14 has a corresponding front side which strikes the actuator stop 36 when retracted.

[0050] In the example shown in Fig.1, the seal 10 is positively connected to the pin 8 and the head 12 via a plug-in coupling 38, 40. This means that the individual parts of the sealing piston 6 are captively connected to one another and optimal guidance during movement is ensured. For example, the pin 8 and the head 12, as shown, each have a pin which is inserted into a complementary recess in the seal 10. The seal 10 then has an H-shaped cross-section along the axial direction A. The contact surfaces 26, 28 of pin 8 and head 12 are each annular. In a variant not shown, no plug-in coupling 38, 40 is present, so that the contact surfaces 26, 28 are perpendicular to the axial direction A over the entire cross-section and are, for example, completely flat, and the head, the seal and the pin simply rest against one another.

[0051] The tool holder 2 shown as an example has, in addition to the bore 4 for the sealing piston 6, a separate filling bore 42 and a ball seal 44 for closing the filling bore 42. The filling bore 42 serves to fill the pressure chamber with fluid and is otherwise closed pressure-tight by means of the ball seal 44. The ball seal 44 is designed similarly to the head 12 of the sealing piston 6 and has a ball 46 which rests inwardly against a sealing seat 48 of the filling bore 42 and thereby closes it. The ball 46 is pressed against the sealing seat 48 by a further actuator 50. In contrast to the sealing piston 6, however, the actuator 50 in the filling bore 42 acts directly on the ball 46, without an additional seal made of an elastic material arranged in between.

Claims

[1] Sealing piston (6) for a hydraulic tool holder (2), comprising: a pin (8), a seal (10) and a head (12) which are arranged one behind the other in an axial direction (A) and thereby form a stack, - wherein the seal (10) has a circumferential sealing lip (16) for contact with and sealing against an inner wall (18) of a bore (4) of the tool holder (2), for realising a first sealing effect, - wherein the head (12) abuts and rests against a sealing seat (20) of the bore (4) and thereby closes the bore (4) to achieve a second sealing effect, wherein the head (12) is formed in two parts and has a plate (32) and a ball (34), - wherein the plate (32) is connected to the seal (10) with a first side, - wherein the plate (32) has a second side which is opposite the first side and against which the ball (34) rests in the end position, so that it is pressed into the sealing seat (20). [2] Sealing piston (6) according to claim 1, wherein the sealing seat (20) is annular and the head (12) is designed on the front side such that it lies in the sealing seat (20) in a form-fitting manner in the end position. [3] Sealing piston (6) according to one of claims 1 to 2, wherein the seal (10) consists of a material which has a higher elasticity than the pin (8) and the head (12). [4] Sealing piston (6) according to one of claims 1 to 3, wherein the seal (10) consists of a plastic and the head (12) and the pin (8) each consist of a metal. [5] Sealing piston (6) according to one of claims 1 to 4, wherein the seal (10) is positively connected to the pin (8) or to the head (12) or to both via a plug-in coupling (38, 40). [6] Hydraulic tool holder (2), with a bore (4) into which a sealing piston (6) according to one of claims 1 to 5 is inserted. [7] Tool holder (2) according to claim 6, wherein it has a separate filling bore (42) and a ball seal (44) for closing the filling bore (42). [8] Tool holder (2) according to one of claims 6 to 7, wherein an actuator (14) is arranged in the bore (4) for moving the sealing piston (6), wherein the bore (4) for the actuator (14) has an actuator stop (36), wherein the seal (10) is designed to be compressible in such a way that in the end position of the sealing piston (6) the actuator (14) can still be retracted up to the actuator stop (36). [9] Tool holder (2) according to one of claims 6 to 8, wherein the bore (4) has an outer portion (22) in which the sealing piston (6) is seated, and an inner portion (24) which is tapered relative to the outer portion (22) and thereby has a diameter (d1) which is smaller than a diameter (d2) of the head (12).

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