Casting piston for a casting machine

Abstract

1. A casting piston for a casting machine. 2.1. The invention relates to a casting piston for a casting machine, the casting piston comprising a coupling portion (1) at a rear end region, a head portion (2) at a front end region, and a piston rod (4) which is held on the coupling portion and extends, by way of a rod portion (4c), from the coupling portion to the head portion. The head portion has a piston ring (5) on an outer circumference. The piston rod terminates at its front end, in the head portion, with a head part (4a), which has an outside diameter (4aD) larger than an outside diameter (4D) of the rod portion (4). 2.2. According to the invention, the head portion includes a piston-ring-receiving unit (21) which has been pushed axially onto the rod portion and bears against the head part and on which the piston ring is held. The piston rod is surrounded, in the rod portion between the piston-ring-receiving unit and the coupling portion, by a spacer sleeve unit (14) which has been pushed axially onto the rod portion. 2.3. Use for example for hot-chamber die-casting machines.

Description

[0001] Casting pistons for a casting machine

[0002] The invention relates to a casting piston for a casting machine according to the preamble of claim 1.

[0003] The casting piston accordingly comprises a coupling section at a rear end, a head section at a front end, and a piston rod held at the coupling section, which extends from the coupling section to the head section. The head section has a piston ring on its outer circumference, which is held in an outer ring groove of the head section. The piston rod terminates at its front end in the head section with a head section having an outer diameter larger than the outer diameter of the rod section.

[0004] Casting pistons of this type are used in many designs in casting machines, and especially die-casting machines, to convey a molten, hot material, such as molten metal, from a preferably hollow cylindrical casting chamber towards a mold or a casting cavity formed by the mold. During operation, the casting piston, primarily at its head, is intermittently or continuously in contact with the molten material, which places specific demands on its corrosion resistance and thermal expansion properties. After each casting operation, the casting piston is returned to its starting position for the next casting operation by a retraction movement.In cold-chamber die-casting machines, the casting piston head section is primarily in contact with the molten material during the feed movement and is usually cooled. In hot-chamber die-casting machines, it is typically in constant contact with the molten material during operation, with molten material being fed into the casting chamber from a melt pool during its retraction movement. When used in die-casting machines of both hot-chamber and cold-chamber types, the casting piston must also withstand relatively high pressure loads.

[0005] Therefore, a casting piston intended for use in, among other things, pressure casting of molten metals such as zinc, magnesium or aluminum in cold chamber or hot chamber type die casting machines must be specially designed with regard to the correspondingly high physical and chemical stresses, while also taking into account the material and cost expenditure for the manufacture of the casting piston.

[0006] The coupling section serves to couple the casting piston to a casting drive, which provides for the forward and retraction movement of the casting piston in the casting chamber during the casting operation.

[0007] The outer piston ring seals the casting piston in its head section against the surrounding casting chamber. Depending on requirements and application, a single piston ring with a uniform outer sealing surface, several axially offset sealing sections, or several axially offset piston rings may be arranged on the head section of the casting piston, as is disclosed, for example, in German patent application DE 10 2009 012 636 A1 and patent application EP 2 701 866 B1 for generic casting pistons of hot-chamber die-casting machines.

[0008] It is known to design the piston ring as a slotted open ring made of a sufficiently elastic or extensible material, so that it can be snapped onto the casting piston head section and snapped into its outer ring groove by expanding or stretching it, usually with the use of a suitable tool such as spreading pliers. Furthermore, the slotted design largely prevents thermal stresses in the piston ring due to temperature fluctuations during the casting process. Optionally, snapping the ring on can be facilitated by corresponding ramps, as disclosed in patent EP 0 423 413 B1 for a generic casting piston intended in particular for cold-chamber die casting of aluminum or brass, where hot-work steel, a copper alloy, and a copper-beryllium (CuBe2) alloy are specified as materials for the piston ring.

[0009] As an alternative to the expanding snap-on mechanism of the piston ring, patent EP 1 483 074 B1 discloses a generic casting piston, also primarily intended for cold-chamber die casting of aluminum, in which an end portion of the head section is designed as a separate cover component. This cover component can be screwed onto the front of the remaining head section and forms an outer ring groove with a ring shoulder of the remaining head section, in which the piston ring is held. For this purpose, the piston ring is pushed axially onto the ring shoulder from the front before the cover is screwed on.

[0010] The invention is based on the technical problem of providing a casting piston of the type mentioned above, which is further improved compared to the prior art mentioned above, in particular with regard to the assembly and functional reliability of its piston ring in operation and with regard to the suitability of the casting piston, if required, especially for hot chamber die casting, e.g. of aluminium.

[0011] The invention solves this problem by providing a casting piston with the features of claim 1. Advantageous embodiments of the invention are specified in the dependent claims, the wording of which is hereby incorporated into the description by reference. This includes, in particular, all embodiments of the invention resulting from the combinations of features defined by the cross-references in the dependent claims.

[0012] In the casting piston according to the invention, the head section includes a piston ring retaining unit that is axially slid onto the rod section and abuts against the head section, and on which the piston ring is held. In the rod section between the piston ring retaining unit and the coupling section, the piston rod is surrounded by a spacer sleeve unit that is axially slid onto the rod section. The head section can be formed integrally with the piston rod or prefabricated as a separate component and attached to its end face. The integral design has the advantage that a connection point for the head section on the piston rod is eliminated, and therefore no problems can arise from such a connection point coming into contact with the molten material.

[0013] With these properties, the casting piston according to the invention enables the piston ring to be mounted without tensile stress, thus eliminating the risk of damage to the piston ring from the expansion or stretching process. The complex and stress-inducing mounting of the piston ring by expansion or stretching is eliminated. Instead, the piston ring can be received by the piston ring receiving unit without having to be expanded. The receiving unit, together with the piston ring, can then be axially slid onto the rod section of the piston rod from the rear until it rests against the head section at the front and is secured by it against further forward movement. The spacer sleeve unit, which is then also axially slid onto the rod section of the piston rod from the rear, secures the receiving unit and the piston ring against axial movement or slippage to the rear.

[0014] Since the piston ring can be mounted on the head section of the casting piston without expansion and therefore without tensile stress, the piston ring material can be selected with other requirements in mind, without having to consider the effects of such tensile stress. This helps to optimally design the casting piston with regard to the requirements of the intended application, such as hot-chamber die casting of aluminum and other metals. Furthermore, the piston ring's physical properties, such as its cross-section and area moment of inertia, can be freely designed according to other requirements without having to ensure sufficient tensile strength.For example, casting pistons made of ferrous materials in the molten metal contact area, where they are in constant contact with the molten metal during operation, are not well suited for hot-chamber die casting of aluminum. This is because iron from the steel material can leach into the molten aluminum, potentially causing corrosion problems. While ceramic materials and aluminum oxide (Al₂O₃) offer higher corrosion resistance to molten aluminum, components made from these materials are relatively brittle and less able to withstand tensile forces compared to those made from steel, such as high-alloy steel. Therefore, especially for casting pistons used in aluminum die casting, it is significantly advantageous to use steel for components subjected to tensile forces, such as the piston rod, and other materials that come into contact with the molten metal.to be able to use a ceramic material in the piston ring. Since the piston ring in the casting piston according to the invention can be installed without expansion, the risk of expansion damage to the piston ring is eliminated.

[0015] The spacer sleeve advantageously serves to hold the piston ring retaining unit in its defined axial position on the piston rod without requiring it to be rigidly fixed to the piston rod. Preferably, the piston ring retaining unit sits loosely on the piston rod; alternatively, for specific applications, it can be fixed in its slid-on operating position on the piston rod, particularly by a detachable connection. The loose seating of the piston ring retaining unit on the piston rod facilitates the compensation of thermal expansion effects that can be caused by the preferably different material choices for the piston rod on the one hand and the piston ring retaining unit on the other, and counteracts thermally induced mechanical stresses in these components.Furthermore, the spacer sleeve unit can be advantageously designed to transmit the compressive forces exerted by the casting piston during the casting process, thus relieving the piston rod of this primary burden. The piston rod, in turn, can be designed to primarily transmit the tensile forces occurring during operation. Additionally, the spacer sleeve unit can be designed to provide corrosion protection for the piston rod, and in particular for its rod section. In other words, the spacer sleeve unit can act as a protective sheath for the piston rod if it is made of a suitable protective material, especially one that protects against corrosion from the molten material. Furthermore, the spacer sleeve unit can fix the position of the piston rod head and exert a preload force on the head, preferably using an associated clamping or screw nut.

[0016] In a further development of the invention, the piston ring receiving unit comprises a receiving sleeve onto which the piston ring is axially pushed, and a support sleeve axially adjacent to the receiving sleeve. The axial pushing allows the piston ring to be attached to or received from the receiving sleeve without the need to expand the piston ring. The support sleeve secures the piston ring in its receiving position on the receiving sleeve against axial movement.

[0017] The receiving sleeve and the support sleeve, along with the mounted piston ring, can be pre-assembled in this way and then axially slid, i.e., threaded, onto the piston rod as a pre-assembled unit in the form of the piston ring receiving unit, for example, from the rear end of the piston rod until the receiving sleeve comes to rest against the piston head. Instead of this pre-assembly of the receiving sleeve, support sleeve, and piston ring, it is also possible to first slide only the receiving sleeve onto the piston rod, then attach the piston ring, and finally slide the support sleeve onto the piston rod. In this case, the receiving sleeve can abut a rear end of the piston head with a front end. The piston head then acts directly as a stop for the receiving sleeve. In alternative designs, the receiving sleeve can be axially spaced from the piston head, for example, by inserting another component of the casting piston.

[0018] The piston ring can be removed just as easily, if necessary, by reversing the assembly steps described above, for example for repair or replacement purposes. Preferably, the receiving sleeve and the support sleeve sit loosely on the piston rod; alternatively, for appropriate applications, they can be fixed to the piston rod in their slid-on operating position, in particular by a releasable connection.

[0019] In one embodiment of the invention, the receiving sleeve has an annular shoulder at a rear end face, which, together with a front end face of the support sleeve, forms an outer ring groove of the piston ring receiving unit in which the piston ring is held. This represents a structurally and functionally advantageous way of receiving the piston ring on the piston ring receiving unit. Alternatively, it is also possible, for example, to form the receiving sleeve from two adjacent sleeve parts with different outer diameters, so that the piston ring can be axially pushed onto the sleeve part with the smaller outer diameter until it comes to rest against the sleeve part with the larger outer diameter.

[0020] In a further embodiment of the invention, the piston ring circumferentially surrounds the receiving sleeve at least over a portion of its axial extent and has a radially inwardly projecting ring flange at a rear end face, which engages in the outer ring groove. In this way, the receiving sleeve can contribute to additional radial inward support of the piston ring over the corresponding axial length adjacent to the outer ring groove, and the piston ring can fulfill its sealing function over a sufficiently large axial length, which is not limited to the area of ​​the axial ring groove into which the piston ring engages with its radially inwardly projecting ring flange. In alternative embodiments, the axial extent of the piston ring is limited to the area of ​​the outer ring groove, which may be sufficient for corresponding applications.

[0021] In a further development of the invention, the spacer sleeve unit comprises at least a first and a second spacer sleeve axially adjacent to it, which have different coefficients of thermal expansion. This implementation of the spacer sleeve unit enables advantageous compensation of thermal expansion effects, as the thermal expansion behavior of the spacer sleeve unit can be adapted to the thermal expansion behavior of the piston rod with the receiving sleeve and the support sleeve by means of the two spacer sleeves with different coefficients of thermal expansion, so that even with temperature fluctuations the axial length of the spacer sleeve unit can always be kept equal to the resulting axial length of the piston rod from the coupling section to the front end region, more precisely to the support sleeve.

[0022] This measure counteracts axial play caused by thermal expansion in the components mounted on the piston rod, particularly the piston ring retaining unit and its components, such as the support sleeve and the retaining sleeve. For example, one spacer sleeve can be made of a steel material, e.g., the same steel material as that used for the piston rod, and the other spacer sleeve can be made of a different material with a different coefficient of thermal expansion, e.g., a different steel material or a different steel alloy. In this case, the other spacer sleeve can compensate for the difference in axial length change between the piston ring retaining unit and the piston ring retaining unit.The spacer sleeve compensates for the differences between the receiving sleeve and support sleeve on the one hand, and the portion of the piston rod made of a different material and surrounded by them on the other, thus helping to maintain the desired preload for the components mounted on the piston rod. In alternative designs, the spacer sleeve unit can be manufactured as a single piece if this is sufficient for the respective application.

[0023] In one embodiment of the invention, the spacer sleeve unit is formed at least partially from a ceramic material or an aluminum oxide material. In this case, the ceramic material or the aluminum oxide (Al₂O₃) material of the spacer sleeve unit can provide corrosion protection for the portion of the piston rod it surrounds, specifically the rod section, as can be useful, for example, in hot-chamber die casting of aluminum. In a further development of the invention, the spacer sleeve unit is circumferentially surrounded by a protective sleeve body made of a ceramic material or an aluminum oxide material. In this embodiment of the casting piston, the protective sleeve body provides corrosion protection for the spacer sleeve unit it surrounds and the inner piston rod. In this case, the spacer sleeve unit can be specifically designed to compensate for thermal expansion effects.

[0024] In one embodiment of the invention, the protective sleeve body is axially supported against the support sleeve on one side and the coupling section on the other by means of a clamping sleeve unit. The clamping sleeve unit enables compensation for differences in thermal expansion between the protective sleeve body, which is made of ceramic or aluminum oxide material, and the spacer sleeve unit, which is made of a different material. For this purpose, the clamping sleeve unit is preferably made of a suitable material with a compensating coefficient of thermal expansion that differs from that of the protective sleeve body.

[0025] In a further development of the invention, the piston ring is formed at least partially from a ceramic material. Since ceramic material has high resistance to molten aluminum, the piston ring formed in this way is particularly well suited for casting pistons intended for use in casting machines for casting molten aluminum, especially for hot-chamber die casting of aluminum.

[0026] The term "ceramic material" in this context also includes, in particular, so-called technical ceramics. The use of ceramic material for corresponding components of die-casting machines is well-known. Depending on requirements and application, the piston ring may consist entirely of the ceramic material, or only a portion of the piston ring may be made of the ceramic material, while the remaining portion is made of another material. It should be noted that in certain designs of the casting piston, the piston ring and other components may be made of TZM material, i.e., a titanium-zirconium-molybdenum (TZM) alloy, instead of the aforementioned ceramic material.

[0027] In a further development of the invention, the piston ring receiving unit is formed at least partially, i.e., completely or only in a partial area or only for a part of its possibly multiple components, from a ceramic material. This material selection for the piston ring receiving unit or at least a part of its components has the same advantageous properties as explained above for the same material selection for the piston ring.

[0028] In a further development of the invention, the piston rod is formed at least partially, i.e., completely or only in a partial section, from a steel material. This choice of material for the piston rod is advantageous with regard to low manufacturing costs and high tensile strength, and can in particular be a high-alloy steel material, as is known per se for casting pistons of die-casting machines.

[0029] In a further development of the invention, the outer diameter of the piston rod head is no larger than the inner diameter of the piston ring. This allows the piston ring to surround the head, if desired, along its entire axial length or only in a portion of its axial extent. For this purpose, the piston ring can extend axially beyond the receiving sleeve.

[0030] In a further development of the invention, the head is made of a steel material and provided with a corrosion protection layer in the molten metal contact area. This measure allows the advantageous choice of a steel material, both for manufacturing and functional reasons, to be combined with enhanced corrosion protection. The corrosion protection layer protects the steel material of the head in the molten metal contact area—that is, the area that comes into contact with the molten metal—from unwanted corrosion caused by the molten metal. The corrosion protection layer can, for example, consist of TZM material, which can be shrink-fitted onto the head or applied in another manner. In alternative embodiments, the head remains without a corrosion protection layer if this is not required for the intended application.

[0031] In a further development of the invention, the piston rod is connected to the coupling section at its rear end by a detachable connection. This measure has the advantage that, for assembly of the casting piston, the piston ring receiving unit, including the receiving sleeve and the support sleeve, along with the piston ring and the spacer sleeve unit, can first be slid onto the piston rod from the rear, as explained above. The piston rod can then be secured to the coupling section at its rear end, for example, using an associated clamping or screw nut. Furthermore, the piston rod can be removed from the coupling section of the casting piston at its rear end if necessary, particularly for subsequent removal or unthreading of the spacer sleeve unit and the piston ring receiving unit, including the piston ring, from the piston rod, for example, as mentioned, for repair or replacement purposes.

[0032] Since the detachable connection is located at the rear end of the piston rod in this case, it remains relatively far from the molten material during operation of the casting piston and is therefore not subjected to the stresses of direct contact with the molten material. Consequently, there is no risk of the detachable connection corroding or becoming stuck due to the influence of the hot molten material for other reasons.

[0033] The detachable connection can be, in particular, a screw connection with which the piston rod, with a variable screw length, can be connected to the coupling section by screwing the piston rod to varying degrees into a clamping or screw nut of the screw connection. This allows the effective length of the piston rod to be changed, especially depending on the spacer sleeve unit. This enables, for example, retightening to compensate for unwanted axial play between components mounted on the piston rod due to thermal expansion effects.

[0034] In other words, the screw connection for the detachable connection of the piston rod at its rear end to the coupling section allows for adjustment or retensioning of the axial distance of the support sleeve, and thus also of the receiving sleeve and the piston ring from the coupling section. Specifically, this adjustment ensures that the piston ring receiving unit, such as the receiving sleeve and the support sleeve, and therefore also the piston ring, always maintain their axially fixed position on the piston rod with a certain preload, particularly via the spacer sleeve assembly. This prevents undesirable axial play between the receiving sleeve and the support sleeve, or between the receiving sleeve or the piston ring receiving unit and the head of the piston rod, caused by temperature fluctuations during operation or by the use of different materials for the various components of the casting piston.

[0035] In a further development of the invention, the coupling section includes a preload adjustment device for setting an axial preload for the assembly consisting of the spacer sleeve unit, piston rod, piston ring retaining unit, and piston ring. In this embodiment of the casting piston, the preload adjustment device allows for variable adjustment of the aforementioned axial preload for this assembly. This preload ensures that the assembly remains free of play and, more importantly, sealed against the molten casting pressure during the alternating compressive and tensile loads encountered during casting. In a corresponding implementation, the aforementioned screw connection between the piston rod and the coupling section is integrated into the preload adjustment device, which in this case may additionally include a locking mechanism or clamping device for securing the screw connection.Advantageous embodiments of the invention are illustrated in the drawings. These and further embodiments of the invention are explained in more detail below. The drawings show:

[0036] Fig. 1 shows a perspective view of a casting piston suitable, for example, for hot chamber casting of aluminium.

[0037] Fig. 2 shows a longitudinal sectional view of the casting piston,

[0038] Fig. 3 shows a detail view from Fig. 2 of a front area of ​​the casting piston,

[0039] Fig. 4 shows the longitudinal section view of Fig. 2 for a variant of the casting piston and

[0040] Fig. 5 shows a detailed view of Fig. 3 for another variant of the casting piston.

[0041] Figures 1 to 5 illustrate the casting piston according to the invention in three different embodiments, which are particularly suitable for use in hot-chamber die-casting machines for casting aluminum parts. For ease of understanding, identical or functionally equivalent components are represented by the same reference numerals. As illustrated in the figures, the casting piston according to the invention comprises a coupling section 1 at a rear end region and a head section 2 at a front end region. The coupling section 1 allows the casting piston to be coupled to a conventional casting drive 22, which is only schematically indicated in Figures 2 and 4, in a manner known per se. The casting piston extends between the front and rear end regions with a central section or shaft section 3.Furthermore, the casting piston according to the invention includes a piston rod 4, which extends with a rod section 4c from the coupling section 1 to the head section 2 and terminates at its front end in the head section 2 with a head part 4a, as can be seen from Figures 2 and 4. The head section 2 of the casting piston has a piston ring 5 on its outer circumference. Preferably, the piston ring 5 is used in a slotted design so that, when the casting piston is inserted into the casting chamber, it can be compressed radially in a manner known per se and thereby reliably presses radially outwards against the wall of the casting chamber, sealing it in a manner known per se. Furthermore, the head section 2 includes a piston ring receiving unit 21, which is axially pushed onto the rod section 4c and rests against the head part 4a, and on which the piston ring 5 is received and held.

[0042] The piston rod 4 is surrounded in the rod section 4c between the piston ring receiving unit 21 and the coupling section 1 by a spacer sleeve unit 14 axially pushed onto the rod section 4c.

[0043] The spacer sleeve unit 14 holds the piston ring receiving unit 21, and thus also the piston ring 5, at the desired axial distance from the coupling section 1, thereby securing these components in their axial position on the piston rod 4. Furthermore, in applications of the casting piston in die-casting machines, the spacer sleeve unit 14 helps to transmit the compressive forces occurring during the mold filling phase between the coupling section 1 and the head section 2 of the casting piston, while the piston rod 4 is primarily designed to transmit the tensile forces occurring between the coupling section 1 and the head section 2.

[0044] In advantageous embodiments, the piston ring receiving unit 21, as in the examples shown, comprises a receiving sleeve 8 onto which the piston ring 5 is axially pushed, and a support sleeve 7 axially adjacent to the receiving sleeve 8. The receiving sleeve 8 follows the support sleeve 7 in the axially forward direction, i.e., the support sleeve 7 is located behind the receiving sleeve 8. In corresponding embodiments, the receiving sleeve 8, as in the examples shown, abuts a rear end face 10 of the head part 4a at a front end 8a, more precisely, at the rear annular end face with which the head part 4a projects radially relative to the adjacent part of the piston rod 4. In corresponding embodiments, the receiving sleeve 8, as in the examples shown, has an annular shoulder 9 at a rear end face, as can be seen particularly in Figures 3 and 5.The ring shoulder 9, together with a front end face 7a of the support sleeve 7, forms an outer ring groove 6 in which the piston ring 5 is held. This has the advantage that the outer ring groove 6 does not need to be formed as a U-shaped groove in a corresponding component, such as a piston component, which saves manufacturing effort and can contribute to increased stability of the bearing surface or support surface for the piston ring 5.

[0045] In the embodiments shown in Figures 1 to 4, the annular shoulder 9 is formed on the one-piece receiving sleeve 8. In the embodiment shown in Figure 5, the receiving sleeve 8 is formed in two parts: a front sleeve part 8! and an adjoining rear sleeve part 82, which has a smaller outer diameter than the front sleeve part 8!. The annular shoulder 9 thus forms a shoulder on the smaller-diameter sleeve part 82 relative to the larger-diameter sleeve part 8!. In this example, the piston ring 5 is pushed onto the smaller-diameter sleeve part 82 without needing to be expanded and rests axially against the larger-diameter sleeve part 8!. The support sleeve 7, together with the larger-diameter sleeve part 8!, secures the piston ring 5 in this position against axial movement.

[0046] In advantageous embodiments, the piston ring 5 surrounds the receiving sleeve 8 circumferentially, at least over a portion of its axial extent, and, as in the examples of Figures 1 to 4, has a radially inwardly projecting ring flange 5a at a rear end face, which engages in the outer ring groove 6. In the examples of Figures 1 to 4, the piston ring 5 surrounds the receiving sleeve 8 over its entire axial length and also projects axially beyond the receiving sleeve 8. The piston ring 5 can then be pushed axially onto the receiving sleeve 8 without radial expansion until its ring flange 5a is in the outer ring groove 6. In corresponding embodiments, the spacer sleeve unit 14, as in the examples shown, has at least a first spacer sleeve 14a and a second spacer sleeve 14b axially adjacent to it, which have different coefficients of thermal expansion.This allows the spacer sleeve unit 14 to be adapted to thermally induced length changes of the piston rod 4 on the one hand and the piston ring receiving unit 21 together with the mounted piston ring 5 on the other.

[0047] In certain embodiments, the spacer sleeve unit 14 is formed, at least partially, from a ceramic material or an aluminum oxide material. In this way, it can protect the piston rod 4 it surrounds from corrosion in the relevant area. In the embodiments shown in Figures 4 and 5, the first, front spacer sleeve 14a is specifically formed from a technical ceramic, or alternatively, an aluminum oxide material, since this area is more likely to be exposed to molten metal contact than the rear area of ​​the piston rod 4 or the casting piston. The other, rear spacer sleeve 14b can be designed for other requirements, in particular for the aforementioned compensation of thermally induced changes in length, for which purpose the spacer sleeve 14b is formed from a suitable material.More precisely, in this case the rear spacer sleeve 14b, in its respective length and material, is designed, together with the front spacer sleeve 14a, to compensate for thermally induced changes in length of the piston rod 4 it surrounds, i.e. to ensure that the spacer sleeve unit 14, together with the piston ring receiving unit 21, experiences the same changes in length under the temperature influences of the casting operation as the piston rod 4.

[0048] In other embodiments, the spacer sleeve unit 14, as shown in the embodiment of Figures 1 to 3, is circumferentially surrounded, at least partially, by a protective sleeve body 15 made of a ceramic material or an aluminum oxide material. In the example shown, the spacer sleeve unit 14 is surrounded by the protective sleeve body 15 along a predominant part of its length. In this case, the spacer sleeve unit 14 can be made entirely of a material that does not need to be corrosion-resistant with respect to the melt material used, since the protective sleeve body 15 protects the spacer sleeve unit 14 from corrosive contact with the melt. Thus, in the embodiment of Figures 1 to 3, the front spacer sleeve 14a can optionally be made of a first steel material and the rear spacer sleeve 14b of a different steel material with a different coefficient of thermal expansion.Specifically, the material and length of the rear spacer sleeve 14b can be selected such that the bolted hybrid assembly consisting of piston rod 4, spacer sleeve unit 14 and piston ring receiving unit 21 with piston ring 5 does not lose its desired preload due to the different thermal expansions of the individual components at operating temperature.

[0049] In corresponding embodiments, the protective sleeve body 15, as in the exemplary embodiment of Figures 1 to 3, is axially supported against the piston ring receiving unit 21 on one side and the coupling section 1 on the other by means of a clamping sleeve unit 16. The clamping sleeve unit 16 ensures that the protective sleeve body 15 remains axially clamped in its position even in the event of thermally induced changes in length of the casting piston components involved, in particular the piston rod 4 and the components clamped to it, such as the spacer sleeve unit 14 and the piston ring receiving unit 21, and is thus secured against axial slippage or axial play. In the example shown, the clamping sleeve unit 16 comprises, for this purpose, a front clamping sleeve 16a in front of the protective sleeve body 15, which abuts the piston ring receiving unit 21, and a rear clamping sleeve 16b behind the protective sleeve body 15, which abuts the coupling section 1.Specifically, the clamping sleeve 16a can be a sealing clamping sleeve that seals between the piston ring receiving unit 21 and the protective sleeve body 15.

[0050] In advantageous embodiments, the piston ring 5 is formed at least partially from a ceramic material, in particular a technical ceramic. In the examples shown, it is preferably formed entirely from the ceramic material. In advantageous embodiments, the piston ring receiving unit 21 is formed at least partially from a ceramic material. This applies optionally to the support sleeve 7 and / or the receiving sleeve 8, whereby, if desired, two different materials can also be used for these two components. In the examples shown, the piston ring receiving unit 21 is preferably formed entirely from a ceramic material, which can be the same or a different ceramic material than that of the piston ring 5.

[0051] In advantageous embodiments, the piston rod 4 is formed at least partially from a steel material. In the examples shown, the piston rod 4 is preferably formed entirely from the steel material, in particular from a steel alloy commonly used for cast piston rods.

[0052] In advantageous embodiments, the outer diameter is 4a D of the head section 4a not larger than an inner diameter 5 Dof the piston ring 5. In this case, as in the example of Figs. 1 to 4, the piston ring 5 can project axially forward beyond the receiving sleeve 8, up to approximately the axial height of the head part 4a of the piston rod 4. This creates an annular gap 19 between the head part 4a and the piston ring 5, axially limited by the receiving sleeve 8, into which molten material can penetrate during the casting process, which additionally ensures that the piston ring 5 is reliably pressed radially outwards in a sealing manner.

[0053] In advantageous embodiments, the head part 4a, as in the examples shown, has a core body 11 made of a steel material and a corrosion protection layer 12 with which the core body 11 is provided in a molten contact area. In the examples shown, the corrosion protection layer 12 preferably consists of a shrink-fitted TZM material. The outer diameter 4a DThe diameter of the head section 4a corresponds in this case to the outer diameter of the core body 11 plus twice the thickness of the corrosion protection layer 12 radially surrounding the core body 11, as shown in Fig. 3. In advantageous embodiments, the piston rod 4, as in the examples shown, is connected at its rear end region 4b to the coupling section 1 by a detachable connection 13. In the examples shown, the detachable connection 13 is a screw connection with an external thread 13a at the rear end region 4b of the piston rod 4 and an internal thread 13b at the coupling section 1. Alternatively, the detachable connection can be implemented in another way, e.g., by a bayonet connection or a snap-fit ​​connection or the like.

[0054] In corresponding embodiments, the coupling section 1, as in the examples shown, has a preload adjustment device 17 for setting an axial preload for the assembly consisting of spacer sleeve unit 14, piston rod 4, receiving sleeve 8, support sleeve 7, and piston ring 5. In the examples shown, the preload adjustment device 17 includes the aforementioned releasable connection 13 in the form of a screw connection, through which the piston rod 4 with its external thread 13a can be screwed into the coupling section 1 in a continuously adjustable manner with variable length. For this purpose, the coupling section 1 has a clamping nut or screw nut 17a with the internal thread 13b and with a conventional external tool interface 18. Furthermore, the preload adjustment device 17 in the illustrated embodiment includes a wrench size 20 at the rear end of the piston rod 4 for attaching a wrench or the like.

[0055] Using a suitable tool, the assembled hybrid assembly consisting of piston rod 4 and attached components can be screwed or clamped together via tool interface 18 and wrench size 20 by screwing the nut 17a onto the external thread 13a. The pre-assembled and clamped casting piston assembly can then be installed into the remaining components of the preload adjustment device 17. In the example shown, these are two coupling locking half-shells 17c, 17d, between which the piston rod 4 can be held rotationally fixed with its wrench size 20. These half-shells engage in an annular groove of the nut 17a, gripping the nut 17a securely and preventing it from rotating relative to the piston rod 4.To mount the casting piston on the casting drive 22, the piston rod 4, with its wrench size 20, is inserted into one of the two coupling locking halves 17c, 17d. The other coupling locking half-shell 17c, 17d can then be radially attached from the outside to create a rotationally fixed connection between the piston rod 4 on one side and the screw nut 17a on the other. The preload adjustment device 17 includes a clamping device 17b, which holds the two coupling locking half-shells 17c, 17d in this locking position, in which the piston rod 4 and the components mounted on it are axially and radially clamped as desired.

[0056] The preload adjustment device 17 allows, if necessary, readjustment of this preload even during casting or in the installed operating state of the casting piston, as an alternative or additional to the aforementioned compensation for thermally induced length changes of the piston rod 4 by means of a corresponding design of the spacer sleeve unit 14. For this purpose, the clamping device 17b, and thus the securing by the coupling locking halves 17c, 17d, is first loosened until the screw nut 17a can rotate between the coupling locking halves 17c, 17d. Subsequently, a tightening torque for reloading can be applied via the tool interface 18. The necessary counter-torque is transmitted from the held preload adjustment device 17 via the wrench size 20 to the external thread 13a of the piston rod 4.

[0057] As the above explanations of exemplary embodiments make clear, the invention provides a casting piston that can be designed to be particularly suitable for casting aluminum parts in hot-chamber die-casting machines. Through the aforementioned selection of appropriate materials, the casting piston according to the invention can be realized as a steel-ceramic hybrid component, combining the advantageous choice of a steel material for certain components with the advantageous choice of a ceramic material or another material with comparably high resistance to molten aluminum for certain other components, and is therefore particularly suitable for this application of hot-chamber die-casting of aluminum.The use of ceramic components minimizes the corrosion susceptibility of the casting piston surface in the molten metal contact area, while the advantageous strength properties of steel, including high tensile strength, can be utilized for the casting piston components in a manner known per se. The piston ring 5 can be installed very easily without the need for expansion, so that a material sensitive to tensile stress but highly resistant to molten aluminum, in particular a ceramic material, can be used for the piston ring 5 without any problems. The piston ring 5 is preferably installed, as mentioned, by pre-assembly, whereby the piston ring 5 is received by the ring shoulder of the receiving sleeve 8 and the support sleeve 7 is placed against it, and this pre-assembled assembly is then slid onto the piston rod 4 from the rear.Subsequently, the other components can also be slid onto the piston rod 4 from the rear, such as the spacer sleeve unit 14 formed by one or more spacer sleeves and the protective sleeve body 15, as well as the one- or multi-part clamping sleeve unit 16. The piston rod 4, thus equipped, is then screwed to the coupling section 1 at its rear end, i.e., mounted in it. The components of the casting piston according to the invention can be replaced relatively easily if necessary, e.g., in case of damage or wear, by disassembling the casting piston into its individual parts in the manner described above, reversing the assembly steps.

[0058] As the illustrated and further embodiments described above clearly demonstrate, the invention provides a casting piston for a casting machine that allows for easy assembly and disassembly of the piston ring on the head section of the casting piston without significant strain, ensures a secure hold of the piston ring during operation, and is process-reliable, particularly in hot-chamber die-casting machines, but not exclusively for hot-chamber casting of aluminum. The casting piston can be designed to optimize its thermal expansion behavior and corrosion resistance during casting, even under the conditions prevailing in metal die-casting, and especially in hot-chamber casting of aluminum. No expansion of brittle components, such as the piston ring, is required for assembly.Where components made of technical ceramics or aluminum oxide are used to provide high corrosion protection and / or high strength, these components can be kept comparatively small and simple in design and can be replaced quickly and easily if necessary. This applies particularly to typical wear parts such as the piston ring and the support sleeve, which are especially exposed to the casting pressures and abrasive influences. Machining processes on components made of sintered technical ceramics, which can lead to minor surface damage or notch effects that weaken the component, can be eliminated. Instead, the relevant cast piston component made of ceramic material can be assembled as a module from several simple parts and does not need to be machined from a blank.This applies particularly to the lightly stressed receiving sleeve with annular groove and the heavily stressed support sleeve, which can be designed as a simple smooth disc. It goes without saying that the casting piston can also be used for other casting applications, e.g., in cold-chamber die-casting machines.

Claims

Patent claims 1. Casting piston for a casting machine, in particular for a hot-chamber die-casting machine, comprising a coupling section (1) at a rear end region, a head section (2) at a front end region, the head section (2) having a piston ring (5) on its outer circumference, and a piston rod (4) held on the coupling section (1), which extends with a rod section (4c) from the coupling section (1) to the head section (2) and terminates at its front end in the head section (2) with a head part (4a) having an outer diameter (4a) D ) has an outer diameter larger than an outer diameter (4 D) of the rod section (4c) is characterized in that the head section (2) has a piston ring receiving unit (21 ) axially pushed onto the rod section (4c) and abutting against the head part (4a), on which the piston ring (5) is held, and the piston rod (4) in the rod section (4c) between the piston ring receiving unit (21 ) and the coupling section (1 ) is surrounded by a spacer sleeve unit (14) axially pushed onto the rod section (4c).

2. Casting piston according to claim 1, further characterized in that the piston ring receiving unit (21) includes a receiving sleeve (8) onto which the piston ring (5) is axially pushed, and a support sleeve (7) axially adjacent to the receiving sleeve (8).

3. Casting piston according to claim 2, further characterized in that the receiving sleeve (8) has an annular shoulder (9) at a rear end face which, together with a front end face (7a) of the support sleeve (7), forms an outer ring groove (6) of the piston ring receiving unit (21) in which the piston ring (5) is held.

4. Casting piston according to claim 3, further characterized in that the piston ring (5) surrounds the receiving sleeve (8) circumferentially at least in a partial region of its axial extent and has a radially inwardly projecting ring flange (5a) at a rear end face which engages in the outer ring groove (6).

5. Casting piston according to one of claims 1 to 4, further characterized in that the spacer sleeve unit (14) has at least a first spacer sleeve (14a) and a second spacer sleeve (14b) axially adjacent to it, which have different coefficients of thermal expansion.

6. Casting piston according to one of claims 1 to 5, further characterized in that the spacer sleeve unit (14) is formed at least partially from a ceramic material or an aluminum oxide material and / or the spacer sleeve unit (14) is surrounded at least partially on its circumference by a protective sleeve body (15) made of a ceramic material or an aluminum oxide material.

7. Casting piston according to claim 6, further characterized in that the protective sleeve body (15) is axially supported against the piston ring receiving unit (21) on the one hand and the coupling section (1) on the other hand by means of a clamping sleeve unit (16).

8. Casting piston according to one of claims 1 to 7, further characterized in that the piston ring (5) is formed at least partially from a ceramic material and / or the piston ring receiving unit (21) is formed at least partially from a ceramic material and / or the piston rod (4) is formed at least partially from a steel material.

9. Casting piston according to one of claims 1 to 8, further characterized in that the outer diameter (4a D ) of the head section (4a) not larger than an inner diameter (5 D ) of the piston ring (5) is.

10. Casting piston according to one of claims 1 to 9, further characterized in that the head part (4a) is made of a steel material and is provided with a corrosion protection layer (12) in a molten contact area.

11. Casting piston according to one of claims 1 to 10, further characterized in that the piston rod (4) is connected at its rear end region (4b) to the coupling section (1) by a detachable connection (13).

12. Casting piston according to one of claims 1 to 11, further characterized in that the coupling section (1) has a preload adjustment device (17) for adjusting an axial preload for the assembly consisting of spacer sleeve unit (14), piston rod (4), piston ring receiving unit (21) and piston ring (9).

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