Patent Application
20110266157
The present invention relates generally to vehicle wheels. More particularly, it is concerned with wheels for trucks and other utility vehicles and wear resistant coatings and methods for applying said coatings.
Vehicle wheels can experience a degree of wear deleterious to their immediate and long-term function due to their extended and rigorous use during and through the operation of motor vehicles. One mechanism by which said wear occurs is the extended frictional contact between the tire mounted on the wheel and the wheel itself. This occurs due to sliding between the tire and wheel, creating consequent abrasion, adhesion, and other wear issues. This problem is particularly acute when dealing with large trucks and other utility vehicles. It is further exacerbated where wheels are used on and with military vehicles, where the degree of wear and tear experienced due to operation for extended periods in harsh conditions can lead to premature wheel wear and/or failure.
Possible solutions for the aforesaid problem include the use of stronger more durable materials in forming wheels, and providing wear resistant coatings between wheels and tires. Providing wheels formed from steel is one obvious approach to the problem of creating more durable wheels. However, though steel wheels are inherently more wear resistant, they have been largely replaced by aluminum wheels due to the lighter weight of the latter. (Steel has 2.8 times the density of aluminum). Anodizing can be used to make aluminum itself more wear resistant. Unfortunately, some types of anodizing can reduce fatigue strength of the metal by up to 50%. Application of wear resistant metallic or ceramic coating has also been tried. (See, e.g., U.S. Pat. No. 6,872,425). However, prior art coating materials/methods, such as those described in the '425 patent, are expensive, complex, and may include or require pre-coating preparation such as mechanical roughening, knurling and/or abrasive grit blasting. Thus, a definite need exists for further advances in the field of wear resistant wheel coatings and methods capable of protecting vehicle wheels from wear and corrosion, particularly from such wear and corrosion as arises from wheel/tire frictional contact, and even more particularly from such wear and corrosion in truck, utility and military vehicle wheels formed from aluminum.
This need is met in a novel and non-obvious way by the method and coating of the invention, which in its most basic embodiments, involves the addition of a slip agent to an appropriate wheel coating. In its more preferred embodiments, the slip agent is one that will not adversely impact intercoat adhesion in a multi-coat wheel coating system. And, in its most preferred embodiment, as discussed in detail herein, the slip agent is included in an intermediate coating applied between a wheel's primer and topcoat. More particularly, the intermediate coating is comprised of a MIL-P-53022 Type I or Type II lead and chromate free, corrosion inhibiting epoxy primer with an addition of 3% polytetrafluoroethylene (PTFE), and is preferably applied to the wheel intermediate the primer and topcoat in accordance with the chemical agent resistant coating (CARC) system used on tactical military equipment.
The foregoing drawing figures are exemplary and not limiting in terms of the scope and application of the invention, which can be used and applied without limitation as to wheel type. However, they do serve to illustrate a typical and advantageous area for the use and application of the coatings of the invention, namely the interface 100 between flange sections of rim portions 5 and the beads of tubeless tires 3. This can advantageously be accomplished, given the fact that one the principal intended fields of use for the invention is on the wheels of military vehicles, in accordance with the coating system applicable in the military field. Application of a chemical agent resistant coating (CARC) system on tactical military equipment consists of four distinct steps: cleaning, pretreating, priming, and topcoating. The cleaning and pretreating procedures are standard methods required in any finishing process. The anticorrosive primers are epoxies or Chemical Agent Resistant Cathodic Electrodeposition Primers (MIL-P-53084), and the topcoats are Chemical Agent resistant Aliphatic Polyurethane Coatings (MIL-C-53039). No additional preparation to the vehicle wheel is required beyond priming.
In accordance with the teachings of the invention, it has been determined that there are numerous products that can act as a slip agent that can be added in suspension form (as liquid or powder) to a wheel coating. Generally, any chemically compatible, low static friction coefficient material that is non-adhesion blocking can be used for this purpose. For example, in the MIL-P-53022 liquid coating, cryo-ground polypropylene powder will toughen the surface and add slip as well. Molybdenum disulfide at low concentrations can also be used and has an extremely low coefficient of friction. Likewise, most polyeolefins can be beneficially used in this context to toughen the coating and lower wear rates significantly. However, polytetrafluoroethylene (PTFE) is deemed to be the most advantageous for the purposes of this invention because of its high melting point for powders (co-extruding) and cryogrind capabilities for wet applications. The wear resistant coating of the invention, typically about 0.001-0.005 inches thick (i.e., 1.0 to 5.0 mils in dry film thickness (“DFT”)) is applied by spraying subsequent to the e-coat primer and prior to the CARC topcoat. The system is then cured accordingly.
The preferred PTFE coating of the invention was applied to samples of aluminum vehicle wheel material in accordance with the method of the invention. Modified Taber abrasion testing was then performed on the samples in accordance with American Society for Testing and Materials (“ASTM”) standard ASTM D4060 for use in testing organic coatings with a Taber Abraser. Taber abrasion testing is done to test a material's resistance to abrasion using a Taber Abrasion Apparatus (or Abraser). Resistance to abrasion is defined as the ability of a material to withstand mechanical action such as rubbing, scraping, or erosion. Abrasion can be difficult to compare, but weight loss is one criterion and is reflected in
Limitations with regards to the addition of PTFE is constrained only by methods of suspension prior to and during application and the intercoat adhesion between the primer MIL-P-53084 and the top CARC coating. The wear resistant intermediate coating requires uniform application as well as top coating while still within the curing pot life to maximize intercoat adhesion between the wear resistant coating and the CARC top coating. In cases where such an application method is not possible, the wear resistant coating may still be recoated after full cure and after light mechanical abrasion. In either case the wear resistant properties are not affected.
The wear resistance coating is advantageously formulated in such a manner so as to allow “wet on wet” application over a cured MIL-P-53084 primer. This application method improves adhesion through surface to surface covalent reaction between the polymerization of polyurethane top coat and the polymerization of intermediate epoxy polyamide wear resistant coating. The wear resistant primer may be used by itself over steel wheels that have been pretreated to TT-C-490, and may be used over anodized, electrocoated, or DOD-P-15328 wash primed aluminum as a standalone non-CARC wear resistant coating. The coating may be pigmented to a color other than buff white in non military applications.
The previously described advantages and features of the invention are advantageously provided through and using the preferred embodiment previously illustrated and discussed for the invention's method of coating a vehicle wheel to increase wear resistance, which includes the steps of providing a vehicle wheel and applying a wear resistant coating at least one of containing polytetrafluoroethylene (PTFE), over an initial primer, and under a topcoat. The wear resistant coating is applied to at least the tire bead flange of the vehicle wheel but may be applied to any area of the wheel where CARC top coating will subsequently be applied. The wear resistant coating is of particular use with vehicle wheels made from cast or forged aluminum, but can be used with wheels formed from other materials such as steel or magnesium. The wear resistant coating is, as previously noted, advantageously comprised of a MIL-P-53022B Type II lead and chromate free, corrosion inhibiting epoxy primer with an addition of 3% polytetrafluoroethylene (PTFE).
However, numerous variations may be possible without deviating from and/or exceeding the spirit and scope of the invention, which includes generally the addition of a slip agent that can be added in suspension form (as liquid or powder) to a wheel coating, as well as the particular slip agents named herein. Thus, the invention includes the use of such slip agents intermediate or as part of any coat/layer of a single or multiple coat system. Moreover, various features and functions disclosed above, or alternatives thereof, may be desirably combined into many other different systems or applications. Further, various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the claims when filed.
