BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a perspective view of a cylinder liner according to the present invention.
FIG. 2 shows a treatment process and apparatus according to the present invention.
FIG. 3 shows an exploded view of the surface of a cylinder liner during a process according to the present invention.
FIG. 4 schematically shows a cylinder liner according to the present invention cast into an engine block.
FIG. 5 shows an exploded view of a surface of the cylinder liner according to the present invention when cast into the engine block.
FIG. 6 shows a photomicrograph of a surface at 100 times magnification of a centrifugal cylinder liner cast-in an aluminum block utilizing prior art
FIG. 7 shows a photomicrograph of a surface at 100 times magnification of a cylinder liner according an embodiment of the present invention cast-in an aluminum block.
FIG. 8 shows another photomicrograph of a surface at 100 times magnification of a cylinder liner according an embodiment of the present invention cast-in an aluminum block.
FIG. 9 shows still another photomicrograph of a surface at 100 times magnification of a cylinder liner according an alternate embodiment of the present invention cast-in an aluminum block.
FIG. 10 shows a photomicrograph of the surface of FIG. 9 at 400 times magnification.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
DETAILED DESCRIPTION OF THE INVENTION
The subject matter under consideration is a cylinder liner having a grit blasted exterior surface of the cylinder liner to form a rough surface exterior on the liner for the purpose of providing a firm bond between the cast iron cylinder liner and a block made up of a casting material, such as aluminum, into which the liner is cast. The bond between the roughened cylinder liner surface and the block cast around the liner preferably takes the form of a mechanical bond, with the cast aluminum material being trapped within the cavities of the rough exterior of the grit blasted iron liner.
The process involves machining the outside surface of the cylinder liner to remove any undesirable microstructural surface effects. The liner with the machined outside diameter is then uniformly grit blasted over a preselected portion of the outside surface, that is, the entire outside surface or a specific portion of the surface to provide small voids and/or cavities that serve as backdrafts for subsequent mechanical bonding with the aluminum block that is cast around it. Backdrafts, as used herein, are areas or cavities into which molten casting material may enter and/or is drawn, wherein at least one surface of the area is at an angle to the surface of the cylinder liner that provides mechanical interlocking sufficient to form a mechanical bond.
The present invention preferably includes grit blasting static cast cylinder liners that have been machined to remove any surface effects and/or defects. Static casting, often referred to as conventional sand casting, involves an expendable blend mold typically formed from mold segments and an optional mold core or other apparatus that forms the interior surface of the cylinder liner. The use of the static casting process with its insulating molding material on the inside and outside surfaces of the castings assist in providing a cylinder liner having a substantially uniform microstructure.
Although the static cast cylinder liner is preferred, the present invention may also be utilized on centrifugally cast or cylinder liners manufactured using other known methods, wherein undesirable microstructure surface effects may be present.
FIG. 1 shows a cylinder liner 100 according to the present invention. The cylinder liner 100 includes an inner surface 103 and an outer surface 105, forming a cylinder. The outer surface 105 is a surface suitable for contacting casting material during a cast-in process. The outer surface 105 is preferably machined to remove any surface effects from the casting process and/or remove any surface defects. The machining may take place using any known machining process suitable for use on the outer diameter surface of cylinder liners. A preferred machining process includes dry machining of the surface, wherein the machining takes without the use of chemicals or lubricant compositions. Dry machining provides surfaces that have little or no contamination.
FIG. 2 shows a cylinder liner 100 being subject to grit blasting according to an embodiment of the invention. A grit-blasting device 201 is arranged and disposed to direct grit particles 203 toward outer surface 105 of the cylinder liner 100 in direction 202. The grit particles 203 suitable for use with the present invention include a size, shape and density that, when forcefully contacted with the cylinder liner outer surface 105, form cavities 301 on the surface of the cylinder liner. In addition, the grit blasting device 201 utilized to accelerate the grit particles 203 provides grit velocities and angles to the cylinder liner surface that provide cavities 301 on the surface having desired geometry. The grit blasting process of the present invention includes directing abrasive grit particles 203 accelerated by compressed air or other media or mechanically thrown against a surface. The high-speed particles remove material from the surface, roughening the surface and form cavities 301. Grit useful for the present invention includes, but is not limited to steel grit, aluminum oxide, silicon carbide, garnet, crushed ceramic material and combinations thereof. Unlike shot, grit has a geometry including sharp angles that are capable of ejecting material present on the surface of the cylinder liner 100. While the geometry is not specifically limited, the grit particles 203 should have a geometry with sufficiently sharp angles to provide the surface with cavities having the desired geometry. Grit suitable for use with the present invention preferably has a size of about 0.125 to about 2.8 mm. A preferred grit particle 203 size is from about 1.70 mm to about 2.36 mm. Likewise, the grit particles from about 6 Moh to about 9 Moh, preferably has a hardness of from about 8 Moh to about 9 Moh. In a preferred embodiment of the present invention, the grit is steel grit, corresponding to SAE Standard G12, wherein the SAE Standard is the standard set forth by the Society of Automotive Engineers in document number J444, dated July 2005.
In another embodiment of the present invention, mixtures of sizes and/or types of grit particles 203 may be used to produce desired cavity 301 geometries. The cylinder liner 100 is rotated in a direction 205 at a speed sufficiently slow to provide sufficient grit particle concentration to form the desired cavities on outer surface 105, and sufficiently fast to prevent or eliminate erosion of cavities previously formed. Likewise, the grit blasting device 201 may be advanced along the surface of the cylinder liner 100 in direction 207 to expose additional surfaces to the grit particles 203 directed from the grit blasting device 201. As shown, the grit particle 203 contact outer surface 105 and eject cylinder liner material 204.
FIG. 3 shows an exploded view from area 211 of FIG. 2. As shown, the grit particles 203 are directed from the grit-blasting device 201 at a predetermined contact angle 303 to the cylinder liner outer surface 105. Once the grit particles 203 contact the surface, at least a portion of the material at the surface is ejected as ejected particles 204. Cavities 301 are exposed as from the locations formally occupied by the material of the ejected particles. The contact angle 303 is an angle that provides cavity 301 formation by producing ejected particles 204, and allows the grit particles 203 to deflect off the outer surface 105 for potential collection and reuse. Contact angle 303 is preferably from about 55° to about 85°. In a preferred embodiment of the invention, the contact angle 303 is about 70°. The cavities 301 formed on the cylinder liner outer surface 105 provide spaces into which molten casting material may enter and solidify. In addition to the velocity of the particles and the contact angle 303, the grit-blasting device 201 is configured to provide a contact time that reduces or eliminates the erosion of formed cavities 301. The contact time is preferably limited by moving either or both of the cylinder liner 100 or the grit blasting device 201 with respect to each other in a manner that provides controlled grit particle 203 concentration on areas of the surface requiring cavity formation. Likewise, the movement of the cylinder liner 100 or the grit-blasting device 201 is such that the overlap in areas in which cavities are formed is minimized to prevent or eliminate erosion of cavities 301 previously formed.
The process of the present invention modifies the outer surface 105 of a cylinder liner 100 in a controlled manner so that the surface has a specific, controlled geometry that results in small back drafted cavities 301 peppered on the outer surface 105 of the liner. The cavities 301 formed, according to the present invention, have a geometry that includes surfaces within the cavities that are non-perpendicular to the surface of the cylinder liner 100. Specifically, the cavities specifically have side surfaces that are angular (more or less than 90°) with the outer surface 105 of the liner (i.e., the surfaces are undercut). These cavities 301 are subsequently filled with molten casting material during casting of the block and provide mechanical bonding between the block material and the cylinder liner 100. The non-perpendicular surface of the cavities 301 provides a surface onto which a mechanical bond between the cylinder liner 100 and the casting material may be formed. Specifically, the cavities 301, including the non-perpendicular surfaces, provide a surface of the cylinder liner 100 which interlocks the material of the cylinder liner and the casting material, wherein forces may be transferred from the casting material to the non-perpendicular surfaces of the liner, creating an adherent bond.
In another embodiment of the invention, a preselected portion of outer surface 105 that is grit blasted only partially covers the outer diameter of the liner with a roughened surface. This embodiment provides bonding at the preselected portions of the liner wherein bonding with aluminum are most important to provide the necessary bond, while minimizing the time cycle and cost of grit blasting.
The use of a grit blasting process to roughen the surface permits the surface to be machined to have a metallurgical microstructure that is substantially uniform across the surface and through the thickness. This uniformity is not achievable in other process, such as centrifugal casting, wherein the castings are typically utilized as-cast. Likewise, static cast liners are likewise typically cast into engine blocks in their as-cast form. The uniformity from the machining prior to grit blasting, among other things, permits the liner to have a reduced thickness as compared to liners with as-cast surfaces, is more easily machined due to its uniform desired microstructure compared to liners with as-cast surfaces and provides a consistently more desirable metallurgical structure at the wear surface of the cylinder liner in operation of the engine. Further, the machining permits a reduction in the number of defective parts. For example, if a centrifugal or static cast liner formed by a known has been rejected due to undesirable grain structure at the surface or a surface defect, the process of the present invention may be utilized to machine the undesirable grain structure at the surface or a surface defect away and grit blast the surface to provide a surface that provides a strong mechanical bond when cast in the aluminum block.
During a cast-in-place process, the cylinder liner is positioned in a mold. A molten metallic material is injected into the mold and permitted to solidify. The molten material preferably has a melting temperature less than the melting temperature of the cast iron. The grit blasted surface includes pores into which the metallic material enters and solidifies. The molten metal may infiltrate the cavities 301 by any suitable means, including, but not limited to, simple mass flow, capillary action, wicking or any other molten casting material flow mechanism.
FIG. 4 shows a cylinder liner 100 that has been cast-in an engine block 401. As discussed above, the molten metallic casting material, preferably aluminum or aluminum alloy, is injected into the mold and permitted to solidify. Casting material infiltrates the cavities 301 of the cylinder liner surface 105 and forms a mechanical bond.
FIG. 5 shows an exploded view of area 403 of FIG. 4. As shown, the solidified casting material is present in cavities 301, wherein the cavities 301 have a geometry that provides an adhesive force, resulting from, among other factors, to the non-perpendicular surfaces of the cavities 301, which do not permit disengagement of the engine block 401. The cylinder liner 100 is adhered to the engine block 401 via a strong mechanical bond. While not wishing to be bound by theory, it is believed that the primary bond is mechanical, wherein metallurgical bonds between the roughened cast iron surface and the cast-in aluminum may be present.
FIG. 6 shows photomicrograph of a surface 105 of a cylinder liner 100 cast into an aluminum block 401 at 100 times magnification according to a process known in the art. This is an example of an as-cast outside bonding surface of a centrifugal liner cast into an aluminum block. This photomicrographs illustrates the presence of residual refractory coating material 601 embedded in the outside surface of the cylinder liner preventing intimate contact between the iron and the aluminum. The photomicrograph in FIG. 6 also illustrates the presence of undesirable microstructures near the surface of the as-cast bonding surface of the cylinder liner.
FIG. 7 shows a photomicrograph of the surface of a cylinder liner 100 at 100 times magnification according to an embodiment of the present invention. FIG. 8 shows another photomicrograph of the surface of a cylinder liner 100 at 100 times magnification according to an embodiment of the present invention. FIG. 9 shows a photomicrograph of the surface of a cylinder liner 100 at 100 times magnification according to an embodiment of the present invention. FIG. 10 shows a photomicrograph of the surface of a cylinder liner 100 shown in FIG. 9 at 400 times magnification. The as-cast cylinder liner 100, as seen in each of the photomicrographs shown in FIGS. 7-10, has a machined surface that is subsequently grit blasted to form cavities 301 and is placed into an engine block mold, wherein an aluminum containing casting material is provided to the mold and allowed to solidify. As seen in the photomicrographs, the surface 105 of the cylinder liner has cavities 301 into which the casting material of the aluminum block 401 may flow into to form a mechanical bond. These photomicrograph illustrates the clean surface of the cylinder liner providing intimate contact between the cast iron and the aluminum. These photomicrographs also illustrate the presence of desirable microstructure of the cast iron at the bonding surface of the cylinder liner using the present invention.
EXAMPLE
A cylinder liner according to the present invention was prepared. A cast iron cylinder liner 4.0 inches long and having an outer diameter of 3.5 inches was machined to provide an outer diameter substantially free of surface effects. A grit size G12 was delivered at an angle of 70° with compressed air delivery of 90 psi through a 0.25″ nozzle located 9.0″ away from the surface of the liner. The cylinder liner was rotated at about 60 RPM as the grit was sprayed uniformly along the surface of the liner. The process was continued for about 30 seconds to cover the outer diameter surface of the liner. The cylinder liner 100 produced included cavities peppered along the surface of the outer diameter.
While the above has been described with respect to cylinder liners 100 and engine blocks 401, the process of the present invention may also find use with cast-in articles requiring strong mechanical bonds and substantially uniform composition and microstructure in the cast-in article.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
Patent Application
20070277771
