Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
  • B22D17/20—Accessories: Details
  • B22D17/2015—Means for forcing the molten metal into the die
  • B22D17/203—Injection pistons

Definitions

• 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.
• 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.
• 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 In this way, the sealing washer is lubricated during the casting stroke, while the piston can be withdrawn without any problems due to its comparatively large play in the die-casting cylinder.
• the invention is based on a sealing ring for a piston of a die-casting cylinder for molten metal, especially molten aluminum, of
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• a poorly, or at least poorly, heat-conducting material such as Steel
• the adjoining area of the piston or it is coated with ceramic material.
• 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.
• 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.
• FIG. 3 shows an enlarged detailed view of the piston area of the die casting machine from FIG. 1;
• Fig. 5 is an end view of the piston, seen in the direction of an arrow V in Fig. 4 and
• FIG. 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.
• molten metal e.g. Aluminum melt
• the metal melt is pressed at high pressure via a sprue 9 into the injection mold (not shown).
• 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.
• 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 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.
• 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 ,
• 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.
• 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.
• the contact ring surface 15 widens due to wear.
• 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.
• FIGS. 1 to 3 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.
• FIGS. 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.
• 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.
• 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.
• 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.
• the annular gap 29a 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.
• 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.
• 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.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Pistons, Piston Rings, And Cylinders (AREA)
• Forging (AREA)
• Encapsulation Of And Coatings For Semiconductor Or Solid State Devices (AREA)
• Injection Moulding Of Plastics Or The Like (AREA)
• Sealing Devices (AREA)

Applications Claiming Priority (1)

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• 2002
  • 2002-03-04 ES ES02727355T patent/ES2287274T3/es not_active Expired - Lifetime
  • 2002-03-04 WO PCT/EP2002/002356 patent/WO2003074214A1/fr not_active Ceased
  • 2002-03-04 AT AT02727355T patent/ATE364464T1/de not_active IP Right Cessation
  • 2002-03-04 AU AU2002257612A patent/AU2002257612A1/en not_active Abandoned
  • 2002-03-04 EP EP02727355A patent/EP1483074B1/fr not_active Expired - Lifetime
  • 2002-03-04 DE DE50210331T patent/DE50210331D1/de not_active Expired - Fee Related
  • 2002-11-11 AU AU2002358495A patent/AU2002358495A1/en not_active Abandoned
  • 2002-11-11 EP EP02792752A patent/EP1483075A2/fr not_active Withdrawn
  • 2002-11-11 WO PCT/EP2002/012585 patent/WO2003074211A2/fr not_active Ceased

Non-Patent Citations (1)

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