EP2554296A2 - Die casting injection piston head - Google Patents

Abstract

The piston head comprises a one-piece piston head (1) made of copper or copper alloy, and a wear ring (2) made of harder material than that of the piston head. The ring is arranged in the region between end face (3) and surface (4) of piston head. The piston head and the ring are coupled mutually. The radially inward edge of the ring is provided with a radially inward bar (5). The ring is formed as a closed one-piece element and it consists of hot-work tool steel, whose external diameter is up to 0.5 mm smaller than the outer diameter of piston head.

Description

The present invention relates to a die-cast piston head for light metal die-casting, comprising a one-piece piston head made of copper or a copper alloy and at least one arranged on this closed wear ring made of a harder material than that of the piston head, wherein the wear ring in the region between an end face and a lateral surface of the Plunger head is arranged and wherein the piston head and the wear ring have mutually complementary connection means.

Die-cast pistons for light metal diecasting usually consist of at least one piston head and one driven piston rod. These components slide wall guided in a filling chamber. The die-cast piston conveys the light metal melt entering the fill chamber for a shot via the gate system into the cavity of the die where the die casting is cast. The die-cast piston head comes with its front face with the molten metals or alloys in contact. Die-cast iron piston heads made of copper or a copper alloy have a high thermal conductivity and dissipate the heat of the applied at the piston end melt during solidification so quickly that the cycle times of the die-casting are not increased, and so slow that a successful Nachpressphase is possible. The heat balance of Druckgusskolbenköpfe is therefore of great importance for die casting quality and economy. Copper or copper alloy die-cast piston heads are relatively soft and thus prone to premature wear. Therefore, they are provided with wear protection rings made of steel, Stellite or other hard materials or are made entirely of steel. The wear protection rings become new after their wear replaced. Due to the mechanical and thermal loading of the piston heads and the requirement of (partial) replacement, which can be accomplished only consuming with special tools, the attachment of wear protection rings on the piston head of particular importance for the handling of the die-cast piston in everyday operations.

From the EP 1 837 102 A1 the Applicant is known such a one-piece piston head, wherein at least one wear protection ring is materially connected to the piston head. As a result, the penetration of molten metal is prevented in the annular gap between wear protection ring and piston head and the piston head over the wear protection rings in the filling chamber.

From the WO 03/074211 A1 a closed sealing ring is known, which is arranged between a first and a releasably connected thereto second piston head part supported by this. This sealing ring consists, viewed from the piston end side, of an axially rear first piston part and an axially front second piston part, wherein a first and / or the second piston part at least partially axially overlapping sealing ring is provided. The first piston part is a bush made of a thermally conductive copper alloy, the second consists of a hot-work steel or a copper alloy with a long service life and the sealing ring is designed as non-slotted or radially resilient slotted wear ring made of steel or copper. First and second piston part are releasably connected to each other by means of circumferentially distributed axially arranged screws, the sealing ring is detachably snapped.

From the EP 1 483 074 B1 is described a wedge-shaped extending wear protection ring to the front, in its axially rear region a groove into which a web of the multi-part piston head engages, so that the wear protection ring is held. This one also in the EP 0 423 413 A2 described wear protection ring has an axially and radially stepped slot.

The US 4,886,107 A discloses a die-cast piston head made of copper having a wear-resistant steel ring in a groove at its front end. This split steel ring is spread apart for mounting, pushed over the die-cast bulb tip, and then secured against axial expansion by soldering its ends together in the position.

The DE 203 09 181 U1 proposes a piston head which, viewed from the piston end side, consists of an axially rear first piston part and an axially front second piston part, wherein a first and / or the second piston part at least partially axially overlapping sealing ring is provided. The first piston part is a sleeve of thermally conductive copper alloy, the second consists of hot-work steel or a copper alloy and the sealing ring is designed as non-slotted or radially resilient slotted wear ring made of steel or copper. First and second piston part are releasably connected to each other by means of circumferentially distributed axially arranged screws, the sealing ring is detachably snapped. This document proposes for applications in the high-vacuum casting technique to provide a second, axially rear sealing ring, which is formed by means of springs outside the filling chamber to an excess radially auffahrend and which leads the die-cast piston within the casting cylinder.

From the WO 96/38246 a one-piece piston head is known, on which a wear protection ring is screwed. The wear protection ring has in its frontal region an axial section with a Plurality of axial passage slots. In this front, the melt-facing region, it also has a conically inwardly extending, radially inner surface. In this area, the piston head has a spherical re-entrant surface, so that the two surfaces enclose between them an annular gap whose opening cross-section at the immediate end side is maximum and decreases axially rearwardly to zero. The contact point of the two surfaces is axially seen before the threaded portion and radially narrower than the thread. This annular gap, together with the axial slots to ensure the penetration of melt and thus the expansion of the wear protection ring, whereby the piston head to be sealed against the chamber wall.

As the closest prior art, the applicant is the EP 0 525 229 A1 considered. There, a die-cast piston is disclosed, the piston head is formed in one piece and also has a sealing ring. According to this document, the sealing ring is detachably supported via a circumferential groove on a circumferential spring arranged on the piston head. The piston head has a chamfer along the circumference of its end face. The joint between the piston head and sealing ring adjoins it without gaps. Due to the high pressure during the pressing process, the melt preferably penetrates into the annular gap between the sealing ring and Füllkammerinnenwand, a so-called bullet, and in the joint between the piston head and sealing ring, wherein at the joint, the chamfer of the piston head acts as a guide surface, the molten metal or the alloy passes directly to the joint.

A disadvantage of this prior art is that at a shoot through the molten metal or alloy, the piston head is damaged and the wear ring from the piston head no longer destructive is solvable, whereby maintenance of Druckgusskolbenkopfes considerably more difficult or impossible.

It is therefore an object of the present invention to provide a Druckgusskolbenkopf, which is characterized by a comparison with the prior art improved durability and ease of maintenance and no special design of the filling chamber needed.

To solve this problem, the invention proposes a die-cast piston head of the type mentioned above, wherein the wear ring has a radially inwardly directed web on its face facing the radially inwardly directed edge. This web forms a barrier to protect the connecting means located in the joint between the piston head and the wearing ring against the penetration of the molten metal. The metal solidifies near the end of the face and thus can not penetrate as far as the connecting devices. At the same time it closes the joint. The connection devices therefore remain fully functional, whereby the connection between the piston head and the wear ring remains stable and the die-cast piston head can be used for a number of working cycles which are increased compared with the prior art. The one-piece nature of the wear protection ring and its closure require a particularly long service life. The wear protection ring according to the invention has no axial or radial slots, it is therefore not prone to penetrating melt. The fact that the outer diameter is up to 0.5 mm smaller than the outer diameter of the piston head, an identical outer diameter for the wear ring and the piston head is reached at operating temperature. It has been found that under operating conditions despite different thermal expansion coefficients of Wear ring material and piston head material an approximately equal temperature distribution is achieved, so that the diameter of the wear ring may be equal to or smaller than that of the axially adjacent piston head portion. As a result, penetration of molten metal and thus a bullet is prevented even over a long period of operation. If the wear ring consists of a hot-work tool steel, its alloy consisting of iron, carbon, silicon, chromium, molybdenum and vanadium is characterized by a hardness substantially exceeding the hardness of the piston head, which is sufficient to protect the piston head effectively from mechanical loads and to allow an economically acceptable service life of the piston head. In order to achieve the same outer diameter for the wear ring and the piston head at operating temperature, essentially two circumstances have to be considered. The thermal expansion coefficient of the wear ring alloy is less than the thermal expansion coefficient of the piston head alloy. However, the thermal conductivity of the wear ring alloy is also lower than the thermal conductivity of the piston head alloy. It has been found that a wear ring made of hot-work steel despite the mentioned differences in operation does not have a much higher temperature than the piston head.

In a first embodiment of the invention it is provided that the connecting means are designed as a spring arranged on the piston head and a groove arranged on the wear ring. This rotationally symmetrical and thus easy to implement in construction and manufacturing connection devices allow easy handling of the die-cast piston head, since it is composed of only two one-piece components, namely from the piston head and the wear ring. When mounting the wear ring the piston head, both components are pushed together until the spring skips the front side facing away from the boundary of the groove and engages in the groove. This is possible, the spring have a low height and the groove accordingly a small depth. In an assembled state, the spring between the two boundaries of the groove, that is arranged in the groove.

Furthermore, it proves to be particularly advantageous according to the invention that the spring on its side facing the radially outwardly facing edge has a radial transition and / or the wear ring on its side facing away from the end, radially inwardly directed edge has a radial transition. Through these radial transitions, the assembly simplifies, as when pushing together of the piston head and wear ring, the radial transitions meet as two sliding surfaces and significantly reduce the force required to skip the spring. On the other hand, the spring on its side facing away from the front, radially outwardly directed edge and the groove are not rounded, so that an unintentional disengagement of the wear ring is effectively prevented. In an alternative embodiment, the radial transitions are formed as chamfers.

In a second embodiment of the invention, the connecting means are designed as two mutually engageable threads, in particular metric fine thread. The wear ring is thus formed screwed to the piston head. This robust, durable and easy-to-handle type of connection has been known in many fields of technology for a long time and is considered one of the basic types of connection, but represents an absolute novelty in the inventive connection of a piston head and a wear ring in the field of die casting Through the web according to the invention, the screw is still functional even after many cycles of Druckgusskolbenkopfes.

In a third embodiment of the invention, it is provided with great advantage that the connecting means are designed as a spring arranged on the piston head and a groove arranged on the wear ring and two threads which can be brought into engagement, in particular metric fine threads. The combination of the two embodiments described above combines the respective advantages. During assembly, the threads serve as mounting means, as during the screwing of the wear ring with the piston head, the feed generated thereby in the axial direction, the groove effectively and metered push over the spring. When assembled, the threads and the tongue and groove combination ensure redundant and permanent retention of the wear ring on the piston head. In addition, the wear ring is secured in the assembled state against rotation relative to the piston head, since a rotational movement due to the thread pitch always implies an axial movement, but this is prevented by the latched spring.

It proves to be particularly advantageous according to the invention that the piston head consists of an essentially copper, nickel, chromium and silicon-containing alloy or of an essentially copper, cobalt, nickel and beryllium-containing alloy. Such alloys are highly thermally conductive and can be made wear-resistant. For further details, reference is made at this point to the copper alloys of the applicant. In addition, further copper alloys with the above properties are conceivable for the piston head according to the invention.

With great advantage, the invention provides that the wear ring has a hardness according to the Rockwell scale C greater than 50, but at least has a significantly higher hardness than the piston head. The compared to the copper-based piston head significantly harder wear ring is used to protect the softer piston head from mechanical wear due to a possible tilting when advancing the Druckgusskolbenkopfes in the filling chamber and against thermal damage by durchschießende melt.

In an alternative embodiment, the wear ring consists of a substantially copper and beryllium-containing alloy and its outer diameter corresponds to the outer diameter of the piston head. It is particularly advantageous that the wear ring and the piston head extend approximately equally thermally. The considerations to be made for steel wear rings thermal expansion omitted. Due to this material similarity between wear ring and piston head, the respective outer diameters are consistent for all relevant temperatures in practice. By the use of special copper alloys, in particular of copper alloys of the applicant, in the manufacture can be sufficiently hard and resistant wear rings form, without using steel.

In an embodiment of the invention it is provided that the two threads are formed in the operating state cohesively with each other. As a result, a fixation of the thread is achieved with advantage, which can not solve even under the harsh operating conditions.

The invention will be described by way of example in preferred embodiments with reference to the drawings, wherein further advantageous details are shown in the figures of the drawings.

• Fig. 1 einen schematischen Querschnitt eines erfindungsgemäßen Druckgusskolbenkopfes entlang seiner Zylinderachse in einer ersten Ausführungsform,
• Fig. 2 einen schematischen Querschnitt eines erfindungsgemäßen Druckgusskolbenkopfes entlang seiner Zylinderachse in einer ersten Ausführungsform in einem demontierten Zustand,
• Fig. 3 einen schematischen Querschnitt eines erfindungsgemäßen Druckgusskolbenkopfes entlang seiner Zylinderachse in einer dritten Ausführungsform,
• Fig. 4 einen schematischen Querschnitt eines erfindungsgemäßen Druckgusskolbenkopfes entlang seiner Zylinderachse in einer dritten Ausführungsform in einem demontierten Zustand und
• Fig. 5 einen schematischen Querschnitt eines erfindungsgemäßen Druckgusskolbenkopfes entlang seiner Zylinderachse in einer ersten Ausführungsform in einer Detailansicht.

The figures of the drawings show in detail:

• Fig. 1 a schematic cross section of a Druckgusskolbenkopfes invention along its cylinder axis in a first embodiment,
• Fig. 2 a schematic cross section of a die-cast piston head according to the invention along its cylinder axis in a first embodiment in a disassembled state,
• Fig. 3 a schematic cross section of a die-cast piston head according to the invention along its cylinder axis in a third embodiment,
• Fig. 4 a schematic cross section of a Druckgusskolbenkopfes invention along its cylinder axis in a third embodiment in a disassembled state and
• Fig. 5 a schematic cross section of a Druckgusskolbenkopfes invention along its cylinder axis in a first embodiment in a detailed view.

In Fig. 1 is a schematic cross section of a die-cast piston according to the invention for the light metal die-casting along its cylinder axis 11 in a first embodiment shown. This die-cast piston head has a one-piece piston head 1 made of a copper alloy and a wear ring 2 made of hot-work steel arranged on the piston head. According to the invention, it would also be conceivable for the wear ring to be made of a copper-beryllium alloy consists. The wear ring 2 is arranged in the region between the end face 3 and the lateral surface 4 of the piston head 1. As mutually complementary connection means, the piston head 1, a spring 6 and the wear ring 2, a groove 7. The spring 6 and / or the groove 7 may be interrupted one or more times along its circumference. These interruptions make the spring 6 and / or the groove 7 less rigid, so that only reduced forces are required when mounting the wear ring 2 on the piston head 1. Of course, the groove 7 may also be arranged on the piston head 1 and the spring 6 on the wear ring 2 accordingly. As inventively particularly advantageous, it proves that the wear ring 2 has a radially inwardly directed web 5 on its the end face 3 facing radially inwardly directed edge. This web 5 protects the connecting means against the penetration of molten metal or a molten alloy. On the opposite side of the end face 3, the piston head 1 has a cylindrical recess which in Fig. 1 not shown fastening means for securing the die-cast piston head to a piston rod or on a Druckgusskolbenkopfträger includes.

The Fig. 2 shows a schematic cross section of a die-cast piston head according to the invention along its cylinder axis 11 in a first embodiment in a disassembled state. This die-cast piston head is identical to that in FIG Fig. 1 pictured die-cast piston head. How out Fig. 2 very graphically shows the Druckgusskolbenkopf consists of only two components, namely a one-piece piston head 1 and a one-piece wear ring 2. The groove 7 has along its arc length four, each offset by 90 ° arranged interruptions.

In Fig. 3 is a schematic cross section of a Druckgusskolbenkopfes invention along its cylinder axis 11 shown in a third embodiment. The basic structure of the die-cast piston head is very similar to that in Fig. 1 shown die-cast piston head. In contrast to the first embodiment described above with a groove 7-spring 6 combination and a non-illustrated second embodiment with threads 10 as connecting means, the third embodiment illustrated here, as acting between the piston head 1 and the wear ring 2 connecting means on the piston head 1 arranged spring 6 and arranged on the wear ring 2 groove 7 and at the same time two mutually engageable thread 10. Preferably, the threads 10 are metric fine threads with substantial self-locking. In order to protect the threads 10 against the penetration of molten metal, the wear ring 2 has on its end face 3 facing, radially inwardly directed edge on a radially inwardly directed web 5. The web 5 shifts the potential entry point of the melt between the piston head 1 and the wear ring 2 away from the sensitive threads 10 and thus acts as a protective cover for the thread 10 and the groove 7-spring 6 combination. When mounting the thread 10 are used with great advantage as an assembly aid. During the screwing of the wear ring 2 with the piston head 1 causes the resulting axial stroke of the thread 10, that the groove 7 is pushed over the spring 6 and the spring 6 engages in the groove 7. After snapping the thread 10 and the groove 7-spring 6 combination provide a redundant and permanent connection between the piston head 1 and the wear ring. 2

The Fig. 4 shows a schematic cross section of a die-cast piston head according to the invention along its cylinder axis 11 in a third embodiment in a disassembled state. This die-cast piston head is identical to that in FIG Fig. 3 pictured die-cast piston head. As Fig. 4 illustrates, the Druckgusskolbenkopf consists of only two one-piece components, namely a piston head 1 and a wear ring 2. In this illustration, the threads of the arranged on the wear ring 2 thread 10 are particularly easy to recognize. The threads 10 are preferably metric fine thread. However, other thread types, for example trapezoidal threads, are encompassed by the present invention. For final assembly, the two threads are provided in the region of the viewed from the piston end from the axially rearmost thread with two to three axially spaced drops of adhesive so that after screwing an approximately continuous adhesive layer, the two threads in this area cohesively connects. Suitable adhesives according to the invention are all suitable adhesives, in particular silane-crosslinked, 2-component adhesives correspondingly high temperature stability, as required when using the pistons according to the invention.

In Fig. 5 is a schematic cross section of a Druckgusskolbenkopfes invention along its cylinder axis 11 in a first embodiment shown in a detailed view. This illustrates in particular the at the front side 3 facing, radially outwardly directed edge of the spring 6 arranged radial transition 8 and facing away from the end face 3, radially inwardly directed edge of the wear ring 2 arranged radial transition 9. During assembly of the wear ring 2 at the piston head 1, the radial transitions 8 and 9 meet, act as sliding surfaces and thus facilitate the skipping of the spring 6. The in Fig. 5 shown Wear ring 2 consists of a hot-work steel. In order to assume an outer diameter identical to the outer diameter of the piston head 1 at operating temperature and thus to optimally protect the jacket 4 against molten metal passing through, the outer diameter of the wear ring 2 is up to 0.5 mm smaller than the outer diameter of the piston head 1 at room temperature.

LIST OF REFERENCE NUMBERS

1

piston head

2

wear ring

3

face

4

lateral surface

5

web

6

feather

7

groove

8th

Radial transition

9

Radial transition

10

thread

11

cylinder axis

Claims (9)

Die-cast piston head for light metal die-casting, comprising a one-piece piston head (1) made of copper or a copper alloy and at least one wear ring (2) arranged thereon of a harder material than that of the piston head (1), wherein the wear ring (2) in the region between an end face (3) and a lateral surface (4) of the piston head (1) is arranged and wherein the piston head (1) and the wear ring (2) complementary to each other connecting means, characterized in that the wear ring (2) at its, the end face (3) facing, radially inwardly directed edge has a radially inwardly directed web (5) that the wear ring (2) is formed integrally and closed and it consists of a hot-work steel and its outer diameter is up to 0.5 mm smaller than that Outer diameter of the piston head (1). Die-cast piston head according to claim 1, characterized in that the connecting means are designed as a spring (6) arranged on the piston head (1) and a groove (7) arranged on the wear ring (2). Die-cast piston head according to claim 2, characterized in that the spring (6) on its the front side (3) facing, radially outwardly directed edge has a radial transition (8) and / or the wear ring (2) facing away from the end face (3) , radially inwardly directed edge has a radial transition (9). Die-cast piston head according to claim 1, characterized in that the connecting means engage as two with each other bringable thread (10), in particular metric fine thread, are formed. Die-cast piston head according to claim 1, characterized in that the connecting means as a on the piston head (1) arranged spring (6) and on the wear ring (2) arranged groove (7) and two mutually engageable thread (10), in particular metric Fine thread, are formed. Die-cast piston head according to one of the preceding claims, characterized in that the piston head (1) consists of an alloy comprising essentially copper, nickel, chromium and silicon or of an alloy comprising essentially copper, cobalt, nickel and beryllium. Die-cast piston head according to one of the preceding claims, characterized in that the wear ring (2) has a hardness according to the Rockwell scale C greater than 50, but at least has a significantly higher hardness than the piston head. Die-cast piston head according to one of claims 1 to 7, characterized in that the wear ring (2) consists of an essentially copper and beryllium-containing alloy and its outer diameter corresponds to the outer diameter of the piston head (1). Die-cast piston head according to one of claims 4 or 5, characterized in that the two threads (10) in the operating state are formed cohesively with each other.

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