WO2004110679A1

WO2004110679A1 - Piston for a cold chamber die casting machine

Info

Publication number: WO2004110679A1
Application number: PCT/EP2004/006321
Authority: WO
Inventors: André Müller; Frédéric MÜLLER
Original assignee: Allper Ag
Priority date: 2003-06-13
Filing date: 2004-06-11
Publication date: 2004-12-23
Also published as: EP1635973B1; DE502004004662D1; DE20309181U1; EP1635973A1; ES2293275T3; ATE369929T1

Abstract

The invention relates to a piston (1) for a cold chamber die casting machine, said piston comprising a first part (3) that is to be fixed to a piston rod (9) of the die casting machine, which moves axially in a casting cylinder on the low pressure side, and a second part (11) that is releasably screwed to the first piston part (3)and which forms a front face (15) on the high pressure side. A sealing ring (27) is fixed to the first (3) and/or second (11) piston part at least in an axially overlapping manner. The outer periphery of the separation surface (33) between the first (3) and the second (11) piston parts is axially staggered towards the low pressure side in relation to the edge of the sealing surface of the sealing ring (27) on the high pressure side. Additionally or alternatively, said first piston part (3) has several axial through holes (35) distributed in peripheral direction, through which the second piston part (11) is fixed to the first piston part (3) by means of fastening screws (37). The separation surface (33) and the insertion holes of the through holes (35) are thus arranged on the low pressure side of the piston (1), thereby preventing the molten metal material from penetrating into and solidifying in the screw thread.

Description

Piston for a cold chamber die casting machine

description

The invention relates to a piston for a cold chamber die casting machine.

The piston of a cold chamber die casting machine and in particular the sealing ring of such a piston is exposed to high pressures at comparatively high temperatures of the molten metal, so that the piston and in particular its sealing ring are exposed to very high stresses during operation, which shorten their lifespan, which adversely affects the Productivity of the casting machine affects when piston wear parts have to be replaced and the casting machine has to be stopped for this.

An uncooled, multi-part piston is known from German patent specification 1 080 739, the slotted sealing ring of which is arranged in a ring recess on the circumference of a first piston part to be fastened to the piston rod of the die casting machine on the low-pressure side. On the high-pressure side of the first piston part, a second piston part, forming the high-pressure side of the piston end, is removably fastened with a central, axial screw. The second piston part delimits the ring recess receiving the sealing ring towards the high-pressure side and contains a plurality of channels distributed in the circumferential direction, which lead into an annular gap between the ring recess and the inner circumference of the sealing ring. Metal melt flowing into the annular gap under the casting pressure forces the sealing ring radially outward against the inner wall of the casting cylinder. In this way, the sealing of the sealing ring that wears out during operation can be improved. However, it has been shown that the one flowing into the parting surface gap between the two piston parts and there solidifying melt makes the separation of the two piston parts difficult and in individual cases also makes it impossible, especially if the melt reaches the fastening screws.

Cooled pistons are known from US 5,048,592 and US 5,233,912. The pistons are designed as a cap which encloses the high-pressure end of the piston rod. The piston rod, together with the cap, forms channels or annular spaces for a circulating cooling liquid which cools the cap, in particular in the region of its end wall on the high-pressure side. A slotted sealing ring is arranged in the area of the front wall. The sealing ring can be designed as a step slot. The cap can be screwed onto the piston rod or fastened with a bayonet connection.

Another cooled piston in the form of a cap is known from US 4,899,804. The cap is screwed onto a threaded shoulder of the piston rod and has a smaller outside diameter than the piston rod. On the outer circumference of the cap there is a closed sealing ring on the high pressure side and a bushing on the low pressure side. These ring parts are axially clamped axially between an annular flange in the region of the end wall of the cap on the one hand and a shoulder of the piston rod on the other hand. With such a piston, the cap is exposed to a high compressive stress during operation and tends to break. The bush rests on the shoulder of the piston rod with a relatively small end face, so that deformations can occur on the bush and the piston rod on the one hand and subsequently on the thread fixing the cap. This complicates the disassembly of the cap. In addition, the thread of the cap is exposed to the coolant, which can lead to corrosion damage and thus disassembly problems.

It is an object of the invention to provide a piston for a cold chamber die casting machine which is easier to operate than before lets and in particular allows easier replacement of wearing parts.

The invention is based on a piston in the form of a cap with a peripheral wall and a front wall that closes the cap on the high pressure side at the end of a high pressure side end of a piston rod that can be axially displaceable in a casting cylinder of a cold chamber die casting machine, at least one sealing ring being arranged on the outer circumference of the peripheral wall , ■ • - ^''

The improvement according to the invention is characterized in that the cap comprises two piston parts axially abutting in a dividing surface, detachably fastened to one another to form a structural unit, of which a first piston part is designed as at least a section of the peripheral wall and a second piston part forms at least the end wall and closes the socket on the high pressure side. Such a cap is divisible so that it can be serviced more easily than before. The two piston parts can each be adapted to the operating requirements better than before. For example, the high-pressure side of the second piston part can be made of heat-resistant, wear-resistant material such as steel, which has the advantage that the end wall formed by the second piston part can be dimensioned thinner than before, which benefits piston cooling. Although the cap is divided, it forms a rigid structural unit which can be attached as a structural unit to the high-pressure end of the piston rod. The casting pressure acting on the end wall can be transmitted via the peripheral wall of the cap. However, the high-pressure side end face of the piston rod preferably abuts the low-pressure side face of the end wall and directly absorbs the casting pressure acting on the end wall. The fastening members, in particular in the form of a bayonet, for the detachable fastening of the piston to the piston rod are expediently provided on the first piston part, which is designed as a bushing. In a preferred embodiment of the invention, the first piston part has a plurality of axial through holes which are arranged distributed in the circumferential direction and through which the second piston part is screwed to the first piston part by means of fastening screws. The axial through holes can be provided in the wall of the socket.

This embodiment of the invention is based on the consideration of laying the outer edge of the dividing surface or / and the exposed mouths of the through holes axially towards the low-pressure side of the piston, in order to take advantage of the throttling effect of the piston in reducing the pressure of the molten metal. In this way it can be prevented that the molten metal penetrates into the threaded area of the fastening screws and can solidify there, which would otherwise lead to screw connections that cannot be detached. Since the two piston parts as well as the sealing ring are detachably connected to one another, the materials of these components can be selected according to the respective purpose of the components. In particular, the two piston parts can be made of different materials, in particular different materials with regard to strength and thermal conductivity.

In a variant, the first and the second piston parts can also be detachably fastened to one another via a bayonet coupling. The coupling members assigned to one another can be molded directly onto the first and the second piston part. However, an intermediate ring with bayonet coupling elements is also suitable both towards the first coupling part and towards the second coupling part, so that the two coupling parts are coupled to one another via this intermediate ring.

The dividing surface is preferably arranged between the two coupling parts on the low-pressure side of at least one sealing ring in order to prevent melt from penetrating into the cap. Between axially one another Opposing end faces of the first and second piston parts, which form the dividing surface, are preferably arranged a sealing ring which seals the end faces against one another and which primarily prevents coolant from escaping from the cap.

A major advantage of the multi-part cap explained above is that it allows the sealing ring to be fixed to the piston in a manner that can be easily removed. The sealing ring is expediently arranged in a ring recess on the outer circumference of the peripheral wall of the cap and overlaps at least partially axially with the first and / or the second piston part. The outer circumference of the dividing surface opens into this ring recess, preferably in such a way that the outer circumference of the dividing surface opens into the ring recess offset to the low-pressure side with respect to the high-pressure side sealing surface edge of the sealing ring. The parting plane expediently opens closer to the low-pressure end of the sealing ring than to the high-pressure end. In this way, the penetration of melt into the cap is made considerably more difficult or impossible. In particular, this prevents the fastening elements, which connect the two piston parts to one another, from baking together with penetrating melt and make it difficult to dismantle the two piston parts.

In a preferred embodiment, the sealing ring is in the form of a slotted sealing ring, in particular a sealing ring provided with a stepped slot, and the dividing surface between the first and the second piston part is offset with respect to the low-pressure side edge of the sealing ring with an axial distance to the low-pressure side. Since the dividing surface lies completely on the low-pressure side of the sealing ring, it is particularly easy to seal. The protrusion on the low-pressure side of the second piston part allows the attachment of a locking pin which engages in the sealing ring for the anti-rotation device. The sealing ring thus always maintains the same angular position relative to the casting cylinder during operation, which reduces abrasion and improves the sealing effect. It goes without saying that the securing pin can optionally also be fastened to the first piston part and reaches over to the sealing ring on the second piston part.

High vacuum casting technology places particularly high demands on the sealing of the piston relative to the casting cylinder. In a preferred embodiment with particularly good sealing properties, it is provided that the above-mentioned sealing ring is axially fixed to the second piston part, that the dividing surface ends in an annular recess which surrounds the outer circumference of the first piston part and overlaps at least part of its axial extent, and that at least one second sealing ring is arranged in the ring recess. The first sealing ring is arranged as a slotted sealing ring so that it can be snapped onto the second piston part. The second sealing ring, which is arranged at an axial distance from the first sealing ring to improve the sealing effect, can be installed in the ring recess of the first piston part when the piston parts are separate from one another.

The second sealing ring is preferably a slotted sealing ring that radially springs out to an oversize outside the pressure cylinder. The second sealing ring is thus able not only to seal the piston with respect to the casting cylinder but also to guide it radially in the casting cylinder. This is particularly advantageous if the radial guiding properties of the first sealing ring are neglected in favor of optimizing the sealing properties of the first sealing ring.

The radially resilient sealing ring preferably has a threading cone on its high-pressure-side outer edge, so that the piston can be pulled out of the casting cylinder at the start of the casting stroke beyond the second sealing ring. In this way, a high casting volume can be achieved without having to lengthen the casting cylinder accordingly. The second sealing ring is expediently wider than the first sealing ring in order to improve its guiding properties in the axial direction. The second sealing ring is also preferably designed as a slotted sealing ring, its edges forming the slot forming at least one tongue projecting in the circumferential direction and one recess lying opposite the tongue in the circumferential direction, into which the tongue engages in an axially tight manner but is movable in the circumferential direction. Each of the two edges of the second sealing ring forming the slot preferably forms at least one tongue each. The resulting meandering structure allows sealing rings that are relatively wide in the axial direction to be sufficiently tight.

The dividing surface can end in an annular recess which surrounds the outer circumference of both the first and the second piston part and axially overlaps both piston parts. The sealing ring can in this case be designed as a sealing bush which is axially fixed in the ring recess. Even if the sealing bush is not slotted and thus not radially resilient, it can effectively seal the piston against the casting cylinder if the tolerances are sufficiently narrow. In this way, a simple and inexpensive piston can be created, in which the comparatively wide sealing bush can consist of a copper alloy, while the first piston part and possibly also the second piston part can consist of a less expensive material, such as steel.

The piston can be produced inexpensively if the first piston part is designed as a bushing, in the wall of which the axial through holes are provided for the fastening screws. In order to be able to connect the piston to the piston rod stably on the one hand and the other

To be able to dimension the wall thickness of the bushing sufficiently thick to accommodate the through holes, a bayonet connection is expediently provided for fastening the piston to the piston rod.

A suitable bayonet connection is described, for example, in US Pat. No. 5,233,912. A suitable for snapping onto a cooled flask ter, slotted sealing ring is described in US 5,048,592 (EP O 422 413 A2).

From EP 1 197 279 A it is known to arrange the sealing ring in an annular recess in the cap in the region of its end wall and to open this annular recess via axial grooves towards the high-pressure side of the end wall. During the casting process, melt is pressed under the sealing ring via the axial grooves. The melt solidifying in the ring recess presses the sealing ring against the casting cylinder when it is worn. The known piston tends to fix the sealing ring on the piston circumference due to the melt penetrating into the ring recess and solidifying there. The sealing ring cannot adapt to the deformation of the casting chamber or can only adapt to a very limited extent, which in turn increases the wear of the sealing ring.

In order to reduce the wear of the sealing ring, it is provided in a preferred embodiment of the invention that the cap can be cooled at least in the area of the end wall of the second piston part by a cooling medium that can be inserted into the cap, and that the sealing ring in the area of the end wall on the outer circumference of the cap in a ring recess axially fixed, but movably arranged, that the second piston part protrudes axially on the high-pressure side over the sealing ring and radially overlaps the sealing ring over a part of its radial thickness on the high-pressure side with a projection, the outer circumferential surface of which is adjacent to the sealing ring on the high-pressure side and between itself and the casting cylinder Casting operation limited to solidification temperature, coolable annular gap.

In the case of such a piston, the sealing ring which is movable in the ring recess remains sufficiently movable even during operation in order to be able to adapt to the shape of the casting cylinder on account of its inherent elasticity. In contrast to conventional pistons, the melt which solidifies in the annular gap upstream of the sealing ring seals the ring recess and the Sealing ring so far that the mobility of the sealing ring is not unduly impaired. During the pressure stroke of the piston, the annular gap fills with melt, which, however, partially or completely solidifies in the annular gap before it reaches the annular recess in the piston body that guides the sealing ring. During the return stroke of the piston, the melt solidified in the annular gap can remain in the annular gap or else it is stripped off in the course of the return stroke. With the help of such a high-pressure pre-seal, radial mobility of the sealing ring can be achieved even with closed sealing rings.

Conventional, slotted sealing rings should rest radially resiliently on the inner circumference of the casting cylinder during operation. In order to increase the radial contact pressure, it is e.g. It is known from DE 1 080 739 to provide an annular gap open to the pressure chamber of the casting cylinder on the inside of the sealing ring, which in operation fills with melt, the pressure of which increases the radial contact pressure of the sealing ring and thus improves the seal.

The sealing effect can be further improved if the outer circumferential surface of the radially elastic ring body of the slotted sealing ring near its high-pressure-side axial end has an outer contact ring surface which is intended for contact with the inner circumferential surface of the casting cylinder and whose axial length is less than that axial length of an inner ring surface axially overlapping with this outer contact ring surface, which can be exposed to the melt, for example the metal melt, on the inner circumference of the ring body, with the outer contact ring surface on the low-pressure side of the outer circumferential surface of the ring body at least over a portion of the remaining axial length the ring body is connected by an annular surface section, the diameter of which is smaller than the diameter of the outer contact ring surface. The reduction in the surface area of the outer contact ring area leads to an increase in pressure in the sealing surface area, which improves the sealing effect. Due to the high radial contact pressure, the contact ring surface grinds better according to the cylinder shape of the casting cylinder. In the case of lubricated operation of the die casting machine, the lubricant introduced into the casting chamber in front of the molten metal can move past the outer contact ring surface to the low pressure side in the region of the reduced-diameter circumferential surface of the sealing ring during the pressure feed of the piston. This lubricant, which collects on the low-pressure side of the sealing ring, lubricates the casting cylinder during the return movement of the piston. The reduced diameter ring surface section can have an approximate truncated cone shape or the shape of a cylindrical step.

The sealing ring is expediently fixed in the region of the end wall on the outer circumference of the cap. In particular in the case of a radially elastic, slotted sealing ring, it can be advantageous to provide an annular gap which is open on the high-pressure side of the ring body of the sealing ring at least over part of its circumferential length to the high-pressure side of the casting cylinder between the inner peripheral surface of the sealing ring and the outer peripheral surface of the cap. The annular gap can be open to the casting cylinder over its entire circumferential length. However, for example in the case of sealing rings which are arranged in a ring recess on the outer circumference of the cap, it is sufficient for the second piston part to radially overlap the sealing ring over a part of its radial thickness on the high-pressure side, the projection being distributed in the circumferential direction, in particular as grooves Has trained axial channels that connect the high pressure side of the casting cylinder with the annular gap. The melt penetrating into the annular gap from the casting chamber at high pressure on the one hand increases the radial contact pressure of the sealing ring against the casting cylinder wall and on the other hand material of the melt solidified in the annular gap seals the sealing ring against the piston.

The sealing of the sealing ring relative to the piston becomes more important with increasing wear of the sealing ring. In a preferred embodiment, in which the sealing ring is in turn arranged in a ring recess on the outer circumference of the cap, and in such a way that the side surfaces of the ring recess run approximately in a contour parallel to the axial end faces of the sealing ring, the wear-dependent inflow of melt for sealing the sealing ring relative to the piston can be carried out easily Are controlled in such a way that the high-pressure-side axial end face and the axially adjacent side surface of the ring recess are designed as conical surfaces. In this way, a conical ring gap is created between the conical surfaces, the gap width of which increases with increasing wear, since the concave-conical end face of the sealing ring lifts radially from the convex-conical side surface of the ring recess with increasing wear and thus better with solidification the annular gap sealing melt can be filled.

In the embodiments of the piston explained above, the radial contact pressure of the slotted sealing ring which is radially resilient due to its inherent elasticity is increased by the pressure of the melt. In a variant it can be provided that a plurality of radially acting spring elements are arranged on the outer circumference of the first piston part, which press the sealing ring radially outwards. The spring elements can be, for example, helical springs or the like which are guided in radial blind holes in the cap.

Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. Here shows:

Figure 1 is an axial longitudinal section through an embodiment of a split piston according to the invention of a cold chamber die casting machine. Fig. 2 shows an axial longitudinal section through part of a variant of

piston; 3 shows an axial longitudinal section through part of a second variant of the piston;

4 shows an axial longitudinal section through part of a third variant of the piston; FIG. 5 shows a radial view of a sealing ring of the piston from FIG. 4;

6 shows an axial longitudinal section through a fourth variant of the piston;

Fig. 7 is an enlarged detail of the piston, which is shown in Fig. 6 by a

Arrow VII is marked; 8 shows an axial longitudinal section through a fifth variant of the piston;

9 is a radial view of the high-pressure side region of the piston from FIG. 8;

FIG. 10 is an end view of the piston, viewed in the direction of an arrow X in FIG. 8;

Figure 1 1 shows an axial longitudinal section through a sixth variant of the piston;

FIG. 12 shows an axial longitudinal section through a variant of a variant of fastening elements and that can be used in the pistons of FIGS. 1 to 11

13 shows an axial cross section through the fastening elements, seen along a line XIII-XIII in FIG. 12.

The piston 1 of a cold chamber die casting machine shown in FIG. 1 in the form of a cap comprises a first piston part 3 designed as a bushing, which is detachable via a bayonet connection 5, as described for example in US Pat. No. 5,233,912, on one in a casting cylinder 7 the casting machine axially displaceable piston rod 9 is attached. On the first piston part 3, a second piston part 11 is screwed on the high pressure side, which covers the end of the piston rod 9 indicated at 13 and forms an end wall 15 of the piston 1 delimiting the high pressure space of the casting cylinder 7. The second piston part 1 1 contains one Central recess 17, the bottom of which is formed by the end wall 15 and, together with the end 13 of the piston rod 9, delimits a coolant chamber 19 for cooling the piston 1 and in particular its end wall 15. The coolant is supplied or discharged to the piston rod 9 via channels indicated at 21 and 23. Details of a suitable cooling system are described in EP 0 423 413 A2 and in US 5 233 912. US 5 233 912 also describes details of a suitable construction of the bayonet connection 5.

To derive the casting pressure acting on the end wall 15 into the end face 13 of the piston rod 9, the end face 13 can lie flat against the inside of the end wall 15. The coolant chamber 19 has an annular space shape here.

On the outer circumference of the second piston part 11, an annular recess 25 is provided, in which a sealing ring 27, which rests against the inner wall of the casting cylinder 7, is seated. Towards the high pressure side, the ring recess 25 ends at an annular shoulder 29 of the second piston part 11. On the low pressure side, the ring recess 25 is delimited by an end face 31 of the first piston part 3, which follows a dividing surface indicated at 33 between the two piston parts 3, 1 1. The dividing surface 33 is thus on the low-pressure end of the sealing ring 27.

For the releasable connection of the two piston parts 3, 1 1, several, here six equally distributed in the circumferential direction, axially extending through holes 35 are provided in the wall of the low-pressure side piston part 3, through which screw bolts 37 pass from the low-pressure side into threaded blind holes 39 of the second Piston part 1 1 are screwed in. The bolts 37 clamp the two piston parts 3, 1 1 flat against one another. An annular seal 41 provided on the radially inner circumference of the dividing surface 33 seals the dividing surface in a coolant-tight manner. Since the dividing surface 33 is located on the low-pressure side of the sealing ring 27 and the bolts 37 are screwed from the low-pressure side into blind-hole threads 39 closed to the high-pressure side, the operating pressure of the melt is not sufficient to penetrate into the threaded region of the bolts 37. The bolts 37 thus do not bake firmly in the casting operation and can be easily removed even after use of the piston for exchanging individual components of the piston 1, in particular the sealing ring 27 or the high-pressure side piston part 11.

The sealing ring 27 can be axially slotted, for example in the form of a stepped slot, as described in US Pat. No. 5,058,592 (EP 0 423 413 A2); but it can also be a ring-shaped closed sealing ring. It is also advantageous if the outer casing of the ring body of the sealing ring 27 near its high-pressure-side axial end has a narrow contact-ring surface 44 intended for contact with the inner casing surface of the casting cylinder 7, which, as indicated at 43, narrows towards the low-pressure side. Such a sealing ring, if it is designed as a slotted, radially resilient sealing ring, produces comparatively high sealing forces in the area of its comparatively narrow, high-pressure side sealing surface 44 due to its large suspension volume.

In a variant of the sealing ring 27, this can be arranged both with axial and radial play in the ring recess 25 if the end wall 15 projecting as a shoulder 29 delimits an annular gap 47 between its axial projection 45 and the casting cylinder 7, in which due to the Cooling of the end wall 15 can solidify the melt during operation and in this way additionally ensures a sealing of the sealing ring 27. At least the second piston part 11, but possibly also the first piston part 3, are preferably made of steel, which reduces the wear of the piston 1.

Variants of the piston from FIG. 1 are described below. Components having the same effect are designated by the reference numerals of FIG. 1 and provided with a letter to distinguish them. To explain the structure and the mode of operation reference is made to the entire preceding description. Variants explained above, in particular of the sealing ring, also apply to the versions of the piston explained below.

Fig. 2 shows a piston 1 a, again in the form of a cap, in which the annular recess 25 a extends almost over the entire axial extent of the two piston parts 3 a and 1 1 a, but at least over three quarters of the length of the piston 1 a. An annularly closed bushing 27a is inserted into the ring recess 25a and is axially fixed by the shoulders 29a and 31a of the piston part 11a and 3a. The dividing surface 33a extends approximately in the middle third of the axial extent of the ring recess 25a. In this variant, too, the two piston parts 3a, 11a are detachably connected to one another by a plurality of screw bolts 37a distributed around the circumference, the screw bolts 37a being screwed into blind hole threads 39a of the piston part 11a from the low-pressure side of the piston part 3a.

The bushing 27a is closed in a ring shape and is adapted to the inside diameter of the casting cylinder 7a with narrow tolerances. The bushing 27a expediently consists of a copper alloy, while at least the piston part 3a, but preferably also the piston part 1 1a, consists of steel. On the high-pressure side of the piston, a gap 47a can be formed between a projection 45a of the end wall 15a and the casting cylinder 7a, in which the melt improves the sealing effect can freeze. The piston 1 a is also cooled in accordance with the piston of FIG. 1 and is detachably connected to the piston rod 9 a by a bayonet connection 5 a.

FIG. 3 shows a piston 1 b designed as a cap, which differs from the piston of FIGS. 1 and 2 by the type of fixing of its sealing ring 27 b. The sealing ring 27b is arranged in accordance with the sealing ring described in US Pat. No. 5,233,912 or EP 0 423413 A2 near the high-pressure-side end of the piston part 11b and is designed as a radially resilient sealing ring which is slotted in the form of a step slot and which has an inner circumferential groove 49 on a radial projecting ring web 51 of the high-pressure piston part 1 1 b is snapped. An annular gap 53 which is open to the pressure chamber of the casting cylinder 7b and which can fill with solidified melt material during operation and forces the sealing ring 27b radially outward to increase the sealing action can be provided between the sealing ring 27b and the peripheral region located on the high-pressure side. Also in the area of its high-pressure side outer edge, the sealing ring 27b, similar to FIG. 1, can be provided with a support area 44b which is narrow compared to the axial ring thickness and, moreover, taper towards the low-pressure side, as indicated at 43b.

The dividing surface 33b is offset from the sealing ring 27b at a distance from it towards the low-pressure side and in the material region of the piston part 11b remaining between the dividing surface 33b and the sealing ring 27b there is a form-fit in a bore 55 in a recess in the sealing ring 27b, not shown in any more detail engaging locking pin 57 is used, which secures the sealing ring 27b against rotation. In this way, constant running-in properties of the sealing ring 27b are ensured.

Fig. 4 shows a particularly well-sealing, designed as a cap piston 1 c with a suitable for metal casting under high vacuum high-pressure side, in the form of a step slot slotted sealing ring 27c, which is snapped onto the outer annular web 51 c of the high-pressure side piston part 1 1 c with an inner annular groove 49c as described in FIG. 3. For an explanation, reference is made to the description of corresponding reference numbers in FIG. 3.

While the high-pressure side sealing ring 27c is fixed to the piston part 11 c, a low-pressure side sealing ring 59 is seated in a ring recess 61 of the piston part 3c, which is in turn detachably connected to the piston rod 9c via a bayonet connection 5c. On the low-pressure side, the recess 61 for the axial fixation of the sealing ring 59 forms a shoulder 63. On the high-pressure side, the sealing ring 59 is fixed by an end face 65, which in this position follows the dividing face 33c.

The sealing ring 59 is designed to be radially resilient and has a radial oversize outside the casting cylinder 7c, so that it is clamped radially when the piston 1c is inserted into the casting cylinder 7c. At its high-pressure side, the sealing ring 59 has a conical threading bevel 67 so that it can emerge from the casting cylinder 7c even when the cold chamber die casting machine is in continuous operation with the piston 1c withdrawn. This shortens the length of the casting cylinder required for a given casting volume.

FIG. 5 shows a top view of the sealing ring 59 which is axially comparatively long compared to the sealing ring 27c and which in the exemplary embodiment shown takes up almost the entire axial length of the piston part 3c. The sealing ring 59 is made of a resilient copper alloy and carries circumferentially projecting tongues 73 on each of the edges 69, 71 lying opposite one another in the circumferential direction, each of which has recesses 75 of the other slot edge opposite. The tongues 73 engage tightly in the axial direction, but move in each case in one of the recesses 75, so that overall there is a meandering axial seal. FIG. 6 shows a piston 1 d, again designed as a cap, which differs from the piston 1 c of FIG. 4 essentially only in that the sealing ring 59 designed there as a wide ring is divided axially in the middle into two separate sealing rings 67, 69 is, each of which has a step slot and which are guided together in the ring recess 61 d of the first piston part 3d. In order to increase the radial pressing force of the sealing rings 67, 69, a plurality of radial blind holes 71 are provided distributed in the circumferential direction of the first piston part 3d, into which prestressed helical compression springs 73 are inserted (FIG. 7). The screw pressure springs 73 rest on pressure bodies 75, here in the form of balls, on the inner circumference of the sealing rings 67 and 69, respectively. The blind holes 71 are offset in the circumferential direction centrally to the through holes 35d of the fastening screws 37d.

As already explained with reference to FIG. 3, the sealing ring 27d can have a narrow contact area in the area of its high-pressure side outer edge, which in comparison with the axial ring width can taper towards the low-pressure side. Otherwise, the piston rod 9d is sealed against the first piston part 3d by means of a sealing ring 77 surrounding it. Such a sealing ring can also be provided in the variants explained above.

The piston 1 e shown in FIGS. 8 to 10, again designed as a cap, differs from the piston 1 explained with reference to FIG. 1 primarily in that the ring recess 25 e extends almost over the entire axial length of the piston 1 e and In addition to the sealing ring 27e arranged on the high-pressure side in the region of the end wall 1 e of the second piston part 1 1 e, a second sealing ring 79 is arranged in the ring recess 25e. The sealing rings 27e and 79 are axially fixed by the end faces 29e of the second piston part 1 1 e on the one hand and the end face 31 e of the first piston part 3e on the other hand. The high-pressure side sealing ring 27e, as shown in FIG. 9, has an axially and radially through provided step slot 81 and sits with radial play radially movable in the ring recess 25e. The low-pressure side sealing ring 79 is designed as a closed sealing ring, the outer diameter of which is closely matched to the casting cylinder 7e.

The radial play between the inner circumference of the sealing ring 27e and the ring bottom of the ring recess 25e forms an annular gap 53e, which is connected to the melt of the casting chamber via a plurality of channels 83 distributed in the circumferential direction. In the exemplary embodiment shown, the channels 83 have the shape of axial grooves on the circumference of the projection 45e protruding radially outward from the end wall 15e and forming the annular shoulder 29e of the annular recess 25e. Melt penetrating into the annular gap 53e solidifies in the annular gap 53e due to the cooling of the piston 1e and ensures an improved seal.

The projection 45e can in turn be designed such that it forms an annular gap 47e with the inner surface of the casting cylinder 7e, as was explained with reference to FIG. 1. The components 43 and 44 of the piston of FIG. 1 can also be present on the high-pressure side sealing ring 27e.

11 shows a variant of the piston of FIGS. 8-10, which differs from this piston essentially in that the ring recess 25f, which guides the two sealing rings 27f and 79f arranged axially next to one another, is on the high-pressure side by a convex-conical, ie end surface 29f tapering towards the low-pressure side is limited, while the high-pressure side end surface 85 of the high-pressure side, slotted sealing ring 27f is concave-conical. The two cone surfaces 29f and 85 have the same cone angle and thus generators that are parallel to one another.

The sealing ring 27f is held radially elastic and with radial play in the ring recess 25f, so that a between the conical surfaces 29f and 85 Conical annular gap 87 remains, through which in turn melt can enter the annular gap 53f, which solidifies due to the cooling in the annular gaps 53f and 87 and ensures a sealing of the sealing ring 27f relative to the piston 1f. With increasing wear of the sealing ring 27f, the annular gap 87 widens, with which more melt material can penetrate into the annular gap 87, which improves the sealing effect after solidification.

The conical design of the high-pressure side face can also be used with sealing rings arranged on the low pressure side, e.g. 6 use the sealing ring 67 of the piston of FIG.

The components 43 and 44 explained with reference to FIG. 1 can also be provided in the sealing ring 27f. In addition, as indicated at 83f in FIG. 11, channels formed as grooves can additionally be distributed around the circumference of the projection 45f and introduce additional melt into the annular gap 53f.

In the case of the pistons explained above, the two piston parts are connected to one another by screws. 12 and 13 show a variant in which the first piston part 3g with the second piston part 11g via a bayonet connection with a plurality of bayonet projections 89 and 91 arranged in a circumferential direction on each of the two piston parts 3g and 11g. The bayonet projections 89, 91 are each separated from one another by gaps 93, so that the piston parts 3g, 11g can be axially inserted into one another and brought into an engagement position by rotating them relative to one another. A sealing ring 41 g is in turn arranged between mutually axially adjacent end faces of the dividing surface 33 g extending over the bayonet projections 89, 91. The bayonet connection of FIGS. 12 and 13 can be used in any of the previous configurations of the piston.

Claims

Expectations

1 . Piston in the form of a cap (1) which can be detachably fastened axially in a casting cylinder (7) of a cold chamber die casting machine and has a peripheral wall and a front wall (15) which closes the cap (1) on the high pressure side, with the outer circumference At least one sealing ring (27) is arranged on the circumferential wall, characterized in that the cap (1) comprises two piston parts (3, 1 1) which abut axially in a dividing surface (33) and which are detachably attached to one another, one of which comprises a first piston part (3) is designed as at least a partial section of the bushing forming the peripheral wall, and a second piston part (11) forms at least the end wall (15), and closes the bushing on the high-pressure side.

2. Piston according to claim 1, characterized in that the first piston part (3) has fastening elements, in particular bayonet fastening elements (5), for the detachable fastening of the piston to the piston rod (9).

3. Piston according to claim 1 or 2, characterized in that the first piston part (3) has a plurality of circumferentially distributed, axial through holes (35) through which the second piston part (1 1) by means of fastening screws (37) on the first Piston part (3) is screwed on.

4. Piston according to claim 3, characterized in that the axial through holes (35) for the fastening screws (37) are provided in the wall of the bush.

5 5. Piston according to claim 1 or 2, characterized in that the first (3g) and the second (1 1 g) piston part are releasably attached to each other via a bayonet coupling (89, 91).

6. Piston according to one of claims 1 to 5, characterized in that between axially opposite end faces of the first (3) and the second (1 1) piston part forming the dividing surface (33), a sealing ring (41) sealing the end faces against one another. is arranged. 5

7. Piston according to one of claims 1-6, characterized in that the second piston part (1 1) in the region of its piston end (15) forms a coolant-charged space (19).

8. Piston according to one of claims 1 to 7, characterized in that the sealing ring (27) is arranged in an annular recess (25) on the outer circumference of the peripheral wall of the cap (1) and with the first (3) or / and the second (1 1) piston part at least partially overlaps axially, and 5 that the outer circumference of the dividing surface (33) opens into the ring recess (25).

9. Piston according to claim 8, characterized in that the outer circumference of the dividing surface 0 (33) with respect to the high-pressure side sealing surface edge of the sealing ring (27) opens at an axial distance to the low-pressure side in the ring recess (25).

10. Piston according to one of claims 1 to 7, characterized in that the sealing ring (27b, c) is designed as a slotted sealing ring surrounding the second piston part (3b, c), in particular a sealing ring provided with a stepped slot, and the dividing surface (33b, c) between the first (3b, c) and the second piston part (11b, c) is offset with respect to the low-pressure side edge of the sealing ring (27b, c) with an axial distance to the low-pressure side.

1 1. Piston according to claim 10, characterized in that an axially extending locking pin (57, 57c) engaging in the sealing ring (27b, c) to secure it against rotation is arranged on the low-pressure side of the sealing ring.

12. Piston according to claim 1 1, characterized in that the locking pin (57, 57c) in the second piston part (1 1 b, c) is held.

13. Piston according to one of claims 10 to 12, characterized in that the first-mentioned sealing ring (27c) is axially fixed to the second piston part (1 1 c), that the dividing surface (33c) in an the outer circumference of the first piston part (3c) enclosing and at least overlapping part of their axial extension ring recess (61) ends and that in the ring recess (61) at least a second sealing ring (59) is arranged.

14. Piston according to claim 13, characterized in that the second sealing ring (59) is arranged at an axial distance from the first sealing ring (27c).

15. Piston according to claim 13 or 14, characterized in that the second sealing ring (59) is designed as a slotted sealing ring which radially springs out to an excess outside the pressure cylinder (7c).

16. Piston according to claim 15, characterized in that the second sealing ring (59) has a threading cone (67) on its high-pressure-side outer edge.

17. Piston according to one of claims 13 to 16, characterized in that the second sealing ring (59) is designed as a slotted sealing ring, the edges forming the slot (69, 71) at least one tongue (73) projecting in the circumferential direction and one of the tongues (73) form opposite recess (75) in the circumferential direction, but engages in the tongue (73) so as to be axially tight but movable in the circumferential direction.

18. Piston according to claim 17, characterized in that each of the two edges (69, 71) of the second sealing ring forming the slot forms at least one tongue (73).

19. Piston according to one of claims 1 to 9, characterized in that the dividing surface (33a) in a piston part enclosing the outer circumference of both the first (3a) and the second (1 1 a) and both piston parts (3a, 1 1 a ) axially overlapping ring recess (25a) ends and that the sealing ring is designed as a sealing bush (27a) axially fixed in the ring recess (25a).

20. Piston according to claim 19, characterized in that the sealing bush (27a) extends over more than three quarters of the axial length of the piston (1 e).

21. Piston according to one of claims 1 to 9, characterized in that the cap (1) can be cooled at least in the region of the end wall (15) of the second piston part (11) by a cooling medium which can be introduced into the cap (1), that the sealing ring ( 27) in the area of the end wall (15) on the outer circumference of the cap (1), fixed in an annular recess (25), but arranged so that it can move with play, that the second piston part (1 1) projects axially on the high-pressure side via the sealing ring (27) and the sealing ring (27) overlaps radially over part of its radial thickness on the high-pressure side with a projection (45) whose radially outer circumferential surface adjacent to the sealing ring (27) on the high-pressure side between itself and the casting cylinder (7) has an annular gap (47) which can be cooled to solidification temperature during casting operation limited.

22. Piston according to one of claims 1 to 21, characterized in that the sealing ring (67, 69) is designed as a slotted sealing ring and is distributed on the outer circumference of the first piston part (3d) in the circumferential direction, and there are more radially acting spring elements (73) are that press the sealing ring (67, 69) radially outwards.

23. Piston according to one of claims 1 to 22, characterized in that the sealing ring (27) has a radially elastic ring body with an axially and radially continuous slot, in particular a slot stepped in the circumferential direction, that the outer peripheral surface of the ring body near its high-pressure axial end, there is an outer ring surface of the plant intended to bear against the inner circumferential surface of the casting cylinder (7)

(44), whose axial length is smaller than the axial length of an axially overlapping with this outer contact ring surface (44), the Melt, in particular molten metal, of the inner ring surface on the inner circumference of the ring body, which can be exposed, and that an annular surface section (43) is connected to the outer contact ring surface (44) on the low-pressure side of the outer circumferential surface of the ring body, at least over a portion of the remaining axial length of the ring body, whose diameter is smaller than the diameter of the outer contact ring surface (44).

24. Piston according to claim 23, characterized in that the reduced-diameter ring surface section (43) has at least approximately the shape of a truncated cone and tapers towards the axial end of the ring body on the low-pressure side.

25. Piston according to one of claims 1 to 24, characterized in that the sealing ring (27b, c, d, e) in the region of the end wall (15b, c, d, e) on the outer circumference of the cap (1 c, c, d , e) is fixed, and that between the inner circumferential surface of the sealing ring (27b, c, d, e) and the outer circumferential surface of the cap (1b, c, d, e) a on the high pressure side of the sealing ring (27b, c, d, e) an annular gap (53, 53c, d, e) is provided at least over part of its circumferential surface to the high pressure side of the casting cylinder (7b, c, d, e).

26. Piston according to claim 25, characterized in that the sealing ring (27e) in one

Ring recess (25e) is arranged on the outer circumference of the cap (1 e), that the second piston part (1 1 e) radially overlaps the sealing ring (27e) over a part of its radial thickness on the high-pressure side with a projection (45e), and that the projection (45e) distributed in the circumferential direction has a plurality of axial channels (83), in particular in the form of grooves, which connect the high-pressure side of the casting cylinder (7e) to the annular gap (53e).

27. Piston according to one of claims 1 to 26, characterized in that the sealing ring (27f) is arranged in an annular recess (25f) on the outer circumference of the cap (1 f), the side surfaces (29f, 31 f) of approximately the same shape as the axial End faces of the sealing ring (27f) run, and that the high-pressure side, axial end face (85) of the sealing ring (27f) and the axially adjacent side face (29f) of the ring recess (25f) are designed as conical surfaces.

28. Piston according to one of claims 1 to 27, characterized in that at least the second piston part (3) consists of steel.