Patent Application
20200254510
This application claims priority to European Patent EP 19156932.6 filed with the European Patent Office on Feb. 13, 2019. The preceding application is herein incorporated by reference in its entirety.
The present invention relates to a riser sleeve comprising a riser body for use when pouring metals into a casting mould, a method for producing a single-piece riser body, as well as an expander element and a core box comprising the expander element for producing a single-piece riser body.
In foundry technology, it is often necessary to arrange additional riser sleeves in the casting moulds, the riser body of which fills with the liquid metal when moulding the casting and compensates for the volume deficits occurring during the solidification of the casting in order to prevent the formation of shrink holes in the casting. For this purpose, the riser sleeves are provided in such a way that the liquid metal fed within is later solidified as the casting so that a transport of metal towards the casting can take place during the solidification process, thereby filling the casting in a manner that is free of shrink holes. For this purpose, the riser sleeves consist of an exothermic and/or insulating material. For this purpose, the riser sleeves have a riser cavity for holding liquid metal as well as a riser opening for joining the riser cavity to a mould cavity of the casting mould during the casting process. In a plurality of applications, the riser sleeve is vertically aligned during the casting process, i.e. an axis defined by the riser opening is vertically aligned. In this case, the riser cavity adjoining the riser opening is usually designed to be rotationally symmetric around the axis, wherein the hydrostatic pressure of the liquid metal located in the riser cavity is sufficient for feeding.
However, there are areas of application where the riser sleeve is horizontally aligned during the casting process with its axis defined by the riser opening. For example, vertical green-sand moulding systems for the production of casting moulds (also known as DISA moulding plants and DISAMATIC®) are known, in which a first model half is mounted on an exclusively linearly adjustable press piston and a second model half is mounted on a pivoting moulding plate, which is movable back and forth between a placement position in which, for example, this is horizontally or vertically aligned and in which it is equipped with a riser sleeve, and one, in particular, vertically aligned casting position. With these vertically divided casting moulds, with which relatively thin-walled castings can be produced and in which the riser sleeve is horizontally aligned during the casting process, the problem is in ensuring that feeding takes place. Thus, for example, from EP 3 003 601 B1, a two-part riser body is known, whose riser cavity limited by two moulding elements with a horizontal arrangement of the axis has a predominant fraction of its volume above the axis so that the hydrostatic pressure of the liquid metal above the axis is sufficient for feeding. The two moulding elements of this riser sleeve can be moved to each other in a telescopic manner so that, during the production of the casting moulding, the one moulding element is moved towards the other moulding element, whereby a compaction of the moulding material of the mould in the region surrounding the riser opening is made possible.
From DE 87 02 296, a riser sleeve is known, which is made of two moulding elements due to the undercut design of the riser cavity to the riser opening, which two mounding elements have to be glued together after their respective production, which increases the producing effort of the riser sleeve. It is therefore desirable to simplify the riser body of a riser sleeve and its production.
For a riser sleeve that is vertically aligned during the casting process, which has a rotationally symmetrical riser cavity, it is known from WO 2017/046007 A1 to produce a single-piece riser body by means of a core shooter where an expandable rotationally symmetrical expander element specifies the geometrical shape of the riser cavity during the shooting operation.
The object of the present invention is therefore to eliminate the disadvantages described with reference to prior art and, in particular, to indicate a riser sleeve, a method for producing a single-piece riser body, as well as an expander element and a core box comprising an expander element, by means of which the production of a riser sleeve arranged horizontally during the casting process is simplified.
The problem is solved by means of a riser sleeve, a method for producing a riser body, as well as by an expander element and a core box of a core shooter with the features of the respective independent claim. Favourable further embodiments of the invention are indicated in the dependant claims and in the description, wherein individual features of the favourable embodiments can be combined with one another in a sensible manner.
The task is solved, in particular, by means of an expander element for producing a riser body, the outer contour of which is expandable and which extends along a central longitudinal axis in an unexpanded state, wherein the expander element has an asymmetrical shape in an expanded state with reference to the longitudinal axis.
In the unexpanded state, in particular, the expander element has a cross-sectional design, which can be conically tapered from a base, which can also be called a foot, of the expander element towards a free end. The cross-sectional design in the unexpanded state of the expander element can be, for example, circular, oval, elliptical, trapezoidal, rectangular or square, wherein, in the case of a rectangular or square cross-sectional design, the corners can be rounded off. In the case of a rectangular or square cross-sectional design, the expander element has two side walls, the cross sections of which are each at least parallel.
According to the invention, it is now provided that the expander element in an expanded state has an asymmetrical shape in relation to the longitudinal axis. The outer contour of the expanded expander element thus extends in one direction with a greater distance from the longitudinal axis defined in the unexpanded state than in an opposite direction (in a cross-sectional plane orthogonal to the longitudinal axis). The expander element is, in particular, designed in such a way that an elongation in the region of the base of the expander element does not take place or only takes place a little so that the base of the expander element specifies the shape of the riser opening of the riser body to be produced.
Such an expander element together with a core shooter is, in particular, used in a core shooter for producing a riser body, wherein the core box comprises at least one first box and one second box. The core box can also comprise further boxes.
Such a core box with a corresponding expander element can be used for producing a single-piece riser body of a riser sleeve, wherein the production method comprises at least the following steps (also in any order provided it is technical reasonable):
Such an asymmetric outer shape of the expanded expander element can be achieved, for example, by means of the expansion of the expander element taking place during production in one direction and not expanding in the opposing direction. Of course, however, a greater expansion in one direction and a lesser expansion in an opposite direction can also take place.
Such an expansion in one direction can be achieved, for example, by the fact that the expander element has a fixed mandrel and comprises a flexible membrane attached to the mandrel, which can be expanded by means of introducing a fluid into an intermediate space between the membrane and the mandrel, wherein the membrane expands orthogonally to the longitudinal axis of the mandrel when expanding on a plane. For example, this can occur by means of the fact that the membrane comprises elasticity modules arranged in an unequally distributed manner on a local level. Alternatively, the expanding in one direction could be due to a boundary element, which is applied onto the flexible membrane from the outside.
It is however preferred that an extension in one direction and no extension into the opposite direction is achieved by means of the membrane is attached with its peripheral edges, for example, by means of vulcanization, to the mandrel both in the axial direction (meaning below in the region of the base and above in the region of the free end of the expander element) as well as in the circumferential direction (meaning, for example, along the longitudinal axis on the surface of the fixed mandrel).
A riser body produced in this way comprises a riser cavity for holding liquid metal and a riser opening for connecting the riser cavity to a mould cavity of the casting mould during the casting process, wherein the riser cavity has a greater diameter than the diameter of the riser opening in at least one portion, wherein the riser opening defines an axis. The riser body is made of an insulating and/or exothermic riser material and is formed as a single piece, wherein the riser cavity is asymmetrical with respect to the axis. Such a riser sleeve can be produced in just one single shooting operation in a core shooter.
Thereby, the riser cavity has a volume, which is designed in such a way that, in the case of a horizontal arrangement of the riser sleeve and the axis defined by the riser opening, a greater volume fraction of the volume of the riser cavity can be positioned above the axis than under the axis. Such a riser sleeve is ideally suited for a vertically divided casting mould, where the riser sleeve is horizontally arranged during the casting process since the liquid metal located above the axis during the casting process provides a sufficient hydrostatic pressure, which is sufficient for a feeding of liquid metal into the mould cavity of the casting mould.
The exothermic and/or insulating material of the riser body is uniformly and homogeneously distributed in the wall region, the lid region and the base region of the riser body comprising the riser opening thereby being so that no boundaries between individual sections of the riser body would be formed, as would be the case, for example, if the riser body were glued together from a plurality of parts. The riser body can, in particular, comprise another (ventilation) opening on a side opposite to the riser opening (meaning in the lid region), which is used for guiding the cap during moulding. For example, such another opening can be created during the producing process of the riser body, while the free end of the expander element opposite to the base of the expander element is not expandable or can relatively be expanded only a little. The asymmetry of the riser cavity is characterized in that, in particular, the riser cavity extends orthogonally to this axis from the axis defined by the riser opening than in an opposite direction. Thus, the riser cavity may be aligned during the casting process in such a way that a larger riser volume is arranged above the axis than below.
Preferably, the riser cavity on its peripheral surface in the area of the asymmetric embodiment has a minimal place, which has a smaller distance to the axis than adjacent points on the peripheral surface, which are arranged adjacent in the axial direction and opposite to the minimum position. Such a minimal place, with which the liquid material first comes into contact when filling the riser cavity, improves the feeding. For example, such a punctiform or (in particular, orientated in the circumferential direction) linear minimal place (also known as a Williams groove or a Williams element) can, during the production of the riser body be produced by the expanded expander element having a corresponding minimal place on its expanded surface, which comprises a smaller distance to the longitudinal axis (of the unexpanded expander element) than axially adjacent points on the expanded surface in both directions.
In order to form the minimal place on the expanded surface of the expander element, the membrane can be connected to the mandrel on its inner side in an expandable region in such a way that the expansion of the membrane is locally limited. For example, the membrane can be directly attached to the mandrel at a punctiform or linear point so that, at this attachment point, no expansion of the membrane takes place. Alternatively, the expansion of the membrane can also be limited using an arrestor strap, which is attached with an end on the mandrel and with another end on the inner side of the membrane.
In a preferred embodiment, in the unexpanded state, the expander element has a rectangular cross-sectional shape, in particular, a square one with parallel side walls, wherein the side wall can be attached to one another due to roundings. The side walls can additionally be formed along the longitudinal axis in a conically tapered manner. Thereby, the produced riser opening of the riser body would also have an essentially rectangular (cross-sectional) shape. In this connection, in particular, it is provided that the membrane is only arranged on one side wall of the expander element. As an alternative, the expander element can have a cross-sectional shape, such as round, oval or elliptical, wherein the membrane preferably only extends in the circumferential direction across one part of the circumference. For example, the membrane extends in the circumferential direction across no more than half of the total circumference.
After the riser body is produced, in particular, the accessories can, in particular, be attached to the riser body for forming a riser neck and thereby for forming a predetermined breaking point of the metallic rest of the riser near the casting part surface for example, a so-called ME sheet in the region of the riser opening on the outside of the riser body. As an alternative, it would also be possible that the accessories are arranged in the core boxes in order to already be connected to the riser body produced in the process already during the shooting process. In particular, the riser sleeve then comprises the riser body and the accessories.
The invention as well as the technical field are explained based on the figures as an example. Schematically, the figures show
The cross-sectional shape of the unexpanded expander element 7 is rectangular, wherein the membrane 10 only extends across a side wall 13 of the mandrel 9. The membrane 10 is completely attached to the mandrel with its peripheral edge 12. Due to lines in the inside of the mandrel 9 (not shown), it is possible to convey a fluid into an intermediate space 11 between the mandrel 9 and the membrane 10 so that the membrane 10 and, thereby, the outer contour of the expander element 7 are expanded.
The accordingly expanded expander element is shown in
Such an expander element 7 is used in a core shooter for producing a riser body 2.
In
Since the volume of the riser cavity 3 is greater above the axis 5 than below the axis 5, during the casting process, a sufficiently high hydrostatic pressure is available due to the liquid metal in order to ensure feeding. The Williams element 6 formed on the peripheral surface of the riser cavity 3 serves as a hotspot for the liquid metal.
With the present invention, an asymmetrical riser body comprising a riser cavity can be produced as a single piece in just one production process so that the effort for producing such a riser body is considerably simplified.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19156932.6 | Feb 2019 | EP | regional |
