WO2005102560A2

WO2005102560A2 - Method and apparatus for casting aluminum engine blocks with cooling liquid passage in ultra thin interliner webs

Info

Publication number: WO2005102560A2
Application number: PCT/IB2005/002331
Authority: WO
Inventors: Oscar Gerardo Cantu-Gonzalez; Ismael Ramirez-Alvarez; Alvaro Ramirez-Morales
Original assignee: Tenedora Nemak, S.A. De C.V.
Priority date: 2004-04-20
Filing date: 2005-04-20
Publication date: 2005-11-03
Also published as: WO2005102560A3; US20050247428A1

Abstract

Casting method and apparatus for forming fluid cooling passages in the webs having a minimum dimension of 3 mm or less between iron cylinder liners (6) in aluminum engine blocks (8) by utilizing very thin pre-formed reinforced cores (10) inserted between adjacent liners (6) and conjoined with the outer water jacket core (16). The reinforced core (10) is made of a supportive very thin reinforcing element (12), preferably in the form of a rectangular metal strip (12), or other material that withstands the casting process, with a thin coating layer (14) that protects such element (12) and permits its ready removal after formation of the casting, which layer (14) may advantageously and inexpensively be formed of conventional casting sand with a typical binder.

Description

Method and Apparatus for Casting Aluminum Engine Blocks with Cooling Liquid Passage in Ultra Thin Interliner Webs FIELD OF THE INVENTION The invention broadly relates to the art of manufacturing narrow passages in thin walled castings and is particularly useful for the manufacture of cast aluminum automotive engine blocks with very thin interliner walls for providing cooling liquid passages therein, preferably using essentially conventional sand core techniques. BACKGROUND OF THE INVENTION The description will be mainly in terms of its applicability to aluminum engine blocks (typically with iron cylinder liners). There is a constant push to increase the power to weight ratio of automotive engines, which results in the desire to utilize a minimum amount of light weight materials in place of traditional heavier materials (such as iron), yet with essentially maintained strength and integrity and thus effectiveness and reliability. In recent years for the manufacturing of engine blocks, particularly for automotive applications, several processes are available among which we can list (1) the sand package either low-pressure or gravity filled, wherein a sand mold comprising sand cores defining cavities of predetermined shapes is filled with liquid aluminum alloys, which after solidification form the motor block, or (2) the semi-permanent low pressure or (3) gravity filled metallic molds with sand cores to form the interior features of the block. The design of the engine blocks has been changing over the time with a tendency to increase the power of engines while reducing size and weight. The dimensions of the motor blocks tend to be fixed by the dimensions of the car body. To satisfy improved technology and design, the blocks need to accommodate cylinders of larger volume, meaning larger diameter, within the same block volume. These designs pose a challenging problem especially to aluminum engine block manufacturers, because the cylinder liners (usually made of iron) are sought to be positioned as close together as possible, while still being able to maintain an effective cooling flow through passages in the aluminum wall between said cylinder liners. This thin web of aluminum is becoming ever thinner (desirably now less than about 3 mm). Attempts to eliminate the gap between the liners altogether in an aluminum block can result in uneven cooling with resulting distortions in the cylinder geometry even of the iron sleeve inserts during operation of the engine and causing increased wear and decreased performance. These continuing concerns and prior attempts at practical solutions are discussed in U.S. patent nos. 4,917,169 April 17, 1990; 4,693,294 September 15, 1987; and 5,217,059 June 8, 1993 (see also DE 3300924, July 19, 1984), all filed in the 1980's and early 1990's. Of these, only the 5,217,059 patent concerns cast aluminum engine blocks. In contrast, note that relative to the other patents which are all understood to teach iron castings, the inherently greater strength of iron relative to aluminum castings allows for wider water passages for a given web thickness than would be appropriate for a web of aluminum of the same dimension. This is especially true where the iron liners in the aluminum castings are not joined as a single cast unit (contrary to the other patents mentioned above, which all have the inline cylinders cast joined together and simultaneously formed with the rest of the block). The general problem caused by the ever narrowing space between adjacent cylinder bores is shown to be common to both cast iron engine blocks and cast aluminum engine blocks, but is clearly more so relative to the aluminum blocks, because of the need for iron or other hardened cylinder liners (which restrict the size of the inter-cylinder web gap available for a cooling water passage). Yet the advantages of the ih proved-power to weight rtion derived from use of aluminum blocks makes the difficulty* in overcoming such dimensional problems worthwhile. In column 1 of Patent no. 5,217,059, for example, in discussing aluminum engine block manufacture, states that "conventional sand coring techniques cannot be used to form the water bypass passages between adjacent cylinders having such a small web." The size of the web contemplated by this comment will be understood from this patent's discussion immediately thereafter of the alternative proposed in patent no. 4,917,169. Patent no. 4,917,169 teaches an expensive ceramic form (having a width "of the minute thickness of 1.5 to 3.0 mm") to use during casting to create the interliner water cooling passages. Removal of the ceramic form from the subsequently hardened casting requires a separate sandblasting step. Patent no. 5,217,059, itself, proposes use of a metal support element 64 covered with a removable woven refractory (fiberglass) sleeve 66 as the casting form for the interliner water cooling passage. This has the distinct disadvantage of requiring the element 64 to extend out the side of the resulting cast block, thus leaving an external hole in the block through into the water jacket, that must be plugged. Also, the apparently expendable woven refractory 66 is again relatively expensive (an important consideration in a mass production operations). Patent no. 4,693,294 will be understood by those skilled in the art to be relevant to an iron casting (not aluminum). It discusses employing special sand cores (unsupported) for use in forming the water channels bridging through the webs separating adjacent cylinders. This is an example of the prior art use of such cores at the extreme of their capabilities; namely at a width apparently still greater than 3mm. In column 1, this patent teaches a web width (between cylinder bores) of "not exceeding 9 mm" or "smaller than 8.5 mm in the finished state." How much narrower the web cores can be is not indicated, but the applicants know from experience that such cores would be very fragile and difficult to handle and thus unreliable especially for mass production purposes, if much narrower. The '294 patent goes on to state that the web wall thicknesses at the web water channels are "in the range of about 2.5 mm or less in the finished states". The difference between twice 2.5 (or less) and 8.5 leaves a water channel thickness (and thus a corresponding core thickness) of 3.5 mm (or more) for the example. At these dimensions, the 4,693,294 patent teaches away from the use of conventional silicon sand technology, and instead had to use "a special sand with a special sand grain which is highly compressed", such as "zircon sand with a very fine grain" that "is expediently 0.15 to 0.2 mm." These highlight the countervailing designs needed to provide for additional or more effective engine cooling passages in the narrowed interliner areas, because there is now less material to dissipate the heat from the adjacent portions of the cylinders; yet just maintaining even past cooling flow rates is becoming more difficult as the interliner space becomes smaller. Current engine block designs now seek aluminum wall interliner thicknesses of about 2 to 3 mm and even less. Thus, the creation of a cooling passage reduces the aluminum wall thickness in such passages to about only 1 mm or less. The wall thickness of the cooling passages needs to be sufficient to prevent leaks (and thus should not touch the liner walls). The present invention also avoids another current practice involving casting a solid section between the cylinder liners and then opening or machining a very thin gap which is later sealed by welding the top of the gap closed, thus forming a passage. This procedure requires expensive precision cutting/machining equipment and tools. OBJECTS AND SUMMARY OF THE INVENTION The present invention overcomes the above drawbacks of the current art by introducing a pre-formed reinforced core, with the required shape to fit in the narrowest space between the adjacent pairs of cylinder liners, typically iron, in an aluminum engine casting. In broader aspects of the invention, it can be used with engine blocks where the liners can be press fit after casting of the engine block (such as when AA 319 or AA 356 alloy is used). In even broader applications, the insert can be between the cylinder bores in aluminum engine blocks made with a high strength high silicon alloy (or equivalent), where iron liners are not needed, but the need for cooling passages in the narrow gaps remain. This core is made of a supportive very thin reinforcing element, preferably in the form of a rectangular metal strip, such as steel (or other material that withstands the casting process), with a thin coating layer that protects such element and permits its ready removal after formation of the casting, which layer may advantageously and inexpensively be formed of conventional casting sand with a typical binder. In the broader aspects of this invention, the coating layer may be formed by anything serving the same function. For example, a refractory coating maybe used of the type long employed to prevent aluminum from sticking to molds, ladles, and the like (but which apparently have never been put to the unexpected use of aiding in the formation of water passages, especially in the interliner webs of aluminum engine blocks). When used such a refractory coating has been applied either with a brush or a pneumatic pistol. Examples of such commercially available refractory coatings known in the art include: DAG 193 and ISOL BM manufactured by ACHESON and Delta Cast 696 by FORDATH. Other appropriate coating layers may be used which serve to prevent the sticking of the thin reinforcing strip to the aluminum as it cools from the liquid to solid state, and allow convenient removal of the strip from the cooling passage formed, and, if needed, to help prevent the melting or warping of the thin strip. The strip from the pre-formed core insert is easily removed after the casting sand has been loosened and the water jacket core thus removed from the solidified casting. It is therefore an object of the invention to provide method and apparatus for manufacturing engine blocks of aluminum alloy wherein cooling passages are formed in the ultra narrow interliner spaces of said block (where the usual sand cores, for all practical purposes, would typically no longer be effective to form such ultra narrow passages between the iron cylinder inserts); preferably by using only a very simple modification of conventional sand casting techniques, so as to be rendered effective in such difficult narrow spaces. BRIEF DESCRIPTION OF THE DRAWINGS Figure la is an isometric view of a reinforced core for use in forming an interliner cooling passage in an engine block (according to one preferred embodiment of the present invention). Figure lb shows a vertical section of the core shown in Figure la. Figure lc shows an end view of the core shown in Figures la. Figure 2 shows a top stylized view of an engine cylinder block with a cylindrical iron insert closely fitted into each of the cylinder bores (showing the relationship of engine parts in which the invention can effectively be practiced), the core of Figures la-c would have been positioned to below the surface of the block paralleling line B-B. Figure 3 shows a stylized vertical section (similar to a view as though taken along section line A-A of Figure 2) of a engine cylinder block (but without a cylindrical iron insert having been press fit in place yet into each of the cylinder bores) and showing core support strip (as in Figures la-c) still surrounded by sand as positioned prior to removal in the newly created cooling flow passage in each of the interliner gaps. Figure 3 A shows an enlarged sectional view taken from a portion of Figure 3 showing a core of slightly modified shape (in the upper part of the insert including a cooling flow passage sandwiched between two cylinder liners). Figure 4 shows a stylized vertical section (as along section line B-B of Figure 2) of a engine cylinder block with its internal water jacket cooling passages including a connecting cooling flow passage through the interliner space between two adjacent cylinder liners (not visible in this view). Figure 4A shows an enlarged sectional view taken from the portion of Figure 4 showing the connecting cooling flow passage through the interliner space. Figure 5 is an isometric view of the main water jacket core of a mold for forming the cooling passages of an engine block incorporating three reinforced bridging cores (according to one preferred embodiment of the present invention), with each such reinforced bridging core being joined with the main water jacket core at the respective interliner positions. Figure 6 shows a stylized vertical view of an exemplary rotary clamp-and-pick mechanism for automatically extracting the metal strip from the core of Figures la-c that remains after the casting has been formed and the sand coating loosened. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION In one preferred embodiment, the reinforced core 10 shown in Figures la-c, serves to overcome the drawbacks of the prior art by being able to maintain the required shape when sized to fit in the narrowed space between the adjacent pairs of cylinder liners 6 in an aluminum engine casting 8. This is a combination of a very thin metal support strip 12 that is coated with thin layer 14 preferably of bound sand to form a reinforced sand core 10 (the combined width of which is on the order of as small as 1 mm, and for most purposes is less than 3 mm wide, and with a vertical dimension on the order of 10-15 mm). The composition of the layer 14 can even be the same as that of the water jacket mold core 16. To the best of the applicants' knowledge (as supported by statements from the prior art previously mentioned), such very thin sand cores 10 were not heretofore possible (without the inclusion of applicants' thin metal strip 12, serving effectively as a support mandrel or armature). In one specific example of the present invention, the support strip 12 is about 0.8 mm wide by 8 to 12 mm high and 20 cm long (more or less, depending upon the dimensions of the block), with a coating of sand of about 0.2 mm thick. In this context, note that the walls of the liners 6 are typically 3 to 6 mm thick. The reinforced core 10 in this first embodiment thus comprises fabricating a sand core 10 of the desired shape (for example a rectangular shape as shown in the figures) and having internally a thin steel sheet or bar 12, or may be a stiff element made of any other material so that the thin sand core maintains its shape while the mold is filled with liquid aluminum. The thin reinforcing element 12 is preferably placed in a centered position within the sand core 10, or even a plurality of said elements 12 (not shown) may be used in several positions within the sand core, to provide strength to said core. The mold assembly (not shown, but including the water jacket mold 16) may comprise as many of the reinforced cores 10 in each of the interbore walls 18 as are deemed desirable. Once the reinforced cores 10 have been assembled in the larger mold 16, the molten aluminum is poured. At the end of the process, the bound sand structure forming the cores and the molds of the cooling channels is destroyed and eliminated by the heat of the molten aluminum whereby the channels 20 for coolant circulation is formed, including channel 20' in the thin interbore wall 18. The metallic reinforcing element 12 remaining loosely contained together with loose sand within the water passage 20' that it helped form is easily removed after the casting is solidified. This removal can be done in a number of ways; as will be understood by those skilled in the art, including such as by a jet of fluid (if the relative dimensions are appropriatae) or by the mechanism 22 shown in Figure 6. This mechanism 22 includes a guide rail 24 along which a clamping, rotating, & lifting device 26 rides in moving from the illustrated lowered clamping position to the remote "discarding" position (shown as device 26', in dotted outline). In action, the jaws 28 of the clamping head 30 fastens onto the exposed end of the strip 12, the head 30 then rotates to pull the strip 12 from the passage 20' by twisting it into a coil 12'. With the coiled strip 12' freed of the casting 8, the device 26 lifts the clamping head 30 with the coil 12' secured in the jaws 28, and then is free to travel to and drop the coil 12' at the discarding position. Although the narrow passages 20' formed webs 18 by the present invention are illustrated in Figures 3 and 6 as being adjacent the top of the cylinder liners 6, it will be understood that there can be one or more such passages 20' in each web 18 and can be placed as needed anywhere along the height of the web 18. Also as previously discussed above, in other embodiments of the invention, the coating layer 14 of the core 10 need not be formed of a conventional sand and binder, but can instead be a refractory or other coating that does not stick to the solidified aluminum and preferably after performing its mold function (as shown in Figure 3 A) is easily crumbled to permit easy removal of the now-loose layer 14' and the strip 12 from the newly formed passage 20'. The present invention can be practiced, for example, in a current process and equipment which comprises a holding furnace for liquid aluminum alloy, a source of pressurized gas, normally nitrogen, which is injected into said holding furnace for pushing upwardly said liquid aluminum alloy through a suitable connecting conduit into a gate of a mold placed on top of said holding furnace. The liquid alloy is forced to enter all the mold cavities and after the mold is filled up, the flow of liquid is stopped by a suitable device, for example a slide valve or gate and said mold is then disconnected from the holding furnace and the process is repeated for a subsequent mold to be filled up. Webs 18 having minimum widths of less than 3 mm is a preferred condition for using this invention, but the method applies as well to thicker interliner dimensions when there is a need to provide interliner flow passages by means of reinforced cores according to the present invention when conventional unreinforced cores are not effective or for any of the other reasons discussed above. *** Those skilled in the art will recognize, or be able to ascertain without undue experimentation any of the numerous equivalents to the embodiments of the invention described herein. All such equivalents are considered to be within the scope of the instant invention and are encompassed by the claims that follow. Unless otherwise explained, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including explanations of terms, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. Although preferred embodiments of the present invention and modifications thereof have been described in detail herein, it is to be understood that this invention is not limited to those precise embodiments and modifications, and that other modifications and variations may be affected by one skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

What is claimed is: 1. A method of casting an open passage in a cast aluminum product in a narrow web of a width of less than about 3mm comprising forming a reinforced coated core having at least one support strip with an coating layer effective to prevent adherence of said strip to the cast aluminum, to retain the outer shape of the core during casting, and permitting release of the strip after casting the product, and casting the said product to form said web with said passage. 2. A method according to claim 1 for casting an engine block with a water jacket; comprising using sand and binder to form said coating layer and inserting said reinforced sand coated core in the interliner space between the pairs of cylinders of the engine block and positioned to form a fluid cooling passage extending between portions of said water jacket . 3. A method according to claim 1 for casting an engine block having iron cylinder liners; wherein the strip is made of a metal that does not melt at the casting temperatures and is of a generally rectangular cross section. 4. A reinforced sand coated core comprising having a width of less than 3 mm, having a reinforcing support strip and a coating of bonded sand or equivalent.