WO2003074214A1

WO2003074214A1 - Sealing ring and piston for a pressure die casting cylinder

Info

Publication number: WO2003074214A1
Application number: PCT/EP2002/002356
Authority: WO
Inventors: André Müller
Original assignee: Allper Ag
Priority date: 2002-03-04
Filing date: 2002-03-04
Publication date: 2003-09-12
Also published as: DE50210331D1; AU2002257612A1; ES2287274T3; WO2003074211A3; EP1483074A1; EP1483074B1; ATE364464T1; EP1483075A2; AU2002358495A8; AU2002358495A1; WO2003074211A2

Abstract

Disclosed is a sealing ring (1) for the piston (3) of a die casting press, comprising an axially and radially continuous staggered slit. The outer surface of the ring body (21) of the sealing ring is provided with a contact ring area (15) near the axial end on the high-pressure side thereof, said contact ring area (15) resting against the inner surface (17) of the pressure die casting cylinder (1). The axial length of the contact ring area (15) is smaller than the axial length of a ring area (27) on the inner surface of the ring body (21), said ring area (27) axially overlapping the outer contact ring area (15) and being exposed to the molten bath. A ring area segment (31, 35), the diameter of which is smaller than the diameter of the outer contact ring area (15), is adjacent to the outer contact ring area (15) in at least one partial section of the remaining axial length of the outer surface of the ring body (21). The preferably tapered ring area segment (31) forms a storage chamber for a lubricant along with a peripheral recess (33) of the piston (3), said lubricant lubricating the piston (3), the sealing ring (11), and the pressure die casting cylinder (1) during withdrawing. The small bearing area of the contact ring area (15) increases the sealing strength of the radially elastic sealing ring (11) and the molten bath invading a ring gap (29) which is arranged between the inner surface (27) and the piston (3) during compression.

Description

Sealing ring and piston for a die casting cylinder

description

The invention relates to a sealing ring for a piston of a die 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 to high pressures at comparatively high temperatures of the metal melt, so that the metal melt is driven under and behind the sealing ring during the casting stroke of the piston. 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 to very high stresses during operation which shorten its service life, which has an adverse effect on the productivity of the casting machine.

From EP 0 423 41 3 A2 it is known to axially and radially continuously slit the sealing ring of the casting piston with a slot that is stepped in the circumferential direction of the ring body of the sealing ring, so that the sealing ring in the die casting cylinder expands radially due to its inherent elasticity can better seal against the inner jacket of the cylinder. The step slot provides an axial seal for the interruption of the sealing ring.

From EP 0 525 229 A1 it is also known to leave an annular gap between the inner jacket of the sealing ring and the outer jacket of the piston which fills with molten metal during the pressure stroke. On- Due to the comparatively low temperature of the cooled piston, the melt solidifies in the annular gap and ensures that the sealing ring is sealed off from the piston.

Finally, it is known to lubricate the piston in the die casting cylinder with a lubricant which liquefies at the temperature of the molten metal, but is viscous or solid at the temperature of the cooled piston, e.g. on a wax base or the like, at least in the printing phase. The lubricant can be introduced into the die-casting cylinder before the metal melt is poured in, or, as explained in DE-AS 1 1 91 934, can be introduced into circumferential grooves of a plate seal made of the metal of the metal melt. The plate seal is placed on the face of the piston before the molten metal is poured in and connects during the pressure stroke with the casting residue remaining in the die casting cylinder. In this way, the sealing washer is lubricated during the casting stroke, while the piston can be withdrawn without any problems due to its comparatively large play in the die-casting 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 also an object of the invention to provide a piston which is suitable for sealing by means of the sealing ring explained above and 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, especially molten aluminum, of

EP 0 423 41 3 A2 of the known type. Such a sealing ring has a radially elastic ring body, which is both axially and radially continuous slot, in particular has a stepped slot in the circumferential direction of the ring body. The improvement according to the invention is characterized in that the outer casing of the ring body near its high-pressure axial end has a contact ring surface intended for contact with the inner surface of the die-casting cylinder, the axial length of which is smaller than the axial length of an axial contact with this outer contact ring surface overlapping inner ring surface to be exposed to the molten metal on the inner casing of the ring body, and that an annular surface section adjoins the outer contact ring surface at least over a portion of the remaining axial length of the outer casing of the ring body, the diameter of which is smaller than the diameter of the outer contact annular surface.

Such a sealing ring can bear radially resiliently against the inner jacket of the cylinder due to its slot due to inherent bias. The contact surface is small in relation to the total axial length of the ring body. The correspondingly large radial expansion force of the ring 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 in according to the cylinder shape, which in turn improves the sealing effect of the sealing ring.

In the non-installed state, the outside diameter of the sealing ring is larger than the inside diameter of the die-casting cylinder, so that the sealing ring sits in the cylinder under its own prestress. At least the area of the inner jacket of the ring body located radially inside the contact ring area is exposed to the metal melt pressure and increased, since the area of this inner jacket area is larger than the outer contact ring area, the radial contact pressure, even if in the low-pressure-side areas between the sealing ring and the annular gap remaining in the piston solidifies due to the piston cooling. In the Areas of this annular gap on the high-pressure side remain the molten metal pressure effective.

The axially adjoining, axially reduced, outer circumferential surface of the ring body to the low-pressure side of the sealing ring creates an annular gap between itself and the cylinder, in which, during lubricated operation, the lubricant introduced into the casting chamber in front of the molten metal during the pressure advance of the piston on the outer contact ring surface can enter. When the piston is withdrawn, the gap formed between the annular body and the cylinder contains lubricant, which is spread by the radially elastic sealing ring on the inner jacket of the cylinder during the withdrawal movement and thus lubricates the withdrawal movement of the piston. In this phase of operation, the lubricant contained in the annular gap is generally solidified due to the low temperature of the cooled piston.

The outer ring surface section of the ring body, which has a reduced diameter, expediently extends to its low-pressure side axial end, and is therefore open to the low-pressure side of the piston. In this way, the piston, which generally also forms an annular gap between itself and the cylinder, on the low-pressure side of the sealing ring can be used for receiving a lubricant supply lubricating the sealing ring.

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

The piston is expediently designed such that it supports the advantages of the sealing ring explained above. Therefore, the inner ring surface of the inner shell of the ring body to be exposed to the molten metal, together with the outer shell of the piston, forms an annular gap open on the high-pressure side of the ring body to the pressure chamber of the die-casting cylinder. In order to keep the high-pressure side access for molten metal to the annular gap between the sealing ring and the piston as large as possible, the piston preferably has a radially projecting ring projection which, for axially fixing the ring body to the piston, into a groove arranged on the low-pressure side of the ring gap in the inner jacket of the ring body intervenes. The fixing members are thus arranged on the low-pressure side of the annular gap provided for the radial increase in sealing force and sealing. It goes without saying that the groove can alternatively also be provided on the piston and the ring projection on the ring body.

Alternatively, the piston can also have an annular saving on its outer jacket, in which the annular body engages in particular with its entire axial length in order to fix it axially and form 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, starting from the high-pressure side end of the piston and opening into the annular gap. In this embodiment, a circumferential melt distributor groove is expediently provided in one of the two lateral surfaces forming the annular gap, in particular in the outer jacket of the ring recess of the piston, which distributes the metal melt entering via the axial recesses evenly in the circumferential direction before the melt solidifies as a result of the piston cooling. The slotted sealing ring can optionally be lifted into the ring recess of the piston assigned to it via the high-pressure side of the piston. In individual cases, however, this type of installation can mean that the diameter of the forehead on the high-pressure side is comparatively small, around the sealing ring without permanent. Being able to lift deformation over the forehead. This can have an adverse effect on the life of the sealing ring, since the inner diameter of the radially elastic sealing ring increases when worn and it can slip over the face of the piston. This disadvantage is avoided if the high-pressure end of the piston is designed as a removable, in particular unscrewable, cover, the separating surface of which ends in the ring recess holding the ring body. In such an embodiment, the diameter of the cover delimiting the ring recess can be dimensioned comparatively large.

The lid is preferably made of a poorly, or at least poorly, heat-conducting material, such as Steel, as the adjoining area of the piston, or it is coated with ceramic material. In this way, even if the remaining piston is made of better heat-conducting material in order to optimize its cooling, the metal melt in the casting chamber is prevented from solidifying before the end of the pressure phase, in particular also before the end of the holding pressure phase.

Although the outer diameter of the piston on the low-pressure side of the sealing ring generally forms an annular gap suitable for receiving lubricant towards the cylinder, it is preferred that, directly after the low-pressure end of the ring body of the sealing ring in the outer jacket of the piston, there is one to the inner cylinder jacket and the annular body open ring recess provided to form a lubricant space in order to be able to store a larger amount of lubricant for the return stroke of the piston. The invention is explained in more detail below with reference to a drawing. Here shows:

Figure 1 is a schematic axial longitudinal section through the die casting cylinder of a cold chamber die casting machine with a piston and a sealing ring arranged to the high pressure side end of the piston according to the invention.

Figure 2 is a detailed view of the sealing ring, seen in the direction of an arrow II.

3 shows an enlarged detailed view of the piston area of the die casting machine from FIG. 1;

4 shows a detailed view of a variant of the piston and sealing ring;

Fig. 5 is an end view of the piston, seen in the direction of an arrow V in Fig. 4 and

6 shows a further variant of the piston from FIG. 4.

Fig. 1 schematically shows a cold chamber die casting machine, in the circular cylindrical casting cylinder 1 of which a piston 3 can be displaced between an advanced position shown in full lines in FIG. 1 and a retracted position shown at 3 'in dash-dot lines. In the retracted position 5 molten metal, e.g. Aluminum melt, poured into the casting chamber 7 delimited by the piston 3 and the casting cylinder 1, and when the piston 3 is pushed forward, the metal melt is pressed at high pressure via a sprue 9 into the injection mold (not shown).

At its high-pressure end, the piston 3 carries a sealing ring 11 fixed in both directions of movement, which seals the casting chamber 7 Seals filling opening 5 out. The sealing ring 11, as shown in FIG. 2, has a stepped slot 13 which is both axially and radially continuous and which allows the sealing ring 11 to expand radially on account of its own elasticity, so that the sealing ring 11 with an outer contact ring surface 15 on the inner jacket 1 7 of the casting cylinder 1 is biased due to its own radial elasticity, as best shown in FIG. 3. The steps 19 running in the circumferential direction in axially normal planes at the ends of the annular body 21 of the sealing ring 11 forming the step slot 13 lie against one another and axially seal the step slot 13. Details of such a step slot are explained in EP 0 423 41 3 A2. The piston 3 contains at 22 indicated cooling channels connected to a cooling system, not shown, via which the piston 3 is cooled to a temperature, for example 40 ° -60 ° C., which is low in relation to the temperature of the molten metal. Details of the construction of a cooled piston suitable within the scope of the invention are also described in EP 0 423 41 3 A2 as well as in EP 0 525 229 A1.

The annular body 21 of the sealing ring 11, which rests radially elastically on the inner jacket 17 of the casting cylinder 1, contains, near its low-pressure side axial end, a circumferential groove 23 into which a circumferential projection 25 protrudes radially from the outer circumference of the piston 3 and the sealing ring 11 in both directions of displacement Piston 3 fixed to this. On the side of the annular groove 23 axially towards the high-pressure side of the piston 3, the annular body 21 is dimensioned such that its inner casing 27, together with the outer casing of the piston 3, delimits an annular gap 29 which is open to the high-pressure side of the casting chamber. When the piston 3 is pushed forward during the pressure phase of the casting process, molten metal is pressed into the annular gap 29, where it increases the radial prestressing force of the annular body 21 acting on the contact ring surface 15 to improve the sealing effect. The contact ring surface 15 intended for contact with 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 there is an increase in the radial compressive force acting on the contact ring surface 15 ,

Starting from the comparatively small contact ring surface 15, the outer jacket region 31 of the ring body 21, which adjoins the low-pressure side, tapers in the shape of a truncated cone, so that the wedge-ring-shaped annular gap 32 formed in this way opens in an annular recess which is open both to the inner jacket 17 and to the ring body 21 33 of the piston 3 opens. This design of the sealing ring 1 1 and the piston 3 also allows lubrication of the piston when retracting into its position 3 '. It is known to fill not only the molten metal through 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 ring recess 33 and in the wedge gap 32 between the frustoconical section 31 and the inner jacket 17 and solidifies due to the low temperature of the cooled piston 3 , When the piston 3 is pulled back into the position 3 ', the radially elastic sealing ring 11 spreads the lubricant along the inner jacket 17 and lubricates the retracting movement of the piston.

The small axial height of the contact ring surface 1 5 compared to the total axial length of the ring body 21 facilitates the initial grinding in and adaptation of the sealing ring 1 1 to the cylinder surface 17. The truncated cone-shaped outer surface 31 expediently extends close to the high-pressure end of the ring body 21 , so that the grinding and fitting phase of the sealing ring 1 1 after just a few Casting cycles is complete. At the end of the life of the sealing ring, the contact ring surface 15 widens due to wear.

It goes without saying that the outer casing of the ring body 21 on the low-pressure side of the contact ring surface 15 can also have a different contour, for example a step-like cylinder contour with a reduced diameter, as indicated by dashed lines at 35 in FIG. 3. The contour 35 extends in the example shown to the low-pressure end of the ring body 21, but can also end in the ring body before this end and form a lubricant storage groove on the outer casing of the ring body 21. The ring recess 33 can be omitted here, as in the variants explained above.

Variants of the cold chamber injection molding machine explained with reference to FIGS. 1 to 3 are described below. Components having the same effect are designated by the reference numerals of FIGS. 1 to 3 and provided with a letter to distinguish them. To explain the structure, the mode of operation and any variants, reference is made to the description of FIGS. 1 to 3.

4 and 5 show a variant of a piston 3a which is displaceable in a casting cylinder 1a and which carries a sealing ring 11a in the region of its high-pressure end. The sealing ring 1 1 a is provided with a step slot in accordance with the sealing ring explained above and has an outer jacket contour with a comparatively short bearing ring surface 15 a in the axial direction and a truncated cone-shaped outer jacket area 31 a adjoining on the low-pressure side and tapering toward the low-pressure side, as previously done was explained. In this variant, too, an annular recess 33a which is open to the annular body 21a and to the inner jacket 17a adjoins the annular body 21a of the sealing ring 11a. The sealing behavior, the grinding behavior and that Lubrication behavior when the piston 3a is withdrawn thus corresponds to the exemplary embodiment in FIGS. 1 to 3.

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

In order to be able to expose the inner shell 27a of the annular body 21a, which extends over the entire axial height of the annular body 21a, to the pressure of the molten metal in the casting chamber, the end of the piston 3a on the high-pressure side has several, here four, in the circumferential direction on its outer circumference Distributed, channel-shaped recesses 39 are provided, which extend axially to below the inner circumferential surface 27a and end in the bottom 41 of the annular recess 37 receiving the annular body 21a. Metal melt flows through the recesses 39 into an annular gap 29a formed between the bottom 41 of the annular recess 37 and the inner jacket 27a of the annular body 21a and increases the radial sealing pressure of the sealing ring 11a. Since the annular gap 29a is only connected to the casting chamber via the recesses 39 which are limited in the circumferential direction, the annular gap 29a contains a melt distribution channel formed by an annular recess 43 of the piston 3a. It goes without saying that the cutouts 39 can also be provided entirely or additionally in the sealing ring 11a.

In the embodiment of FIGS. 4 and 5, the ring recess 37 is provided in an integral area of the piston 3a. During assembly, the ring body 21 a of the sealing ring 11 a must therefore be lifted over the high-pressure, soapy shoulder of the ring recess 37, which limits the maximum radial height of this shoulder in terms of design. With increasing wear of the sealing ring 1 1 a, this can then, under certain circumstances the recess 37 slip out. To avoid this, FIG. 6 shows a variant of the piston of FIGS. 4 and 5, in which the high-pressure end of the piston 3b is designed as a removable cover 47, which is detachably attached to the piston 3b here by means of a threaded attachment 45. The separating surface 49 of the cover cuts the annular recess 37b of the piston 3b receiving the annular body 21b of the sealing ring 11b and forms the high-pressure side limiting shoulder 51 of this annular recess 37b. The radial height of the limiting shoulder 51 can now be chosen freely, since after removing the cover 47 the sealing ring 11b can be pulled off axially. The design of the sealing ring 11b corresponds to the variant explained with reference to FIGS. 4 and 5, the recesses 39b being provided in the cover 47 here, but also extending here under the ring body 21b.

While the piston 3b can be made of a good heat-conducting material, for example a copper alloy, for better cooling, the cover 47 is made of a poorly heat-conducting material, for example steel or is thermally insulated by a ceramic coating in order to cool the metal melt during the casting process, in particular into the Retarding the holding pressure phase in which cavities of the melt are to be closed.

It goes without saying that the variants of the outer jacket of the sealing ring explained with reference to FIGS. 1 to 3 can also be used advantageously with the sealing ring of FIGS. 4 to 6.

Claims

Expectations

1 . Sealing ring for a piston of a die-casting cylinder for molten metal, in particular aluminum melt, with a radially elastic ring body (21) which has a slot (13) which is both axially and radially continuous, in particular a slot stepped in the circumferential direction of the ring body, characterized in that the outer casing of the ring body (21) near its high-pressure-side axial end has a plant-ring surface (15) intended for contact with the inner casing surface (17) of the die-casting cylinder (1), the axial length of which is smaller than the axial length of one with this outer plant -Ring surface (1 5) axially overlapping, to be exposed to the molten metal, inner ring surface (27) on the inner surface of the ring body (21), and that on the low pressure side of the outer contact ring surface (1 5) to the outer contact ring surface (1 5 ) an R at least over part of the remaining axial length of the outer casing of the ring body (21) ing surface section (31; 35) connects, the diameter of which is smaller than the diameter of the outer contact ring surface (15).

2. Sealing ring according to claim 1, characterized in that the reduced diameter outer ring surface portion (31; 35) up to the low-pressure side axial end of the ring body

(21) extends.

3. Sealing ring according to claim 2, characterized in that the reduced diameter ring surface section (31) has at least approximately the shape of a truncated cone and tapers towards the low-pressure side axial end of the ring body (21).

4. Sealing ring according to one of claims 1 to 3, characterized in that the inner jacket of the ring body (21), in particular near its low-pressure side axial end, has a circumferential ring recess (23).

5. Piston for a die-casting cylinder for molten metal, in particular aluminum melt, with a sealing ring (11) axially fixed near the high-pressure side piston end according to one of claims 1 to 4, characterized in that the inner ring surface to be exposed to the molten metal (27) of the inner shell of the Ring body (21) together with the outer jacket of the piston (3) forms an annular gap (29) which is open on the high-pressure side of the ring body (21) to the pressure chamber (7) of the die-casting cylinder (1).

6. Piston according to claim 5, characterized in that it has a radially projecting ring projection (25) which for axially fixing the ring body (21) on the piston (3) in a on the low pressure side of the annular gap (29) in the inner jacket (27 ) of

Ring body (21) arranged annular groove (23) engages.

7. Piston according to claim 5, characterized in that it has on its outer casing an annular recess (37) into which the annular body (21 a) for its axial fixation to form the

Annular gap (29a) engages, and that the piston (3a) distributed in the circumferential direction has a plurality of recesses (39) opening into the annular gap (29a) from the high-pressure end of the piston (3a).

8. Piston according to claim 7, characterized in that a circumferential melting distributor groove (43) is arranged in one of the two lateral surfaces forming the annular gap (39), in particular the outer jacket of the annular recess (37).

9. Piston according to claim 7 or 8, characterized in that its high-pressure side end is designed as a removable, in particular unscrewable cover (47), the separating surface (49) of which ends in the ring body (21b) holding the ring recess (37b).

10. Piston according to claim 9, characterized in that the cover (47) consists of a poorer heat-conducting material than the adjoining region of the piston (3b).

1 1. Piston according to claim 9 or 10, characterized in that the cover (47) consists of steel or a copper alloy and / or is coated with ceramic material.

1 2. Piston according to one of claims 5 to 1 1, characterized in that it directly after the low-pressure side end of the ring body (21) of the sealing ring (1 1) in its outer jacket one to the cylinder inner jacket (1 7) and to the ring body (21 ) has open ring recess (33) to form a lubricant chamber.

1 3. Piston according to one of claims 5 to 1 2, characterized in that it contains means for piston cooling in the region of the sealing ring (1 1).