EP1483074B1 - Sealing ring and piston for a pressure die casting cylinder - Google Patents

Abstract

The invention relates to a plunger for a cold chamber diecasting machine in whose casting cylinder (3) the plunger (1) defines a pressure chamber (5) for the molten metal in an axially displaceable manner. The plunger (1) has a plunger base (7) and a sealing ring (17) that is fixed in the range of the pressure chamber-side plunger front in an outer annular recess (19) of the plunger base (7). The plunger base (7) axially projects beyond the sealing ring on the pressure chamber side and radially extends on the pressure chamber side across the sealing ring across a part of its radial thickness. The plunger base (7) can be cooled at least in the area of its plunger front (15). The sealing ring (17) is movably disposed with a radial and axial play in the annular recess (19). A projection (43) of the plunger base (7) that radially extends across the sealing ring (17) defines with its outer peripheral surface (46) an annular gap (47) between itself and the casting cylinder, said annular gap being cooled to solidification temperature during casting. The melt that solidifies in the annular gap (47) additionally seals the sealing ring (17) and prevents the melt from reaching the play of the sealing ring (17) or getting between the sealing ring (17) and the casting cylinder (3), thereby reducing wear of the sealing ring (17).

Description

The invention relates to a sealing ring for a piston of a pressure casting cylinder, in particular a cold chamber die casting machine for molten metal, in particular aluminum melt. The invention further relates to such a piston.

The piston of a cold chamber die casting machine and in particular the sealing ring of such a piston is exposed on the one hand high pressures at relatively high temperatures of the molten metal, so that the molten metal is driven during the casting stroke of the piston under and behind the sealing ring. On the other hand, the melt solidifies there due to the comparatively low temperature of the otherwise cooled piston. The piston and in particular its sealing ring are therefore exposed during operation very high stresses shorten its life, which adversely affects the productivity of the casting machine.

Out EP 0 423 413 A2 It is known to slit the sealing ring of the casting piston axially and radially continuously with a stepped in the circumferential direction of the annular body of the sealing ring slot so that the sealing ring radially expand in the Druckgießzylinder due to its inherent elasticity and better sealing against the inner surface of the cylinder. The stepped slot ensures axial sealing of the interruption of the sealing ring.

Out EP 0 525 229 A1 It is also known to leave an annular gap between the inner shell of the sealing ring and the outer jacket of the piston, which fills with molten metal during the compression stroke. by virtue of the comparatively low temperature of the cooled piston solidifies the melt in the annular gap and ensures a sealing of the sealing ring to the piston.

Finally, it is known to lubricate the piston in the Druckgießzylinder with a at the temperature of the molten metal liquefying, but at the temperature of the cooled piston viscous or solid lubricant, for example on a wax base or the like, at least in the printing phase. The lubricant may be introduced into the die cylinder prior to filling the molten metal or, as shown in FIG DE-AS 1 191 934 is explained, are introduced in circumferential grooves of a existing of the metal of the molten metal plate seal. The plate seal is applied before the filling of the molten metal to the front of the piston and connects during the compression stroke with the casting residue remaining in the die cylinder. In this way, the sealing disk is lubricated during the casting stroke, while the piston can be easily withdrawn due to its relatively large clearance in the die cylinder.

It is an object of the invention to provide a sealing ring for the piston of a die casting machine, in particular a cold chamber die casting machine, which has a long service life with a good sealing effect. As far as the sealing ring is used in a lubricated mode of operation, it should support the lubricating effect. It is a further object of the invention to provide a suitable for sealing by means of the above-described sealing ring piston, which additionally supports the sealing effect of the sealing ring.

The invention is based on a sealing ring for a piston of a die-casting cylinder for molten metal, in particular aluminum melt, of EP 0 423 413 A2 known type. Such a sealing ring has a radially elastic annular body which has a both axial and radial having continuous slot, in particular a stepped in the circumferential direction of the annular body slot. The improvement according to the invention is characterized in that the outer jacket of the annular body near its high-pressure-side axial end has an abutment annular surface intended to bear against the inner lateral surface of the die-casting cylinder whose axial length is smaller than the axial length of an axially overlapping with this outer abutment annular surface, the metal melt auszusetzenden inner annular surface on the inner surface of the annular body, and that adjoins the outer abutment annular surface at least over a portion of the remaining axial length of the outer shell of the annular body an annular surface portion whose diameter is smaller than the diameter of the outer abutment annular surface.

Such a sealing ring can bear due to its slot due to inherent inherent bias radially resiliently on the inner surface of the cylinder. The contact surface is, based on the total axial length of the annular body, small. The correspondingly large radial spreading force of the annular body ensures a high radial contact pressure on the contact ring surface, which improves the sealing effect. Due to the high radial contact pressure, the contact ring surface grinds according to the cylindrical shape, which in turn improves the sealing effect of the sealing ring.

In the non-installed state, the outer diameter of the sealing ring is greater than the inner diameter of the die-cast cylinder, so that the sealing ring sits under self-bias in the cylinder. At least the region of the inner shell of the annular body which is located radially inside the abutment annular surface is exposed to the metal melt pressure and increases, since the surface of this inner sheath region is larger than the outer abutment annular surface, the radial contact pressure, even if in the low pressure side regions of the between the sealing ring and the remaining annular gap the metal melt solidifies due to the piston cooling. In the high pressure side areas of this annular gap, the metal smear pressure remains effective.

The low-pressure side of the sealing ring to the outer abutment annular surface axially adjacent, reduced in diameter outer surface of the annular body creates between itself and the cylinder an annular gap in which in lubricated operation introduced into the casting chamber before the molten metal lubricant during the pressure feed of the piston on the outer plant annular surface can enter past. Upon retraction of the piston, this gap formed between the annular body and the cylinder contains lubricant which, in the retraction movement, passes from the radially elastic sealing ring on the inner surface of the cylinder and thus lubricates the return movement of the piston. In this phase of operation, the lubricant contained in the annular gap is usually solidified due to the low temperature of the cooled piston.
Appropriately, the reduced in diameter outer annular surface portion of the annular body extends to its low-pressure side axial end, so it is open to the low pressure side of the piston. In this way, on the low-pressure side of the sealing ring as a rule also an annular gap between itself and the cylinder forming piston for receiving a sealing ring lubricating lubricant supply can be exploited.

In a preferred embodiment, the reduced in diameter annular surface portion of the annular body has at least approximately truncated cone shape and tapers towards the low pressure side axial end of the annular space. This design has the advantage that the outer abutment annular surface in the new condition of the sealing ring can be kept very narrow in the axial direction, so that the sealing ring already initially grinds in accordance with the shape of the die-casting cylinder after a few casting cycles. Due to the truncated cone shape, however, the increased outer abutment ring surface with increasing wear, which reduces the wear rate.

The piston is expediently designed so that it supports the above-explained advantages of the sealing ring. Preferably, therefore, the metal ring to be expelled inner annular surface of the inner shell of the annular body together with the outer surface of the piston forms an open on the high pressure side of the annular body to the pressure chamber of the die-casting cylinder annular gap. In order to keep the high-pressure side access to molten metal to the annular gap between the sealing ring and piston as large as possible, the piston preferably has a radially projecting annular projection, which is arranged for axially fixing the annular body on the piston in a arranged on the low pressure side of the annular gap in the inner shell of the annular body groove intervenes. The fixing organs are thus arranged on the low-pressure side of the radial sealing force increase and sealing provided annular gap. It is understood that alternatively the groove can also be provided on the piston and the annular projection on the annular body.

Alternatively, however, the piston can also have a ring recess on its outer jacket into which the annular body engages, in particular with its entire axial length, for its axial fixing and formation of the annular gap. For the high-pressure side access of the molten metal to this annular gap, the piston preferably has a plurality of recesses distributed in the circumferential direction and extending from the high-pressure-side front end of the piston and opening into the annular gap. Appropriately, in this embodiment, in one of the two annular surfaces forming the annular gap, in particular in the outer shell of the annular recess of the piston, a circumferential melt distribution groove is provided which evenly distributed over the axial recesses molten metal in the circumferential direction before the melt solidifies due to the piston cooling.

If necessary, the slotted sealing ring can be pushed into the ring recess of the piston assigned to it via the high-pressure-side end of the piston. However, this type of mounting may require in individual cases that the diameter of the high-pressure side end is comparatively small in order to prevent the sealing ring from becoming permanent. To be able to lift deformation over the forehead. This can adversely affect the life of the sealing ring, since the inner diameter of the radially elastic sealing ring increases in wear and it can slip over the front of the piston. This disadvantage is avoided if the high-pressure side end of the piston is designed as a removable, in particular unscrewable cover whose dividing surface terminates in the annular recess holding the annular body. In such a configuration, the diameter of the lid limiting the annular recess may be dimensioned comparatively large.

Preferably, the lid is made of a poor, but at least poor, heat-conducting material, such as e.g. Steel, as the adjoining area of the piston, or it is coated with ceramic material. Even if the remaining piston to optimize its cooling consists of better heat-conducting material is prevented in this way that the metal melt located in the casting chamber before the completion of the printing phase, especially before completion of the emphasis phase, solidifies.

Although the outer diameter of the piston on the low pressure side of the sealing ring usually forms an annular gap suitable for receiving lubricant, so it is preferred directly after the low pressure end of the annular body of the sealing ring in the outer jacket of the piston to the cylinder inner shell and the annular body provided open annular recess for forming a lubricant space to store a larger amount of lubricant for the return stroke of the piston can.

• Fig. 1 einen schematischen Axiallängsschnitt durch den Druckgießzylinder einer Kaltkammer-Druckgießmaschine mit einem Kolben und einem zum hochdruckseitigen Ende des Kolbens angeordneten Dichtring gemäß der Erfindung;
• Fig. 2 eine Detailansicht des Dichtrings, gesehen in Richtung eines Pfeils II;
• Fig. 3 eine vergrößerte Detailansicht des Kolbenbereichs der Druckgießmaschine aus Fig. 1;
• Fig. 4 eine Detailansicht einer Variante von Kolben und Dichtring;
• Fig. 5 eine Stirnansicht des Kolbens, gesehen in Richtung eines Pfeils V in Fig. 4 und
• Fig. 6 eine weitere Variante des Kolbens aus Fig. 4.

In the following the invention will be explained in more detail with reference to a drawing. Hereby shows:

• 1 shows a schematic Axiallängsschnitt through the die cylinder of a cold chamber die casting machine with a piston and a high-pressure end of the piston arranged sealing ring according to the invention.
• FIG. 2 shows a detailed view of the sealing ring, seen in the direction of an arrow II; FIG.
• FIG. 3 is an enlarged detail view of the piston portion of the die casting machine of FIG. 1; FIG.
• 4 shows a detailed view of a variant of piston and sealing ring;
• Fig. 5 is an end view of the piston, as seen in the direction of arrow V in Fig. 4 and
• 6 shows a further variant of the piston from FIG. 4.

Fig. 1 shows schematically a cold chamber die casting machine, in whose circular cylindrical casting cylinder 1, a piston 3 between an advanced position shown in FIG. 1 with solid lines and a 3 'dash-dotted retracted position is displaced. In the retracted position, molten metal, e.g. Aluminum melt, filled in the limited by the piston 3 and the casting cylinder 1 casting chamber 7 and the advancing of the piston 3, the molten metal is pressed at high pressure via a sprue 9 in the injection mold, not shown.

The piston 3 carries at its high-pressure end a fixed in two directions of movement sealing ring 11, the casting chamber 7 to Fill opening 5 seals off. The sealing ring 11 has, as shown in FIG. 2, a both axially and radially continuous step slot 13, which allows radial expansion of the sealing ring 11 due to inherent elasticity, so that the sealing ring 11 with an outer abutment annular surface 15 on the inner shell 17 of the casting cylinder. 1 biased due to its own radial elasticity, as best shown in FIG. 3. The extending in the circumferential direction in achsnormalen levels stages 19 at the step slot 13 forming ends of the annular body 21 of the sealing ring 11 abut each other and seal the step slot 13 axially. Details of such a step slot are in EP 0 423 413 A2 explained. The piston 3 contains at 22 indicated, connected to a not-shown cooling system cooling channels, via which the piston 3 is cooled to a low temperature based on the temperature of the molten metal, for example 40 ° - 60 ° C. Details of the construction of a suitable in the context of the invention, cooled piston are also in EP 0 423 413 A2 as well as in EP 0 525 229 A1 described.

The inner shell 17 of the casting cylinder 1 radially resilient annular body 21 of the sealing ring 11 includes near its low-pressure side axial end a circumferential groove 23 into which engages a radially projecting from the outer periphery of the piston 3, circumferential projection 25 and the sealing ring 11 in both displacement directions of the piston. 3 fixed on this. On the axially to the high pressure side of the piston 3 side of the annular groove 23 of the annular body 21 is dimensioned so that its inner shell 27 together with the outer shell of the piston 3 defines an annular gap 29 which is open to the high pressure side of the casting chamber. When advancing the piston 3 during the pressure phase of the casting process molten metal is forced into the annular gap 29, where it increases the force acting on the abutment annular surface 15 radial biasing force of the annular body 21 to improve the sealing effect.

The investment annular surface 15 intended to bear against the inner jacket 17 of the casting cylinder 1 is smaller in the axial direction than the inner jacket surface 27 exposed to the melt pressure in the annular gap 29, so that a reinforcement of the radial compressive force acting on the abutment annular surface 15 results.

Starting from the comparatively small abutment annular surface 15, the outer jacket region 31 of the annular body 21, which tapers towards the low pressure side, tapers in the shape of a truncated cone, so that the annular annular gap 32 produced in this way opens in a ring recess 33 of the piston which is open both to the inner jacket 17 and to the annular body 21 3 opens. This design of the sealing ring 11 and the piston 3 also allows lubrication of the piston during retraction in its position 3 '. It is known to fill not only the molten metal via the filling opening 5 of the casting cylinder 1 (FIG. 1), but also a certain amount of viscous or solid lubricant, which liquefies on contact with the molten metal and the advancing movement of the piston 3 during the casting phase lubricates. A portion of the lubricant overcomes the sealing ring 11 and reaches the cooled low pressure side, where it collects in the annular recess 33 and in the wedge gap 32 between the frusto-conical portion 31 and the inner shell 17 and solidifies due to the low temperature of the cooled piston 3. Upon retraction of the piston 3 in the position 3 'of the radially elastic sealing ring 11 passes the lubricant along the inner shell 17 and lubricates the retraction movement of the piston.

The small axial height of the abutment annular surface 15 compared to the axial overall length of the annular body 21 facilitates initial grinding and fitting of the sealing ring 11 to the cylindrical surface 17. Conveniently, the frustoconical lateral surface 31 extends close to the high pressure end of the annular body 21, so that the Einschleif and fitting phase of the sealing ring 11 already after a few Casting cycles is completed. Towards the end of the life of the sealing ring, the abutment annular surface 15 becomes wider due to the wear.

It is understood that the outer shell of the annular body 21 on the low pressure side of the abutment annular surface 15 may also have a different contour, for example, a stepped, reduced in diameter cylinder contour, as indicated by dashed lines at 35 in Fig. 3. The contour 35 extends in the illustrated example to the low-pressure end of the annular body 21, but may also end in the ring body before this end and form a Schmiermittelspeichernut on the outer surface of the annular body 21. The annular recess 33 can be omitted here, as in the previously explained variants.

In the following, variants of the described with reference to FIGS. 1 to 3 cold chamber injection molding machine will be described. Equivalent components are denoted by the reference numerals of FIGS. 1 to 3 and provided with a letter for distinction. To explain the structure, the mode of action and possibly variants, reference is made to the description of FIGS. 1 to 3.

4 and 5 show a variant of a in a casting cylinder 1 a displaceable piston 3a, which carries a sealing ring 11 a in the region of its high-pressure side end face. The sealing ring 11 a is provided according to the above-described sealing ring with a stepped slot and has an outer shell contour with a comparatively short in the axial direction abutment annular surface 15 a and a low pressure side subsequent frustoconical and low pressure side tapered outer sheath portion 31 a, as has been explained above , Also in this variant closes to the annular body 21 a of the sealing ring 1 1 a to the ring body 21 a and the inner shell 17 a through open ring recess 33 a. The sealing behavior, the Einschleifverhalten and the Lubricating behavior during retraction of the piston 3a thus corresponds to the embodiment of FIGS. 1 to 3.

Different from the embodiment of FIGS. 1 to 3 is primarily the axial fixation of the sealing ring 11 a on the piston 3 a. The piston 3a carries near its high-pressure end at its outer periphery an annular groove 37 into which the annular body 21 a engages over its entire axial length and in which it is fixed axially in both piston movement directions with a certain play.

In order to expose over the entire axial height of the annular body 21 a extending inner shell 27a of the annular body 21 a the pressure of the molten metal in the casting chamber, the high-pressure end of the piston 3a is arranged on its outer circumference with a plurality, here four, distributed in the circumferential direction , Trough-shaped recesses 39 which extend axially below the inner circumferential surface 27 a and in the bottom 41 of the ring body 21 a receiving annular recess 37 end. Via the recesses 39, molten metal flows into an annular gap 29 a formed between the bottom 41 of the annular recess 37 and the inner jacket 27 a of the annular body 21 a and increases the radial sealing pressure of the sealing ring 11 a. Since the annular gap 29a is connected to the casting chamber only via the circumferentially limited recesses 39, the annular gap 29a contains a melt distribution channel formed by a ring recess 43 of the piston 3a. It is understood that the recesses 39 may be provided wholly or additionally in the sealing ring 11a.

In the embodiment of Figs. 4 and 5, the annular recess 37 is provided in an integral region of the piston 3a. During assembly, therefore, the annular body 21 a of the sealing ring 1 1 a over the high pressure side shoulder of the ring recess 37 must be lifted, which limits the maximum radial height of this shoulder constructive. With increasing wear of the sealing ring 11a, this may under certain circumstances the recess 37 slip out. In order to avoid this, FIG. 6 shows a variant of the piston of FIGS. 4 and 5, in which the high-pressure-side front end of the piston 3b is designed as a removable cover 47 which is fastened releasably to the piston 3b by means of a threaded projection 45. The separating surface 49 of the lid intersects the annular body 21 b of the sealing ring 11 b receiving annular recess 37 b of the piston 3 b and forms the high-pressure side limiting shoulder 51 of this annular recess 37 b. The radial height of the boundary shoulder 51 can now be chosen freely, since after removing the cover 47, the sealing ring 11 b can be pulled off axially. The design of the sealing ring 1 1 b corresponds to the explained with reference to FIGS. 4 and 5 variant, in which case the recesses 39 b are provided in the lid 47, but also here can extend to below the ring body 21 b.

While the piston 3b may consist of good heat-conducting material, such as a copper alloy for better cooling, the lid 47 is made of a poorer heat-conducting material, such as steel or is thermally insulated by a ceramic coating to the cooling of the molten metal during the casting process in particular into the Nachdruckphase in which cavities of the melt to be closed to delay.

It is understood that the illustrated with reference to FIGS. 1 to 3 variants of the outer jacket of the sealing ring can also be used with advantage in the sealing ring of Fig. 4 to 6.

Claims (13)

1. Sealing ring for a piston of a pressure die-casting cylinder for metal melts, in particular aluminium melts, with a radially elastic annular body (21), which comprises an axially and radially continuous slot (13), in particular a slot that is stepped in the circumferential direction of the annular body, characterised in that
   the external casing of the annular body (21) close to its high pressure side axial end has a bearing annular surface (15) specifically for bearing against the inner casing surface (17) of the pressure die-casting cylinder (1), the axial length of which is smaller than the axial length of an inner annular surface (27) overlapping axially with said outer bearing annular surface (15) and exposed to the metal melt, and in that on the low pressure side of the outer bearing annular surface (15) an annular surface section (31; 35) adjoins the outer bearing annular surface (15) at least over a partial area of the remaining axial length of the external casing of the annular body (21), the diameter of which section is smaller than the diameter of the outer bearing annular surface (15).
2. Sealing ring according to claim 1, characterised in that the external annular surface section (31; 35) of reduced diameter extends up to the low pressure side axial end of the annular body (21).
3. Sealing ring according to claim 2, characterised in that the annular surface section (31) of reduced diameter has at least an approximately truncated cone shape and tapers towards the low pressure side axial end of the annular body (21).
4. Sealing ring according to one of claims 1 to 3, characterised in that the inner casing of the annular body (21), in particular close to its low pressure side axial end, has a peripheral annular recess (23).
5. Piston for a compression die-casting cylinder for metal melts, in particular aluminium melts, with a sealing ring (11) secured axially close to the high pressure side piston end according to one of claims 1 to 4, characterised in that the annular surface (27) of the inner sleeve of the ring body (21) to be exposed to the metal melt together with the external casing of the piston (3) forms an annular gap (29) that is open on the high pressure side of the annular body (21) towards the pressure chamber (7) of the compression die-casting cylinder (1).
6. Piston according to claim 5, characterised in that it has a radially projecting annular projection (25), which for axially securing the annular body (21) onto the piston (3) engages in an annular groove (23) arranged on the low pressure side of the annular gap (29) in the inner casing (27) of the annular body (21).
7. Piston according to claim 5, characterised in that on its external casing it has an annular recess (37) in which the annular body (21a) engages to be fixed axially forming the annular gap (29a), and in that the piston (3a) has several recesses (39) distributed in peripheral direction emerging from the high-pressure side end of the piston (3a) opening into the annular gap (29a).
8. Piston according to claim 7, characterised in that in one of the two casing surfaces forming the annular gap (39), in particular of the external casing of the annular recess (37) a peripheral melt distribution groove (43) is arranged.
9. Piston according to claim 7 or 8, characterised in that its high-pressure side end is designed as a removable lid (47), in particular one that can be unscrewed, the interface (49) of which ends in the annular recess (37b) holding the annular body (21b).
10. Piston according to claim 9, characterised in that the lid (47) is made of a material that conducts heat less well than the adjoining area of the piston (3b).
11. Piston according to claim 9 or 10, characterised in that the lid (47) is made of steel or a copper alloy and/or is coated with a ceramic material.
12. Piston according to one of claims 5 to 11, characterised in that directly adjoining the low pressure side end of the annular body (21) of the sealing ring (11) in its external casing it has an annular recess (33) that is open towards the cylinder internal casing (17) and to the annular body (21) to form a lubricant chamber.
13. Piston according to one of claims 5 to 12, characterised in that in the region of the sealing ring (11) it contains means for cooling the piston.

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