Coating Glossary

A

ABRASION: wearing, grinding, or rubbing away by friction.
ADDITIVE: a substance added to a formulation in relatively small amounts to impart or improve desirable properties or suppress undesirable properties.
ADHESION: the bond strength of a coating to the substrate whether metallic, nonmetallic, plastic or rubber.
ALKALINE WASH: cleaning process that employs a high ph solution (caustic). a good choice for parts with little buildup of contaminants.
ALUMINUM OXIDE: hard particulate medium used in grit blasting to clean and roughen surfaces that are to be coated.
ANODIZING: creating a hard surface on aluminum parts via electrolytic process. unsealed anodized surfaces have a porosity that makes them excellent substrates for coatings.

B

BINDER: tough polymer that acts as an adhesive to join elements of matrix coating.
BREAK-IN: initial wear of mechanical components when large surface asperities can cause high friction and wear rates.
BURN-OFF: a method of removing a coating. temperature is elevated above the degradation point of the coating and held there until the coating breaks down.
BURNISHING: process of polishing a cured coating to improve release and low friction.

C

CARRIER: the liquid portion of a coating (solvent or water) in which solids are dissolved or suspended.
COEFFICIENT OF FRICTION: a number expressing the amount of frictional effect: static or dynamic.
COLD FLOW: tendency of plastic materials to migrate slowly under heavy loads and/or over time.
CONDUCTOR: material that can support flow of electric current. fluoropolymer coatings are normally insulators, but can be modified with certain fillers and pigments to make them conductive.
CORROSION: process of metal decomposition (oxidation) in which metal ions are united with oxygen to form metal oxides. fluoropolymer coatings provide excellent barriers against corrosion.
CROSSLINKING: quality of thermosetting plastic resins in which polymer chains combine during the curing process. in general, the greater the crosslinking, the tougher and more chemically resistant the coating.
CRYOGENIC: relating to very low temperatures. temperatures less than -130°c/-200°f, bonded dry film lubricants continue to perform at these temperatures.
cure end point: the point either during or following the cure schedule at which the coating film is determined to have developed specified properties.
CURE SCHEDULE: the time/temperature relationship required to cure a coating.
CURE TEST: a solvent rub testing using mek or other solvent to test the coating for completeness of cure base on no attack of the solvent on the cured coating after a specific amount of rubs with a q-tip.
CURING: process of bonding or fusing a coating to a substrate with heat and developing specified properties in the coating.

D

DFT: dry film thickness.
DIELECTRIC STRENGTH: ability of a coating to resist the passage of electric current.
DIP/SPIN: coating application technique in which small parts are placed in a basket that is lowered into a coating bath, then raised and spun to remove excess coating. an economical system for coating high volumes of parts.
DRY(SOLID)LUBRICANTS: solid materials such as ptfe, moly disulfide, teflon® and graphite that have low coefficients of friction.

E

ECTFE (ETHYLENE CHLOROTRIFLUOROETHYLENE): known by the trade name halar® . ectfe has excellent chemical and mechanical properties, impact strength, flame resistance and high purity.
EDGE COVERAGE: a coating’s ability to flow over, build and adhere to sharp corners, angles and edges.
ELECTROSTATIC SPRAY: a deposition method of spraying and charging a coating so that it is deposited on a grounded substrate. a spray application process in which the coating and part to be coated are oppositely charged; process provides excellent “wrap” of coating around the part, even on sides opposite the spray gun.
ENGINEERING PLASTICS: plastic resins that have high-performance properties such as high temperature stability, hot hardness, abrasion resistance and corrosion resistance.
ETFE (ETHYLENE TETRAFLUOROETHYLENE): a thermoplastic member of the fluorpolymer family. etfe is noted for exceptional chemical resistance, toughness and abrasion resistance.

F

FARADAY CAGE EFFECT: repulsion of charged particles because of the part’s concave shape. charges build at the entry area, preventing penetration into the cavity.
FEP (FLUORINATED ETHYLENE PROPYLENE): a thermoplastic member of the fluoropolymer family. fep has excellent nonstick and non-wetting properties.
FINAL CURE: the final time and temperature required to complete the final cure, sintering, melt flow or crosslinking of a coating.
FILLERS: pigments and other solids used to alter properties of coatings.
FLASH POINT: the lowest temperature at which a solvent will generate sufficient vapors to ignite in the presence of heat.
FLASHING: a brief sub-cure (at lower temperatures than the final cure) to drive off solvents or carriers prior to full cure. this helps prevent bubbling or blistering.
FLOCKING DEPOSITION: a deposition method of applying powder by spray to a substrate heated above the melt point of the powder.
FLUIDIZED BED COATING: a method of applying a coating to an article in which the article is immersed in a dense-phase fluidized bed (a fixed container in which powder is aerated) of powdered resin. preheated objects may be coated by dipping directly into the fluidized powder. in an electrostatic fluidized bed the part is usually not heated but is charged and passed through a fluidized bed of powder which has the opposite charge.
FLUOROPOLYMERS: family of engineering plastics containing fluorine, characterized by high thermal stability, almost universal chemical resistance and low friction.
FRETTING: wear phenomenon caused by vibration among tightly clamped or fastened surfaces.
FRICTION (DYNAMIC): resistance to continued motion between two surfaces; also know as sliding friction.
FRICTION (STATIC): resistance to initial motion between two surfaces.
FUSION: the melting and flowing of heated polymer particles to form a continuous film.

G

GRAPHITE: a carbon-based dry lubricant that is preferred for high-temperature applications.

H

HOT HARDNESS: ability of coating to retain hardness and wear resistance at elevated temperatures. usually a characteristic of coatings based on thermosetting resin binders.
HVLP (HIGH VOLUME, LOW PRESSURE): a spray technique utilizing high pressure in combination with low air velocity to increase transfer efficiency and reduce air pollution.
HYDROGEN EMBRITTLEMENT: embrittlement of carbon steel caused by absorption of atomic hydrogen in plating, pickling or acid cleaning processes.

I

INTERCOAT ADHESION: a coating’s ability to adhere to previously applied films, including primers.

M

MATRIX COATING: one in which some ingredients, such as the lubricant (ptfe), which is soft, are enveloped in others (the matrix, such as the harder, more wear-resistant binders). also referred to as “resin bonded coating”
MELT POINT: the temperature at which a polymer particle will begin to melt and flow.
MICRO-INCH: µ inch, a millionth of an inch.
MICRON: µ, one micron, one millionth of a meter. also expressed as µm or micro-meter.
MICRON: as commonly used in the coating industry, is equivalent to 1/25th of a mil, i.e. 25 microns are equivalent to one mil of coating thickness, or one mil of coating is equivalent to 25 microns.
MIGRATION (OF LUBRICANT): characteristic of any lubricant which is under pressure to move away from bearing area.
MIL: one thousandth (0.001) of an inch (25.4 microns). most common non-metric measurement of coating thickness.
moly, moly disulfide, molybdenum disulfide, mos2: four names for the same naturally occurring substance that has good low friction and high load-bearing properties.

N

NOISE REDUCTION: the absorption of sound vibrations. fluoropolymer coatings form good noise dampening surfaces.

O

OLEOPHOBIC: repels oil. oil does not wet out on the surface of coating but beads up on it.
ORANGE PEEL: the varying degrees surface roughness of finish similar to that of an orange.

P

PARTIAL CURE: process sometimes utilized when multiple layers of fluoropolymer coatings are to be applied. the first coat is incompletely cured; the second is applied and both are fully cured together.
PENCIL HARDNESS: a value determined by measuring the relative hardness of a coating based upon the ability of the coating to resist penetration and gouging by pencil lead of varying hardness. the order of pencils from softest to hardest is 4b, 3b, 2b, b, hb, f, h, 2h, 3h, 4h, 5h, 6h, 7h and 8h. the hardness rating of the coating is equal to the first pencil which does not penetrate and gouge the coating when tested form softest to hardest.
PFA (PERFLUOROALKOXY ETHYLENE): thermoplastic member of fluoropolymer family of engineering plastics, one characterized by excellent release, chemical resistance and toughness.
PH: an expression of the degree of acidity or alkalinity of a substance expressed as a number from 0 to 14. neutrality is ph7. acid solutions are less than 7 and alkaline solutions are greater than 7.
PHENOLIC: a resin or plastic, usually thermosetting, made by condensation of a phenol with an aldehyde and used for molding, insulating, coatings and adhesives.
PHOSPHATING: surface pretreatment used on ferrous parts that provide a very thin crystalline film that enhances both corrosion resistance and adhesion.
PIGMENT: finely divided, insoluble colored substance used to impart color to a coating.
PINHOLE: a tiny hole in a coating as if made by a pin that allows potential exposure or leak path to the substrate beneath the coating.
PLASMA DEPOSITION TECHNIQUE: a method of applying powder using compressed gas and melting the powder in a flame before the powder impinges on a surfaces.
POLYAMIDE-IMIDE (PAI): a high strength plastic with the highest strength and stiffness of any thermoplastic up to 275°c (525°f). it has outstanding resistance to wear, creep and chemicals-including strong acids and most organics-and is ideally suited for severe service environments.
POLYMER FUME FEVER: an illness characterized by temporary flu-like symptoms (with no long-term effects) caused by inhaling the products released during the decomposition of fluoropolymers.
POROSITY: pinholes or minute pores in a coating that allows potential exposure or leak path in the coating to the substrate, one reason for the failure of chemical, electrical or corrosion resistant coating. can be detected with a spark check test or holiday checker.
POST-CURE: a second cure at high temperature to enhance specific properties such as release and non-wetting.
POWDER COATINGS: finely divided particles of organic polymers, pigments and additives alloyed to form a coating.
PREHEATING: warming of parts prior to application of a coating, recommended when adhesion is critical and when parts are being coated in humid atmospheres. in some cases, this technique can be used to achieve higher-than-normal film builds.
PRELOADS (FOR FASTENERS): the “tightness” of a fastener, equal to the make-up energy applied minus the energy required to overcome friction at the fastener’s bearing surfaces and threads.
PRESSURE SPRAYING: coating technique similar to siphon spraying, except that the coating is delivered from a pressurized pot to the spray nozzle under positive pressure. generally used for high-volume production.
PRETREATMENT: processes for cleaning and conditioning a substrate to be coated. next to the choice for coating, this may be the most important factor in the use of high-performance coatings.
PTFE (POLYTETRAFLUOROETHYLENE): ptfe has the lowest coefficient of friction of any known solid and the highest operating temperatures of the fluoropolymers.
PVDF (POLYVINYLIDENE FLUORIDE): high-molecular weight thermoplastic of vinylidene fluoride with excellent strength, wear resistance and creep resistance.

R

RESISTANCE (ELECTRICAL): the opposition offered by a coating to the passage of an electric current through it.

S

SALT FOG: astm b-117 test procedure that simulates the corrosive environment caused by road salt and marine spray.
SAND BLASTING (ALSO GRIT BLASTING): the process of surface cleaning and roughening that provides a mechanical “tooth” to aid coating adhesion. media include aluminum oxide, even crushed walnut shells. the medium must be chosen to match the substrate and the foreign material on the substrate to be removed.
SINTERING: a process where the temperature of ptfe is raised to the point where ptfe particles soften and form a bond with each other.
SIPHON SPRAYING: most common technique for applying coatings, also known as “conventional air spray”. the coating is drawn from a reservoir into an atomizing air nozzle and propelled toward the surface to be coated.
SPARK CHECK: a dc electrical test that can be used to detect pinholes or porosity in a coating. the dc voltage is variable to allow for different levels of testing. the testing voltage is anywhere from 50 to 5000 vdc depending on the coating and the application or specification requirements.
STATIC ELECTRICITY: buildup of stationary electrical charge on a coating powder or a coated surface.
STICK-SLIP (CHATTER): unstable sliding condition in which movement of one part over another starts and stops, caused by temporary overcoming of static friction.
STORAGE STABILITY: the ability of a coating material to maintain uniform physical and chemical properties while in storage over an extended period of time.
SUBSTRATE: any surface to be coated. this can include metals such as steel, cast iron, bronze, aluminum, stainless steel, chromium and, with special precautions, nickel. paper, most plastics, wood, leather, fabrics and glass can also be coated.
SURFACE APPEARANCE: the smoothness, gloss and presence or lack of surface defects in a coating.
SURFACE TREATMENT: conditioning the substrate before coating through grit blast, phosphate, etc. may include the removal of a coating (see burn-off).

T

TAPE TEST: an astm method d3359-02 for measuring the adhesion of a coating to a substrate using a specific tape and technique.
TETRAFLUOROETHYLENE (TFE): monomer used as a chemical feedstock in the production of ptfe or teflon®.
THERMOPLASTIC RESIN: a resin which will melt when heated and solidifies when cooled, and softens when reheated.
THERMOPLASTIC: plastic resin that softens when reheated and hardens when cooled.
THERMOSETTING RESIN (THERMOSET): a resin designed to undergo an irreversible chemical and physical change during heat-cure schedule, i.e., a plastic resin that crosslinks during cure so that it does not soften when reheated.
TRANSFER EFFICIENCY: the ratio of the amount of coating deposited on a substrate compared to the total amount directed at the part to be coated.

W

WEAR: deterioration by friction (abrasion, spalling, cutting, fretting).
WRAP: a characteristic of liquid and powder coatings in electrostatic application to adhere to areas of the substrate not in direct line of sight of the delivery system end point.