Self-applied engine coatingsTags : coatings
Several firms now offer specialty engine coating systems for use by individual builders and engine shops for a variety of applications. Common usages include thermal barriers, dry film surface lubricants, and anticorrosion coatings. In some cases, coatings can serve two functions, such as thermal barrier finishes for exhaust systems that also act as rust preventatives when applied to a mild steel exhaust header.While these materials have been available for quite some time, reports of inconsistent performance have caused them to be dismissed by many as ineffective, or not sufficiently durable.
A lingering skepticism among hard-nosed engine builders often brought into question the actual value of something like a ceramic coating on a piston crown, or the inside of a combustion chamber. Moreover, ceramic thermal barrier coatings frequently were said to peel or flake off from the surfaces on which they were applied, further arousing suspicion. In recent years, however, several racing and motoring publications have conducted convincing “before and after” tests of performance coatings, and there is also a general perception that the most advanced teams at the highest level of the sport are now regularly using advanced coating technologies.In the area of friction reduction, for example, Teflon coated piston skirts have become very common. In addition increased lubricity, TFE also provides increased component survival time should oil starvation occur. Dry film lubrication is not limited to fluoropolymer coatings, and “wash on” thin film lubricants are also available for bearings, valve stems, buckets, and the like.Many of today’s manufacturers of high-performance surface coatings trace their origins to an aerospace background. They point to their extensive research and development programs. Today’s engine coatings are said to be easier to use than before, with some companies even offering water-based materials designed to spray on using standard HLVP equipment. All manufacturers are clear that users must adhere to proper safety precautions, particularly in regard to filters and respirators, as well as proper waste material removal.Manufacturers point out that most coating failures occur because of improper application. In particular, incomplete surface preparation appears to be the biggest culprit. Materials to be coated need to be completely decreased with a non petroleum-based solvent that will not leave even the slightest amount of residue. Aluminum surfaces, for example, should normally be blasted at low pressure with a sharp, angular media. Glass beads, or any media used for cleaning should be completely avoided, since these will close the pores on the surface of the object, thereby rendering incomplete adhesion. Sprayed thickness should normally not exceed .0015”; typically this occurs as soon as an opaque color coat is achieved. Manufacturer guidelines for baking out the coating should be followed with care, and it is wise to use a separate, calibrated, thermometer to validate oven temperature. (Baking or curing time refers to the time that the coated object is at baking temperature, not the oven cycle time.) Manufacturers say that adhering to good procedures almost invariably produces a successful outcome.For individual engine builders, this is good news. Tight rebuild schedules, especially during the racing season, often preclude the possibility of sending out components for processing. Even if the vendor has a quick turnaround capability, there is still shipping both ways, which often makes the service non-viable. Frequently this inconvenience factor is more significant than cost when a decision to coat or not coat must be made. With these new materials and processes, the choice of applying an advanced surface coat can be made on the technical merits, without regard to schedules.