GB2047139A - A mould gating system - Google Patents

Abstract

The system is of general application for pouring foundry molds by gravity, and has a prefabricated dirt or slag strainer 1, located along a conduit forming a flow path to the casting cavity. The strainer is supported by an anchor to withstand the impact of falling molten metal and the consequent metalstatic pressure, while the cavity is filled through apertures 8. The anchor may take the form of legs, as shown, or be a chapelet which is placed between the strainer and a mould wall. <IMAGE>

Description

SPECIFICATION A gating system for gravity poured foundry molds This invention relates to a gravity poured foundry mold and more particularly to a gating system that is part of the mold, wherein the gating system includes the complete assembly of sprues, runners, ingates, flow-offs, feeders, necessary to pour and produce a casting.

Through the gating system the flow of melted metal is controlled in order to avoid turbulences and inclusions, and in order to properly fill the entire mold casting cavity. Afte the mold filling action is completed, the gating system if properly designed, and when necessary, also promotes a good feeding action, that is a good directional solidification through the casting.

The aim of the feeding action is to compensate for the contraction of the melted metal which, for most metals and alloys, takes place at the solidification stage. For achieving good directional solidification in a casting, the melted metal solidification in the mold casting cavity must be such that feeding metal is always available from the gating system for that portion of the casting just solidifying.

The gating systems presently in common use, generally solve the problem of obtaining sound castings but at the same time, very frequently, present some adverse economical aspects which among others are: 1) Relatively high proportion of metal involved in the gating system, 2) Increased mold volume for accommodating the gating system, 3) Necessitates finishing operations for separating the gating system from the casting, and 4) Creation of obstacles while the casting is cooling and contracting, which promotes deformations and internal stresses in the casting in addition to those deformations and stresses coming from the casting shape itself.

Accordingly the invention provides a gating system for a gravity poured foundry mold having at least one casting cavity and at least one mold parting surface connecting the full contour of the mold casting cavity with the external surface of the mold, said gating system establishing necessary flow paths between the outside of the mold and the mold casting cavity, comprising a conduit formed by at least one of the flow paths established by said gating system, said conduit being open on opposite ends thereof and extending directly from an outer mold surface to the surface of said cavity, said conduit being arranged to receive molten metal and guide said metal directly toward the mold casting cavity, such that during pouring of the mold, all molten metal passing through said conduit flows directly toward the mold casting cavity; a stationary skinstrainer distinct from said conduit and said mold and interposed between said conduit and said mold casting cavity along the surface of the mold casting cavity and such that said skin-strainer follows the contour of the surface of said mold casting cavity, said skin-strainer being operative in its stationary position to communicate to the mold cavity all molten metal to be received by said cavity from said conduit during the casting-operation, said skinstrainer defining at least one aperture and having a total aperture cross-sectional area which is.substan- tially smaller-than the minimum cross-sectional area of the conduit to significantly control the rate of flow of molten metal from the conduit to the mold casting cavity, said skin-strainer being arranged to choke said.conduit such that conduit quickly fills with molten metal upon pouring of said molten metal to saidaconduit, said skin-strainer being prefabricated and sufficiently strong to withstand the full impact of falling molten metal poured into said conduit and to support the full metalstatic pressure of the molten metal contained in the choked conduit during filling of said cavity; and, retaining means for supporting the skin-strainer in position along the surface of the mold casting cavity throughout pouring and solidification-of said molten metal, said retaining means being sufficiently strong to transfer the impact and pressure of said molten metal to the mold body substantially independently of the positioning of said skin-strainer with respect to the parting surface of the mold; whereby the combination of said skin-strainer and said retaining means, withstands the impact of the molten metal during pouring thereof into said conduit, and supports the full pressure of a column of molten metal contained in the choked conduit during filling of said mold casting cavity.

To obtain a high quality casting, several filling and feeding areas may be necessary and as many skin-strainers and their corresponding sprue-feeders are then required. In these instances, in order to avoid the necessity of having one pouring ladle per each sprue-feeder, an overhead melt distributor is provided on the top of the mold. This distributor permits the pouring from one ladle into one distributor point from which the melt distributor simultaneously dejivers-the melt at the necessary rate required by each sprue-feeder and skin-strainer.

The melt distributor also enables the pouring of a mold which has several cavities, which can correspond to the same casting or to different castings.

While many foundry casting cases can be dealt with by only applying the gating system of the present specification, there will also be other cases where the present gating system will profitably be combined with the traditional established ways of gating a casting.

Quite often it will be possible to change the casting design without affecting its purpose but favouring the application of the present new system with its numerous advantages.

The main advantages of the gating system according to this invention, summarized as follows, involve the ability: 1) To control, which means to restrict to any required degree, the flow of metal or alloy being poured into a gravity foundry mold.

2) To limit sharply or even avoid melt turbulences inside the mold casting cavity, which turbulences most generally produce casting defects.

3) To limit sharply or even avoid the entry of any detrimental melt inclusion into the mold casting cavity.

4) To assure the desired directional solidification of the casting.

5) To provide a gating system with a minimum volume, thus allowing the pouring of more molds per melt batch.

6) To minimize or even eliminate the fettling operations originated by the gating system.

7) To reduce the molding cost as a result of a more compact gating system which requires smaller molds and allows more molds in the same molding area.

8) To reduce the internal stresses and deformations associated with casting solidification and cooling, by minimizing the connections between the casting and the gating system.

9) To allow, when necessary, an adequate venting of the mold casting cavity around the ingate, which venting is sometimes difficult to achieve properly.

This gating system is to be applied to any type of mold poured by gravity such as molds that are sand based, graphite based, metallic based, made of a combination of different materials, etc., for pouring any metal or alloy compatible with the general properties, like refractority, solubility in the poured metal and mechanical resistance, of the materials available for making the skin-strainers. This gating system is also to be applied for pouring castings with a wide range of size and shape.

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which: Figure 1 is a side view of a gravity poured mold and gating system according to one embodiment of the invention; Figure 2 is a side view of a gravity poured mold and gating system according to a second embodiment of the invention, Figure 3 is a side view of a gravity poured mold and gating system according to a third embodiment of the invention, Figure 4 is a side view of a gravity poured mold and gating system according to a fourth embodiment of the invention additionally illustrating further venting and skin-strainer retaining techniques;; FigureS is a side view of a fifth embodiment of the invention, illustrating further venting and skinstrainer retaining techniques; and Figure 6 is a top view of the particular skin-strainer shown in Figure 5.

Before discussing the invention in detail, a few definitions of terminology are firstly presented to facilitate the understanding thereof. Thus, the word metal referred to hereinafter is used to mean a pure metal or an alloy. A gravity mold is any foundry mold filled with melted metal under the effect of gravity. The mold casting cavity is the part of the mold which corresponds to the casting to be produced as defined per sample, pattern or per casting drawing. The mold casting cavity surface is the internal mold surface which corresponds to the surface of the casting to be produced with that mold.

Fettling, also called foundry finishing operations or just finishing, is the process of removing, after the mold has been poured and shaken out, the complete gating system and flashes from the casting, and carrying out any necessary operation to produce the casting, dimensioned and shaped, in accordance with the casting drawing, foundry pattern or sample.

Sometimes modification of the casting surface is introduced in the foundry for fabrication reasons, being that modification either accepted by the casting customer or corrected by the foundry at the fettling stage. In any of these cases, that modified casting surface is the one considered in the present invention.

A direct sprue is the mold conduit fulfilling simultaneously the object of a sprue, a runner and an ingate. It is usually unsuitable for producing a good quality casting, but can be made suitable in many cases by using a skin-strainer as defined in the present specification. A sprue-feeder is the conduit fulfilling simultaneously the object of a sprue, a runner, an ingate and also the role of a feeder. This is also, most generally, unsuitable for producing a good quality casting but, according to the invention, and when used in conjunction with a skin-strainer, advantageously results in an inexpensively produced high quality casting.

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to Figure 1 thereof, there is illustrated the skin-strainer 1, serving as a form of barrage, and constituting the inner end of the conduit 2 along a mold casting cavity surface 3.

Figure 1 also shows a mold top part 4 and a mold bottom part 5, both made in this particular case of particulate material like molding sand; the casting mold cavity 6; the mold top surface 7; and the skin-strainer holes or apertures 8. Plural holes 8 are shown, having a combined area as necessary to assure proper filling and also, when necessary, the proper feeding of the casting. In the case of Figure 1 the skin-strainer 1, which may be considered as made of metallic material, has been extended from the mold casting cavity surface in a cup-like shape to create an anchorage of the skin-strainer 1 within the refractory particulate material of the mold top part 4.

Holes 9 in the cup-like shape are disposed if necessary to increase the degree of that anchorage.

Furthermore, some sort of venting passage must be disposed, if not naturally provided by the mold and casting configuration, for evacuating any gas from the mold casting cavity while this cavity is being filled during the pouring operation. Passage 10 in Figure 1 is one possible venting passage.

Figure 2 shows one way of forming a skin-strainer comprising at least two different elements: element 11 which is mechanically resistant, for example made of metal; and element 12 which is more resistant than element 11 to the effects of direct contact with said molten metal, such as heating, solubility or the like. Element 12 can be made of any refractory material like ceramic or core sand. The element 11 is in contact with the molten metal when the cavity is filled; but by then, and because of even metalstatic pressure on both sides of the skinstrainer, there is no longer a requirement of mechanical resistance. In some cases a third element, like an isolating wash applied on element 11 may be necessary. Such wash can be for example of the type conventionally used to protect the mold casting cavity in permanent molds.In some cases such as isolating wash or coating, applied all over element 11, may eliminate the necessity of the element 12.

Figure 2 also shows a different way of supporting the skin-strainer 1, which is supported directly by the bottom part 15 of the mold, and a different way of venting the casting mold cavity through passages 10 disposed along the mold parting surface 13. In Figure 2, the mold top and bottom parts, 14 and 15, are made of any kind of material which can be considered as being refractory with respect to the temperature of the molten metal to be poured in the mold. For example such refractory material can be ceramic, molding sand, some metals or the like.

The skin-strainer will generally, but not necessarily, be located at the upper part of the mold casting cavity surface, as this position is generally chosen to minimize the distance between the ladle and the mold casting cavity, and to assure later feeding of the casting, with the view of bringing the metal as close as possible to the central part of the cavity, instead of to the cavity edges as is usual with conventional gating systems and so for maximizing the filling and feeding actions.

The skin-strainers can be used in any type of gravity mold, whether sand based, graphite based, plaster based, metallic based or the like. The mold can also be a gravity mold combining the use of different materials as for example a metallic mold with bonded sand cores. Also the skin-strainers can be used for pouring any type of metal compatible with the strength, refractority, solubility, resistance and general properties of the materials availableto make the skin-strainers. Whatever the material used and whatever its thickness, the strength of the skin-strainer at the metal pouring temperature must be compatible with its size, shape and support, and must be sufficient to withstand the impact and pressure which takes place when the mold is being poured.

The skin-strainer 1 must generally be clean and must be kept in this condition. It can be protected, but the protective material used most not be damaging to the quality of the metal to be poured.

The refractority of a skin-strainer and also its resistance to any action coming from the contact with the molten metal can be increased by protecting it with some material more refractory or more contact resisting than itself, as shown in Figure 2 or for example, by embedding a steel part in a bonded sand core material.

It is important to note that the impact and pressure applied on a skin-strainer only lasts for a short period of time, that is the pouring time, which is usually only a matter of seconds. It does not matter if the skin-strainer reaches a collapsing temperature when the mold has been already filled. However, the skin-strainer must remain intact with its original shape and position and a district material to ensure an easy separation between the casting and the conduit. In that regard, it is noted that the skinstraineris preferably positioned at that point requiring feeding after the mold has been filled, that is a point which usually would need to have a conventional feeder.

The skin-strainer is made coincident with the casting surface, preferably as shown in Figures 1 and 2 where the skin-strainer is shown embedded in the mold volume. On the other hand, the skin-strainer 1 may also be embedded in the mold casting cavity if it is considered that the skin-strainer would then not damage the casting in any way or cause an inconvenience by leaving a depression on the casting surface. Thus, in some applications the skin-strainer 1 may be left permanently in the casting.

The skin-strainer in general-can be easily retained in a requisite position, depending an.the casting, mold, and skin-strainer particularities.-The positioning can for example be achieved by having a mold depression- corresponding to the skin-strainer thickness and contour as shown in Figure 2.

In order to obtain a quiet flowing of the metal into the mold without turbulence through the skinstrainer and into the mold casting cavity, it is essential to adequately vent this cavity to avoid any internal gas-or air pressure occurring in the mold, particularly around the skin-strainer area.

Returning to the Figures, Figure 3 when compared with Figure 1 again illustrates-the retention and positioning of the skin-strainer 1 but now along a perturbation or modification 16 of the casting surface as deemed necessary by the foundry in charge of manufacturing that casting.

Figure 4 illustrates several other important aspects of the gating system according to this invention, and shows a skin-strainer 1 which is again a two material skin-strainer formed by two elements, 17 and 18, wherein element 17 is the retaining part of the skin-strainer and element 18 is its heat and molten metal contact resistant part. For example, element 17 could be made of metal and element 18 of ceramic. Furthermore, in Figure 4 the mold casting cavity surface 3 along which the skin-strainer is located is cylindrical, that is, it is not flat. The mold part 19 can be the mold bottom part or a core reproducing the inner surface of the casting, while the skin-strainer holder 20 is formed of a bonded refractory material within which the skin-strainer is anchored. The skin-strainer holder 20 is-a removable part of the mold in which the skin-strainer is embedded; if the weight of this holder is not sufficient to offset the metalstatic pressure when the mold is full, it must be loaded with some extra weight not shown in the figure. Venting passages 10 are disposed around the laternal external surface of the skin-strainer holder. During the pouring operation, the element 17 of the skin-strainer substantially has no direct contact with the molten metal, except toward the end of the filling of the cavity, when a part of 17, which is along the mold casting cavity surface 3, is contacted by the molten metal. In Figure 4 the top part 21 of the mold can be made of metal, or any refractory material like ceramic, bonded sand, plaster and the like. Mold part 19 also can be made of that variety of materials.

In Figure 5 the skin-strainer 1 is made of refractory material, like ceramic, and is supported and retained by, and centred over a chaplet 22, which is itself located on the mold bottom part through a locating peg 23. In this case, the use of a chaplet 22 in the mold must be compatible with the casting to be produced. The skin-strainer in Figure 5 features the communication apertures between the conduit 2 and the cavity 6 as being formed by the gaps between the skin-strainer contour and the wall of the conduit 2. As is usual in foundry technology, core chaplet 22 will also be generally made of metal.

The skin-strainer total apertures, which is the sum of all the individual holes and gap areas through which the metal flows, is selected and adjusted as required. The hole size, shape, distribution and number of holes, or the number of gaps, width and length of the gaps around the skin-strainer, or a combination of the two, holes and gaps, are selected to give the required filling of the mold with the minimum of turbulence, the required filtering of the inclusions, the required straining of the metal flow and the required feeding effect once the mold is full.

Usually, the holes through the skin-strainer will generally be made of the same size and evenly distributed in order to obtain a flow of metal as even as possible all around the pouring area, but sometimes the necessity to avoid some metal cascading, depending on the casting shape, requires a selective location of the strainer apertures.

It is emphasized that a non-metaliic skin-strainer formed of a relatively breakabie and more refractory material than a metallic material such as steel, whether the refractory material is a core bonded sand or a ceramic material or the like, can be reinforced by having embedded therein a metallic material such as expanded perforated mesh or the like.

Alternatively, as shown in Figures 2 and 4, the ceramic or core bonded sand element 12 or 18, of the skin-strainer, form a sort of cladding over the other skin-strainer steel element 11 or 17. Thus, element 12 or 18 isolates element 11 or 17 during the short lapse corresponding to the pouring time.

The shape of the aperture can be any desired one, such as round, square, oblique, orfili-form in the case of a gap. Furthermore, the apertures can be tapered or parallel throughout their length through the skin-strainer.

The gating system of the invention, having a sprue-feeder and a skin-strainer at the inner end thereof, with the skin-strainer having an appropriate thickness and appropriately sized apertures, enables not only the proper filling of the cavity but also ensures proper feeding of the casting through the skin-strainer. The skin-strainer by being a small element immersed in the flow of metal quickly reaches the melt temperature, which allows, after the mold is full and before the metal is solidified, melted metal continuity between both sides of the skin-strainer, even if the aperture size is relatively small. If the size of the sprue-feeder is apportioned with the casting, this melted metal continuity lasts throughout the solidification of the casting.Stated somewhat differently, it is possible to say that the evolution of the isothermic lines during the solidification process is not substantially impaired whether or not a skin-strainer is retained between the spruefeeder and the casting.

The use of exothermic or insulating sleeves, the use of exothermic powder or of insulating covers for reducing the volume of the feeders can be combined with the gating system object of this invention in order to minimize further the amount of metal involved in the gating system.

The sprue-feeder must be prefilled and choked as quickly as possible during the pouring operation in order to assure that the pouring is uniform through the straining surface, that the sucking of air into the mold is avoided and that the filtering effect is maximized.

In any type of gating system, the cost of its separation from the casting must be considered and kept to a minimum as the fettling operations in the foundry industry are generally costly. The present gating system with its skin-strainers reduce the fettling costs substantially, since there are no classical runners and ingates to eliminate and since the sprue-feeder separation is made much easier by having residual sprue-feeder metal connected to the casting only through the skin-strainer's apertures.If the metal poured into the mold is too tough when cold and then presents resistance to the knocking off of the sprue-feeder, it is noted that separation can be done while the casting is already solid but still hot and not too resistant, by using a properly designed sprue-feeder pulling extractor, which applies a pulling force in a direction perpendicular to the casting cavity surface, to free the sprue-feeder from the casting.

The skin-strainers can be manufactured by conventional techniques, and if formed from ductile materials, which are generally metallic, the skinstrainer is successively blanked, pressed and pierced or punched or drilled. Alternatively, the skinstrainers can be manufactured or pre-perforated, expanded, woven metallic materials or the like. If they are formed from rigid metallic materials, the skin-strainer would be cast, machined from wrought materials, by a combination of casting and machining procedures, or by any other similar process.

When utilizing highly metallic refractory materials to make the skin-strainers, powder metallurgy techniques can be applied.

When using rigid non-metallic materials such as sand core materials, ceramics or non-metallic refractory materials, any of the known techniques can be used for making these skin-strainers.

From Figures 1,3,4 and 5 it is especially seen that the skin-strainer 1 according to the invention is capable of being retained along the surface of the mold-casting cavity independently of a mold parting surface, i.e. the parting surface at the interface of the various mold parts. Thus, the skin-strainer retaining means of the invention, while nevertheless transferring the impact and pressure of the falling molten metal to the mold, allows the skin-strainer to be located at virtually any position on the surface of the mold casting cavity, without resort to any elaborate auxiliary ingating common to the prior art, and the concomittant complication in mold design and fabrication, and in the casting filling and feeding operations.

Obviously, numerous (additional) modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended Claims, the invention may be practised otherwise than as specifically described herein.

Claims (3)

1. A gating system for a gravity poured foundry mold having at least one casting cavity and at least one mold parting surface connecting the full contour of the mold casting cavity with the external surface of the mold, said gating system establishing necessark flow paths between the outside of the mold and the mold casting cavity, comprising: a conduit formed by at least one of the flow paths established by said gating system, said conduit being open on opposite ends thereof and extending directly from an outer mold surface to the surface of said cavity, said conduit being arranged to receive molten metal and guide said metal directly toward the mold casting cavity, such that during pouring of the mold, all molten metal passing through said conduit flows directly toward the mold casting cavity; a stationary skin-strainer distinct from said conduit and said mold and interposed between said conduit and said mold casting cavity along the surface of the mold casting cavity and such that said skin-strainer follows the contour of the surface of said mold casting cavity, said skin-strainer being operative in its stationary position to communicate to the mold cavity all molten metal to be received by said cavity frorn said conduit during the casting operation, said skin-strainer defining at least one aperture and having a total aperture cross-sectional area which is substantially smaller than the minimum crosssectional area of the conduit to significantly control the rate of flow of molten metal from the conduit to the mold casting cavity, said skin-strainer being arranged to choke said conduit such that conduit quickly fills with molten metal upon pouring of said molten metal to said conduit, said skin-strainer being prefabricated and sufficiently strong to withstand the full impact of fall molten metal poured into said conduit and to support the full metalstatic pressure of the molten metal contained in the choked conduit during filling of said cavity; and, retaining means for supporting the skin-strainer in position along the surface of the mold casting cavity throughout pouring and solidification of said molten metal, said retaining means being sufficiently strong to transfer the impact and pressure of said molten metal to the mold body substantially independently of the positioning of said skin-strainer with respect to the parting surface of the mold; whereby the combination of said skin-strainer and said retaining means, withstands the impact of the molten metal during pouring thereof into said conduit, and supports the full pressure of a column of molten metal contained in the choked conduit during filling of said mold casting cavity.

2. A gating system for a gravity poured foundry mold having at least one casting cavity, said gating system establishing necessary flow paths between the outside of the mold and the casting cavity, comprising: a conduit formed by at least one of the flow paths established by said gating system, said conduit being open on opposite ends thereof and extending directly from an outer mold surface to the surface of said cavity, said conduit receiving molten metal and guiding said metal directly toward the mold casting cavity such that during pouring of the mold all molten metal passing through said conduit flows directly toward the mold casting cavity; a stationary skin-strainer distinct from said conduit and said mold and interposed between said conduit and said mold casting cavity along the surface of said cavity such that said skin-strainer follows the contour of the surface of said mold casting cavity, said skin-strainer being operative in its stationary position to communicate to the mold cavity all molten metal to be received by said mold cavity from said conduit during the casting operation, said skin-strainer defining at least one aperture and having a total aperture cross-sectional area which is substantially smaller than the minimum crosssectional area of the conduit to significantly control the rate of flow of molten metal from the conduit to the mold casting cavity, said skin-strainer choking said conduit such that said conduit quickly fills with molten metal upon pouring of said molten metal to said conduit, said skin-strainer prefabricated and sufficiently strong to withstand the full impact of falling molten metal poured into said conduit, and to support the full metalstatic pressure of the molten metal contained in the choked conduit during filling of said cavity, said skin-strainer comprising at least two different elements whose combined effects results in a skin-strainer with enough mechanical strength while presenting at the same time enough resistance to the action of direct contact with said molten metal; and, retaining means for supporting the skin-strainer in position along the surface of the mold casting cavity throughout the pouring and solidification of molten metal, said retaining means sufficiently strong to transfer the impact and pressure of said molten metal to the mold body; whereby the combination of said skin-strainer and said retaining means withstands the impact of molten metal during pouring thereof into said conduit, and supports the full pressure of a column of molten metal contained in the choked conduit during filling of said mold casting cavity.

3. A gating system for a gravity poured foundry mold substantially as herein described with reference to the accompanying drawings.