1. Field of the Invention
The present invention generally relates to metal-plated automobile wheels. More specifically, this invention relates to a composite automobile wheel having a permanently attached metal-plated overlay which is formed from a high impact plastic and whose bond strength with the metal plating permits the overlay to be shaped and contoured to closely conform to the shape of the wheel without concern for the deleterious effects of heat and corrosion on the high impact plastic or the integrity of the metal plating bond.
2. Description of the Prior Art
Motor vehicles often include substantial amounts of metal-plated trim elements which provide both decorative and functional purposes. In particular, chrome-plated aluminum wheels have been very popular since the time chromium plating was first introduced, and have recently become particularly fashionable with both sports cars and prestige automobiles. Chrome-plated wheels are often significantly contoured to enhance their effect on the overall appearance of the vehicle by exploiting the highly reflective nature of the chromium surface.
However, automobile manufacturers have not generally provided chrome-plated cast aluminum wheels as original equipment on their automobiles because the porosity of the cast aluminum makes such wheels very difficult to plate. Moreover, the porosity of cast aluminum wheels results in a somewhat porous chromium plate layer which generally exhibits poor corrosion resistance to the wheel, causing the chromium plating to be susceptible to corrosion. Specifically, it is well known in the art that chrome-plated cast aluminum wheels have been unable to pass the automobile manufacturers"" corrosion tests due to the inability of the copper-nickel-chrome layer to effectively cover the porous aluminum cast wheel. As a result, chrome-plated cast aluminum wheels have been provided to the public exclusively by aftermarket suppliers who adapt expensive plating techniques to attempt to solve this problem with limited success.
To obtain better plating results, current plating practices generally entail plating only machined surfaces of a cast aluminum wheel, the machining being intended to xe2x80x9cclosexe2x80x9d the pores in the cast aluminum surface to promote a better subsurface to which the chromium may be plated. However, this approach severely limits the surfaces of a cast aluminum wheel which can be chrome-plated since known machining techniques are incapable of adequately machining deep recesses in cast aluminum wheels, such as the turbine openings formed in xe2x80x9cspokexe2x80x9d wheels. Nevertheless, the entire wheel is often chrome-plated, resulting in poor adherence on surfaces which were not machined or inadequately machined, leaving these areas highly susceptible to delamination and corrosion. Chromium plating the entire wheel also incurs up to three pounds of additional weight, which detracts from the weight advantage of cast aluminum wheels.
In addition to the adverse effects of porosity and resulting corrosion, the adhesive strength of a chromium plating must be sufficient to endure deformation of the wheel as the automobile is driven down the road, or when the automobile is involved in a collision, or strikes road debris, roadway abutments or the like. Such hazards further challenge the ability of the chromium to adhere to the wheel without cracking or delamination. One known approach to avoiding this threat is to provide an ornamental wheel cover which is attached to the wheel so as to partially isolate the wheel cover from wheel deflections. U.S. Pat. No. 3,915,502 to Connell adopts this approach, providing an annular-shaped wheel cover that is permanently attached with double-sided adhesive tape to the wheel midway between the rim and the center hub area of the wheel. The remainder of the wheel cover is spaced apart from the outboard surface of the wheel, presumably to avoid the deleterious effects of heat generated by the tire, the wheel and the brake. However, Connell teaches nothing toward improving the subsurface of a metal-plating to the wheel cover such that the metal-plating might survive an automobile manufacturer""s corrosion tests. In addition, the bulky structure taught by Connell almost completely hides or obscures the styling of a wheel, thereby significantly defeating the purpose of using a cast aluminum wheelxe2x80x94that is, the prestigious appeal associated with its appearance.
As another substitute for directly plating wheels, it is also known in the prior art to use a plastic overlay which is bonded to the outboard surface of the wheel for purposes of appearance and aesthetics. Generally, this approach is taken to allow the wheel to be designed for structural purposes, allowing the wheel""s appearance to be determined by the ornamental design of the overlay.
As taught by U.S. Pat. No. 3,669,501 to Derleth, the ornamental surface of an annular-shaped overlay is a thin plastic cover, preferably formed from acrylonitrile-butadiene-styrene (ABS), which is axially spaced away from the outboard surface of the wheel to provide a cavity between the cover and the wheel into which an adherent polyurethane foam is disposed. Derleth teaches that the polyurethane foam adhesive provides a low-density, semi-resilient reinforcement for the thin gauge plastic cover while also providing sound insulation for tire and wind noise. However, it is understood by those skilled in the art that another reason for spacing the overlay""s cover from the wheel surface is to avoid the deleterious effects of heat generated by the wheel and brake which would otherwise distort the plastic cover and delaminate any metal plating applied thereto. This is particularly true in the immediate region of the wheel hub where temperatures tend to be much higher than in the remainder of the wheel. As a result, definite styling and design limitations are associated with the use of the overlay taught by Derleth. Moreover, the styling of the wheel is obscured by the overlay. In addition, Derleth does not teach an overlay with improved adhesion between the overlay and its aesthetic treatments which might successfully pass an automobile manufacturer""s corrosion tests.
Another example of an overlay is taught in U.S. Pat. No. 4,416,926 to Maglio, which discloses adhering a wheel cover to a wheel with a resin matrix containing hollow microspheres. Similar to the teachings of Connell and Derleth, the wheel cover taught by Maglio is also axially spaced away from the wheel to avoid the wheel""s potentially high temperatures, particularly near the center of the wheel. U.S. Pat. No. 4,659,148 to Grill emphasizes this concern, teaching an overlay which is attached only to the outer regions of the wheel, while extending radially inward toward the center of the wheel a limited distance. A retainer is provided to space the overlay axially away from the center of the wheel, thus avoiding thermal conduction from the wheel center to the overlay. In contrast to Grill, U.S. Pat. No. 4,682,820 to Stalter teaches a plastic cap which completely covers but is axially spaced from the region of the wheel center. The cap relies upon an interference fit with an annular-shaped overlay to remain attached to the wheel.
In addition to their styling being significantly limited by the adverse effects of high temperatures, the ornamental plastic overlays of the above prior art all share a common disadvantage in their inability to permanently adhere a metal plating, particularly when exposed to a corrosive environment. Though the prior art fails to emphasize this aspect as a recurring problem, its existence is clear from the fact that automobile manufacturers have not to date provided chrome-plated plastic overlays as original equipment. As with the aforementioned chrome-plated wheels, metal-plated plastic overlays have been unable to pass the automobile manufacturers"" corrosion tests, and therefore have been provided to the public exclusively by aftermarket suppliers.
A wide variety of platable plastics are known. For example, unmodified acrylonitrile-butadiene-styrene (ABS) has been plated to provide decorative articles such as headlamp surrounds, and plumbing and marine hardware. Unmodified polycarbonate (PC) has been utilized as the substrate for plated motor vehicle door handles. In addition, several other plastics have been successfully plated for various decorative purposes. However, these plastics, even though platable, do not provide a satisfactory substrate if the finished article must be capable of sustaining significant impacts or temperatures. Accordingly, the use of these materials within an automobile is limited. These plated plastics are characterized by a tendency to fail at low energy levels of impact, resulting in the delamination of the chromium plating from its plastic substrate. In addition, as an extreme example, the unmodified ABS may even shatter upon impact. Thus, for a plastic to be suitable as a substrate for a metal-plated wheel cover or overlay, the adhesion between the plating and the substrate must generally have sufficient impact resistance, as well as temperature and corrosion resistance.
From the above discussion, it can be readily appreciated that the prior art does not disclose a metal-plated cast aluminum wheel whose metal plating is provided uniformly over the surface of the wheel, including the contours and deep recesses of the wheel, while also being capable of passing an automobile manufacturer""s corrosion resistance test. In addition, the prior art does not disclose a metal-plated overlay which can be permanently adhered directly to the wheel to closely follow the contours of the wheel while also being resistant to delamination of the metal plating due to corrosion, high temperatures and impact. In effect, the design requirements of such overlays restrict the location of the overlays on the surface of the wheel, while also limiting the appearance of the overlay by requiring that the metal-plated surface be axially spaced and isolated from the outboard surface of the wheel to avoid the adverse effects of the elevated wheel temperatures. Finally, the prior art has not provided a metal-plated overlay which permits the cast aluminum wheel to define the overall styling and structural appearance of the wheel, while the overlay is specifically limited to contributing the reflective character of the wheel for purposes of aesthetics.
Accordingly, what is needed is a low-cost ornamental metal-plated overlay for an automobile wheel which can be permanently secured directly to the wheel to closely follow the contours of the wheel, without needing to insulate the metal-plated surface of the overlay from the wheel and without needing to drastically limit the location of the overlay such that the overlay is isolated from the center and periphery of the wheel. As a result, styling and design flexibility would be enhanced because the overlay would be capable of closely conforming to the contours of the entire wheel surface. As such, the wheel would be permitted to define the outward styling configuration of the wheel while the overlay provides the aesthetically-pleasing reflective appearance. In addition, a metal plating or colorful paint on such an overlay would remain securely adhered to the overlay, even when exposed to adverse physical, chemical and thermal attack.
According to the present invention there is provided a method of providing a cast aluminum wheel which has the aesthetic appearance of being metal plated, even in deep recesses in the wheel, wherein the adhesive strength of the metal plating is sufficient to pass an automobile manufacturer""s corrosion resistance test. The above appearance is provided by an overlay which is characterized as being a metal-plated plastic panel which is permanently adhered directly to the surface of the wheel and closely follows the contours of the wheel, including deep recesses such as turbine openings in the wheel. The metal plating on the overlay is highly resistant to the adverse thermal environment of the wheel while also providing corrosion and impact resistance which is superior to that of the prior art. Together, the cast aluminum wheel and the metal-plated overlay form a composite metal-plated wheel that can be provided as an integral and permanent unit available as original equipment by automobile manufacturers.
The metal-plated overlay of the present invention promotes design flexibility in that the overlay is fabricated as a thin panel structure which completely and closely conforms to the contours of a wheel, including the turbine openings in the wheel. The metal-plated exterior surface of the overlay closely follows the contours of the wheel to give the appearance of being the actual surface of the cast aluminum wheel, all without concern for poor adhesion due to porosity of the cast aluminum wheel. In addition, the metal plating is highly resistant to delamination from heat such that there is no need to axially space the metal-plated exterior surface from the outboard surface of the wheel. As a result, the cast aluminum wheel""s outboard surface is permitted to define the outward shape and styling of the wheel while the overlay provides the wheel""s aesthetically-pleasing reflective appearance without appearing to be a separately formed overlay.
The composite metal-plated wheel of the present invention includes the typical structure of an automotive wheel, including a central disk portion, or wheel disk, and a rim which circumscribes the disk portion for retaining a tire. The overlay is a metal-plated plastic panel which is attached to the outboard surface of the disk portion. The plastic panel has a pair of oppositely disposed surfaces which form interior and exterior surfaces of the overlay. The interior surface of the overlay mates with the outboard surface of the wheel such that the exterior surface uniformly follows and conforms to the surrounding surface of the wheel surface, including any recesses in the wheel""s surface. The thickness of the plastic panel can be as little as about 2 to about 4 millimeters while still providing sufficient impact strength and without concern for the adverse effects that wheel temperatures have on the metal plating.
The plastic panel is preferably formed from a polycarbonate substrate which is modified with less than about 50 percent by weight of acrylonitrile-butadiene-styrene (ABS) and conditioned to increase the amount of exposed ABS at the exterior surface of the plastic panel. The exterior surface is then etched and electrochemically plated with a metal, such as chromium. Due to the thinness of the plastic panel, its metal-plated exterior surface can uniformly and closely follow the contours of the outboard surface of the wheel to provide a pleasing aesthetic effect to the wheel. The material composition of the plastic panel and the preferred plating method permit the exterior surface to be positioned in close proximity to the outboard surface of the wheel while resisting delamination of the metal plating due to heat.
According to a preferred aspect of this invention, the metal-plated overlay of the present invention provides an aesthetically pleasing, permanently attached ornamental cover to a cast aluminum wheel without the appearance of being a separately manufactured attachment to the wheel. Because the overlay conforms to the contours of the wheel, the overlay appears to be the actual outboard surface of the cast aluminum wheel. As a result, the aesthetic styling and appeal of the wheel is established by the cast aluminum wheel, whereas the overlay need only contribute the reflective surface to the wheel. Because it is permanently attached and does not appear to be an attachment to the wheel, the overlay is not prone to being stolen or accidently detached as would be other overlays or conventional wheel covers. Moreover, the wheel can be readily mounted and removed without ever having to tamper with the overlay.
In addition, the adhesion of the metal plating to the overlay is sufficient to exhibit excellent resistance to both corrosion and heat. Testing has shown that a composite wheel incorporating the overlay of the present invention can successfully pass a typical automobile manufacturer""s corrosion test so as to permit its use as an original equipment item. Moreover, the adhesion between the metal plating and the plastic panel exhibits extremely good resistance to high temperatures such that the metal-plated surface need not be spaced away from the surface of the wheel, nor is there a need for an insulating layer of foam between the metal-plated surface and the wheel. Design flexibility of the composite wheel is maximized because the overlay does not pose any significant styling limitations to the wheel as a consequence of needing to design around the high temperature areas of the wheel.
Another significant advantage of the present invention is that the overlay can cover substantially the entire visible surface of the wheel, including deep recesses in the surface of the wheel, because the porosity of the cast aluminum wheel is not a factor in the adhesive strength of the metal plating. Whereas in their application due to surface porosity cast aluminum wheels of the prior art were limited as to the coverage of the metal plating or highly susceptible to corrosion and delamination, the overlay of the present invention is able to follow the contours of the wheel, even such features as turbine openings. Yet the overlay adds significantly less weight to the wheel than metal plating the wheel itself, while also being significantly less costly.
The overlays of the prior art were also unable to provide a closely conforming reflective surface because of the need to carefully provide sufficient spacing or thermal insulation between the metal plating and the surface of the wheel. In contrast, the overlay of the present invention performs well at temperatures which may occur practically anywhere on the surface of the wheel.
The teachings of the present invention are also applicable to various wheel materials and surface treatments, including steel and magnesium wheels, polished and machined aluminum wheels, textured cast aluminum wheels and painted aluminum wheels. The surface condition of the wheel is not critical as long as an adhesive can form a sufficient bond between the wheel and the overlay.
Accordingly, it is an object of the present invention to provide an ornamental overlay for a cast aluminum wheel in which the overlay closely conforms to the contours of the wheel, such that the aesthetic styling of the wheel is provided by the cast aluminum wheel while the overlay contributes the reflective surface effect to the wheel.
It is a further object of the invention that the overlay provide maximum styling and design flexibility as to the locations on the wheel where the overlay can be secured.
It is still a further object of the invention that the overlay be capable of being permanently secured to the surface of the wheel so as to provide a composite wheel which does not have the appearance of being an assembly of two separately manufactured components.
It is another object of the invention that the overlay be formed from a suitable material which is both heat and impact resistant, and which can permanently adhere a metal plating.
It is yet another object of the invention that the overlay can be formed from a thin panel without the need to space or insulate the overlay from the wheel to avoid the adverse effects of high temperatures on the integrity of the ornamental surface.
It is still another object of the invention that the composite wheel formed with the overlay be suitably reliable in terms of corrosion resistance to be capable of being provided as an original equipment item by automobile manufacturers.
Other objects and advantages of this invention will be more apparent after a reading of the following detailed description taken in conjunction with the drawings provided.