GB2330099A

GB2330099A - Crystallization grain selection device for use in casting monocrystalline components

Info

Publication number: GB2330099A
Application number: GB9011282A
Authority: GB
Inventors: Ghislaine Elisabeth Lamanthe; Jean-Louis Pierre Ragot
Original assignee: Societe Nationale dEtude et de Construction de Moteurs dAviation SNECMA; SNECMA SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 1989-05-24
Filing date: 1990-05-21
Publication date: 1999-04-14
Anticipated expiration: 2010-05-21
Also published as: GB9011282D0; FR2734189A1; DE4016477A1; SE9001856D0; FR2734189B1; SE9001856L; DE4016477C2; GB2330099B; SE510193C2

Abstract

A crystallization grain selector (30) for monocrystalline castings comprises, in succession, a first vertical passage (34) connected to a base piece (10), an inclined second passage (35) extending from the first passage at an angle thereto of between 95‹ and 135‹, a vertical third passage (36) extending from the second passage, an inclined fourth passage (37) extending from the third passage at an angle thereto of between 95‹ and 135‹, and a vertical fifth passage (38) extending, in alignment with the first passage (34), from the fourth passage to the outlet of the selector which is connected to the base of the casting mould (39).

Description

2330099 1 - CRYSTALLIZATION GRAIN SELECTION DEVICE FOR USE IN CASTING

MONOCRYSTALLINE COMPONENTS The invention relates to a crystallization grain selection device for use in a casting process for manufacturing monocrystalline components, especially superalloy blades or vanes for turboshaft engines.

In known processes of this type, a mould is fed with molten metal at the top and a controlled solidification is carried out so that the solidification front advances vertically upwards from a cooled hearth. In order to obtain a monocrystalline component, a selection device is placed at the bottom of the mould, the device being designed to form a single crystal grain at the outlet thereof.

FR-A-1,481,366 and FRA-2,037,187 describe examples of processes of this type for casting monocrystalline components.

In order to impose a specific crystallographic orientation on the component, a processing technique is also known which is based on starting from a seed crystal consisting of a solid fragment which has the desired orientations. These techniques may, however, be difficult to implement in certain applications.

2 Various forms of grain selectors have been used. A selector with helical baffles is known, for example, from EP-A-0,105,823, and GBA-2,030,233 discloses a selector including several right angles.

However, these known solutions have not been entirely satisfactory with regard to meeting the following criteria: a) the single columnar grain selected at the outlet of the selector and developed in the cast monocrystalline component must be extremely close to having the crystallographic direction (001) coinciding with a chosen axis of the component and the secondary directions also corresponding to specific axes; b) a sufficiently high success rate for obtaining a satisfactory component from each casting must be achieved, regardless of permissible variations in the operational parameters such as, in particular, temperature of the mould, casting temperature, nature and volume of the component and, in the case of cluster casting, the position of the component in the cluster or the geometry of the cluster; and, c) the size of the selector, particularly its height, should be as small as possible.

According to the invention there is provided a device for the selection of a crystallization grain having a predetermined transverse orientation and its [0011 direction coinciding with the vertical for use in the manufacture of monocrystalline components by casting, comprising a base piece and a selector of the bi-dimensional baffle type formed by a succession of straight bars having a common median plane of symmetry, characterized in that at least one bar of the selector has a bar extending at each of its ends at an angle thereto of 0 0 between 95 and 135 Preferably the selector comprises, in succession, a vertical first bar connected to the base piece, an inclined second bar extending from the first bar at angle 0 0 thereto of between 95 and 135 a vertical third bar extending from the second bar, an inclined fourth bar extending from the third bar at an angle thereto of 0 0 between 95 and 135 and a vertical fifth bar extending, in alignment with the vertical first bar, from the fourth bar to the outlet of the selector.

Preferably the angle between the first and second bars, 0 and between the third and fourth bars, is 120 A preferred embodiment of the invention will now be described, by way of example only, with reference to the 1 accompanying drawings, in which:

Figure 1 is a diagrammatic perspective view of a known form of crystallization grain selection device; and, Figure 2 is a perspective view similar to that of Figure 1 but showing an example of a crystallization grain selection device in accordance with the invention.

In monocrystalline casting applications, particularly in the manufacture of turbine blades or vanes, it is known to use a crystallization grain selection device of the type shown in Figure 1. The device comprises a base piece 1 disposed on a furnace hearth 2, and a grain selector 3 mounted on the base piece. The furnace, which is not shown and which receives a mould designed to be fed with molten metal at the top, is of a construction known per se for carrying out this type of operation. Although the furnace does not need to be described in detail, it will be appreciated that it comprises heating means and means for imposing specific thermal gradients in a preferred direction of solidification of the molten metal, in particular a cooled hearth.

In contact with the cooled hearth 2, columnar crystallization grains following the direction 001 are formed in the base piece 1, the hearth 2 being considered horizontal and the direction of solidification perpendicular to the hearth being considered vertical. The grain selector 3 mounted on the base piece 1 comprises hollow elements in the form of straight bars, all having a common median plane of symmetry. These elements are disposed so as to form baffles, and comprise a vertical first bar 4 above the base piece 1, followed by a horizontal second bar 5, followed by a vertical third bar 6, followed by a horizontal fourth bar 7 which is located above the second bar, and a vertical fifth bar 8 which is aligned with the first bar 4 and forms the outlet of the selector which is connected to the actual mould. By imposing a particular path, during their growth, on the columnar grains emerging from the base piece 1, the selector 3 makes it possible to end up, at its outlet, with a single grain which then expands to the shape of the desired monocrystalline component in the mould.

However, this known selection device has given results which are open to improvement, particularly regarding reduction in the failure rate in the selection of a predetermined transverse orientation and (001) direction coinciding with the vertical, and reducing sensitivity to variations in operational parameters.

i 1 j 6 - The grain selection device shown in Figure 2 is an example of a device in accordance with the invention which makes it possible to obtain such improved results. The base piece 10 is similar to that of the known device shown in Figure 1. Also retained is the principle of a tubular grain selector 30 comprising hollow elements in the form of straight bars which are all arranged with a common median plane. of symmetry. In the arrangement in accordance with the invention, however, a vertical first bar 34 above the base piece 10 is followed by a second bar 35 which is inclined to the horizontal at an angle a which 0 0 is between 5 and 45 the preferred value of the angle a being 30 0 as represented in Figure 2 so that the median axes of the first and second bars 34 and 35 located in the common plane of symmetry together define an angle of 1200. The third bar 36 following the second bar 35 is again vertical, and the following fourth bar 37 is inclined to the horizontal, as shown, at an angle b which 0 0 is also between 5 and 45 ' the preferred value of the angle b being 30 0 so that the median axes of the bars 36 and 37 in the common plane of symmetry together define an 0 angle of 120 A fifth bar 38, which leads from the fourth bar 37 to the outlet of the selector 30 which is connected to the mould 39 for casting a monocrystalline component, is vertical and is located in alignment with the first bar 34.

11L - 7 The selection device is entirely surrounded, in a manner known per se, by a shell 40 made from a ceramic-type thermal ly-insulating material which is resistant to high temperatures. The dimensional parameters of the grain selector are determined as a function of the dimensions of the furnace used and of the components to be produced, and as a function of the thermal gradients resulting from the oprational conditions under which the components are cast. The base piece 10, which is preferably cylindrical, thus has a diameter D chosen to enhance the number of grains, whereas the bars of the selector have an identical cross-section, preferably of rectangular shape with sides e and f, which limits the number of grains and limits the edge effects. The presence of the angles a and b for the nonhorizontal bars 35 and 37 makes it possible to avoid deterioration of the selector through sagging of these bars and the appearance, during use, of an angle which less than 90 degrees between each of the said bars 35 37 and the associated vertical bars. In particular, is and the non-horizontal arrangement of the said bars 35 and 37 makes it possible to eliminate grains emerging from the base piece 10 whose crystallographic orientation is unsatisfactory, thus ensuring an improved quality of the single grain obtained at the outlet of the selector. Furthrmore, the length of the said bars 35 and 37 is determined so as to control the thermal gradient.

- 8 In the case of one particular application, the following dimensional parameters of the selection device in accordance with the invention shown in Figure 2 have been obtained, expressed in millimetres:

D = 15 to 20; H 1 = 10 to 15 H 2 = 10 to 15 a = 25 to (height of the block); (height of the first and the third bars) (horizontal length); e = f = 4 to 5 i = 5 (outlet height), a = b = 30 degrees H = 60 to 70 (total height) - 9

Claims

1. A device for the selection of a crystallization grain having a predetermined transverse orientation and its (001) direction coinciding with the vertical for use in the manufacture of monocrystalline components by casting, comprising a base piece and a selector of the bi- dimensional baffle type formed by a succession of straight bars having a common median plane of symmetry, characterized in that at least one bar of the selector has a bar extending at each of its ends at an angle thereto of 0 0 between 95 and 135

2. A selection device according to claim 1, in which the selector comprises, in succession, a vertical first bar connected to the base piece, an inclined second bar extending from the first bar at angle thereto of between 0 0 and 135 a vertical third bar extending from the second bar, an inclined fourth bar extending from the 0 0 third bar at an angle thereto of between 95 and 135 and a vertical fifth bar extending, in alignment with the vertical first bar, from the fourth bar to the outlet of the selector.

3. A selection device according to claim 2, in which the angle between the first and second bars, and between the - 0 third and fourth bars, is 120.

4. A selection device according to claim 11 substantially as described with reference to Figure 2 of the accompanying drawings.