How Ceramic Coatings Work and Common Coating Terms

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Here at Rukse Coatings the high performance coatings leader in Utah we apply only the finest and race-ready coatings. The process of applying your coatings is a very difficult and demanding process. Many customers ask us what is involved in applying ceramic coatings and how their parts are processed. Outlined below is the basic process your parts go through.

Step 1 – We remove all coatings, oils, and contaminants from the substrate with either a de-greasing chemical and/or by heating substrate to temperatures high enough to remove coatings or contaminants. Our preferred method is to burn out the parts in the oven at a very high temperature for about an hour. If the part is chromed, plated, or ceramic coated we may have to do a chemical strip before burning out the part.

Step 2 – A lightly blasted profile (~40 psi) must be applied to
the substrate to remove any rust, scale, or other coatings. This is also required to ensure maximum adhesion. We use a dry grit material such as aluminum oxide or garnet equivalent to a 100 – 120 mesh size. We do not use glass beading because it is not aggressive enough to produce a sufficient blast profile. We have perfected a process that uses a blast that is not to strong that can blast through parts and leave tiny holes in the substrate but is aggressive enough to etch a profile for the coating to adhere to.

Step 3 – The parts are then hung on wires and racks making sure not to be touched by bare hand which contain oils and acids that can deter adhesion. Parts are then moved into the coating booth to be sprayed.

Step 4 – We blow off the substrate with a high-pressure air nozzle to remove any blasting dust left on the surface. We then use a HPLV gun to spray the liquid ceramic onto the part. Our booth is well ventilated and we have several mixing areas to insure our coatings are properly maintained for spraying. We spray a light coat of about 0.1 – 0.5 mil film thickness. In some cases multiple coats are applied to your part.

Step 5 Air Dry – Parts are then re-hung on the racks carefully avoiding any contact with them, and allowed to dry for about 1 hour. The parts are then visually inspected for runs, light areas, and coating failure. If it passes inspection parts are then allowed to cure for 24 hours before they are packaged. Full cure is about 72 hours and part should not be installed before this  time.

Step 5 Oven Cure – For our oven cure coatings we generally apply two coats at a combined thickness of 2 mils. After spraying parts are inspected for coating failure and any touch ups are performed. We air-dry for 20 minutes, and then place in an oven at 175°F for 20 minutes to allow excess solvents from the coating to out-gas. We them ramp the oven up to 500°F (minimum) to 700°F. After desired temperature is reached we cure parts for 60 minutes.

Step 6 – Polishing ceramic coated products in polished aluminum; after the cure cycle is complete, we lightly buff the parts with super fine steel wool (0000 or 4/0) or scotch brite pads then polish them in a vibratory polisher for 15 to 60 minutes, depending on the shine desired. For additional shine we may due some hand and or machine polishing in areas that are not reached in the vibratory.

COATING DEFINITIONS

Annealing – refers to the changes made in a substrate after it is heated to or above its critical temperature.  For the coating world this means a reduction in the strength of substrate material. This process typically softens the metal. Heat is important for the cure of some coatings and the various substrates the coatings are applied to. Aluminum parts such as pistons and bearings are affected the most by high temperatures so we use ambient cure coatings for these types of parts to ensure the strength and integrity is still intact after coating.

Electrical conductivity – measures a materials ability to transfer electrons or conduct an electric current.  This electrical conductivity is important for the sacrificial protection ceramic metallic coatings offer to the substrates they are applied to. This provides corrosion protection and helps to prevent undercutting of the applied coating if damaged.

Emissivity – describes the ability of a material to emit energy by radiation to absorb or reject heat. Low emissivity reflects heat (highly polished silver or aluminum foil). High emissivity attracts heat (black or dull finish).

Ferrous – iron containing material that can rust or heavily oxidize with thermal cycles.

Non Ferrous – Material that doesn’t contain iron or if present in very low amounts.

Fretting – refers to the wearing or sometimes corrosion of metal by vibrations or agitation to the surface.

Galling – is a form of wear by friction and adhesion created between two sliding surfaces. Similar metals undergo galling and seize to each other. This is why softer metals are used for bearings and bushings to resist galling.  This can also be reduced by coating the contact surface where galling is most likely to occur.  Piston skirts are commonly coated to prevent galling.

Galvanic activity – the ability to transfer electrons from an anode to a cathode. This is important for sacrificial coating protection from oxidation to the substrate most commonly caused by contact between two different metals that have physical or electrical contact with each other.

Oxidation (thermal and chemical) – when a chemical change occurs in a metal substrate or other material resulting in oxide formation (rust and corrosion). Steel and iron containing substrates will have brown and red oxidation and aluminum will have white corrosion. Heat combined with the elements speeds this process up.

Passivation – refers to a material becoming a boundary layer that is less affected by environmental factors such as air or water.  Passivation improves corrosion protection of the primary coating layer. Topcoats are a form of passivation for some ceramic coatings.

Pre-ignition causes – refers to the air fuel mixture igniting before the spark plug fires.  This occurs when something else is igniting the air fuel mixture such as hot spots in the combustion chamber or on a piston, spark plug that runs too hot for the application, or even carbon deposits left in the combustion chamber that become superheated from previous combustion cycles.  This can be referred to as dieseling as well.  This dramatically increases the temperature in the combustion chamber and can result in damage to pistons, valves and springs, crank, etc.

Sacrificial – A materials ability to transfer protective electrons to a substrate to prevent undercutting and corrosion from forming on the interface of the substrate material and the protective layer.  Some ceramic coatings offer this protection to the substrates they are applied to.

Thermal conductivity – refers to a materials ability to transfer heat. Materials of high thermal conductivity transfer heat faster than materials of low thermal conductivity.  Low thermal conductivity is good for insulation benefits and ceramic coatings offer this insulation. This can help reduce under hood temperatures.

Thermal fatigue – occurs on steel substrates when carbon is being lost from the steel through loading and unloading of an engine resulting in cracks, pitting and scale formation (rust).  Also referred to as thermal cycling.

Care and Maintenance

There is maintenance required on certain coatings. The polished aluminum ceramic coating requires constant care and cleaning. If anything gets on the polished finish like water, road grime, oil, etc. the coating will need to be cleaned and polished with soap and water and an aluminum polish. Be sure not to use anything abrasive to clean the polished finish. All of the other coatings don’t really require any maintenance besides a spray off and wipe down with a rag. If anything gets on the black ceramic coating, High Temp, or powder colors you cannot use anything abrasive to clean them or you run the risk of scratching the coating.

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