When one thinks of automotive lubricants, motor oils and bearing greases naturally come to mind. Yet, all automobiles use a different type of lubricant that works like no other. It is quietly tucked away beneath the hood and slipped between interior materials, in operator controls, under seats, atop seals and right down to the vehicles nuts and bolts.
Anti-Friction Coatings, also known as dry-film bonded lubricants, are proven, effective surface treatments that provide lubrication in a variety of vehicle design and assembly applications. In almost every vehicle in the European market, whether for transporting people or moving cargo, Anti-Friction Coatings are used as high-performance, long-lasting materials that optimize friction and wear control.
These lubricants are clean, dry and nontacky. And they withstand extreme heat in the engine compartment, carry heavy loads, quiet squeaks and rattles, and help ensure proper fastener tightening. As a result, Anti-Friction Coatings are widely used in specialty lubrication jobs in all passenger car segments from mini-cars to luxury makes to sport coupes; in multipurpose cars and sport utilities; in pickup trucks and commercial vehicles; and on motorbikes, tractors and construction equipment.
Unlike typical petroleum-based oils and greases, antifriction coatings are synthetics with surface-active solid lubricants. They work without concerns about staining clothes or interior fabrics. And they resist the effects of dust, dirt and water wash out.
How Anti-Friction Coatings Work
Sometimes called lubricating paints, Anti-Friction Coatings combine submicron-size particles of solid lubricants blended with resin binders, solvent carriers and a small amount of additives. When applied, the coatings form a clean and dry slippery film that fills surface asperities and smooths surface roughness. The solids can be precisely engineered to provide a consistent coefficient of friction for durable, long-lasting lubrication, unaffected by a host of factors that can degrade conventional lubricants.
Typical solid lubricants include molybdenum disulfide, graphite and polytetrafluoroethylene. The resins can be epoxy, polyamideimide, phenolic, polyurethane or a host of other materials. They help bind the solids to the surfaces and provide some corrosion protection.
The solvent can be solvent- or water-based and serves as a carrier for the coating application and film-building. It evaporates away during cure. Additives are used to impart special properties to the coating or surface.
Oils and greases provide hydrodynamic lubrication to keep opposing surfaces separated, but Anti-Friction Coatings provide lubrication under boundary and mixed-film conditions. The coatings typically outperform oils and greases under heavy loads, at lower speeds and across a much wider temperature range. Maximum loads can be as high as 1,000 Newtons per square millimeter with peaks up to 2,300 N/mm2. Temperature range is minus 40 to +300 degrees C depending on the coating.
Other key advantages of antifriction coatings include:
Dry, clean lubrication uncompromised by dust, dirt or moisture;
Lifetime lubrication without aging, evaporation or oxidation;
Corrosion and rust resistance;
Nonflammable, nonstaining lubrication on metals and plastics;
Controlled film thickness for exact load-carrying capabilities; and Fully effective lubrication, even after prolonged shutdown.
Where to Use Anti-Friction Coatings
While Anti-Friction Coatings typically contain molybdenum disulfide, graphite or PTFE lubricating solids, depending on the application, formulations can be engineered with other solids to meet custom performance requirements. Selection criteria are based on operating conditions, coating method and specific needs of the application.
Solid-film bonded lubricants can be used across the whole spectrum of modern vehicles, including construction and off-road equipment. Application areas include vehicle powertrains, chassis and brakes, body and lighting parts, interior parts and electrical/electronic components.
Powertrain: Anti-Friction Coatings can be applied to piston skirts and rings to help reduce engine noise, scuffing and wear. Increased fuel efficiency and reduced emissions are added benefits. The process applies to gasoline and diesel engines for all types of vehicles. The coatings also can be used to boost fuel efficiency while quieting noise on two-wheel vehicles.
Anti-Friction Coatings also help reduce camshaft and tappet friction and wear. Coated exhaust manifold gaskets can eliminate the ping in exhaust systems. Coated cylinder head gaskets are easier to remove. Wear and maintenance can be reduced on tractor clutch tubes and control cables.
Chassis and Brakes: Anti-Friction Coatings are used to optimize friction to reduce noise and wear on brake-pad retainer clips in several car and light-duty truck programs. Other coatings protect spindles and unlocking pins on electric hand brakes. The same lubricants can be used on two-wheelers, tractors and construction equipment to provide wear and corrosion resistance.
Body and Lighting: Colorless, non-staining Anti-Friction Coatings are used on seals for doors and retractable rooftops. These coatings enhance tactile feel and help deliver smooth-operating outside mirrors, antennas and auto-adjusting lighting systems. They lubricate and protect against corrosion, binding and seizing on locking, latching and lever mechanisms on hoods, doors, trunks and lift gates. Anti-Friction Coatings also can help extend the life of window and door seals.
Interior: Anti-Friction Coatings are especially effective and used throughout the custom-tailored interiors of todays vehicles. They add a velvety touch to sunroof guides, cupholders and media controls. Some lubricate and protect seat belt actuator parts and anchor bolts; others coat and protect seat guides, tracks, locking mechanisms and anchor bolts. Anti-Friction Coatings help eliminate stick-slip squeaking from materials used for door and seat trims, instrument panels, consoles, glove boxes, clips and fasteners. Colorless, nonstaining lubricating films muffle noise and add smoothness to sun visors, mirrors and adjustable headrest slides.
Electrical/Electronics: Anti-Friction Coatings are routinely used to quiet and smooth the operation of fingertip switches, smart actuators and component controls. They are especially effective for miniature motors with plastic gear sets as well as for climate-control components and outlets. These Anti-Friction Coatings also are used to lubricate starter magnet anchors, while reducing fretting and preventing corrosion.
Application Methods
Like most engineered materials used in vehicle design and assembly, Anti-Friction Coatings have some application best practices to maximize their effectiveness and service life. These include surface or component pretreatments, specific types of application processes and proper curing to secure the coatings in place.
Pretreatment may include degreasing, phosphating, sandblasting, anodizing or acid washing. Degreasing can be done with solvents and either alkaline or neutral detergents. Phosphating can be used on steel and zinc plating, acid washing on stainless steel, and anodizing on aluminum.
Dry sandblasting can remove dirt and rust as well as roughen the surface to increase adhesion strength of the coating. Most importantly, the surfaces must be dry, clean and grease-free before the coating is applied.
Application methods can vary from manual or electrostatic spraying, brushing or dipping to more sophisticated methods such as screen printing, centrifuging (dip spinning) or roll coating. The size, shape, weight and quantity of parts being coated determine the method selected. Film thickness and sliding-surface requirements are others factors. While Anti-Friction Coatings are considered economical lubricants, the application process can contribute considerably to the per-part lubrication cost.
Pre-applied coatings typically are heat cured for up to one hour in circulation ovens, or in less time with infrared or induction systems. Air-cured Anti-Friction Coatings are often applied during vehicle assembly and require as little as three minutes to dry.
Different application methods provide varying results, depending on the coating. Each method has certain selection parameters, advantages and disadvantages, as shown in the Coating Application Methods Chart.