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 piston for a cold chamber die casting machine, in the casting cylinder of which the piston axially displaceably delimits a pressure chamber.
• a main problem of such pistons intended for metal die casting, for example aluminum casting, is the high wear of the sealing ring sealing the piston body against the casting cylinder due to the high temperature of the molten metal and possibly solidified metal residues which hinder the sliding movement of the piston in the casting cylinder.
• the sealing ring arranged in the region of the piston end has a stepped slot which allows the sealing ring which is axially guided on an annular projection of the piston body to expand radially and also seal against wear when worn Can create inner wall of the casting cylinder.
• the known pistons tend to fix the sealing ring on due to the melt penetrating into the ring recess and solidifying there
• the sealing ring can thus deform the casting chamber. do not adjust or only very limited, which in turn increases the wear of the sealing ring.
• the casting cylinder ends in the antechamber of the machine.
• the piston In normal casting operation, the piston is only advanced to the prechamber so that the sealing ring remains in the casting cylinder. If the melt volume is insufficient, the sealing ring can emerge from the casting cylinder and must be re-threaded via a threading cone on the end of the casting cylinder when the piston is returned.
• the threading bevel in the axial direction In conventional pistons, in which the sealing ring on the piston can be fixed by solidified material, the threading bevel in the axial direction must be very long, for example several centimeters long, in order to prevent the casting cylinder end from shearing off the sealing ring. Due to this insertion cone, the casting cylinder and the piston in conventional cold chamber die casting machines have to be specially adapted to each other.
• the invention is based on a piston for a cold chamber die casting machine, in the casting cylinder of which the piston axially displaceably delimits a pressure chamber, with a piston body and a sealing ring fixed in the region of the piston chamber on the pressure chamber side in an outer ring recess of the piston body, the piston body on the pressure chamber side via the sealing ring protrudes axially and radially overlaps the sealing ring over part of its radial thickness on the pressure chamber side, and the piston body can be cooled at least in the region of its piston face.
• the improvement according to the invention consists in that the sealing ring is movably arranged in the ring recess with play and the piston body radially overlaps the sealing ring on the pressure chamber side with a projection, the outer peripheral surface between itself and the casting cylinder limits an annular gap which can be cooled to solidification temperature in the casting operation.
• the sealing ring which is movable in the ring recess also remains sufficiently movable during operation to move because of it
• the annular gap fills with melt, which, however, partially or completely solidifies in the annular gap before it reaches the annular recess in the piston body which guides the sealing ring.
• the melt solidified in the annular gap can remain in the annular gap or it is stripped off in the course of the return stroke.
• the casting cylinder can be shortened in this way and on the other hand the piston according to the invention can be retrofitted without special adaptation of the casting chamber.
• the projection which delimits the annular gap radially on the inside can have a circumferential surface section tapering conically towards the pressure chamber on the pressure chamber side, or better a straight, circular cylindrical circumferential surface section.
• the straight, circular-cylindrical circumferential surface section ensures that the melt solidifies in whole or in part in the annular gap before it is rinsed up to the sealing ring by the operating pressure of the casting process.
• the transition to the usually axially normal end face of the piston body can be crowned and preferably in the form of a circular section in the axial longitudinal section be rounded.
• the spherical or circular segment-shaped curvature increases the area available for cooling.
• the rounded section expediently has an average radius of curvature of several millimeters.
• annular gaps that have a radial width of 0.2 to 3 mm, but preferably of 1 to 1.5 mm, adjacent to the ring recess.
• the axial or radial play of the sealing ring in the ring recess should not be too great, but ensure the free movement of the sealing ring relative to the piston body.
• An axial play of 5/100 to 1/10 mm or / and a radial play of 2/10 mm to 4/10 mm are suitable.
• the sealing ring is designed as a closed sealing ring, the outer diameter of which in the cold state is closely matched to the inner diameter of the casting cylinder in the cold state.
• the sealing ring in the casting cylinder preferably has a radial play of less than 5/100 mm, for example about 3/100 mm, in the cold state. If the casting cylinder is at operating temperature of heated to 250 ° C, for example, its diameter can expand by a few hundredths or even tenths of a millimeter compared to the closed sealing ring, without the sealing of the piston being impaired relative to the casting cylinder. At the operating temperature, such a sealing ring has a comparatively large play with the casting cylinder and, accordingly, it wears out only slightly during operation. The life of the sealing ring is considerably increased in this way.
• the projection of the piston body delimits the ring recess on the pressure chamber side and the projection is fastened to the piston body in a manner that is removable during operation.
• the ring recess is accessible from the end face of the piston body, so that the sealing ring can be fitted axially without any problems.
• not only slotted sealing rings can be used with this type of fastening, but also ring-shaped sealing rings which fit snugly in the casting cylinder, but can compensate for deformations of the casting cylinder due to their play relative to the piston body. It goes without saying that such a configuration of the piston body, which facilitates the exchange of the sealing ring, can also be used with other piston variants, in particular those without an annular gap that solidifies the melt.
• the removable design of the projection has independent inventive importance.
• the component forming the projection determines the shape of the piston front. Since this component can be removed from the piston body, the front of the piston can be varied and adapted to the requirements of the die casting machine without the entire piston having to be specially manufactured.
• the projection can be formed by an operationally removable end cover of the piston body.
• Such an end cover expediently extends over the entire end face of the piston and can 02 12585
• the front cover can have a central screw attachment with which it engages in a central threaded opening of the piston body.
• the screw attachment can be directly connected to coolant inside the piston.
• the end cover must be able to withstand the casting pressure during operation. In individual cases, cooling of the face in the area of the end face may be impeded, in particular if the end cover is solid.
• the front cover contains one or more coolant channels connected to coolant circulation channels of the piston.
• the end cover can contain a plurality of radially extending cooling channels arranged distributed in the circumferential direction.
• a sealing ring can be provided for sealing the end cover relative to the piston body, or a sealing cone is formed on / on the end cover and / or the sleeve part.
• this central recess is designed as a tool engagement recess with a polygonal contour, for example, in order to facilitate screwing or unscrewing the end cover from the piston body.
• the projection delimiting the ring recess of the sealing ring can also be formed by an operationally removable end ring of the piston body, for example in the form of a ring nut or the like, which is screwed onto a threaded shoulder of the piston body.
• the coolant of the piston body can be designed conventionally.
• the piston body can be a cap which is placed on a piston rod which forms the coolant feeds and is fastened there.
• a suitable embodiment, in which the cap is held on the piston rod by means of a bayonet connection without any problems, is described in EP 0 525 229 A.
• FIG. 1 shows a partially broken axial longitudinal section through a piston according to the invention of a cold chamber die casting machine for metal die casting
• FIG. 3 shows an axial longitudinal section through a second variant of the piston; 4 shows an axial longitudinal section through a third variant of the piston, and FIG. 5 shows an axial longitudinal section through an end cover of the piston along a line V-V in FIG. 4.
• Fig. 1 shows a piston generally designated 1 of a cold chamber die casting machine, in the casting cylinder indicated at 3 by a dash-dotted line, the piston 1 axially displaceably delimits a pressure chamber 5 containing the molten metal.
• the piston 1 has a cap-shaped piston body 7, which will be explained in more detail below, and is detachably fastened by means of a bayonet connection 9 to the end of a piston carrier 11 on the pressure chamber side.
• the bayonet connection 9 locks the piston body 7 axially fixed to the piston carrier 11.
• a locking screw 1 3 prevents unintentional loosening of the piston body 7. Details of a suitable bayonet connection are described in EP 0 525 229 A.
• a tubular section-shaped sealing ring 19 is arranged in an annular recess 17 encircling the outer circumference and seals the piston 1 against the inner jacket of the casting cylinder 3.
• the piston 1 shown has only a single sealing ring. In individual cases, however, one or more additional sealing rings can be provided on the side of the sealing ring 19 remote from the pressure chamber, i
• the piston 7 is cooled in the region of its end face 15 and the sealing ring 19 adjacent to it.
• the piston carrier 11 is hollow and contains, coaxially, a pipe 23 which opens near the end face 15 in a chamber 21 which may be formed by a plurality of radial channels, for the supply of the coolant.
• the chamber 21 is connected via axial channels 23 and an annular space 25 as well as one or more radial channels 27 to the cavity 29 of the piston carrier 11 containing the tube 23.
• the coolant is supplied to the end chamber 21 via the pipe 23 and flows through the piston 1 via the channels 23, the annular space 25 and the channel 27 and the cavity 29. Details of a suitable cooling system are again described in EP 0 525 229 A.
• the piston body 7 consists of a tubular cylindrical sleeve part 31 which has at its end facing the pressure chamber 5 the ring recess 19 receiving the sealing ring 17.
• an end cover 33 forming the end face 15 engages, which is screwed sealed with a screw extension 35 adapted to the inside diameter of the sleeve part 31 into a central thread 37 cut into the sleeve part 31.
• the end face 39 of the screw attachment 35 which faces axially away from the pressure chamber 5, simultaneously forms the boundary wall of the chamber 21 on the pressure chamber side and ensures direct coolant contact of the end cover 33.
• a sealing ring surrounding the screw attachment 33 42 seals the end cover 33 against the sleeve part 31.
• engagement openings 41 are provided for a screwing tool.
• the end cover 33 engages with a radial ring projection 43 not only in the radial direction on the pressure-chamber-side end face of the sleeve part 31, but also on the pressure-chamber end face of the sealing ring 17.
• the end of the projection 43 which faces the sleeve part 31 and is remote from the pressure chamber forms a boundary surface of the ring recess 19, so that the sealing ring 17 can be easily fitted or exchanged when the end cover 33 is unscrewed.
• the parting plane between the end cover 33 and the sleeve part 31 can also run at a different location than shown in FIG. 1.
• the ring recess 19 can extend into the end cover 33 or extend overall in the end cover 33, in which case the sleeve part 31 then forms only a boundary surface of the ring recess otherwise provided in the end cover 33.
• the ring recess 19 is dimensioned such that the sealing ring 17 has a slight play of less than 0.2 mm, preferably 5/100 mm to 1/10 mm in the axial direction and in the axial direction and in the radial direction relative to the piston 1 has less than 0.7 mm, preferably between 0.2 and 0.4 mm in the radial direction.
• annular gap 47 is formed, the radial width of which is so small in the area adjacent to the sealing ring 17 that metal melt penetrating into the annular gap 47 completely or partially solidifies in the annular gap 47 due to the cooling of the piston 1 before the melt seals the sealing ring 17 reached.
• annular preliminary seal is formed from completely or partially solidified melt, which prevents the melt from penetrating into the clearance gap of the sealing ring 17 or between the sealing ring 17 and the casting cylinder 3.
• the sealing ring 17 can thus move freely in the ring recess 19 relative to the piston body 7, which considerably reduces the wear of the sealing ring 17.
• the melt solidified in the annular gap 47 can be stripped off; but it can also remain in the annular gap 47 for the next stroke.
• the radial thickness of the annular gap 47 next to the sealing ring 17 is between 0.2 to 3 mm.
• a radial thickness of 1 to 1.5 mm has proven to be particularly suitable.
• the peripheral surface 45 of the projection 43 has a steeply conical shape which merges into the end face 15 via a rounding. This circumferential design ensures that even in the case of an annular gap 47 with a comparatively small thickness, the solidified melt can optionally be stripped off.
• the melt which solidifies completely or partially in the annular gap 47 forms a type of pre-seal, on the basis of which the requirements for the sealing effect of the sealing ring 19 can be reduced.
• the sealing ring 19, which is an annular sealing ring, has one
• the piston 1a shown in FIG. 2 differs from the piston from FIG. 1 essentially only in the outer contour of the end cover 33a, in particular in the area of the annular gap 47a. Components 9 to 13, 21 to 29 and 35 to 41 are not shown, but are present.
• the circumferential surface 45 delimiting the annular gap 47 of the piston 1 from FIG. 1 is conical in the region of the annular gap 47
• the circumferential surface 45a of the projection 43a is designed as a straight circular cylinder in a circumferential surface area 49 adjoining the sealing ring 17a End surface 15a passes section 51, which is circular in cross section.
• This design has the advantage that the cylindrical section 49, which is a few millimeters in the axial direction, for example 2 to 4 mm long, can be made so long that the melt penetrating into the annular gap 47a from the pressure chamber 5a will certainly solidify sufficiently before it seals the sealing ring 17a can achieve.
• the circular arc region 51 connecting the cylindrical region 49 to the end face 15a has the advantage of the largest possible surface compared to the conical approximation form from FIG. 1, which benefits the cooling of the melt in the front region of the annular gap 47a.
• annular groove 53 machined into the piston body 7a, which improves the sealing of the piston, since it can absorb melt residues stripped from the sealing ring 17a.
• Such a groove can also be provided in the variant of FIG. 1.
• Fig. 3 shows a piston 1 b
• the piston body 7b is integrally formed as a cap.
• the end cover 33b forming the end face 15b is integrally and non-detachably connected to the sleeve part 31b of the piston body 7b which is detachably fastened to the piston carrier (not shown).
• a bayonet connection can again be provided for the fastening, as is realized in the piston of FIG. 1 with the components 9 to 13.
• the cooling device with the components 21 to 29 from FIG. 1 is likewise not shown, but is present.
• the projection 43b which together with the casting cylinder 3b delimits the annular gap 47b and radially overlaps the sealing ring 17b, is provided on an annular nut 55 which is screwed onto a threaded shoulder 57 of the piston body 7b projecting towards the pressure chamber 5b.
• the ring nut 55 delimits the ring recess 19b receiving the sealing ring 17b on the pressure chamber side in such a way that the sealing ring 17b is guided in the ring recess 19b with radial and axial play.
• the peripheral surface 45b of the projection 43b extends on the pressure chamber side to the annular recess 19b in the form of a straight circular cylinder 49b, as has already been explained with reference to FIG.
• the region 49b merges into a steeply conical region 59 on the pressure chamber side, and is rounded at 63 to form a stop flange 61 of the ring nut 55 which radially inwardly extends over the threaded shoulder 57.
• the ring nut 55 forms a recess 65 axially countersunk in the piston toward the end face 15b, the peripheral surface of which has a polygonal contour, for example a hexagonal contour, and at the same time forms a " tool receiving opening for screwing the ring nut 55 on and off.
• the recess 65 also brings the melt closer to the coolant system arranged in the interior of the piston.
• the circumferential surface 45b together with the casting cylinder 3b in turn forms an annular gap 47b in which the Melt can solidify early, before it can reach the sealing ring 1 7b and its gap.
• the end cover 33 is in heat transfer contact with the coolant on the end face 39 of its screw attachment 35.
• the heat transfer path in the screw attachment 35 adds. Under certain massive end covers, this can adversely affect the cooling properties of the piston 1 in the area of the annular gap 47 and in the area of the end face 15.
• 4 and 5 show a variant of a piston 1c, the piston body 7c of which is in turn formed from a sleeve part 31c and an end cover 33c screwed into the sleeve part 31c by means of a screw attachment 35c.
• the end cover 33c delimits an annular recess 17c in the pressure chamber 5c with a projection 43c, in which the sealing ring 19c formed as a closed ring is fixed with both axial and radial play.
• the outer contour of the projection 43c has a contour corresponding to the exemplary embodiment in FIG. 2 and forms an annular gap 47c between it and the inner jacket of the casting cylinder 3c, in which, for the preliminary sealing of the sealing ring 1 9c, the melt can solidify in whole or in part.
• the sealing ring 19c and the game column are dimensioned in accordance with the explanations for Fig. 1.
• the tube 23c supplying the coolant or coolant ends in a central blind hole 67 in the end face 39c remote from the pressure chamber 5c of the front cover 33c.
• radial channels 69 extend evenly distributed in the circumferential direction, which are closed at their radially outer ends by screw plugs 71 and otherwise connected by transverse channels 73 to the annular space 25c collecting the outflowing coolant are.
• the coolant is removed from the annular space 25c in the manner explained with reference to FIG. 1. Since the channels run in the end cover 69, the heat transfer path between 'is shortened the end face 15c and the projection 43c to the cooling system.
• a central recess 75 is axially recessed in the end face 15c of the end cover 33c, which brings the end face 15c closer to the cooling channels 69, thereby improving the cooling of the end face 15c.
• the peripheral surface of the recess 75 has a polygonal contour, for example the shape of a hexagon, and forms the tool engagement opening 41c for screwing the front cover 33c in and out.
• the sealing of the end cover 33c relative to the sleeve part 31c takes place by means of cone surfaces which are assigned to one another in the region of the radially inner end edge of the sleeve part 31c, as is indicated at 77.
• the cone angle of the end cover 33c is dimensioned somewhat smaller than the cone angle of the sleeve part 31c.
• sealing rings can be used in the circumferential direction.
• the sealing ring can also be designed as a slotted ring, in particular a step-shaped slotted ring.
• the sealing ring has a rectangular contour and is seated in a substantially rectangular shape
• sealing rings with a different contour can also be used, provided that they are guided on the piston with axial and radial play.
• the sealing ring can only be guided in a ring recess over part of its axial length, and over another part it can be fixed on an annular shoulder of the piston, as is described, for example, in EP 0 423 413 A or EP 0 525 229 A.
• the sealing rings have an outer contour in the form of a straight cylinder.
• This contour can also be designed differently.
• the outer contour of the sealing ring can taper conically or step-wise towards the side remote from the pressure chamber, so that the sealing ring only rests on the casting cylinder in an area adjacent to the pressure chamber.

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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)

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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

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